JP2008021728A - Wiring board - Google Patents

Abstract

Provided is a wiring board that can dissipate heat with high efficiency and is lightweight, thin, and inexpensive.
A wiring board is formed by laminating a metal layer 1 made of a metal foil and an insulating layer 2 made of a polyimide film, and a wiring pattern is formed on the metal layer 1. And in order to thermally radiate the heat by self-heating etc. efficiently, it adheres to the heat radiating material 10 comprised with the metal etc. Since the insulating layer 2 is fixed to the heat dissipation material 10, the insulation between the metal layer 1 and the heat dissipation material 10 is ensured.
[Selection] Figure 1

Description

  The present invention relates to a wiring board.

  Since an in-vehicle electronic control unit is often used for an application that requires a large current control, a large current is often applied to a wiring board incorporated in the in-vehicle electronic control unit. Further, it is often used at high temperatures, and particularly when it is arranged in an engine room or incorporated in a motor or the like, it tends to be hot. Therefore, there is a need for a wiring board that has low electrical loss due to energization of a large current at high temperatures and can efficiently dissipate heat due to self-heating.

As such a wiring board, one in which a wiring metal layer made of an aluminum alloy is formed on one surface of a ceramic plate and a back metal layer made of the same aluminum alloy is formed on the other surface is known (Patent Document). 1).
In this wiring board, a back surface metal layer is fixed to a heat dissipating material which is a metal material with an adhesive, a screw or the like, and heat is dissipated through the heat dissipating material. Further, in order to ensure insulation from the heat dissipation material, the wiring metal layer is formed on a ceramic plate (for example, an aluminum nitride plate or a silicon nitride plate) which is an insulating material. Furthermore, the thickness of the wiring metal layer is set to be as large as possible so that energization of a large current can be realized in a necessary minimum area (for example, 500 μm when the metal constituting the wiring metal layer is copper). Is).

Furthermore, since the linear expansion coefficient is different between a metal material and an insulating material, stress may concentrate on the adhesive layer with the weakest mechanical strength and the adhesive layer may break when subjected to a thermal shock due to a rapid change in temperature. . Therefore, in the conventional wiring board as described above, the same kind of metal material (that is, the same linear expansion coefficient) (that is, the wiring metal layer and the back surface) is formed on both surfaces of the ceramic plate as an insulating material for the purpose of canceling stress. A metal layer).
JP 2003-243803 A

However, the conventional wiring board as described above has a problem that the cost and the mass increase because the backside metal layer is provided to alleviate the thermal shock. In particular, in applications where a large current is applied, the thickness of the wiring metal layer needs to be increased, and thus the above-described problems are significant.
Moreover, only a flat wiring board can be manufactured on the manufacturing method of a material and the manufacturing method of a wiring board. Furthermore, since the ceramic plate as an insulating material is hard and inflexible, it is impossible to bend the wiring board after mounting the components. Therefore, when a wiring board is incorporated into a controlled body such as a motor, the arrangement restriction tends to increase.

Furthermore, electrical wiring between a controlled body such as a motor and a wiring board must be performed via an external terminal, and accordingly, accompanying wire bonding, which is necessary, the increase in wiring resistance and process increase Difficulties in ensuring quality and an increase in parts costs are problems.
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a wiring board that solves the problems of the prior art as described above and that can dissipate heat with high efficiency and is lightweight, thin, and inexpensive.

  In order to solve the above problems, the present invention has the following configuration. That is, the wiring board according to the present invention is a wiring board in which a metal layer on which a wiring pattern is formed and an insulating layer are laminated, and is fixed to a heat dissipation material for radiating the heat of the wiring board. The insulating layer that secures insulation between the metal layer and the heat dissipation material is made of polyimide.

The coefficient of linear expansion of polyimide is almost the same as that of metal, and even when subjected to thermal shock due to a sudden change in temperature, large stress does not occur. Therefore, the boundary between the metal layer and the insulating layer (for example, the adhesive layer) Stress concentration is unlikely to occur. Therefore, peeling between the metal layer and the insulating layer due to breakage of the adhesive layer or the like hardly occurs.
Further, it is not necessary to dispose the same kind of metal material on both sides of the insulating layer in order to cancel the stress when subjected to thermal shock, and the metal material is only the metal layer on which the wiring pattern is formed. Is lightweight, thin and inexpensive.

Although the kind of metal which comprises a metal layer is not specifically limited, Copper, aluminum, gold | metal | money, an aluminum alloy etc. are preferable. Moreover, although the kind of polyimide is not specifically limited, it is preferable to select what has a linear expansion coefficient equivalent to the linear expansion coefficient of the metal which comprises a metal layer.
In such a wiring board of the present invention, it is preferable to divide the insulating layer into a plurality of parts by cutting the insulating layer substantially linearly. Then, since the problem of the residual tensile load between the metal layer and the insulating layer can be avoided, it is easy to freely bend the wiring board along the divided portion generated by cutting substantially linearly. Become. Since such a wiring board can be bent after mounting a semiconductor element or a chip component, there are few restrictions on arrangement when the wiring board is incorporated into a controlled body such as a motor.

  Moreover, in the wiring board of the present invention, it is preferable that a part of the insulating layer is removed and at least a part of the metal layer exposed by the removal of the insulating layer is removed. Then, it is possible to make an electrical connection directly from the insulating layer side to the metal layer through the hole provided in the metal layer by the removal (for example, securing conduction by screw tightening). It is not necessary to provide an external terminal for electrical connection between the controlled body and the wiring board, and therefore wire bonding is not required. Therefore, there are advantages such that the wiring resistance can be reduced, the manufacturing process is reduced, the quality can be easily ensured, and the parts cost can be reduced.

  Furthermore, in the wiring board of the present invention, it is preferable to remove a portion of the insulating layer that faces the position where the semiconductor element or chip component that generates heat is mounted. Then, when the wiring board (insulating layer) is fixed to the heat dissipation material, the portion of the metal layer on which the semiconductor element or chip component is mounted directly contacts the heat dissipation material. The heat possessed by can be dissipated very efficiently.

  The wiring board of the present invention can dissipate heat with high efficiency, and is lightweight, thin, and inexpensive.

DESCRIPTION OF EMBODIMENTS Embodiments of a wiring board according to the present invention will be described in detail with reference to the drawings.
[First embodiment]
FIG. 1 is a cross-sectional view for explaining an embodiment of a wiring board according to the present invention. The wiring board of FIG. 1 is formed by laminating a metal layer 1 made of a metal foil and an insulating layer 2 made of a polyimide film, and a wiring pattern is formed on the metal layer 1.
Such a wiring board is manufactured by forming a wiring pattern on the metal layer 1 by etching or the like after fixing a metal foil and a polyimide film by thermocompression bonding or an adhesive. Alternatively, a polyimide film or a polyimide precursor solution may be applied to a metal foil and heated to form a polyimide film on the metal foil, and then a wiring pattern may be formed on the metal layer 1 by etching or the like.

  The metal layer 1 is made of an electrolytic copper foil or a rolled copper foil having a thickness of, for example, 400 μm or more and 500 μm or less, and has a linear expansion coefficient of 17.3 ppm / ° C. The thickness of the polyimide film is, for example, 20 μm or more and 50 μm or less, and the linear expansion coefficient is 16 ppm / ° C. Thus, since the linear expansion coefficients of the metal layer 1 and the insulating layer 2 are substantially equal, even if a thermal shock is caused by a rapid change in temperature, almost no stress is generated. Therefore, stress concentration hardly occurs at the boundary portion (for example, the adhesive layer) between the metal layer 1 and the insulating layer 2, so that the metal layer 1 and the insulating layer 2 are hardly separated.

  When a ceramic plate is used as an insulating layer as in the prior art, the linear expansion coefficient is very different between the metal layer and the insulating layer (for example, the linear expansion coefficients of aluminum nitride and silicon nitride are 4.6 ppm / ° C, 2.7 ppm / ° C.), it is necessary to dispose the same kind of metal material on both sides of the insulating layer in order to offset the stress when subjected to thermal shock. However, since the wiring board of this embodiment uses a polyimide film having a linear expansion coefficient substantially equal to that of the metal layer as the insulating layer, it is not necessary to arrange the same kind of metal material on both surfaces of the insulating layer. Is only a metal layer on which a wiring pattern is formed. Therefore, the wiring board of this embodiment is lighter, thinner, and less expensive than the conventional one. In particular, when the metal foil and the polyimide film are fixed by thermocompression bonding, an adhesive is not required, so that the configuration of the parts and the manufacturing process are simple, and it is advantageous in ensuring quality during manufacturing.

In addition, the kind of metal which comprises the metal layer 1 is not limited to copper, Aluminum, gold | metal | money, an aluminum alloy etc. can be used, However, Copper is the most common. Moreover, although the kind of polyimide is not specifically limited, it is preferable to select what has a linear expansion coefficient equivalent to the linear expansion coefficient of the metal which comprises the metal layer 1. FIG.
Moreover, although the thermal resistance as a material physical property of the polyimide which comprises this polyimide film is comparatively high, since the thickness is very thin as mentioned above, the thermal resistance as a wiring board is a favorable value. It was 0.69 degreeC / W when the thermal resistance of this polyimide film was measured using the sample of length 10mm, width 10mm, and thickness 20micrometer. The thermal resistance of aluminum was measured using a sample with a length of 10 mm, a width of 10 mm, and a thickness of 1.0 mm. As a result, it was 0.5 ° C./W, so the polyimide film had a performance comparable to that of an aluminum plate. It can be said that it has. The thermal resistance of aluminum nitride and silicon nitride measured using a sample of the same size as aluminum was 0.037 ° C./W and 0.053 ° C./W, respectively.

  Such a wiring board of the present embodiment is fixed to the heat radiating material 10 made of metal or the like in order to efficiently dissipate heat due to self-heating or the like. Since the insulating layer 2 is fixed to the heat dissipation material 10, the insulation between the metal layer 1 and the heat dissipation material 10 is ensured. Since the heat of the wiring board is efficiently radiated through the heat dissipation material 10, even when the wiring board self-heats, when a semiconductor element or chip component with heat generation is mounted, even when used under high temperature, Difficult to cause problems due to heat. Therefore, it can be used without any problem for an on-vehicle electronic control unit that tends to become high temperature, and in particular, it can be suitably used even when it is arranged in an engine room or incorporated in a motor or the like.

[Second Embodiment]
FIG. 2 is a diagram illustrating a wiring board according to the second embodiment of the present invention. Since the configuration and operational effects of the wiring board of the second embodiment are almost the same as those of the first embodiment, only different parts will be described, and description of similar parts will be omitted. In FIG. 2, the same reference numerals as those in FIG. 1 are assigned to the same or corresponding parts as in FIG.

  As shown in the plan view of FIG. 2A and the cross-sectional view of FIG. 2B, the wiring board of the second embodiment has an insulating layer 2 cut along a straight line and divided into two. A part 4 having no 2 is formed. As a result, the problem of the residual tensile load between the metal layer 1 and the insulating layer 2 can be avoided, so that the wiring board can be easily bent along the divided portion 4. Since such a wiring board can be bent after mounting a semiconductor element or a chip component, there are few restrictions on arrangement when the wiring board is incorporated into a controlled body such as a motor.

In general flexible boards, the metal layer thickness is as thin as 9 to 35 μm, so there is no problem of residual tensile load. In the case of bending with the metal layer facing outside, there is a possibility that the wiring pattern of the metal layer may be damaged due to partial shrinkage of the polyimide film when the bending angle of the substrate is limited due to the limit of the elongation rate of the polyimide film. .
The method for forming the divided portion 4 without the insulating layer 2 is not particularly limited, and for example, the insulating layer 2 can be removed by etching. Moreover, the dividing part 4 is not limited to one place, You may divide the insulating layer 2 into three or more by providing two or more places. Furthermore, the width of the divided portion 4 is not particularly limited.

[Third embodiment]
FIG. 3 is a view for explaining a wiring board according to the third embodiment of the present invention. Since the configuration and operational effects of the wiring board of the third embodiment are almost the same as those of the first and second embodiments, only different parts will be described, and description of similar parts will be omitted. In FIG. 3, the same reference numerals as those in FIGS. 1 and 2 are given to the same or corresponding parts as those in FIGS.

In the wiring board of the third embodiment, as shown in the plan view of FIG. 3A and the back view of FIG. 3B, a part of the insulating layer 2 is removed. The hole 5 is formed by removing a part of the metal layer 1a exposed on the back side by removing the insulating layer 2. As a result, electrical connection can be made directly from the back surface side (that is, the insulating layer 2 side) to the metal layer 1 through the hole 5 (for example, ensuring conduction by screw tightening), so that the motor or the like is controlled. It is not necessary to provide an external terminal for electrical connection between the body and the wiring board, and therefore wire bonding is also unnecessary. Therefore, there are advantages such that the wiring resistance can be reduced, the manufacturing process is reduced, the quality can be easily ensured, and the parts cost can be reduced.
Note that the method for removing the insulating layer 2 and the method for forming the holes 5 are not particularly limited, and examples thereof include removal of the insulating layer 2 and the metal layer 1 by etching.

[Fourth embodiment]
FIG. 4 is a view for explaining a wiring board according to the fourth embodiment of the present invention. Since the configuration and operational effects of the wiring board of the fourth embodiment are substantially the same as those of the first to third embodiments, only different parts will be described, and description of the same parts will be omitted. In FIG. 4, the same reference numerals as those in FIGS.

In the wiring board of the fourth embodiment, the semiconductor element (or chip component) 20 is mounted on the metal layer 1, but the semiconductor element 20 is mounted in the insulating layer 2 as shown in the rear view of FIG. The part opposite the position has been removed. Thereby, when the wiring board (insulating layer 2) is fixed to the heat radiating material 10, the portion of the metal layer 1 on which the semiconductor element 20 is mounted is in direct contact with the heat radiating material 10. The heat generated by 20 can be dissipated very efficiently without going through the insulating layer 2.
Note that the method for removing the insulating layer 2 is not particularly limited, and examples thereof include etching.

It is a figure explaining the wiring board which concerns on 1st embodiment of this invention. It is a figure explaining the wiring board which concerns on 2nd embodiment of this invention. It is a figure explaining the wiring board which concerns on 3rd embodiment of this invention. It is a figure explaining the wiring board which concerns on 4th embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal layer 2 Insulating layer 4 Dividing part 5 Hole 10 Heat dissipation

Claims (4)

  In a wiring board in which a metal layer on which a wiring pattern is formed and an insulating layer are laminated, the wiring board is fixed to a heat dissipating material for dissipating heat, and the metal layer and the heat dissipating material are insulated. A wiring board characterized in that the insulating layer for ensuring the resistance is made of polyimide.   The wiring board according to claim 1, wherein the insulating layer is cut substantially linearly and divided into a plurality of pieces so that the wiring board can be bent.   By removing a part of the insulating layer and removing at least a part of the metal layer exposed by removing the insulating layer, electrical connection from the insulating layer side to the metal layer becomes possible. The wiring board according to claim 1, wherein the wiring board is provided.   The wiring board according to any one of claims 1 to 3, wherein a portion of the insulating layer corresponding to a position where a semiconductor element or chip component that generates heat is mounted is removed.

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