JP2013229456A - Heat sink and heat sink integrated semiconductor module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To securely place fins in surface contact with a fin base thereby stabilizing heat radiation performance of a heat sink.SOLUTION: A heat sink includes: a fin base having caulking parts, each of which is disposed between facing protruding wall parts and has a two pronged tip, and multiple fins, each of which is disposed between the caulking part of the fin base and the protruding wall part, is caulked to be fixed thereto, and is harder than the fin base. In each protruding wall part of the fin base, both side surfaces may be inclined and a root part may be wider than an upper end part.

Description

  The present application relates to a heat sink used for cooling electronic devices and the like, and more particularly, to a heat sink composed of a fin and a fin base.

  The heat sink is attached to an electronic device having a heat generating component such as an LSI (Large Scale Integration) or a diode, and dissipates heat generated from the heat generating component to the outside as a heat radiator by heat conduction and heat transfer. In a general heat sink integrated semiconductor module, a bottom surface of a semiconductor module finished to a flat surface and a heat sink finished to a flat surface are thermally connected by thermally conductive grease to secure a heat radiation path. Although heat conductive grease exhibits good heat transfer performance under normal use conditions, it is known that the thermal resistance of the heat conductive grease portion is deteriorated by the generation of a bleed that separates the filler and the resin. Further, the warpage of the bottom surface of the semiconductor module due to the temperature change of the semiconductor module changes, so that the distance between the bottom surface of the semiconductor module and the bottom surface of the heat sink changes, and a phenomenon such as dryout that extrudes grease occurs. Dryout increases contact thermal resistance.

  In contrast, semiconductor modules that do not use thermally conductive grease have also been developed. In the fin base of the caulking heat sink, the fin is inserted into a fin insertion groove provided on a plane. The caulking portion is deformed by caulking the fin, and the fin base and the fin are integrated (for example, refer to FIGS. 1 and 2 of Patent Document 1). There is also known a fin-integrated semiconductor module in which a corrugated heat sink is integrated by fitting the corrugated heat sink into the irregularities of the base of the bottom surface of the resin-encapsulated semiconductor module (for example, FIG. 1 of Patent Document 2). The corrugated fin is produced by bending. If there are many gaps between the fins and the irregularities on the bottom surface of the semiconductor module, the contact thermal resistance increases.

Japanese Patent Laid-Open No. 7-161882 JP 2009-33065 A

  In the caulking heat sink, the fin base and the fin, which are separate members, are integrated by caulking. If the surface contact of the contact portion is not ensured stably, the heat dissipation performance of the caulking heat sink after caulking will vary. This invention was made in order to solve such a subject, and it aims at making the surface contact of a fin and a fin base reliably, and stabilizing the heat dissipation performance of a heat sink.

  The heat sink according to the present application is disposed between the opposed protruding wall portions and has a fin base having a crimped portion with a bifurcated tip, and is disposed between the crimped portion and the protruding wall portion of the fin base. It has a plurality of fins that are fixed and harder than the fin base.

This invention makes the hardness of the fin higher than the hardness of the fin base. Since the caulking portion of the fin base to be plastically processed by caulking is softer than the fin, the caulking portion is in close contact with the fin having high smoothness, and the fin is in close contact with the protruding wall portion of the fin base. For this reason, the heat dissipation performance of the caulking heat sink after integration is stabilized.

It is a section lineblock diagram showing a heat sink integrated type semiconductor module. FIG. 4 is a cross-sectional view (a) showing the fin base before caulking, and a cross-sectional view (b) showing the integrated fin base and fin after caulking, in connection with the first embodiment. Figure (a) showing how a load is applied to the projecting wall of the fin base in a vertically slanted downward direction through the caulking portion during caulking, and a cross section showing a sample in which the fin is fixed in parallel after caulking It is sectional drawing (c) which shows the sample in which the location where the gap | interval of the fin was wide and the narrow location produced after caulking was performed. A sectional view (a) showing the fin base before caulking, a diagram (b) showing a phenomenon when the fin is inserted into the fin base, and a diagram showing a phenomenon of caulking with a press tool in connection with the second embodiment. c) It is sectional drawing (d) which shows the integrated fin base and fin after caulking. FIG. 6 is a cross-sectional view (a) showing a fin base before caulking, and a cross-sectional view (b) showing an integrated fin base and fin after caulking, in connection with the third embodiment. It is sectional drawing which concerns on Embodiment 4 and shows the fin base before a crimping process. FIG. 4A is a diagram showing a cross-sectional photograph showing a fin base before caulking, and a diagram showing a cross-sectional photograph showing an integrated fin base and fin after caulking. FIG. 7A is a diagram showing a cross-sectional photograph showing a fin base before caulking, and a diagram showing a cross-sectional photograph showing an integrated fin base and fin after caulking.

  Embodiments of a semiconductor module and a manufacturing method thereof according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably.

Embodiment 1 FIG.
FIG. 1 shows a heat sink integrated semiconductor module according to the present invention. The semiconductor module 100 includes a control board 11, a lead frame 12, a mold resin 13, a semiconductor chip 14, an insulating sheet 15, a heat sink 16, and the like. The heat sink 16 includes a metal fin base 1 and a plurality of fins 4 that are caulked and fixed to the fin base 1. The semiconductor module 100 is obtained by embedding the fin base 1 in the heat radiating surface, and integrating the fins 4 by retrofitting. The fin 4 after caulking is upright with respect to the fin base 1. FIG. 1 shows an example of a semiconductor module in which a semiconductor chip 14 is mounted on a lead frame 12, adhered to a fin base 1 through an insulating sheet 15, and sealed with a mold resin 13 integrally with a control substrate 11. However, the same structure can be used for other structures, so that the fin 4 can be caulked upright with respect to the fin base 1.

  The structure of the heat sink will be described with reference to FIG. FIG. 2A shows the state of the fin base before caulking. The fin base 1 includes a projecting wall portion 2, a caulking portion 3, and a base portion 21. The protruding wall portions 2 and the caulking portions 3 are alternately formed on the base portion 21. The projecting wall portion 2 has a rectangular cross section, and includes a first side surface 2a, a tip surface 2b, and a second side surface 2c. The tip surface 2b is flat. The caulking portion 3 has a bifurcated tip, and the tip is plastically deformed by a press load during caulking. The fins 4 are inserted one by one into the fin insertion groove 7 formed between the protruding wall portion 2 and the caulking portion 3. FIG. 2B shows a state in which the fin base and the fin after the caulking process are integrated. A protruding wall portion 9 is formed by plastic processing by a press load. By caulking, the caulking portion 3 is plastically deformed toward the fin side, and the fin base and the fin are integrated by bringing the fin 4 into contact with both sides of the projecting wall portion 2 of the fin base. Between the fin base according to the present invention, there is a relationship that the hardness of the fin base <the hardness of the fin. By making the hardness of the fin 4 larger than the hardness of the fin base 1, the caulking portion 3 of the fin base 1, which is softer than the fin 4, is made harder than the fin base 1 during the caulking process. In close contact. Further, since the fin 4 is in close contact with the protruding wall portion 2 of the fin base 1, the contact thermal resistance is stabilized.

  In the caulking process, a press tool 5 is used as shown in FIG. At this time, a vertically downward load F is generated in the protruding wall portion 2 through the caulking portion. In the heat sink according to the present application, since the fins 4 are harder than the fin base 1, as shown in FIG. 3B, the fin base 1 is plastically deformed and closely contacts the fins 4 having a high hardness. On the other hand, when the fin 4 is softer than the fin base 1, the caulking process causes the caulking portion to be plastically deformed toward the fin side, and when the fin is pressed against the projecting wall portion of the fin base from both sides, the projecting wall The part is deformed plastically. As a result, as shown in FIG.3 (c), the location with a large fin gap and a small location generate | occur | produce.

  In order to stabilize the heat dissipation performance of the caulking heat sink after caulking, it is required that the contact thermal resistance between the fin and the protruding wall portion of the fin base is sufficiently low. In order to sufficiently reduce the contact thermal resistance, it is necessary to increase the surface pressure between the fin and the protruding wall portion of the fin base. If the press load at the time of caulking is increased in order to increase the surface pressure between the fin and the fin base, a vertically downward load F increases to the protruding wall portion through the caulking portion. If the load F in the vertically diagonal direction applied to the projecting wall portion of the fin base is excessively increased, the projecting wall portion itself is plastically deformed. As a result, there are places where the fin gap is large and small. If there is a portion where the gap between the fins is small, a sufficient wind speed from the heat radiating fan cannot be obtained, so that the heat radiating performance of the produced caulking heat sink becomes insufficient.

  Further, in places where the gaps between the fins are small, foreign matters such as dust are likely to be clogged during long-term use, so that the heat dissipation performance of the entire heat sink is lowered, and there is a concern that the electronic circuit unit may malfunction. If the gap between the fins is set large in order to prevent such a problem, the size of the heat sink becomes large in order to achieve a predetermined heat dissipation property. Unlike the method of attaching the corrugated fins, the semiconductor module 100 performs post-caulking on the fin base 1 integrated with the mold resin 13. The fins 4 can be adhered to the projecting wall portion 2 of the fin base 1 as much as possible, and a semiconductor module having a sufficiently small contact thermal resistance can be obtained. According to the present embodiment, the contact thermal resistance is suppressed to a very small value, and furthermore, the fins after caulking work stand upright with respect to the fin base, so that it is possible to avoid deterioration of heat dissipation performance and clogging of foreign matters during long-term use.

  As for the fins 4, it is possible to achieve both workability and heat dissipation by using a plate material such as aluminum or an aluminum alloy. The fin base 1 is preferably made of aluminum or an aluminum alloy and processed by machining, die casting, forging, extrusion, or the like. However, the fin and the fin base are not limited to the aluminum material, and each may be a combination of different materials. For example, by making the fin 4 a copper-based plate material, the heat dissipation is further improved as compared with the case of aluminum. In the case of the present invention, the heat radiation performance can be improved by setting the thickness of the fin 4 to 0.6 to 1.0 mm, the width of the fin insertion groove 7 to 0.8 mm to 1.2 mm, and the fin pitch to 3 to 5 mm. In addition, said numerical value shows an example, Comprising: It is not necessarily limited to these numerical values, The length of a fin, the depth length of a fin base, etc. can be set arbitrarily.

  By adopting a structure in which the fins 4 are pressed from both sides of one protruding wall portion 2 as in this example, the fin base and the fins can be integrated with a low press load. As the surface roughness of the fin-based protruding wall portion 2, the contact thermal resistance was lowered by setting the surface roughness to be extremely smooth, such as Ra = 0.5 μm. As for the surface roughness of the fin 4, Ra = 0.1 μm or less could be realized without any special cost increase by using a rolled material. The smaller the surface roughness, the smaller the contact thermal resistance.

  The stabilization phenomenon of contact thermal resistance is due to the following action. When viewed microscopically between the contact surfaces, a true contact portion is formed at the tips of the irregularities due to microscopic irregularities on the surface of the material. In the non-contact part around the true contact part, heat transfer is performed by air molecule jump. Heat transfer by air jumping to the true contact portion is remarkably low in heat transfer performance. For this reason, heat concentrates on the true contact portion around the true contact portion. The heat moves to spread again through the true contact area. Such a phenomenon is called concentrated resistance. For this reason, if the period of the unevenness is large, that is, if the surface roughness is large, the distance to the true contact portion is increased, and the concentrated resistance is increased. Such a phenomenon is known as “Tachibana's Expression”.

  In order to promote heat transfer between the contact surfaces, it is required to cause plastic deformation so that the protruding wall portion and the surface of the fin at the time of caulking work are sufficiently close to each other. As a plastic deformation mechanism of metal atoms, a phenomenon in which a defect such as a slip line appears on the surface occurs, so that the surface roughness increases with plastic deformation. In other words, it is important to secure the heat transfer coefficient of the contact interface with plastic deformation by increasing the number of occurrence points of the true contact portion due to macro unevenness between the contact surfaces by plastic deformation without increasing the surface roughness as much as possible. . As a method for obtaining this effect to the maximum, it is effective that the contact surface is made of a different material, the side having a small surface roughness is a hard material, and the side having a large surface roughness is a soft material.

  When forming the contact surface accompanied by plastic deformation, many true contact portions are formed, and the heat transfer coefficient between the contact surfaces decreases. In the present application, a cold rolling process is applied to the plate material used for the fin, and the fin is formed from the plate material. The fin subjected to the cold rolling process became harder and harder due to work hardening. Further, it is possible to harden the fin plate material by utilizing a phenomenon such as alloying in terms of material and metallurgy to reduce the grain boundary. The fin base for caulking the fin is made of, for example, a material with a small amount of pure Al-based alloy components, heat treatment such as annealing is performed to reduce the hardness, and the crystal grain size tends to increase, for example, die casting Soften by molding method. Since the fins are hardened and the fin base is softened in this way, the contact thermal resistance of the contact portion formed by caulking is reduced, and the heat resistance of the heat sink is stabilized.

Embodiment 2. FIG.
The structure of the caulking heat sink in Embodiment 2 of the present invention will be described with reference to FIG. As shown in FIG. 4A, the fin base 1 is formed with tapered fin base protruding wall portions 8 and caulking portions 3 alternately. The side surface of the tapered fin base protruding wall portion 8 is inclined. When viewed in cross section, the width increases toward the bottom surface 7 a of the fin insertion groove 7. The taper angle of the fin base protruding wall is preferably about 5 degrees. In addition, since the fin base is manufactured by die casting, extrusion, forging, or the like, providing a taper of about several degrees on the protruding wall portion of the fin base can be manufactured at no additional cost.

By caulking, the caulking portion 3 is plastically deformed toward the fin side, and the fin base and the fin are integrated by bringing the fin into contact with both sides of the projecting wall portion of the fin base. Also in the heat sink according to Embodiment 3, the relationship between the fin base and the fin satisfies the hardness of the fin base <the hardness of the fin. By setting the relationship between the fin base and the hardness of the fin to be the hardness of the fin base <the hardness of the fin, the caulking portion of the fin base, whose hardness is softer than that of the fin, is harder than the fin base. Adheres to hard fins. Since the fin is in close contact with the protruding wall portion of the fin base, the contact thermal resistance is stabilized.

  As shown in FIG. 4B, a load F in a vertically diagonal direction is applied to the tapered fin base protruding wall portion 8. By providing the fin base protruding wall portion with a taper of about several degrees, the influence of the plastic deformation of the protruding wall portion due to the vertically downward load F during caulking can be reduced. In the fin base having a tapered protrusion wall portion, when the fins are inserted, if the upper surfaces of the fins are aligned, as shown in FIG. 4C, the tip of the fin inevitably is the fin base protrusion wall portion. Slide the taper part to the deepest position. Therefore, the fin is inserted to the deepest position as long as it comes into contact with the tapered portion of the protruding wall portion of the fin base.

  The fin after caulking was in an upright state as shown in FIG. For this reason, since the contact area between the fin and the protruding wall portion of the fin base can be secured stably, the state in which the contact thermal resistance is low continues. According to the second embodiment, in the automatic caulking apparatus that inserts fins into the fin insertion grooves of the fin base and performs caulking, even if the positional relationship between the fin insertion position on the apparatus side and the fin base is slightly shifted, the tip of the fin As long as it comes into contact with the taper of the projecting wall of the fin base, the taper slides and moves to its deepest position by its own weight.

  Compared to the case where there is no taper on the fin base's protruding wall when adjusting the alignment of the fin and the fin base, if the fin base's protruding wall has a taper, simple alignment and fin insertion to caulking Became possible. Therefore, at the time of mass production, the defective rate when the fin is inserted into the fin groove of the fin base is reduced, and high production efficiency can be obtained. Furthermore, the taper of the fin base protruding wall portion functions as a draft for die casting, forging, and the like, thus contributing to the improvement of the die life.

Embodiment 3 FIG.
In the third embodiment, the base portion 21 is provided with the stepped fin base protruding wall portion 6. The structure of the caulking heat sink in the second embodiment will be described with reference to FIG. In order to crimp the fin after crimping in an upright state with respect to the fin base, as shown in FIG. 5A, the width of the projecting wall portion of the fin base is made so that the bottom surface side of the fin insertion groove 7 is thick. A step 20 is provided on the side of the wall. By adopting a step structure that increases the width of the fin base protruding wall on the fin insertion groove bottom surface side, the influence of plastic deformation of the fin base protruding wall during caulking is reduced, and the fin after caulking As shown in FIG. 5B, it was in an upright state with respect to the fin base.

  In the semiconductor module according to the third embodiment, since the relationship between the fin base and the fin is such that the hardness of the fin base is less than the hardness of the fin, the contact thermal resistance between the fin base and the fin can be stably reduced. Was stable. In addition, by adopting a step structure in which the width of the projecting wall of the fin base becomes thicker on the bottom surface side of the fin insertion groove, the fin 4 after the caulking process stands upright with respect to the fin base 1, and thus the heat radiation performance is more stable. To do.

Embodiment 4 FIG.
The structure of the caulking heat sink in Embodiment 4 of the present invention will be described with reference to FIG. In the fin base 1, a curved fin base protruding wall portion 10 that contacts the fin 4 is formed between the adjacent caulking portions 3. By crimping, the caulking portion 3 is plastically deformed toward the fin side, and the fin base and the fin are integrated by bringing the fin 4 into contact with both sides of the protruding wall portion of the fin base 1. Also in the fourth embodiment, the relationship between the fin base and the fin according to the present invention satisfies the hardness of the fin base <the hardness of the fin. By setting the relationship between the fin base and the hardness of the fin to be the hardness of the fin base <the hardness of the fin, the caulking portion of the fin base, whose hardness is softer than that of the fin, is harder than the fin base. Adheres to hard fins. Since the fin is in close contact with the fin base protruding wall, the contact thermal resistance is stable. By configuring the projecting wall portion of the fin base with a curved surface, the same effects as in the first, second, and third embodiments can be obtained. The structure of the projecting wall portion of the fin base is not limited to the curved surface as shown in FIG. 6, but may be any structure (slope, curved surface, compound surface) in which the width of the projecting wall portion increases toward the bottom surface of the fin insertion groove. .

Example 1.
An experiment was performed to actually verify the heat sink according to the first embodiment. FIG. 7 shows the result of cutting the prepared heat sink in cross section for observation. As shown in FIG. 7A, the protruding wall portion of the fin base is perpendicular to the bottom surface of the fin insertion groove. FIG. 7B shows the shape of the fin and the protruding wall portion of the fin base after the caulking process. Before caulking, the projecting wall portion of the fin base is perpendicular to the bottom surface of the fin insertion groove, and the projecting wall portion of the fin and the fin base is in surface contact. When caulking is performed using a press tool, the projecting wall portion of the fin base tilts to the left as shown in FIG. 7B and is plastically deformed. From the observation image shown in FIG. 7B, the inclination of the fin was about 2 degrees from the vertical direction. If the height of the fin is low, this degree of tilt will not cause a big problem.

Example 2
Next, an experiment was conducted to actually verify the heat sink according to the second embodiment. FIG. 8 shows a cross-sectional cut observation result on the fin base in which the protruding wall portion of the fin base is provided with a taper whose width increases toward the bottom surface of the fin insertion groove. As shown in FIG. 8A, the protruding wall portion of the fin base is provided with a taper of about 5 degrees. FIG. 8B shows the fins and the protruding wall portions of the fin base after the caulking process. By providing a taper on the projecting wall portion of the fin base, the plastic deformation of the projecting wall portion after caulking is extremely small. For this reason, the fin after caulking is upright with respect to the fin base.

  Next, in order to evaluate the improvement of the fin gap, a certain value was set as the standard value of the fin gap. A number of heat sinks were created and the fin gap was measured. The securing ratio satisfying the standard value was calculated from the measurement results. Since there was no taper on the fin base protruding wall, the securing rate was improved by a factor of 1.5 by providing the fin base protruding wall with a taper of about 5 degrees. It was experimentally confirmed that the fin gap could be improved. By optimizing the shape of the caulking portion, the fin clearance securing rate is further improved.

  It should be noted that the present invention can be freely combined with each other within the scope of the invention, and each embodiment can be appropriately modified or omitted.

DESCRIPTION OF SYMBOLS 1 Fin base, 2 protruding wall part, 3 crimping part, 4 fin, 5 press tool, 6 stepped fin base protruding wall part, 7 fin insertion groove, 7a bottom face, 8 taper fin base protruding wall part, 9 plastic processing Projection wall, 10 Curved fin base projection, 11 Control board, 12 Lead frame, 13 Mold resin, 14 Semiconductor chip, 15 Insulation sheet, 16 Heat sink, 21 Base, 100 Semiconductor module

Claims (6)

  A fin base having a caulking portion disposed between the projecting wall portions facing each other and having a bifurcated tip, and being caulked and fixed between the caulking portion and the projecting wall portion of the fin base, A heat sink comprising a plurality of fins harder than a fin base.   The heat sink according to claim 1, wherein the projecting wall portion of the fin base has inclined side surfaces on both sides, and has a base wider than an upper end portion.   The heat sink according to claim 2, wherein a side surface of the protruding wall portion is curved.   The heat sink according to claim 1, wherein the projecting wall portion of the fin base is provided with steps on both side surfaces. A heat sink according to any one of claims 1 to 4,
A semiconductor chip mounted on the heat sink;
A heat sink integrated semiconductor module comprising: a mold resin for sealing the semiconductor chip. A plurality of plate-shaped metal fins;
A metal fin base having a crimped portion with a bifurcated tip and a flat projection with a flat tip formed alternately on the plate-like base portion;
The plurality of fins are inserted and fixed one by one between the caulking portion and the protruding portion, and the plurality of fins are harder than the fin base.