JP2008294282A - Semiconductor device and method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device which can easily be manufactured and suppress cracking and peeling due to thermal stress, and to provide a method of manufacturing the semiconductor device. <P>SOLUTION: The semiconductor device 10 has a semiconductor element 12 bonded to one surface 14a of a ceramic substrate 14 and a heat sink 13 thermally coupled to the other surface 14b through a metal plate 16. The heat sink 13 is provided with a projection portion 20 having a bonding surface 20a, having smaller area than the metal plate 16, and the bonding surface 20a is disposed inside a peripheral edge 16c of the metal plate 16 to thermally be coupled to the metal plate 16. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor device in which a semiconductor element is thermally coupled to one surface of a circuit board and a heat dissipation device is thermally coupled to the other surface via a metal layer, and a method for manufacturing the same.

  Conventionally, a metal layer is provided on both front and back surfaces of a ceramic substrate such as aluminum nitride, a semiconductor element is thermally coupled (bonded) to the front surface metal layer, and a heat sink for dissipating heat generated by the semiconductor element to the back surface metal layer. 2. Description of the Related Art A semiconductor device is known in which a (heat radiating device) is thermally coupled (joined) to form a module. By the way, in a semiconductor device, it is requested | required that the thermal radiation performance of a heat sink is maintained over a long period of time. However, according to the conventional configuration, depending on the use conditions, cracks occur at the joint between the ceramic substrate and the back metal layer due to the thermal stress generated due to the difference in coefficient of linear expansion between the ceramic substrate, the metal layer, and the heat sink. Or, further, peeling due to the extension of cracks may occur, resulting in a decrease in heat dissipation performance.

Therefore, conventionally, in order to solve such a problem, a semiconductor module described in Patent Document 1 has been proposed. As shown in FIG. 6, the semiconductor module 70 described in Patent Document 1 is provided with a thermal stress relaxation portion 71 a formed by steps, grooves, and recessed portions having a predetermined depth on the metal plate 71 on the back surface side of the ceramic substrate 74. A solder layer (not shown) having a thick solder portion is formed in a part between the heat sink 72 and the metal plate 71 on the back surface side. In the semiconductor module 70 described in Patent Document 1, the semiconductor element 75 is bonded to the metal plate 73 on the surface side of the ceramic substrate 74. Moreover, the thermal stress relaxation part 71a is provided in the metal plate 71 so that the volume ratio of the metal plate 71 on the back surface side to the volume of the metal plate 73 on the front surface side is 0.6 or less. In the semiconductor module 70 described in Patent Document 1, the thermal stress generated in the solder layer by the solder portion is greatly relaxed and reduced, so that solder cracks are less likely to occur, and the warp of the heat sink 72 is also caused by the thermal stress relaxation portion 71a. Absorbed in.
JP 2003-17627 A

  By the way, in the semiconductor module 70, the thermal stress relaxation portion 71a for relaxing the thermal stress and suppressing the deterioration of the heat radiation performance is formed by etching or pressing the metal plate 71 on the back surface side, which is very manufactured. It is difficult to manufacture the semiconductor module 70.

  The present invention has been made paying attention to such problems existing in the prior art, and its purpose is to be able to manufacture easily and to suppress the occurrence of cracks and peeling due to thermal stress. It is an object of the present invention to provide a semiconductor device and a method for manufacturing the semiconductor device.

  In order to solve the above problems, the invention according to claim 1 is characterized in that the semiconductor element is thermally coupled to one surface of the ceramic substrate and the heat dissipation device is thermally coupled to the other surface via a metal layer. In the semiconductor device, the heat radiating device is provided with a convex portion provided with a joining surface having a smaller area than the metal layer at the tip, and the joining surface is disposed on the inner side of the periphery of the metal layer. Thermally coupled.

  The invention according to claim 5 is a method of manufacturing a semiconductor device in which a semiconductor element is thermally coupled to one surface of a ceramic substrate and a heat dissipation device is thermally coupled to the other surface via a metal layer. And forming a protrusion having a bonding surface having a smaller area than the metal layer at the tip of the heat dissipation device, and disposing the bonding surface of the protrusion on the inner side of the periphery of the metal layer. Are thermally coupled.

  According to invention of Claim 1 and Claim 5, a joining surface is arrange | positioned inside the periphery of a metal layer, and a joining surface joins in the position away from the periphery of this metal layer toward the inside in the metal layer. Has been. For this reason, when thermal stress is generated due to the difference in the linear expansion coefficient between the ceramic substrate and the metal layer, the joint surface is not joined to the peripheral portion where the thermal stress acts intensively in the metal layer. Therefore, for example, the thermal stress can be relaxed as compared with the case where the bonding surface is also bonded to the peripheral portion of the metal layer. Further, since the joining surface is not joined to the peripheral portion of the metal layer, deformation of the peripheral portion of the metal layer is allowed when thermal stress is applied. Therefore, the thermal stress at the joint between the ceramic substrate and the metal layer is relieved as compared with the case where the heat dissipation device is joined to the peripheral edge of the metal layer. As a result, it is possible to suppress the occurrence of cracks and peeling at the joint between the ceramic substrate and the metal layer. And the convex part (joint surface) provided in order to relieve a thermal stress is formed by processing a thermal radiation apparatus. For this reason, in order to relieve thermal stress, a semiconductor device can be easily manufactured as compared with a case where a metal layer having a small thickness and a small size is etched.

  According to a second aspect of the present invention, in the semiconductor device according to the first aspect, the entire joint surface is thermally coupled to the metal layer. According to the present invention, heat generated from the semiconductor element is conducted from the convex portion to the heat dissipation device via the ceramic substrate and the metal layer. At this time, since the entire bonding surface is bonded to the metal layer, for example, the heat generated by the semiconductor element is more efficiently transmitted to the heat dissipation device than when the protrusion has a non-bonding region to the metal layer. Can conduct well.

  According to a third aspect of the present invention, in the semiconductor device according to the first or second aspect, the joint surface is directly brazed to the metal layer. According to the present invention, heat generated by the semiconductor element can be efficiently conducted to the heat radiating device as compared with the case where another member is interposed between the joint surface and the metal layer.

  According to a fourth aspect of the present invention, in the semiconductor device according to any one of the first to third aspects, the convex portion and the metal layer are formed of a similar metal material. The “similar metal material” means a material which is the same as the base material and does not form an interface between the two materials when they are melted and joined to the other material. For example, pure aluminum and various aluminum alloys are similar metal materials. Hereinafter, in this specification, “similar metal material” is used in the same meaning as described above. And according to this invention, since formation of the interface which inhibits heat conduction is suppressed in the part which joined the convex part and the metal layer directly or via the brazing material which is a similar metal material, high heat conduction The degree can be secured.

  According to a sixth aspect of the present invention, in the method for manufacturing a semiconductor device according to the fifth aspect, the convex portion is formed by pressing the heat dissipation device. According to the present invention, for example, compared to the case where the metal layer or the heat dissipation device is etched to form a convex portion, the formation of the convex portion can be simplified, and thus the manufacturing of the semiconductor device can be simplified. .

  According to this invention, while being able to manufacture easily, generation | occurrence | production of the crack and peeling by a thermal stress can be suppressed.

  Hereinafter, an embodiment embodying a semiconductor device and a method for manufacturing the semiconductor device of the present invention will be described with reference to FIGS. 1 to 3 schematically show the semiconductor device. For the sake of illustration, the width, length, and thickness of each part are exaggerated for easy understanding. The ratio of dimensions is different from the actual ratio.

  As shown in FIG. 2, the semiconductor device 10 is configured by joining a semiconductor element 12 and a heat sink 13 as a heat dissipation device to a circuit board 11. In the circuit board 11, a metal circuit 15 is bonded to one surface 14a (front surface) of the ceramic substrate (insulating substrate) 14, and a metal plate 16 is bonded to the other surface 14b (back surface) facing away from the one surface 14a in the ceramic substrate 14. Configured. As shown in FIG. 3, the ceramic substrate 14 and the metal plate 16 in the circuit board 11 are formed in a square shape in plan view. Note that FIG. 3 does not show the semiconductor element 12 and the metal circuit 15 in the semiconductor device 10 for easy understanding. As shown in FIGS. 1 and 2, the semiconductor element 12 has a rectangular shape in plan view and is bonded to the metal circuit 15 via the solder layer H. The semiconductor element 12 is connected to the one surface 14 a of the ceramic substrate 14 via the metal circuit 15. Are thermally coupled.

  As the semiconductor element 12, for example, an insulated gate bipolar transistor (IGBT), a MOSFET, or a diode is used, and a plurality of semiconductor elements 12 are bonded to the circuit board 11. Further, as shown in FIG. 2, the metal plate 16 that is the other surface 14 b of the ceramic substrate 14 functions as a metal layer that joins the ceramic substrate 14 and the heat sink 13. The semiconductor element 12 and the heat sink 13 are thermally coupled via the circuit board 11.

  In the circuit board 11, the ceramic substrate 14 is formed of, for example, aluminum nitride, alumina, silicon nitride, or the like. The metal circuit 15 and the metal plate 16 are made of aluminum. The heat sink 13 is made of aluminum. Aluminum means pure aluminum or an aluminum alloy. Further, as the high thermal conductivity material other than aluminum, the metal circuit 15, the metal plate 16, and the heat sink 13 may be formed of, for example, copper or copper alloy. The heat sink 13 is formed of the same metal material in accordance with the material for forming the metal plate 16 in the circuit board 11, and the metal plate 16 and the heat sink 13 have the same linear expansion coefficient. Inside the heat sink 13, a coolant channel 13a through which a cooling medium (for example, cooling water) flows is formed.

Next, the convex part 20 provided in the heat sink 13 is demonstrated in detail.
As shown in FIG. 2, a convex portion 20 is formed on the upper surface 13b as one surface of the heat sink 13 so as to stand upright from the upper surface 13b. The convex portion 20 is formed by pressing the upper surface 13 b of the heat sink 13. As shown in FIG. 2 and FIG. 3, a joint surface 20 a is formed at the tip of the convex portion 20 so that the planar shape is a square shape and a smooth surface. The planar shape of the joining surface 20a is similar to the planar shape of the metal plate 16. Moreover, the area of the joining surface 20a is smaller than the area of the lower surface 16a as a surface to which the joining surface 20a is joined in the metal plate 16.

  The heat sink 13 and the metal plate 16 on the circuit board 11 are directly joined by brazing the joining surface 20a to the lower surface 16a of the metal plate 16, and the circuit board 11 and the heat sink 13 are thermally coupled. Yes. The entire joining surface 20 a is joined to the lower surface 16 a of the metal plate 16. The joining surface 20a is joined to the lower surface 16a of the metal plate 16 so as to be within the range of the metal plate 16 (lower surface 16a). For this reason, a peripheral edge portion 16b extending at a constant width over the entire circumference of the metal plate 16 is present at a position outside the edge of the joint surface 20a. Therefore, the bonding surface 20a is not bonded to the entire lower surface 16a of the metal plate 16, but is bonded to the metal plate 16 in a state of being disposed at a position farther inward than the peripheral edge 16c of the metal plate 16. Has been.

  In addition, in the said peripheral part 16b, the area of the joining surface 20a is set so that the length (henceforth the width W of the peripheral part 16b) to the direction orthogonal to the circumferential direction of the metal plate 16 may become a predetermined value. That is, the size of the convex portion 20 is set. This is because if the area of the joint surface 20a becomes too small and the width W of the peripheral edge portion 16b becomes too long, the heat conduction efficiency to the heat sink 13 via the convex portion 20 is not preferable. Further, if the area of the joint surface 20a becomes too large and the width W of the peripheral edge portion 16b becomes too short, the stress relaxation function described below cannot be sufficiently exhibited, which is not preferable.

  A stress relaxation space S is formed between the lower surface 16 a of the metal plate 16 and the upper surface 13 b of the heat sink 13. By forming this stress relaxation space S, when the metal plate 16 is thermally expanded, deformation at the peripheral edge portion 16b of the metal plate 16 is allowed.

Next, a method for manufacturing the semiconductor device 10 of this embodiment will be described.
As the circuit board 11 to be joined to the heat sink 13, a commercially available board in which a metal circuit 15 and a metal plate 16 are joined in advance to a ceramic substrate 14 is used.

  First, the convex portion 20 is formed on the upper surface 13b of the heat sink 13 by pressing, and the joining surface 20a is formed in a smooth surface at the tip of the convex portion 20. Next, the heat sink 13, the circuit board 11, and the brazing material are placed so that an aluminum brazing material (not shown) is interposed between the joint surface 20 a of the convex portion 20 and the lower surface 16 a of the metal plate 16. Arrange in a stack. At this time, the joining surface 20a is located inside the peripheral edge 16c of the metal plate 16, and the peripheral edge portion 16b is formed with a constant width around the convex portion 20 (joining surface 20a) on the lower surface 16a of the metal plate 16. The heat sink 13 and the circuit board 11 are laminated.

  Then, the laminate of the heat sink 13, the brazing material, and the circuit board 11 is heated. Note that brazing is performed in a heating apparatus adjusted to an inert gas atmosphere or a reducing gas atmosphere. Moreover, a reflow furnace etc. are used as a heating apparatus. Brazing is performed by heating to a temperature equal to or higher than the melting temperature of the brazing material to melt the brazing material, and then cooling the molten brazing material below the melting temperature to solidify. The heat sink 13 (convex portion 20) and the circuit board 11 (metal plate 16) are integrated by joining the entire joint surface 20a of the convex portion 20 to the lower surface 16a of the metal plate 16 with a brazing material. As a result, the circuit board 11 and the heat sink 13 are bonded to manufacture the semiconductor device 10.

  Now, the semiconductor device 10 configured as described above is applied to driving of an in-vehicle electric motor, for example, thereby controlling electric power supplied to the in-vehicle electric motor according to the driving state of the vehicle. The heat generated from the semiconductor element 12 in the semiconductor device 10 is conducted to the heat sink 13 through the metal circuit 15, the ceramic substrate 14, and the metal plate 16. When the heat generated from the semiconductor element 12 is conducted to the heat sink 13, the heat sink 13 in addition to the circuit board 11 becomes high temperature and thermally expands. On the other hand, when the heat generation from the semiconductor element 12 is stopped, the temperature of the circuit board 11 and the heat sink 13 is lowered and the heat shrinks. During thermal expansion and contraction, thermal stress is generated in the semiconductor device 10 due to the difference in linear expansion coefficient between the heat sink 13 and the ceramic substrate 14.

  However, in the semiconductor device 10 of this embodiment, since the metal plate 16 and the heat sink 13 are formed of the same material, the linear expansion coefficients of the metal plate 16 and the convex portion 20 are the same. Further, the joining surface 20 a is not joined over the entire lower surface 16 a of the metal plate 16, but is joined to the inner side of the peripheral edge 16 c of the metal plate 16. Between these, a stress relaxation space S is formed. For this reason, the peripheral edge portion 16b is allowed to deform toward the stress relaxation space S, and the thermal stress is relaxed as compared with the case where the bonding surface 20a is also bonded to the peripheral edge portion 16b of the metal plate 16.

  Further, since the ceramic substrate 14 and the metal plate 16 have different linear expansion coefficients, thermal stress acts between the ceramic substrate 14 and the metal plate 16. Here, the joining surface 20a is joined in a state of being disposed inside the peripheral edge 16c of the metal plate 16. That is, the joining surface 20a is joined to avoid the peripheral edge portion 16b where the thermal stress concentrates on the metal plate 16. For this reason, compared with the case where the joining surface 20a is joined also to the peripheral part 16b of the metal plate 16, the thermal stress in the joined part of the ceramic substrate 14 and the metal plate 16 is relieved.

  Further, the heat generated from the semiconductor element 12 is conducted to the heat sink 13 through the metal circuit 15, the ceramic substrate 14, the metal plate 16, and the convex portion 20. The heat conducted to the heat sink 13 is conducted to the cooling medium flowing through the refrigerant flow path 13a in the heat sink 13 and taken away. That is, since the heat sink 13 is forcibly cooled by the cooling medium flowing through the refrigerant flow path 13a, the heat generated by the semiconductor element 12 is efficiently removed. As a result, the semiconductor element 12 is coupled to the circuit board 11 (bonding). From the side).

  In the semiconductor device 10, the bonding surface 20 a of the convex portion 20 is located via the circuit board 11 at a position directly below the semiconductor element 12. The entire joining surface 20 a is joined to the lower surface 16 a of the metal plate 16. Moreover, even if it is the structure joined in the state arrange | positioned inside the periphery 16c of the metal plate 16 from the joining surface 20a, the width | variety of the peripheral part 16b from which the joining surface 20a becomes non-joining in the metal plate 16 becomes long. The size of the joint surface 20a is set so that it does not pass. For this reason, even if it provides the structure which relieves a thermal stress, the thermal conductivity from the semiconductor element 12 to the heat sink 13 does not fall extremely.

According to the above embodiment, the following effects can be obtained.
(1) The convex portion 20 is formed on the heat sink 13, the joint surface 20 a to the metal plate 16 (lower surface 16 a) is provided at the tip of the convex portion 20, and the area of the joint surface 20 a is smaller than the area of the metal plate 16. did. A stress relaxation space S is formed between the lower surface 16 a of the peripheral edge portion 16 b of the metal plate 16 and the upper surface 13 b of the heat sink 13. For this reason, deformation of the metal plate 16 subjected to thermal stress is allowed by the stress relaxation space S, and the thermal stress is relaxed compared to the case where the bonding surface 20a is bonded to the entire lower surface 16a of the metal plate 16.

  Further, since the joint surface 20a is not joined to the peripheral edge portion 16b where the thermal stress acts intensively in the metal plate 16, the metal plate is compared with the case where the joint surface 20a is joined to the entire surface of the metal plate 16. The amount of deformation due to thermal expansion and contraction on the 16 side is suppressed, and the thermal stress at the joint between the ceramic substrate 14 and the metal plate 16 is relaxed. As a result, it is possible to suppress the occurrence of cracks or peeling at the joint between the ceramic substrate 14 and the metal plate 16. And the convex part 20 provided in order to relieve | moderate a thermal stress is formed by processing the upper surface 13b of the heat sink 13. FIG. For this reason, in order to relieve thermal stress, the semiconductor device 10 can be easily manufactured as compared with the case where the metal plate 16 having a small thickness and a small size is etched.

  (2) The semiconductor device 10 is only formed with the protrusions 20 on the heat sink 13 to alleviate thermal stress. In the semiconductor device 10, the circuit board 11 is bonded to the bonding surface 20a without processing or processing the commercially available circuit board 11 and without using another member for thermal stress relaxation. Thermal stress can be alleviated by simply doing. Therefore, the semiconductor device 10 that can relieve the thermal stress can be easily manufactured.

  (3) The entire joining surface 20 a is joined to the lower surface 16 a of the metal plate 16. For this reason, the heat generated from the semiconductor element 12 can be efficiently conducted to the convex portion 20 via the metal plate 16.

  (4) The material for forming the convex portion 20 (heat sink 13) and the material for forming the metal plate 16 in the circuit board 11 are the same. For this reason, compared with the case where the convex part 20 and the metal plate 16 are formed with different materials, it is suppressed that the interface which inhibits heat conduction is formed between both, and the metal plate 16 and the convex part 20 The thermal conductivity between them can be increased.

  (5) The convex portion 20 is formed by pressing the heat sink 13. For this reason, compared with the case where the convex part 20 is formed by etching the metal plate 16 and the heat sink 13, for example, the formation of the convex part 20 can be simplified, and the manufacturing of the semiconductor device 10 can be simplified. .

In addition, you may change the said embodiment as follows.
O As shown to Fig.4 (a) and (b), you may form several recessed part 20b in the front-end | tip of the convex part 20. As shown in FIG. If comprised in this way, when the thermal stress generate | occur | produces in the semiconductor device 10, the deformation | transformation of the convex part 20 will be accept | permitted by the recessed part 20b, and a thermal stress will be relieved.

  As shown in FIGS. 5A and 5B, a plurality of groove portions 20 c may be formed at the tip of the convex portion 20. If comprised in this way, when the thermal stress generate | occur | produces in the semiconductor device 10, the deformation | transformation of the convex part 20 will be accept | permitted by the groove part 20c, and a thermal stress will be relieved.

The convex portion 20 may be formed by etching the upper surface 13b (one surface) of the heat sink 13.
The metal plate 16 and the heat sink 13 may be formed of the same material, not the same material. For example, the metal plate 16 is formed of pure aluminum, and the heat sink 13 (projection 20) is formed of an aluminum alloy. May be.

  The heat sink 13 may be a forced-cooling type cooler, and the cooling medium flowing through the heat sink 13 is not limited to water, and may be other liquids or gases such as air. Further, it may be a boiling cooling type cooler.

  ○ Not only the configuration in which two metal circuits 15 are formed on the circuit board 11, but also one or three or more metal circuits 15 are formed, and one or three or more semiconductor elements 12 are formed on the metal circuit 15. It is good also as a joined structure.

The semiconductor device 10 may be applied not only to in-vehicle use but also to other uses.
Next, the technical idea that can be grasped from the above embodiment and other examples will be described below.
(1) A stress relaxation space is formed between a peripheral portion located outside the joint surface in the metal layer and a surface facing the peripheral portion in the heat dissipation device. The semiconductor device as described in any one.

FIG. 3 is a plan view showing the semiconductor device of the embodiment. AA sectional view taken on the line AA of FIG. The top view which shows the circuit board and convex part in a semiconductor device. (A) is a top view which shows another example of a convex part, (b) is the 4b-4b sectional view taken on the line which shows a convex part. (A) is a top view which shows another example of a convex part, (b) is 5b-5b sectional drawing which shows a convex part. Sectional drawing which shows the semiconductor module of background art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Semiconductor device, 12 ... Semiconductor element, 13 ... Heat sink as heat dissipation device, 14 ... Ceramic substrate, 14a ... One side, 14b ... Other side, 16 ... Metal plate as metal layer, 16c ... Periphery, 20 ... Convex part 20a: Joint surface.

Claims (6)

A semiconductor device in which a semiconductor element is thermally coupled to one surface of a ceramic substrate and a heat dissipation device is thermally coupled to the other surface via a metal layer,
The heat radiating device is provided with a convex portion having a joining surface having a smaller area than the metal layer at the tip, and the joining surface is disposed on the inner side of the periphery of the metal layer and thermally coupled to the metal layer. A semiconductor device.   The semiconductor device according to claim 1, wherein the entire bonding surface is thermally coupled to the metal layer.   The semiconductor device according to claim 1, wherein the joining surface is directly brazed to the metal layer.   The semiconductor device according to claim 1, wherein the convex portion and the metal layer are formed of a similar metal material. A semiconductor device manufacturing method in which a semiconductor element is thermally coupled to one surface of a ceramic substrate and a heat dissipation device is thermally coupled to the other surface via a metal layer,
The heat radiating device is formed with a convex portion having a joint surface having a smaller area than the metal layer at the tip, and the joint surface of the convex portion is disposed inside the periphery of the metal layer to heat the joint surface and the metal layer For manufacturing a semiconductor device to be coupled to each other.   The method of manufacturing a semiconductor device according to claim 5, wherein the convex portion is formed by pressing the heat dissipation device.

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