Heat sink and heat sink integrated insulating circuit board

Abstract

To provide a heat sink that has a copper layer and an aluminum layer, is excellent in bonding reliability between the copper layer and the aluminum layer, capable of suppressing deformation of a member made of aluminum or an aluminum alloy, and stably used.SOLUTION: A heat sink 10 having a top plate portion 11 and a heat radiation fin 18. One surface of the top plate portion 11 is used as a mounting surface on which another member is mounted, and a heat radiating fin 18 is formed on the other surface of the top plate portion 11. The top plate portion 11 has a clad structure in which an aluminum layer 12 made of aluminum or an aluminum alloy and a copper layer 13 made of copper or a copper alloy are solid-phase diffusion bonded. The average crystal grain size of the aluminum layer 12 is in a range of 50 μm or more and less than 500 μm, and the thickness of an Al-Cu intermetallic compound layer formed between the aluminum layer 12 and the copper layer 13 is within a range of more than 10 μm and 40 μm or less.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a heat sink having a top plate portion and heat dissipation fins, and to a heat sink-integrated insulating circuit board having this heat sink. [Background technology]

[0002] In power modules, LED modules, and thermoelectric modules, power semiconductor elements, LED elements, and thermoelectric elements are bonded to an insulating circuit board having a circuit layer made of a conductive material formed on one side of an insulating layer. As the insulating layer, those using ceramics or insulating resin have been proposed.

[0003] Furthermore, in these insulating circuit boards, a heat sink is provided to dissipate heat from the mounted elements. For example, Patent Document 1 proposes a heat sink integrated insulating circuit board in which the heat sink and the circuit layer are insulated by an insulating resin sheet. Furthermore, Patent Document 2 proposes an insulating circuit board with a heat sink, in which an insulating circuit board having metal plates bonded to both sides of a ceramic substrate and a heat sink are bonded to the insulating circuit board.

[0004] The heat sink described above has a structure including a top plate and heat dissipation fins. One surface of the top plate is used as a mounting surface for an insulating circuit board, and the other surface of the top plate is provided with heat dissipation fins. As the heat dissipating fins, fins of various shapes, such as pin fins, comb fins, corrugated fins, etc. have been proposed.

[0005] Here, examples of materials constituting the above-mentioned heat sink include copper or a copper alloy, and aluminum or an aluminum alloy, which have excellent thermal conductivity. Copper members made of copper or a copper alloy have characteristics such as particularly excellent thermal conductivity, high mechanical strength, and high deformation resistance. On the other hand, aluminum members made of aluminum or an aluminum alloy have slightly inferior thermal conductivity compared to copper, but have characteristics such as being lightweight, having low deformation resistance, and being easy to form into complex shapes.

[0006] For this reason, in the above-mentioned heat sinks, copper or a copper alloy and aluminum or an aluminum alloy are selected and used depending on the required performance, and recently, there has been a demand for a structure in which a copper member and an aluminum member are joined together. Here, as a method for joining a copper member and an aluminum member, for example, as described in Patent Documents 3 and 4, a solid-phase diffusion bonding method has been proposed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-204700 [Patent Document 2] JP 2004-022914 A [Patent Document 3] JP 2014-076486 A [Patent Document 4] Republished WO2011 / 155379 Summary of the Invention [Problem to be solved by the invention]

[0008] In Patent Document 3, a copper member and an aluminum member are solid-phase diffusion bonded together, and the average crystal grain size of the aluminum member after bonding is set to 500 μm or more. If the average crystal grain size is coarse in this way, the aluminum member has low deformation resistance and may easily deform during use.

[0009] In addition, in Patent Document 4, the Al-Cu intermetallic compound layer formed between the copper layer and the aluminum layer has a relatively thin average thickness of 0.5 μm to 10 μm. When the Al-Cu intermetallic compound layer is thin, copper and aluminum do not diffuse sufficiently in a solid phase, which may result in reduced bonding reliability.

[0010] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a heat sink which has a copper layer made of copper or a copper alloy and an aluminum layer made of aluminum or an aluminum alloy, which has excellent bonding reliability between the copper layer and the aluminum layer, which can suppress deformation of a member made of aluminum or an aluminum alloy, and which can be used stably, and a heat sink-integrated insulating circuit board which is equipped with this heat sink. [Means for solving the problem]

[0011] In order to solve such problems and achieve the above-mentioned object, the heat sink of the present invention is a heat sink comprising a top plate portion and heat dissipation fins, one surface of the top plate portion being a mounting surface on which another member is placed, and the heat dissipation fins being formed on the other surface of the top plate portion, and the top plate portion having a clad structure in which an aluminum layer made of aluminum or an aluminum alloy and a copper layer made of copper or a copper alloy are solid-phase diffusion bonded, The aluminum layer and the heat dissipation fins are integrally molded, The aluminum layer has an average crystal grain size in the range of 50 μm or more and less than 500 μm, and the thickness of an Al-Cu intermetallic compound layer formed between the aluminum layer and the copper layer is in the range of more than 10 μm and not more than 40 μm.

[0012] According to the heat sink of this configuration, the top plate has a clad structure in which an aluminum layer made of aluminum or an aluminum alloy and a copper layer made of copper or a copper alloy are solid-phase diffusion bonded, so that the heat from other components placed on the mounting surface can be efficiently spread along the plate surface of the top plate by the copper layer, and the heat sink has excellent heat dissipation properties. In addition, the aluminum layer allows the weight of the heat sink to be reduced.

[0013] Furthermore, since the aluminum layer and the copper layer are solid-phase diffusion bonded and the average crystal grain size of the aluminum layer is 50 μm or more and less than 500 μm, the aluminum layer becomes appropriately hard and deformation of the aluminum layer can be suppressed. In addition, since the thickness of the Al-Cu intermetallic compound layer formed between the aluminum layer and the copper layer is within the range of more than 10 μm and not more than 40 μm, copper and aluminum are sufficiently diffused in a solid phase, and the bonding reliability between the copper layer and the aluminum layer is excellent.

[0014] Also, By integrally molding the aluminum layer and the heat dissipation fins using aluminum or an aluminum alloy, which is relatively easy to mold, it is possible to form heat dissipation fins with complex shapes, which makes it possible to further improve the heat dissipation characteristics. Furthermore, since the heat dissipating fins are molded integrally with the aluminum layer, it is possible to prevent the heat dissipating fins from falling off or becoming deformed.

[0015] In the heat sink of the present invention, the aluminum layer preferably has an aluminum purity of 99.5 mass % or less. In this case, since the aluminum purity in the aluminum layer is 99.5 mass% or less and contains a certain amount of impurities, the impurities suppress the growth of crystal grains, thereby reliably suppressing the coarsening of crystal grains in the aluminum layer after bonding.

[0016] The heat sink-integrated insulating circuit board of the present invention is characterized by comprising the above-mentioned heat sink, an insulating layer formed on the mounting surface of the top plate portion of the heat sink, and a circuit layer formed on the surface of the insulating layer opposite the top plate portion. According to the heat sink-integrated insulating circuit board of this configuration, since it is equipped with the above-mentioned heat sink, it is possible to efficiently dissipate heat from the insulating circuit board side and to suppress deformation of the heat sink, thereby enabling stable use. Effect of the Invention

[0017] According to the present invention, it is possible to provide a heat sink which has a copper layer made of copper or a copper alloy and an aluminum layer made of aluminum or an aluminum alloy, which has excellent bonding reliability between the copper layer and the aluminum layer, and which can suppress deformation of a member made of aluminum or an aluminum alloy and can be used stably, and a heat sink-integrated insulating circuit board which is equipped with this heat sink. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic explanatory diagram of a power module including a heat sink and a heat sink-integrated insulating circuit board according to an embodiment of the present invention. [Diagram 2] 1 is an explanatory diagram of a heat sink according to an embodiment of the present invention; [Diagram 3] FIG. 2 is an enlarged explanatory view of a top plate portion of the heat sink according to the embodiment of the present invention. [Figure 4] 4 is a photograph showing the bonding interface between the copper layer and the aluminum layer of the top plate portion shown in FIG. 3. [Diagram 5] FIG. 2 is a flow diagram showing a method for manufacturing a heat sink according to an embodiment of the present invention. [Figure 6] 5A to 5C are explanatory diagrams showing a method for manufacturing a heat sink according to an embodiment of the present invention. [Figure 7] FIG. 2 is a flow diagram showing a method for manufacturing a heat sink-integrated insulating circuit board according to an embodiment of the present invention. [Figure 8]5A to 5C are explanatory diagrams showing a method for manufacturing a heat sink-integrated insulating circuit board according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments are specifically described to better understand the gist of the invention, and do not limit the present invention unless otherwise specified. In addition, the drawings used in the following description may show essential parts in an enlarged scale for the sake of convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of each component may not necessarily be the same as the actual ones.

[0020] FIG. 1 shows a heat sink 10 according to an embodiment of the present invention, a heat sink integrated insulating circuit board 30, and a power module 1 using this heat sink integrated insulating circuit board 30.

[0021] The power module 1 shown in FIG. 1 includes a heat sink integrated insulating circuit board 30, and a semiconductor element 3 joined to one surface (the upper surface in FIG. 1) of the heat sink integrated insulating circuit board 30 via a solder layer 2.

[0022] The heat sink integrated insulating circuit board 30 includes the heat sink 10 of this embodiment, an insulating layer 31 formed on one surface (upper surface in FIG. 1) of a top plate portion 11 of the heat sink 10, and a circuit layer 32 formed on one surface (upper surface in FIG. 1) of the insulating layer 31. The semiconductor element 3 described above is bonded to one surface (upper surface in FIG. 1) of the circuit layer 32.

[0023] The insulating layer 31 prevents electrical connection between the circuit layer 32 and the heat sink 10, and in this embodiment, is made of an insulating resin. In this embodiment, in order to ensure the strength of the insulating layer 31 and to ensure thermal conductivity, it is preferable to use a resin containing a filler of an inorganic material as the resin constituting the insulating layer 31. Here, examples of the filler that can be used include alumina, boron nitride, and aluminum nitride. From the viewpoint of ensuring thermal conductivity in the insulating layer 31, the filler content is preferably 50 mass% or more, and more preferably 70 mass% or more. The thermosetting resin may be an epoxy resin, a polyimide resin, a silicone resin, etc. Here, the silicone resin may contain 70 mass% or more of the above-mentioned filler, and the epoxy resin may contain 80 mass% or more of the above-mentioned filler.

[0024] In order to ensure sufficient insulation in the insulating layer 31, the lower limit of the thickness of the insulating layer 31 is preferably 25 μm or more, and more preferably 50 μm or more. On the other hand, in order to further ensure the heat dissipation properties of the heat sink-integrated insulating circuit board 30, the upper limit of the thickness of the insulating layer 31 is preferably 300 μm or less, and more preferably 200 μm or less.

[0025] 8, the circuit layer 32 is formed by bonding a metal piece 42 made of a metal with excellent conductivity to one surface of the insulating layer 31. The metal piece 42 may be made of copper or a copper alloy, aluminum or an aluminum alloy, or the like. In this embodiment, the metal piece 42 constituting the circuit layer 32 is made by punching out a rolled plate of oxygen-free copper. A circuit pattern is formed on this circuit layer 32, and one surface thereof (the upper surface in FIG. 1) serves as a mounting surface on which a semiconductor element 3 is mounted.

[0026] The heat sink 10 of this embodiment includes a top plate portion 11 and heat dissipating fins 18 protruding from the other surface of the top plate portion 11 (the lower surface in Figs. 1 and 2). The heat dissipation fins 18 may be pin fins, may have a comb-like structure, or may be corrugated fins. In this embodiment, pin fins are used.

[0027] The top plate portion 11 has a clad structure in which an aluminum layer 12 made of aluminum or an aluminum alloy and a copper layer 13 made of copper or a copper alloy are bonded by solid-state diffusion bonding. In this embodiment, the aluminum layer 12 and the heat dissipation fins 18 are integrally formed, and the copper layer 13 is laminated on the aluminum layer 12.

[0028] 3 and 4, at the bonding interface between the aluminum layer 12 and the copper layer 13, an Al-Cu intermetallic compound layer 15 is formed by interdiffusion of Al of the aluminum layer 12 and Cu of the copper layer 13. In FIG. 4, the black portion is the Al-Cu intermetallic compound layer 15. There are a plurality of phases having different composition ratios in the intermetallic compound of Al and Cu, and in this embodiment, the Al-Cu intermetallic compound layer 15 has a structure in which these various phases are laminated.

[0029] In this embodiment, the thickness t of the Al-Cu intermetallic compound layer 15 is set within a range of more than 10 μm and not more than 40 μm. Here, if the thickness t of the Al-Cu intermetallic compound layer 15 is 10 μm or less, the interdiffusion of Al and Cu is insufficient, and the bonding strength between the aluminum layer 12 and the copper layer 13 may be reduced. On the other hand, if the thickness t of the Al-Cu intermetallic compound layer 15 exceeds 40 μm, the bonding interface may become harder than necessary, and cracks may occur near the bonding interface when subjected to a thermal cycle, resulting in reduced bonding reliability. For this reason, in this embodiment, the thickness t of the Al-Cu intermetallic compound layer 15 is set within the range of more than 10 μm and not more than 40 μm.

[0030] In order to further improve the bonding strength between the aluminum layer 12 and the copper layer 13, the thickness t of the Al-Cu intermetallic compound layer 15 is preferably 15 μm or more, and more preferably 20 μm or more. In order to further improve the bonding reliability during thermal cycle loading, the thickness t of the Al-Cu intermetallic compound layer 15 is preferably set to 35 μm or less, and more preferably set to 30 μm or less.

[0031] In this embodiment, the average crystal grain size D1 of the aluminum layer 12 is set within the range of 50 μm or more and less than 500 μm. Here, if the average crystal grain size D1 of the aluminum layer 12 is less than 50 μm, the aluminum layer 12 becomes hard and is unable to relieve thermal stress when subjected to a thermal cycle, which may cause cracks to occur near the bonding interface and reduce bonding reliability. On the other hand, if the average crystal grain size D1 of the aluminum layer 12 exceeds 500 μm, the aluminum layer 12 becomes soft and has low deformation resistance, which may cause it to easily deform. For this reason, in this embodiment, the average crystal grain size D1 of the aluminum layer 12 is set within the range of 50 μm or more and less than 500 μm.

[0032] In order to further improve the bonding reliability during thermal cycle loading, the average crystal grain size D1 of the aluminum layer 12 is preferably 100 μm or more, and more preferably 150 μm or more. In order to further suppress deformation of the aluminum layer 12, the average crystal grain size D1 of the aluminum layer 12 is preferably set to 300 μm or less, and more preferably set to 200 μm or less.

[0033] Here, the aluminum layer 12 is preferably made of aluminum or an aluminum alloy with an aluminum purity of 99.5 mass% or less, and may be made of, for example, A1050, A6063, ADC12, etc. In this embodiment, the aluminum layer 12 and the heat dissipation fins 18 are integrally molded, and therefore the aluminum layer 12 and the heat dissipation fins 18 are made of the same material.

[0034] Furthermore, in this embodiment, the average crystal grain size of the copper layer 13 is not particularly limited, but is preferably within the range of 50 μm or more and 300 μm or less, for example. The copper or copper alloy constituting the copper layer 13 is not particularly limited, and for example, oxygen-free copper, tough pitch copper, etc. can be used.

[0035] Next, a method for manufacturing the heat sink 10 according to the present embodiment will be described with reference to FIGS.

[0036] (Material preparation process S01) First, an aluminum member 22 which will become the aluminum layer 12, and a copper member 23 which will become the copper layer 13 are prepared. It is preferable that the bonding surfaces of the aluminum member 22 and the copper member 23 be finished in advance to a smooth surface by polishing or the like to remove scratches or the like.

[0037] Here, the aluminum member 22 has a structure in which an aluminum plate 22A which becomes the aluminum layer 12 and a fin body 22B which becomes the heat dissipating fin 18 are integrally molded. The aluminum member 22 is preferably made of aluminum or an aluminum alloy having an aluminum purity of 99.5 mass % or less. Moreover, the average crystal grain size of the aluminum member 22 before bonding is preferably within a range of 5 μm to 30 μm.

[0038] (Lamination process S02) Then, the copper member 23 is laminated on the aluminum plate 22A of the aluminum member 22.

[0039] (Joining process S03) Next, the laminated aluminum member 22 and copper member 23 are placed in a vacuum furnace, and pressurized in the lamination direction and heated in a vacuum atmosphere, thereby solid-phase diffusion bonding the aluminum member 22 and the copper member 23 together. At this time, it is preferable that the pressure load in the stacking direction is in the range of 0.3 MPa to 3.5 MPa, the bonding temperature is in the range of 400°C to 545°C, the holding time at the bonding temperature is in the range of 5 minutes to 240 minutes, and the degree of vacuum is 0.1 Pa or less.

[0040] The pressure load is more preferably 0.5 MPa or more, and even more preferably 0.8 MPa or more, and is more preferably 2.0 MPa or less, and even more preferably 1.5 MPa or less. The bonding temperature is more preferably 450° C. or higher, and even more preferably 480° C. or higher. The bonding temperature is more preferably 540° C. or lower, and even more preferably 535° C. or lower.

[0041] The holding time at the bonding temperature is more preferably 10 minutes or more, and even more preferably 15 minutes or more, and is more preferably 180 minutes or less, and even more preferably 120 minutes or less. The degree of vacuum is more preferably 0.05 Pa or less, and even more preferably 0.01 Pa or less.

[0042] Here, in this embodiment, when the average crystal grain size of the aluminum member 22 (aluminum plate 22A) before joining is D0 and the average crystal grain size of the aluminum layer 12 after joining is D1, the change in crystal grains as shown in the following formula is set to 90% or less. Change (%) = (D1-D0) / D1 x 100 In this embodiment, the pressure load, bonding temperature, and holding time in the bonding step S03 are adjusted within the above-mentioned ranges so that the above-mentioned change amount is 90% or less.

[0043] In the joining step S03, diffusion and grain growth occur simultaneously. Therefore, by limiting the amount of change to 90% or less, the diffusion path is stabilized, the diffusion can proceed uniformly, and the thickness of the Al-Cu intermetallic compound layer 15 can be made uniform. The amount of change is more preferably 80% or less, and even more preferably 70% or less.

[0044] Through the above steps, the aluminum member 22 and the copper member 23 are solid-phase diffusion bonded together, and the heat sink 10 of this embodiment can be manufactured.

[0045] Next, a method for manufacturing the heat sink-integrated insulating circuit board 30 according to this embodiment will be described with reference to FIGS.

[0046] (Resin composition disposing step S11) 8, a resin composition 41 containing an inorganic filler, a resin, and a curing agent is disposed on one surface (the upper surface in FIG. 8) of the top plate portion 11 (copper layer 13) of the heat sink 10. In this embodiment, the resin composition 41 is in the form of a sheet.

[0047] (Metal piece placement process S12) Next, on one surface of the resin composition 41 (the upper surface in FIG. 5), a plurality of metal pieces 42 which will become the circuit layer 32 are arranged in a circuit pattern.

[0048] (Pressure and heating step S13) Next, a pressure device is used to pressurize and heat the heat sink 10, the resin composition 41, and the metal piece 42 in the stacking direction, thereby hardening the resin composition 41 to form the insulating layer 31 and bonding the top plate portion 11 of the heat sink 10 to the insulating layer 31, and the insulating layer 31 to the metal piece 42.

[0049] In the pressurizing and heating step S13, the heating temperature is preferably in the range of 120° C. to 350° C., and the holding time at the heating temperature is preferably in the range of 10 minutes to 180 minutes. Also, the pressurizing load in the stacking direction is preferably in the range of 1 MPa to 30 MPa.

[0050] Here, the lower limit of the heating temperature is more preferably 150° C. or more, and even more preferably 170° C. or more. On the other hand, the upper limit of the heating temperature is more preferably 320° C. or less, and even more preferably 300° C. or less. The lower limit of the holding time at the heating temperature is more preferably 30 minutes or more, and even more preferably 60 minutes or more, while the upper limit of the holding time at the heating temperature is more preferably 120 minutes or less, and even more preferably 90 minutes or less. The lower limit of the pressure load in the stacking direction is more preferably 3 MPa or more, and even more preferably 5 MPa or more, while the upper limit of the pressure load in the stacking direction is more preferably 15 MPa or less, and even more preferably 10 MPa or less.

[0051] Through the above-mentioned steps, the heat sink-integrated insulating circuit board 30 according to this embodiment is manufactured.

[0052] According to the heat sink 10 of the present embodiment configured as described above, the top plate 11 has a clad structure in which the aluminum layer 12 made of aluminum or an aluminum alloy and the copper layer 13 made of copper or a copper alloy are solid-phase diffusion bonded, so that the heat from the semiconductor element 3 can be efficiently spread along the plate surface of the top plate 11 by the copper layer 13, and the heat sink 10 has excellent heat dissipation characteristics. In addition, since the aluminum layer 12 is provided, the weight of the heat sink 10 can be reduced.

[0053] Furthermore, since the aluminum layer 12 and the copper layer 13 are solid-phase diffusion bonded and the average crystal grain size D1 of the aluminum layer 12 is 50 μm or more and less than 500 μm, the aluminum layer 12 becomes appropriately hard and deformation of the aluminum layer can be suppressed. In addition, the thickness t of the Al-Cu intermetallic compound layer 15 formed between the aluminum layer 12 and the copper layer 13 is within the range of more than 10 μm and not more than 40 μm, so that copper and aluminum are sufficiently diffused in a solid phase, and the bonding reliability between the copper layer 13 and the aluminum layer 12 is excellent.

[0054] Furthermore, in this embodiment, when the aluminum layer 12 and the heat dissipation fins 18 are integrally molded, the heat dissipation fins 18 can be formed in a complex shape, which can further improve the heat dissipation characteristics. Furthermore, since the heat dissipating fins 18 are molded integrally with the aluminum layer 12, the heat dissipating fins 18 can be prevented from falling off or becoming deformed.

[0055] In this embodiment, when the purity of aluminum in the aluminum layer 12 is 99.5 mass% or less, it contains a certain amount of impurities, which suppress the growth of crystal grains, thereby reliably suppressing the coarsening of crystal grains in the aluminum layer 12 after bonding.

[0056] The heatsink-integrated insulating circuit board 30 of this embodiment comprises the heatsink 10 of this embodiment, an insulating layer 31 formed on the mounting surface of the top plate portion 11 of the heatsink 10, and a circuit layer 32 formed on the surface of the insulating layer 31 opposite the top plate portion 11. Therefore, it is possible to efficiently dissipate heat from the semiconductor element 3 mounted on the circuit layer 32, and to suppress deformation of the heatsink 10, thereby enabling stable use.

[0057] Although the embodiment of the present invention has been described above, the present invention is not limited to this, and can be modified as appropriate without departing from the technical concept of the invention. For example, in the present embodiment, the heat sink has been described as having a pin fin structure, but the present invention is not limited to this, and the heat sink may be one having comb-shaped fins or corrugated fins.

[0058] In addition, in the present embodiment, an example has been described in which an insulating layer is formed on the top plate portion of a heat sink. However, an insulating circuit board with a heat sink may also be configured in which an insulating circuit board having metal plates bonded to both sides of a ceramic substrate is placed on the top plate portion of a heat sink.

[0059] Furthermore, in the present embodiment, a power module is configured by mounting a semiconductor element on the circuit layer, but this is not limited to this. For example, an LED module may be configured by mounting an LED element on the circuit layer, or a thermoelectric module may be configured by mounting a thermoelectric element on the circuit layer. EXAMPLES

[0060] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0061] First, we prepared a copper member and an aluminum member made of the materials shown in Table 1. The copper member was a copper plate measuring 100 mm×100 mm and having a thickness of 1.0 mm. The aluminum member was an aluminum plate measuring 100 mm x 100 mm and 4.0 mm thick, and had cylindrical pin fins (pin diameter 1.5 mm, length 10 mm) integrally molded with the aluminum plate. The number of pin fins was 500.

[0062] The bonding surfaces of the copper member and the aluminum member were polished in advance to a smooth surface, and the copper member and the aluminum member were then laminated together. The laminated copper and aluminum members were placed in a vacuum furnace and pressurized and heated under the conditions shown in Table 1 in an atmosphere with a vacuum degree of 0.05 Pa, thereby solid-phase diffusion bonding the copper and aluminum members.

[0063] The heat sink obtained as described above was evaluated for the average crystal grain size D1 of the aluminum layer, the thickness of the Al-Cu intermetallic compound layer, the presence or absence of deformation of the heat dissipation fins, and the bonding rate after thermal cycle loading as follows. The evaluation results are shown in Table 2.

[0064] (Average grain size of aluminum layer) The cross section of the top plate along the thickness direction was ion-etched using a cross-section polisher (SM-09010 manufactured by JEOL Ltd.) at an ion acceleration voltage of 5 kV, processing time of 14 hours, and protrusion from the shielding plate of 100 μm, and then observed, and the average crystal grain size of the aluminum layer was measured using a scanning electron microscope (SEM). The average crystal grain size was measured in accordance with the cutting method described in JIS H 0501.

[0065] (Thickness of Al-Cu intermetallic compound layer) The cross section of the bonding interface between the aluminum layer and the copper layer was ion etched using a cross-section polisher (SM-09010 manufactured by JEOL Ltd.) at an ion accelerating voltage of 5 kV, a processing time of 14 hours, and a protrusion from the shielding plate of 100 μm. The cross section was then observed, and the thickness of the Al-Cu intermetallic compound layer formed at the bonding interface was measured. The thickness of the Al-Cu intermetallic compound layer was measured by line analysis in the thickness direction of the bonding interface between the aluminum layer and the copper layer using EPMA (JXA-8530F manufactured by JEOL, accelerating voltage: 15 kV, spot diameter: 1 μm or less, magnification: 500 times, interval: 0.3 μm). The region where the Al concentration and Cu concentration were 1 at% or more was regarded as the Al-Cu intermetallic compound layer, and the thickness was measured.

[0066] (Joint rate after thermal cycle loading) Using an Espec Corp. TSB-51 thermal shock tester, the heat sink was subjected to 4,000 thermal cycles of -40°C x 10 minutes ←→ 150°C x 10 minutes in liquid phase (Fluorinert). The bonding rate of the heat sink after the thermal cycle test (bonding rate between the aluminum layer and the copper layer) was evaluated using an ultrasonic inspection device (FineSAT200 manufactured by Hitachi Power Solutions Co., Ltd.) and calculated using the following formula. Here, the initial bonding area is the area to be bonded before bonding. Since peeling is indicated by a white area in the bonded area in the image obtained by binarizing the ultrasonic inspection image, the area of ​​this white area was taken as the peeled area. (Bonding rate)={(Initial bonding area)-(Non-bonding area)} / (Initial bonding area)×100

[0067] (Whether or not the heat sink fins are deformed) The heat sink's heat dissipation fins were set in the water jacket, and cooling water (20°C) was passed through it, with the flow rate adjusted according to the cross-sectional area of ​​the water channel so that the average flow velocity was 1 m / s. After the cooling water was circulated for 10 minutes, the heat dissipation fins were removed from the water jacket and visually inspected for deformation of the heat dissipation fins.

[0068] [Table 1]

[0069] [Table 2]

[0070] In Comparative Example 1, the average crystal grain size of the aluminum layer was 42 μm, and the bonding rate after thermal cycle loading was low at 75%. This is presumably because the aluminum layer became hard and was unable to sufficiently relieve the thermal stress during thermal cycle loading. In Comparative Example 2, the average crystal grain size of the aluminum layer was 515 μm, and deformation of the heat dissipation fin was observed. This is presumably because crystal growth of the aluminum layer and the heat dissipation fin integrally molded with the aluminum layer was promoted during bonding, resulting in a decrease in deformation resistance.

[0071] In Comparative Example 3, the thickness of the Al-Cu intermetallic compound layer was 8 μm, and the bonding rate after thermal cycle loading was 74%. This is presumably because interdiffusion between Al in the aluminum layer and Cu in the copper layer was insufficient. In Comparative Example 4, the thickness of the Al-Cu intermetallic compound layer was 42 μm, and the bonding rate after thermal cycle loading was 78%. It is presumed that this is because the vicinity of the bonding interface became hard, causing cracks during thermal cycle loading.

[0072] In contrast, in Examples 1 to 6 of the present invention, the average crystal grain size of the aluminum layer was within the range of 50 μm or more and less than 500 μm, the thickness of the Al-Cu intermetallic compound layer was within the range of more than 10 μm and 40 μm or less, the bonding rate after thermal cycle loading was 83% or more, and the bonding reliability was excellent. Also, no deformation of the heat sink was observed.

[0073] As a result of the above confirmation experiments, it was confirmed that according to the present invention, it is possible to provide a heat sink that has a copper layer made of copper or a copper alloy and an aluminum layer made of aluminum or an aluminum alloy, has excellent bonding reliability between the copper layer and the aluminum layer, is capable of suppressing deformation of the component made of aluminum or an aluminum alloy, and can be used stably. [Explanation of symbols]

[0074] 10 Heat sink 11 Top plate 12 Aluminum Layer 13 Copper layer 18 Heat dissipation fin 30 Heat sink integrated insulating circuit board 31 Insulating layer 32 circuit layers

Claims

1. A heat sink having a top plate portion and heat dissipation fins, One surface of the top plate portion is a mounting surface on which another member is placed, and the heat dissipation fins are formed on the other surface of the top plate portion, The top plate portion has a clad structure in which an aluminum layer made of aluminum or an aluminum alloy and a copper layer made of copper or a copper alloy are solid-phase diffusion bonded, and the aluminum layer and the heat dissipation fins are integrally molded, The average crystal grain size of the aluminum layer is in the range of 50 μm or more and less than 500 μm, A heat sink, characterized in that a thickness of an Al-Cu intermetallic compound layer formed between the aluminum layer and the copper layer is within a range of more than 10 μm and not more than 40 μm.

2. 2. The heat sink according to claim 1, wherein the purity of aluminum in the aluminum layer is 99.5 mass % or less.

3. A heatsink-integrated insulated circuit board comprising: a heatsink as described in claim 1 or claim 2; an insulating layer formed on the mounting surface of the top plate portion of the heatsink; and a circuit layer formed on the surface of the insulating layer opposite the top plate portion.

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