GB2220107A

GB2220107A - Housing for a circuit board assembly

Info

Publication number: GB2220107A
Application number: GB8810359A
Authority: GB
Inventors: Michael John Jepson
Original assignee: Pressac Ltd
Current assignee: Pressac Ltd
Priority date: 1988-04-30
Filing date: 1988-04-30
Publication date: 1989-12-28
Anticipated expiration: 2008-04-30
Also published as: GB2220107B; GB8810359D0

Abstract

A circuit board assembly (10) for use in a vehicle instrumentation region comprises a housing (14) formed of a plastics material moulded onto a circuit board (12). The assembly is formed by disposing the circuit board in a mould and moulding a plastics material to the circuit board so that the plastics material forms the housing for the circuit board. <IMAGE>

Description

CIRCUIT BOARD ASSEMBLY This invention relates to a circuit board assembly.

In the electrical industry and those other industries in which electrical components are used, for example, the car industry, the use of circuit boards is often necessary.

Typically circuit boards are manufactured separately from the article in which they will be used, for example an instrument housing in a car. Some circuit boards especially those intended for use in a vehicle instrument housing region, are flexible and so are sometimes difficult to fit into place.

It is an object of this invention to provide an improved circuit board assembly.

According to one aspect of this invention there is provided a circuit board assembly comprising a circuit board and a housing of a plastics material moulded to the circuit board.

Desirably, the housing is of a thermoplastics polymeric material and said housing may be integrally moulded with the circuit board. Preferably, the housing is of a styrene copolymer and, more preferably, of an acrylonitrile-butadiene-styrene copolymer, hereinafter referred to as an ABS copolymer.

The circuit board preferably comprises a carrier of an electrically insulating material. Desirably, the electrically insulating material is a polyester, preferably a polyester of a type commonly used in the manufacture of circuit boards.

The carrier may comprise two layers of electrically insulating material. The melting point of one of said layers is preferably higher than the melting point of the other of said layers. In the formation of the carrier the layers are preferably co-extruded onto one another.

The layer having the higher melting point may have the circuit thereon. The lower melting point layer may be disposed such that it is adjacent the housing when the housing is moulded onto the circuit board.

An adhesion promoting material may be applied to the circuit board in order to assist in the moulding of the housing therewith. Preferably, with a board where the carrier is polyester and the housing is an ABS copolymer, the adhesion promoting material is a polyurethane material which may be applied to the higher melting point polyester layer. The adhesion promoting material may be applied by any convenient means e.g. a spray or roller coating.

The preferred circuit board comprises a flexible carrier, although it will be appreciated that the circuit board may be rigid.

According to another aspect of this invention there is provided a process for forming a circuit board assembly, said process comprising disposing a circuit board in a mould, and moulding a plastics material to the circuit board so that the plastics material forms a housing of a desired shape.

Preferably, the circuit board assembly is as described above. Desirably, the two layers of the electrically insulating material are co-extruded together. A suitable electroconductive material for example copper or other suitable material may then be applied to one face of the polyester material.

Preferably, the electroconductive material is applied to the higher melting point layer of the electrically insulating material. The circuit board may then be manufactured by any suitable means well known in the art.

An adhesion promoter may be applied to the circuit board to assist in moulding the plastics material onto the circuit board. Preferably, the adhesion promoter is applied to the lower melting point layer of the electrically insulating material. The adhesion promoter may comprise a polyurethane material which may be applied as a spray.

The circuit board is preferably introduced to the mould so that the face of the layer of the electrically insulating material having the electroconductive material applied thereto is disposed adjacent one wall of the mould.

The mould preferably comprises holding means for holding the circuit board in place while the plastics material is moulded thereonto. Preferably, the holding means comprises suction means to apply suction to the circuit board.

The plastics material may be introduced into the mould either before, or at the same time as the circuit board is introduced onto the mould. Preferably the plastics material is in the form of a fluid which is injected into the mould.

When the moulding takes place, the temperature of the mould should be such that it activates the adhesion promoter and the lower melting point layer of the thermally insulating material; however, the temperature should not be such that it causes the materials in the mould to degrade.

Suitably the temperature of the mould may be between 500C and 950C, and preferably, the temperature is approximately 650C.

The melting temperature of the plastics material may be between ISOOC and 2800 C, and preferably about 2400 -2500C.

The process may be a continuous process whereby a reel of the carrier and a reel of the electroconductive material feed respectively the carrier and the electoconductive material onto each other to form a sheet having the electroconductive material printed thereon.

The continuous sheet may be fed through the stages described above. At the penultimate stage, the continuous sheet may be cut into separate circuit boards before it is fed into the mould.

Alternatively, the process may be a stepwise process whereby as soon as one step has been carried out the materials are then transferred to the next step.

Reference is now made to the accompanying drawings, in which: Figure 1 is a diagram of a circuit board assembly in accordance with this invention; Figure 2 is a schematic diagram of a mould for use in this invention; Figure 3 is a diagram of a circuit board according to this invention; Figures 4 to 6 are schematic representations of three moulds for use in different methods of making a circuit board assembly in accordance with this invention.

Referring to the drawings, a circuit board assembly is shown, generally designated 10. The circuit board assembly 10 comprises a housing 14 which has been moulded onto a circuit board 12.

The circuit board 12 comprises a carrier 16 in the form of two layers 18, 20 of an electrically insulating material. The electrically insulating material comprises a polyester material which is of a flexible nature so that the circuit board 12 is flexible.

The layers 18, 20 of the polyester material are coextruded onto one another by a technique which is well known in the art. The layer 18 is of a higher melting point than the layer 20. The reasons for this will become apparent as the description progresses.

Into the circuit board 12, apertures 22, 24 can be formed. These apertures 22, 24 are used to receive suitable electrical components for example switches or transistors.

An electrically conductive material, for example copper, is disposed in strips 26; on the circuit board 12. A cover film 28 of an insulating material well known in the art is disposed over the surface of the polyester layer 18 and over the copper strips 26.

The housing 14 is formed from a thermoplastics material which is preferably an ABS resin.

The manufacture of the circuit board 12 is carried out by first co-extruding together the layers 18, 20 of the polyester material. A layer of copper is then disposed onto the higher melting point layer 18 of the polyester material.

The next stage is for the copper to be die stamped into the shape of the circuit of the circuit board 12.

Excess copper is then removed. The layers 18, 20 and the copper disposed thereon are passed to a bonding means known in the art, which bonding means is typically heated, to bond the copper to the polyester layer 18.

The cover film 28 is then disposed on the surface of the layer 18 and over the copper 26. The cover film 28 is bonded to the layer 18 and the copper 26 by further bonding means? known in the art.

An adhesion promoting material can then be applied to the lower melting point layer 20 of the polyester material. The adhesion promoting material assists in bonding the ABS resin, which forms the housing, to the lower melting point layer 20 of the polyester material.

The adhesion promoting material can comprise an aqueous polyurethane resin dispersion, having a polymer content of about 50%, a pH value of about 7-8 and a viscosity at 200C of about 10 poise.

Figure 2 shows schematically a mould 30 which is used in moulding the housing 14 onto the circuit board 12. The mould 30 comprises a core 40, which is of the shape of the housing 14.

The circuit board 12 is shown in place on the bottom of the mould 30. The circuit board 12 is disposed so that the face of layer 18 having the copper 16 thereon is disposed against the bottom of the mould 30.

Conduits 32 are present in the mould 30. The conduits pass to holding means in the form of suction apparatus (not shown). The suction apparatus applies suction via the conduits 32 to hold the circuit 12 in place. The mould 30 also comprises an inlet 34 through which the ABS resin is injected.

In order to manufacture the circuit board assembly 10, a circuit board 12 is disposed in the mould 30 face down as shown in Figure 2. Liquid ABS resin at approximately 245or is then injected into the mould 30, using known injection moulding equipment, via the inlet 34. The mould 30 is maintained at approximately 900C by suitable cooling means, for example, cooling water pipes (not shown).

When the liquid ABS resin enters the mould, it is believed that it causes the layer 20 of the lower melting point polyester material to melt partially. Also, it is believed that the temperature of the molten ABS resin activates the adhesion promoting material which has been applied to the layer 20.

It is further believed that the partially molten layer 20, the activated adhesion promotion material and the ABS resin interact so that the circuit board 12 is moulded to the ABS resin.

The inside of the mould 30 is of any desired shape and when the ABS resin is injected and cooled it takes on that desired shape.

In addition, in certain circumstances, it is necessary for the circuit board 12 to be of a desired three dimensional configuration. In such circumstances the circuit board 12 may be preshaped during manufacture to its desired configuration, and it is necessary also to adapt the mould to the desired configuration.

Mountings for electrical components to be fitted onto the circuit board 12 can be formed on the circuit board 12 either during manufacture thereof or during the moulding of the ABS resin onto the circuit board 12. If the mountings are formed on the circuit board 12 during the moulding, it will be necessary to adjust the mould 30 to the shape of the mountings.

One embodiment of the process for manufacturing the circuit board assembly 10 is a continuous process. In this process, an elongate sheet (see Figures 4, 5 and 6) of the carrier 16 is used, in which the sheet consists of a plurality of circuit boards 12 connected integrally by webs of the carrier 16.

In this continuous process it is necessary to separate individual circuit boards 12 from the remainder of the sheet. This can be done in the mould.

Figures 4, 5 and 6 show different ways in which this severing can take place.

In Figures 4, 5 and 6 a mould 50 is shown schematically. The mould 50 is of a type suitable for use in a continuous moulding process.

The mould 50 consists of first and second relatively movable moulding members 52, 54. The moulding members 52, 54 define a mould cavity 56. The mould 50 also consists of a base 53 which defines the bottom of the mould cavity 56.

Referring particularly to Figure 4, a cutting means comprising a blade 58, are disposed beneath the sheet 48.

When the circuit board 12, which is integrally attached to the remainder of the sheet 48, is disposed within the mould cavity 56 at the bottom thereof, the second moulding member 52 is moved into the position as shown in Figure 4. Plastics material can then be injected into the mould cavity 56 by any means well known in the art. The plastics material forms the housing and is moulded onto the circuit board 12 to form the circuit board assembly.

In order to sever the circuit board 12 from the remainder of the sheet 48 the blade 58 reacts against the bottom of the first moulding member 52. Since the blade 58 is disposed beneath the second moulding member 52 a portion 60 of the sheet 48 remains attached to the circuit board 12.

Another method for severing the circuit board 12 from the remainder of the sheet 48 involves the use of blades 58 as shown in Figure 5. The blade 58 projects into the cavity 56 between the moulding members D2 54.

As the plastics material is injected into the mould cavity 56 the sheet 48 of the material is forced, by the pressure of the plastics material entering the mould cavity 56, onto the blades 58. This causes the circuit board 12 to be severed from the remainder of the sheet 48.

With this method, the mould for which is shown in Figure D, the blade should be approximately 0.001 inch (0.02do mm) from the wall of the first moulding member 52, otherwise a clean cut of the plastics material cannot be guaranteed.

A further method of severing the circuit board 10 from the remainder of the sheet 48 will now be described with reference to Figure 6. In this method a moulding 62 is formed on the portion 60 of the sheet of plastics material beneath the first moulding members 52.

The blade 58 can then be used to sever the circuit board 10 from the remainder of the sheet 48.

The blade 58 can either project into the mould cavity 56 as shown on the left hand side of the second moulding member 54 in Figure 5. This would result in a recess in the moulded circuit board assembly 10.

Alternatively, the blade can remain below the circuit board 12, as shown to the right hand side of the second moulding member 54 in Figure D and designated 58'. This would result in a varied portion on the circuit board assembly 10.

In either case, the provision of the moulding 62 enables the sheet 48 of the plastics material to be severed cleanly, even if the blade 58 (or D81 are at a greater distance than 0.001 inch (0.0254 mm) as specified above.

In each of the above methods for severing the circuit board 12 from the remainder of the sheet 48 of the plastics material, the circuit board 12 can be first partially severed from the sheet 48, defining the peripheral shape of the board but leaving small amounts of the plastics material which attaches the circuit board 12 to the sheet 48. The blades 58 (58') will then serve only to sever these small amounts of the plastics material.

An alternative method is by using a robotic loader to feed individually precut circuit boards 12 into a mould. The precut circuit boards can be disposed in a stack prior to feeding.

Claims

1. A circuit board assembly comprising a circuit board and a housing of a plastics material moulded to the circuit board.

2. An assembly according to Claim 1 wherein the housing is formed of a thermoplastics polymeric material and is integrally moulded with the circuit board.

3. An assembly according to Claim 1 or 2 wherein the housing is formed of a styrene copolymer.

4. An assembly according to Claim 1, 2 or 3 wherein the circuit board comprises a carrier of an electrically insulating material to carry the circuit.

5. An assembly according to . Claim ' 4 wherein the electrically insulating material is a polyester.

6. An assembly according to Claim 4 or 5 wherein the carrier comprises two layers of electrically insulating material, the melting point of one of said layers being higher than the melting point of the other of said layers.

7. An assembly according to Claim 6 wherein the layer having the higher melting point carries the circuit thereon and the lower melting point layer is disposed such that it is adjacent the housing when the housing is moulded onto the circuit board.

8. An assembly according to any preceding claim wherein an adhesion promoting material is applied to the circuit board in order to assist in the moulding of the housing therewith.

9. An assembly according to Claim 8 wherein the adhesion promoting material is a polyurethane material which is applied to the higher melting point layer.

10. A process for forming a circuit board assembly, said process comprising disposing a circuit board in a mould, and moulding a plastics material to the circuit board so that the plastics material forms a housing of a desired shape.

11. A process according to Claim 10 wherein the two layers of an electrically insulating material one of said layers having a lower melting point than the other are co-extruded together, a suitable electroconductive material is then applied to one face of the isulating material.

12. A process according to Claim 11 wherein the electroconductive material is applied to the higher melting point layer of the electrically insulating material.

13. A process according to Claim 11 or 12 wherein an adhesion promoter is applied to the circuit board to assist in moulding the plastics material onto the circuit board.

14. A process according to Claim 13 wherein the adhesion promoter is applied to the lower melting point layer of the electrically insulating material.

15. A process according to any of Claims 11 to 14 wherein the circuit board is introduced to the mould so that the face of the layer of the electrically insulating material having the electroconductive material applied thereto is disposed adjacent one wall of the mould.

16. A process according to any of Claims 10 to 15 wherein the circuit board is held in place in the mould by suction while the plastics material is moulded thereontot

17. A prowess according to any of Claims 10 to 16 wherein the plastics material is introduced into the mould either before, or at the same time as the circuit board is introduced onto the mould.

18. A process according to any of Claims 10 to 17 wherein the temperature of the mould may be between 50 C and 95-C,

19. A process according to any of Claims 10 to 18 wherein the temperature in the mould is approximately 65*C.

20. A process according to any of claims 10 to 19 wherein the melting temperature of the plastics material is between 1800C and 280#C.

21. A process according to any of claims 9 to 19 wherein the melting temperature of the plastics material is about 2400C to 2500C.

22. A circuit board substantially as herein described with reference to and as shown in the accompanying drawings.

23. A process substantially as herein described with reference to and as shown in the accompanying drawings.