JP2008211166A - Wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board which has electric wirings on at least one surface and is mounted with a heat generating component so that heat radiation characteristics can be improved and adhesiveness between a metal layer and a resin insulating layer can also be improved by reducing thermal stress of the resin insulating layer due to a difference in coefficient of thermal expansion between a first metal layer 3 and a third metal layer 6 even when the difference in coefficient of thermal expansion is large. <P>SOLUTION: A first metal layer 3 of ≥0.5 mm in thickness, a second metal layer 5, and a third metal layer 7 of ≥1 mm in thickness are arranged in this order, and the first metal layer 3 and the second metal layer 5 are united together with a conductive adhesive layer. The second metal layer 5 and the third metal layer 7 are united together with a resin insulating layer 6. Representing the coefficient of thermal expansion of the first metal layer 3 as α1, the coefficient of thermal expansion of the second metal layer 5 as α2, and the coefficient of thermal expansion of the third metal layer 7 as α3, the coefficients of thermal expansion are so set to satisfy α1<α2<α3 when the difference between α1 and α3 is ≥10 ppm/°C. Further, the thickness of the second metal layer 5 is ≥20% of the thickness of the first metal layer 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wiring board having high heat dissipation characteristics and good adhesion between a metal layer and a resin insulating layer even in a configuration in which a heating element is mounted.

  A wiring board mounted on an electronic device is required to have a technology for fine wiring and high-density mounting in accordance with a reduction in the thickness and size of the electronic device, and a technology for high heat dissipation corresponding to heat generation is also required. In particular, in electronic circuits such as automobiles that use a large current for various controls and operations, heat generation due to the resistance of the conductive circuit and heat generation from the power element are very large, and the heat dissipation characteristics of the wiring board may be high. It has become essential.

  As a countermeasure, for example, in FIG. 1B, the first metal layer 3 and the third metal layer 7 integrated on both surfaces of the resin insulating layer 6 having a thermal conductivity of 4 W / m · K or more are combined with a copper-molybdenum alloy. There is a wiring board constituted by (FIG. 1 of Patent Document 1). In this configuration, since the first metal layer 3 is made of a copper-molybdenum alloy, which is a low thermal expansion metal, even when a heat-generating component such as a power element is mounted on the first metal layer 3, cracks in the solder portion are suppressed. can do. Further, since the first metal layer 3 and the third metal layer 7 are made of the same material, no thermal stress is generated in the resin insulating layer 6 even when a heat treatment such as a solder reflow process is performed.

  However, when using the 3rd metal layer 7 as a heat sink, it is common to use aluminum with good workability and cheap. In this case, the difference between the thermal expansion coefficient of the first metal layer 3 (about 9 ppm / ° C. in the case of a copper-molybdenum alloy) and the thermal expansion coefficient of the third metal layer 7 (about 24 ppm / ° C. in the case of aluminum) becomes large. . For this reason, when heat processing, such as a soldering reflow process, is performed, there is a problem that thermal stress is generated in the resin insulating layer 6 and adhesion between the metal layer and the resin insulating layer is lowered.

On the other hand, in a wiring board formed by mounting a metal fitting via a low-temperature fired insulating substrate, an intermediate layer containing ceramic, and a brazing material, the thermal expansion coefficient of each layer is specified, and the adhesion strength of the metal fitting during brazing is determined. There is a technique to improve (Patent Document 2). However, in a wiring board in which a resin insulating layer having a modulus of elasticity of about 1/1000 smaller than that of the ceramic-containing intermediate layer or brazing material is arranged, the thermal stress of the resin insulating layer becomes very large. The improvement which becomes becomes necessary.
JP 2006-82370 A Japanese Patent No. 2525870

  A problem to be solved by the present invention is a wiring board in which both surfaces are constituted by a first metal layer and a third metal layer integrated through a resin insulating layer, and at least the first metal layer has a function of electric wiring. Further, even when the heat dissipation characteristics are improved and the difference in thermal expansion coefficient between the first metal layer and the third metal layer is large, the thermal stress of the resin insulation layer due to the difference in thermal expansion coefficient is reduced, and the metal layer and the resin insulation layer It is to improve the adhesiveness.

  In order to achieve the above object, the wiring board according to the present invention (Claim 1) includes a first metal layer having a thickness of 0.5 mm or more, a second metal layer, and a third metal layer having a thickness of 1 mm or more in this order. In a wiring board disposed and having at least a first metal layer having a function of electrical wiring, the first metal layer and the second metal layer are integrated with a conductive adhesive layer, and the second metal layer and the third metal layer are made of resin. It is integrated with an insulating layer. When the thermal expansion coefficient of the first metal layer is α1, the thermal expansion coefficient of the second metal layer is α2, and the thermal expansion coefficient of the third metal layer is α3, the difference between α1 and α3 is 10 ppm / ° C. or more. Sometimes, α1 <α2 <α3 is set. Furthermore, the thickness of the second metal layer is 20% or more of the thickness of the first metal layer.

  In another wiring board according to the present invention (Claim 2), at least two or more second metal layers are arranged in the first aspect. The second metal layers are integrated with a conductive adhesive layer, and the total thickness of the second metal layers is 20% or more of the thickness of the first metal layer. The total thickness of the second metal layer may be thicker than the thickness of the first metal layer. Preferably, the difference in coefficient of thermal expansion between adjacent metal layers through the conductive adhesive layer and the resin insulating layer is set to 8 ppm / ° C. or less (claim 4).

  In the wiring board according to any one of claims 1 to 4, preferably, the thermal conductivity of the second metal layer is set larger than the thermal conductivity of the first metal layer (Claim 5). The thermal conductivity of the first metal layer is 150 W / m · K or more (Claim 6), and the thermal conductivity of the resin insulating layer is 4 W / m · K or more (Claim 7).

  In the wiring board according to any one of claims 1 to 7, preferably, the second metal layer is electrically connected to an output terminal having one polarity of a DC power source. A plurality of first metal layers are integrated on the second metal layer using a conductive adhesive layer. A corresponding one of the plurality of heating elements is soldered on the plurality of first metal layers, and the plurality of heating elements are electrically connected to the second metal layer, respectively. 8).

  In the wiring board according to any one of claims 1 to 7, preferably, the second metal layer is electrically connected to an output terminal having one polarity of a DC power source. On the first metal layer, a plurality of heating elements are respectively connected by soldering, and the plurality of heating elements are electrically connected to the second metal layer, respectively.

  In the wiring board, the second metal layer is electrically connected to the output terminal of one polarity of the DC power source, and the first metal layer is integrated on the second metal layer by using the conductive adhesive layer, A plurality of element units configured by soldering and connecting one heat generating element on the first metal layer may be arranged in an electrically insulated state (claim 10).

  In the wiring board according to any one of claims 1 to 7, preferably, the second metal layer includes a portion where the first metal layer is integrated and an electric wiring portion. Further, one or more fourth metal layers constituting another electric wiring portion are integrated on the wiring portion via an electric insulating resin layer. Then, the heating element and the fourth metal layer are connected via the electrical connection means so that the direction of the current flowing through the second metal layer is opposite to the direction of the current flowing through the fourth metal layer. ).

  In the wiring board according to the present invention, since the second metal layer is disposed between the first metal layer and the third metal layer, heat conduction is less likely to be hindered by the conductive adhesive layer or the resin insulating layer. The thermal conductivity of the first metal layer and the third metal layer through the second metal layer is ensured, and the heat dissipation characteristics can be improved. At this time, the thickness of the first metal layer is 0.5 mm or more, and the thickness of the third metal layer is 1 mm or more. Thereby, sufficient heat dissipation characteristics can be ensured.

  When a heat-generating component such as a power element is mounted on the first metal layer having the function of electrical wiring, the thermal expansion coefficient of the power element is about 4 ppm / ° C. On the other hand, when the first metal layer immediately below the power element is copper, the coefficient of thermal expansion is about 17 ppm / ° C. If the heat cycle of the power element is repeated and the heat generation is stopped, stress is concentrated on the solder part that joins the two due to the difference in the coefficient of thermal expansion between them, and the solder part is cracked and connected. Reliability decreases. As a countermeasure, it is possible to suppress cracks in the solder portion by using a low thermal expansion metal (thermal expansion coefficient: about 7 to 10 ppm / ° C.) such as a copper-molybdenum alloy for the first metal layer directly under the power element. it can.

  On the other hand, when the third metal layer is used as a heat sink, it is common to use aluminum that has good workability and is inexpensive. In this case, the difference between the coefficient of thermal expansion of aluminum (20 to 24 ppm / ° C.) and the coefficient of thermal expansion of the low thermal expansion metal is as large as 10 ppm / ° C. or more. For this reason, when heat treatment such as a soldering reflow process is performed, thermal stress is generated in the resin insulating layer, and the adhesion between the metal layer and the resin insulating layer is lowered. When the thickness of the first metal layer is 0.5 mm or more and the thickness of the third metal layer is 1.0 mm or more, the thermal stress is increased, and the adhesion between the metal layer and the resin insulating layer is greatly reduced. .

  However, in the wiring board according to the present invention, when the thermal expansion coefficient of the first metal layer is α1, the thermal expansion coefficient of the second metal layer is α2, and the thermal expansion coefficient of the third metal layer is α3, α1 <α2 Since the relationship of <α3 is set, the difference in coefficient of thermal expansion between the first metal layer and the third metal layer is relaxed by the second metal layer, and the thermal stress applied to the resin insulating layer can be reduced. At this time, the thickness of the second metal layer is set to 20% or more of the thickness of the first metal layer. When the thickness of the second metal layer is less than 20%, the strength of the second metal layer is lowered, and the effect of reducing the thermal stress applied to the resin insulating layer cannot be sufficiently obtained.

  With the above configuration, even if the difference in coefficient of thermal expansion between the first metal layer and the third metal layer is 10 ppm / ° C. or more, the thermal stress applied to the resin insulating layer is reduced, and the metal layer and the resin insulating layer are reduced. Adhesion can be improved.

  In the other wiring board according to the present invention, at least two or more second metal layers are arranged between the first metal layer and the third metal layer in the above configuration. The second metal layers are integrated with a conductive adhesive layer. If the coefficient of thermal expansion is increased toward the third metal layer even between two or more second metal layers arranged between the first metal layer and the third metal layer, the heat of the first metal layer and the third metal layer is increased. The difference in expansion coefficient can be gradually eased, and the thermal stress applied to the resin insulating layer can be further reduced. Further, the heat insulation is further inhibited by the resin insulating layer, and the heat dissipation characteristics can be further improved. Here, in the first to third metal layers, it is preferable to set the difference in coefficient of thermal expansion between adjacent metal layers through the conductive adhesive layer or the resin insulating layer to 8 ppm / ° C. or less. When two or more second metal layers are present via the conductive adhesive layer, the difference in thermal expansion coefficient between the metal layers is preferably 8 ppm / ° C. or less.

  At this time, the total thickness of the second metal layer is set to 20% or more of the thickness of the first metal layer. When the total thickness of the second metal layer is less than 20%, the strength of the second metal layer is lowered, and the effect of reducing the thermal stress applied to the resin insulating layer cannot be sufficiently obtained. By setting the total thickness of the second metal layer to be thicker than the thickness of the first metal layer, the heat dissipation effect is further increased.

  Furthermore, the heat dissipation effect is increased by setting the thermal conductivity of the second metal layer to be larger than the thermal conductivity of the first metal layer. The thermal conductivity of the first metal layer is preferably 150 W / m · K or higher, and the thermal conductivity of the resin insulating layer is preferably 4 W / m · K or higher.

  When a heating element such as a power transistor is mounted on the wiring board of the present invention, the second metal layer can be electrically connected to the output terminal of one polarity of the DC power supply. Then, a plurality of first metal layers are integrated on the second metal layer using a conductive adhesive layer. A corresponding one of the plurality of heating elements is soldered on the plurality of first metal layers, and the plurality of heating elements are electrically connected to the second metal layer via the first metal layer, respectively. Connect. In this case, not only the second metal layer can be used as a means for reducing thermal stress but also the second metal layer can be used as a wiring, so that a member for wiring can be omitted. In particular, when a plurality of first metal layers are integrated on the second metal layer, electric power can be supplied from one second metal layer to the plurality of heating elements via the plurality of first metal layers. When the price of the material of the first metal layer is high, it is preferable to provide the first metal layer individually for each heating element. However, when the first metal layer is formed of a low-cost material, one first metal layer may be provided for a plurality of heating elements. In this case, the size of one first metal layer to be used may be made large enough to mount a plurality of heating elements. In this way, the number of parts can be reduced. In addition, the above-described configuration in which the second metal layer is also used for a plurality of heating elements constitutes a part of an inverter bridge circuit that converts direct current into alternating current and a part of a bridge circuit of a rectifier circuit that converts alternating current into direct current. Can be used if you want.

  In addition, the second metal layer is electrically connected to the output terminal of one polarity of the DC power supply, and the first metal layer is integrated on the second metal layer using the conductive adhesive layer. A plurality of element units configured by soldering and connecting one heat generating element on the first metal layer may be arranged in an electrically insulated state. When such a plurality of element units are provided, a power conversion circuit such as a DC-DC converter can be easily configured on the wiring board.

  Further, when the second metal layer is composed of a part where the first metal layer is integrated and an electric wiring part, another electric wiring part is formed on the wiring part via an electric insulating resin layer. It is preferable to integrate the fourth metal layer. Then, if the heating element and the fourth metal layer are connected via the electrical connection means so that the direction of the current flowing through the second metal layer and the direction of the current flowing through the fourth metal layer are opposite to each other, Since the magnetic flux generated by the current flowing through the metal layer and the magnetic flux generated by the current flowing through the fourth metal layer act so as to cancel each other, the inductance of the circuit can be reduced.

  As a specific form for carrying out the present invention, for example, a configuration as shown in FIG. A first metal layer 3 having a thickness of 0.5 mm or more, a second metal layer 5 and a third metal layer 7 having a thickness of 1 mm or more are arranged in this order. At least the first metal layer 3 has a function of electric wiring. The heating element 1 is mounted with solder 2 on the first metal layer 3 having the function of electrical wiring. The first metal layer 3 and the second metal layer 5 are integrated with the conductive adhesive layer 4. The second metal layer 5 and the third metal layer 7 are integrated with a resin insulating layer 6. Further, when the thermal expansion coefficient of the first metal layer 3 is α1, the thermal expansion coefficient of the second metal layer 5 is α2, and the thermal expansion coefficient of the third metal layer 7 is α3, the difference between α1 and α3 is 10 ppm / ° C. When this is the case, the relationship α1 <α2 <α3 is set. The thickness of the second metal layer 5 is 20% or more of the thickness of the first metal layer.

  Another specific mode for carrying out the present invention is, for example, a configuration as shown in FIG. The first metal layer 3 having a thickness of 0.5 mm or more, the second metal layers 15 and 25, and the third metal layer 7 having a thickness of 1 mm or more are arranged in this order. At least the first metal layer 3 has a function of electric wiring. The heating element 1 is mounted with solder 2 on the first metal layer 3 having the function of electrical wiring. The first metal layer 3 and the second metal layer 15 are integrated with the conductive adhesive layer 4. The second metal layers 15 and 25 are also integrated with the conductive adhesive layer 14. The second metal layer 25 and the third metal layer 7 are integrated by the resin insulating layer 6. Further, when the thermal expansion coefficient of the first metal layer 3 is α1, the thermal expansion coefficients of the second metal layers 15 and 25 are α21 and α22, and the thermal expansion coefficient of the third metal layer 7 is α3, the difference between α1 and α3. Is set such that α1 <α21 <α22 <α3. The thickness of the second metal layer 5 is 20% or more of the thickness of the first metal layer.

  When the difference in coefficient of thermal expansion between the first metal layer and the third metal layer is less than 10 ppm / ° C., the thermal stress applied to the resin insulating layer is small, and therefore the effect of relaxing the thermal stress by arranging the second metal layer is effective. small. On the other hand, when the difference in thermal expansion coefficient is 10 ppm / ° C. or more, the effect of relaxing the thermal stress by arranging the second metal layer appears greatly. Furthermore, when the difference in thermal expansion coefficient is 15 ppm / ° C. or more, two or more second metal layers are disposed between the first metal layer and the third metal layer, and the first metal layer and the third metal layer are disposed. The thermal stress applied to the resin insulating layer can be further reduced by gradually easing the difference in thermal expansion coefficient. At this time, it is preferable to set the difference in coefficient of thermal expansion between adjacent metal layers to 8 ppm / ° C. or less.

  The above-described configuration can be applied to, for example, a generally used method for manufacturing a laminated board or a multilayer board. That is, each material can be arranged in a predetermined configuration and integrated by heat and pressure molding as in the method of manufacturing a laminated plate. Moreover, you may integrate sequentially by heating-press molding for every predetermined structural unit like the manufacturing method of a multilayer board. Then, the predetermined heating element 1 is mounted on a mounting region on the first metal layer 3 that has been processed into a predetermined shape by means such as solder reflow.

  A thermal expansion coefficient of the first metal layer of 7 to 10 ppm / ° C. is preferable because the solder connection reliability is improved. For example, copper alloys such as copper / molybdenum, copper / invar, copper / tungsten, and copper / chromium can be used. Among these, a copper / chromium alloy is preferable because it is inexpensive and can maintain connection reliability equivalent to that of a copper / molybdenum alloy. Although the electrical conductivity of these copper alloys is inferior to copper, there is no practical problem. Alternatively, an aluminum alloy that is a composite material of aluminum and ceramic particles may be used. Although the electrical conductivity of the aluminum alloy is inferior to that of the copper alloy, there is no practical problem.

  Further, it is preferable that the thermal conductivity of the first metal layer is 150 W / m · K or more because the heat dissipation characteristics are improved. Furthermore, if the thickness of the first metal layer is 0.5 mm or more, the heat dissipation characteristics can be improved. However, since composite materials such as copper alloys are higher in strength and price than copper, workability and cost are reduced. It can be set as appropriate in consideration.

  If the thermal expansion coefficient of the second metal layer is an intermediate value between the first metal layer and the third metal layer, it is preferable because the thermal stress applied to the resin insulating layer can be reduced. For example, SUS or copper can be used. Among them, copper is preferable because it has a high thermal conductivity of 394 W / m · K and can further improve heat dissipation characteristics. Furthermore, if the total thickness of the second metal layer is 20% or more of the thickness of the first metal layer, thermal stress relaxation and heat dissipation characteristics can be improved, but the total thickness of the second metal layer is reduced to the thickness of the first metal layer. It is preferable that the thickness is larger than that because the heat dissipation characteristics can be further improved.

  When the third metal layer is used as a heat sink, aluminum or an aluminum alloy can be used. Aluminum or aluminum alloy is very suitable as a heat sink because of its good workability, low cost, no rust, and high thermal conductivity. Furthermore, if the thickness of the third metal layer is 1 mm or more, strength and heat dissipation characteristics can be secured, but about 2 to 3 mm is generally used. The shape of the third metal layer may be a simple flat plate. However, in order to increase the cooling efficiency, the thickness may be about 4 to 10 mm, and the opposite surface in contact with the resin insulating layer may be shaped like a cooling fin. .

  For the conductive adhesive layer, a metal having a relatively low melting point such as solder, silver brazing material, or copper brazing material can be used. If the first metal layer and the second metal layer are bonded with these metals, the conductivity between the first metal layer and the second metal layer is excellent and the heat conduction is promoted, so the heat dissipation characteristics are very excellent. . Moreover, you may use the resin adhesive containing a metal particle. For example, a conductive resin paste in which copper particles are added to an epoxy resin. In particular, a conductive resin paste having a very low electric resistance is preferable because the conductivity between the first metal layer and the second metal layer is good and the heat conductivity is good.

  The formation of the conductive adhesive layer can be performed in the following process. When the conductive adhesive layer is a low melting point metal such as solder, a conductive adhesive layer is formed between the first metal layer and the second metal layer to integrate the first metal layer and the second metal layer. Thereafter, a resin insulating layer to be described later is formed. When the conductive adhesive layer is a conductive resin paste or the like, the first metal layer and the second metal layer are formed after forming the resin insulating layer described later and integrating the second metal layer and the third metal layer. A conductive adhesive layer may be formed between the first metal layer and the second metal layer, or may be formed and integrated at the same time when the resin insulating layer is formed.

  It is preferable that the thickness of each resin insulating layer is 150 μm or less because the heat conduction is hardly hindered by the resin insulating layer and the heat dissipation characteristics can be improved. In addition, it is preferable that the thermal conductivity of the resin insulating layer is 4 W / m · K because the heat dissipation characteristics can be improved.

  The sheet-like fiber base material which comprises a resin insulating layer is the woven fabric and nonwoven fabric which were comprised with glass fiber or organic fiber. The thermosetting resin impregnated in the sheet-like fiber base material can be produced by adding a highly heat-conductive inorganic filler to a phenol resin or an epoxy resin. In particular, when the resin insulating layer is required to have high thermal conductivity, for example, the following resin composition is used.

That is, an epoxy resin composition containing an inorganic filler and containing an epoxy resin monomer having a molecular structure represented by (Formula 1) is employed. The inorganic filler has a thermal conductivity of 20 W / m · K or more, and is present in the insulating layer in an amount of 50 to 250 parts by volume with respect to 100 parts by volume of the resin solid content.

  The epoxy resin monomers having the molecular structure represented by the above (formula 1) are all epoxy compounds having a biphenyl skeleton or a biphenyl derivative skeleton and having two or more epoxy groups in one molecule. In order to advance the curing reaction of the epoxy resin monomer, a curing agent is blended. Examples of the curing agent include amine compounds and derivatives thereof, acid anhydrides, imidazoles and derivatives thereof, phenols or compounds and polymers thereof, and the like. Moreover, in order to accelerate | stimulate reaction of an epoxy resin monomer and a hardening | curing agent, a hardening accelerator can be used. Examples of the curing accelerator include triphenylphosphine, imidazole and derivatives thereof, tertiary amine compounds and derivatives thereof, and the like.

  The inorganic filler having a thermal conductivity of 20 W / m · K or more blended in the epoxy resin composition blended with the curing agent or curing accelerator is a metal oxide, hydroxide, inorganic ceramic, or other filler. For example, inorganic powder fillers such as boron nitride, aluminum nitride, silicon nitride, silicon carbide, titanium nitride, zinc oxide, tungsten carbide, alumina, magnesium oxide, fibrous fillers such as synthetic fibers and ceramic fibers, colorants, etc. is there. Two or more of these inorganic fillers may be used in combination.

  An inorganic filler is mix | blended so that it may become the quantity of 50-250 volume parts with respect to 100 volume parts of resin solid content. The lower limit value of the thermal conductivity and the blending amount of the inorganic filler is necessary when the thermal conductivity of the resin insulating layer is 4 W / m · K or more. Moreover, when there are few inorganic fillers mix | blended with an epoxy resin composition, it will become difficult to disperse | distribute an inorganic filler uniformly in an epoxy resin composition. In this respect as well as ensuring thermal conductivity, it is important to define the lower limit value of the inorganic filler content. On the other hand, when the blending amount of the inorganic filler is increased, the viscosity of the epoxy resin composition is increased and the handling becomes difficult. Therefore, the upper limit value of the blending amount of the inorganic filler is defined from this viewpoint.

  In addition, it is preferable if the thermal conductivity of the inorganic filler is 30 W / m · K or more because the thermal conductivity of the resin insulating layer can be further increased. In addition, the inorganic filler may have any shape such as powder (bulk, sphere), short fiber, long fiber, etc. However, when a flat plate is selected, the inorganic filler itself with high thermal conductivity is resin. It exists in the state which accumulated in the inside, and since the heat conductivity of the thickness direction of a resin insulating layer can be made still higher, it is preferable. In addition to the above epoxy resin composition, a flame retardant, a diluent, a plasticizer, a coupling agent, and the like can be blended as necessary.

  The resin insulation layer is formed by preparing a prepreg in which the epoxy resin composition is diluted with a solvent as necessary to prepare a varnish, impregnating the varnish into a sheet-like fiber base material, and drying by heating to a semi-cured state. And these are heat-press-molded and it is set as a resin insulating layer. In the heat and pressure molding, the third metal layer, the prepreg and the second metal layer are arranged and stacked in this order, and these are integrated by heat and pressure molding.

  When the varnish is prepared by diluting the epoxy resin composition in a solvent, the blending and use of the solvent does not affect the thermal conductivity of the cured epoxy resin.

  FIG. 3 shows an example of a specific configuration of the embodiment when a plurality of (three shown in FIG. 3) heating elements 31 are mounted using the structure shown in FIG. Show. FIG. 3 is a close-up drawing of the main part of the wiring board according to the present invention, and another wiring or component is mounted on the actual wiring board. In the embodiment shown in FIG. 3, the same members as those constituting the structure shown in FIG. Detailed descriptions of materials and the like are omitted. In the embodiment of FIG. 3, when the heating element 31 such as a power transistor is mounted on the wiring board, the second metal layer 35 is an output terminal (one of a plus terminal and a minus terminal) of one polarity of a DC power source (not shown). Is electrically connected. In FIG. 3, the second metal layer 35 has substantially the same size as the third metal layer 37. On the second metal layer 35, a plurality (three) of the first metal layers 33 are joined via the conductive adhesive layer 34. On the three first metal layers 33, the heat generating elements 31 are joined by solder 32, respectively. In such a heating element 31, the bottom wall portion of the outer case is made of metal to form an electrical terminal, and other electrical terminals are placed on the upper wall portion facing the bottom wall portion of the outer case. It is a part of the type provided. Therefore, the first metal layer 33 and the heat generating element 31 are mechanically and electrically connected only by directly connecting the heat generating element 31 to the first metal layer 33 with the solder 32. The heating element 31 is electrically connected to the second conductive layer 35 via the solder 32, the first metal layer 33, and the conductive adhesive layer 34. As a result, according to the present embodiment, not only can the second metal layer 35 be used as means for reducing thermal stress, but also the second metal layer 35 can be used as wiring.

  In the present embodiment, the second metal layer 35 is composed of a part 35A where the first metal layer 33 is integrated (connected) and an electric wiring part 35B. On the wiring portion 35B, three fourth metal layers 38 constituting another electric wiring portion are arranged via an electric insulating resin layer 39 such as an epoxy resin and integrated with the wiring board. The fourth metal layer 38 functions to electrically connect the three heating elements 31 to, for example, three output terminals (not shown). In this example, the fourth metal layer 38 is formed of Cu or a Cu alloy. The electrically insulating resin layer 39 is also present between the two adjacent fourth metal layers 38, between the two adjacent first metal layers 33, and between the adjacent first metal layer 33 and the fourth metal layer 38. Thus, electrical insulation between these metal layers is achieved. Further, the heating element 31 and the fourth metal layer 38 are electrically connected to each other by an electrical connection means 40 formed by wire bonding. In FIG. 3, the direction of current flow is shown as indicated by arrows. In this example, the second metal layer 35 → the conductive adhesive layer 34 → the three first metal layers 33 → the solder 32 → the three heating elements 31 → the electrical connection means 40 → the three fourth metal layers 38. Current is flowing. As a result, the direction of the current flowing through the second metal layer 35 and the direction of the current flowing through the fourth metal layer 38 are opposite. As a result, since the magnetic flux generated by the current flowing through the second metal layer 35 and the magnetic flux generated by the current flowing through the fourth metal layer 38 cancel each other, the inductance of the circuit is reduced.

  When a plurality of first metal layers 33 are integrated on the second metal layer 35 as in the present embodiment, a plurality of heating elements are formed from one second metal layer 35 via the plurality of first metal layers 33. Power can be supplied to 31. When the price of the material of the first metal layer 33 is high, it is preferable to provide the first metal layer 33 individually for each heating element 31, as in the embodiment of FIG. However, as shown in FIG. 4, when the first metal layer 33 ′ is formed of a low cost material, one first metal layer 33 ′ may be provided for the plurality of heating elements 31. In this case, one second metal layer 35 and two first metal layers 33 ′ are mechanically and electrically connected by one conductive adhesive layer 34 ′, so that the number of parts is reduced. be able to. In the configuration shown in FIGS. 3 and 4, three heating elements 31 are electrically connected to one second metal layer 35, so a part of the bridge circuit of the DC-three-phase AC inverter module, the semiconductor three This can be used when configuring a part of the bridge circuit of the phase rectifier circuit module.

  Further, for example, in the structure shown in FIG. 3, the second metal layer 35 is separated corresponding to the individual first metal layers 33, and the plurality of separated second metal layers are electrically insulated from each other so as to electrically isolate the plurality of element units. May be configured. If such a plurality of element units are provided on the wiring board, other power conversion circuits such as a DC-DC converter can be configured on the wiring board with a small number of components.

  In the embodiment shown in FIGS. 3 and 4, the second metal layer may of course have a structure of two or more layers as shown in FIG.

  Examples of the present invention will be described below, and the present invention will be described in detail. In the following examples and comparative examples, “part” means “part by mass”. Moreover, this invention is not limited to a present Example, unless it deviates from the summary.

  The material specifications used in the examples are as follows.

(A) Epoxy resin varnish a; 100 parts of an epoxy resin monomer having a biphenyl skeleton as an epoxy resin monomer component (Japan Epoxy Resin “YL6121H”, epoxy equivalent 175) is prepared, and this is methyl isobutyl ketone (Wako Pure Chemical Industries, Ltd.) It melt | dissolved in 100 parts at 100 degreeC, and returned to room temperature. The “YL6121H” includes an epoxy resin monomer in which R = —CH ₃ and n = 0.1 in the molecular structural formula (formula 1) described above and R = —H, n in the molecular structural formula (formula 1). = 0.1 An epoxy resin monomer containing an equimolar amount of an epoxy resin monomer of 0.1.

  As a curing agent, 22 parts of 1,5-diaminonaphthalene (“1,5-DAN” manufactured by Wako Pure Chemical Industries, Ltd., amine equivalent 40) is prepared and dissolved in 100 parts of dimethylformamide (manufactured by Wako Pure Chemical Industries) at 100 ° C. , Returned to room temperature.

  The above epoxy resin monomer solution and curing agent solution are mixed and stirred to form a uniform varnish, and alumina (DAW-10 manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size: 10 μm, thermal conductivity 30 W / m as an inorganic filler. -K, particle shape: spherical) 425 parts (equivalent to 100 parts by volume with respect to 100 parts by volume of the resin solid content) were added and kneaded to prepare an epoxy resin varnish a.

(B) Epoxy resin varnish b; alumina as an inorganic filler in the epoxy resin varnish a (“DAW-10” manufactured by Denki Kagaku Kogyo, average particle size: 10 μm, thermal conductivity 30 W / m · K, particle shape: spherical An epoxy resin varnish b was prepared in the same manner as the epoxy resin varnish a except that 540 parts by weight (corresponding to 185 parts by volume with respect to 100 parts by volume of the resin solid content) was added and kneaded.

(C) Prepreg a: Epoxy resin varnish a was impregnated into a glass nonwoven fabric having a thickness of 100 μm and dried by heating to obtain a prepreg having a thickness of 120 μm.

(D) Prepreg b: Epoxy resin varnish b was impregnated into a glass nonwoven fabric having a thickness of 100 μm and dried by heating to obtain a prepreg having a thickness of 120 μm.

Example 1
The following materials were prepared as the constituent materials in FIG.

1) First metal layer 3: Copper / Invar alloy (thickness 0.5 mm, thermal expansion coefficient 10 ppm / ° C., thermal conductivity 90 W / m · K)
2) Second metal layer 5: SUS304 (thickness 0.1 mm, thermal expansion coefficient 17 ppm / ° C., thermal conductivity 14 W / m · K)
3) Third metal layer 7: Aluminum alloy 4032 (thickness 1.0 mm, thermal expansion coefficient 20 ppm / ° C., thermal conductivity 150 W / m · K)
4) Resin insulation layer 6: prepreg a
A silver brazing material is applied as a conductive adhesive on the first metal layer (thickness: 200 μm), and the second metal layer is placed on the silver brazing material and placed in a heating furnace until the silver brazing material melts. The first metal layer and the second metal layer were integrated by heating.

  Next, as shown in FIG. 1A, the third metal layer-the prepreg a1 sheet- (the second metal layer in which the first metal layer is integrated) are arranged and stacked in this order, and these are heated and applied. The laminate was pressed and integrated to obtain a laminated plate having a thickness of 1.84 mm. The heating and pressing were performed under the conditions of heating and pressing for 90 minutes at a temperature of 175 ° C. and a pressure of 6 MPa. Then, the first metal layer of the laminated board was processed into a predetermined shape to obtain a wiring board. The thermal conductivity of the resin insulating layer is 3 W / m · K.

  Table 1 shows the results of measuring the element heat generation temperature, the peeled area ratio, and the solder connection reliability of the wiring board obtained in Example 1 together with the configurations of the metal layer and the resin insulating layer. The measurement is based on the method shown below.

  Thermal expansion coefficient: A plate sample of 5 × 10 mm was cut out from the wiring board, and the thermal expansion coefficient in the plane direction in the range of 30 ° C. to 260 ° C. was measured by TMA measurement.

  Thermal conductivity: The heat conduction in the thickness direction of each metal layer and resin insulation layer was measured by a heat flow meter method (based on JIS-A1412).

  Element heating temperature: A heating element (ceramic heater chip) is soldered to the first metal layer that has been processed into a circuit in a predetermined shape, and the third metal layer is cooled by cooling fins and maintained at a constant temperature. A power of 80 W was input to the heating element, and the element temperature after 2 minutes of input was measured.

  Peeling area ratio: The wiring board processed into a predetermined shape was heat-treated for 60 seconds in a reflow furnace having a maximum temperature of 260 ° C. Then, it observed from the upper part of the wiring board with the ultrasonic flaw detector, and measured the peeling area of the metal and resin interface. Then, (peeled area / total area of wiring board) × 100 was defined as a peeled area ratio (%).

Example 2
In Example 1, a wiring board was obtained in the same manner as in Example 1 except that copper (thickness 0.1 mm, thermal expansion coefficient 17 ppm / ° C., thermal conductivity 394 W / m · K) was used as the second metal layer. . By increasing the thermal conductivity of the second metal layer, the element heat generation temperature was reduced and the heat dissipation characteristics were improved.

Example 3
In Example 2, a wiring board was obtained in the same manner as in Example 2 except that aluminum 1100 (thickness 1.0 mm, thermal expansion coefficient 24 ppm / ° C., thermal conductivity 220 W / m · K) was used as the third metal layer. It was. By increasing the thermal conductivity of the third metal layer, the element heat generation temperature was reduced and the heat dissipation characteristics were improved.

Example 4
A wiring board in the same manner as in Example 3, except that a copper / molybdenum alloy (thickness 0.5 mm, thermal expansion coefficient 9 ppm / ° C., thermal conductivity 150 W / m · K) is used as the first metal layer in Example 3. Got. By increasing the thermal conductivity of the first metal layer, the element heat generation temperature was reduced and the heat dissipation characteristics were improved.

Example 5
In Example 4, a wiring board was obtained in the same manner as in Example 4 except that prepreg b was used as the resin insulating layer. The thermal conductivity of the resin insulating layer is 4 W / m · K. By increasing the thermal conductivity of the resin insulation layer, the element heat generation temperature was reduced and the heat dissipation characteristics were improved.

Example 6
In Example 5, a wiring board was obtained in the same manner as in Example 5 except that copper (thickness 0.6 mm, thermal expansion coefficient 17 ppm / ° C., thermal conductivity 394 W / m · K) was used as the second metal layer. . By increasing the thickness of the second metal layer, the element heat generation temperature was reduced and the heat dissipation characteristics were improved.

Example 7
A wiring board in the same manner as in Example 6 except that a copper / chromium alloy (thickness 0.5 mm, thermal expansion coefficient 10 ppm / ° C., thermal conductivity 180 W / m · K) is used as the first metal layer in Example 6. Got. By increasing the thermal conductivity of the first metal layer, the element heat generation temperature was reduced and the heat dissipation characteristics were improved.

Comparative Example 1
In Example 1, the wiring board was obtained like Example 1 except not having arrange | positioned a 2nd metal layer. In Comparative Example 1, since the second metal layer is not disposed, a thermal stress is applied to the resin insulating layer due to the difference in thermal expansion coefficient between the first metal layer and the third metal layer, and the interface between the metal and the resin is wide. The peeling has occurred. In addition, the element heat generation temperature increased, and the heat dissipation characteristics deteriorated significantly.

Comparative Example 2
A wiring board in the same manner as in Example 4 except that a copper / molybdenum alloy (thickness 0.4 mm, thermal expansion coefficient 9 ppm / ° C., thermal conductivity 150 W / m · K) is used as the first metal layer in Example 4. Got. In Comparative Example 2, since the thickness of the first metal layer is thin, the thermal stress applied to the resin insulating layer is reduced. Therefore, even if the second metal layer is disposed, the effect of relaxing the stress is not much. In addition, the element heat generation temperature increased and the heat dissipation characteristics deteriorated.

Comparative Example 3
In Example 4, a wiring board was obtained in the same manner as in Example 4 except that aluminum 1100 (thickness 0.5 mm, thermal expansion coefficient 24 ppm / ° C., thermal conductivity 220 W / m · K) was used as the third metal layer. It was. In Comparative Example 3, since the thickness of the third metal layer is thin, the thermal stress applied to the resin insulating layer is reduced. Therefore, even if the second metal layer is disposed, the effect of relaxing the stress is not much. In addition, the element heat generation temperature increased and the heat dissipation characteristics deteriorated.

Comparative Example 4
In Example 4, a wiring board was obtained in the same manner as in Example 4 except that copper (thickness 0.05 mm, thermal expansion coefficient 17 ppm / ° C., thermal conductivity 394 W / m · K) was used as the second metal layer. It was. In Comparative Example 4, since the thickness of the second metal layer is less than 20% of the first metal layer, the effect of reducing the difference in thermal expansion coefficient between the first metal layer and the third metal layer is reduced. Peeling occurs at the resin interface. In addition, the element heat generation temperature increased, and the heat dissipation characteristics deteriorated significantly.

Comparative Example 5
In Example 4, a copper / chromium alloy (thickness 0.5 mm, thermal expansion coefficient 10 ppm / ° C., thermal conductivity 180 W / m · K) was used as the first metal layer, and a copper / molybdenum alloy ( A wiring board was obtained in the same manner as in Example 4 except that a thickness of 0.1 mm, a thermal expansion coefficient of 9 ppm / ° C., and a thermal conductivity of 150 W / m · K were used. In Comparative Example 5, since the thermal expansion coefficient of the second metal layer is larger than that of the first metal layer, the interface between the metal and the resin is caused by the difference in thermal expansion coefficient between the second metal layer and the third metal layer. Exfoliation occurs in a wide range. In addition, the element heat generation temperature increased with peeling, and the heat dissipation characteristics were greatly deteriorated.

Comparative Example 6
In Example 4, a wiring board was obtained in the same manner as in Example 4 except that copper (thickness 1.0 mm, thermal expansion coefficient 17 ppm / ° C., thermal conductivity 394 W / m · K) was used as the third metal layer. It was. In Comparative Example 6, since the difference in coefficient of thermal expansion between the first metal layer and the third metal layer is less than 10 ppm / ° C., the thermal stress applied to the resin insulating layer is reduced, so the second metal layer is disposed. However, there is not much effect of stress relaxation. In addition, when using copper as a 3rd metal layer, there exists a problem that cost is high, rusts, and cannot be reduced compared with the case where aluminum and aluminum alloy are used, and it is not suitable as a heat sink.

About the wiring board of Examples 2-7 and Comparative Examples 1-6, the characteristic was measured similarly to Example 1, and the result was shown to Tables 1-2.

  As shown in the above table, in the embodiment according to the present invention, the thermal expansion coefficient of the first metal layer is α1, the thermal expansion coefficient of the second metal layer is α2, and the thermal expansion coefficient of the third metal layer is α3. Then, when the difference between α1 and α3 is 10 ppm / ° C. or more, the relationship of α1 <α2 <α3 is set, and the thickness of the second metal layer is 20% of the thickness of the first metal layer. Since it was set as the above, it can be understood that the thermal radiation characteristic is improved and the peeling area ratio is suppressed (contrast with Examples 1-8 and Comparative Examples 1-6).

(A) is a wiring board sectional view concerning an embodiment of the invention, and (b) is a conventional wiring board sectional view. It is a wiring board sectional view concerning other embodiments of the present invention. It is a perspective view of the principal part of the wiring board of other embodiment at the time of mounting a several heat generating element. It is a perspective view of the principal part of the wiring board of further another embodiment in the case of mounting a plurality of exothermic elements.

Explanation of symbols

1, 31 Heating element 2, 32 Solder 3, 33, 33 'First metal layer 4, 14, 34, 34' Conductive adhesive layer 5, 15, 25, 35 Second metal layer 6, 36 Resin insulating layer 7 37 Third metal layer

Claims (11)

In a wiring board in which a first metal layer having a thickness of 0.5 mm or more, a second metal layer, and a third metal layer having a thickness of 1 mm or more are arranged in this order, and at least the first metal layer has a function of electric wiring.
The first metal layer and the second metal layer are integrated with a conductive adhesive layer, the second metal layer and the third metal layer are integrated with a resin insulating layer,
When the thermal expansion coefficient of the first metal layer is α1, the thermal expansion coefficient of the second metal layer is α2, and the thermal expansion coefficient of the third metal layer is α3, the difference between α1 and α3 is 10 ppm / ° C. or more. , Α1 <α2 <α3,
A wiring board, wherein the thickness of the second metal layer is 20% or more of the thickness of the first metal layer.   Two or more second metal layers are arranged, the second metal layers are integrated with each other by a conductive adhesive layer, and the total thickness of the second metal layers is 20% of the thickness of the first metal layer. It is the above, The wiring board of Claim 1 characterized by the above-mentioned.   The total thickness of a 2nd metal layer is thicker than the thickness of a 1st metal layer, The wiring board in any one of Claim 1 or 2 characterized by the above-mentioned.   The difference in coefficient of thermal expansion between adjacent metal layers through each of the conductive adhesive layer and the resin insulating layer is set so as to be 8 ppm / ° C or less. Wiring board as described in.   The wiring board according to any one of claims 1 to 4, wherein the thermal conductivity of the second metal layer is greater than the thermal conductivity of the first metal layer.   6. The wiring board according to claim 1, wherein the first metal layer has a thermal conductivity of 150 W / m · K or more.   The wiring board according to claim 1, wherein the resin insulating layer has a thermal conductivity of 4 W / m · K or more. The second metal layer is electrically connected to one polarity output terminal of a DC power source;
A plurality of the first metal layers are integrated on the second metal layer using the conductive adhesive layer,
A corresponding one of the plurality of heating elements is soldered on the plurality of first metal layers, and the plurality of heating elements are electrically connected to the second metal layer, respectively. It is connected, The wiring board of any one of Claims 1-7 characterized by the above-mentioned. The second metal layer is electrically connected to one polarity output terminal of a DC power source;
The plurality of heating elements are respectively connected by soldering on the first metal layer, and the plurality of heating elements are electrically connected to the second metal layer, respectively. The wiring board according to any one of 1 to 7. The second metal layer is electrically connected to an output terminal of one polarity of a DC power source;
The first metal layer is integrated on the second metal layer using the conductive adhesive layer,
8. A plurality of element units configured by soldering one heating element on the first metal layer are arranged in an electrically insulated state. The wiring board of any one of Claims. The second metal layer includes a portion where the first metal layer is integrated and an electric wiring portion,
On the wiring part, one or more fourth metal layers constituting another electric wiring part are integrated via an electrically insulating resin layer,
The heating element and the fourth metal layer are connected via an electrical connection means so that the direction of the current flowing through the second metal layer is opposite to the direction of the current flowing through the fourth metal layer. The wiring board according to any one of claims 8 to 10.

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