GB2290912A

GB2290912A - Wiring board

Info

Publication number: GB2290912A
Application number: GB9512782A
Authority: GB
Inventors: Satoshi Shimada; Hitoshi Suda
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1994-06-28
Filing date: 1995-06-22
Publication date: 1996-01-10
Also published as: DE19523364A1; JPH0818170A; DE19523364B4; GB9512782D0

Description

2290912 WIRING BOARD The present invention relates to a wiring board for

supporting electronic components thereon, and more particularly to a wiring board having metal electric conductors of a large current-carrying capacity and wiring patterns of a small current-carrying capacity.

FIGS. 6 and 7 of the accompanying drawings show conventional wiring boards.

In FIG. 6, the conventional wiring board, generally designated by the reference numeral 30, includes a printed wiring board 31 having a pattern photographically printed on a copper-covered laminated board of glass epoxy, the pattern being processed with a photoresist and etched or otherwise chemically processed into wiring patterns for carrying large and small currents. The printed wiring board 31 supports thereon various electronic components including a bus bar (metal electric conductor) 32A for carrying a large current, a shunt resistor 32B, a power FET 34 for controlling the large current, a radial component 33A for carrying a large current, an axial component 33B for carrying a small current, an integrated circuit 33C, and a connector 32 for connection to an external circuit. These electronic components are soldered to the wiring patterns on the printed wiring board 31.

The conventional wiring board 30 also has a case 36 including as part thereof a heat radiator 35 for dissipating heat generated by the power FET 34. The case 36 covers the entire printed wiring board 31 with the electronic components mounted thereon. The conventional wiring board 30 in which the printed wiring board 31 with the electronic components mounted thereon is covered by the case 36 serves as a functional block.

In FIG. 7, the conventional wiring board, generally designated by the reference numeral 40, includes an insert molded board 41 with a lead frame (metal electric conductor) 42B embedded therein, and a single printed wiring board 46 having a pattern photographically printed on a copper-covered laminated board of glass epoxy. The insert-molded board 41 supports thereon electronic components for carrying a large current which include power FETs 43A, a shunt resistor 42A, and a radial component 43B, these electronic components being soldered to the lead frame 42B. The printed wiring board 46 supports thereon electronic components for carrying a small current which include a radial component 47A, an axial component 47B, and an integrated circuit 47C.

The conventional wiring board 40 also has a molded case having a portion integral with the insert-molded board 41 and housing the printed wiring board 46, the case including an integral connector 41A for connection to an external circuit.

The printed wiring board 46 is fixedly mounted on the insert molded board 41 by posts 45. One side of the case is covered with a heat radiator 44 with the power FETs 43A attached thereto, and the opposite side of the case with a cover 48.

The conventional wiring board 40 in which the insert-molded board 41 and the printed wiring board 46 with the electronic components mounted thereon are covered by the case serves as a functional block.

The conventional wiring board 30 shown in FIG. 6 is problematic in that if the bus bar 32A is complex in shape, it cannot automatically be installed on the printed wiring board 31, and the conventional wiring board 30 cannot be manufactured inexpensively. Furthermore, since the bus bar 32A reduces the space for installing other electronic components, the functional block is necessarily large in size.

The conventional wiring board 40 shown in FIG. 7 is also disadvantageous in that the functional block is large in size because it includes both the insert-molded board 41 and the printed wiring board 46 and wires or interconnections required between these boards 41, 46 make the assembling process complicated, resulting in an increase in the cost of the conventional wiring board 40.

It is therefore an object of the present invention to provide a wiring board which can be manufactured inexpensively, is small in size, and can be assembled with ease.

According to the present invention, there is provided a wiring board comprising a block made of a synthetic resin, an electric conductor embedded in the block and a wiring pattern disposed on each surface of the block. The electric conductor may have an end projecting from the block as a connector terminal. The block may include a body of a first synthetic resin containing a catalyst that can be deposited by electroless plating and insert-molded around the electric conductor, and may further include a pair of surface layers of a second synthetic resin disposed on surfaces of the body and free of a catalyst that can be deposited by electroless plating, the surface layers being insert-molded on the surfaces of the body. The wiring pattern may be deposited by electroless plating on each surface of the block. The block may include a plurality of bodies stacked into a laminated structure and made of a first synthetic resin containing a catalyst that can be deposited by electroless plating, each body having the electric conductor and insertmolded around the electric conductor, and a pair of surface layers of a second synthetic resin disposed by insert-molding on surfaces of the laminated structure of the bodies and free of a catalyst that can be deposited by electroless plating. The block may comprise a body of a single synthetic resin insert-molded around the electric conductor, the wiring pattern'being printed on each surface of the block.

The wiring board may have a case housing the block, the case having side walls surrounding the block and integral therewith and a bottom wall attached to the lower ends of the side walls, the bottom wall being a heat radiator.

According to the present invention, there is also provided a method of making a wiring board, comprising the steps of setting an electric conductor in a mold; insertmolding a body of a block, made of a f irst synthetic resin containing a catalyst that can be deposited by electroless plating, around the electric conductor; insert- molding a pair of surf ace layers of said block, made of a second synthetic resin free of a catalyst that can be deposited by electroless plating, on surfaces of the body; and disposing a wiring pattern on each surf ace of the block. The pair of surf ace layers may be insert-molded on surfaces of the body leaving selected portions of the body exposed through the surface layers, the wiring pattern being deposited on the exposed portions of the body.

According to the present invention, there is further provided a method of making a wiring board, comprising the steps of: setting an electric conductor in a mold; insert molding a block of a single resin around the electric conductor in the mold to embed the electric conductor in the block; and printing a wiring pattern on each surface of the block.

The above and further details and advantages of the present invention will become apparent from the following detailed description of preferred embodiments thereof, when read in conjunction with the accompanying drawings, in which: - FIG. 1 is perspective view of a wiring board according to an embodiment of the present invention; FIG. 2 is perspective view of a wiring board according to another embodiment of the present invention; FIG. 3 is a cross-sectional view of the wiring board shown in FIG. 2; FIG. 4 is a view similar to FIG. 1 showing a modification of the wiring board according to the embodiment of FIG.'1; FIG. 5 is a view showing another modification of the wiring board according to the embodiment of FIG. 1; FIG. 6 is a cross-sectional view of a conventional wiring board; and FIG. 7 is a cross-sectional view of another conventional wiring board.

As shown in FIG. 1, a wiring board 1 according to an embodiment of the present invention comprises a block 20 made of a sythetic resin, a plurality of lead frames 2 embedded in the block 20, each in the form of a metal electric conductor for carrying a large current, and a pair of metal wiring patterns 5 of copper, for example, deposited by electroless plating on surfaces of the block 20 and having a uniform thickness.

The block 20 has a body 3 of a first synthetic resin with the lead frames 2 embedded therein, the first synthetic resin containing a catalyst that can be deposited by electroless plating, and a pair of surface layers 4 of a second synthetic resin disposed on opposite surfaces of the body 3 and free of a catalyst that can be deposited by electroless plating. The metal wiring patterns 5 are actually deposited on the surfaces of the body 3 which are exposed through layers of the second insert-molded parts 4. The surface layers 4 have holes 6 for supporting the lead frames 2 when the body 3 is insert-molded around the lead frames 2 and also for severing the fixed lead frames 2 to provide circuits after the body 3 is insert-molded around the lead frames 2.

The wiring board 1 is manufactured by a process composed of three steps, which will be described below.

In the first step, the body 3 of the block 20, made of the first synthetic resin which contains a catalyst that can be deposited by electroless plating, is insert-molded around the lead frames 2 which were preset in a mold, thereby producing a molded block in which the lead frames 2 are disposed in multiple layers.

In the second step, the surface layers 4 of the block 20, made of the second synthetic resin that is free of a catalyst that can be deposited by electroless plating, are insert-molded on the respective opposite surfaces of the molded block of the body 3 to produce the block 20, leaving selected portions of the body 3 exposed through the surface layers for subsequent deposition thereon of the wiring patterns 5 of copper foil.

In the third step, copper foils are deposited as the wiring patterns 5 on the exposed portions of the body 3 by an electroless plating process. Specifically, in the electroless plating process, metal ions of copper in a solution are reduced and separated using a chemical reducer of formaldehyde, for example. Because the copper that is reduced and separated is also catalytic, it is possible to increase the thickness of the plated wiring patterns 5. The wiring patterns 5 are formed on upper, lower, and side surfaces of the wiring board 1.

Since the multilayer lead frames 2 for carrying a large current are embedded in the block 20 and the wiring patterns 5 for carrying small signals (a small current) are disposed on the surfaces of the wiring board 1, the single wiring board 1 has patterns capable of handling both large and small currents, and the patterns are separate from each other as regions in which large and small currents flow.

The lead frames 2 have ends projecting out of the molded block or body 3 of the block 20 as connector terminals for carrying a large current (large electric energy). The connector terminals may be encased in a case molded integrally with the wiring board 1, thus providing connectors, as described later on.

In the first step, the lead frames 2 may be partly disposed on the surface of the body 3 of the block 20, and in the third step, wiring patterns 5 of copper may be deposited on surfaces of the exposed portions of the lead frames 2.

Therefore, the wiring patterns 5 for carrying a small current may be electrically connected to the lead frames 2 for carrying a large current, and the projecting ends of the lead frames 2 may be used as connector terminals for connecting the wiring patterns 5 to an external circuit.

The wiring board 1 may be manufactured by a process other than the process described above.

For example, as shown in FIG. 4, a body 3' of a single resin such as a liquid crystal polymer or the like may be insert-molded around lead frames V, producing a block 20', and wiring patterns 51 may be printed on surfaces of the block Furthermore, as shown in FIG. 5, a plurality of the bodies W' may be stacked into a laminated structure which has lead frames T' in multiple layers, e.g., three or more layers.

The laminated structure of the bodies W' are sandwiched between a pair of surface layers C to provide a block 20".

The bodies X' and the surface layers 4" are respectively made of the same synthetic resins as the body 3 and the surface layers 4 of the block 20 in FIG. 1.

As described above, the wiring patterns 5 are disposed on the surfaces of the block 20 with the lead frames 2 embedded therein. The wiring board 1 of such a structure can support electronic components for carrying a small current on the wiring patterns 5 and also can support electronic components for carrying a large current on the lead frames 2. Therefore, a control circuit assembly composed of such electronic components for carrying a small current and a drive circuit assembly composed of such electronic components for carrying a large current can be installed on the wiring board 1 in a compact configuration. The wiring board 1 can be manufactured inexpensively.

FIGS. 2 and 3 show a wiring board 10 according to another embodiment of the present invention.

As shown in FIGS. 2 and 3, the wiring board 10 includes the wiring board 1 shown in FIG. 1 and a case 7 including side walls 8 surrounding the side edges of the wiring board 1 and a heat radiator 15, serving as a bottom wall, attached to the lower ends of the side walls 8. The walls 8 are molded integrally with the block 20 and extend substantially perpendicularly to the block 20 in opposite directions beyond upper and lower surfaces thereof. One of the side walls 8 has a pair of connectors 3A, 3B molded integrally therewith, the connector 3A serving to carry a large current (large electric energyY and the connector 3B a small current (small electric energy). The connectors 3A, 3B are molded with the side walls 8 at the same time that the side walls 8 are molded. Electronic components 11 including resistors, capacitors, integrated circuits, etc. are soldered to the wiring pattern 5 on the upper surface of the wiring board 1. These electronic components 11 are first temporarily bonded to the wiring pattern 5 on the upper surface of the wiring board 1 by an adhesive, and subsequently soldered to the wiring pattern 5 at the same time that other electronic components are soldered to the wiring pattern 5 on the lower surface of the wiring board 1 as described later on. Since wiring patterns 5 may also be deposited on the side walls 8, electronic components 11 may also be soldered on the wiring patterns 5 on the side walls 8. The electronic components 11 thus mounted on the wiring patterns 5 on the wiring board 1 and the side walls 8 are in a three- dimensional arrangement.

Some of the lead frames 2 embedded in multiple layers in the block 20 have ends projecting from side edges of the block 20 and extending into the side walls 8. The ends of the lead frames 2 in one of the side walls 8 extend into the connector 3A.

Other lead frames 2 are positioned on the surfaces of the block 20, and wiring patterns 5 are plated on these lead frames 2. These lead frames 2 have ends projecting from side edges of the block 20 and extending into the side walls 8. The ends of the lead frames 2 in one of the side walls 8 extend into the connector 3B.

Electronic components including radial components 12, axial components 13, shunt resistors 14, and power FETs 16 are soldered to the wiring pattern 5 on the lower surface of the block 20. Specifically, the block 20 has attachment holes 17A defined in a lower surface portion thereof and tapered soldering holes 17B defined in an upper surface portion thereof in registry with the respective attachment holes 17A. The lead frames 2 in the block 3 also have holes defined therein in registry with the attachment holes 17A and the tapered soldering holes 17B. To install the electronic compondnts on the lower surface of the block 20, the legs of these electronic components are inserted upwardly into the holes 17A, 17B and the holes in the lead frames 2, and thereafter the tip ends of the legs which project upwardly into the tapered soldering holes 17B are soldered to the lead frames 2 from above the block 20. When these electronic components are thus soldered to the lead frames 2, the electronic components 11 temporarily bonded to the wiring pattern 5 on the upper surf ace of the wiring board 1 are soldered thereto.

The power FETs 16 are supported on the inner surface of the heat radiator 15. The heat radiator 15 therefore serves to dissipate heat generated by the power FETs 16.

A cover 19 is attached to the upper ends of the side walls 8 of the case 7 and fastened thereto by screws 18.

The wiring board 10 with the wiring board 1 supporting the electronic components and encased in the case 7 serves as a single functional block.

In the embodiment shown in FIGS. 2 and 3, the electronic components 11 are mounted on the wiring pattern 5 on both the upper and lower surfaces of the wiring board 1, and the radial components 12, the axial components 13, the shunt resistors 14, and the power FETs 16 are mounted on the lower surface of the wiring board 1. However, the electronic components 11 may be mounted only on the upper surface of the wiring board 1. Further, the radial components 12, the axial components 13, the shunt resistors 14, and the power FETs 16 may be mounted on both the upper and lower surfaces of the wiring board 1 for increased packaging density and reduced functional block size.

The electronic components 11 soldered to the wiring pattern 5 handle small currents and jointly make up a control circuit assembly, and the radial components 12, the axial components 13, the shunt resistors 14, and the power FETs 16 which are soldered to the lead frames 2 handle large currents and jointly make up a drive circuit assembly. Since these control and drive circuit assemblies are mounted on the same block 3, they are made relatively compact in shape and can easily be assembled. The wiring board 10 can be manufactured inexpefisively.

Although there have been described what are at present considered to be the preferred embodiments of the invention, it will be understood that the invention may be em bodied in other specific forms without departing from the essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative, and not restrictive.

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Claims

CLAIMS:

1. A wiring board comprising: a block made of a synthetic resin; an electric conductor embedded in said block; and a wiring pattern disposed on each surface of said block.

2. A wiring board according to claim 1, wherein said electric conductor has an end projecting from said block as a connector terminal.

3. A wiring board according to claim 1 or 2, wherein said block includes a body of a first synthetic resin containing a catalyst that can be deposited by electroless plating and insert-molded around said electric conductor.

4. A wiring board according to claim 3, wherein said block further includes a pair of surface layers of a second synthetic resin disposed on surfaces of said body and free of a catalyst that can be deposited by electroless plating.

5. A wiring board according to claim 4, wherein said surf ace layers of said block are insert-molded on the surfaces of said body.

6. A wiring board according to claim 4 or 5, wherein said wiring pattern is deposited by electroless plating on each surface of said block.

7. A wiring board according to claim 6, wherein said body has portions exposed to the surfaces of said block through said surface layers, said wiring pattern being deposited on each of said exposed portions of said body.

8. A wiring board according to claim 1, wherein said block includes a plurality of bodies stacked into a laminated structure and made of a first synthetic resin containing a catalyst that can be deposited by electroless plating, each body having said electric conductor and insert- molded around said electric conductor, and a pair of surface layers of a second synthetic resin disposed by insert-molding on surfaces of said laminated structure of said bodies and free of a catalyst that can be deposited by electroless plating.

9. A wiring board according to claim 8, wherein said wiring pattern is deposited by electroless plating on each surface of said block.

10. A wiring board according to claim 1, wherein said block comprises a body of a single synthetic resin insert-molded around said electric conductor, said wiring pattern being printed on each surface of said block.

11. A wiring board according to claim 1, wherein a plurality of said electric conductors are embedded in a plurality of layers in said block.

12. A wiring board according to claim 1, further comprising: a case housing said block, said case having side walls surrounding said block and integral therewith and a bottom wall attached to the lower ends of said side walls, said bottom wall being a heat radiator.

13. A wiring board according to claim 12, wherein said electric conductor has an end projecting from said block as a connector terminal and wherein said case further includes a connector integral with said side walls, said connector terminal being disposed in said connector.

14. A wiring board according to claim 12 or 13, wherein a plurality of said electric conductors are embedded in a plurality of layers in said block.

15. A method of making a wiring board, comprising the steps of: setting an electric conductor in a mold; insert-molding a body of a block, made of a first synthetic resin containing a catalyst that can be deposited by a 11 a electroless plating, around said electric conductor; insert-molding a pair of surface layers of said block, made of a second synthetic resin free of a catalyst that can be deposited by electroless plating, on surfaces of said body; and disposing a wiring pattern on each surface of said block.

16. A method according to claim 15, wherein said wiring pattern is deposited by electroless plating on each surface of said block.

17. A method according to claim 16, wherein said pair of surface layers are insert-molded on surfaces of said body leaving selected portions of said body exposed through said surface layers, said wiring pattern being deposited on said exposed portions of said body.

18. A method of making a wiring board, comprising the steps of:

setting an electric conductor in a mold; insert-molding a block of a single resin around said electric conductor in said mold to embed said electric conductor in said block; and p2inting a wiring pattern on each surface of said block.

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