JP2016066660A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an art to simply inhibit grease leakage in a semiconductor device in which a power card encapsulating a semiconductor element and a cooling member are layered and a load is applied in a layered direction.SOLUTION: A semiconductor device disclosed in the present specification includes a heat sink 16a provided on a surface of a power card 10, which faces a cooling member 6 and a grease sandwiched between the heat sink 16a and the cooling member 6. The heat sink 16a has lengths different from each other in two direction orthogonal to each other in plan view. Polish marks 46a remaining on the surface of the heat sink 16a, which faces the cooling member 6 extend along a longer direction of the heat sink 16a.SELECTED DRAWING: Figure 5A

Description

  The present invention relates to a semiconductor device. In particular, the present invention relates to a semiconductor device in which a power card in which a semiconductor element is sealed is in contact with a cooling member with grease interposed therebetween.

  An example of the above-described type of semiconductor device is disclosed in Patent Document 1. In the semiconductor device of Patent Document 1, a power card in which a semiconductor element is sealed is provided with a heat radiating plate, and a groove is provided on at least one of the facing surfaces of the heat radiating plate and the cooling member. And either of a heat sink or a cooling member is provided with the hole for grease injection | pouring between a heat sink and a cooling member. The injected grease is easy to spread along the groove over the entire surface between the heat sink and the cooling member.

  Patent Document 2 also discloses a semiconductor device of the type described above. The semiconductor device of Patent Document 2 includes an element module (power card) that stores a heating element and a casing that stores the element module. The element module is fixed to the casing with grease. A plurality of parallel linear grooves are provided on the housing surface facing the element module to collect grease. In the drawing of Patent Document 2, a linear groove provided along the longitudinal direction of the element module is described.

JP 2005-101259 A JP 2013-165202 A

  In a semiconductor device as disclosed in Patent Document 1 and Patent Document 2, the thinner the grease layer, the higher the cooling capacity for the power card. Therefore, a load is applied to the laminate of the power card and the cooling member in the lamination direction, and the grease layer is thinly extended. The thickness of the grease is preferably 100 microns or less (sub-milli order). If the thickness of the grease is on the order of sub-millimeters, there is a risk that the grease will flow out due to a phenomenon called bleed-out or pumping that occurs due to repeated heat generation and cooling (thermal cycle) of the semiconductor element. Details of bleed out and pumping will be described in Examples. In general, the outflow of grease from between the power card and the cooling member may be expressed as “the grease comes off”. Such expressions are also used herein.

  The present specification provides a technique for suppressing grease loss due to bleed-out or pumping without bothering to form grooves as in Patent Documents 1 and 2.

  Polishing marks (tool marks) remain on the surface of the heat sink. The polishing mark is a parallel protrusion having a height of several microns to several tens of microns. The inventors have noticed that when the thickness of the grease layer is on the order of submillimeters, the movement direction of the grease is limited by the polishing marks, and the grease easily moves along the polishing marks. The technique disclosed in this specification uses this polishing mark. In the semiconductor device disclosed in this specification, the heat dissipation plate is provided on a surface facing the cooling member of the power card. The heatsinks have different lengths in two directions orthogonal to each other when viewed in plan. The polishing marks remaining on the surface of the heat radiating plate facing the cooling member are made to extend along the longitudinal direction of the heat radiating plate. By doing so, the direction which grease spreads is controlled to the longitudinal direction of a heat sink. Compared with the case where the polishing marks extend in the short direction of the heat sink, the distance that the grease can move becomes longer when the polishing marks extend in the longitudinal direction of the heat sink. By controlling the direction in which the grease spreads in the longitudinal direction, the distance that the grease can move on the heat radiating plate can be extended, and the grease can be easily maintained on the heat radiating plate. The technology disclosed in this specification makes it easy to maintain the grease on the heat sink without providing the groove of Patent Document 1 or the linear groove of Patent Document 2.

  According to the technology disclosed in this specification, in a semiconductor device in which a power card and a cooling member are stacked with grease interposed therebetween, by utilizing polishing marks remaining on the heat sink, bleed-out or pumping is performed. Grease omission can be suppressed. Details and further improvements of the technology disclosed in this specification will be described in the following “DETAILED DESCRIPTION”.

It is a perspective view of the semiconductor device of an Example. It is the perspective view which looked at the power card from the back. It is sectional drawing of the semiconductor device cut | disconnected by XY plane in the coordinate system of FIG. It is sectional drawing of the semiconductor device cut | disconnected by the XZ plane in the coordinate system of FIG. It is a front view of a power card. It is a reverse view of a power card. It is a fragmentary sectional view in the VI-VI line of FIG. 5B of a heat sink. It is a front view of the power card in a modification.

  A semiconductor device according to an embodiment will be described with reference to the drawings. FIG. 1 is a perspective view of a semiconductor device 2 according to the first embodiment. The semiconductor device 2 is a unit in which a plurality of power cards 10 and a plurality of coolers 3 are stacked. In FIG. 1, reference numeral 10 is given to only one power card, and reference numerals are omitted for the other power cards. Similarly, reference numeral 3 is given to only one cooler, and reference numerals are omitted for the other coolers. In addition, the case 31 for housing the semiconductor device 2 is drawn with imaginary lines so that the entire semiconductor device 2 can be seen. In addition, although grease is apply | coated between the power card 10 and the insulating board 6, and between the insulating board 6 and the cooler 3, illustration of grease is abbreviate | omitted in FIG. 1 and FIG.

  One power card 10 accommodates four semiconductor elements. Specifically, the four semiconductor elements are two transistors Ta and Tb and two diodes Da and Db. The internal structure of the power card 10 will be described in detail later. The semiconductor element is cooled by the refrigerant passing through the cooler 3. The refrigerant is a liquid, typically water.

  The power card 10 and the cooler 3 are both flat plate types, and are laminated so that the flat surfaces having the largest areas face each other among the plurality of side surfaces. The power card 10 and the cooler 3 are alternately stacked, and coolers are located at both ends in the stacking direction of the units. An insulating plate 6 is sandwiched between the power card 10 and the cooler 3. In each power card 10, the cooler 3 faces the both surfaces in the stacking direction with the insulating plate 6 interposed therebetween.

  The plurality of coolers 3 are connected by connecting pipes 5a and 5b. A refrigerant supply pipe 4a and a refrigerant discharge pipe 4b are connected to the cooler 3 at one end in the stacking direction. The refrigerant supplied through the refrigerant supply pipe 4a is distributed to all the coolers 3 through the connection pipe 5a. The refrigerant absorbs heat from the adjacent power card 10 while passing through each cooler 3. The refrigerant passing through each cooler 3 passes through the connecting pipe 5b and is discharged from the refrigerant discharge pipe 4b.

  When the semiconductor device 2 is accommodated in the case 31, a leaf spring 32 is inserted on one end side in the stacking direction. Due to the leaf spring 32, a load is applied to the laminated unit of the power card 10, the insulating plate 6, and the cooler 3 from both sides in the lamination direction. The load is, for example, 3 [kN]. As will be described later, grease is applied between the insulating plate 6 and the power card 10, but a high load of 3 [kN] extends the grease layer thinly to improve the heat transfer efficiency from the power card 10 to the cooler 3. Increase. The power card 10 is directly deprived of heat by the insulating plate 6. Therefore, the insulating plate 6 corresponds to a cooling member. In the semiconductor device 2, an insulating plate 6 (cooling member) is in contact with a power card 10 containing semiconductor elements (two transistors Ta and Tb and two diodes Da and Db) with grease interposed therebetween. In this device, a load is applied in the stacking direction so that 10 and the insulating plate 6 are in close contact with each other.

  The power card 10 will be described. In the power card 10, the heat radiating plates 16 a and 16 b are exposed on one flat surface 10 a facing the insulating plate 6. The insulating plate 6 is in contact with the heat radiating plates 16a and 16b with grease, and the cooler 3 is in contact with the insulating plate 6 with the grease interposed therebetween. For convenience of explanation, the side on which the flat surface 10 a is located is referred to as the front surface of the power card 10. FIG. 2 shows a view of the power card 10 as seen from the back surface (negative direction of the X axis). Another heat radiating plate 17 is exposed on the flat surface 10b opposite to the flat surface 10a. Another insulating plate 6 is in contact with the heat radiating plate 17 with grease, and another cooler 3 is in contact with the insulating plate 6 with the grease interposed therebetween. Three electrode terminals 7a, 7b, and 7c extend from the upper surface of the power card 10 (the surface facing the positive direction of the Z-axis in the figure), and from the lower surface (the surface facing the negative direction of the Z-axis direction in the figure). The control terminal 29 is extended.

  From here, the internal structure of the power card 10 will be described with reference to FIGS. 3 and 4 together with FIGS. FIG. 3 is a cross-sectional view of the power card 10 of FIG. 1 cut along a plane parallel to the XY plane of the coordinate system in the drawing and across the transistors Ta and Tb. FIG. 4 is a cross-sectional view of the power card 10 of FIG. 1 cut along a plane parallel to the XZ plane of the coordinate system in the drawing, and is a cross-sectional view cut along a plane crossing the transistor Ta and the diode Da. In other words, FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3, and FIG. 3 is a cross-sectional view taken along line III-III in FIG.

  The four semiconductor elements (transistors Ta and Tb, diodes Da and Db) are sealed in a resin casing 13. The housing 13 seals the semiconductor element by injection molding. Each semiconductor element is a flat chip, and is arranged so that the flat surface is parallel to the flat surface of the housing 13 (the flat surfaces 10a and 10b of the power card 10). Hereinafter, the flat surfaces 10 a and 10 b of the power card 10 may be referred to as the flat surfaces 10 a and 10 b of the housing 13.

  The transistors Ta and Tb are IGBTs. The transistors Ta and Tb have a collector electrode, an emitter electrode, and a gate electrode. The collector electrode is exposed on one flat surface of the chip of the transistor Ta (Tb), and the emitter electrode is exposed on the other flat surface. The gate of the transistor Ta (Tb) is provided at the end of one flat surface of the chip. The electrode on one flat surface of the transistor Ta is joined to the back surface of the heat radiating plate 16 a by solder 15. The front surface of the heat radiating plate 16 a is exposed on the flat surface 10 a of the housing 13. In the heat sink, the surface exposed from the housing 13 is referred to as a “front surface”, and the opposite surface is referred to as a “back surface”. On the other hand, the electrode on the other flat surface of the transistor Ta is joined to the back surface of the heat sink 17 via the solder 15 and the conductive member (spacer 14). The front surface of the heat radiating plate 17 is exposed on the flat surface 10 b of the housing 13. A gate is located at the end of the other flat surface of the transistor Ta, and the gate is connected to the control terminal 29 via a wire. In FIG. 4, the wires are drawn in broken lines. The transistor Tb has the same configuration, and the collector electrode and emitter electrode of the transistor Tb are connected to the heat sinks 16a and 17, respectively.

  As well shown in FIG. 4, the heat sink 16a is a part of the electrode terminal 7a. An extending portion extends from the side edge of the heat radiating plate 16a inside the housing. The extending portion passes through the inside of the housing 13 and faces the upper surface of the housing 13 (in the positive Z-axis direction of the coordinate system in the drawing). Surface) to the outside. That is, in the electrode terminal 7a for connecting the electrode of the transistor Ta to another external device, a portion exposed to the flat surface 10a of the housing 13 corresponds to the heat radiating plate 16a. Since the electrode terminal 7a is in contact with the electrode of the transistor Ta, it easily conducts heat inside the transistor Ta. Since part of the electrode terminal 7a is exposed as the heat sink 16a from the housing 13, the heat inside the transistor Ta is well transmitted to the heat sink 16a. On the other hand, since the cooler 3 is made of aluminum (conductive metal), it is necessary to insulate it from the heat sink 16a. Therefore, the semiconductor device 2 has the insulating plate 6 sandwiched between the cooler 3 and the heat radiating plate 16a (power card 10). The insulating plate 6 is made of a ceramic that is thin, highly insulating, and has good heat conductivity. The heat sink 16a (electrode terminal 7a) is made of copper having excellent conductivity and heat conductivity. The spacer 14 is also made of copper having excellent conductivity and heat conductivity.

  The diodes Da and Db are also flat chips, with the anode electrode exposed on one flat surface and the cathode electrode exposed on the other flat surface. The electrode exposed on one flat surface of the diode Da is connected to the back surface of the heat radiating plate 16a through the solder 15 like the transistor Ta. The electrode exposed on the other flat surface of the diode Da is also connected to the back surface of the heat radiating plate 17 via the solder 15 and the spacer 14 like the transistor Ta. That is, the transistor Ta and the diode Da are connected in parallel (reverse parallel) between the heat sink 16a (that is, the electrode terminal 7a) and the heat sink 17. The heat sink 17 is also a part of the electrode terminal 7c like the heat sink 16a.

  The set of the transistor Tb and the diode Db has the same structure as the set of the transistor Ta and the diode Da. The electrodes on one surface of the transistor Ta and the diode Db are connected to the back surface of the heat sink 16b via the solder 15, and the electrodes on the other surface are connected to the back surface of the heat sink 17 via the solder 15 and the spacer 14. ing. The transistor Tb and the diode Db are also connected in parallel (in reverse parallel) inside the housing 13. The heat sink 16b is also a part of the electrode terminal 7b like the heat sink 16a.

  The heat sinks 16a and 16b are exposed on one flat surface 10a of the maximum area of the flat power card 10 (housing 13), and the heat sink 17 has a maximum area of the power card 10 (housing 13). It is exposed on the other flat surface 10b. As well shown in FIGS. 3 and 4, grease 9a is applied between the insulating plate 6 and the heat radiating plate 16a. Similarly, grease 9a is also applied between the insulating plate 6 and the heat radiating plates 16b and 17. Grease 9 b is also applied between the insulating plate 6 and the cooler 3. The grease 9a and the grease 9b are the same type of grease.

  The front surface of the heat sink will be described with reference to FIGS. 5A and 5B. FIG. 5A shows a front view of the power card 10, and FIG. 5B shows a back view of the power card 10. 5A is a diagram of the power card 10 viewed from the positive direction of the X axis, and FIG. 5B is a diagram of the power card 10 viewed from the negative direction of the X axis. In FIG. 5A and FIG. 5B, the insulating plate 6 is drawn with a virtual line. The transistors Ta and Tb and the diodes Da and Db are drawn with broken lines. As shown in FIG. 5A, the heat radiating plate 16a has different lengths in two orthogonal directions when viewed in plan. The length of the heat radiating plate 16a in the Z-axis direction is referred to as L1, and the length in the Y-axis direction is referred to as L2. The heat sink 16a is L1> L2. That is, the Z-axis direction is the longitudinal direction of the heat sink 16a, and the Y-axis direction is the short direction of the heat sink 16a. The heat sink 16b is the same as the heat sink 16a. Further, as shown in FIG. 5B, the length of the heat radiating plate 17 is also different in two directions orthogonal to each other when viewed in plan. The length of the heat sink 17 in the Y-axis direction is referred to as L3, and the length in the Z-axis direction is referred to as L4. The heat sink 17 is L3> L4. That is, the Y-axis direction is the longitudinal direction of the heat radiating plate 17, and the Z-axis direction is the short direction of the radiating plate 17. The longitudinal direction of the radiator plates 16a and 16b and the longitudinal direction of the radiator plate 17 are orthogonal to each other.

  The front surface of the heat radiating plate 16a (the surface exposed to the flat surface 10a of the housing 13) is polished to a flat surface. This is for managing the thermal resistance of the grease between the heat radiating plate 16a and the insulating plate 6 to be uniform over the entire surface of the heat radiating plate 16a. A plurality of polishing marks (tool marks) at the time of polishing remain on the front surface of the heat radiating plate 16a. The tool mark is a parallel protrusion having a height of several microns to several tens of microns. As shown in FIG. 5A, a plurality of tool marks 46a extend in parallel along the longitudinal direction (Z-axis direction) of the heat sink 16a. In other words, the front surface of the heat sink 16a is polished so that the tool mark 46a extends in parallel along the longitudinal direction of the heat sink 16a. The tool mark 46a is linear, and the tool mark 46a extends from one end in the longitudinal direction of the heat radiating plate 16a toward the other end. A tool mark 46b similar to that of the heat sink 16a remains on the front surface of the heat sink 16b. Further, the front surface of the heat radiating plate 17 is also polished. As shown in FIG. 5B, the plurality of tool marks 47 extend in parallel along the longitudinal direction (Y-axis direction) of the heat radiating plate 17. The tool mark 47 is also linear, and the tool mark 47 extends from one end in the longitudinal direction of the heat radiating plate 17 toward the other end.

  The shape of the tool mark will be described. FIG. 6 is a partial cross-sectional view of the heat dissipation plate 16a taken along line VI-VI in FIG. 5A. In FIG. 6, the tool mark 46a is drawn in a large size with emphasis. The tool mark 46a protrudes from the front surface of the heat sink 16a in the orthogonal direction. Further, as described above, the tool mark 46a is a protrusion extending in the longitudinal direction of the heat radiating plate 16a. Its height H1 is 1 to 10 microns. In the figure, only the height of one tool mark 46a is denoted by reference numeral H1, but the height of other tool marks 46a is also H1. Further, the interval W between the plurality of tool marks 46a extending in parallel is sufficiently wider than the height H1 of the tool mark 46a. The interval W is 500 to 700 microns. In the drawing, the symbol W is attached to only one interval of the tool mark 46a, but the interval of other intervals of the tool mark 46a is also W.

  In the semiconductor device 2, the thinner the grease layer, the higher the cooling capacity for the power card. As described above, in the semiconductor device 2, a load is applied to the stacked unit of the power card 10, the insulating plate 6, and the cooler 3 in the stacking direction by the leaf spring 32, and the layers of grease 9 a and 9 b are thinly extended. The thickness of the grease is preferably 100 microns or less (sub-milli order). If the thickness of the grease is on the order of sub-millimeters, there is a risk that the grease will flow out due to a phenomenon called pumping or bleedout that occurs due to repeated heat generation and cooling (thermal cycle) of the semiconductor element.

  Pumping is a phenomenon in which the gap width between the power card and the cooling member is locally reduced or restored due to thermal deformation of the power card. When the gap width is narrowed, the grease is compressed by the power card and the cooling member, and the grease spreads around the heat sink. When the gap width returns, the grease is sucked into the gap. Here, when the gap width returns to the original state, a part of the grease that has spread to the outside of the heat radiating plate may remain flowing out of the heat radiating plate. If a part of the grease is left flowing out of the heat sink, air enters a gap generated by a part of the grease that has flowed out. Air has a lower thermal conductivity than grease. When air enters the gap, the thermal resistance between the heat sink and the cooling member increases. Bleed-out is a phenomenon in which grease is removed from the gap between the power card and the cooling member due to thermal expansion and contraction of the grease itself. As the grease expands, the grease spreads around the heat sink. When expanded, a part of the grease that has spread to the outside of the heat sink may remain flowing out of the heat sink. Thereby, like pumping, air enters into the gap generated by part of the grease that has flowed out, and the thermal resistance between the heat sink and the cooling member increases.

  The flat surface 10a of the housing 13 is made of resin, and the surface roughness thereof is larger than the surface roughness of the heat sinks 16a and 16b. When the power card 10 is viewed in plan, the flat surface 10a of the housing 13 having a higher surface roughness than the heat radiating plates 16a and 16b is located around the heat radiating plates 16a and 16b. When grease is lost due to pumping or bleed-out, part of the grease flows out to the flat surface 10a having a high surface roughness. The grease becomes difficult to move as the surface roughness increases. Therefore, some of the grease that has flowed out to the flat surface 10a having a high surface roughness tends to stay on the flat surface 10a.

  The inventors have noticed that when the thickness of the grease layer becomes submillimeter order, the movement direction of the grease is limited by the tool mark, and the grease easily moves along the tool mark. In particular, the more the tool marks extend in parallel, the easier it is for the grease to move along the tool marks. A plurality of tool marks 46a extending in parallel remain on the front surface of the heat sink 16a of the embodiment. In the embodiment, the tool mark 46a extends along the longitudinal direction of the heat sink 16a. According to such a configuration, the distance that the grease 9a can move is longer when the tool mark 46a extends in the longitudinal direction of the heat sink 16a than when the tool mark 46a extends in the shorter direction of the heat sink 16a. Becomes longer. By controlling the direction in which the grease 9a spreads in the longitudinal direction of the heat radiating plate 16a, the distance that the grease 9a can move on the heat radiating plate 16a can be extended, and the grease 9a can be easily maintained on the heat radiating plate 16a. That is, grease loss due to bleed out or pumping can be suppressed.

  The tool mark is a mark generated in the process of polishing the heat sink. That is, it is not necessary to add another process. The polishing machine usually has a rotating disk coated with polishing powder. In order for the tool mark to extend in the longitudinal direction of the heat sink, a polishing machine may be applied to the heat sink so that the circumferential direction of the rotating disk coincides with the longitudinal direction of the heat sink. By doing so, it is possible to leave a tool mark so as to suppress grease loss due to bleeding out or pumping.

  The tool mark 46b (47) remaining on the front surface of the heat sink 16b (17) also extends in the longitudinal direction of the heat sink 16b (17). The tool mark 46b (47) also contributes to suppression of grease loss.

  A modified semiconductor device will be described with reference to FIG. The configuration of the semiconductor device of the modification is the same as that of the above-described embodiment except for the tool mark of the heat sink. The tool mark of the heat sink of a modification is demonstrated. FIG. 7 shows a front view of a modified power card 110. A plurality of tool marks 56a extending in parallel remain on the front surface of the heat sink 116a of the power card 110. The tool mark 56a extends along the longitudinal direction of the heat sink 116a as in the embodiment, and the tool mark 56a is curved in the short direction. A tool mark 56b similar to that of the heat sink 116a remains on the front surface of the heat sink 116b. Even in such a configuration, the direction in which the grease spreads can be controlled in the longitudinal direction of the heat radiating plate, as in the embodiment. That is, it is possible to easily maintain the grease on the heat radiating plate, and it is possible to suppress the loss of grease due to bleed out or pumping.

  Hereinafter, points to be noted regarding the technology shown in the embodiments will be described. The semiconductor element (transistor) used in the semiconductor device is not limited to the IGBT. For example, a MOSFET may be used. In this case, the “collector electrode” is called a “source electrode”, and the “emitter electrode” is called a “drain electrode”. Further, the intervals between the tool marks need not be the same. As shown in the modification of FIG. 7, the tool mark may be curved. The tool mark may not be parallel to the longitudinal direction of the heat sink.

  What is necessary is just to distinguish the shape of a heat sink at the time of planar view in a longitudinal direction and a transversal direction. For example, the shape of the heat sink when viewed in plan may be an ellipse.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2: Semiconductor device 3: Coolers 4a, 4b: Refrigerant supply pipes 5a, 5b: Connection pipe 6: Insulating plates 7a, 7b, 7c: Electrode terminals 9a, 9b: Grease 10, 110: Power card 13: Housing 14: Spacer 15: Solder 16a, 16b, 17, 116a, 116b: Heat sink 29: Control terminal 31: Case 32: Plate springs 46a, 46b, 47, 56a, 56b: Tool mark (polishing mark)
Ta, Tb: transistors Da, Db: diodes

Claims (1)

In a semiconductor device in which a power card sealing a semiconductor element and a cooling member are stacked and a load is applied in the stacking direction,
A heat sink provided on a surface of the power card facing the cooling member, and having different lengths in two directions orthogonal to each other when viewed in plan;
Grease sandwiched between the heat sink and the cooling member;
With
Polishing traces remaining on the surface of the heat sink facing the cooling member extend along the longitudinal direction of the heat sink,
A semiconductor device.