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Injection Molding Large Current Circuit Board
1.

INTRODUCTION

Table 1

Electric Vehicles (EVs), Plug-in Hybrid Electric Vehicles(PHEVs) and Hybrid Electric Vehicles (HEVs) are expected to become the mainstream of the automobile market
in the future. Those vehicles need voltage conversion
devices which are applicable in a large current and hightemperature environment inside the vehicles, such as
inverter circuits which convert the battery voltage of several hundred volts for driving, and converter circuits which
lower the battery voltage of several hundred volts for control. We have already commercialized a thick copper circuit board and a metal core circuit board, which are applicable to the power circuits stated above. This time, wehave developed a large current circuit board using a technology called an injection molding technology. The technology is different from the existing manufacturing methods of circuit boards. We describe the developed large
current circuit board in the following sections.

2.

STRUCTURE

The injection molding large current circuit board is manufactured according to the following process: Blanking circuit conductors from a copper strip of equal to or thicker
than 0.5 mm. Then, joint each conductor by arc welding,etc. if necessary. Finally, mold these conductors in blockby injection molding. Figure 1 shows the manufacturing
process, and Table 1 shows the main specifications.

Blanking

Circuitconductor

Main specification.

Material of circuit conductor

Copper system material(tinned on surface)Thickness of circuit conductor

Equal to or thicker than 0.5 mm

Material of injection molding resin

Polyphenylene sulfide（PPS）

Thickness of injection molding resin Equal to or thicker than 0.8 mm
Number of circuit layers

Can be set arbitrarily

Joint between circuit conductors

WeldA high heat resistance PPS is used for the injection
molding resin. The number and the location of the circuit
layers can be set arbitrarily, which is different from theexisting glass-epoxy circuit, etc. Each circuit conductor is
jointed by welding. By using a welding method which
joints each base material by melting (such as arc welding), a high joint reliability can be obtained.

3.

FEATURES

3.1 Available for Surface Mounting
As Figure 2 shows, surface mounting parts such as
diodes and ceramic condensers can be mounted on thisproduct by lead free solder in a reflow oven. Surface
mounting became available because the circuit board wasable to be processed in a reflow oven by using a highresistance PPS, and also because the solderability of thecircuit board became good by tinning the conductors.
With respect to the solder joint reliability of the surface
mounting parts, the level which is equivalent to the one ofglass-epoxy circuit board was obtained in a vehicle
installed condition (high temperature 120°C, low temperature -40°C) by a unique structure which absorbs linear
expansion and contraction of the circuit board (Figure 3).
DiodeWelding
jointInjection
molding resin

Injection
molding

Figure 1 Manufacturing process.

Ceramiccondenser

Figure 2 Surface mounting on injection molding large current
circuit board.

Furukawa Review, No. 43

2013

39

Injection Molding Large Current Circuit Board

After 1000 cycles of -40℃ /120℃ thermal shock test
Ceramic condenser C2012
Glass-epoxy
circuit board

product’s restraining effect for the rise in temperature isabout 20% in ΔT compared with the aluminum-base circuit board. That is, this product has a superior heat dissipation performance.

Injection
molding circuit
board

Table 3Ceramic condenser C3216

Part

Comparison of heat dissipation.
Existing productDeveloped product

Metal-base circuit board

Injection molding large
current circuit board

Thickness ofcircuit conductor : 70 µm
Thickness ofaluminum-base : 1 mm

Thickness ofconductor : 1 mm

Glass-epoxy
circuit board
Injection
molding circuit
board

Construction※ Red lines indicate welding cracks.
Figure 3 Solder joint reliability.
Temperature
Distribution

3.2Example of Application Enabled by JointingParts
The circuit conductor parts, which are discrete in theexisting products, can be jointed by injection molding inblock. Table 2 shows the examples of the application for aconverter circuit. A converter circuit basically consists of atrans-coil part and a circuit board part which is mountedwith switching heater elements. Each part needed to bejointed by a terminal screw clamp, etc. before. However,as in this product, the technology of molding in block
enabled the joint of the parts. This jointing method contributes to the reduction of the needed parts for jointing
and to space-saving.
Table 2

Example of application to a converter circuit.
Existing product

PartCircuit board

TransDeveloped productCircuit board jointedby injection molding

ShapeSize

130 × 95 mm

105 × 77 mm

Component

Metal base circuit board,trans-coil, litz wire, screw

Circuit board only

Heatingcondition

4.

Four diodes × 17.4 W Output 100 A

CONCLUSION

This product is suitable for the heat dissipation of power
elements which have large heat generated values, suchas MOS-FETs (Metal-Oxide-Semiconductor Field-EffectTransistor) and diodes. Also, it can joint the parts, such astrans-coils, which can’t be assembled or mounted on regular circuit boards. Other than the application to converter
circuits stated in 3.2, it is applicable to inverter circuits, toswitching supply circuits and to other various purposes
which require a large current and a high heat dissipation.
For more information, please contact:
Automotive Products Business Group
Automotive Products Division
TEL: +81-3-3286-3355 FAX: +81-3-3286-3667
e-mail: apb_group@furukawa.co.jp

3.3

Resistance to Large Current and High HeatDissipation
In the existing circuit boards, the thicker the circuit conductors are, the longer the molding time becomes,
because the circuit forming is processed by etching, etc.
On the other hand, in this product, the circuit forming canbe processed without problems even when the circuit
conductors are thicker because of the conductors blanking. Therefore, it is optimal for the use in a large current
and in a high heat dissipation. As Table 3 shows, thisFurukawa Review, No. 43201340