JP2009043814A - Manufacturing method of heat radiation structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a heat radiation structure which has high reliability of a joint portion and whose manufacturing cost is low and which has satisfactory shape precision. <P>SOLUTION: The heat radiation structure A has a sprayed metal layer 28 deposited on a heat sink 21 by a thermal spraying method (cold spraying method). Thus, the sprayed metal layer 28 is deposited by using the thermal spraying method to form the heat radiation structure A. At this time, processing strain is caused nearby the top surface of the heat sink 21 owing to the thermal spraying and the heat radiation structure A curves such that the top surface side of a plane portion 21a of the heat sink becomes a projection. Then the heat radiation structure A is pressed after or while being heated. Recrytallization progresses and then the processing strain caused in the heat sink 21 owing to the thermal spraying is relaxed to correct deformation of the heat radiation structure A. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a heat dissipation structure having a cooling function against heat generation of a semiconductor chip or the like.

  As a heat dissipation structure for releasing heat generated by a semiconductor element as a power device, a structure including a heat sink made of aluminum or an aluminum alloy is generally employed. The heat sink is often provided with fins and is devised to increase the heat dissipation efficiency. Moreover, what provided the member which consists of copper or a copper alloy in the heat sink which consists of aluminum or an aluminum alloy is known.

For example, in Patent Document 1, a metal layer made of silver is formed on the joint surface of a copper member, and the metal layer and an aluminum heat sink are brazed to form an Al-Ag intermetallic compound. A technique for realizing a high bonding strength is disclosed.
JP 2004-1069 A

  However, in the technique of Patent Document 1, since brazing is performed at a temperature of 500 ° C. or higher, there is a possibility that warping may occur after cooling due to a difference in thermal expansion coefficient between copper and aluminum. Moreover, in order to ensure the reliability of joining, since the metal layer which consists of silver was provided in order to prevent the diffusion reaction of copper and aluminum, there existed a malfunction that manufacturing cost became expensive.

  An object of the present invention is to provide a heat dissipating structure with high reliability of the joint, low manufacturing cost, and small deformation such as warpage.

  In the method for manufacturing a heat dissipation structure of the present invention, a heat sink is formed, a sprayed metal layer is formed on the heat sink, and then the heat sink is placed on the lower mold and heated while being heated with the upper mold. It is a method of pressing a layer.

By this method, it is possible to suppress warpage caused by a difference in thermal expansion coefficient between the thermal spray metal layer formed by the thermal spraying process, which is a process at a relatively low temperature, and the heat sink. Further, since it is not necessary to use an expensive material such as Ag, the manufacturing cost is relatively low.
On the other hand, by using the thermal spraying method, a deformation occurs in which the upper surface side of the thermal spray metal layer is curved in a convex shape. The cause is considered to be that compressive stress remains in the vicinity of the surface of the heat sink due to processing strain due to particle collision during thermal spraying.
Therefore, by pressing between the lower mold and the upper mold while heating the heat dissipation structure, recrystallization of the metal constituting the heat sink proceeds, the residual compressive stress in the heat sink is relaxed, and deformation occurs. Is corrected. Therefore, it is possible to obtain a heat dissipating structure with high reliability of the joint, low manufacturing cost, small deformation from the design shape, that is, good shape accuracy.

  By forming a heat sink having fin portions, a heat sink having a particularly high heat dissipation function can be obtained. In that case, the shape of the heat sink is deformed in the direction opposite to the deformation at the time of thermal spraying from the design shape at least in the cross section orthogonal to the direction in which the fin portion extends, so that the deformation after the formation of the thermal spray metal layer is performed. It can be suppressed to a slight amount, and deformation correction by a press becomes easy.

  The lower mold used for pressing may be any one that supports at least two sides of the heat sink. However, by using a lower mold having comb teeth inserted into the gaps between the fins of the heat sink, the back surface of the flat part of the heat sink is supported by the lower mold even in the gaps of the fin parts when pressed. Therefore, the shape of the entire heat sink can be more accurately approximated to the design shape.

  The heating temperature during pressing is preferably in the range of 350 ° C. to 550 ° C. in order to alleviate the processing strain while avoiding the formation of intermetallic compounds between the heat sink and the sprayed metal layer.

  According to the method for manufacturing a heat dissipation structure of the present invention, it is possible to obtain a heat dissipation structure that is inexpensive and has good shape accuracy while maintaining the reliability of bonding.

(Embodiment 1)
-Structure of heat dissipation structure-
FIG. 1 is a cross-sectional view of a heat dissipation structure A according to the first embodiment. The heat dissipation structure A of the present embodiment includes a heat sink 21 having a flat plate portion 21a and a fin portion 21b, and a sprayed metal layer 28 formed on the flat plate portion 21a. The fin portion 21b is configured to be exposed to cooling water that is a heat exchange medium to enhance heat exchange efficiency.

In the present embodiment, the heat sink 21 is formed by extrusion using aluminum (Al) or an aluminum alloy (Al alloy). However, die casting may be used.
In the present embodiment, the thickness of the flat portion 21a of the heat sink 21 is about 4 mm, the fin length of the fin portion 21b is about 15 mm, and the thickness of the sprayed metal layer 28 is about 1 mm.

  In the present embodiment, the sprayed metal layer 28 is made of copper (Cu) or a copper alloy (Cu alloy), and is formed using a cold spray method. As will be described later, since the sprayed metal layer 28 formed using the cold spray method is formed at a relatively low temperature (several hundred degrees Celsius), there is a difference in thermal expansion coefficient from the heat sink 21 made of Al or Al alloy. Even if it exists, the warpage is relatively small. In addition, it has been confirmed that the film formed using the cold spray method is dense. In the cold spray method, the deposition efficiency of the film is high and the manufacturing cost is low.

  The heat sink 21 is preferably made of Al, Al alloy, Cu or Cu alloy. As will be described later, although the heat sink 21 can be formed by extrusion molding, the manufacturing cost can be reduced. However, these materials can be extrusion molded and have high thermal conductivity. This is a suitable material for the heat sink.

-Manufacturing method of heat dissipation structure-
FIGS. 2A to 2D are perspective views showing a manufacturing process of the heat dissipation structure A in the first embodiment. In the step shown in FIG. 2A, the heat sink continuous body 21x is formed by extrusion molding using Al or an Al alloy. The heat sink continuous body 21x includes a flat plate portion 21a and a fin portion 21b. In place of Al or Al alloy, Cu or Cu alloy having higher thermal conductivity may be used. However, using Al or Al alloy has an advantage that fin portions 21b having a small pitch can be formed. .

  Next, in the step shown in FIG. 2B, a sprayed metal layer 28 made of Cu or a Cu alloy is formed on the heat sink continuum 21x using a cold spray method. FIG. 4 is a sectional view for explaining the outline of the cold spray method. The cold spray device 60 includes a hopper 61 into which particles are introduced from above, a heater 62 that heats compressed air, a gun 63 for spraying particles, and pipes 64 and 65. And the heat sink continuous body 21x is installed in the position about 5-30 mm away from the gun 63. FIG. Instead of compressed air, compressed gas such as helium or nitrogen may be used.

  When Cu or Cu alloy particles (particle size of 10 to 40 μm) as a coating material is put into the hopper 61, it is sent to the gun 63 by compressed air sent from the pipe 64. On the other hand, the compressed air sent from the pipe 65 is heated to 300 to 500 ° C. by the heater 62 and sent to the gun 63. Then, in a state where the heated compressed air and the particles are mixed with each other by the gun 63, the jet is injected in a supersonic flow. The particles collide with the heat sink continuum 21x at a high speed of 500 m / s or more, and the particles are plastically deformed and deposited by the kinetic energy of the particles, so that the sprayed metal layer 28 is formed.

  At this time, as shown in FIG. 2B, a compressive stress remains in the surface region of the flat portion 21a of the heat sink continuum 21x adjacent to the sprayed metal layer 28 due to processing strain due to particle collision. Therefore, the heat sink continuum 21x and the sprayed metal layer 28 are warped so that the sprayed metal layer 28 is convex. Next, although not shown, the heat sink continuous body 21x is cut and separated into individual heat dissipation structures A composed of the heat sink 21 and the sprayed metal layer 28.

  Next, in the step shown in FIG. 2C, the heat dissipation structure A is placed on the lower die 30a of the press die. In the present embodiment, the lower mold 30a has a shape that supports only both end portions of the flat surface portion 21a excluding the fin portion 21b on the upper surface of the heat sink 21, but, as shown by a broken line, in the gap between the fin portions 21b. You may have the comb-tooth part inserted.

  Next, in the step shown in FIG. 2D, after the heat dissipation structure A is heated, the upper mold 30b is gradually lowered, and the heat dissipation structure A is pressed by the lower mold 30a and the upper mold 30b. To do. Or you may press, heating. In any case, it is preferable not to return the upper mold 30b to the upper position immediately after pressing, but to maintain the pressed state after the heat dissipation structure A is cooled to room temperature for a certain time. This is because if the press is stopped in a high temperature state, warpage due to the difference in thermal expansion coefficient between the sprayed metal layer 28 and the heat sink 21 may occur. The warp of the heat dissipation structure A is corrected by recovering the processing strain generated during the formation of the sprayed metal layer 28 by any of the above treatments. When the lower mold 30 a includes a comb tooth portion indicated by a broken line, the tip of the comb tooth portion supports the back surface of the flat portion 21 a of the heat sink 21.

  According to the manufacturing method of the heat dissipation structure A of the present embodiment, the sprayed metal layer can be formed at a relatively low temperature by adopting a spraying method such as a cold spray method in the step of forming the sprayed metal layer 28. . At that time, although compressed air heated to 300 to 400 ° C. by the heater 62 is used, it is rapidly cooled by the expansion of the air. Therefore, when it collides with the heat sink continuum 21x, it becomes a low temperature of room temperature to 100 ° C. Because. Therefore, it is possible to suppress warping caused by the difference in thermal expansion coefficient between the heat sink 21 and the sprayed metal layer 28 after processing. Moreover, since the thermal spray metal layer 28 is formed on the heat sink continuous body 21x including a large number of heat sinks 21, the manufacturing process can be simplified and the manufacturing cost can be reduced.

  On the other hand, in the heat dissipation structure A in which the sprayed metal layer 28 is formed by such a spraying method, the upper surface side of the sprayed metal layer 28 is deformed to be convex. The cause is considered to be that compressive stress remains in the vicinity of the surface of the heat sink 21 due to processing strain due to particle collision during thermal spraying.

  Therefore, after the heat dissipation structure A is heated, it is pressed between the lower mold 30a and the upper mold 30b, or the heat dissipation structure A is pressed while being heated, thereby recrystallizing Al constituting the heat sink 21. To reduce the processing strain in the heat sink 21 and correct the deformation. Therefore, it is possible to obtain a heat dissipating structure with high reliability of the joint, low manufacturing cost, small deformation from the design shape, that is, good shape accuracy.

  The pressure applied between the lower mold 30a and the upper mold 30b in the pressing step may be 1 Pa to 5 Pa. Moreover, it is preferable that heating temperature is the range of 350 to 550 degreeC. The heating temperature will be described below.

  In that case, the higher the heating temperature and the longer the heating time, the easier it is to reduce the processing strain and correct the warpage. However, when an intermetallic compound is generated in the interface region between the heat sink 21 and the sprayed metal layer 28 by the reaction between Al constituting the heat sink 21 and Cu constituting the sprayed metal layer 28, the strength of the interface region becomes weak. The sprayed metal layer 28 may be partially or entirely peeled off. Then, the heat processing conditions for suppressing the production | generation of an intermetallic compound are demonstrated.

  FIG. 5 is a graph showing the recrystallization temperature when various elements are added to 99.99% pure Al (99.99% Al). The heat treatment time in the data in the figure is 30 minutes. As shown in the figure, the recrystallization temperature of 99.99% Al is 350 ° C., and when other elements are added, even the highest recrystallization temperature is less than 550 ° C. Therefore, if the heat treatment temperature is in the range of 350 ° C. to 550 ° C., recrystallization in the heat sink 21 can be advanced to reduce the processing strain. The holding time varies depending on the heating temperature. If the temperature is low, it is necessary to hold the heating state for a long time. The higher the temperature is, the shorter the holding time is. For example, by holding at 350 ° C. for about 1 hour, the processing distortion of the heat sink 21 can be relaxed and the warpage can be corrected.

In general, when the diffusion coefficient is D and the diffusion distance is L, the following equations (1) and (2)
D = D0 · exp (−Q / RT) (1)
L = √ (D · t) (2)
The following relational expression holds. Where D0 is a constant part of the diffusion coefficient and is a frequency factor (m ² / sec) specific to each element, Q is the activation energy (kJ / mol) of the intermetallic compound, and t is heat treatment. Time, R = 8.315 (J / mol · K).
From the formulas (1) and (2), the following formula (3)
L = √ {D0 · exp (−Q / RT) · t} (3)
Therefore, if the values of the constants D0 and Q are known, the diffusion distance of Cu and Al can be obtained from the equation (3).

FIG. 6 is a table showing data relating to diffusion of Cu and Al. For example, when the heat treatment temperature is 350 ° C. (623 K) and the heat treatment time is 1 hour (3600 sec), the diffusion distance L1 of Al in Cu is 5.4 × 10 ⁻⁹ from the data of the formula (3) and FIG. m, and the diffusion distance L2 of Cu in Al is 9.6 × 10 ⁻⁷ m. Further, when the heat treatment temperature is 550 ° C. (823 K) and the heat treatment time is 5 seconds, the diffusion distance L1 of Al in Cu is 1.1 × 10 ⁻⁸ m from the data of the formula (3) and FIG. The diffusion distance L2 of Cu inside is 8.7 × 10 ⁻⁷ m. The diffusion distances L1 and L2 are both 1 μm (1 × 10 ⁻⁶ m) or less, and an intermetallic compound hardly occurs under these conditions. Although an appropriate heat treatment time varies depending on the heat treatment temperature, the above formula (3) can be determined together with the data shown in FIGS.

(Modification)
In the above embodiment, the cold spray method is used as the thermal spraying method, but other thermal spraying methods can also be used.
FIG. 7 is a cross-sectional view for explaining the outline of the HVAF (High Velocity Aero Fuel) method. The HVAF device 60B includes a hopper 67 that mixes material (particles) input from the raw material supply pipe 68 with compressed air, a heater 62 that heats compressed air and combustible gas, a gun 63 for spraying particles, and a compression Pipes 64 and 65 for supplying air and a gas pipe 66 for supplying a combustible gas (such as propane gas) are provided. A substrate (such as a heat sink) is installed at a position about 5 to 30 mm away from the gun 63.

  When a particle group (particle size: 10 to 40 μm) of material (Cu) is introduced into the hopper 67 from the raw material supply pipe 68, it is mixed with the compressed air in the hopper 67 and then compressed air fed from the pipe 64. Sent to gun 63. On the other hand, the compressed air and combustible gas sent from the pipe 65 and the gas pipe 66 are accelerated by the ignition plug 69 and sent to the gun 63. Then, in a state where combustion gas, compressed air, and particle groups are mixed with each other by the gun 63, the fuel is injected together with the frame in supersonic flow. The particles collide with the substrate at approximately the same temperature (300 to 500 ° C.) and higher speed (600 to 800 m / s) as in the cold spray method, and the particles are entangled by plastic deformation due to the kinetic energy of the particles. Are bonded together to form the sprayed metal layer 28. The particle size of the particles is 10 to 40 μm.

  Further, when the HVOF (High Velocity Oxigen Fuel) method is used, an apparatus as shown in FIG. 6 is used except that oxygen is supplied from the supply pipes 64 and 65. In that case, a frame speed of 2000 m / s or more and a particle speed of 750 m / s are achieved.

  FIG. 8 is a sectional view for explaining the outline of the AD (Aerosol Deposition) method. A work holder 73, a substrate, a metal mask 75, and a nozzle 76 are arranged in a film forming chamber 71 provided with a vacuum pump VP. In addition, a particle group of material (Cu) is supplied to the aerosolization chamber 78 from the raw material supply pipe 79 and is sent into the aerosolization chamber 78. The particles are carried on a gas flow supplied from a compressed gas cylinder such as air, He, Ar, nitrogen, etc., are transported from the connecting pipe 77 to the nozzle 76, and are ejected at high speed. Then, a sprayed metal layer 28 is deposited on the substrate.

(Embodiment 2)
3A to 3D are perspective views showing a manufacturing process of the heat dissipation structure A in the second embodiment. In the step shown in FIG. 3A, the heat sink continuous body 21x is formed by extrusion molding using Al or an Al alloy. At this time, the heat sink continuous body 21x has the flat plate portion 21a and the fin portion 21b. However, in the cross section orthogonal to the longitudinal direction, which is the direction in which the fin portion 21b extends, the sprayed metal layer 28 is formed from the design shape. It is deformed in the opposite direction to the deformation at the time. That is, it is curved so that the upper surface of the flat portion 21a is on the concave side. However, since it is extrusion molding, it is not deformed in the longitudinal direction. When the heat sink 21 is formed by die casting, it can be curved so that the upper surface of the flat portion 21a is concave on a cross section parallel to the longitudinal direction.

  Next, in the step shown in FIG. 3B, the sprayed metal layer 28 made of Cu or a Cu alloy is formed on the heat sink continuum 21x using the cold spray method as in the first embodiment.

At this time, as shown in FIG. 3B, a compressive stress remains in the surface region of the flat portion 21a of the heat sink continuum 21x adjacent to the sprayed metal layer 28 due to processing strain caused by particle collision. Therefore, in the cross section orthogonal to the direction in which the fin portion 21b extends, the flat portion 21a is substantially planar, and the fin portion 21b extends in a substantially vertical direction.
On the other hand, in the direction parallel to the cross section in which the fin portion 21b extends, the heat sink continuous body 21x and the sprayed metal layer 28 are warped so that the sprayed metal layer 28 is located on the convex side. However, since the bending strength of the heat sink 21 is high in the direction in which the fin portion 21B extends, the deformation is negligible.
Next, although not shown, the heat sink continuous body 21x is cut and separated into individual heat dissipation structures A composed of the heat sink 21 and the sprayed metal layer 28.

  Next, in the step shown in FIG. 3C, the heat dissipation structure A is placed on the lower die 30a of the press die. In the present embodiment, the lower mold 30a is provided with a comb tooth portion 31 to be inserted into the gap between the fin portions 21b. And, in the cross section orthogonal to the longitudinal direction (direction in which the fin portion 21b extends), since each fin portion 21b extends in a substantially vertical direction when the heat dissipation structure A is placed on the lower mold 30a, Compared with the first embodiment (see the broken lines in FIGS. 2C and 2D), the thickness of the comb teeth 31 can be made sufficiently large. Therefore, the press pressure can be increased sufficiently to correct the deformation more reliably.

  Next, in the step shown in FIG. 3D, as in the first embodiment, after the heat dissipation structure A is heated, the heat dissipation structure A is pressed by the lower mold 30a and the upper mold 30b. Press while heating. In the present embodiment, in this step, the thick comb tooth portion 31 of the lower mold 30b is inserted into the gap between the fin portions 21b and is in contact with the back surface of the flat portion 21a. Can be high.

  According to the present embodiment, in addition to the effect of the first embodiment, when the heat sink 21 is molded, the design shape is deformed in the direction opposite to the deformation of the heat sink caused by thermal spraying. The amount of correction of the shape of the heat dissipation structure A is small. In particular, the thickness of the comb teeth 31 of the lower mold 30b can be set large, and the heat sink 21 having the fin portions 21b with a fine pitch can be used for the heat dissipation structure A having a designed shape with the comb teeth 31. Can be formed.

  In the second embodiment, extrusion molding is used when the heat sink continuous body 21x is formed. However, when die casting is used, a cross section orthogonal to the longitudinal direction (direction in which the fin portion 21b extends) and a parallel section are used. Both the cross sections can be deformed in the direction opposite to the deformation generated in the heat sink 21 by thermal spraying from the design shape. Therefore, when the heat dissipating structure A is placed on the lower mold 30a, the tips of the comb teeth 31 of the lower mold 30a can be substantially in contact with the back surface of the flat portion 21a.

(Embodiment 3)
-Power module structure-
FIG. 9 is a cross-sectional view of the power module set according to the third embodiment. In the figure, the illustration of the wiring structure is omitted. The power module set of the present embodiment is configured by mounting a plurality of power modules 10 on a radiator 50 (only one power module 10 is shown in the figure). The radiator 50 includes a top plate 50a and a container 50b joined to the top plate 50a. The top plate 50a is provided with a number of rectangular through holes for incorporating the power module 10 therein. The top plate 50a and the container 50b constituting the radiator 50 are made of aluminum or an aluminum alloy, and can be assembled by die casting, extrusion, forging, casting, machining, or the like.

  In the present embodiment, the radiator 50 is formed by individually forming the top plate 50a and the container 50b and then joining the two. However, the top plate and the container may be integrally formed. In that case, the radiator can be formed, for example, by die casting using an integral type.

  In the power module set of the present embodiment, cooling water as a heat exchange medium flows in a direction orthogonal to the paper surface in the space 51 between the top plate 50a and the container 50b of the radiator 50. The power module 10 is screwed to the top plate 50 a by bolts 54 while being kept airtight by the O-ring 25.

  The power module 10 includes a semiconductor chip 11 in which a semiconductor element such as an IGBT is formed in addition to the heat dissipation structure A including the heat sink 21 and the sprayed metal layer 28 having the same configuration as that of the first embodiment, and a semiconductor Metal wiring 23 for electrically connecting a semiconductor element in chip 11 and an external member, solder layer 14 including Pb-free solder for joining metal wiring 23 and semiconductor chip 11, and metal wiring 23 and thermal spraying An insulating resin layer 26 interposed between the metal layer 28 is provided. Although not shown, an upper surface electrode and a back surface electrode connected to an active region of a semiconductor element such as an IGBT are provided on the upper surface and the lower surface of the semiconductor chip 11, respectively. The back electrode of the semiconductor chip 11 is joined to the metal wiring 23 in a conductive state by the solder layer 14.

  A module resin frame 53 surrounding the semiconductor chip 11 and the like is provided on the top plate 50 a of the radiator 50, and the module resin frame 53 is fixed to the top plate 50 a by bolts 54. An electrode terminal layer 56 (bus bar) is provided on the inner and outer surfaces of the module resin frame 53 by integral molding. The electrode terminal layer 56 and the metal wiring 23 are connected by the high power wiring 18, and the electrode terminal layer 56 and a part of the upper surface electrode 12 of the semiconductor chip 11 are connected by the signal wiring 17. As a result, the power module 10 and the external device can be electrically connected. Further, a gel layer 40 made of silicon gel is provided on the inner side of the module resin frame 53, and the semiconductor chip 11, the signal wiring 17, the high power wiring 18, the metal wiring 23, the solder on the upper surface side of the heat sink 21. Members such as the layer 14 and the insulating resin layer 26 are embedded in the gel layer 40.

  The power module 10 according to the present embodiment includes the solder layer 14 made of the Pb-free solder and the insulating resin layer 26. In general, Pb-free solder includes the following. For example, Sn (liquid phase point 232 ° C.), Sn-3.5% Ag (liquid phase point 221 ° C.), Sn-3.0% Ag (liquid phase point 222 ° C.), Sn-3.5% Ag−0.55% Cu (liquid phase point) 220 ° C.), Sn-3.0% Ag-0.5% Cu (liquid phase point 220 ° C.), Sn-1.5% Ag-0.85% Cu-2.0 Bi (liquid phase point 223 ° C.), Sn-2.5% Ag-0.5% Cu -1.0Bi (liquid phase point 219 ° C), Sn-5.8Bi (liquid phase point 138 ° C), Sn-0.55% Cu (liquid phase point 226 ° C), Sn-0.55% Cu-others (liquid phase point 226 ° C) , Sn-0.55% Cu-0.3% Ag (liquid phase point 226 ° C), Sn-5.0% Cu (liquid phase point 358 ° C), Sn-3.0% Cu-0.3% Ag (liquid phase point 312 ° C), Sn- 3.5% Ag-0.5% Bi-3.0In (liquid phase point 216 ° C), Sn-3.5% Ag-0.5% Bi-4.0In (liquid phase point 211 ° C), Sn-3.5% Ag-0.5% Bi-8.0In (Liquid phase point 208 ° C), Sn-8.0% Zn 3.0% Bi (liquidus point 197 ° C.), and the like. In this embodiment, a low melting point Pb-free solder having a liquidus point of 300 ° C. or lower, for example, Sn-3.0% Ag-0.5% Cu (liquidus point 220 ° C.) is used. It is not a thing. However, high melting point Pb-free solder such as Sn-5.0% Cu (liquid phase point 358 ° C), Sn-3.0% Cu-0.3% Ag (liquid phase point 312 ° C) (liquid phase point exceeding 300 ° C) Shall be excluded.

  In the present embodiment, an epoxy resin containing a metal or ceramic filler is used for the insulating resin layer 26. Although the usable temperature of the epoxy resin varies depending on the type, it is easy to select a temperature exceeding 300 ° C. In this embodiment, a temperature higher than the liquid phase point of Pb-free solder is used. Therefore, it becomes possible to perform a Pb-free solder reflow process after the insulating resin layer 26 is formed in the power module assembly process described later. For example, an epoxy resin filled with alumina, silica, aluminum, aluminum nitride, or the like can be used, and the thermal conductivity is preferably 1.0 (W / m · K) or more, and 5.0 ( W / m · K) or more is more preferable.

  In the present embodiment, the surface of the sprayed metal layer 28 that is the base of the insulating resin layer 26 is in a state of being sprayed and is not polished. In the thermal sprayed state, the surface is rough, which is advantageous in that the adhesive force of the adhesive is higher than that of the polished surface, for example, the contact area with the insulating resin layer 26 is increased.

  The thickness of the insulating resin layer 26 is preferably 0.4 mm or less, and more preferably 0.2 mm or less. The thermal resistance of the insulating resin layer 26 is determined depending on the thermal conductivity and thickness, but the thermal resistance decreases as the thickness decreases. Therefore, when the thickness is 0.4 mm or less, the heat dissipation function is enhanced.

  According to the present embodiment, the metal wiring 23 is connected to the sprayed metal layer 28 of the heat dissipation structure A with the insulating resin layer 26 interposed therebetween, so that the manufacturing cost can be reduced by reducing the number of components. it can. In addition, since the surface of the sprayed metal layer 28 is left sprayed, the bonding strength between the sprayed metal layer 28 and the metal wiring 23 of the heat dissipation structure A by the insulating resin layer 26 is improved, and the reliability of the joint portion is increased. Can be kept high.

  In addition, since one solder layer 14 and an insulating resin layer 26 made of a resin adhesive are used, a low melting point Pb-free solder and a high melting point are provided depending on the process before and after the process, as in the case of providing two solder layers. There is no need to use a Pb-free solder, and only a low-melting point Pb-free solder is required. Currently, Pb-free solder with relatively high Cu composition ratio (for example, Sn-5.0% Cu, Sn-3.0% Cu-0.3% Ag with a lamination point of 300 ° C. or higher) has been developed as Pb-free solder. It is difficult to obtain a high melting point Pb-free solder having excellent connection reliability. On the other hand, as the low melting point Pb-free solder, for example, a solder having high connection reliability such as Sn-3.0% Ag-0.5% Cu (JEITA recommended alloy) having a liquidus point of 220 ° C. has been obtained. Moreover, as the resin adhesive, an epoxy resin having a usable temperature exceeding 300 ° C. can easily be obtained that can withstand a higher temperature than the liquid phase point of the low melting point Pb-free solder. Therefore, according to the present embodiment, the solder layer 14 can be made Pb-free and Pb-free can be achieved while ensuring connection reliability. The heating time in the reflow process is about 5 minutes.

  That is, when two solder layers are used, high melting point solder (Sn-90% Pb) having a liquidus point of 300 ° C. to 330 ° C. is used for the solder layer to be soldered first, and solder to be soldered later. For the layer, low melting point solder (Sn-50% Pb) having a liquidus point of about 216 ° C. is used. That is, high melting point solder is used in the previous soldering process, and low melting point solder is used in the subsequent soldering process so that the solder layer formed in the previous process does not melt in the reflow furnace.

  On the other hand, it is being obliged to use so-called Pb-free (lead-free) parts that do not use Pb (lead) as various products due to environmental problems, but low melting point solder (Sn-50% Pb), for example, (Sn It is possible to replace with low melting point Pb-free solder such as -3.0% Ag-0.5% Cu), but it is possible to replace with conventional high melting point solder (Sn-90% Pb). It is difficult to use high melting point Pb-free solder.

  On the other hand, as in the present embodiment, the insulating resin layer 26 is used for the connection between the sprayed metal layer 28 and the metal wiring 23 (wiring member), so that the solder layer is only bonded to the semiconductor chip 11 and the metal wiring 23. 14 can be used. Therefore, the solder layer 14 can be made Pb-free while using Pb-free solder having a low melting point while ensuring connection reliability.

  In the present embodiment, Al or Al alloy is used as the material of the heat sink 21, but the material is not limited to this. For example, Cu or Cu alloy can be extruded, and the thermal conductivity is higher than that of Al or Al alloy. In addition, a composite material such as Al—SiC, Cu—W, or Cu—Mo may be used unless extrusion molding is performed.

  In the present embodiment, Cu or Cu alloy is used as the material of the metal wiring 23, but the material is not limited to this. For example, a composite material such as Al, Al alloy, Al—SiC, Cu—W, or Cu—Mo may be used.

  In the present embodiment, Cu or Cu alloy is used as the material of the sprayed metal layer 28. However, by setting the thickness to 0.5 mm or more (about 1 mm in the present embodiment), A so-called heat spreader function that expands the heat dissipation path in the horizontal direction can be enhanced. Further, the thermal spraying metal layer 28 is subjected to thermal stress due to a difference in thermal expansion coefficient from the heat sink 21, the insulating resin layer 26, the metal wiring 23, and the like. Further, when the sprayed metal layer 28 is formed, residual compressive strain is generated in the heat sink 21 due to the impact of the ultra-high velocity flow of particles, and stress is also applied to the sprayed metal layer 28 by this residual compressive strain. Therefore, by setting the thickness of the sprayed metal layer 28 to 0.5 mm or more, strength that can withstand various stresses is ensured.

  Further, the heat sink 21 is made of Al or an Al alloy, the sprayed metal layer 28 is made of Cu or a Cu alloy, and the metal wiring 23 is made of Cu or a Cu alloy. be able to. First, when the heat sink 21 is made of Al or an Al alloy, the fine pitch fin portions 21b can be easily formed by extrusion molding, and the heat dissipation function can be further enhanced.

  Further, by forming the sprayed metal layer 28 from Cu or Cu alloy, the above-described heat spreader function can be exhibited, and the metal wiring 23 and the sprayed metal layer 28 also made of Cu or Cu alloy form the insulating resin layer 26. Since the structure is sandwiched, there is an advantage that almost no thermal stress due to the difference in thermal expansion coefficient is applied to the resin insulating layer 26 having a bonding function lower than that of brazing or soldering. That is, it is an advantageous structure for realizing Pb-free by using only low-melting-point Pb-free solder.

(Other embodiments)
The semiconductor element disposed in the power module of the present invention may be a power device using a wide band gap semiconductor (SiC, GaN, etc.) or a power device using Si.

  In the third embodiment, the IGBT is formed on the semiconductor chip 11, but a semiconductor chip on which a MOSFET, a diode, a JFET, or the like is formed may be used.

  In the third embodiment, a structure in which a large number of power modules 10 are attached to the top plate 50a is employed. However, a large number of semiconductor chips may be mounted on a single heat sink member 24 that also serves as the top plate.

  The heat exchange medium for exchanging heat with the heat sink 21 is preferably a liquid such as fluorinate or water in consideration of cooling ability and cost. However, it may be a gas such as helium, argon, nitrogen or air.

  In Embodiment 3 described above, the insulating resin layer 26 is made of an epoxy resin that is a thermosetting resin, but may be made of a thermoplastic resin such as PPS. In that case, even when the metal wiring 23 is placed on the insulating resin layer 26, it is easy to remove the bubbles, so that the adhesive layer only needs to be applied once and the manufacturing cost becomes lower.

  The structure of the embodiment of the present invention disclosed above is merely an example, and the scope of the present invention is not limited to the scope of these descriptions. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  The heat dissipation structure of the present invention can be used for various devices as a power module on which MOSFET, IGBT, diode, JFET and the like are mounted.

3 is a cross-sectional view of the heat dissipation structure according to Embodiment 1. FIG. (A)-(d) is a perspective view which shows the manufacturing process of the thermal radiation structure in Embodiment 1. FIG. (A)-(d) is a perspective view which shows the manufacturing process of the thermal radiation structure in Embodiment 2. FIG. It is sectional drawing explaining the outline of the cold spray method. It is a graph which shows the recrystallization temperature when various elements are added to 99.99% Al. It is a figure which shows the data regarding the spreading | diffusion of Cu and Al by a table | surface. It is sectional drawing explaining the outline of HVAF method. It is sectional drawing explaining the outline of AD method. It is sectional drawing of the power module set in Embodiment 3. FIG.

Explanation of symbols

A Heat dissipation structure 10 Power module 11 Semiconductor chip 14 Solder layer 17 Signal wiring 18 High power wiring 21 Heat sink 21a Flat plate portion 21b Fin portion 21x Heat sink continuous body 23 Metal wiring 25 O-ring 26 Insulating resin layer 28 Thermal spray metal layer 30a Lower metal Mold 30b Upper mold 31 Comb tooth portion 40 Gel layer 50 Radiator 50a Top plate 50b Container 51 Space 53 Module resin frame 56 Electrode terminal layer

Claims (5)

Forming a heat sink having at least a planar portion (a);
Forming a sprayed metal layer containing at least one metal on the flat portion of the heat sink;
A step (c) of placing the heat sink on a lower mold after the step (b);
A step (d) of pressing the thermally sprayed metal layer and the heat sink with the upper mold while the heat sink is placed on the lower mold; and
The manufacturing method of the thermal radiation structure containing this. In the manufacturing method of the heat dissipation structure according to claim 1,
In the step (a), a heat radiating structure manufacturing method, wherein a heat sink having a plurality of fins protruding from the planar portion is formed. In the manufacturing method of the heat dissipation structure according to claim 2,
In the step (a), the shape of the heat sink is deformed from a design shape in a direction opposite to the deformation in the step (b) at least in a cross section orthogonal to the direction in which the fin portion extends. Manufacturing method. In the manufacturing method of the thermal radiation structure of Claim 2 or 3,
In the step (c), a method for manufacturing a heat dissipation structure using a lower mold having comb teeth inserted into the gaps between the fins of the heat sink. In the manufacturing method of the thermal radiation structure in any one of Claims 1-4,
The said process (d) is a manufacturing method of the thermal radiation structure performed at the temperature of 350 to 550 degreeC.

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