GB2156742A - Etching plastics encapsulated electronic packages - Google Patents
Etching plastics encapsulated electronic packages Download PDFInfo
- Publication number
- GB2156742A GB2156742A GB8408993A GB8408993A GB2156742A GB 2156742 A GB2156742 A GB 2156742A GB 8408993 A GB8408993 A GB 8408993A GB 8408993 A GB8408993 A GB 8408993A GB 2156742 A GB2156742 A GB 2156742A
- Authority
- GB
- United Kingdom
- Prior art keywords
- etchant
- package
- encapsulated electronic
- etching
- laser beam
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000005530 etching Methods 0.000 title claims abstract description 20
- 239000004033 plastic Substances 0.000 title claims abstract description 9
- 229920003023 plastic Polymers 0.000 title claims abstract description 9
- 238000009835 boiling Methods 0.000 claims abstract description 10
- 238000005538 encapsulation Methods 0.000 claims abstract description 9
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims abstract description 4
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims abstract description 3
- 235000011149 sulphuric acid Nutrition 0.000 claims abstract description 3
- 239000001117 sulphuric acid Substances 0.000 claims abstract description 3
- 238000000034 method Methods 0.000 claims description 22
- XKRFYHLGVUSROY-UHFFFAOYSA-N argon Substances [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 4
- 229910052786 argon Inorganic materials 0.000 claims description 3
- -1 argon ion Chemical class 0.000 claims description 3
- 239000007788 liquid Substances 0.000 claims description 3
- 230000005855 radiation Effects 0.000 abstract description 4
- 230000008569 process Effects 0.000 description 5
- 239000004593 Epoxy Substances 0.000 description 3
- 239000008393 encapsulating agent Substances 0.000 description 3
- 238000000605 extraction Methods 0.000 description 3
- 239000003517 fume Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 238000011109 contamination Methods 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 239000000945 filler Substances 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 239000002253 acid Substances 0.000 description 1
- 238000013019 agitation Methods 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000000637 aluminium metallisation Methods 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000003745 diagnosis Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052743 krypton Inorganic materials 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000004377 microelectronic Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000008439 repair process Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/0011—Working of insulating substrates or insulating layers
- H05K3/0017—Etching of the substrate by chemical or physical means
- H05K3/002—Etching of the substrate by chemical or physical means by liquid chemical etching
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/50—Assembly of semiconductor devices using processes or apparatus not provided for in a single one of the subgroups H01L21/06 - H01L21/326, e.g. sealing of a cap to a base of a container
- H01L21/56—Encapsulations, e.g. encapsulation layers, coatings
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/0001—Technical content checked by a classifier
- H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
- H05K2203/07—Treatments involving liquids, e.g. plating, rinsing
- H05K2203/0779—Treatments involving liquids, e.g. plating, rinsing characterised by the specific liquids involved
- H05K2203/0786—Using an aqueous solution, e.g. for cleaning or during drilling of holes
- H05K2203/0789—Aqueous acid solution, e.g. for cleaning or etching
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
- H05K2203/10—Using electric, magnetic and electromagnetic fields; Using laser light
- H05K2203/107—Using laser light
Landscapes
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Microelectronics & Electronic Packaging (AREA)
- General Physics & Mathematics (AREA)
- Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- Power Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Encapsulation Of And Coatings For Semiconductor Or Solid State Devices (AREA)
- Laser Beam Processing (AREA)
Abstract
In order to remove a region of encapsulation from a plastics encapsulated electronic package 10 to expose a portion of the encapsulated component, the package is placed in etchant 11 e.g. fuming nitric acid or concentrated sulphuric acid, and then a sharply defined beam of laser radiation is directed on to the surface to produce localised boiling of the etchant and thus localised etching action. <IMAGE>
Description
SPECIFICATION
Etching plastics encapsulated electronic packages
This invention relates to a technique for the selective etching of plastics encapsulated electronic packages to remove the encapsulant so as to expose a region of the surface of a component encapsulated therein. The widespread practice of encapsulating sensitive electronic components, particularly microelectronic components, in inert plastics material for purposes of environmental protection has compounded the problems encountered in exposing the encapsulated component for subsequent evaluation, fault diagnosis, repair or modification. General, non-selective etching is a commonly adopted procedure, but can cause considerable damage to the package as a whole and to its terminal leads. Another technique is to use jet-etching, which, whilst being fairly selective, can cause damage to more sensitive areas of the component.
The present invention is concerned with an alternative selective etching technique that is capable of relatively sharp delineation of the etched area, and that is readily controllable.
According to the present invention there is provided a method of selectively etching a plastics encapsulated electronic package to expose at least a region of the surface of the component encapsulated therein, wherein the region of the package to be selectively etched is covered with a liquid etchant that is substantially inoperative at room temperature, but is active at its boiling point, and wherein an intense laser beam is directed upon the surface of the package to produce localised boiling of the etchant adjacent that surface.
The principle underlying of the method of the invention is that the package to be etched is immersed in a suitable etching solution, and laser radiation is directed onto the portion of the package which is to be removed. Absorption of the laser energy at the surface of the package produces local heating, which in turn induces local boiling of the etchant. The combination of elevated temperature and strong microstirring produced by the local boiling, results in a rapid dissolution of the encapsulation. An important feature of the process is that the vigorous microstirring and the ensuing rapid agitation of the etchant is extremely effective in thoroughly cleaning traces of encapsulation from the component.
Furthermore, removal of material is confined to those areas where the laser is incident.
The selectivity of this technique is based on the fact that etching only occurs where the laser beam is incident. Therefore, the area to be removed must be delineated in some way.
For less demanding applications, the simplest approach is to control the size of the laser beam by means of a focussing or de-focussing arrangement, and then to adjust the position of the package and/or the position of the laser beam. However, in more critical applications, a more accurate definition of the etched area may be necessary. In such cases, the shape of the etched area can be defined by a non-contacting mask. Use of a beam homogeniser, such as a light pipe,will ensure that the intensity is uniform across the whole of the etched area. The intensity of the laser beam should be sufficient to induce local boiling. Typically this requires a power density of the order of 1 00Wcm - 2 The laser should be capable of providing continuous intensities of this order, for several minutes.
The selectivity of the process is enhanced by positioning the surface to be etched face upwards in a horizontal plane, and directing the laser bsa;n vertically down onto the surface. This provides a greater degree of control over the local convection current produced, which would otherwise produce etching of contiguous unilluminated areas.
Many encapsulation compounds presently in use contain fillers to improve the thermal and mechanical properties of the encapsulant.
The effect of these fillers is to produce a cloudy suspension upon dissolution, which impedes the transmission of the laser beam.
Particularly in these instances it is desirable, therefore, that the etchant is circulated and filtered in order to remove such particulate contamination. Where corrosive etchants are to be handled, it is imperative that the circulation and filtration system be fully compatible with the etchant.
The selectivity of this laser enhanced etching of encapsulant materials is based on the premise that etching only occurs at elevated temperatures. Therefore, an etchant is selected which does not appreciably attack the encapsulation at the ambient temperature, but which rapidly removes the encapsulation at temperatures near to the boiling point. Clearly the etchant must not damage the component or its connectors, once exposed. Provided these conditions can be fulfilled, then almost any electronic package is amenable to this process. Additionally, it is possible that the etchant may produce harmful vapours. If this is the case, it is essential to provide some means for fume extraction.
To be of practical benefit, the laser must be able to deliver sufficient power, and above all, its radiation must be transmitted by the etchant. Since most liquids display strong absorption not only in the mid-far infra-red region of the spectrum, but also in the deep ultraviolet, the useful wavelength range for etching is generally restricted to the range 300-1000nm. Furthermore, the laser is preferably c.w. or quasi c.w. and must be capable of delivering the required power. Typically, this means that it should be capable of delivering at least 5W. The class of laser most favoured by these considertions is the continuous wave ion laser, for instance an argon or krypton ion laser.
There follows a description of the selective etching of a dual-in-line package comprising an epoxy encapsulated microchip by a method embodying the invention in a preferred form.
The description refers to the accompanying drawings which diagrammatically depicts the apparatus employed.
A small portion of the radiation output from a c.w. argon ion laser 1 capable of delivering up to about 20W of continuous power in the spectral range 450-540nm is tapped off by means of a beam splitter 2, and is directed on to a power monitoring photodetector 3. The remainder is directed via a lens 4 into one end of a solid glass rod light pipe 5 that functions as a beam intensity homogeniser. At the far end of the rod 5 is situated a mask 6, and beyond this is a further lens 7 and beam deflecting prism 8. Vertically beneath the prism 8 is a vessel 9 containing a dual-in-line package 10 covered with fuming nitric acid 11. The package 10, which is an epoxy encapsulated microchip, is located so that the mask 6 is imaged by the lens 7 upon the substantially horizontal package surface so that the area illuminated conforms to the shape of the aperture of the mask 6.Optionally a duct 12 is provided that is connected to a fume extraction means (not shown). Optionally, means (also not shown) may be provided for continuously circulating the etchant through a filter to remove etch debris.
Fuming nitric acid was found to be the most effective etchant, although concentrated sulphuric acid was found nearly as effective.
Because of the harmful nature of these substances, fume extraction was provided. The laser power was then increased until local boiling occurred. As an approximate guide to the powers used, to etch a circular hole of 2mm diameter required a power of about 4-5W. Etching of the epoxy encapsulation
proceeded rapidly, and usually no more than 4-5 mins was required to remove the 2mm of encapsulation necessary to expose the chip.
When no filtration of the etchant was employed it was occasionally found that the surface of the chip was contaminated by debris, however, this was easily removed by cleaning with fesh, clean acid. In each instance, when the process was completed, the surface of the microchip was left clean and free of contamination, the demarcation between the etched and non-etched areas being
extremely well defined. The gold of the wire
bonds to the microchip appeared to have sustained no damage from the etching process, and neither did the aluminium
metallisation of the microchip suffer any attack at least to any appreciable extent. It is
believed that the aluminium metal must have
been saved from etching by the formation of an impervious oxide layer.
Claims (8)
1. A method of selectively etching a plastics encapsulated electronic package to expose at least a region of the surface of the component encapsulated therein, wherein the region of the package to be selectively etched is covered with a liquid etchant that is substantially inoperative at room temperature, but is active at its boiling point, and wherein an intense laser beam is directed upon the surface of the package to produce localised boiling of the etchant adjacent that surface.
2. A method as claimed in claim 1, wherein the surface exposed to the laser beam is face upwards in a substantially horizontal plane.
3. A method as claimed in claim 1 or 2, wherein the etchant is continuously filtered to remove etch debris.
4. A method as claimed in any preceding claim, wherein the intense laser beam is provided by an argon ion laser.
5. A method as claimed in any preceding claim, wherein the etchant is fuming nitric acid.
6. A method as claimed in any claim of claims 1 to 4, wherein the etchant is concentrated sulphuric acid.
7. A method of selectively etching a plastics encapsulated electronic package which
method is substantially as hereinbefore described with reference to the accompanying drawing.
8. A plastics encapsulated electronic package from which a portion of encapsulation has
been removed by the method claimed in any
preceding claim.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8408993A GB2156742B (en) | 1984-04-06 | 1984-04-06 | Etching plastics encapsulated electronic packages |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8408993A GB2156742B (en) | 1984-04-06 | 1984-04-06 | Etching plastics encapsulated electronic packages |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8408993D0 GB8408993D0 (en) | 1984-05-16 |
| GB2156742A true GB2156742A (en) | 1985-10-16 |
| GB2156742B GB2156742B (en) | 1987-01-28 |
Family
ID=10559314
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8408993A Expired GB2156742B (en) | 1984-04-06 | 1984-04-06 | Etching plastics encapsulated electronic packages |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2156742B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1276142A2 (en) * | 2001-07-11 | 2003-01-15 | Data Storage Institute | Method and apparatus for decapping integrated circuit packages |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114486439B (en) * | 2022-01-27 | 2023-08-29 | 上海季丰电子股份有限公司 | Method for taking crystal grains in back-illuminated CMOS sensor and application |
-
1984
- 1984-04-06 GB GB8408993A patent/GB2156742B/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1276142A2 (en) * | 2001-07-11 | 2003-01-15 | Data Storage Institute | Method and apparatus for decapping integrated circuit packages |
| EP1276142A3 (en) * | 2001-07-11 | 2005-06-01 | Data Storage Institute | Method and apparatus for decapping integrated circuit packages |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2156742B (en) | 1987-01-28 |
| GB8408993D0 (en) | 1984-05-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |