Power conversion device, and method for manufacturing power conversion device

Abstract

This power conversion device comprises: a semiconductor package (10) that incorporates a semiconductor element (1) joined onto a lead frame (11, 12); and a substrate (50) that has a flat plate shape having a front surface and a rear surface, has the semiconductor package mounted on the front surface, and is electrically connected to the lead frame. The substrate is provided with a first through hole (91) and second through holes (92) obtained by metal films being applied to the inner periphery of holes that penetrate in the thickness direction connecting the front surface and the rear surface. The first through hole is provided in a region that overlaps the semiconductor element in the thickness direction, and the second through holes are provided in a region that does not overlap the semiconductor element in the thickness direction. Further provided is a bonding material that connects the lead frame and thickness-direction ends of the first through hole and the second through holes on the side closer to the semiconductor element, and that is filled in the first through hole. The holes constituting the second through holes are filled with a filler. The difference in the linear expansion coefficient between the filler and the metal films is greater than the difference in the linear expansion coefficient between the bonding material and the metal films.

Description

Power conversion device and method for manufacturing the same

[0001] The present invention relates to a power converter and a method for manufacturing a power converter.

[0002] Patent Document 1 discloses a printed circuit board having a conductor pattern and lands made of copper foil formed on both sides of an insulating substrate, a heat dissipation soldering land on one side where an electronic component is mounted, a solder absorption land on the other opposite side, and via holes with openings at both ends to the heat dissipation soldering land and the solder absorption land, a solder resist formed on solder unnecessary areas on both sides of the printed circuit board, the heat dissipation soldering land and the solder absorption land surrounded by the solder resist, a metal mask placed on one side, and cream solder applied to the land and the heat dissipation soldering land, an electronic component placed on the one side, and a flattened wiring board. The method for manufacturing a printed circuit board with a heat dissipation structure is disclosed, which comprises melting the cream solder by first reflow to solder-connect the lead terminals of the electronic component to the land portion and to form a solder layer that adheres the heat dissipation soldering land portion to the back surface of the electronic component, causing the molten solder that leaks to the other side through the via hole to flow onto the solder absorption land portion and adhere flatly to the opening, then placing a metal mask on the other side of the printed circuit board, applying cream solder to the solder absorption land portion while covering the solder that has solidified in the opening of the via hole, and then performing a second reflow of the cream solder to form a solder layer on the solder absorption land portion.

[0003] Japanese Patent Application Publication No. 2008-078271

[0004] The invention described in Patent Document 1 cannot ensure the solder thickness and improve the reliability of heat dissipation at the same time.

[0005] A power conversion device according to a first aspect of the present invention comprises: a semiconductor package incorporating a semiconductor element bonded onto a lead frame; and a flat substrate having a front surface and a back surface, the semiconductor package being mounted on the front surface and electrically connected to the lead frame; the substrate having a first through hole and a second through hole which are metal films applied to the inner periphery of holes which penetrate in a thickness direction connecting the front surface and the back surface; the first through hole being provided in an area which overlaps with the semiconductor element in the thickness direction; the second through hole being provided in an area which does not overlap with the semiconductor element in the thickness direction; a bonding material which connects the thickness direction ends of the first through hole and the second through hole which are closer to the semiconductor element to the lead frame and which is filled into the first through hole; a filler is filled into the hole which constitutes the second through hole; and the difference in linear expansion coefficient between the filler and the metal film is greater than the difference in linear expansion coefficient between the bonding material and the metal film. A method for manufacturing a power conversion device according to a second aspect of the present invention includes a hole forming step of forming a plurality of holes penetrating a thickness direction of a flat substrate, a hole forming step of forming first through holes and second through holes by forming a metal film on the inner periphery of each of the plurality of holes, a filler filling step of filling the inside of the holes constituting the second through holes with a filler, and an arrangement step of arranging a bonding material on the upper surface of the substrate so as to cover the first through holes and the second through holes, and arranging a semiconductor package having a semiconductor element bonded to a lead frame on the bonding material, wherein in the arrangement step, the first through holes and the semiconductor element are arranged so as to overlap in the thickness direction, and after the arrangement step, a bonding step of filling the inside of the holes constituting the first through holes with the heated and melted bonding material, wherein the difference in linear expansion coefficient between the filler and the metal film is greater than the difference in linear expansion coefficient between the bonding material and the metal film.

[0006] According to the present invention, it is possible to ensure the solder thickness and improve the reliability of heat dissipation at the same time.

[0007] Electrical circuit diagram of the power converter. Cross-sectional view of the power converter in the embodiment. View from a different perspective of FIG. 2. Diagram showing the arrangement process and the joining process. Cross-sectional view of the power converter in Modification 1. Cross-sectional view of the power converter in Modification 2. Cross-sectional view of the power converter in Modification 3.

[0008] -Embodiment- Hereinafter, an embodiment of a power conversion device will be described with reference to Figs.

[0009] (Circuit Diagram) FIG. 1 is an electrical circuit diagram of a power conversion device 100. The power conversion device 100 includes a U-phase circuit 100U that processes the U-phase, a V-phase circuit 100V that processes the V-phase, and a W-phase circuit 100W that processes the W-phase. Since the configuration of each phase circuit is identical, only the U-phase circuit 100U will be described here. The U-phase circuit 100U includes four sets of upper and lower arms, each of which has a semiconductor element 1. The U-phase circuit 100U includes a positive wiring 71 at the top of the illustration, an AC wiring 72 at the center of the illustration, a negative wiring 73 at the bottom of the illustration, and a ceramic capacitor 75 at the left of the illustration. The two boxes shown inside the V-phase circuit 100V represent the upper arm element circuit 1U and the lower arm element circuit 1D.

[0010] The semiconductor element 1 is, for example, an IGBT or a MOSFET. The semiconductor element 1 has a main terminal and a signal terminal 17. The main terminal has a high-voltage potential for the main circuit (collector potential for an IGBT, drain potential for a MOSFET) and a low-voltage electrode for the main circuit (emitter potential for an IGBT, source potential for a MOSFET). By connecting multiple semiconductor elements 1 in parallel, the output current of the power conversion device 100 can be increased. A power conversion circuit for one phase is configured by pairing an upper arm semiconductor element, a lower arm semiconductor element, and a capacitor that are connected in series. The output wiring for each phase is connected to a load such as a motor.

[0011] The capacitor may be a film capacitor with a large capacitance or a small ceramic capacitor. By arranging the capacitor near the semiconductor element 1, the wiring inductance of the positive electrode wiring 71 and the negative electrode wiring 73 can be reduced. The signal terminal 17 of the semiconductor element 1 is connected to a control circuit (not shown), and is turned on or off based on a signal input from a higher-level control device such as a microcomputer, thereby outputting an AC voltage to a load such as a motor. The structures of the upper arm element circuit 1U and the lower arm element circuit 1D will be described below.

[0012] (Configuration) Figure 2 is a cross-sectional view of the power conversion device 100, specifically a cross-sectional view of the upper arm element circuit 1U and the lower arm element circuit 1D. From Figure 2 onwards, mutually orthogonal X, Y and Z axes are shown to clarify the correlation between the figures. In Figure 2, the positive side of the X axis is the right side of the figure, the positive side of the Y axis is the back side of the figure, and the positive side of the Z axis is the top side of the figure. Note that these X, Y and Z axes are shown merely for the convenience of explaining the configuration of the power conversion device 100, and are not related to the direction of gravity.

[0013] The power conversion device 100 includes a flat wiring board 50 and a semiconductor package 10 disposed on the positive side of the wiring board 50 along the Z axis, sandwiched between heat dissipation members 500 on both sides of the Z axis. The heat dissipation member 500 may be a heat dissipation fin, or a cooling medium may flow through it. The heat dissipation member 500 includes an upper heat dissipation member 500U and a lower heat dissipation member 500D. The wiring board 50 is a multilayer board having multiple wiring layers. A first main circuit wiring 61 is formed on the right side of the first layer of the wiring board 50 in the illustration. A second main circuit wiring 62 is formed in the center of the wiring board 50 in the illustration. In the case of the upper arm element circuit 1U shown in FIG. 2, the first main circuit wiring 61 corresponds to the positive electrode wiring 71, and the second main circuit wiring 62 corresponds to the AC wiring 72. In the case of the lower arm element circuit 1D shown in FIG. 2, the first main circuit wiring 61 corresponds to the AC wiring 72, and the second main circuit wiring 62 corresponds to the negative electrode wiring 73.

[0014] The semiconductor package 10 includes a semiconductor element 1, a first lead frame 11 at the top as shown in the figure, a second lead frame 12 at the bottom as shown in the figure, a semiconductor element bonding material 13, a sealing member 14, a first terminal 16, and a signal terminal 17. The first lead frame 11 is connected to a first main circuit wiring 61. The signal terminal 17 is connected to a signal wiring 63.

[0015] The semiconductor element 1 is flat and has a first main electrode on the positive side of the Z axis and a second main electrode 1S on the negative side of the Z axis. The first main electrode is connected to the first lead frame 11 via a semiconductor element bonding material 13. The second main electrode 1S is connected to the second lead frame 12 via the semiconductor element bonding material 13. In other words, the semiconductor element 1 is in contact with the first lead frame 11 at the top and with the second lead frame 12 at the bottom, and is surrounded by a sealing member 14 on the sides.

[0016] The first lead frame 11 is electrically connected to the first terminal 16. The surface of the first lead frame 11 on the positive side of the Z axis is exposed from the sealing member 14, and this exposed surface contacts the upper heat dissipation member 500U via the heat dissipation member bonding material 23. Therefore, when the movement of heat generated by the semiconductor element 1 is followed toward the positive side of the Z axis, the heat travels from the semiconductor element 1 toward the positive side of the Z axis, passes through the semiconductor element bonding material 13, the first lead frame 11, and the heat dissipation member bonding material 23, and reaches the upper heat dissipation member 500U.

[0017] The second lead frame 12 has a second conductor exposed surface 12E, which is the surface on the negative Z-axis side, exposed from the sealing member 14 and contacts the surface on the positive Z-axis side of the wiring substrate 50 via the first bonding material 81. Hereinafter, the surface on the positive Z-axis side of the wiring substrate 50 will be referred to as the "front surface," and the surface on the negative Z-axis side will be referred to as the "back surface." The surface on the negative Z-axis side of the wiring substrate 50 contacts the lower heat dissipation member 500D via the third bonding material 83 and the heat dissipation member bonding material 23. However, as described below, the second bonding material 82 penetrates a portion of the wiring substrate 50 in the Z-axis direction. When the heat generated by the semiconductor element 1 moves toward the negative Z-axis side, the heat travels from the semiconductor element 1 through the semiconductor element bonding material 13, the second lead frame 12, the first bonding material 81, the wiring substrate 50, the third bonding material 83, and the heat dissipation member bonding material 23 to the lower heat dissipation member 500D.

[0018] The second main circuit wiring 62, which is present in the illustrated center of the wiring board 50, includes a surface wiring 621 formed on the surface and a back surface wiring 622 formed on the back surface. The surface wiring 621 and the back surface wiring 622 include an area obtained by projecting the second lead frame 12 in the Z-axis direction. In other words, when the second lead frame 12, the surface wiring 621, and the back surface wiring 622 are projected in the Z-axis direction, the three projection planes may approximately coincide, or the projection planes of the surface wiring 621 and the back surface wiring 622 may be wider. Furthermore, both the surface wiring 621 and the back surface wiring 622 contact the end faces of the first through hole 91 and the second through hole 92.

[0019] The first through-holes 91 penetrating the wiring substrate 50 are filled with the second bonding material 82, which has high thermal conductivity. The second through-holes 92 are filled with the filler 59, which is a resin, but the thermal conductivity of the filler 59 is inferior to that of the second bonding material 82. Therefore, heat transfer across the wiring substrate 50 occurs mainly via the first through-holes 91.

[0020] The first bonding material 81, the second bonding material 82, and the third bonding material 83 are made of the same material, such as solder. The first bonding material 81, the second bonding material 82, and the third bonding material 83 have the same composition, but for convenience of explanation, they are given different names depending on where they are placed. The first bonding material 81, the second bonding material 82, and the third bonding material 83 are collectively referred to as bonding material 80. Note that the first terminal 16, the signal terminal 17, and the connecting conductor 18 are shown in FIG. 2 as being connected to the wiring board 50 at only one point. However, in reality, as will be described later, they also exist in the Y-axis direction and are connected to the wiring board 50 at multiple positions.

[0021] In this embodiment, the term "through hole" refers to a metal coating formed in a through hole in wiring substrate 50, and does not include the space formed by the through hole. That is, a through hole has roughly the shape of the side surface of a cylinder. The area surrounded by a vertically elongated ellipse in the center of the figure is first through hole 91, and to the left and right of it are second through holes 92. The space formed by first through hole 91, in other words, the space that is the solid part of the same cylinder as first through hole 91, which is like the side surface of a cylinder, is filled with second bonding material 82. The space formed by second through hole 92 is filled with filler 59.

[0022] The second lead frame 12 and the wiring substrate 50 are bonded together by a first bonding material 81. The first bonding material 81 overlaps with the first through-hole 91 and the second through-hole 92 in the XY plane, and therefore the ends of the first through-hole 91 and the second through-hole 92 on the positive side of the Z axis contact the first bonding material 81. The holes constituting all of the through-holes have the same diameter, and the diameter of the hole is constant regardless of the distance from the surface of the wiring substrate 50.

[0023] The filler 59 filled in the second through-hole 92 is resin. Resin has a relatively large linear expansion coefficient. As described above, the first through-hole 91 and the second through-hole 92 are metal coatings formed in the through-holes, and this metal is, for example, copper. Of the three metal coatings (i.e., the first through-hole 91 and the second through-hole 92), the bonding material 80, and the filler 59, the filler 59 is resin and therefore has the largest linear expansion coefficient. Because the metal coating and the bonding material 80 are metal-based, their linear expansion coefficients are significantly smaller than those of the filler 59. Comparing the metal coating and the bonding material 80, the metal coating has a larger linear expansion coefficient. The difference in the linear expansion coefficient between the filler 59 and the metal coating is large, while the difference in the linear expansion coefficient between the metal coating and the bonding material 80 is small. The filler 59 has a lower thermal conductivity than the metal coating and the bonding material 80, making it less likely to conduct heat.

[0024] FIG. 3 is a view obtained by changing the viewpoint of FIG. 2 . The rectangle on the periphery of FIG. 3 represents the wiring substrate 50. Two signal wirings 63 are shown on the left side of FIG. 3 , two semiconductor packages 10 are shown in the center of FIG. 3 , and a first main circuit wiring 61 is shown on the right side of FIG. 3 . In FIG. 3 , two semiconductor packages 10 are lined up in the Y-axis direction. Each semiconductor package 10 is connected to the signal wiring 63 via a signal terminal 17 and to the first main circuit wiring 61 via a first terminal 16. The rectangle shown in the center of each semiconductor package 10 represents the semiconductor element 1, and the circles represent the first through-hole 91 and the second through-hole 92. However, since the semiconductor element 1, the first through-hole 91, and the second through-hole 92 are not actually visible from the viewpoint of FIG. 3 , they are shown with dashed lines.

[0025] The circles that exist within the rectangular region of the semiconductor element 1 are first through holes 91, and the circles that exist outside the region of the semiconductor element 1 are second through holes 92. The first through holes 91 are arranged in the Y-axis direction, which is the same as the arrangement direction of the semiconductor package 10. The second through holes 92 are also arranged in the Y-axis direction.

[0026] 3, two first through holes 91 are provided per semiconductor element 1, but it is sufficient that at least one first through hole 91 is provided per semiconductor element 1. In FIG. 3, two second through holes 92 are provided per first through hole 91, but the ratio of the first through holes 91 to the second through holes 92 is arbitrary. In FIG. 3, the first through holes 91 and the second through holes 92 are aligned in the X-axis direction and have the same Y-coordinate value, but the Y-coordinate values ​​may be different.

[0027] (Manufacturing Method) A manufacturing method for the power conversion device 100 will be described. However, the following description will omit the upper heat dissipation member 500U and the lower heat dissipation member 500D. The manufacturing of the power conversion device 100 includes the following five processes: a hole forming process, a film forming process, a filler filling process, an arrangement process, and a bonding process. In the first hole forming process, a plurality of through holes are formed in the wiring substrate 50 to form the first through holes 91 and the second through holes 92. These through holes penetrate the wiring substrate 50 in the thickness direction, i.e., the Z-axis direction. The diameters of the plurality of holes are the same, and the diameters of the holes are constant regardless of the distance from the surface of the wiring substrate 50. In the next film forming process, a metal film is formed in the plurality of through holes formed in the hole forming process to form the first through holes 91 and the second through holes 92. In the third filling process, the inner periphery of the second through hole 92 is filled with filler 59.

[0028] FIG. 4 illustrates the placement process and the bonding process. The downward direction in FIG. 4 indicates the direction in which gravitational acceleration acts, and the terms "upper" and "lower" in the descriptions of the placement process and the bonding process refer to positions based on gravitational acceleration. In the fourth placement process, a pre-deformation bonding material 80P is placed on the upper surface of the wiring substrate 50 to cover the first through-hole 91 and the second through-hole 92, and a semiconductor package 10 incorporating a semiconductor element 1 bonded to a lead frame is placed on the pre-deformation bonding material 80P. The pre-deformation bonding material 80P is a material that will become the bonding material 80 through processing in the bonding process and has the same composition as the bonding material 80. Because the shape of the pre-deformation bonding material 80P is different from that of the bonding material 80 shown in FIG. 2, the pre-deformation bonding material 80P has a different name and symbol.

[0029] As shown in the upper part of FIG. 4 , in the placement process, the wiring substrate 50 is placed at the bottom in the direction of gravitational acceleration, the pre-deformation bonding material 80P is in the center, and the semiconductor package 10 is placed at the top in the direction of gravity. At this time, the first through-hole 91 and the semiconductor element 1 are placed so that they overlap in the thickness direction. The final bonding process is performed, for example, in a reflow furnace. In the bonding process, the heated and melted pre-deformation bonding material 80P bonds the second lead frame 12 and the wiring substrate 50. Furthermore, the load from the semiconductor package 10 due to gravity and the weight of the pre-deformation bonding material 80P itself cause the pre-deformation bonding material 80P to flow into the inner periphery of the first through-hole 91 and become the second bonding material 82. Furthermore, the pre-deformation bonding material 80P that reaches the wiring substrate 50 from the first through-hole 91 spreads along the back surface wiring 622 and becomes the third bonding material 83.

[0030] Because the second through-hole 92 is filled with the filler 59, the pre-deformation bonding material 80P does not flow into the second through-hole 92. Therefore, the pre-deformation bonding material 80P remaining on the upper part of the wiring substrate 50, i.e., the thickness of the first bonding material 81, is secured. If the first bonding material thickness 81W were small, distortion of the solder during temperature changes could increase. Therefore, by filling the inside of the second through-hole 92 with the filler 59, the reliability of the solder is improved.

[0031] The above-described embodiment provides the following advantageous effects. (1) The power conversion device 100 includes a semiconductor package 10 incorporating a semiconductor element 1 bonded to a lead frame, and a wiring substrate 50 having a flat plate shape with a front and back surface, on which the semiconductor package 10 is mounted and which is electrically connected to a second lead frame 12. The wiring substrate 50 includes a first through hole 91 and a second through hole 92, which are metal coatings formed on the inner peripheries of holes that penetrate the wiring substrate 50 in the thickness direction connecting the front and back surfaces. The first through hole 91 is provided in a region that overlaps the semiconductor element 1 in the thickness direction. The second through hole 92 is provided in a region that does not overlap the semiconductor element 1 in the thickness direction. A second bonding material 82 is provided that connects the thickness direction ends of the first through hole 91 and the second through hole 92 that are closer to the semiconductor element 1 to the second lead frame 12 and is filled into the first through hole 91. A filler 59 is filled into the hole that constitutes the second through hole 92. The difference in the linear expansion coefficient between the filler 59 and the metal film is greater than the difference in the linear expansion coefficient between the bonding material 80 and the metal film. Therefore, it is possible to ensure the solder thickness and improve the reliability of heat dissipation at the same time.

[0032] (2) The bonding material 80 has a higher thermal conductivity than the filler 59. Therefore, directly below the semiconductor element 1 where heat is concentrated, the second bonding material 82 in the first through-hole 91, which has a high thermal conductivity, can efficiently dissipate heat.

[0033] (3) The wiring substrate 50 has wiring on both the front surface, which is the surface on which the semiconductor package 10 is mounted, and the back surface. The first through-holes 91 and the second through-holes 92 are in contact with both the wiring on the front surface and the wiring on the back surface. Therefore, by having wiring on the back surface as well, the bonding material 80 is more likely to spread to the back surface during manufacturing of the power conversion device 100.

[0034] (4) The wiring on the front surface and the wiring on the back surface extend over approximately the same area in the thickness direction. Therefore, when the bonding material 80 passes through the first through-holes 91 and spreads onto the back surface of the wiring substrate 50, the wide back surface inner circumferential wiring 53B makes it easier for the bonding material 80 to spread, and prevents the bonding material 80 from protruding.

[0035] (5) As shown in FIG. 3 , a plurality of semiconductor packages 10 are provided on a wiring substrate in a depth direction perpendicular to the thickness direction. The first through holes 91 and the second through holes 92 are aligned in a direction perpendicular to the thickness direction and the depth direction. Therefore, when a plurality of semiconductor packages 10 are aligned, arranging the first through holes 91 filled with the bonding material 80 in the same direction facilitates an inspection to confirm the filling of the bonding material 80.

[0036] (6) Each semiconductor element 1 has two or more first through holes 91. Therefore, heat generated by the semiconductor element 1 can be efficiently transferred downward in the figure via the second bonding material 82.

[0037] (7) The manufacturing method of the power conversion device 100 includes a hole forming process of forming a plurality of holes penetrating the flat wiring substrate 50 in the thickness direction, a film forming process of forming first through holes 91 and second through holes 92 by forming a metal film on the inner periphery of each of the plurality of holes, a filler filling process of filling the interior of the holes constituting the second through holes 92 with filler 59, and an arrangement process of arranging a pre-deformation bonding material 80P on the upper surface of the wiring substrate 50 so as to cover the first through holes 91 and the second through holes 92, and arranging a semiconductor package 10 including a semiconductor element 1 bonded to a second lead frame 12 on the pre-deformation bonding material 80P. In the arrangement process, the first through holes 91 and the semiconductor element 1 are arranged so as to overlap in the thickness direction. The manufacturing method of the power conversion device 100 includes a bonding process, after the arrangement process, of filling the interior of the holes constituting the first through holes 91 with a heated and melted second bonding material 82. The difference in the linear expansion coefficient between the filler 59 and the metal film is greater than the difference in the linear expansion coefficient between the bonding material 80 and the metal film.

[0038] 5 is a cross-sectional view of the power conversion device 100 in Modification 1, and corresponds to FIG. 2 in the embodiment. In the embodiment described above, the holes constituting the first through holes 91 and the holes constituting the second through holes 92 are the same. However, the diameters of the two may be different, and in particular, the diameter of the holes constituting the first through holes 91 may be larger than the diameter of the holes constituting the second through holes 92.

[0039] In addition to the effects of the embodiment, this modification provides the following effects: (8) The diameter of the hole constituting the first through-hole 91 is larger than the diameter of the hole constituting the second through-hole 92. Therefore, in the joining process for manufacturing the power conversion device 100, the pre-deformation joining material 80P is more likely to flow into the inner periphery of the first through-hole 91.

[0040] (Modification 2) Fig. 6 is a cross-sectional view of the power conversion device 100 in Modification 2, corresponding to Fig. 2 in the embodiment. In the above-described embodiment, the diameter of the hole constituting the first through hole 91 was constant regardless of the distance from the surface. However, the diameter of the hole may vary depending on the distance from the surface, and the diameter may be larger particularly as it approaches the surface. That is, as shown in Fig. 6, the diameter may always increase as it approaches the surface, which is the surface on the positive side of the Z axis of the wiring substrate 50, or a section may be included in which the diameter remains constant even when it approaches the surface.

[0041] In addition to the effects of the embodiment, this modification provides the following effects: (9) The diameter of the hole constituting the first through-hole 91 is smaller on the side farther from the semiconductor element 1 than on the side closer to the semiconductor element 1. Therefore, by providing a taper in the hole constituting the first through-hole 91, it becomes easier to fill the pre-deformation bonding material 80P into the hole constituting the first through-hole 91 in the bonding process of manufacturing the power conversion device 100.

[0042] (Modification 3) Fig. 7 is a cross-sectional view of the power conversion device 100 in Modification 3, and corresponds to Fig. 2 in the embodiment. In the above-described embodiment, the thickness of the metal film forming each through-hole is constant. However, the thickness of the metal film may be different, and in particular, the thickness of the metal film of the first through-hole 91 may be thicker than that of the second through-hole 92.

[0043] In addition to the effects of the embodiment, this modification provides the following effects: (10) The first through-holes 91 are thicker than the second through-holes 92. Therefore, the increased thickness of the metal film improves the rigidity of the through-holes and reduces deformation due to temperature changes. Furthermore, by increasing the thickness of the metal film in the first through-holes 91, which are located directly below the semiconductor element 1 and therefore prone to temperature increases, heat generated by the semiconductor package 10 is more easily dissipated.

[0044] (Variation 4) The thermal conductivity of the bonding material 80 may be equal to or lower than the thermal conductivity of the filler 59. Furthermore, the thermal conductivity of the bonding material 80 may be higher than the thermal conductivity of the metal coating that forms the first through-hole 91 and the second through-hole 92.

[0045] (Variation 5) The linear expansion coefficient of the bonding material 80 may be higher than the thermal conductivity of the metal film that forms the first through hole 91 and the second through hole 92. However, even in this case, the linear expansion coefficient of the filler 59 is sufficiently higher than the metal film and the bonding material 80.

[0046] (Variation 6) In the above-described embodiment, the third bonding material 83 disposed on the back surface of the wiring board 50 has approximately the same area as the first bonding material 81 disposed on the front surface of the wiring board 50. However, the area of ​​the third bonding material 83 may be smaller than the area of ​​the first bonding material 81, or the third bonding material 83 may not be present.

[0047] (Seventh Modification) In the above-described embodiment, the power conversion device 100 has been described as a three-phase AC power conversion device having four sets of upper and lower arms for each of the phases U, V, and W. However, the power conversion device 100 may have only one set of upper and lower arms for each phase, or may be for single phase use.

[0048] The above-described embodiments and modifications may be combined with each other. Although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments conceivable within the scope of the technical concept of the present invention are also included within the scope of the present invention.

[0049] 1: Semiconductor element 10: Semiconductor package 50: Wiring board 51: First through-hole 52: Second through-hole 59: Filler 80: Bonding material 81: First bonding material 82: Second bonding material 83: Third bonding material 91: First through-hole 92: Second through-hole 100: Power conversion device

Claims

1. A power conversion device comprising: a semiconductor package incorporating a semiconductor element bonded onto a lead frame; and a flat substrate having a front surface and a back surface, the semiconductor package being mounted on the front surface and electrically connected to the lead frame, wherein the substrate has first and second through holes which are metal films formed on the inner peripheries of holes passing through in a thickness direction connecting the front surface and the back surface, the first through hole being provided in an area which overlaps with the semiconductor element in the thickness direction, and the second through hole being provided in an area which does not overlap with the semiconductor element in the thickness direction, the power conversion device further comprising: a bonding material which connects the ends of the first and second through holes in the thickness direction which are closer to the semiconductor element to the lead frame and which is filled into the first through hole, the hole which constitutes the second through hole being filled with a filler, and the difference in linear expansion coefficient between the filler and the metal film being greater than the difference in linear expansion coefficient between the bonding material and the metal film.

2. The power conversion device according to claim 1, wherein the bonding material has a higher thermal conductivity than the filler.

3. A power conversion device according to claim 1, wherein the diameter of the hole constituting the first through hole is larger than the diameter of the hole constituting the second through hole.

4. A power conversion device according to claim 1, wherein the diameter of the hole constituting the first through hole is smaller on the side farther from the semiconductor element than on the side closer to the semiconductor element.

5. The power conversion device according to claim 1, wherein the first through-hole is thicker than the second through-hole.

6. A power conversion device according to claim 1, wherein the substrate has wiring on both the front surface and the back surface, and the first through-hole and the second through-hole each contact both the wiring on the front surface and the wiring on the back surface.

7. A power conversion device according to claim 1, wherein the wiring on the front surface and the wiring on the back surface extend over substantially the same range in the thickness direction.

8. A power conversion device according to claim 1, wherein the semiconductor packages are provided in multiple locations on the substrate in a depth direction perpendicular to the thickness direction, and the first through holes and the second through holes are aligned in a direction perpendicular to the thickness direction and the depth direction.

9. The power conversion device according to claim 1, wherein one of the semiconductor elements has two or more of the first through holes.

10. A method for manufacturing a power conversion device, comprising: a hole forming step of forming a plurality of holes penetrating a flat substrate in the thickness direction; a film forming step of forming first through holes and second through holes by forming a metal film on the inner periphery of each of the plurality of holes; a filler filling step of filling the interiors of the holes constituting the second through holes with a filler; and an arrangement step of arranging a bonding material on the upper surface of the substrate so as to cover the first through holes and the second through holes, and arranging a semiconductor package having a semiconductor element bonded to a lead frame on the bonding material, wherein in the arrangement step, the first through holes and the semiconductor element are arranged so as to overlap in the thickness direction; and after the arrangement step, a bonding step of filling the interiors of the holes constituting the first through holes with the bonding material that has been heated and melted, wherein the difference in linear expansion coefficient between the filler and the metal film is greater than the difference in linear expansion coefficient between the bonding material and the metal film.

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