CA2223746A1 - Method and apparatus for a surface-mountable device for protection against electrostatic damage to electronic components - Google Patents
Method and apparatus for a surface-mountable device for protection against electrostatic damage to electronic components Download PDFInfo
- Publication number
- CA2223746A1 CA2223746A1 CA002223746A CA2223746A CA2223746A1 CA 2223746 A1 CA2223746 A1 CA 2223746A1 CA 002223746 A CA002223746 A CA 002223746A CA 2223746 A CA2223746 A CA 2223746A CA 2223746 A1 CA2223746 A1 CA 2223746A1
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- Prior art keywords
- electrodes
- substrate
- gap
- protection device
- mount
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01C—RESISTORS
- H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
- H01C7/006—Thin film resistors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01C—RESISTORS
- H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
- H01C17/06—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base
- H01C17/075—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base by thin film techniques
- H01C17/08—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base by thin film techniques by vapour deposition
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01C—RESISTORS
- H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
- H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
- H01C7/1013—Thin film varistors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01C—RESISTORS
- H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
- H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
- H01C7/12—Overvoltage protection resistors
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- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Manufacturing & Machinery (AREA)
- Non-Metallic Protective Coatings For Printed Circuits (AREA)
- Encapsulation Of And Coatings For Semiconductor Or Solid State Devices (AREA)
- Manufacturing Of Printed Circuit Boards (AREA)
- Thermistors And Varistors (AREA)
- Semiconductor Integrated Circuits (AREA)
Abstract
The thin film, circuit device is a subminiature overvoltage protection device in a surface mountable configuration for use in printed circuit board or thick film hybrid circuit technology. The surface mountable device (SMD) is designed to protect against electrostatic discharge (ESD) damage to electronic components. The circuit protection device comprises three material subassemblies. The first subassembly generally includes a substrate carrier, electrodes, and terminal pads for connecting the protection device (60) to a PC board. The second subassembly includes a voltage variable polymer material with non-linear characteristics, and the third subassembly includes a cover coat for protecting other elements of the circuit protection device.
Description
GES.VC'I:EPA MUENCHEN 01 ;21~ 9CA oi2~23746 l997-l2-0523994465 tt4122 74û 1~ 35;# 2~ 2 .
8 0 4 P 4 0 7 PATE;~r ( 2 8 6 ~ 0 ) M~3TEIOD AND APPARATUS FOR A 5~RFACE -iIJU ~ LA33LE
DE:~ICE FOR PROTE:CT:rON AGAINST ELBCTROgTAT:~C
r~AC:P! TO E:LEC'rRONIC COMPC~ r,L;i '. .
0~0 S~
21/11 '97 FRI 13: 56 [TX~RX N~ 9311 1 CA 02223746 1997-12-0~
DESCRIPTION
Technical Field The present invention relates gener-ally to sur~ace-mountable devices (SMDs) ~or the protectlon of electrical circuits. More particularly, this invention relates to sur~ace-mountable devices ~or protection against electrostatic discharge within electrical circuits.
Backqround Prior Art Printed circuit (PC) boards have ~ound increasing application in electrical and electronic equipment o~ all kinds. The electrical circuits ~ormed on these PC boards, like larger scale, conventional electrical circuits, need protection against electrical overvoltage. This protection is typically provided by commonly known electrostatic discharge devices that are physically secured to the PC board.
Examples o~ such a devices include silicon diodes and metal oxide varistor (MOV) devices. Document WO83/01153 discloses an integrated protection device ~or the protection o~ circuits and semiconductors against static overvoltages or dynamic voltage overloads.
That device comprises the deposition on the support (3) and on the external access connections (4, 5) to the circuit o~ a non-linear resistance or varistance (6), such that the threshold voltage o~ the varistance i-s AMEI~DED S,iEET
CA 02223746 l997-l2-0 t 3 lower than the critical overvoltage ~or the circuit. However, there are several problems with these devices. First, there are numerous aging problems associated with these types o~
devices, as is well known. Second, these types o~ devices can experience catastopic **SHOULD
THIS WORD BE CATASTROPHIC??? failures, also as is well known. Third, these types o~ devices may burn or ~ail during a short mode situation.
Numerous other disadvantages come to mind when using these devices during the manu~acture o~ a PC board It has been ~ound in the past that certain types o~ materials can provide protection against ~ast transient overvoltage pulses within electronic circuitry. These materials at least include those types o~
materials ~ound in U.S. Patent Nos. 4,097,834, 4,726,991, 4,977,357, and 5,262,754. However, the time and costs associated with incorporating and e~ectively using these materials in microelectronic circuitry is and has been signi~icant. The present invention is provided to alleviate and solve these and other problems.
Summary o~ the Invention The present invention is a thin ~ilm, electrostatic discharge sur~ace mounted device (ESD/SMD) which comprises three material subassemblies. The ~irst subassembly includes the substrate carrier.
. ~
= CA 02223746 1997-12-0~
4 ........................... . .
The ~irst or substrate-carrier subassembly comprises a carrier base havlng two electrodes on the top sur~ace which are separated by a gap o~ controlled width, and wrap-around terminal pads on the side and bottom o~ the carrier base. The second subassembly or voltage variable polymeric material is applied between the two electrodes and ef~ectively bridges gap between the electrodes. The third subassembly or cover coat is placed over the polymeric material and electrodes on the top sur~ace o~ the ~irst or substrate subassembly. The third subassembly provides a protective layer which overlies the second subassembly and electrodes, as well as part o~ the terminal pads connected to the electrodes, so as to provide protection from impacts, oxidation, and other e~ects, as will be described ~urther below.
The third subassembly or protective layer is pre~erably made o~ a polymeric material, such as polyurethane or polycarbonate. In addition, the most pre~erred supporting substrate is an FR-4 epoxy or a polyimide.
Another aspect o~ the invention is a thin ~iIm, sur~ace-mounted con~iguration o~ the ESD/SMD. In particular, the device comprises electrodes made o~ a conductive metal. The ~irst conductive metal is preferably, but not exclusively, selected ~rom ,~:. . , CA 02223746 1997-12-0~
the group including copper, silver, nickel, titanium, aluminum or alloys o~ these conductive metals. One pre~erred metal ~or the electrodes o~ the ESD/SMD invention is copper.
The ~irst conductive metal or electrodes may be deposited onto the ~irst subassembly in many shapes. Photolithographic, mechanical and laser processing techniques may be employed to create very small, intricate and complex electrode geometries, as well as creating an appropriate gap width. This capability, when combined with the extremely thin ~ilm coatings applied through electrochemical and physical vapor deposition (PVD) techniques, enables these subminiature protective devices 60 to control the gap between the electrodes and protect circuits ~rom signi~icant levels o~ overvoltage.
The location o~ the electrodes at the top o~ the substrate o~ the ESD/SMD enables one to use laser processing methods as a high precision secondary operation, in that way trimming the gap width, and thus, the rating o~
the device.
Other ~eatures and advantages o~ the invention will be apparent ~rom the ~ollowing speci~ication taken in conjunction with the ~ollowing drawings.
Brie~ Description o~ Drawinqs FIG. 1 is a perspective view o~ a copper-plated, FR-4 epoxy sheet used to make a CA 02223746 1997-12-0~
subminiature ESD/SMDs in accordance with the present invention.
FIG. 2 is a cross-sectional view o~ a portion o~ the sheet o~ FIG. 1, and taken along lines 2-2 o~ FIG. 1.
FIG. 3 is a perspective view o~ the FR-4 epoxy sheet o~ FIG. 1, but stripped o~ its copper plating, and with a plurality o~ slots, each having a width W1 and a length L, routed into separate quadrants o~ that sheet.
FIG. 4 is an enlarged, cut-away perspective view o~ a portion o~ the routed sheet o~ FIG. 3, but with a copper plating layer having been reapplied.
FIG. 5 is a top perspective view o~
several portions o~ the ~lat, upward-~acing sur~aces o~ the replated copper sheet ~rom FIG.
4, a~ter each o~ those portions were masked with a patterned panel o~ an ultraviolet (W) light-opaque substance.
FIG. 6 is a perspective view o~ the reverse side o~ FIG. 5, but a~ter the removal o~ a strip-like portion o~ copper plating ~rom the replated sheet o~ FIG. 5.
FIG 7 is a perspective view o~ the top 57 o~ the strips 26 o~ FIG. 6, and showing linear regions 40 de~ined by dotted lines.
FIG. 8 is a view o~ a single strip 26 a~ter dipping into a copper plating bath and then a nickel plating bath, with the result that additional copper layer and a nickel layer - CA 02223746 1997-12-0~
are deposited onto the terminal-pads portions o~ the base copper layer.
FIG. 9 is a perspective view o~ the strip o~ FIG. 8, but after immersion into a tin-lead bath to create another layer over the copper and nickel layers o~ the terminal pads.
FIG. 10 shows the strip o~ FIG. 9, depicting the region where the voltage variable polymeric strip will be applied.
FIG. 11 shows the strip o~ FIG. 10, but with an added polymeric material 43 into the gap 25 o~ the strip 26.
FIG. 12 shows the strip o~ FIG. 11, but with an added cover coat 56 over the electrodes 21 and polymeric material 43.
FIG. 13 shows the individual ESD/SMD
in accordance with the invention as it is ~inally made, and a~ter a so-called dicing operation in which a diamond saw is used to cut the strips along parallel planes to ~orm the individual devices.
FIG. 14 is a ~ront view o~ the stencil printing machine used to per~orm the stencil printing step o~ the ESD/SMD
manu~acturing process.
Detailed Description While this invention is susceptible o~ embodiments in many di~erent ~orms, there is shown in the drawings and will herein be described in detail, a pre~erred embodiment o~
the invention with the understanding that the CA 02223746 1997-12-0~
present dlsclosure is to be considered as an exempli~ication o~ the principles o~ the inven-tion and is not intended to limit the broad aspects of the invention to the embodiment illustrated.
One pre~erred embodiment o~ the present invention is shown in FIG. 13. The thin ~ilm, circuit device is an subminiature overvoltage protection device in a sur~ace mountable con~iguration ~or use in printed circuit board or thick film hybrid circuit technology. One given name ~or the device is an electrostatic discharge sur~ace-mounted device (ESD/SMD). The sur~ace mountable device (SMD) is designed to protect against electrostatic discharge (ESD) damage to electronic components. The layout and design o~ the ESD/SMD device is such that it can be manu~actured in many sizes. One standard industry size ~or sur~ace mount devices, generally, is 3.175 mm (125 mils.) long by 1.524 mm (60 mils.) wide. This sizing is applicable to the present invention, and can be designated, ~or shorthand purposes, as "1206"
sized devices. It will be understood, however, that the present invention can be used on all other standard sizes ~or sur~ace mountable devices, such as 1210, 0~05, 0603 and 0402 devices, as well as non-standard sizes. The protection device o~ the present invention are designed to replace silicon diodes and MOV
AAfiENOED SHE~T
- CA 02223746 1997-12-0~
technologies which are commonly used ~or low power protection applications.
The protection device generally comprises three material subassemblies. As 5 will be seen, the first subassembly generally includes a substrate carrier or substrate 13, electrodes 21, and terminal pads 34, 36 ~or connecting the protection device 60 to the PC
board. The second subassembly includes the voltage variable polymer material 43, and the third subassembly includes the cover coat 56.
The ~irst or substrate carrier subassembly comprises a carrier base 13 having two electrodes 21 on the top sur~ace which are 15 separated by a gap 25 O~ controlled width W2, and wrap-around terminal pads 34, 36 on the top 57, bottom 58, and side 59 D~ the ~irst subassembly 13. The second subassembly or voltage variable polymeric material 43 iS
applied between these two electrodes 21 and e~ectively bridges the gap 25. A cover coat 56 iS placed over the polymeric material 43 and the electrodes 21 on the top sur~ace 57 O~ the substrate subassembly, and partially on the top 57 O~ the terminal pads 34, 36. The third subassembly provides protection ~rom impacts which may occur during automated assembly, and protection ~rom oxidation and other e~ects during use.
More particularly, the ~irst or substrate subassembly incorporates a carrier r ~ S~EIET
CA 02223746 1997-12-0~
10 ' ;' ' base 13 made o~ a seml-rigid epoxy material.
This material exhibits physical properties nearly identical with the standard substrate material used in the printed circuit board industry, thus providing ~or extremely well matched thermal and mechanical properties between the device and the board. Other types o~ material can be used as well.
The ~irst subassembly ~urther includes two metal electrodes 21 which are a part o~ the pads 34, 36 as one continuous layer or ~ilm. As will be seen, the pads 34, 36 are made up o~ several layers, including a base copper layer 44 which also makes up the electrodes 21, a supplemental copper layer 46, a nickel layer 48, and a tin-lead layer 52 to make up the rest o~ the pads 34, 36. In another embodiment, the supplemental copper layer 46 also makes up a second copper layer o~
the electrodes 21 (not shown), thereby increasing the thickness o~ the electrodes 21.
The base copper layer o~ the pads and the electrodes are simultaneously deposited by (1) electrochemical processes, such as the plating described in the pre~erred embodiment below; or (2) by physical vapor deposition (PVD). Such simultaneous deposition ensures a good conductive path between the pads 34, 36, electrodes 21, and second subassembly 43 when an overvoltage situation occurs. This type o~
deposition also ~acilitates manu~acture, and - CA 02223746 l997-l2-0~
permits very precise control of the thickness of the layers, including the electrodes 21.
After initial placement of the base copper 44 on~o the substrate or core 13, additional 5 layers 46, 48, 52 of a conductive metal are placed onto the terminal pads, as mentioned above. These additional layers could be defined and placed onto these pads by photolithography and deposition techniques, respectively.
The two metal electrodes, whether one or two layers (or more) thick are separated by a gap 25 Ci~ a controlled width W2. The substrate subassembly also contains and supports the two (2) terminal pads 34, 36 on the top 57, bottom 58, and sides 59 off the protection device These bottom 58 and/or sides 59 off the terminal pads 34, 36 serve to at~ach the device to the board and provide an electrical path :~rom the board to the electrodes 21. Again, the electrodes 21 and the terminal pads consist of a copper sheet 44 laminated to the case substrate material 13.
The other layers are deposited, either electrochemically or physical vapor deposition (PVD), simultaneously to ensure a good, continuous conductive path between the electrodes on the top sur~ace of the substrate, and the terminal pads 34, 36 on the bottom o~
the substrate 13. This configuration allows for ease o~ manufacture ~or surface mount - CA 02223746 1997-12-0~
assembly techniques to allow for a wrap around configuration o~ the terminal pads. The gap width W2 between the electrodes 21 are de~ined by photolithographic techniques and through an etching process. The nature of the photolithographic process allows for very precise control of the width W2 of the separation o~ the electrode metallization. The gap 25 separating the electrodes 21 extends on a straight line across the top sur~ace o~ the substrate 13. Proper sizing and configuration o~ the gap provides for proper trigger voltages and clamping voltages along with fast response time and reliable operation during an overvaltage condition. The electrode metallization can be selected from a variety of elemental or alloy materials, i.e. Cu, Ag, Ni, Ti, Al, NiCr, Tin, etc., to obtain coatings which exhibit desired physical, electrical, and metallurgical characteristics.
Photolithography, mechanical, or laser processing techniques are employed ~or de~ining the physical dimensions and width o~
the gap 25 and o~ the terminal pads 34, 36.
Subsequent photolithography and deposition operations are employed to deposit additional metallization to the terminal pads, i.e. Cu, Ni, and Sn/Pb, to a specified thickness.
The voltage variable polymeric material 43 provides the protection from ~ast transient overvoltage pulses. The polymeric CA 02223746 1997-12-0~
material 43 provides ~or a non-linear electrical response to an overvoltage condition. The polymer 43 is a material comprising ~inely divided particles dispersed in an organic resin or an insulating medium.
The polymeric material 43 consists o~
conductive particles which are uni~ormly dispersed throughout an insulating binder.
This polymer material 43 exhibits a non-linear resistance characteristic which is dependent on the particle spacing and the electrical properties o~ the binder. This polymer material is available from many sources and is disclosed by a variety o~ patents as was lS mentioned above.
The cover coat 56 subassembly is applied a~ter the metal deposition, pattern de~inition, and polymer 43 application process, to the top sur~ace o~ the substrate/polymer subassembly to provide a means ~or protecting the polymeric material 43 and to provide a ~lat top sur~ace ~or pick-and-place sur~ace mount technology automated assembly equipment. The : cover coat 56 prevents excessive oxidation o~
the electrodes 21 and the polymer 43 which can degrade the per~ormance o~ the protection device 60. The cover coat 56 can be comprised of a variety o~ materials including plastics, con~ormal coatings, polymers, and epoxies. The cover coat 56 also serves as a vehicle ~or marking the protective devices 60 with the marklng being placed between separate layers, or on the sur~ace o~ the cover coat 56 through an ink trans~er process or laser marking.
This protective device 60 may be made 5 by the following process. Shown in FIGS. 1 and 2 is a solid sheet 10 o:E an FR-4 epoxy with copper plating 12. The copper plating 12 and the FR-4 epoxy core 13 o~ this solid sheet 10 may best be seen in FIG. 2. This copper-plated 10 FR-4 epoxy sheet 10 is available ~rom Allied Signal T.~m; n~te Systems, Hoosick Falls, New York, as Part No. 0200BED130C1/ClGFN0200 C1/ClA2C. Although FR-4 epoxy is a pre~erred material, other suitable materials include any 15 material that is compatible with, i . e ., o:E a chemically, physically and structurally similar nature to, the materials ~rom which PC boards are made, as ment ioned above . Thus, another suitable material ~or this solid sheet 10 is 20 polyimide . FR- 4 epoxy and polyimide are among the class o:E materials having physical properties that are nearly identical with the standard substrate material used in the PC
board industry. As a result, the protective 25 device 60 and the PC board to which that protection device 60 is secured have extremely well-matched thermal and mechanical properties.
The substrate oi~ the protective device 60 o~
the present invention also provides desired 30 arc-tracking characteristics, and simultaneously exhibits su~lcient mechanical - CA 02223746 1997-12-0~
~lexibility to remain intact when exposed to the rapid release o~ energy associated with overvoltage.
In the next step o~ the process o~
manu~acturing the protective devices 60, the copper plating 12 is etched away ~rom the solid sheet 10 by a conventional etching process. In this conventional etching process, the copper is etched away from the substrate by a ~erric chloride solution.
Although it will be understood that a~ter completion o~ this step, all o~ the copper layer 12 of FIG. 2 is etched away ~rom FR-4 epoxy core 13 o~ this solid sheet 10, the remaining epoxy core 13 o~ this FR-4 epoxy sheet 10 is di~erent ~rom a "clean" sheet o~
FR-4 epoxy that had not initially been treated with a copper layer. In particular, a chemically etched sur~ace treatment remains on the sur~ace of the epoxy core 13 a~ter the copper layer 12 has been removed by etching.
This treated sur~ace o~ the epoxy core 13 is more receptive to subsequent operations that are necessary in the manu~acture o~ the present sur~ace-mounted subminiature protective device 60.
The FR-4 epoxy sheet 10 having this treated, copper-~ree sur~ace is then routed or punched to create slots 14 along quadrants o~
the sheet 10, as may be seen in FIG. 3. Dotted lines visually separate these ~our quadrants in CA 02223746 l997-l2-05 FIG. 3. The width Wl o~ the slots 14 (FIG. 4) is about 0.0625 inches. The length L o~ each o~ the slots 14 (FIG. 3) is approximately 5.125 When the routing or punching has been completed, the etched and routed or punched sheet 10 shown in FIG. 3 is again plated with copper. This reapplication o~ copper occurs through the immersion o~ the etched and routed sheet o~ FIG. 3 into an electroless copper plating bath. This method o~ copper plating is well-known in the art.
This copper plating step results in the placement o~ a copper layer having a uni~orm thickness along each o~ the exposed sur~aces of the sheet 10. For example, as may be seen in FIG. 4, the copper plating 18 resulting ~rom this step covers both (1) the flat, upper sur~aces 22 o~ the sheet 10; and (2) the vertical, interstitial regions 16 that de~ine at least a portion o~ the slots 14.
These interstitial regions 16 must be copper-plated because they will ultimately ~orm a portion o~ the terminal pads 34, 36 o~ the ~inal protection device 60. The uni~orm thickness o~ the copper plating will depend upon the ultimate needs o~ the user.
A~ter plating has been completed, to arrive at the copper-plated structure o~ FIG.
4, the entire exposed sur~ace o~ this structure CA 02223746 l997-l2-0 is covered with a so-called photoresist polymer.
An otherwise clear mask is placed over the replated copper sheet 20 a~ter it has been covered with the photoresist. Patterned panels are a part o~, and are evenly spaced across, this clear mask. These patterned panels are made o~ an W light-opaque substance, and are o~ a size and shape corresponding to the size and shape generally o~ the patterns 30 shown in FIG. 5.
Essentially, by placing this mask having these panels onto the replated copper sheet 20, several portions o~ the ~lat, upward-~acing sur~aces 22 o~ the replated copper sheet 20 are e~ectively shielded ~rom the e~ects o~ W
light.
It will be understood ~rom the following discussion that the pattern 30 will essentially de~ine the shapes and sizes o~ the electrodes 21 and polymer strip 43. A later step de~ines the remainder o~ terminal pads 34, 36. It will be appreciated that the width, ~ length and shape o~ the electrodes 21 and polymer strip 43 may be altered by changing the size and shape o~ the W light-opaque panel patterns. In particular, one embodiment o~ the present invention includes having curved corners 19 (not shown) instead o~ sharp corners 19 as shown. In ~act, it has been seen that it is pre~erable to curve the corners 19.
CA 02223746 l997-l2-0 This step, therefore, defines the gap 25 between the electrodes 21, as well as the notches 23 in the electrodes 21. As mentioned above, photolithographic, mechanical, and laser processing techniques can be employed to configure very small, intricate, and complex electrode 21 and gap 25 geometries. The electrode 21 configuration can be conveniently modified to obtain specific electrical characteristics in resultant protective devices 60. The gap width W2 can be changed to provide control of triggering and clamping voltages during an overload event. The indicated device construction results in a triggering and clamping voltage rating similar to devices o~
previous construction. Tests have been conducted with peak voltages o~ 2kV, 4kV, and 8kV as the ESD waveform. The use o~ a 2 mil and 4 mil gap width resulted in triggering voltages o~ loO-150 V and clamping voltages o~
30-50 V.
Additionally within this step, the backside o~ the sheet is covered with a photoresist material and an otherwise clear mask is placed over the replated copper sheet after it has been covered with the photoresist. A rectangular panel is a part o~
this clear mask. The rectangular panels are made of a W light-opaque substance, and are of a size corresponding to the size o~ the panel 28 shown in FIG. 6. Essentially, by placing ~ CA 02223746 1997-12-0~
thls mask having these panels onto the replated copper sheet 20, several strips of the flat, downward-facing surfaces 28 of the replated copper sheet 20 are ef~ectively shielded from the e~fects of the W light.
The rectangular panels will essentially define the shapes and sizes of the wide terminal pads 34 and 36 and the lower middle portion 28 of the bottom 58 of the strip 26. Thus, the copper plating from a portion of the bottom 58 of a strip 26 is defined by a photoresist mask. Particularly, the copper plating from the lower, middle portion 28 of the bottom 58 of the strip 26 is removed. A
perspective view of this section of this replated sheet 20 is shown in FIG. 6.
The entire replated, photoresist-covered sheet 20, i.e., the top 57, bottom 58, and sides 59 of that sheet 20, is then subjected to W light. The replated sheet 20 is subjected to the W light for a time sufficient to ensure curing of all of the photoresist that is not covered by the square panels and rectangular -strips of the masks.
Thereafter, the masks containing these square panels and rectangular strips are removed from the replated sheet 20. The photoresist that was formerly below these square panels remains uncured. This uncured photoresist may be washed from the replated sheet 20 using a solvent.
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=
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- i The cured photoresist on the remainder o:E the replated sheet 20 provides protection against the next step in the process. Particularly, the cured photoresist prevents the removal of copper beneath those areas of cured photoresist. The regions ~ormerly below the patterned panels have no cured photoresist and no such protection.
Thus, the copper ~rom those regions can be removed by etching. This etching is per~ormed with a ~erric chloride solution.
A~ter the copper has been removed, as may be seen in FIGS. 5 and 6, the regions formerly below the patterned panels and the rectangular strips o~ the mask are not covered at all. Rather, those regions now comprise areas 28 and 30 o~ clear epoxy.
The replated sheet 20 is then placed in a chemical bath to remove all o~ the remaining cured photoresist ~rom the previously cured areas o~ that sheet 20.
For the purposes o~ this speci~ication, the portion o~ the sheet 20 between adjacent slots 14 is known as a strip 26. This strip has a dimension D as shown in FIG. 4 which defines the length of the device.
After completion o~ several o~ the operations described in this speci~ication, this strip 26 will ultimately be cut into a plurality o~
pieces, and each o~ these pieces becomes an AMrN.~, t~
~ CA 02223746 1997-12-0~
ESD/SMD or protective device 60 in accordance with the invention.
As may also be seen ~rom FIG. 6, the underside 58 o~ the strip 26 has regions along its periphery which still include copper plating. These peripheral regions 34 and 36 o~
the underside 58 o~ the strip 26 ~orm portions o~ the pads. These pads will ultimately serve as the means ~or securing the entire, ~inished protective device 60 to the PC board.
FIG. 7 is a perspective view o~ the top-side 57 o~ the strips 26 o~ FIG. 6.
Generally opposite and coinciding with the lower, middle portions 28 o~ these strips 26 are linear regions 40 on this top-side 38.
These linear regions 40 are defined by the dotted lines o~ FIG. 7.
FIG. 7 is to be re~erred to in connection with the next step in the manu~acture o~ the invention. In this next step, a photoresist polymer is placed along each o~ the linear regions 40 o~ the top side 57 o~ the strips 26. Through the covering o~
these linear regions 40, photoresist polymer is also placed along the gap 25 and electrodes 21.
These electrodes 21 are made 0? a conductive metal, here copper. The photoresist is then treated with W light, resulting in a curing o~
the photoresist onto linear region 40.
As a result o~ the curing o~ this photoresist onto the linear region 40, metal ~,? '~
CA 02223746 l997-l2-0 will not adhere to this linear region 40 when the strip 26 iS dipped into an electrolytic bath containing a metal ~or plating purposes.
In addition, as explained above, the middle portion 28 oi~ the underside 58 o:E the strip 26 will also not be subject to platlng when the strip 26 is dipped into the electrolytic plating bath. Copper metal previously covering this metal portion had been removed, revealing the bare epoxy that ~orms the base o~ the sheet 20. Metal will not adhere to or plate onto this bare epoxy using an electrolytic plating process.
The entire strip 26 is dipped into an electrolytic copper plating bath and then an electrolytic nickel plating bath. As a result, as may be seen in FIG. 8, copper 46 and nickel layers 48 are deposited on the base copper layer 44. Ai~ter deposition of~ these copper 46 and nickel layers 48, an additional tin-lead layer 52 is deposited in these same areas through an electrolytic tin-lead bath as shown in FIG. 9. The cured photoresist polymer on the linear region 40 is then removed.
As shown in FIGS. 10 and 11, the polymer material 43 iS then applied. The polymer 43 can be applied in a number o~ ways.
For example, the polymer 43 can be applied using the stencil printing machine shown in FIG. 14 in a manner similar to the use oi~ the stencil printing described ~urther below. In - CA 02223746 l997-l2-0~
addition, the polymer 43 can be applied manually with a tube o~ the polymer 43. Other automated means for applying the polymer 43 are possible as well. Once the polymer 43 has been applied and deposited within region 42, and in between regions 41, the sheet 20 is heat cured to solidi~y the polymer 43 to obtain strips 26 that look like the strip 26 in FIG. 11.
The next step in the manu~acture o~
the protective device 60 is the placement, across the length o~ the most of the top 57 o~
the strip 26, o~ a protective layer 56 ( FIG.
12). This protective layer 56 iS the third subassembly o~ the present protective device 60, and ~orms a relatively tight seal over the electrodes 21 and polymer strip 43 area. In this way, the protective layer 56 provides protection from oxidation and impacts during attachment to the PC board. This protective layer also serves as a means o~ providing ~or a sur~ace ~or pick and place operations which use a vacuum pick-up tool.
This protective layer 56 helps to control the melting, ionization and arcing which occur in the ~usible link 42 during current overload conditions. The protective layer 56 or cover coat material provides desired arc-quenching characteristics, especially important upon interruption o~ the ~usible link 42.
- CA 02223746 1997-12-0~
24 ' The application o~ the cover coat 56 is such that it can be performed in a single processing step using a simple ~ixture to de~ine the shape o~ the body o~ the device.
This method of manufacture provides ~or advantages over current methodologies in protecting the electrodes 21, gap 25, and polymer 43 ~rom physical and environmental damage. The application o~ the conformal coating 56 is performed in such a fashion that the physical location o~ the electrode gap 25 is not critical, as in a clamping or die mold method. The con~ormal coating may be mixed with a colored dye prior to application to provide for a color-coded voltage rated protective device 60.
The protective layer 56 may be comprised of a polymer, pre~erably a polyurethane gel or paste when a stencil printing cover coat application process is used, and pre~erably a polycarbonate adhesive when an injection mold cover coat application process is used. A pre~erred polyurethane is made by Dymax. Other similar gels, pastes, and adhesives are suitable ~or the invention depending on the cover coat application process used. In addition to polymers, the protective layer 56 may also be comprised of plastics, con~ormal coatings and epoxies.
This protective layer 56 is applied to the strips 26 using a stencil printing - CA 02223746 1997-12-0~
process which includes the use of a common stencil printing machine shown in FIG. 14. It has been found that stencil printing is faster than some alternative processes for applying the cover coat 56, such as with an injection mold process using die molds. Specifically, it has been found that the use of a stencil printing process while using a stencil printing machine, at least, doubles production output from the injection mold operation. The stencil printing machine is made by Affiliated Manufacturers, Inc. of Northbranch, New Jersey, Model No. CP-885.
In the stencil printing process, the material is applied to all of the strips 26 in one quadrant of the sheet 20, simultaneously.
Using the stencil print process, the material cured much faster than the injection mold process because the cover coat material is directly exposed to the W radiation, while the W light must travel through a filter in the injection mold process. Furthermore, the stencil printing process produces a more uni~orm cover coat than the injection filling process, in terms of the height and the width of the cover coat 56. Because of that uniformity, the fuses can be tested and packaged in a relatively fast automated process. With the injection filling process it may be difficult to precisely align the protective devices 60 in testing and packaging CA 02223746 l997-l2-0 equipment due to some non-uniform heights and widths of the cover coat 56.
The stencil printing machine comprises a slidable plate 70, a base 72, a squeegee arm 74, a squeegee 76, and an overlay 78. The overlay 78 is mounted on the base 72 and the squeegee 76 is mc;vably mounted on the squeegee arm 74 above the base 72 and overlay 78. The plate 70 is slidable underneath the base 72 and overlay 78. The overlay 78 has parallel openings 80 which correspond to the width of the cover coat 56.
The stencil printing process begins by attaching an adhesive tape under the sheet 20. The sheet 20, with the adhesive tape attached, is placed on the plate 70 with the adhesive tape between the plate 70 and the fuse sheet 20. The cover coat 56 material is then applied with a syringe at one end of the overlay 78. The plate 70 slides underneath the overlay 78 and lodges the sheet 20 underneath the overlay 78 in correct alignment with the parallel openings 80. The squeegee 76 then lowers to contact the overlay 78 beyond the material on the top of the overlay 78. The squeegee 76 then moves across the overlay 78 where the openings 80 exist, thereby forcing the cover coat 56 material through the openings 80 and onto each of the strips 26 of the sheet 20. Thus, the cover coat now covers the electrodes 21, the gap, 25, and the polymer CA 02223746 1997-12-0~
strip 43 (FIGS. 12 and 13). The squeegee 76 is then raised, and the sheet 20 is unlodged ~rom the overlay 78. The openings 80 in the overlay 78 are wide enough so that the protective layer partially overlaps the pads 34, 36, as shown in FIGS. 12 & 13. In additlon, the material used as the cover coat material should have a viscosity in the paste or gel region so that a~ter the material is spread onto the sheet 20, it will ~low in a manner which creates a generally ~lat top sur~ace 49, but such that the material 56 will not ~low into the slots 14. The sheet 20 o~ strips 26 are then W
cured in a W chamber. At the end of this curing, the polyurethane gel or paste has solidi~ied, ~orming the protective layer 56 (FIGS. 12 and 13).
Although a colorless, clear cover coat is aesthetically pleasing, alternative types of cover coats may be used. For example, colored, clear or transparent cover coat materials may be used. These colored materials may be simply manu~actured by the addition o~ a dye to a clear cover coat material. Color coding may be accomplished through the use o~
these colored materials. In other words, di~erent colors o~ the cover coat can correspond to di~erent ratings, providing the user with a ready means o~ determining the rating o~ any given protective device 60. The transparency o~ both o~ these coatings permit CA 02i23746 1997-12-0~ -.
the user to visually inspect the polymer strip 43 prior to installation, and during use.
The strips 26 are then ready for a so-called dicing operation, which separates those strips 26 into individual fuses. In this dicing operation, a diamond saw or the like is used to cut the strips 26 along parallel planes 61 (FIG. 12) into individual thin film surface-mounted fuses 60 (FIG. 13). The cuts bisect the notches 23 in the electrodes 21. At this point, it can more easily be understood that the metallization of the electrodes 21 is removed from the notches 23 or notched areas 23. Specifically, it is easier to cut through notched areas 23 without the electrodes. In addition, during dicing, curling of the metallization may take place along the cut, -thereby causing a curl of metal (part of an electrode) to move into the gap area and effectively reduce the gap width W2. Putting the notches 23 in the places where the dicing is to take place alleviates this possible problem and other possible problems. It should be noted that the notches 23 can extend further toward the pads 34, 36, and that the corners 19 of the notches 23 can be curved in alternative embodiments.
This cutting operation completes the manufacture of the thin film protective device 60 (FIG. 13) of the present invention.
All o~ the preceding ~eatures combine to produce an ESD/SMD device assembly which exhibits improved control o~ triggering and clamping voltage characteristics by regulating electrode and gap geometries, and the polymer 43 composition. The dimensional control aspects o~ the deposition and photolithographic processes, coupled with the proper selection o~
electrode and polymer 43 material, provide ~or consistent triggering and clamping voltages.
However, it wlll be understood that the - invention may be embodied in other speci~ic ~orms without departing ~rom the spirit or central characteristics thereo~.
. . . i AMEI~ID~D SHEET
8 0 4 P 4 0 7 PATE;~r ( 2 8 6 ~ 0 ) M~3TEIOD AND APPARATUS FOR A 5~RFACE -iIJU ~ LA33LE
DE:~ICE FOR PROTE:CT:rON AGAINST ELBCTROgTAT:~C
r~AC:P! TO E:LEC'rRONIC COMPC~ r,L;i '. .
0~0 S~
21/11 '97 FRI 13: 56 [TX~RX N~ 9311 1 CA 02223746 1997-12-0~
DESCRIPTION
Technical Field The present invention relates gener-ally to sur~ace-mountable devices (SMDs) ~or the protectlon of electrical circuits. More particularly, this invention relates to sur~ace-mountable devices ~or protection against electrostatic discharge within electrical circuits.
Backqround Prior Art Printed circuit (PC) boards have ~ound increasing application in electrical and electronic equipment o~ all kinds. The electrical circuits ~ormed on these PC boards, like larger scale, conventional electrical circuits, need protection against electrical overvoltage. This protection is typically provided by commonly known electrostatic discharge devices that are physically secured to the PC board.
Examples o~ such a devices include silicon diodes and metal oxide varistor (MOV) devices. Document WO83/01153 discloses an integrated protection device ~or the protection o~ circuits and semiconductors against static overvoltages or dynamic voltage overloads.
That device comprises the deposition on the support (3) and on the external access connections (4, 5) to the circuit o~ a non-linear resistance or varistance (6), such that the threshold voltage o~ the varistance i-s AMEI~DED S,iEET
CA 02223746 l997-l2-0 t 3 lower than the critical overvoltage ~or the circuit. However, there are several problems with these devices. First, there are numerous aging problems associated with these types o~
devices, as is well known. Second, these types o~ devices can experience catastopic **SHOULD
THIS WORD BE CATASTROPHIC??? failures, also as is well known. Third, these types o~ devices may burn or ~ail during a short mode situation.
Numerous other disadvantages come to mind when using these devices during the manu~acture o~ a PC board It has been ~ound in the past that certain types o~ materials can provide protection against ~ast transient overvoltage pulses within electronic circuitry. These materials at least include those types o~
materials ~ound in U.S. Patent Nos. 4,097,834, 4,726,991, 4,977,357, and 5,262,754. However, the time and costs associated with incorporating and e~ectively using these materials in microelectronic circuitry is and has been signi~icant. The present invention is provided to alleviate and solve these and other problems.
Summary o~ the Invention The present invention is a thin ~ilm, electrostatic discharge sur~ace mounted device (ESD/SMD) which comprises three material subassemblies. The ~irst subassembly includes the substrate carrier.
. ~
= CA 02223746 1997-12-0~
4 ........................... . .
The ~irst or substrate-carrier subassembly comprises a carrier base havlng two electrodes on the top sur~ace which are separated by a gap o~ controlled width, and wrap-around terminal pads on the side and bottom o~ the carrier base. The second subassembly or voltage variable polymeric material is applied between the two electrodes and ef~ectively bridges gap between the electrodes. The third subassembly or cover coat is placed over the polymeric material and electrodes on the top sur~ace o~ the ~irst or substrate subassembly. The third subassembly provides a protective layer which overlies the second subassembly and electrodes, as well as part o~ the terminal pads connected to the electrodes, so as to provide protection from impacts, oxidation, and other e~ects, as will be described ~urther below.
The third subassembly or protective layer is pre~erably made o~ a polymeric material, such as polyurethane or polycarbonate. In addition, the most pre~erred supporting substrate is an FR-4 epoxy or a polyimide.
Another aspect o~ the invention is a thin ~iIm, sur~ace-mounted con~iguration o~ the ESD/SMD. In particular, the device comprises electrodes made o~ a conductive metal. The ~irst conductive metal is preferably, but not exclusively, selected ~rom ,~:. . , CA 02223746 1997-12-0~
the group including copper, silver, nickel, titanium, aluminum or alloys o~ these conductive metals. One pre~erred metal ~or the electrodes o~ the ESD/SMD invention is copper.
The ~irst conductive metal or electrodes may be deposited onto the ~irst subassembly in many shapes. Photolithographic, mechanical and laser processing techniques may be employed to create very small, intricate and complex electrode geometries, as well as creating an appropriate gap width. This capability, when combined with the extremely thin ~ilm coatings applied through electrochemical and physical vapor deposition (PVD) techniques, enables these subminiature protective devices 60 to control the gap between the electrodes and protect circuits ~rom signi~icant levels o~ overvoltage.
The location o~ the electrodes at the top o~ the substrate o~ the ESD/SMD enables one to use laser processing methods as a high precision secondary operation, in that way trimming the gap width, and thus, the rating o~
the device.
Other ~eatures and advantages o~ the invention will be apparent ~rom the ~ollowing speci~ication taken in conjunction with the ~ollowing drawings.
Brie~ Description o~ Drawinqs FIG. 1 is a perspective view o~ a copper-plated, FR-4 epoxy sheet used to make a CA 02223746 1997-12-0~
subminiature ESD/SMDs in accordance with the present invention.
FIG. 2 is a cross-sectional view o~ a portion o~ the sheet o~ FIG. 1, and taken along lines 2-2 o~ FIG. 1.
FIG. 3 is a perspective view o~ the FR-4 epoxy sheet o~ FIG. 1, but stripped o~ its copper plating, and with a plurality o~ slots, each having a width W1 and a length L, routed into separate quadrants o~ that sheet.
FIG. 4 is an enlarged, cut-away perspective view o~ a portion o~ the routed sheet o~ FIG. 3, but with a copper plating layer having been reapplied.
FIG. 5 is a top perspective view o~
several portions o~ the ~lat, upward-~acing sur~aces o~ the replated copper sheet ~rom FIG.
4, a~ter each o~ those portions were masked with a patterned panel o~ an ultraviolet (W) light-opaque substance.
FIG. 6 is a perspective view o~ the reverse side o~ FIG. 5, but a~ter the removal o~ a strip-like portion o~ copper plating ~rom the replated sheet o~ FIG. 5.
FIG 7 is a perspective view o~ the top 57 o~ the strips 26 o~ FIG. 6, and showing linear regions 40 de~ined by dotted lines.
FIG. 8 is a view o~ a single strip 26 a~ter dipping into a copper plating bath and then a nickel plating bath, with the result that additional copper layer and a nickel layer - CA 02223746 1997-12-0~
are deposited onto the terminal-pads portions o~ the base copper layer.
FIG. 9 is a perspective view o~ the strip o~ FIG. 8, but after immersion into a tin-lead bath to create another layer over the copper and nickel layers o~ the terminal pads.
FIG. 10 shows the strip o~ FIG. 9, depicting the region where the voltage variable polymeric strip will be applied.
FIG. 11 shows the strip o~ FIG. 10, but with an added polymeric material 43 into the gap 25 o~ the strip 26.
FIG. 12 shows the strip o~ FIG. 11, but with an added cover coat 56 over the electrodes 21 and polymeric material 43.
FIG. 13 shows the individual ESD/SMD
in accordance with the invention as it is ~inally made, and a~ter a so-called dicing operation in which a diamond saw is used to cut the strips along parallel planes to ~orm the individual devices.
FIG. 14 is a ~ront view o~ the stencil printing machine used to per~orm the stencil printing step o~ the ESD/SMD
manu~acturing process.
Detailed Description While this invention is susceptible o~ embodiments in many di~erent ~orms, there is shown in the drawings and will herein be described in detail, a pre~erred embodiment o~
the invention with the understanding that the CA 02223746 1997-12-0~
present dlsclosure is to be considered as an exempli~ication o~ the principles o~ the inven-tion and is not intended to limit the broad aspects of the invention to the embodiment illustrated.
One pre~erred embodiment o~ the present invention is shown in FIG. 13. The thin ~ilm, circuit device is an subminiature overvoltage protection device in a sur~ace mountable con~iguration ~or use in printed circuit board or thick film hybrid circuit technology. One given name ~or the device is an electrostatic discharge sur~ace-mounted device (ESD/SMD). The sur~ace mountable device (SMD) is designed to protect against electrostatic discharge (ESD) damage to electronic components. The layout and design o~ the ESD/SMD device is such that it can be manu~actured in many sizes. One standard industry size ~or sur~ace mount devices, generally, is 3.175 mm (125 mils.) long by 1.524 mm (60 mils.) wide. This sizing is applicable to the present invention, and can be designated, ~or shorthand purposes, as "1206"
sized devices. It will be understood, however, that the present invention can be used on all other standard sizes ~or sur~ace mountable devices, such as 1210, 0~05, 0603 and 0402 devices, as well as non-standard sizes. The protection device o~ the present invention are designed to replace silicon diodes and MOV
AAfiENOED SHE~T
- CA 02223746 1997-12-0~
technologies which are commonly used ~or low power protection applications.
The protection device generally comprises three material subassemblies. As 5 will be seen, the first subassembly generally includes a substrate carrier or substrate 13, electrodes 21, and terminal pads 34, 36 ~or connecting the protection device 60 to the PC
board. The second subassembly includes the voltage variable polymer material 43, and the third subassembly includes the cover coat 56.
The ~irst or substrate carrier subassembly comprises a carrier base 13 having two electrodes 21 on the top sur~ace which are 15 separated by a gap 25 O~ controlled width W2, and wrap-around terminal pads 34, 36 on the top 57, bottom 58, and side 59 D~ the ~irst subassembly 13. The second subassembly or voltage variable polymeric material 43 iS
applied between these two electrodes 21 and e~ectively bridges the gap 25. A cover coat 56 iS placed over the polymeric material 43 and the electrodes 21 on the top sur~ace 57 O~ the substrate subassembly, and partially on the top 57 O~ the terminal pads 34, 36. The third subassembly provides protection ~rom impacts which may occur during automated assembly, and protection ~rom oxidation and other e~ects during use.
More particularly, the ~irst or substrate subassembly incorporates a carrier r ~ S~EIET
CA 02223746 1997-12-0~
10 ' ;' ' base 13 made o~ a seml-rigid epoxy material.
This material exhibits physical properties nearly identical with the standard substrate material used in the printed circuit board industry, thus providing ~or extremely well matched thermal and mechanical properties between the device and the board. Other types o~ material can be used as well.
The ~irst subassembly ~urther includes two metal electrodes 21 which are a part o~ the pads 34, 36 as one continuous layer or ~ilm. As will be seen, the pads 34, 36 are made up o~ several layers, including a base copper layer 44 which also makes up the electrodes 21, a supplemental copper layer 46, a nickel layer 48, and a tin-lead layer 52 to make up the rest o~ the pads 34, 36. In another embodiment, the supplemental copper layer 46 also makes up a second copper layer o~
the electrodes 21 (not shown), thereby increasing the thickness o~ the electrodes 21.
The base copper layer o~ the pads and the electrodes are simultaneously deposited by (1) electrochemical processes, such as the plating described in the pre~erred embodiment below; or (2) by physical vapor deposition (PVD). Such simultaneous deposition ensures a good conductive path between the pads 34, 36, electrodes 21, and second subassembly 43 when an overvoltage situation occurs. This type o~
deposition also ~acilitates manu~acture, and - CA 02223746 l997-l2-0~
permits very precise control of the thickness of the layers, including the electrodes 21.
After initial placement of the base copper 44 on~o the substrate or core 13, additional 5 layers 46, 48, 52 of a conductive metal are placed onto the terminal pads, as mentioned above. These additional layers could be defined and placed onto these pads by photolithography and deposition techniques, respectively.
The two metal electrodes, whether one or two layers (or more) thick are separated by a gap 25 Ci~ a controlled width W2. The substrate subassembly also contains and supports the two (2) terminal pads 34, 36 on the top 57, bottom 58, and sides 59 off the protection device These bottom 58 and/or sides 59 off the terminal pads 34, 36 serve to at~ach the device to the board and provide an electrical path :~rom the board to the electrodes 21. Again, the electrodes 21 and the terminal pads consist of a copper sheet 44 laminated to the case substrate material 13.
The other layers are deposited, either electrochemically or physical vapor deposition (PVD), simultaneously to ensure a good, continuous conductive path between the electrodes on the top sur~ace of the substrate, and the terminal pads 34, 36 on the bottom o~
the substrate 13. This configuration allows for ease o~ manufacture ~or surface mount - CA 02223746 1997-12-0~
assembly techniques to allow for a wrap around configuration o~ the terminal pads. The gap width W2 between the electrodes 21 are de~ined by photolithographic techniques and through an etching process. The nature of the photolithographic process allows for very precise control of the width W2 of the separation o~ the electrode metallization. The gap 25 separating the electrodes 21 extends on a straight line across the top sur~ace o~ the substrate 13. Proper sizing and configuration o~ the gap provides for proper trigger voltages and clamping voltages along with fast response time and reliable operation during an overvaltage condition. The electrode metallization can be selected from a variety of elemental or alloy materials, i.e. Cu, Ag, Ni, Ti, Al, NiCr, Tin, etc., to obtain coatings which exhibit desired physical, electrical, and metallurgical characteristics.
Photolithography, mechanical, or laser processing techniques are employed ~or de~ining the physical dimensions and width o~
the gap 25 and o~ the terminal pads 34, 36.
Subsequent photolithography and deposition operations are employed to deposit additional metallization to the terminal pads, i.e. Cu, Ni, and Sn/Pb, to a specified thickness.
The voltage variable polymeric material 43 provides the protection from ~ast transient overvoltage pulses. The polymeric CA 02223746 1997-12-0~
material 43 provides ~or a non-linear electrical response to an overvoltage condition. The polymer 43 is a material comprising ~inely divided particles dispersed in an organic resin or an insulating medium.
The polymeric material 43 consists o~
conductive particles which are uni~ormly dispersed throughout an insulating binder.
This polymer material 43 exhibits a non-linear resistance characteristic which is dependent on the particle spacing and the electrical properties o~ the binder. This polymer material is available from many sources and is disclosed by a variety o~ patents as was lS mentioned above.
The cover coat 56 subassembly is applied a~ter the metal deposition, pattern de~inition, and polymer 43 application process, to the top sur~ace o~ the substrate/polymer subassembly to provide a means ~or protecting the polymeric material 43 and to provide a ~lat top sur~ace ~or pick-and-place sur~ace mount technology automated assembly equipment. The : cover coat 56 prevents excessive oxidation o~
the electrodes 21 and the polymer 43 which can degrade the per~ormance o~ the protection device 60. The cover coat 56 can be comprised of a variety o~ materials including plastics, con~ormal coatings, polymers, and epoxies. The cover coat 56 also serves as a vehicle ~or marking the protective devices 60 with the marklng being placed between separate layers, or on the sur~ace o~ the cover coat 56 through an ink trans~er process or laser marking.
This protective device 60 may be made 5 by the following process. Shown in FIGS. 1 and 2 is a solid sheet 10 o:E an FR-4 epoxy with copper plating 12. The copper plating 12 and the FR-4 epoxy core 13 o~ this solid sheet 10 may best be seen in FIG. 2. This copper-plated 10 FR-4 epoxy sheet 10 is available ~rom Allied Signal T.~m; n~te Systems, Hoosick Falls, New York, as Part No. 0200BED130C1/ClGFN0200 C1/ClA2C. Although FR-4 epoxy is a pre~erred material, other suitable materials include any 15 material that is compatible with, i . e ., o:E a chemically, physically and structurally similar nature to, the materials ~rom which PC boards are made, as ment ioned above . Thus, another suitable material ~or this solid sheet 10 is 20 polyimide . FR- 4 epoxy and polyimide are among the class o:E materials having physical properties that are nearly identical with the standard substrate material used in the PC
board industry. As a result, the protective 25 device 60 and the PC board to which that protection device 60 is secured have extremely well-matched thermal and mechanical properties.
The substrate oi~ the protective device 60 o~
the present invention also provides desired 30 arc-tracking characteristics, and simultaneously exhibits su~lcient mechanical - CA 02223746 1997-12-0~
~lexibility to remain intact when exposed to the rapid release o~ energy associated with overvoltage.
In the next step o~ the process o~
manu~acturing the protective devices 60, the copper plating 12 is etched away ~rom the solid sheet 10 by a conventional etching process. In this conventional etching process, the copper is etched away from the substrate by a ~erric chloride solution.
Although it will be understood that a~ter completion o~ this step, all o~ the copper layer 12 of FIG. 2 is etched away ~rom FR-4 epoxy core 13 o~ this solid sheet 10, the remaining epoxy core 13 o~ this FR-4 epoxy sheet 10 is di~erent ~rom a "clean" sheet o~
FR-4 epoxy that had not initially been treated with a copper layer. In particular, a chemically etched sur~ace treatment remains on the sur~ace of the epoxy core 13 a~ter the copper layer 12 has been removed by etching.
This treated sur~ace o~ the epoxy core 13 is more receptive to subsequent operations that are necessary in the manu~acture o~ the present sur~ace-mounted subminiature protective device 60.
The FR-4 epoxy sheet 10 having this treated, copper-~ree sur~ace is then routed or punched to create slots 14 along quadrants o~
the sheet 10, as may be seen in FIG. 3. Dotted lines visually separate these ~our quadrants in CA 02223746 l997-l2-05 FIG. 3. The width Wl o~ the slots 14 (FIG. 4) is about 0.0625 inches. The length L o~ each o~ the slots 14 (FIG. 3) is approximately 5.125 When the routing or punching has been completed, the etched and routed or punched sheet 10 shown in FIG. 3 is again plated with copper. This reapplication o~ copper occurs through the immersion o~ the etched and routed sheet o~ FIG. 3 into an electroless copper plating bath. This method o~ copper plating is well-known in the art.
This copper plating step results in the placement o~ a copper layer having a uni~orm thickness along each o~ the exposed sur~aces of the sheet 10. For example, as may be seen in FIG. 4, the copper plating 18 resulting ~rom this step covers both (1) the flat, upper sur~aces 22 o~ the sheet 10; and (2) the vertical, interstitial regions 16 that de~ine at least a portion o~ the slots 14.
These interstitial regions 16 must be copper-plated because they will ultimately ~orm a portion o~ the terminal pads 34, 36 o~ the ~inal protection device 60. The uni~orm thickness o~ the copper plating will depend upon the ultimate needs o~ the user.
A~ter plating has been completed, to arrive at the copper-plated structure o~ FIG.
4, the entire exposed sur~ace o~ this structure CA 02223746 l997-l2-0 is covered with a so-called photoresist polymer.
An otherwise clear mask is placed over the replated copper sheet 20 a~ter it has been covered with the photoresist. Patterned panels are a part o~, and are evenly spaced across, this clear mask. These patterned panels are made o~ an W light-opaque substance, and are o~ a size and shape corresponding to the size and shape generally o~ the patterns 30 shown in FIG. 5.
Essentially, by placing this mask having these panels onto the replated copper sheet 20, several portions o~ the ~lat, upward-~acing sur~aces 22 o~ the replated copper sheet 20 are e~ectively shielded ~rom the e~ects o~ W
light.
It will be understood ~rom the following discussion that the pattern 30 will essentially de~ine the shapes and sizes o~ the electrodes 21 and polymer strip 43. A later step de~ines the remainder o~ terminal pads 34, 36. It will be appreciated that the width, ~ length and shape o~ the electrodes 21 and polymer strip 43 may be altered by changing the size and shape o~ the W light-opaque panel patterns. In particular, one embodiment o~ the present invention includes having curved corners 19 (not shown) instead o~ sharp corners 19 as shown. In ~act, it has been seen that it is pre~erable to curve the corners 19.
CA 02223746 l997-l2-0 This step, therefore, defines the gap 25 between the electrodes 21, as well as the notches 23 in the electrodes 21. As mentioned above, photolithographic, mechanical, and laser processing techniques can be employed to configure very small, intricate, and complex electrode 21 and gap 25 geometries. The electrode 21 configuration can be conveniently modified to obtain specific electrical characteristics in resultant protective devices 60. The gap width W2 can be changed to provide control of triggering and clamping voltages during an overload event. The indicated device construction results in a triggering and clamping voltage rating similar to devices o~
previous construction. Tests have been conducted with peak voltages o~ 2kV, 4kV, and 8kV as the ESD waveform. The use o~ a 2 mil and 4 mil gap width resulted in triggering voltages o~ loO-150 V and clamping voltages o~
30-50 V.
Additionally within this step, the backside o~ the sheet is covered with a photoresist material and an otherwise clear mask is placed over the replated copper sheet after it has been covered with the photoresist. A rectangular panel is a part o~
this clear mask. The rectangular panels are made of a W light-opaque substance, and are of a size corresponding to the size o~ the panel 28 shown in FIG. 6. Essentially, by placing ~ CA 02223746 1997-12-0~
thls mask having these panels onto the replated copper sheet 20, several strips of the flat, downward-facing surfaces 28 of the replated copper sheet 20 are ef~ectively shielded from the e~fects of the W light.
The rectangular panels will essentially define the shapes and sizes of the wide terminal pads 34 and 36 and the lower middle portion 28 of the bottom 58 of the strip 26. Thus, the copper plating from a portion of the bottom 58 of a strip 26 is defined by a photoresist mask. Particularly, the copper plating from the lower, middle portion 28 of the bottom 58 of the strip 26 is removed. A
perspective view of this section of this replated sheet 20 is shown in FIG. 6.
The entire replated, photoresist-covered sheet 20, i.e., the top 57, bottom 58, and sides 59 of that sheet 20, is then subjected to W light. The replated sheet 20 is subjected to the W light for a time sufficient to ensure curing of all of the photoresist that is not covered by the square panels and rectangular -strips of the masks.
Thereafter, the masks containing these square panels and rectangular strips are removed from the replated sheet 20. The photoresist that was formerly below these square panels remains uncured. This uncured photoresist may be washed from the replated sheet 20 using a solvent.
~/~cNOE
=
~ - }
- i The cured photoresist on the remainder o:E the replated sheet 20 provides protection against the next step in the process. Particularly, the cured photoresist prevents the removal of copper beneath those areas of cured photoresist. The regions ~ormerly below the patterned panels have no cured photoresist and no such protection.
Thus, the copper ~rom those regions can be removed by etching. This etching is per~ormed with a ~erric chloride solution.
A~ter the copper has been removed, as may be seen in FIGS. 5 and 6, the regions formerly below the patterned panels and the rectangular strips o~ the mask are not covered at all. Rather, those regions now comprise areas 28 and 30 o~ clear epoxy.
The replated sheet 20 is then placed in a chemical bath to remove all o~ the remaining cured photoresist ~rom the previously cured areas o~ that sheet 20.
For the purposes o~ this speci~ication, the portion o~ the sheet 20 between adjacent slots 14 is known as a strip 26. This strip has a dimension D as shown in FIG. 4 which defines the length of the device.
After completion o~ several o~ the operations described in this speci~ication, this strip 26 will ultimately be cut into a plurality o~
pieces, and each o~ these pieces becomes an AMrN.~, t~
~ CA 02223746 1997-12-0~
ESD/SMD or protective device 60 in accordance with the invention.
As may also be seen ~rom FIG. 6, the underside 58 o~ the strip 26 has regions along its periphery which still include copper plating. These peripheral regions 34 and 36 o~
the underside 58 o~ the strip 26 ~orm portions o~ the pads. These pads will ultimately serve as the means ~or securing the entire, ~inished protective device 60 to the PC board.
FIG. 7 is a perspective view o~ the top-side 57 o~ the strips 26 o~ FIG. 6.
Generally opposite and coinciding with the lower, middle portions 28 o~ these strips 26 are linear regions 40 on this top-side 38.
These linear regions 40 are defined by the dotted lines o~ FIG. 7.
FIG. 7 is to be re~erred to in connection with the next step in the manu~acture o~ the invention. In this next step, a photoresist polymer is placed along each o~ the linear regions 40 o~ the top side 57 o~ the strips 26. Through the covering o~
these linear regions 40, photoresist polymer is also placed along the gap 25 and electrodes 21.
These electrodes 21 are made 0? a conductive metal, here copper. The photoresist is then treated with W light, resulting in a curing o~
the photoresist onto linear region 40.
As a result o~ the curing o~ this photoresist onto the linear region 40, metal ~,? '~
CA 02223746 l997-l2-0 will not adhere to this linear region 40 when the strip 26 iS dipped into an electrolytic bath containing a metal ~or plating purposes.
In addition, as explained above, the middle portion 28 oi~ the underside 58 o:E the strip 26 will also not be subject to platlng when the strip 26 is dipped into the electrolytic plating bath. Copper metal previously covering this metal portion had been removed, revealing the bare epoxy that ~orms the base o~ the sheet 20. Metal will not adhere to or plate onto this bare epoxy using an electrolytic plating process.
The entire strip 26 is dipped into an electrolytic copper plating bath and then an electrolytic nickel plating bath. As a result, as may be seen in FIG. 8, copper 46 and nickel layers 48 are deposited on the base copper layer 44. Ai~ter deposition of~ these copper 46 and nickel layers 48, an additional tin-lead layer 52 is deposited in these same areas through an electrolytic tin-lead bath as shown in FIG. 9. The cured photoresist polymer on the linear region 40 is then removed.
As shown in FIGS. 10 and 11, the polymer material 43 iS then applied. The polymer 43 can be applied in a number o~ ways.
For example, the polymer 43 can be applied using the stencil printing machine shown in FIG. 14 in a manner similar to the use oi~ the stencil printing described ~urther below. In - CA 02223746 l997-l2-0~
addition, the polymer 43 can be applied manually with a tube o~ the polymer 43. Other automated means for applying the polymer 43 are possible as well. Once the polymer 43 has been applied and deposited within region 42, and in between regions 41, the sheet 20 is heat cured to solidi~y the polymer 43 to obtain strips 26 that look like the strip 26 in FIG. 11.
The next step in the manu~acture o~
the protective device 60 is the placement, across the length o~ the most of the top 57 o~
the strip 26, o~ a protective layer 56 ( FIG.
12). This protective layer 56 iS the third subassembly o~ the present protective device 60, and ~orms a relatively tight seal over the electrodes 21 and polymer strip 43 area. In this way, the protective layer 56 provides protection from oxidation and impacts during attachment to the PC board. This protective layer also serves as a means o~ providing ~or a sur~ace ~or pick and place operations which use a vacuum pick-up tool.
This protective layer 56 helps to control the melting, ionization and arcing which occur in the ~usible link 42 during current overload conditions. The protective layer 56 or cover coat material provides desired arc-quenching characteristics, especially important upon interruption o~ the ~usible link 42.
- CA 02223746 1997-12-0~
24 ' The application o~ the cover coat 56 is such that it can be performed in a single processing step using a simple ~ixture to de~ine the shape o~ the body o~ the device.
This method of manufacture provides ~or advantages over current methodologies in protecting the electrodes 21, gap 25, and polymer 43 ~rom physical and environmental damage. The application o~ the conformal coating 56 is performed in such a fashion that the physical location o~ the electrode gap 25 is not critical, as in a clamping or die mold method. The con~ormal coating may be mixed with a colored dye prior to application to provide for a color-coded voltage rated protective device 60.
The protective layer 56 may be comprised of a polymer, pre~erably a polyurethane gel or paste when a stencil printing cover coat application process is used, and pre~erably a polycarbonate adhesive when an injection mold cover coat application process is used. A pre~erred polyurethane is made by Dymax. Other similar gels, pastes, and adhesives are suitable ~or the invention depending on the cover coat application process used. In addition to polymers, the protective layer 56 may also be comprised of plastics, con~ormal coatings and epoxies.
This protective layer 56 is applied to the strips 26 using a stencil printing - CA 02223746 1997-12-0~
process which includes the use of a common stencil printing machine shown in FIG. 14. It has been found that stencil printing is faster than some alternative processes for applying the cover coat 56, such as with an injection mold process using die molds. Specifically, it has been found that the use of a stencil printing process while using a stencil printing machine, at least, doubles production output from the injection mold operation. The stencil printing machine is made by Affiliated Manufacturers, Inc. of Northbranch, New Jersey, Model No. CP-885.
In the stencil printing process, the material is applied to all of the strips 26 in one quadrant of the sheet 20, simultaneously.
Using the stencil print process, the material cured much faster than the injection mold process because the cover coat material is directly exposed to the W radiation, while the W light must travel through a filter in the injection mold process. Furthermore, the stencil printing process produces a more uni~orm cover coat than the injection filling process, in terms of the height and the width of the cover coat 56. Because of that uniformity, the fuses can be tested and packaged in a relatively fast automated process. With the injection filling process it may be difficult to precisely align the protective devices 60 in testing and packaging CA 02223746 l997-l2-0 equipment due to some non-uniform heights and widths of the cover coat 56.
The stencil printing machine comprises a slidable plate 70, a base 72, a squeegee arm 74, a squeegee 76, and an overlay 78. The overlay 78 is mounted on the base 72 and the squeegee 76 is mc;vably mounted on the squeegee arm 74 above the base 72 and overlay 78. The plate 70 is slidable underneath the base 72 and overlay 78. The overlay 78 has parallel openings 80 which correspond to the width of the cover coat 56.
The stencil printing process begins by attaching an adhesive tape under the sheet 20. The sheet 20, with the adhesive tape attached, is placed on the plate 70 with the adhesive tape between the plate 70 and the fuse sheet 20. The cover coat 56 material is then applied with a syringe at one end of the overlay 78. The plate 70 slides underneath the overlay 78 and lodges the sheet 20 underneath the overlay 78 in correct alignment with the parallel openings 80. The squeegee 76 then lowers to contact the overlay 78 beyond the material on the top of the overlay 78. The squeegee 76 then moves across the overlay 78 where the openings 80 exist, thereby forcing the cover coat 56 material through the openings 80 and onto each of the strips 26 of the sheet 20. Thus, the cover coat now covers the electrodes 21, the gap, 25, and the polymer CA 02223746 1997-12-0~
strip 43 (FIGS. 12 and 13). The squeegee 76 is then raised, and the sheet 20 is unlodged ~rom the overlay 78. The openings 80 in the overlay 78 are wide enough so that the protective layer partially overlaps the pads 34, 36, as shown in FIGS. 12 & 13. In additlon, the material used as the cover coat material should have a viscosity in the paste or gel region so that a~ter the material is spread onto the sheet 20, it will ~low in a manner which creates a generally ~lat top sur~ace 49, but such that the material 56 will not ~low into the slots 14. The sheet 20 o~ strips 26 are then W
cured in a W chamber. At the end of this curing, the polyurethane gel or paste has solidi~ied, ~orming the protective layer 56 (FIGS. 12 and 13).
Although a colorless, clear cover coat is aesthetically pleasing, alternative types of cover coats may be used. For example, colored, clear or transparent cover coat materials may be used. These colored materials may be simply manu~actured by the addition o~ a dye to a clear cover coat material. Color coding may be accomplished through the use o~
these colored materials. In other words, di~erent colors o~ the cover coat can correspond to di~erent ratings, providing the user with a ready means o~ determining the rating o~ any given protective device 60. The transparency o~ both o~ these coatings permit CA 02i23746 1997-12-0~ -.
the user to visually inspect the polymer strip 43 prior to installation, and during use.
The strips 26 are then ready for a so-called dicing operation, which separates those strips 26 into individual fuses. In this dicing operation, a diamond saw or the like is used to cut the strips 26 along parallel planes 61 (FIG. 12) into individual thin film surface-mounted fuses 60 (FIG. 13). The cuts bisect the notches 23 in the electrodes 21. At this point, it can more easily be understood that the metallization of the electrodes 21 is removed from the notches 23 or notched areas 23. Specifically, it is easier to cut through notched areas 23 without the electrodes. In addition, during dicing, curling of the metallization may take place along the cut, -thereby causing a curl of metal (part of an electrode) to move into the gap area and effectively reduce the gap width W2. Putting the notches 23 in the places where the dicing is to take place alleviates this possible problem and other possible problems. It should be noted that the notches 23 can extend further toward the pads 34, 36, and that the corners 19 of the notches 23 can be curved in alternative embodiments.
This cutting operation completes the manufacture of the thin film protective device 60 (FIG. 13) of the present invention.
All o~ the preceding ~eatures combine to produce an ESD/SMD device assembly which exhibits improved control o~ triggering and clamping voltage characteristics by regulating electrode and gap geometries, and the polymer 43 composition. The dimensional control aspects o~ the deposition and photolithographic processes, coupled with the proper selection o~
electrode and polymer 43 material, provide ~or consistent triggering and clamping voltages.
However, it wlll be understood that the - invention may be embodied in other speci~ic ~orms without departing ~rom the spirit or central characteristics thereo~.
. . . i AMEI~ID~D SHEET
Claims (16)
1. A thin film surface-mount circuit protection device comprising:
a substrate (13) having a top surface (57), a bottom surface (58) and opposing side surfaces (59);
a pair of electrodes (21) disposed on the top surface (57) of the substrate (13), the electrodes (21) being made of a first conductive metal and being spaced apart by a gap (25);
a pair of multi-layered terminal pads (34, 36) electrically connected to the pair of electrodes (21), the terminal pads (34, 36) extending over the side surfaces (59) of the substrate (13) and terminating on the bottom surface (58) of the substrate (13); and, a voltage variable polymeric material deposited between the electrodes (21) in the gap (25).
a substrate (13) having a top surface (57), a bottom surface (58) and opposing side surfaces (59);
a pair of electrodes (21) disposed on the top surface (57) of the substrate (13), the electrodes (21) being made of a first conductive metal and being spaced apart by a gap (25);
a pair of multi-layered terminal pads (34, 36) electrically connected to the pair of electrodes (21), the terminal pads (34, 36) extending over the side surfaces (59) of the substrate (13) and terminating on the bottom surface (58) of the substrate (13); and, a voltage variable polymeric material deposited between the electrodes (21) in the gap (25).
2. The surface-mount protection device of Claim 1, wherein said first conductive metal is selected from the group including copper, silver, nickel, titanium, aluminum or alloys thereof.
3. The surface-mount protection device of Claim 1 wherein the layer of the first conductive metal of the electrodes (21) forms a part of the multi-layered terminal pads (34, 36).
4. The surface-mount protection device of Claim 3, wherein the layer of the first conductive metal of the electrodes 21 and part of the pads 34, 36 is one continuous layer.
5. The surface-mount protection device of Claim 1, wherein the electrodes 21 extend substantially the width of the circuit protection device.
6. A thin film surface-mount circuit protection device comprising:
a first subassembly including a substrate (13) having a top surface (57), a bottom surface (58) and opposing side surfaces (59), first and second multi-layered terminal pads (34, 36), and first and second electrodes (21), the first and second electrodes (21) being disposed on the top surface (57) of the substrate (13) and being spaced apart to form a gap (25), the first and second terminal pads (34, 36) being electrically connected to the first and second electrodes (21) respectively, the first and second terminal pads (34, 36) extending over the side surfaces (59) of the substrate (13) and terminating on the bottom surface (58) of the substrate (13); and, a second subassembly including a voltage variable polymeric material deposited in the gap (25).
a first subassembly including a substrate (13) having a top surface (57), a bottom surface (58) and opposing side surfaces (59), first and second multi-layered terminal pads (34, 36), and first and second electrodes (21), the first and second electrodes (21) being disposed on the top surface (57) of the substrate (13) and being spaced apart to form a gap (25), the first and second terminal pads (34, 36) being electrically connected to the first and second electrodes (21) respectively, the first and second terminal pads (34, 36) extending over the side surfaces (59) of the substrate (13) and terminating on the bottom surface (58) of the substrate (13); and, a second subassembly including a voltage variable polymeric material deposited in the gap (25).
7. The surface-mount protection device of Claim 6, further comprising a third subassembly including a protective layer (56) having a generally flat top surface (49) which overlies the voltage variable polymeric material and electrodes (21) so as to provide protection from impacts and oxidation.
8. The surface-mount protection device of Claim 7, wherein said protective layer 56 is made of a polymeric material.
9. The surface-mount protection device of Claim 6, wherein said supporting substrate 13 is made of an FR-4 epoxy or a polyimide.
10. The surface-mount protection device of Claim 7, wherein the protective layer (56), having a generally flat top surface (49), is transparent and colorless.
11. The surface-mount protection device of Claim 7, wherein the protective layer (56), having a generally flat top surface (49), is transparent and colored.
12. A method of manufacturing a thin film surface-mount circuit device for protection against electrostatic transient voltage damage to electrical components, comprising the steps of:
a. providing a substrate (13) having a top (57), a bottom (58) and opposing sides (59);
b. depositing, upon the top (13) of a substrate, a first conductive layer to simultaneously form a pair of electrodes (21) and a first terminal pad layer, the electrodes (13) being spaced apart by a gap (25) having a gap width (W2), wherein the gap width (W2), at least, partially determines a triggering voltage and a clamping voltage rating for the circuit device, and wherein depositing the electrodes (21) creates a gap width (W) of less than half of the width of one of the electrodes 21);
c. depositing a voltage variable polymeric material in the gap (25), wherein the voltage variable polymer is highly resistive when a normal voltage is applied across the voltage variable polymer, and wherein the voltage variable polymer switches to a highly conductive state when a high electrostatic transient voltage is applied across the voltage variable polymeric material, for protection against electrostatic transient voltage damage to electrical components.
a. providing a substrate (13) having a top (57), a bottom (58) and opposing sides (59);
b. depositing, upon the top (13) of a substrate, a first conductive layer to simultaneously form a pair of electrodes (21) and a first terminal pad layer, the electrodes (13) being spaced apart by a gap (25) having a gap width (W2), wherein the gap width (W2), at least, partially determines a triggering voltage and a clamping voltage rating for the circuit device, and wherein depositing the electrodes (21) creates a gap width (W) of less than half of the width of one of the electrodes 21);
c. depositing a voltage variable polymeric material in the gap (25), wherein the voltage variable polymer is highly resistive when a normal voltage is applied across the voltage variable polymer, and wherein the voltage variable polymer switches to a highly conductive state when a high electrostatic transient voltage is applied across the voltage variable polymeric material, for protection against electrostatic transient voltage damage to electrical components.
13. The method as set forth in Claim 12, wherein the first terminal pad layer extends from the top of the substrate (13) and is deposited upon the sides of the substrate (13) simultaneously with the depositing of the first terminal pad layer on the top of the substrate (13) and the depositing of the electrodes (21) on the top of the substrate (13).
14. The method as set forth in Claim 12, wherein the first conductive layer which forms the electrodes (21) and the first terminal pad layer is deposited by vapor deposition, and wherein the gap width (W2) is intricately dimensioned through photolithography, in order to obtain specific electrical characteristics for the circuit device.
15. The method as set forth in Claim 12, wherein the first conductive layer which forms the electrodes (21) and the first terminal pad layer is electrochemically deposited, and wherein the gap width (W2) is intricately dimensioned through photolithography, in order to obtain specific electrical characteristics for the circuit device.
16. A method of protecting a thin film surface-mount circuit device for protection against electrostatic transient voltage damage to electrical components having a pair of electrodes (21) separated by a gap (25) having a gap width (W2), on the top surface (57) of a substrate (13), wherein the gap width (W2), at least, partially determines a triggering voltage and a clamping voltage rating for the circuit device, and wherein the gap width (W2) is less than half of the width of one of the electrodes (21), with a voltage variable polymeric material deposited in the gap, the method comprising placing a protective layer (56) having a flat top surface (49) over the electrodes (21), the voltage variable polymeric material, and the gap (56).
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US47450295A | 1995-06-07 | 1995-06-07 | |
| US08/474,502 | 1995-06-07 | ||
| US08/474,940 | 1995-06-07 | ||
| US08/474,940 US6023028A (en) | 1994-05-27 | 1995-06-07 | Surface-mountable device having a voltage variable polgmeric material for protection against electrostatic damage to electronic components |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2223746A1 true CA2223746A1 (en) | 1996-12-19 |
Family
ID=27044479
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002223746A Abandoned CA2223746A1 (en) | 1995-06-07 | 1996-06-06 | Method and apparatus for a surface-mountable device for protection against electrostatic damage to electronic components |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0834180B1 (en) |
| JP (1) | JPH11507766A (en) |
| CN (1) | CN1191623A (en) |
| AT (1) | ATE193149T1 (en) |
| AU (1) | AU6597296A (en) |
| CA (1) | CA2223746A1 (en) |
| DE (1) | DE69608440T2 (en) |
| WO (1) | WO1996041356A2 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1997028543A1 (en) * | 1996-01-22 | 1997-08-07 | Littelfuse, Inc. | Surface mountable electrical device comprising a ptc element |
| US6023403A (en) * | 1996-05-03 | 2000-02-08 | Littlefuse, Inc. | Surface mountable electrical device comprising a PTC and fusible element |
| NL1014319C2 (en) * | 2000-02-08 | 2001-08-09 | Fci S Hertogenbosch B V | Connector comprising an ESD suppressor. |
| US7258819B2 (en) | 2001-10-11 | 2007-08-21 | Littelfuse, Inc. | Voltage variable substrate material |
| US7567416B2 (en) * | 2005-07-21 | 2009-07-28 | Cooper Technologies Company | Transient voltage protection device, material, and manufacturing methods |
| US7567415B2 (en) * | 2006-07-11 | 2009-07-28 | Honeywell International Inc. | Separable transient voltage suppression device |
| CN101950645A (en) * | 2010-08-27 | 2011-01-19 | 广东风华高新科技股份有限公司 | Chip overvoltage protector and manufacturing method thereof |
| US20120307467A1 (en) * | 2011-06-03 | 2012-12-06 | Navarro Luis A | Oxygen-Barrier Packaged Surface Mount Device |
| KR20130117397A (en) * | 2012-04-17 | 2013-10-28 | 주식회사 이노칩테크놀로지 | Circuit protection device |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4097834A (en) * | 1976-04-12 | 1978-06-27 | Motorola, Inc. | Non-linear resistors |
| FR2513032B1 (en) * | 1981-09-14 | 1985-12-13 | Carreras Michelle | INTEGRATED PROTECTION AGAINST OVERVOLTAGES OF AN ELECTRONIC CIRCUIT, AND ELECTRONIC CIRCUIT PROTECTED BY THIS DEVICE |
| US4726991A (en) * | 1986-07-10 | 1988-02-23 | Eos Technologies Inc. | Electrical overstress protection material and process |
| US4977357A (en) * | 1988-01-11 | 1990-12-11 | Shrier Karen P | Overvoltage protection device and material |
| US5262754A (en) * | 1992-09-23 | 1993-11-16 | Electromer Corporation | Overvoltage protection element |
| US5552757A (en) * | 1994-05-27 | 1996-09-03 | Littelfuse, Inc. | Surface-mounted fuse device |
-
1996
- 1996-06-06 AU AU65972/96A patent/AU6597296A/en not_active Abandoned
- 1996-06-06 CA CA002223746A patent/CA2223746A1/en not_active Abandoned
- 1996-06-06 WO PCT/US1996/012217 patent/WO1996041356A2/en not_active Application Discontinuation
- 1996-06-06 DE DE69608440T patent/DE69608440T2/en not_active Expired - Fee Related
- 1996-06-06 JP JP9502323A patent/JPH11507766A/en active Pending
- 1996-06-06 CN CN96195759A patent/CN1191623A/en active Pending
- 1996-06-06 AT AT96925471T patent/ATE193149T1/en not_active IP Right Cessation
- 1996-06-06 EP EP96925471A patent/EP0834180B1/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| AU6597296A (en) | 1996-12-30 |
| EP0834180B1 (en) | 2000-05-17 |
| WO1996041356A2 (en) | 1996-12-19 |
| DE69608440D1 (en) | 2000-06-21 |
| MX9709973A (en) | 1998-06-28 |
| JPH11507766A (en) | 1999-07-06 |
| ATE193149T1 (en) | 2000-06-15 |
| CN1191623A (en) | 1998-08-26 |
| DE69608440T2 (en) | 2001-01-04 |
| WO1996041356A3 (en) | 1997-01-30 |
| EP0834180A2 (en) | 1998-04-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |