GB2246667A - Manufacturing printed circuit boards - Google Patents

Abstract

A method of manufacturing a printed circuit board 1 having through-holes 5 and shield layers comprises filling a through-hole 5 with a conductive filling material 8 and coating a shield layer with a conductive coating material through a mask 13 while injecting through a filling and coating nozzle 14 said filling and coating material to which compressed air is applied, said filling of the through-hole with the filling material and coating of the shield layer being performed simultaneously. <IMAGE>

Description

METHOD OF MANUFACTURING PRINTED CIRCUIT BOARDS The present invention relates to a method of manufacturing printed circuit boards, which method comprises filling a through-hole or the like in printed circuit boards with an electrically conductive material or the like, and simultaneously coating a shield layer with the same material.

Heretofore, as a method filling a conducting hole (through-hole) in printed circuit boards with an electrically conductive material, two methods have been employed: one method by which an electrically conductive material is allowed to adhere to a filling pin, and then the pin is inserted into a through-hole opening in a printed circuit board, thereby allowing the electrically conductive material adhering to the outer periphery of said filling pin to adhere to the inside of the through hole to effect filling; and the other method by which a silk screen plate for printing corresponding to the circuit design of printed circuit boards is prepared, and an electrically conductive material is filled through the silk screen plate into respective through holes of the printed circuit board.

In manufacturing the known printed circuit boards, in addition to the filling of an electrically conductive material into said through-hole, coating of a shield layer, an over coat or the like has been performed by means of an additional independent step.

That is, as shown in Figure 4 of the accompanying drawings, printed circuits 61 and 62 with a required circuit pattern are formed on both surfaces of an insulation board 60, and the surfaces are coated with solder resists 63 and 64.

A through-hole required for connection between the printed circuits 61 and 62 on the surfaces of the board 60 is formed in such a manner that a conducting hole 65 is opened by a machining step such as punching, and the conducting hole 65 is filled with an electrically conductive material 66 by the abovementioned method, thereby electrically connecting the printed circuits 61 and 62 on the surfaces of the insulation board 60.

The printed circuit 61 is coated with a shield layer 67 in such a manner that the upper surface of the solder resist 63 is coated with a shield material by a silk printing technique, and then the shield material is hardened to form the shield layer.

In Figure 4, numeral 68 indicates an earth circuit, and numeral 69 does an overcoat for protecting the shield layer 67.

Of the filling methods in the method of manufacturing the above-mentioned prior art printed circuit boards, the former filling method by use of a pin has the disadvantage that the adhesion quantity of the electrically conductive material adhering to the filling pin is very small, and filling the throughhole with the electrically conductive material requires a plurality of repeated steps to allow the electrically conductive material to adhere to the filling pin, as well as a plurality of repeated steps to insert the pin to which the material has adhered into each through-hole of a printed circuit board, thereby making the work complex and lowering the working efficiency.

The above-mentioned method has a disadvantage that the electrically conductive material, having adhered to the inside of the through-hole by means of the filling pin, must be hardened for each filling step, whereby the raw material of the printed circuit board is subject to serious thermal damage, causing the dimensional stability of the printed circuit board to be significantly reduced.

Further, where a printed circuit board has a large number of through-holes, a large number of pins are required for one step. One thousand or more pins cannot usually be employed, and the number of pins is limited for design, with the result that the size of the printed circuit board is restricted (usually, a size of 300 m/m2 or more cannot be used).

Accordingly, the former filling method has a disadvantage of poor mass productivity because it is difficult to manufacture a pin jig whose pins are disposed in a manner to correspond to respective through-holes of a printed circuit board, and to perform the process, as well as the work.

For the silk screen method of the abovementioned latter filling method, the squeegee pressure to the screen is not uniform, and it is difficult to fill completely the electrically conductive material into respective through-holes of a printed circuit board when a usual squeegee pressure is employed.

For example, if the thickness of the printed circuit board becomes reduced, or the size of the through-hole becomes small, the filling cannot be performed. (For example, when the thickness is 1.6 mm, the minimum size of the through-hole is 0.7 mm with the current technology, and a size larger than that value makes it impossible to perform the filling with the electrically conductive material.) With such method, the fluidity of an electrically conductive material has affected largely the uniformity of filling, thereby increasing the complexity of work.Accordingly, a solvent is usually added to the electrically conductive material to establish a uniform fluidity thereof, but on the other hand, the solvent is vaporised in the throughhole because of heating applied when the electrically conductive material is hardened after filling, thereby developing entrapped bubbles and cracks which result in a cause of defective continuity. Thus, the method has a serious problem with respect to the solvent removal.

That is, a higher alcohol based solvent which has a higher boiling point and is hardly vaporised is used to maintain the fluidity of the electrically conductive material. To vaporise and remove completely the solvent, a proper temperature and time during which no bubble occurs is required. Thus, the complete removal of the solvent assures the reliability of the printed circuit boards.

In addition to the above-mentioned method of manufacturing through-holes, the coating work of the shield layer 67 is performed in another process to cause the work man-hours to be increased. Further, the hardening treatment after the layer is coated with the shield material requires means to overcome the thermal deterioration of the board 60 and the printed circuits 61 and 62. Thus, it has been desirable that the manufacture of printed circuit boards is made simple.

Accordingly, the present invention has been developed to eliminate the disadvantage in the method of manufacturing prior art printed circuit boards, and seeks to provide a method of manufacturing printed circuit boards enabling the uniform filling of through-holes with an electrically conductive material regardless of the thickness of printed circuit boards and the number and size of through-holes, and at the same time enabling the forming of shield layers.

According to the invention, there is provided a method of manufacturing printed circuit boards having through-holes and shield layers, said method comprising filling a through-hole with a filling material and coating a shield layer with a coating material through a mask while injecting through a filling and coating nozzle said filling material and coating material to which compressed air is applied, said filling of the through-hole with the filling material and coating of the shield layer being performed simultaneously.

In order that the invention may be better understood, several embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which: Figures 1 to 3 are illustrative views respectively showing first, second and third embodiments of a filling method according to the present invention; and Figure 4 is an illustrative view showing a prior art printed circuit board.

With reference to the drawings, embodiments of the method of manufacturing printed circuit boards according to the present invention will be explained hereinafter.

In Figure 1, numeral 1 indicates a printed circuit board, which is composed in such a manner that required printed circuits (not shown) with a conductor circuit are formed on the two side surfaces of a board 2 consisting of an insulating material, connecting lands 3 and 4 for connecting electrically the printed circuits on the two side surfaces are disposed in the printed circuits on the two side surfaces of the board 2, and a through-hole 5 is formed between the connecting lands 3 and 4 by punching (pressing) or drilling.

Printed circuit boards 56 on the two side surfaces of the board 2 are coated with under resists (solder resists) 6 and 7, while an earth circuit 57 of a shield layer is not coated with the resist.

When the through-hole of the printed circuit board 1 comprising said composition is filled with an electrically conductive material 8, and an area is coated with the electrically conductive material 8 as a shield material to form the shield layer, the printed circuit board 1 is set by being placed on a cover plate 10 laid on a frame 9.

At this point, as shown in Figure 1, a relief hole 11 of the cover plate 10 is set in a manner to be matched (aligned) with the through-hole 5 of the printed circuit board 1.

A mask 13 having filling and coating permeable holes 12 is set by being placed on said printed circuit board 1 in such a manner that the filling and coating permeable holes 12 are aligned with the through-hole 5 and a shield coated area 58 of the printed circuit board 1.

Thereafter, the electrically conductive material 8 is discharged through a nozzle end 15 of a filling and coating nozzle 14 constructed movably in the horizontal direction on said mask 13, and the through-hole 5 and the shield coated area 58 of the printed circuit board 1 are filled and coated through the filling and coating permeable holes 12 of the mask 13 with the electrically conductive material 8.

Said filling and coating nozzle 14 comprises a nozzle body 17 including a filling and coating section 16 for the electrically conductive material 8 and an operating section 18 for a discharge valve provided above the filling and coating section 16 of the nozzle body 17.

Said filling and coating section 16 is supplied with the electrically conductive material 8 through a supply port 19 from a unit (not shown) for supplying the electrically conductive material 8, and the nozzle end 15 is detachably mounted by mounting screws 21 to a discharge hole 20 of the filling and coating section 16.

A discharge valve 23 is mounted through an operating rod 22 to the discharge hole of the filling and coating section 16, and the upper end of said operating rod 22 is connected to an operating valve 26 which is yieldingly urged by a spring 25 in an operating chamber 24 provided above the nozzle body 17.

The operating chamber 24 of said operating section 18 is connected through a connecting port 27 and a control unit (not shown) to an operation air pressure source (not shown).

Numeral 28 indicates a slide bearing for the operating rod 22.

Accordingly, when the through-hole 5 and the shield coated area 58 are filled and coated through the mask 13 with the electrically conductive material 8 by the filling and coating nozzle 14 comprising said composition, the nozzle end 15 of the filling and coating nozzle 14 is abutted through an operating unit (not shown) on the mask 13, and moved in the horizontal direction.

While the through-hole 5 and the shield coated area 58 of the printed circuit board 1 are scanned during the movement of the nozzle end in the horizontal direction, the discharge hole 20 is opened at the positions corresponding to the through-hole 5 and the shield coated area 58 by raising the operating rod 22 against the resilience of the spring to open the discharge valve 23, the electrically conductive material 8 supplied under pressure through the connecting port 19 into the filling and coating section 16 is discharged through the nozzle end 15, and the through-hole 5 and the shield coated area 58 are thus filled and coated through the filling and coating permeable holes 12 of the mask 13 with the electrically conductive material 8 while being injected.

The electrically conductive material 8 injected into the through-hole 5, though exposed (8b) on the back of the board 2, actually protrudes into the relief hole 11 of the cover plate 10, whereby the junction of the exposed part 8b with the connecting land 4 can be completely assured to avoid the occurrence of an electrically defective connection.

It is desirable that the inside diameter of the relief hole 11 of the cover plate 10 is somewhat larger than that of the through-hole 5.

Said mask 13 is formed by a silk screen plate (for example, 180 to 300), or can be implemented by another mask which is designed in such a manner that the electrically conductive material 8 discharged from the filling and coating nozzle 14 does not flow out at positions other than those corresponding to the through-hole 5 and the shield coated area 58.

Having described one through-hole 5 opening in the printed circuit board 1 in Figure 1, a plurality of through-holes 5 can also be continuously filled and coated in the same method as the above-mentioned one.

An example of the filling conditions in which said filling nozzle 14 is used will be shown hereinafter: Scanning speed of filling nozzle 1.0 mm/sec Thickness of printed circuit board 1.6 mm Through hole diameter 0/4 mm Injection pressure 6.0 kg/cm~ Viscosity of electrically conductive 0 material 1000 cps/25 C A solvent-free type copper paste has been used as an electrically conductive material.

A continuity circuit has been formed in the through-hole by drying the electrically conductive material 8 in the through-hole 5 by means of an oven heater at 1500C for 30 minutes to harden the material.

Figure 2 is an illustrative view of a second embodiment of the invention.

In this embodiment, the composition of the filling and coating nozzle 14 is different from that used in the above-mentioned first embodiment, but the other methods are the same as used in the first embodiment, so that the same components in this embodiment are designated by the same numerals, and the specific explanation of the methods are omitted.

The composition of the filling and coating nozzle 14 in this embodiment is such that a squeegee 29 is mounted on one side of the nozzle end 15.

The squeegee 29 is mounted in a manner to be positioned behind the filling and coating nozzle 14 moving forward in the horizontal direction.

Accordingly, after the through-hole 5 and the shield coated area 58 are filled and coated through the filling and coating nozzle 14 with the electrically conductive material 8, with the horizontal moving of the filling and coating nozzle 14, the electrically conductive material 8 exposed above the through-hole 5 and the shield coated area 58 can be removed at the filling and coating permeable holes 12 by the squeegee 29 mounted to the nozzle end 15.

The nozzle end 15 can be interchanged by use of the mounting screws 21 to select the size of a discharge hole 15a thereof. It is desirable that the nozzle end 15 is formed with a plastic material, a synthetic rubber or the like to provide the surface abutting on the mask 13 with wear resistance and to protect the mask 13, and that the material of the squeegee 29 is selected as with the above.

Figure 3 is an illustrative view of a third embodiment of the invention.

This embodiment employs a filling and coating method by which, instead of the through-hole 5 and the shield coated area 58 of the printed circuit board 1 having printed circuits on both sides thereof, as in the first embodiment, through-holes 34 and 35, a connecting hole 36 and the shield coated area 58 in a multi-layer printed circuit board 30 laminating three boards 31, 32 and 33 are filled and coated with the electrically conductive material 8.

Printed circuits 37, 38, 39 and 40 are disposed on the two sides of respective boards 31, 32 and 33 of said printed circuit board 30; connecting lands 41, 42, 43 and 44 to connect respective printed circuits of the boards 31, 32 and 33 to each other are disposed in the printed circuits of the boards 31, 32 and 33. Said through-holes 34 and 35 are provided through said boards 31, 32 and 33 to connect electrically the connecting lands 42 and 43 together and the connecting lands 41, 42, 43 and 44 together; said connecting hole 36 is provided through the board 31 to connect electrically the connecting land 41 in the outside printed circuit 37 thereof to the connecting land 45 in the inside printed circuit 38 thereof.

The uppermost board 31 and the lowermost board 33 of the printed circuit board 30 are coated with solder resists 46 and 47 to cover respective printed circuits 37 and 40.

The through-holes 34 and 35 are machined by punching or drilling, and the connecting hole 36 is machined by drilling.

The through-holes 34 and 35, the connecting hole 36 and the shield coated area 58 in the printed circuit board 30 comprising said compositions are filled and coated with the electrically conductive material 8 in such a manner that a cover plate 48 is placed on the frame 9 as with said first embodiment, the printed circuit board 30 is set by being placed on the cover plate 48, and a mask 49 is set by being placed on the printed circuit board 30, and thereafter, by moving horizontally the filling and coating nozzle 14 from the shield coated area 58 toward the through-hole 35 and the connecting hole 36 through the mask 49 as with said first embodiment, the shield coated area 58, the through-holes 34 and 35 and the connecting hole 36 are filled and coated with the electrically conductive material 8.

In said cover plate 48 and the mask 49 are disposed relief holes 50 and 51, and filling and coating permeable holes 52, 53 and 54 at the positions corresponding to those at which the through-holes 34 and 35, and the connecting hole 36 of printed circuit board 30 are disposed. Said cover plate 48 and the mask 49 are set while respective relief holes 50 and 51, and filling and coating permeable holes 52, 53 and 54 are aligned with the through-holes 34 and 35, the connecting hole 36 and the shield coated area 58 of the printed circuit board 30.

Further, as with said second embodiment, the squeegee 29 is mounted to the filling and coating nozzle 14, whereby, of the electrically conductive material 8 with which the through-holes 34 and 35, the connecting hole 36 and the shield coated area 58 are filled, an extra electrically conductive material 8 exposed on the board can be removed along the filling and coating permeable holes 52, 53 and 54 of the mask 49 during filling and coating.

Having described the filling of an electrically conductive material in the above embodiments, other filling materials, for example, a filling material for filling a hole can also be filled in the same manner.

According to the first, second and third embodiments, by use of the filling and coating nozzle 14, the through-holes 5, 34 and 35, or the connecting hole 36 and the shield coated area 58 are filled and coated through the filling and coating permeable holes 12, 52, 53 and 54 of the mask 13 or 49 with the electrically conductive material 8 which is injected by being supplied with compressed air, whereby small size holes can be filled by adjustment and control of the injection condition regardless of the fluidity of filling material and the thickness of boards, and consequently the density of circuits can be made higher.

Further, the filling can be performed regardless of the fluidity of filling material, so that means such as the addition of solvent is not required to obtain a proper fluidity of the electrically conductive material. Accordingly, difficulties due to the addition of solvent can be avoided, in other words, a solvent-free type filling can be accomplished by injection using a filling nozzle.

The nozzle end 15 of the filling and coating nozzle 14 is interchangeable, whereby the injection filling meeting the condition of filling material discharge and the conditions such as through-hole size and thickness can be uniformly and stably performed.

Also, the filling and coating through a mask allows the filling of a filling material into and the adhesion of a shield material to an unnecessary place to be prevented.

Further, the filled and coated places corresponding to the circuit design of printed circuit boards can be continuously filled and coated, thereby allowing the workability of filling and coating works to be improved.

As apparent from the above description, according to the method of manufacturing printed circuit boards of the present invention, through-holes and the like can be uniformly and stably filled with a filling material such as an electrically conductive material regardless of the thickness of printed circuit boards, or the fluidity of a filling material such as an electrically conductive material, and shield layers be simultaneously coated with such material, thereby allowing the workability in manufacturing printed circuit boards to be increased.

Claims (6)

1. A method of manufacturing printed circuit boards having through-holes and shield layers, said method comprising filling a through-hole with a filling material and coating a shield layer with a coating material through a mask while injecting through a filling and coating nozzle said filling material and coating material to which compressed air is applied, said filling of the through-hole with the filling material and coating of the shield layer being performed simultaneously.

2. A method as claimed in claim 1, wherein said mask employs a silk screen plate which has filling and coating permeable holes at positions corresponding to those of filling and coating of the through-hole and the like in said printed circuit boards.

3. A method as claimed in claim 1, wherein said nozzle is provided with a filling and coating section for the filling material and coating material and with a nozzle end at the head of the filling and coating section, and comprises an operating section of a discharge valve for the filling material and coating material to said nozzle end and a supplying section for the filling material and coating material connected to the operating section.

4. A method as claimed in claim 1, wherein a cover plate corresponding to said mask is used.

5. A method as claimed in claim 1, wherein said filling material and coating material are those of the solvent-free type.

6. A method as claimed in claim 1, substantially as hereinbefore described.