SEMICONDUCTOR DEVICE, AND MANUFACTURING METHOD THEREFOR

A power module includes an insulating substrate, a heat dissipation member, and an electrode plate. An IGBT and a diode are mounted on the insulating substrate. The heat dissipation member is bonded to the insulating substrate by first solder. The electrode plate is disposed so as to overlap at least a part of the semiconductor element. The main surface of the insulating substrate is curved so as to have a shape convex toward the heat dissipation member. The first solder is thicker at the edges than at the center in a plan view. The semiconductor element is bonded to the electrode plate by second solder.

TECHNICAL FIELD

The present disclosure relates to a semiconductor device and a manufacturing method therefor.

BACKGROUND ART

A so-called power module as a semiconductor device is becoming widespread in various products from industrial machines to home appliances and information terminals. A power module mounted on an electric vehicle is required to have high reliability. It is further required that the power module for an electric vehicle be high in operating temperature and high in efficiency. It is therefore required that the power module for an electric vehicle be in a package form applicable to a silicon-carbide semiconductor which is highly likely to become the mainstream in the future.

For example, in Japanese Patent Laying-Open No. 2016-058563 (PTL 1), the thickness and linear expansion coefficient of an encapsulant resin are adjusted to fall within appropriate numerical ranges. This causes an insulating substrate to curve so as to have a shape convex downward and thus prevents air from being caught in a heat dissipation grease portion between a heat dissipation member and the insulating substrate.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the configuration where the curved and inclined insulating substrate is bonded onto the base plate as disclosed in Japanese Patent Laying-Open No. 2016-058563, contact of a wire tool varies when the wiring for circuit formation is wire-bonded to the semiconductor element on the insulating substrate. That is, when a plurality of semiconductor elements are mounted on the insulating substrate, the inclination angle of the surface of each of the plurality of semiconductor element from the horizontal direction differs in a manner that depends on a location of the semiconductor element, for example. This makes it necessary to readjust the contact of the wire tool each time each of the plurality of semiconductor elements is wire-bonded. This may cause, when the adjustment is insufficient, the wire tool to damage the semiconductor element and make it difficult to wire-bond the wiring with high reliability.

The present disclosure has been made in view of the above-described problems.

It is therefore an object of the present disclosure to provide a semiconductor device with high reliability including a circuit stably connected to a semiconductor element mounted on an insulating substrate having a curved main surface, and a manufacturing method therefor.

Solution to Problem

A semiconductor device according to the present embodiment includes an insulating substrate, a heat dissipation member, and an electrode plate. A semiconductor element is mounted on the insulating substrate. The heat dissipation member is bonded to the insulating substrate by first solder. The electrode plate is disposed so as to overlap at least a part of the semiconductor element. A main surface of the insulating substrate is curved so as to have a shape convex toward the heat dissipation member. The first solder is thicker at the edges than at the center in a plan view. The semiconductor element is bonded to the electrode plate by second solder.

Under a manufacturing method for a semiconductor device according to the present embodiment, a heat dissipation member and an insulating substrate are bonded together by first solder. A semiconductor element is bonded to the insulating substrate. After the bonding with the first solder and the bonding the semiconductor element, an electrode plate overlapping at least a part of the semiconductor element is bonded to the semiconductor element by second solder. The insulating substrate is bonded to the heat dissipation member to cause a main surface of the insulating substrate to curve so as to have a shape convex toward the heat dissipation member. The first solder is formed thicker at the edges than at the center in a plan view.

Advantageous Effects of Invention

According to the present disclosure, it is possible to provide the semiconductor device with high reliability including a circuit stably connected to a semiconductor element mounted on an insulating substrate having a curved main surface, and the manufacturing method therefor.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a power module100as a semiconductor device according to the present embodiment will be described with reference to the drawings. For convenience of description, an X direction, a Y direction, and a Z direction are introduced.

First Embodiment

FIG.1is a schematic cross-sectional view of a configuration of a power module according to a first embodiment. With reference toFIG.1, power module100according to the present embodiment mainly includes an insulating substrate10, a heat dissipation member20, and an electrode plate30.

Insulating substrate10includes a base member11, a conductor layer12, and a conductor layer13. Base member11has, for example, a rectangular shape in a plan view and has a thickness along the Z direction. Base member11has one surface11A as an upper main surface in the Z direction and other surface11B on a side opposite from one surface11A, that is, a lower main surface in the Z direction. Conductor layer12is a thin plate-shaped conductor material, and at least one conductor layer12is bonded onto one surface11A. Conductor layer13is a thin plate-shaped conductor material, and at least one conductor layer13is bonded onto other surface11B.

A main surface of insulating substrate10means a surface extending along the XY plane of an object obtained by bonding thin conductor layer12and thin conductor layer13to one surface11A and other surface11B, respectively. Therefore, the main surface of insulating substrate10extends in substantially the same direction as one surface11A and other surface11B. Therefore, the main surface of insulating substrate10in its entirety, and one surface11A and other surface11B may be considered to be the same hereinafter.

An integrated gate bipolar transistor (IGBT)41and a diode42as semiconductor elements are mounted on conductor layer12of insulating substrate10. Such semiconductor elements are constructed in chip form. In general, as illustrated inFIG.1, IGBT41as a second semiconductor element is disposed outside relative to diode42as a first semiconductor element in the plan view. The configuration, however, is not limited to the above, and IGBT41may be disposed inside relative to diode42in the plan view.

Heat dissipation member20includes a base plate21and fins22. Base plate21is a plate-shaped member having a surface extending along the XY plane. Fins22are members extending in the Z direction from, for example, a lowermost surface of base plate21in the Z direction. The plurality of fins22extend downward in the Z direction from the lowermost surface of base plate21at intervals in the X direction and the Y direction. Note that fins22may be integrated with or separated from base plate21.

An uppermost surface, in the Z direction, of base plate21of heat dissipation member20is bonded to the lower main surface of insulating substrate10by first solder51. Insulating substrate10protrudes toward heat dissipation member20, that is, downward in the Z direction, and has the main surface curved so as to have a shape convex over a plurality of IGBTs41and diodes42. That is, insulating substrate10is curved a such that other surface11B of base member11has a convex shape as viewed from the outside, and one surface11A has a concave shape as viewed from the outside. The convex shape of insulating substrate10is single convex shape extending acrossFIG.1in the X direction, and the single convex shape causes all of the plurality of IGBTs41and diodes42to slightly incline from the horizontal direction. This makes the center of the lower main surface of insulating substrate10in the X direction inFIG.1closer to heat dissipation member20in the Z direction than the edges of the lower main surface in the X direction inFIG.1. This makes the center of first solder51in the plan view thicker in the Z direction than the edges of first solder51. That is, first solder51gradually increases in thickness from the center toward the edges in the plan view. In other words, the thickness of first solder51monotonously increases from the center toward the edges.

First solder51bonds with the whole surface of conductor layer13on other surface11B. The whole surface here is not limited to the complete whole surface, and includes, for example, a case where first solder layer51covers at least 95% of the surface area of conductor layer13.

Electrode plate30is disposed so as to overlap at least a part of IGBT41and diode42in the plan view. That is, for example, electrode plate30may overlap only a part of IGBT41in plan view, or may overlap all IGBT41. Electrode plate30is disposed above IGBT41and diode42in the Z direction at a distance from IGBT41and diode42. Electrode plate30illustrated inFIG.1has a planar shape whose surface extends along the XY plane. That is, the surface of electrode plate30illustrated inFIG.1extending along the XY plane has almost no curved portion. IGBT41and diode42are bonded to electrode plate30by second solder52. Here, main electrodes (not illustrated) formed in IGBT41and diode42are bonded to electrode plate30by second solder52. This forms a circuit including IGBT41, diode42, and electrode plate30. Further, IGBT41and diode42are bonded to conductor layer12of insulating substrate10by a conductive member59.

Power module100further includes a frame member60in an outer region in the plan view. Frame member60is disposed so as to surround insulating substrate10on which IGBT41and diode42are mounted at a distance from insulating substrate10in the X direction and the Y direction, for example. Furthermore, frame member60is disposed so as to surround base plate21that is at least a part of heat dissipation member20, and (at least a part of) a main body30A that is a part of electrode plate30, for example. Note that base plate21may be bonded to frame member60by an adhesive (not illustrated). Further, main body30A may be partially brought into contact with frame member60or embedded in frame member60. This causes electrode plate30to be disposed in frame member60so as to face insulating substrate10in the Z direction.

A signal electrode71is disposed inside frame member60. More specifically, signal electrode71is disposed so as to be partially embedded in frame member60. Signal electrode71includes a portion exposed outside frame member60, a portion embedded in frame member60, and a portion exposed from inside frame member60. Note that the portion of signal electrode71exposed from inside frame member60is embedded in encapsulant90as described later. Herein, as described above, the portion of signal electrode71inside frame member60that is embedded in encapsulant90but exposed from at least frame member60in the form of a final product may be expressed as “exposed from frame member60”. Among the portions, the portion of signal electrode71facing upward in the Z direction inside frame member60is electrically connected to IGBT41and diode42by a bonding wire81.

Further, main body30A of electrode plate30has a portion extending in the horizontal direction and facing IGBT41and diode42, and a portion bent from the portion extending in the horizontal direction and extending in the Z direction. Main body30A extends in the Z direction in a rightmost region in the X direction inFIG.1. Of the portion of main body30A extending in the Z direction and the portion bent from the portion extending in the Z direction and extending in the horizontal direction in the rightmost region in the X direction inFIG.1, the rightmost region inFIG.1is a main terminal-side edge33as a main terminal72. On the other hand, a leftmost edge in the X direction inFIG.1of the portion of main body30A extending in the horizontal direction is a semiconductor element-side edge34. Semiconductor element-side edge34is an edge on a side opposite from main terminal-side edge33. As described above, electrode plate30includes main terminal-side edge33and semiconductor element-side edge34.

Main terminal-side edge33has a first portion31extending in the Z direction and exposed outside frame member60and a second portion32embedded in frame member60. Second portion32includes a portion where main terminal72is bent. This causes electrode plate30to electrically connect the inside and the outside of frame member60in the plan view.

As described above, inFIG.1, the portion of electrode plate30extending in the horizontal direction, that is, along the XY plane, is integrated with main terminal72. This causes electrode plate30to electrically connect to main terminal72.

Note that signal electrode71and main body30A of electrode plate30including main terminal72may be made of a single lead frame divided into two.

The region that is surrounded by frame member60and base plate21and where insulating substrate10and the like are disposed is filled with encapsulant90. That is, IGBT41and diode42are encapsulated in encapsulant90as an encapsulant resin. First solder51is in contact with encapsulant90.

Next, materials, dimensions, and the like of each of the above-described members will be described.

Base member11that is a part of insulating substrate10is made of, for example, aluminum nitride. Alternatively, base member11may be made of, for example, either alumina or silicon nitride instead of aluminum nitride. As described above, base member11is preferably made of a ceramic material. The material, however, is not limited to the above, and base member11may be made of either a glass epoxy resin or a metal base resin. Alternatively, base member11may be low temperature co-fired ceramics (LTCC) that is a low temperature fired substrate. Base member11has dimensions of, for example, 65 mm*65 mm*a thickness of 0.64 mm.

Conductor layers12,13are made of, for example, copper. Alternatively, conductor layers12,13may be made of, for example, either nickel or nickel-plated aluminum instead of copper. Each of a plurality of conductor layers12obtained by division has dimensions of, for example, 30 mm*61 mm*a thickness of 0.4 mm. Conductor layer13has dimensions of, for example, 61 mm*61 mm*a thickness of 0.4 mm.

Base plate21and fins22constituting heat dissipation member20are made of, for example, aluminum. The material, however, is not limited to the above, and heat dissipation member20may be made of an aluminum alloy material such as a so-called A6063. Alternatively, heat dissipation member20may be made of either copper or a copper alloy. The surface of each material constituting heat dissipation member20may be plated with nickel or the like.

Note that heat dissipation member20illustrated inFIG.1includes base plate21and fins22. However, when the cooling capacity of base plate21is sufficiently high, heat dissipation member20may be constituted of only base plate21without fins22. Further, base plate21of heat dissipation member20may include either an air-cooling fan or a heat sink, and in this case as well, may or may not have fins22.

Main body30A of electrode plate30and signal electrode71are preferably made of a metal material such as copper.

The chips of IGBT41and diode42are made of silicon. Note that, instead of diode42, any one of a so-called integrated circuit (IC) chip or a chip on which a so-called metal-oxide-semiconductor field effect transistor (MOSFET) is mounted may be used. The chip of IGBT41has dimensions of, for example, 13 mm*13 mm*a thickness of 0.2 mm. The chip of diode42has dimensions of, for example, 13 mm* 10 mm*a thickness of 0.2 mm.

InFIG.1, IGBT41and diode42are arranged in two pairs, that is, a so-called 2in1 module configuration. The configuration, however, is not limited to the above, and for example, IGBT41and diode42may be arranged in one pair, that is, a so-called 1in1 module configuration. Alternatively, for example, IGBT41and diode42may be arranged in six pairs, that is, a so-called 6in1 module configuration. Alternatively, instead of the above-described configurations, for example, a discrete component on which only one power semiconductor element is mounted may be used.

IGBT41includes signal electrodes provided for a gate signal, a temperature sensor, and the like (not illustrated). Bonding wires are used to connect such signal electrodes to frame member60. For this reason, as illustrated inFIG.1, IGBT41is generally disposed on the outer side adjacent to frame member60in the plan view, and diode42is generally disposed on the inner side.

Here, the portion of first solder51that overlaps the center of insulating substrate10in the plan view is smaller in thickness and is thus significantly low in thermal resistance. From this viewpoint, it may be preferable that IGBT41that is larger in amount of heat generated than diode42be disposed at the center of insulating substrate10. However, even with IGBT41disposed on the outer side in the plan view as illustrated inFIG.1, when heat of IGBT41is conducted to insulating substrate10, the center of insulating substrate10becomes highest in temperature due to thermal interference. Therefore, IGBT41may be disposed on the outer side relative to diode42. It is preferable that the center of insulating substrate10where the temperature becomes highest due to thermal interference and the center, that is, the tip, of the convex shape formed by insulating substrate10curved downward substantially coincide with each other.

First solder51has a thickness of, for example, 0.2 mm at the center in the X direction inFIG.1. On the other hand, first solder51has a thickness of, for example, 0.4 mm at the edges in the X direction inFIG.1. The thickness of second solder52illustrated inFIG.1varies in a manner that depends on the place where second solder52is disposed. That is, the maximum thickness of second solder52between electrode plate30and diode42is larger than the maximum thickness of second solder52between electrode plate30and IGBT41.

First solder51and second solder52are preferably made of, for example, so-called 96Sn—3.5Ag—0.5Cu. That is, such solders are made of a material containing 96.5 mass % of tin, 3.5 mass % of silver, and 0.5 mass % of copper. The material, however, is not limited to the above. First solder51and second solder52may be made of a material containing 98.5 mass % of tin, 1 mass % of silver, and 0.5 mass % of copper. First solder51and second solder52may be made of a material containing 96 mass % of tin, 3 mass % of antimony, and 1 mass % of silver.

Conductive member59may be made of a solder material that is the same in composition as first solder51and second solder52. Conductive member59, however, is not limited to the solder material, and may be made of another type of conductive material. For example, conductive member59may be a so-called Cu—Sn paste containing a dispersed copper powder and isothermally solidified. The Cu—Sn paste can have high heat resistance. Alternatively, conductive member59may be a so-called nanosilver paste containing low temperature fired nanosilver particles used for bonding.

Frame member60is made of a polyphenylene sulfide (PPS) resin. The material of frame member60, however, is not limited to the above, and frame member60may be made of a liquid crystal polymer resin, that is, an LCP resin. The outermost portion of frame member60has dimensions of, for example, 75 mm*75 mm*a thickness of 8 mm. The thickness of 8 mm is a dimension in the Z direction.

In frame member60illustrated inFIG.1, an inner wall portion at the position where main terminal72is embedded in the Z direction, that is, the thickness direction and the position where base plate21is disposed is positioned on the outer side relative to an inner wall portion at other positions. An outer wall of base plate21is uniform in position in the X direction (Y direction) over a whole section in the thickness direction. As described above, in frame member60, a side wall at at least either the position where main terminal72is embedded in the thickness direction or the position where base plate21is disposed may be thinner than the other position, that is, the center in the thickness direction.

Bonding wire81is preferably a thin aluminum wire. Bonding wire81, however, is not limited to the above and may be any one of a thin copper wire, a thin wire of copper coated with aluminum, or a gold wire. It is preferable that a diameter of a cross section of bonding wire81taken along a plane orthogonal to the extending direction of bonding wire81be, for example, 0.15 mm.

As encapsulant90, a silica filler-containing epoxy resin is used, for example. Encapsulant90is not limited to the above, and a silicone gel or the like may be used as encapsulant90.

FIG.2is a schematic cross-sectional view of a modification of the configuration of the power module according to the first embodiment. With reference toFIG.2, a power module100according to the modification of the present embodiment is basically the same in configuration as power module100illustrated inFIG.1. Therefore, inFIG.2, the same components as the components illustrated inFIG.1are denoted by the same reference numerals, and no description will be given below of such components as long as their functions and the like are the same. The same applies to the following power modules unless otherwise specified.

Note that, in power module100illustrated inFIG.2, the main surface of main body30A of electrode plate30facing insulating substrate10is curved along the shape of insulating substrate10convex toward heat dissipation member20. That is, on insulating substrate10, the main surface of electrode plate30is curved so as to have a shape convex toward heat dissipation member20like insulating substrate10. As with insulating substrate10, electrode plate30is curved such that the lower surface has a convex shape as viewed from the outside and the upper surface has a concave shape as viewed from the outside. In this respect, electrode plate30illustrated inFIG.2is different from electrode plate30illustrated inFIG.1in that the surface extending along the XY plane has almost no curved portion.

FIG.3is a schematic cross-sectional view of a second modification of the configuration of the power module according to the first embodiment.FIG.4is a schematic cross-sectional view of a third modification of the configuration of the power module according to the first embodiment. With reference toFIG.3, the configuration is basically the same as the configuration illustrated inFIG.1, but is different from the configuration illustrated inFIG.1in that conductor layer12on one surface11A is formed thicker than conductor layer13on other surface11B. Likewise, with reference toFIG.4, the configuration is basically the same as the configuration illustrated inFIG.2, but is different from the configuration illustrated inFIG.2in that conductor layer12on one surface11A is formed thicker than conductor layer13on other surface11B.

When conductor layer12on one surface11A is formed thicker than conductor layer13on other surface11B, insulating substrate10is curved so as to have a shape convex toward heat dissipation member20.

Further, a first region on one surface11A where conductor layer12is not bonded and a second region on other surface11B where conductor layer13is not bonded are considered. When the first region is larger in area than the second region, insulating substrate10is curved so as to have a shape convex toward heat dissipation member20. Furthermore, for example, when conductor layer12on one surface11A is formed thicker than conductor layer13on other surface11B, insulating substrate10is curved so as to have a shape convex toward heat dissipation member20even when the first region and the second region are the same in area.

FIG.5is a schematic cross-sectional view of a fourth modification of the configuration of the power module according to the first embodiment.FIG.6is a schematic cross-sectional view of a fifth modification of the configuration of the power module according to the first embodiment. With reference toFIG.5, the configuration is basically the same as the configuration illustrated inFIG.1, but other conductor layer12ais disposed between conductor layer12on one surface11A, and IGBT41and diode42. Other conductor layer12ais bonded by fourth solder59aso as to overlap conductor layer12. Likewise, with reference toFIG.6, the configuration is basically the same as the configuration illustrated inFIG.2, but other conductor layer12ais disposed between conductor layer12on one surface11A, and IGBT41and diode42. Other conductor layer12ais bonded by fourth solder59aso as to overlap conductor layer12. In this respect,FIGS.5and6are different fromFIGS.1and2in which other conductor layer12aand fourth solder59aare not provided. This makes, as illustrated inFIGS.5and6, as inFIGS.3and4, the conductor layer on one surface11A of base member11substantially thicker than conductor layer13on other surface11B. Therefore, as illustrated inFIGS.5and6, as inFIGS.3and4, insulating substrate10is curved so as to have a shape convex toward heat dissipation member20.

Next, a manufacturing method for power module100according to the present embodiment will be described with reference toFIGS.7to13. Note that, inFIGS.7to10, a manufacturing method for power module100illustrated inFIG.2will be described.

FIG.7is a schematic cross-sectional view of the power module according to the first embodiment illustrated inFIG.2, illustrating a first process of the manufacturing method for the power module. With reference toFIG.7, first, insulating substrate10, heat dissipation member20, the semiconductor elements, that is, IGBT41, diode42, and the like, first solder51, and conductive member59are prepared.

Insulating substrate10includes base member11. At least one conductor layer12is bonded onto one surface11A of base member11, and at least one conductor layer13is bonded onto other surface11B on a side opposite from one surface11A. The first region on one surface11A where conductor layer12is not bonded and the second region on other surface11B where conductor layer13is not bonded are considered. A difference in area between the first region and the second region is adjusted. This causes the direction and degree of the curvature of the convex shape of insulating substrate10after each member is bonded by solder to be adjusted. Therefore, although insulating substrate10illustrated inFIG.7looks like insulating substrate10is not curved, insulating substrate10is actually slightly curved at this point of time.

Each of the above-described members is positioned to constitute power module100illustrated inFIGS.1and2. That is, plate-shaped first solder51is disposed between heat dissipation member20and conductor layer13of insulating substrate10. Plate-shaped conductive member59is disposed between conductor layer12of insulating substrate10, and IGBT41and diode42. Such members are each positioned ready to be bonded.

FIG.8is a schematic cross-sectional view of the power module according to the first embodiment illustrated inFIG.2, illustrating a second process of the manufacturing method for the power module. With reference toFIG.8, in the state illustrated in FIG.

7, the above-described members are bonded by first solder51and conductive member59using a reflow device. This causes all the above-described members to simultaneously bonded. That is, heat dissipation member20and insulating substrate10are bonded by first solder51. IGBT41and diode42are bonded to insulating substrate10. As described above, the direction and degree of the curvature of the convex shape of insulating substrate10after bonding are determined by conductor layers12,13of insulating substrate10. Therefore, insulating substrate10is bonded to heat dissipation member20to cause the main surface of insulating substrate10to curve so as to have a shape convex toward heat dissipation member20. In order for insulating substrate10to have the convex shape, first solder51is formed thicker at the edges than at the center in the plan view.

As described above, the bonding between heat dissipation member20and insulating substrate10by first solder51and the bonding between insulating substrate10, and IGBT41and the like by conductive member59may be performed at the same time. The bonding, however, may be performed at different timings rather than at the same time. Note that, in this case, it is preferable that heat dissipation member20and insulating substrate10be first bonded together by first solder51, and then insulating substrate10, and IGBT41and the like be bonded together by conductive member59. If insulating substrate10, and IGBT41and the like are first bonded together by conductive member59, and then insulating substrate10and heat dissipation member20are bonded together, conductive member59under IGBT41may be melted again by heat generated when insulating substrate10and heat dissipation member20are bonded together. When conductive member59is melted again, IGBT41and the like may be displaced relative to insulating substrate10due to residual stress applied to a bonding wire (not illustrated) used for forming a circuit in IGBT41. From the viewpoint of preventing such a problem, the bonding is preferably performed in the above-described order.

As described above, the following processes are performed after the process of bonding, with first solder51, heat dissipation member20and insulating substrate10together and the process of bonding IGBT41and diode42to insulating substrate10with conductive member59. Second solder52and frame member60are prepared.

Signal electrode71and electrode plate30are partially embedded in frame member60. On the left side of frame member60inFIG.8, signal electrode71is insert-molded into frame member60so as to be partially exposed from frame member60. The second portion of main terminal-side edge33that is a part of main body30A of electrode plate30, the bent portion, and the rightmost region inFIG.8of the portion of main body30A along the XY plane are embedded in the right side of frame member60inFIG.8. Electrode plate30is insert-molded so that such regions are embedded. This causes first portion31of main terminal-side edge33as main terminal72to be exposed upward from frame member60, and causes the portion of electrode plate30along the XY plane and semiconductor element-side edge34to be exposed in the region surrounded by frame member60.

Plate-shaped second solder52is disposed on IGBT41and diode42. The portion of electrode plate30along the XY plane is disposed on second solder52. Note that, when the main surface of electrode plate30is curved along the convex shape of insulating substrate10as illustrated inFIG.2, it is preferable that electrode plate30be curved in advance by a publicly-known method. Alternatively, a pre-curved electrode plate30may be purchased. This causes second solder52, electrode plate30, and frame member60to be positioned ready to be bonded.

FIG.9is a schematic cross-sectional view of the power module according to the first embodiment illustrated inFIG.2, illustrating a third process of the manufacturing method for the power module. With reference toFIG.9, frame member60in which second portion32of main terminal-side edge33is embedded is disposed so as to surround insulating substrate10at a distance from insulating substrate10. Heating using a reflow furnace causes second solder52to bond electrode plate30to IGBT41and diode42. That is, electrode plate30is bonded to IGBT41and diode42by second solder52so as to overlap at least a part of IGBT41and diode42. More specifically, in this process, the main electrodes (not illustrated) of IGBT41and diode42are bonded, by second solder52, to the portion of electrode plate30extending along the XY plane.

FIG.10is a schematic cross-sectional view of the power module according to the first embodiment, illustrating a fourth process of the manufacturing method for the power module. With reference toFIG.10, the portion of signal electrode71exposed to the inside of frame member60is electrically connected to the main electrode (not illustrated) or the like of IGBT21by bonding wire81. Subsequently, liquid encapsulant90is injected into the region surrounded by frame member60and heat dissipation member20. It is heated, for example, at 150° C. for 1.5 hours. This cures encapsulant90. As a result, the members surrounded by frame member60are electrically insulated from each other.

Next, the manufacturing method for power module100illustrated inFIG.1will be described with reference toFIGS.11to13.FIG.11is a schematic cross-sectional view of the power module according to the first embodiment illustrated inFIG.1, illustrating a first process of the manufacturing method for the power module.FIG.12is a schematic cross-sectional view of the power module according to the first embodiment illustrated inFIG.1, illustrating a second process of the manufacturing method for the power module.FIG.13is a schematic cross-sectional view of the power module according to the first embodiment illustrated inFIG.1, illustrating a third process of the manufacturing method for the power module. With reference toFIGS.11to13, even for the example where main body30A of electrode plate30has almost no curved portion as illustrated inFIG.1, the manufacturing method is basically the same as for the example where main body30A of electrode plate30has a shape along the convex shape as illustrated inFIGS.7to10. First, as inFIG.7, each member is prepared and positioned. Next, as illustrated inFIG.11, processing basically the same as illustrated inFIG.8is performed. Note that, as illustrated inFIG.11, main body30A of electrode plate30has almost no curved portion. Further, as illustrated inFIG.11, from the viewpoint of bonding plate-shaped electrode plate30and the semiconductor element together, second solder52adjacent to the center is made larger in thickness than second solder52adjacent to the edges. Next, as illustrated inFIG.12, processing basically the same as illustrated inFIG.9is performed. Next, as inFIG.13, processing basically the same as illustrated inFIG.10is performed.

Note that, under the manufacturing method illustrated inFIGS.7to10andFIGS.11to13, as illustrated inFIGS.3and4, conductor layer12on one surface11A may be formed thicker than conductor layer13on other surface11B. Alternatively, under the manufacturing method illustrated inFIGS.7to10andFIGS.11to13, as illustrated inFIGS.5and6, other conductor layer12amay be bonded to between conductor layer12on one surface11A, and IGBT41and diode42so as to overlap conductor layer12. Accordingly, the curvature of the convex shape is adjusted such that insulating substrate10is curved so as to have a shape convex toward heat dissipation member20.

Next, a description will be given of the actions and effects of the present embodiment together with the background and problem of the present embodiment.

There is a strong demand for making power modules for automobile use compact and lightweight. For this reason, in such a power module for automobile use, it is necessary to arrange semiconductor elements to which a high voltage and a large current can be applied at high density. As a result, thermal interference between the plurality of semiconductor elements thus arranged may become a problem, and thus efficient heat dissipation to a heat dissipation member is an important design requirement. Further, the power module is mounted on transportation equipment, so that high reliability is required from the viewpoint of stably transporting passengers and the like.

A base plate and fins constituting the heat dissipation member are often made of copper or aluminum having high thermal conductivity. Copper and aluminum, however, are largely different in thermal expansion coefficient from aluminum nitride of which a base member of an insulating substrate is made and silicon of which a semiconductor element is made. Power modules for automobile use and electric-train use generate a large amount of heat, so that it is necessary to bond the heat dissipation member and the insulating substrate together with solder that is higher in thermal conductivity than heat dissipation grease. For this reason, large thermal stress is applied to a joint between the heat dissipation member and the insulating substrate and may cause a crack in the joint in evaluation of long-term reliability such as temperature cycle resistance.

Further, bonding the insulating substrate to the heat dissipation member with solder may unintentionally cause the insulating substrate to curve or incline relative to the horizontal direction. In a case where wire bonding is performed for forming a circuit on the insulating substrate, the IGBT, or the like having such an inclination or the like, contact of a wire tool varies for each place where the wire bonding is to be performed. For this reason, it is necessary to adjust the contact of the wire tool for each of the plurality of semiconductor elements, that is, each time the wire bonding is performed at different positions having different inclinations. When this adjustment is insufficient, the wire tool may damage the semiconductor element to make it difficult to wire-bond wiring with high reliability.

Therefore, power module100as the semiconductor device according to the present embodiment includes insulating substrate10, heat dissipation member20, and electrode plate30. IGBT41and diode42as semiconductor elements are mounted on insulating substrate10. Heat dissipation member20is bonded to insulating substrate10by first solder51. Electrode plate30is disposed so as to overlap at least a part of the semiconductor elements. The main surface of insulating substrate10is curved so as to have a shape convex toward heat dissipation member20and extending over the plurality of semiconductor elements. First solder51is thicker at the edges than at the center in the plan view. Each semiconductor element is bonded to electrode plate30by second solder52.

Heat dissipation member20is bonded to insulating substrate10by, for example, first solder51high in thermal conductivity than heat dissipation grease. Therefore, a large amount of heat generated by the semiconductor elements is dissipated from first solder51to heat dissipation member20with high efficiency.

The main surface of insulating substrate10is curved so as to have a shape convex toward heat dissipation member20, and first solder51is thicker at the edges than at the center. This makes it possible to first reduce concentration of thermal stress generated in the joint between insulating substrate10and heat dissipation member20by first solder51on the edges in the plan view. Although thermal strain on the edges of first solder51in the plan view increases, first solder51increases in thickness toward the edges due to the convex shape, so that the thermal strain on the edges can be reduced. This can make long-term reliability such as temperature cycle resistance higher, and specifically can curb the generation of cracks in first solder51. Second, first solder51is made thinner at the center where the temperature becomes highest due to thermal interference, so that the thermal resistance is reduced. This allows heat to be dissipated from first solder51to heat dissipation member20with high efficiency.

The semiconductor element is bonded to electrode plate30by second solder52. This eliminates the need of adjustment of the contact of the wire tool based on the inclination angle of insulating substrate10and the semiconductor element from the horizontal direction, which may occur when power module100is electrically connected to the outside by, for example, direct wire bonding to the semiconductor element. It is therefore possible to prevent the wire tool from damaging the semiconductor element due to the adjustment of the contact of the wire tool. This makes the reliability of electrical connection between the semiconductor element inclined from the horizontal direction due to the curvature of insulating substrate10and the outside of power module100high as compared with a case where the electrical connection is made by a bonding wire.

In power module100, insulating substrate10includes base member11. At least one conductor layer12is bonded onto one surface11A of base member11, and at least one conductor layer13is bonded onto other surface11B on a side opposite from one surface11A. First solder51bonds with the whole surface of conductor layer13on other surface11B. First solder51gradually increases in thickness from the center toward the edges in the plan view. Such a configuration may be employed and can produce the same actions and effects as described above.

It is preferable that power module100further include frame member60disposed so as to surround insulating substrate10at a distance from insulating substrate10.

In the present embodiment, the semiconductor element and electrode plate30are bonded together by second solder52. Therefore, for example, unlike bonding at room temperature by wire bonding, second solder52is heated and melted at the time of bonding. This heating may unintentionally cause insulating substrate10to curve. This makes insulating substrate10deformed more than expected to interfere with frame member60to generate stress in insulating substrate10, which may cause a corner of insulating substrate10to chip or crack.

Therefore, as described above, frame member60is disposed at a distance from insulating substrate10and the semiconductor element. This causes the space around insulating substrate10and first solder51in the plan view to be covered with encapsulant90made of a silica filler-containing epoxy resin or the like. Base member11of insulating substrate10and heat dissipation member20are largely different in thermal expansion coefficient from each other, and there is a possibility that first solder51will crack during the evaluation of the temperature cycle resistance of first solder51. Interposing encapsulant90between base member11and heat dissipation member20, however, can make differences in thermal expansion coefficient between base member11and encapsulant90and between heat dissipation member20and encapsulant90smaller than the above. This makes the possibility that first solder51will crack during the evaluation of long-term reliability such as temperature cycle resistance lower and makes the reliability of power module100higher.

In power module100described above, electrode plate30is disposed so as to face insulating substrate10in frame member60. The main surface of electrode plate30may be curved along the convex shape of insulating substrate10. This makes the thickness of second solder52bonding electrode plate30and the semiconductor element together uniform among the plurality of semiconductor elements. This allows electrode plate30and the semiconductor element to be reliably and stably bonded together by second solder52.

In power module100, the semiconductor element includes diode42as the first semiconductor element, and IGBT41as the second semiconductor element disposed adjacent to the frame member in the plan view relative to the first semiconductor element. The maximum thickness of second solder52between electrode plate30and the first semiconductor element may be larger than the maximum thickness of second solder52between electrode plate30and the second semiconductor element. For example, when electrode plate30has a planar main surface that is not curved along the convex shape of insulating substrate10and is not curved along the XY plane or the like, such a configuration is employed.

That is, for example, when the second semiconductor element becomes higher in temperature than the first semiconductor element, second solder52in contact with the second semiconductor element is thinner than second solder52in contact with the first semiconductor element. This can make the total thermal resistance from the semiconductor element to heat dissipation member20lower.

In power module100described above, electrode plate30includes main terminal-side edge33as main terminal72and semiconductor element-side edge34that is an edge on a side opposite from the main terminal-side edge. Main terminal-side edge33has first portion31exposed outside frame member60and second portion32embedded in the frame member. Such a configuration is preferable. As described above, in the present embodiment, electrode plate30is integrally and electrically connected with main terminal72. This can make the electrical connection structure between the semiconductor element and the outside of power module100simpler.

Power module100described above further includes encapsulant90as an encapsulant resin for encapsulating the semiconductor element. First solder51is in contact with encapsulant90. This causes the space around insulating substrate10and first solder51in the plan view to be covered with encapsulant90made of a silica filler-containing epoxy resin or the like. Base member11of insulating substrate10and heat dissipation member20are largely different in thermal expansion coefficient from each other, and there is a possibility that first solder51will crack during the evaluation of the temperature cycle resistance of first solder51. Interposing encapsulant90between base member11and heat dissipation member20, however, can make differences in thermal expansion coefficient between base member11and encapsulant90and between heat dissipation member20and encapsulant90smaller than the above. This makes the possibility that first solder51will crack during the evaluation of long-term reliability such as temperature cycle resistance lower and makes the reliability of power module100higher.

Under the manufacturing method for the semiconductor device, that is, power module100, according to the present embodiment, heat dissipation member20and insulating substrate10are bonded together by first solder51. IGBT41and diode42as semiconductor elements are bonded to insulating substrate10. After the process of bonding with first solder51and the process of bonding the semiconductor element, electrode plate30overlapping at least a part of the semiconductor element is bonded to the semiconductor element by second solder52. Insulating substrate10is bonded to heat dissipation member20to cause the main surface of insulating substrate10to curve so as to have a shape convex toward heat dissipation member20. First solder51is formed thicker at the edges than at the center in the plan view. The actions and effects produced by the above-described configuration are the same as the actions and effects produced by the basic configuration of power module100, and thus no description will be given below of the actions and effects.

Under the manufacturing method for power module100, insulating substrate10includes base member11. At least one conductor layer12is bonded onto one surface11A of base member11, and at least one conductor layer13is bonded onto other surface11B on a side opposite from one surface11A. The curvature of the convex shape is adjusted by adjusting a difference in area between the first region on one surface11A where conductor layer12is not bonded and the second region on other surface11B where conductor layer13is not bonded. This makes it possible to control the direction and degree of the curvature of the main surface of insulating substrate10.

Under the manufacturing method for power module100, conductor layer12on one surface11A may be formed thicker than conductor layer13on other surface11B so as to adjust the curvature of the convex shape. Accordingly, the curvature of the convex shape is adjusted such that insulating substrate10is curved so as to have a shape convex toward heat dissipation member20.

Under the manufacturing method for power module100, the curvature of the convex shape may be adjusted by further including the process of bonding other conductor layer12ato between conductor layer12on one surface11A, and IGBT41and diode42so as to overlap conductor layer12. Accordingly, the curvature of the convex shape is adjusted such that insulating substrate10is curved so as to have a shape convex toward heat dissipation member20.

Second Embodiment

FIG.14is a schematic cross-sectional view of a configuration of a power module according to a second embodiment. With reference toFIG.14, in a power module100according to the present embodiment, base plate21of heat dissipation member20includes a first heat dissipation member portion21A and a second heat dissipation member portion21B. As with base plate21according to the first embodiment, first heat dissipation member portion21A is a plate-shaped portion having a surface extending along the XY plane. An uppermost surface, in the Z direction, of first heat dissipation member portion21A is bonded to the lower main surface of insulating substrate10by first solder51. Second heat dissipation member portion21B is disposed outside first heat dissipation member portion21A in the plan view so as to be integrated with first heat dissipation member portion21A. Second heat dissipation member portion21B is disposed so as to surround first heat dissipation member portion21A and first solder51on first heat dissipation member portion21A in the plan view. Second heat dissipation member portion21B is disposed at a position that is identical in coordinate in the Z direction to first heat dissipation member portion21A and in a region extending upward in the Z direction from the position. Therefore, second heat dissipation member portion21B is formed thicker than first heat dissipation member portion21A so as to extend upward in the Z direction (toward insulating substrate10). Frame member60is mounted on second heat dissipation member portion21B formed thicker than first heat dissipation member portion21A.

Therefore, first heat dissipation member portion21A and second heat dissipation member portion21B integrated with and disposed outside first heat dissipation member portion21A form a depression. This depression houses first solder51and insulating substrate10. In this respect, base plate21illustrated inFIG.14is different from base plate21illustrated inFIG.1that has only the flat plate member and does not form such a depression as illustrated inFIG.1.

Next, a description will be given of actions and effects of the present embodiment. The present embodiment produces the following actions and effects in addition to the actions and effects produced by the basic configuration according to the first embodiment. The same applies to the following embodiments unless otherwise specified.

Power module100according to the present embodiment includes first heat dissipation member portion21A and second heat dissipation member portion21B. First heat dissipation member portion21A is bonded to insulating substrate10by first solder51. Second heat dissipation member portion21B surrounds first heat dissipation member portion21A and first solder51outside first heat dissipation member portion21A in the plan view, and frame member60is mounted on second heat dissipation member portion21B. In heat dissipation member20, the depression formed by first heat dissipation member portion21A and second heat dissipation member portion21B houses first solder51and insulating substrate10.

This can make first solder51thinner to lower rigidity of first solder51without lowering the rigidity of entire base plate21as compared with the first embodiment. This therefore can prevent first solder51from cracking during the evaluation of the long-term reliability such as temperature cycle resistance. Further, the thickness of frame member60disposed on second heat dissipation member portion21B is reduced by the thickness of second heat dissipation member portion21B. The PPS resin of which frame member60is made is low in adhesion to encapsulant90. Therefore, making the dimension of frame member60in the Z direction smaller allows a reduction in area of the adhesion interface between encapsulant90and frame member60, thereby reducing the possibility of separation between encapsulant90and frame member60.

Third Embodiment

FIG.15is a schematic cross-sectional view of a configuration of a power module according to a third embodiment. With reference toFIG.15, in power module100according to the present embodiment, electrode plate30has no region corresponding to main terminal72, and further includes a main terminal73in frame member60on the right side of the drawing. Main terminal73corresponds to main terminal72according to the first embodiment. Main terminal73, however, is not integrated with electrode plate30, that is, not a part of main body30A of electrode plate30. Main terminal73is a member separate from electrode plate30.

Main terminal73includes a first portion73A, a second portion73B, and a third portion73C. First portion73A corresponds first portion31of main terminal72illustrated inFIG.1. First portion73A is exposed outside frame member60so as to extend in the Z direction. Second portion73B corresponds to second portion32of main terminal72illustrated inFIG.1. Second portion73B is embedded in frame member60, and includes a portion where main terminal73is bent inFIG.15. Third portion73C serves as a connecting portion where main terminal73is connected to main terminal-side edge33of electrode plate30inside frame member60. Note that third portion73C serving as the connecting portion is exposed from inside frame member60, but is embedded in encapsulant90. Since third portion73C is exposed from at least frame member60even when third portion73C is embedded in encapsulant90in the form of a final product, third portion73C may be expressed as “exposed from frame member60”.

As described above, main terminal73is disposed as a member separate from electrode plate30. Therefore, a main body30B of electrode plate30has no main terminal, and has only a portion extending in the horizontal direction along the XY plane. Main body30B of electrode plate30illustrated inFIG.15, however, includes main terminal-side edge33and semiconductor element-side edge34. Main terminal-side edge33is the rightmost region in the X direction of main body30B illustrated inFIG.15. Main terminal-side edge33is connected to main terminal73. Semiconductor element-side edge34is a region on a side opposite from main terminal-side edge33, that is, a region as the leftmost edge in the X direction of main body30B illustrated inFIG.15.

InFIG.15, main terminal-side edge33of electrode plate30and third portion73C serving as the connecting portion of main terminal73are bonded together by third solder53. That is, a portion of main terminal-side edge33facing downward in the Z direction and a portion of third portion73C facing upward in the Z direction are bonded together by third solder53. Therefore, the rightmost region of main terminal-side edge33in the X direction inFIG.15preferably extends so as to overlap third portion73C of main terminal73in the plan view. Main body30B of electrode plate30and main terminal73according to the present embodiment are made of a metal material such as copper that is the same as the material of main body30A of electrode plate30and signal electrode71according to the first embodiment.

Note that signal electrode71, main terminal73, and main body30B of electrode plate30may be made of a single lead frame divided into three. Main body30B is preferably made of a metal material such as copper.

In the present embodiment, electrode plate30and main terminal73are separate members, and are electrically connected to each other by third solder53. In this respect, the present embodiment is different in configuration from the first and second embodiments in which electrode plate30is integrated with the main terminal to directly connect to the main terminal.

Next, a manufacturing method for power module100illustrated inFIG.15will be described with reference toFIGS.16to19. Note that a description will be given below using an example where electrode plate30is not curved in advance and the main surface has a planar shape, but as illustrated inFIGS.7to10, electrode plate30curved in advance may be used in the present embodiment. The same applies to the following embodiments.

FIG.16is a schematic cross-sectional view of the power module according to the third embodiment, illustrating a first process of the manufacturing method for the power module. With reference toFIG.16, first, processing the same as illustrated inFIG.7is performed, and the members illustrated inFIG.7are bonded by first solder51and conductive member59using a reflow device. Second solder52and electrode plate30are prepared after the process of bonding the members using a reflow device. This corresponds to the process of preparing second solder52and frame member60after the bonding process illustrated inFIG.8.

InFIG.16, electrode plate30including plate-shaped main body30B without the main terminal as illustrated inFIG.15and thus without the bent portion is prepared. Further, second solder52is thicker at the center than at the edges from the viewpoint of bonding plate-shaped electrode plate30and the semiconductor element together.

FIG.17is a schematic cross-sectional view of the power module according to the third embodiment, illustrating a second process of the manufacturing method for the power module. With reference toFIG.17, as with the process illustrated inFIG.9, electrode plate30is bonded to IGBT41and diode42by second solder52so as to overlap at least a part of IGBT41and diode42.

FIG.18is a schematic cross-sectional view of the power module according to the third embodiment, illustrating a third process of the manufacturing method for the power module. With reference toFIG.18, frame member60is prepared. On the left side of frame member60inFIG.18, signal electrode71is insert-molded into frame member60so as to be partially exposed from frame member60. On the right side of frame member60inFIG.18, main terminal73is insert-molded into frame member60so as to be partially exposed from frame member60.

FIG.19is a schematic cross-sectional view of the power module according to the third embodiment, illustrating a fourth process of the manufacturing method for the power module. With reference toFIG.19, in the state illustrated inFIG.18, heating using a reflow furnace causes third solder53to bond electrode plate30and third portion73C of main terminal73together. Subsequently, base plate21and frame member60are bonded together by the adhesive illustrated inFIG.9, and the same processing as illustrated inFIG.10is performed to form power module100illustrated inFIG.15.

Next, actions and effects of the present embodiment will be described. Power module100according to the present embodiment further includes main terminal73. Main terminal73includes third portion73C serving as the connecting portion exposed from inside frame member60. Electrode plate30includes main terminal-side edge33connected to main terminal73and semiconductor element-side edge34that is an edge on a side opposite from main terminal-side edge33. Main terminal-side edge33of electrode plate30and third portion73C are bonded together by third solder53.

Under the manufacturing method for power module100according to the present embodiment, frame member60disposed so as to surround insulating substrate10at a distance from insulating substrate10and in which main terminal73is embedded is prepared. After the process of bonding electrode plate30to the semiconductor element with second solder52, electrode plate30and main terminal73are bonded together by third solder53.

For example, as illustrated inFIGS.15to19, a difference between the thickness of second solder52at the center in the plan view and the thickness of second solder52at the edges in the plan view may increase. In this case, even when insulating substrate10is unintentionally deformed, for example, curved greatly, it is possible to curb the generation of flaws such as a partial tearing of second solder52. After electrode plate30and the semiconductor element are bonded together by second solder52, main terminal73and electrode plate30are bonded together by third solder53. Accordingly, adjusting the supply amount of third solder53and the like allows the joint made by third solder53to absorb stress applied to second solder52due to the deformation of electrode plate30.

Fourth Embodiment

FIG.20is a schematic cross-sectional view of a configuration of a power module according to a fourth embodiment. With reference toFIG.20, a power module100according to the present embodiment is basically the same in configuration as power module100according to the third embodiment illustrated inFIG.15. As with main body30B, a main body30C of electrode plate30has no main terminal and has only a portion extending in the horizontal direction along the XY plane. Therefore, inFIG.20, the same components as the components illustrated inFIG.15are denoted by the same reference numerals, and no description will be given below of such components as long as their functions and the like are the same. Note that, inFIG.20, main terminal-side edge33of electrode plate30and third portion73C serving as the connecting portion of main terminal73are bonded together by a bonding wire82. Bonding wire82extends in the X direction. Therefore, in main body30C of electrode plate30, the rightmost region of main terminal-side edge33in the X direction need not extend to a position where main terminal73is exposed from frame member60, and main terminal-side edge33overlaps third portion73C connected to electrode plate30in the plan view as illustrated inFIG.15. InFIG.20, main terminal-side edge33extends so as to overlap IGBT41on the right side inFIG.20in the plan view, and does not extend further rightward. Note that bonding wire82are preferably the same in material and dimensions as bonding wire81. Main body30C is preferably made of a metal material such as copper that is the same as the material of main bodies30A,30B.

In the present embodiment, electrode plate30and main terminal73are separate members, and are electrically connected to each other by bonding wire82. In this respect, the present embodiment is different in configuration from the first and second embodiments in which electrode plate30is integrated with the main terminal to directly connect to the main terminal.

Next, a manufacturing method for power module100illustrated inFIG.20will be described with reference toFIGS.21and22.FIG.21is a schematic cross-sectional view of the power module according to the fourth embodiment, illustrating a first process of the manufacturing method for the power module. With reference toFIG.21, first, processing the same as illustrated inFIGS.16to18of the third embodiment is performed. The rightmost region of main terminal-side edge33of plate-shaped main body30C located closest to main terminal73may be disposed on the left side as compared with the third embodiment.

FIG.22is a schematic cross-sectional view of the power module according to the fourth embodiment, illustrating a second process of the manufacturing method for the power module. With reference toFIG.22, in the state illustrated inFIG.21, electrode plate30and third portion73C of main terminal73are bonded together by the wire bonding process, that is, by bonding wire82. The subsequent processes are the same as the processes in the third embodiment. As a result, power module100illustrated inFIG.20is formed.

Next, a description will be given of actions and effects of the present embodiment. Power module100according to the present embodiment further includes main terminal73. Main terminal73includes third portion73C serving as the connecting portion exposed from inside frame member60. Electrode plate30includes main terminal-side edge33connected to main terminal73and semiconductor element-side edge34that is an edge on a side opposite from main terminal-side edge33. Main terminal-side edge33of electrode plate30and third portion73C are bonded together by bonding wire82.

Under the manufacturing method for power module100according to the present embodiment, frame member60disposed so as to surround insulating substrate10at a distance from insulating substrate10and in which main terminal73is embedded is prepared. After the process of bonding electrode plate30to the semiconductor element with second solder52, electrode plate30and main terminal73are bonded together by the wire bonding process.

As described as the background and problem of the first embodiment, when wire bonding for forming a circuit is directly performed on the insulating substrate and the semiconductor element such as the IGBT having an inclination or the like, the wire tool may damage the semiconductor element. As in the present embodiment, however, electrode plate30is bonded to main terminal73by wire bonding via electrode plate30between the semiconductor element and main terminal73. This allows a reduction in the number of bonding wires81,82as compared with a case where wire bonding is directly performed on the semiconductor element. Further, the possibility that the wire tool will damage the semiconductor element due to the inclination of the surface of the semiconductor element caused by the curvature of insulating substrate10can be reduced, and the reliability of bonding wires81,82can be improved.

Fifth Embodiment

FIG.23is a schematic cross-sectional view of a configuration of a power module according to a fifth embodiment. With reference toFIG.23, in power module100according to the present embodiment, a protrusion21C is formed in heat dissipation member20. Specifically, base plate21of heat dissipation member20has protrusion21C whose tip is positioned to overlap, in the plan view, a region where the temperature becomes highest on other surface11B, which is the back surface of insulating substrate10, when the semiconductor element is in operation. As an example,FIG.23illustrates an example where the temperature becomes highest at the center of insulating substrate10in the plan view when the semiconductor element is in operation. That is, protrusion21C having the tip at a position of base plate21overlapping the center of insulating substrate10in the plan view. Precisely speaking, the semiconductor element reaches the highest temperature when the semiconductor element is in operation, but when viewed on the back surface of insulating substrate10, heat is diffused to make the peak of heat distribution unclear, so that the temperature is highest at the center.

Protrusion21C is formed on the uppermost surface where base plate21is in contact with first solder51. The uppermost surface of base plate21is curved upward in a convex shape so as to make the uppermost surface at the tip of protrusion21C highest in position. Therefore, the thickness of base plate21is largest at protrusion21C. It is preferable that the tip of protrusion21C be larger in thickness by about 0.1 mm than the edges of base plate21that are smallest in thickness.

Accordingly, first solder51in the region where the temperature becomes high can be made thinner, and first solder51at the edges can be made thicker. This reduces the thermal resistance of first solder51in the center region where the temperature becomes high, so that heat dissipation is increased. It is further possible to reduce the thermal strain applied to first solder51at the edges and to curb the generation of cracks in first solder51.

Sixth Embodiment

FIG.24is a schematic cross-sectional view of a configuration of a power module according to a sixth embodiment. With reference toFIG.24, in power module100according to the present embodiment, insulating substrate10includes a curved portion10A and a non-curved portion10B. Curved portion10A is a portion where the main surface of insulating substrate10is curved so as to have a shape convex toward heat dissipation member20as in the other embodiments described above. Non-curved portion10B is a region where insulating substrate10is not curved, unlike curved portion10A, and the main surface extends roughly flat along the XY plane. Curved portion10A and non-curved portion10B are arranged side by side in the horizontal direction. Therefore, in the present embodiment, with attention paid to only curved portion10A of insulating substrate10excluding non-curved portion10B, the center portion having a convex shape is formed at the center of curved portion10A in the plan view. It is preferable that first solder51be thinnest at a position where first solder51overlaps the center of curved portion10A. Note that, in the present embodiment as well as in the other embodiments, first solder51may be thinnest at a position where first solder51overlaps the center, in the overall plan view, of insulating substrate10obtained by combining curved portion10A and non-curved portion10B, and first solder51may be thicker at the edges.

As in the other embodiments, IGBT41and diode42are mounted on conductor layer12in curved portion10A. On the other hand, a control semiconductor element43is mounted on conductor layer12in non-curved portion10B. Control semiconductor element43is typically an integrated circuit (IC) in which a program for driving IGBT41, diode42, and the like is written, that is, a so-called microcomputer.

FIG.24illustrates conductor layer12extending from curved portion10A to non-curved portion10B. Conductor layer12, however, may be divided into separate members, each provided for a corresponding one of curved portion10A and non-curved portion10B.

Power module100may have such a configuration. Control semiconductor element43generates little heat. Therefore, first solder51at the position where first solder51overlaps control semiconductor element43may be entirely formed as thick as the edges of first solder51. That is, the thickness of first solder51may be substantially uniform over non-curved portion10B. Accordingly, the surface of control semiconductor element43in non-curved portion10B is disposed along the horizontal direction, that is, so as to have almost no inclination. Therefore, control semiconductor element43can reduce the possibility of damaging the control semiconductor element due to the inclination when wire bonding is performed on control semiconductor element43.

Seventh Embodiment

FIG.25is a schematic cross-sectional view of a configuration of a power module according to a seventh embodiment. With reference toFIG.25, power module100need not include frame member60. In the present embodiment, with at least a part of the lowermost surface of base plate21and all fins22exposed outside, encapsulant91of power module100encapsulates each of the other members. Since frame member60is not provided, encapsulant91forms the outermost surface of power module100.

InFIG.25, a main body30D of electrode plate30is disposed as a member separate from main terminal73and signal electrode71. Note that main body30D has only a portion extending in the horizontal direction along the XY plane. As illustrated inFIG.25, in the present embodiment, signal electrode71and main terminal73may be arranged side by side on the same plane so as to be along the same plane as the XY plane where main body30D extends. Main body30D and signal electrode71are connected by bonding wire81as in the other embodiments. Main body30D and main terminal73may be connected by any means, specifically, by either third solder53or bonding wire82.

Note that signal electrode71, main terminal73, and main body30D of electrode plate30may be made of a single lead frame divided into three. Alternatively, as in the first embodiment, main body30D and main terminal73may be integrated with each other. Therefore, main body30D is preferably made of a metal material such as copper.

Encapsulant91is preferably a silica filler-containing epoxy resin formed by transfer molding. Specifically, during the transfer molding, for example, the following processing is performed. Members such as base plate21, insulating substrate10, and the semiconductor element illustrated inFIG.25are laminated in a mold so as to include at least a part of main body30D and signal electrode71and fixed, that is, sandwiched. At this time, the mold is heated to 170° C. The mold is a machined stainless steel. Next, solid resin tablets for transfer molding are poured into the mold with the solid resin tablet heated and pressurized. The mold is heated in its entirety at 170° C. for 1 minute to cure the resin. Subsequently, all the components including encapsulant91as the cured resin are removed from the mold. All the components removed from the mold are heated in an oven at 170° C. for 2 hours. Accordingly, power module100including encapsulant91illustrated inFIG.25is formed. Since the actions and effects of the present embodiment are the same as the actions and effects of the first embodiment, no description will be given below of the actions and effects.

FIRST EXAMPLE

The long-term reliability such as temperature cycle resistance, as described above, of first solder51by which insulating substrate10and heat dissipation member20are bonded together was evaluated. Specifically, a sample was prepared for each of the following three types of power modules.

A first sample has a configuration similar to the configuration of power module100illustrated inFIG.1. That is, the first sample is curved to cause the main surface of insulating substrate10to curve so as to have a shape convex toward heat dissipation member20. In the first sample, the thickness of first solder51illustrated inFIG.1is 0.2 mm at the center and 0.4 mm at the edges. That is, as in the first embodiment, first solder51is thicker at the edges than at the center. A second sample is basically the same in configuration as the first sample, but the thickness of first solder51is the same at the center and the edges. In the second sample, the thickness of first solder51is 0.3 mm at both the center and the edges. A third sample is basically the same in configuration as the first sample, but the thickness of first solder51is 0.3 mm at the center and 0.2 mm at the edges. That is, first solder51is thinner at the edges than at the center, contrary to the first embodiment.

The three samples were each placed in an atmosphere at 125° C. for 30 minutes and placed in an atmosphere at 40° C. below zero for 30 minutes. Temperature cycle testing was conducted in which the above-described processing regarded as one cycle was repeated a plurality of times. Subsequently, an ultrasonic testing image of first solder51was taken.

FIG.26is a graph showing a result of measuring a maximum length of cracks formed at an edge of the first solder. The horizontal axis ofFIG.26indicates the number of times the above-described one cycle is repeated for each sample. The vertical axis ofFIG.26indicates the maximum length of cracks at the edge of first solder51after the above-described one cycle is repeated a plurality of times. Note that black circles inFIG.26indicate the first sample. White triangles inFIG.26indicate the second sample. White squares inFIG.26indicate the third sample.

With reference toFIG.26, for the first sample, cracks hardly developed even after the cycle was repeated 1000 times. On the other hand, for the second sample, after the cycle was repeated 1000 times, cracks developed from the edge of first solder51by about 10 mm. For the third sample, after the cycle was repeated 1000 times, cracks developed from the edge of first solder51by about 22 mm.

FIG.27is an ultrasonic testing image of the edge of the first solder after the temperature cycle testing conducted on the first sample.FIG.28is an ultrasonic testing image of the edge of the first solder after the temperature cycle testing conducted on the third sample. With reference toFIG.27, for the first sample, cracks in first solder51hardly developed before the temperature cycle testing and after 1000 cycles. On the other hand, with reference toFIG.28, for the third sample, cracks in first solder51hardly developed before the temperature cycle testing, whereas cracks having a length L in the drawing were formed after 1000 cycles. It was therefore confirmed that making the first solder thicker at the edges than at the center in the plan view can curb the generation of cracks.

The features described in (each example included in) each of the above-described embodiments may be appropriately combined and applied within a range where there is no technical contradiction. For example, as in the third and fourth embodiments, a configuration including main bodies30B,30C and main terminal73may be applied to the fifth and sixth embodiments.

It should be understood that the embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims rather than the above description, and the present disclosure is intended to include the claims, equivalents of the claims, and all modifications within the scope.

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