Semiconductor module

Abstract

In semiconductor modules, this suppresses the occurrence of cracks in the insulating layer of the wiring board. [Solution] In a semiconductor module (1) according to one embodiment, in a cross section passing through the corner of the insulating layer (23) in a plan view and the corner of the second conductor layer (22), the distance (L1) from the second conductor layer (22) to the periphery of the bonding material (S) on the second surface (23b) of the insulating layer (23) on the heat dissipation base (30) side is less than or equal to the thickness (L2) of the bonding material (S) between the second conductor layer (22) and the heat dissipation base (30). A non-bonded portion (R) is provided around the bonding material (S) on the heat dissipation base (30), and in the above cross section, the distance (L4) in a plan view from the second conductor layer (22) to the non-bonded portion (R) is less than or equal to the distance (L3) from the second conductor layer (22) to the periphery of the insulating layer (23) on the second surface (23b).

Description

Technical Field

[0001] The present invention relates to a semiconductor module including a wiring board on which semiconductor elements are mounted and a heat dissipation base to which the wiring board is joined.

Background Art

[0002] Conventionally, as a semiconductor module used in a power conversion device or the like, a semiconductor module in which a wiring board on which semiconductor elements are mounted and a heat dissipation base are joined is known (see, for example, Patent Documents 1 to 6). In this type of semiconductor module, the wiring board has an insulating layer such as a ceramic substrate provided with conductor layers on the front and back surfaces, and is joined to the heat dissipation base by a joining material such as solder on the back surface side of the wiring board.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the bonding material used to join a circuit board to a heat dissipation base is compressed during melting by the weight of the circuit board, mounted components, and jigs, the contact area with the insulating layer increases. Then, when the bonding material cools (during thermal contraction), the insulating layer, which has a relatively small coefficient of linear expansion, is pulled by the bonding material and the conductor layer, which have relatively large coefficients of linear expansion. Since the insulating layer is not bonded to the bonding material, stress concentrates at the boundary between the bonding material and the conductor layer, which can cause cracks.

[0005] In one aspect, an object of the present invention is to provide a semiconductor module that can suppress the occurrence of cracks in the insulating layer of a wiring board. [Means for solving the problem]

[0006] In one embodiment, a semiconductor module comprises a semiconductor element, a wiring board on which the semiconductor element is mounted, and a heat dissipation base joined to the wiring board by a bonding material, wherein the wiring board has an insulating layer, a first conductor layer provided on the first surface of the insulating layer on the semiconductor element side, and a second conductor layer provided on the second surface of the insulating layer on the heat dissipation base side, wherein in a cross section passing through the corner of the insulating layer in a plan view and the corner of the second conductor layer, the distance from the second conductor layer to the periphery of the bonding material on the second surface is less than or equal to the thickness of the bonding material between the second conductor layer and the heat dissipation base, a non-bonded portion is provided around the bonding material on the heat dissipation base, the wettability between the bonding material and the second conductor layer, and between the bonding material and the heat dissipation base is greater than the wettability between the non-bonded portion and the bonding material, and in the cross section, the distance in the plan view from the second conductor layer to the non-bonded portion is less than or equal to the distance from the second conductor layer to the periphery of the insulating layer on the second surface.

[0007] In another embodiment, the semiconductor module comprises a semiconductor element, a wiring board on which the semiconductor element is mounted, and a heat dissipation base joined to the wiring board by a bonding material, wherein the wiring board has an insulating layer, a first conductor layer provided on the first surface of the insulating layer on the semiconductor element side, and a second conductor layer provided on the second surface of the insulating layer on the heat dissipation base side, wherein in a cross section passing through the corner of the insulating layer in a plan view and the corner of the second conductor layer, the distance from the second conductor layer to the periphery of the insulating layer on the second surface is less than or equal to the thickness of the bonding material between the second conductor layer and the heat dissipation base. [Effects of the Invention]

[0008] According to the above embodiment, it is possible to suppress the occurrence of cracks in the insulating layer of the wiring board. [Brief explanation of the drawing]

[0009] [Figure 1] This is a plan view showing a semiconductor module according to one embodiment. [Figure 2] This is a cross-sectional view taken along line II-II in Figure 1. [Figure 3] This is a plan view showing solder resist provided on a heat dissipation base in adjacent portions of multiple insulating layers in one embodiment. [Figure 4] This is a plan view showing solder resist provided on a heat dissipation base only in adjacent portions of the corners of multiple insulating layers, according to one embodiment. [Figure 5] This is a plan view showing solder resist on a heat dissipation base in one embodiment. [Figure 6] This is a cross-sectional view illustrating the increased contact area between the bonding material and the insulating layer in the center of the heat dissipation base. [Figure 7] This is a cross-sectional view illustrating the spread of the bonding material in a comparative example (without solder resist). [Figure 8] This is a cross-sectional view illustrating the occurrence of cracks in the comparative example. [Figure 9] This figure shows an example of the maximum principal stress of the insulating layer in one embodiment and a comparative example. [Figure 10] A plan view showing a solder resist on a heat dissipation base in a first modification to an embodiment. [Figure 11] A plan view showing a solder resist on a heat dissipation base in a second modification to an embodiment. [Figure 12] A cross-sectional view (corresponding to the cutting line II-II in FIG. 1) showing a wiring board or the like in another embodiment.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, a semiconductor module 1 according to an embodiment and other embodiments of the present invention will be described in detail with reference to the drawings. In each of the drawings referred to, the X, Y, and Z axes are shown for the purpose of defining directions and respective surfaces in the illustrated semiconductor module 1 and the like. The X, Y, and Z axes are orthogonal to each other and form a right-handed system. In the following description, the Z direction may sometimes be referred to as the vertical direction. Also, the plane including the X axis and the Y axis may sometimes be referred to as the upper surface or the lower surface. These directions and surfaces are expressions used for convenience of explanation, and depending on the mounting posture of the semiconductor module 1 and the like, the corresponding relationships with each of the XYZ directions may change. For example, in this specification, the surface facing the positive side in the Z direction (+Z direction) in the members constituting the semiconductor module 1 is referred to as the upper surface, and the surface facing the negative side in the Z direction (-Z direction) is referred to as the lower surface, but the surface facing the negative side in the Z direction may be referred to as the upper surface, and the surface facing the positive side in the Z direction may be referred to as the lower surface. Also, in this specification, a plan view means a case where the upper surface (XY plane) of the semiconductor module 1 and the like is seen perspectively from the positive side in the Z direction toward the negative side in the Z direction.

[0011] The vertical and horizontal ratios in each drawing and the size relationships between members are merely schematically represented and do not necessarily match the relationships in the actually manufactured semiconductor module 1 and the like. For convenience of explanation, the size relationships between members may be exaggerated in some cases. Also, between different drawings, the shapes of the same members may be different.

[0012] In the following description, as an example of the semiconductor module 1 according to one embodiment and other embodiments, an apparatus applied to a power conversion apparatus such as an inverter device for an industrial or in-vehicle motor will be cited. For this reason, in the following description, detailed descriptions of the same or similar configurations, functions, operations, assembly methods, etc. as those of known semiconductor modules will be omitted.

[0013] <One embodiment> FIG. 1 is a plan view showing a semiconductor module 1 according to one embodiment. FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1.

[0014] The semiconductor module 1 shown in FIG. 1 includes a plurality of semiconductor elements 10, a plurality of wiring boards 20, and a heat dissipation base 30. The semiconductor module 1 also includes a case 40 (illustrated by a two-dot chain line which is an imaginary line) and a sealing material 50 shown in FIG. 2.

[0015] The semiconductor elements 10 are mounted on the wiring boards 20. In the example of FIG. 1, the semiconductor module 1 includes four wiring boards 20 arranged in two rows each in the X direction and the Y direction, and semiconductor elements 10 arranged eight each on each of these four wiring boards 20.

[0016] For example, the semiconductor element 10 may be an IGBT (Insulated Gate Bipolar Transistor) which is a switching element, or an FWD (Free Wheeling Diode) which is a diode element. Other semiconductor elements such as an RC (Reverse Conducting)-IGBT element, which integrates a switching element and a diode element connected in antiparallel to the switching element, may also be arranged as the semiconductor element 10. The switching element and diode element in the semiconductor element 10 are not limited to a Si substrate, but may be formed on a semiconductor substrate using a wide bandgap semiconductor such as SiC (Silicon Carbide) or GaN (Gallium Nitride). The switching element may be composed of, for example, a SiC-MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or a BJT (Bipolar Junction Transistor). The diode element may be composed of, for example, a SiC-SBD (Schottky Barrier Diode), a JBS (Junction Barrier Schottky) diode, an MPS (Merged PN Schottky) diode, or a PN diode.

[0017] The main electrode provided on the upper surface of the semiconductor element 10 is electrically connected to other semiconductor elements 10, the first conductor layer 21, etc., by main current wiring W1. In addition, the control electrode (e.g., gate electrode) provided on the upper surface of the semiconductor element 10 is electrically connected indirectly or directly to a control terminal (not shown) via the first conductor layer 21 by control wiring W2. The main terminals, which are the input and output terminals of the semiconductor module 1, and the control terminals may be integrally fixed to a case 40 (shown by dashed lines, which are dashed lines), which will be described later, and which surrounds the four wiring boards 20.

[0018] Each of the four wiring boards 20 is joined to a common single heat dissipation base 30 at its lower surface (second conductor layer 22) by a bonding material S such as solder. The wiring board 20 has a rectangular shape in plan view and includes a first conductor layer 21, a second conductor layer 22, and an insulating layer 23. The wiring board 20 may be, for example, a DCB (Direct Copper Bonding) substrate or an AMB (Active Metal Brazing) substrate. The wiring board 20 may also be called a laminated substrate, an insulating circuit board, an insulating heat dissipation circuit board, etc.

[0019] The first conductor layer 21 is a component that functions as a wiring member in an inverter circuit, for example, and is provided in multiple separate sections on the first surface 23a of the insulating layer 23 on the semiconductor element 10 side, made of a metal plate or metal foil such as copper or aluminum. The first conductor layer 21 is electrically connected to other first conductor layers 21, main electrodes, main terminals, control terminals, etc., provided on the upper surface of the semiconductor element 10, by main current wiring W1 or control wiring W2. The first conductor layer 21 may also be called a conductor plate, conductor pattern, conductive layer, wiring pattern, etc. The main current wiring W1 and control wiring W2 are, for example, metallic bonding wires. The main current wiring W1 and control wiring W2 (especially the main current wiring W1) may be replaced with other wiring such as leads formed by processing a metal plate such as a copper plate.

[0020] The second conductor layer 22 functions as a heat conduction member that conducts heat generated in the inverter circuit to the heat dissipation base 30, and is provided on the second surface 23b of the insulating layer 23 on the heat dissipation base 30 side using a metal plate or metal foil such as copper or aluminum. The second conductor layer 22 (wiring board 20) is joined to the heat dissipation base 30 by a bonding material S such as solder. The second conductor layer 22 may also be called a heat dissipation layer, heat sink, heat dissipation pattern, conductor pattern, etc.

[0021] The insulating layer 23 is, for example, a ceramic substrate. The insulating layer 23 is not limited to a specific substrate, but may be a ceramic substrate formed from a ceramic material such as aluminum nitride (AlN), aluminum oxide (Al2O3), silicon nitride (Si3N4), and a composite material of aluminum oxide (Al2O3) and zirconium oxide (ZrO2). The insulating layer 23 may also be, for example, a substrate molded from an insulating resin such as epoxy resin, a substrate impregnated with an insulating resin onto a base material such as glass fiber, or a substrate whose surface is coated with an insulating resin on a flat metal core. Here, the bonding material S that joins the wiring board 20 and the heat dissipation base 30 covers the second conductor layer 22 and is in contact with the insulating layer 23. However, the bonding material S does not have to be in contact with the insulating layer 23.

[0022] The shape, number, and placement of the semiconductor elements 10 and the wiring boards 20 can be changed as appropriate. While it is desirable to have multiple wiring boards 20, the number of semiconductor elements 10 and wiring boards 20 can be any number of one or more.

[0023] The heat dissipation base 30 has a rectangular shape in plan view. The heat dissipation base 30 has fastening holes 31 at its four corners in plan view. The heat dissipation base 30 is fastened to a cooler (not shown) together with the case 40 by screws inserted into the fastening holes 31.

[0024] The heat dissipation base 30 functions as a heat conductive member that conducts the heat generated by the semiconductor element 10 to the cooler, and is formed from a metal plate such as a copper plate or an aluminum plate. In order to spread the heat conductive material such as thermal grease or thermal compound, which is inserted between the heat dissipation base 30 and the cooler, radially from the center of the heat dissipation base 30, the entire flat metal plate is curved, for example by press working, as shown in Figure 6, so that the lower surface becomes a convex curved surface and the upper surface becomes a concave curved surface. After the heat dissipation base 30 is fastened to the cooler by screws inserted into fastening holes 31, it approaches a flat plate shape as shown in Figure 2.

[0025] The case 40, for example, has a rectangular cylindrical shape with the Z-direction as its central axis, and houses the semiconductor element 10 and the wiring board 20 in its hollow portion 41. The case 40 is fixed, for example, to the periphery of the upper surface of the heat dissipation base 30 by adhesive and fastened to the cooler together with the heat dissipation base 30.

[0026] The sealing material 50 shown in Figure 2 seals the semiconductor element 10 and the wiring board 20 inside the case 40. The sealing material 50 is, for example, epoxy resin, silicone gel, etc.

[0027] As shown in Figure 2, a solder resist R is provided around the bonding material S in the heat dissipation base 30. The solder resist R has the property of repelling the bonding material S even when it comes into contact with it, and therefore does not bond to the bonding material S. Note that the solder resist R is an example of a non-bonding processed area. This non-bonding processed area can be any processed area that prevents bonding between the bonding material S and the heat dissipation base 30, and is not limited to the solder resist R. For example, the non-bonding processed area may be a part that is filled in with a pencil or the like (a part coated with a filling material such as graphite) or an oxide film. Here, the wettability between the solder resist R (non-bonding processed area) and the bonding material S is lower than the wettability between the bonding material S and the first conductor layer 21, the second conductor layer 22, and the heat dissipation base 30. Furthermore, it is even more preferable that the wettability between the solder resist R and the bonding material S is lower than the wettability between the bonding material S and the insulating layer 23.

[0028] The solder resist R is positioned around the bonding material S in the heat dissipation base 30, for example, between adjacent wiring boards 20 (insulating layer 23) in a plan view. In the example shown in Figure 1, since the wiring boards 20 are arranged in pairs in both the X and Y directions, the solder resist R takes on a cross shape in a plan view. However, the solder resist R may also be provided so as to surround the bonding material S around the entire circumference of the wiring board 20.

[0029] The solder resist R should be provided with a width such that the bonding material S does not cross over it. Furthermore, in order to prevent the bonding material S from connecting between adjacent wiring boards 20, the solder resist R should be arranged in the cross shape described above, extending across the entire area between adjacent insulating layers 23 in a plan view, as shown in Figures 1 and 3. Alternatively, the solder resist R may be placed only at the corners of the insulating layer 23 in a plan view, as shown in Figure 4. These corners may be only where the corners of two or four insulating layers 23 face each other, or only where the corners of four insulating layers 23 face each other. The solder resist R shown in Figure 4 exhibits a right-angled triangle with two sides parallel to the periphery of the insulating layer 23 in a plan view, but the shape is arbitrary. Note that in Figures 3 and 4, the first conductor layer 21 and the insulating layer 23 are located above the bonding material S and the solder resist R, so the first conductor layer 21 and the insulating layer 23 are shown with dashed lines.

[0030] Here, as shown in Figure 2, in the II-II cross section of Figure 1 (a cross section passing through the corner of the insulating layer 23 in a plan view and the same corner of the second conductor layer 22), the distance (length L1) from the second conductor layer 22 to the periphery of the bonding material S on the second surface 23b of the insulating layer 23 is less than or equal to the thickness (length L2) of the bonding material S between the second conductor layer 22 and the heat dissipation base 30. Note that the cross section in Figure 2 extends in the diagonal direction D in a plan view of the insulating layer 23. Furthermore, the periphery of the bonding material S and the insulating layer 23 in the above cross section can be called a corner, but it may also be curved.

[0031] Furthermore, in the cross-section shown in Figure 2, the distance (length L4) in a plan view (in a direction perpendicular to the thickness direction (Z direction) of the bonding material S (in the XY plane)) from the second conductor layer 22 to the solder resist R (the same as to the periphery of the bonding material S on the heat dissipation base 30) is less than or equal to the distance (length L3) from the second conductor layer 22 to the periphery of the insulating layer 23 on the second surface 23b. If length L4 is smaller than length L3, the solder resist R will be located below the insulating layer 23. As an example, length L4 is 1 mm or less.

[0032] Furthermore, in the cross-section shown in Figure 2, the distance (length L4) in a plan view from the second conductor layer 22 to the periphery of the bonding material S on the heat dissipation base 30 (the same as up to the solder resist R) is shorter than the distance (length L5) from the first conductor layer 21 to the periphery of the first surface 23a of the insulating layer 23.

[0033] Furthermore, in the cross-section shown in Figure 2, the distance (length L4) in a plan view from the second conductor layer 22 to the periphery of the bonding material S on the heat dissipation base 30 (the same distance as up to the solder resist R) is longer than the distance (length L6) between the insulating layer 23 and the heat dissipation base 30 in the thickness direction (Z direction) of the bonding material S.

[0034] Furthermore, in the cross-section of Figure 2, the distance from the first conductor layer 21 to the periphery of the first surface 23a of the insulating layer 23 (length L5) is approximately the same as the distance from the second conductor layer 22 to the periphery of the insulating layer 23 on the second surface 23b (length L3) in Figure 2, but it is preferable for it to be longer than this length L3.

[0035] Here, the periphery (corner) of the insulating layer 23 in the cross-section of Figure 2 is preferably adjacent to another insulating layer 23. Also, as shown in Figure 5, the solder resist R may have a longitudinally wide portion Ra and a transversely wide portion Rb in the portion where two or four insulating layers 23 are adjacent at a corner. The longitudinally wide portion Ra extends in the longitudinal direction (Y direction) of the heat dissipation base 30, and the transversely wide portion Rb extends in the transverse direction (X direction) of the heat dissipation base 30. The width (length L12) of the longitudinally wide portion Ra and the transversely wide portion Rb from the intermediate position P is longer than the width (length L11) of the two insulating layers 23 from the intermediate position P in the portion where the two insulating layers 23 are adjacent at an edge. Furthermore, the length (L13) of the longitudinally wide portion Ra extending in the longitudinal direction (Y direction) is longer than the width (length L12) from the intermediate position P between the longitudinally wide portion Ra and the transversely wide portion Rb. Also, the length (L14) of the transversely wide portion Rb extending in the transverse direction (X direction) is, for example, more than twice as long as the length (L13) of the longitudinally wide portion Ra extending in the longitudinal direction (Y direction). Note that the longitudinally wide portion Ra and the transversely wide portion Rb may be provided only in the parts where the four insulating layers 23 are adjacent at the corners. Also, of the longitudinally wide portion Ra and the transversely wide portion Rb, only the transversely wide portion Rb may be provided. Furthermore, if the heat dissipation base 30 is square in plan view, the lengths of the wide portions (longitudinally wide portion Ra and transversely wide portion Rb) may be the same.

[0036] As described above, the heat dissipation base 30 is curved so that its lower surface is a convex curved surface and its upper surface is a concave curved surface. Therefore, as shown in Figure 6, the bonding material S during molten state is concentrated in the center of the heat dissipation base 30 in a plan view due to gravity (see arrow in Figure 6). In areas where the amount of bonding material S increases, the fillet tends to widen, and as the wiring board 20 (semiconductor element 10) sinks due to the weight of the wiring board 20 and the jig, the insulating layer 23 (second surface 23b) and the bonding material S come into contact more easily. On the other hand, at the periphery of the heat dissipation base 30, there is less bonding material S, so the fillet is smaller, and even if the wiring board 20 sinks, the contact area between the bonding material S and the insulating layer 23 does not increase easily.

[0037] In this regard, as described above, the solder resist R is positioned between adjacent wiring boards 20 (insulating layer 23). Therefore, the spreading of the bonding material S can be suppressed in the central part of the heat dissipation base 30, where the contact area with the insulating layer 23 is more likely to increase than in the peripheral part of the heat dissipation base 30 where the wiring boards 20 are not adjacent to other wiring boards 20. Furthermore, as shown in Figure 5 above, the length (L14) of the short-width portion Rb extending in the short direction (X direction) is longer than the length (L13) of the long-width portion Ra extending in the long direction (Y direction). As a result, the wide portion (short-width portion Rb) of the solder resist R becomes longer in the center of the heat dissipation base 30 in the longitudinal direction, where the contact area with the insulating layer 23 is particularly likely to increase, thus further suppressing the spreading of the bonding material S.

[0038] As shown in the comparative example in Figure 7, if the solder resist R is omitted (the position of the solder resist R and the bonding material S when the solder resist R is provided are shown by dashed lines), in the above cross-section, the distance (length L21) from the second conductor layer 22 to the periphery of the bonding material S on the second surface 23b of the insulating layer 23 is longer than the thickness (length L22) of the bonding material S between the second conductor layer 22 and the heat dissipation base 30.

[0039] As a result, when the insulating layer 23 cools, as shown in Figure 8, the insulating layer 23, which has a relatively small coefficient of thermal expansion, is pulled by the bonding material S and the second conductor layer 22, which have relatively large coefficients of thermal expansion. Since the insulating layer 23 is not bonded by the bonding material S, stress concentrates at the boundary between the bonding material S and the second conductor layer 22, causing cracks C to form in the insulating layer 23. These cracks C are more likely to occur when the insulating layer 23 is made of a material with low flexural strength, such as AlN-based ceramics.

[0040] In contrast, as in this embodiment, the presence of solder resist R reduces the distance (length L1) from the second conductor layer 22 to the periphery of the bonding material S on the second surface 23b of the insulating layer 23 in the cross-section shown in Figure 2 to less than or equal to the thickness (length L2) of the bonding material S between the second conductor layer 22 and the heat dissipation base 30, thereby easing the stress on the insulating layer 23 during heat cycling. As a result, as shown in Figure 9, in this embodiment, compared to the comparative example shown in Figure 7 where length L21 (corresponding to length L1) is longer than length L22 (corresponding to length L2), the maximum principal stress [MPa] of the insulating layer 23 is reduced to approximately 0.55 times (652.9 → 362.9). This reduces the rate of ceramic cracking due to heating and cooling during operation of the semiconductor module 1 from, for example, 80% to 10 ppm (Parts Per Million) or less, improving quality.

[0041] In the embodiment described above, the semiconductor module 1 comprises a semiconductor element 10, a wiring board 20 on which the semiconductor element 10 is mounted, and a heat dissipation base 30 joined to the wiring board 20 by a bonding material S. The wiring board 20 has an insulating layer 23, a first conductor layer 21 provided on the first surface 23a of the insulating layer 23 on the semiconductor element 10 side, and a second conductor layer 22 provided on the second surface 23b of the insulating layer 23 on the heat dissipation base 30 side. In a cross-section (see Figure 2) passing through the corner of the insulating layer 23 in a plan view and the corner of the second conductor layer 22, the distance (length L1) from the second conductor layer 22 to the periphery of the bonding material S on the second surface 23b of the insulating layer 23 is less than or equal to the thickness (length L2) of the bonding material S between the second conductor layer 22 and the heat dissipation base 30. Solder resist R (an example of a non-bonded portion) is provided around the bonding material S on the heat dissipation base 30. The wettability between the bonding material S and the second conductor layer 22, and between the bonding material S and the heat dissipation base 30, is greater than the wettability between the solder resist R and the bonding material S. More preferably, the wettability between the solder resist R and the bonding material S is lower than the wettability between the insulating layer 23 and the bonding material S. In the above cross-section, the distance (length L4) in plan view from the second conductor layer 22 to the solder resist R is less than or equal to the distance (length L3) from the second conductor layer 22 to the periphery of the insulating layer 23 on the second surface 23b.

[0042] As a result, the solder resist R is positioned below or around the periphery of the insulating layer 23, so that in the cross-section of Figure 2, the distance (length L1) from the second conductor layer 22 to the periphery of the bonding material S on the second surface 23b of the insulating layer 23 can be made less than or equal to the thickness (length L2) of the bonding material S between the second conductor layer 22 and the heat dissipation base 30. Therefore, when the bonding material S cools (during thermal contraction), even if the insulating layer 23, which has a relatively small coefficient of linear expansion, is pulled by the bonding material S and the second conductor layer 22, which have relatively large coefficients of linear expansion, the stress concentrated at the boundary between the bonding material S and the second conductor layer 22 in the insulating layer 23 can be alleviated. Thus, according to this embodiment, it is possible to suppress the occurrence of cracks C in the insulating layer 23 of the wiring board 20.

[0043] Furthermore, in this embodiment, the semiconductor module 1 comprises a plurality of wiring boards 20, and the corners of the insulating layers 23 in the cross-section are adjacent to other insulating layers 23.

[0044] This makes it possible to alleviate the stress concentrated at the boundary between the bonding material S and the second conductor layer 22 in the insulating layer 23, where stress tends to concentrate, in areas where multiple insulating layers 23 are adjacent to each other. Therefore, it is possible to further suppress the occurrence of cracks C in the insulating layer 23 of the wiring board 20.

[0045] Furthermore, in this embodiment, in the cross-section described above, the distance (length L4) in plan view from the second conductor layer 22 to the periphery of the bonding material S (solder resist R) in the heat dissipation base 30 is shorter than the distance (length L5) from the first conductor layer 21 to the periphery of the first surface 23a of the insulating layer 23.

[0046] As a result, even if the spread of the bonding material S increases and the contact area between the bonding material S and the second surface 23b of the insulating layer 23 increases, the creepage distance of the insulating layer 23 can be secured.

[0047] Furthermore, in this embodiment, in the cross-section described above, the distance (length L4) in a plan view from the second conductor layer 22 to the periphery (solder resist R) of the bonding material S on the heat dissipation base 30 is longer than the distance (length L6) between the insulating layer 23 and the heat dissipation base 30 in the thickness direction of the bonding material S.

[0048] This makes it possible to avoid defects such as cracks forming in the joining material S itself due to thermal cycling, which is caused by the narrowing of the joining material S's width.

[0049] Furthermore, in this embodiment, in the cross-section described above, the distance from the first conductor layer 21 to the periphery of the first surface 23a of the insulating layer 23 (length L5) is longer than the distance from the second conductor layer 22 to the periphery of the second surface 23b of the insulating layer 23 (length L3).

[0050] As a result, even if the spread of the bonding material S increases and the contact area between the bonding material S and the second surface 23b of the insulating layer 23 increases, the creepage distance of the insulating layer 23 can be secured.

[0051] In this embodiment, the bonding material S covers the second conductor layer 22 and is in contact with the insulating layer 23.

[0052] In this embodiment, as described above, even if the bonding material S comes into contact with the second surface 23b of the insulating layer 23, it is possible to suppress the occurrence of cracks C in the insulating layer 23. Therefore, by having the bonding material S cover the second conductor layer 22, the heat dissipation from the semiconductor element 10 to the heat dissipation base 30 via the wiring board 20 (second conductor layer 22) can be improved.

[0053] <First modified example of one embodiment> Figure 10 is a plan view showing the solder resist R on the heat dissipation base 230 in a first modified example of one embodiment.

[0054] The semiconductor module 2 shown in Figure 10 includes semiconductor elements 10, a wiring board 20, a case 40, a sealing material 50, etc., similar to the semiconductor module 1 shown in Figures 1 and 2 above, but these are not shown in Figure 10.

[0055] As shown in Figure 10, in this first modified example, only two wiring boards (insulating layers 223 shown by dashed lines) are arranged in the Y direction. Therefore, the heat dissipation base 230 shown in Figure 10 has a more elongated rectangular shape in plan view than the heat dissipation base 30 shown in Figure 5. The heat dissipation base 230 is provided with fastening holes 231 at the four corners in plan view.

[0056] The solder resist R is positioned over the entire area between adjacent insulating layers 223. Furthermore, the solder resist R has a longitudinally wide portion Ra and a transversely wide portion Rb where the two insulating layers 223 meet at a corner. The longitudinally wide portion Ra extends in the longitudinal direction (Y direction) of the heat dissipation base 230, and the transversely wide portion Rb extends in the transverse direction (X direction) of the heat dissipation base 230. The width (length L12) of the longitudinally wide portion Ra and the transversely wide portion Rb is greater than the width (length L11) of the solder resist R from the intermediate position P between the two insulating layers 223 where they meet at an edge. Also, the length (L13) of the longitudinally wide portion Ra extending in the longitudinal direction (Y direction) is greater than the width (length L12) of the longitudinally wide portion Ra and the transversely wide portion Rb from the intermediate position P. Furthermore, the length (L14) of the wide portion Rb in the short direction extending in the short direction (X direction) is longer than the length (L13) of the wide portion Ra in the long direction extending in the long direction (Y direction).

[0057] <Second modified example of one embodiment> Figure 11 is a plan view showing the solder resist R on the heat dissipation base 330 in a second modified example of one embodiment.

[0058] The semiconductor module 3 shown in Figure 11 includes semiconductor elements 10, a wiring board 20, a case 40, a sealing material 50, etc., similar to the semiconductor module 1 shown in Figures 1 and 2 above, but these are not shown in Figure 11.

[0059] As shown in Figure 11, in this second modified example, only six wiring boards (insulating layers 323) are arranged in the Y direction. Therefore, the heat dissipation base 230 shown in Figure 11 has a more elongated rectangular shape in plan view in the Y direction than the heat dissipation base 230 shown in Figure 10. The heat dissipation base 330 has seven fastening holes 331 arranged in the Y direction at both the end on one side in the X direction and the other end on the other side.

[0060] The solder resist R is positioned over the entire area between adjacent insulating layers 323. Furthermore, the solder resist R has a longitudinally wide portion Ra and a transversely wide portion Rb at the corners where each insulating layer 323 is adjacent. The longitudinally wide portion Ra extends in the longitudinal direction (Y direction) of the heat dissipation base 330, and the transversely wide portion Rb extends in the transverse direction (X direction) of the heat dissipation base 330. The width (length L12) of the longitudinally wide portion Ra and the transversely wide portion Rb is greater than the width (length L11) of the solder resist R from the midpoint P between the two insulating layers 323 at the edge where the two insulating layers 323 are adjacent. Also, the length (L13) of the longitudinally wide portion Ra extending in the longitudinal direction (Y direction) is greater than the width (length L12) of the longitudinally wide portion Ra and the transversely wide portion Rb from the midpoint P. Furthermore, the length (L14) of the wide portion Rb in the short direction extending in the short direction (X direction) is longer than the length (L13) of the wide portion Ra in the long direction extending in the long direction (Y direction).

[0061] As mentioned above, when melted, the bonding material S gathers in the center of the heat dissipation base 330 in a plan view due to gravity, making it easy for the insulating layer 323 and the bonding material S to come into contact. Therefore, the solder resist R may be provided only in the center of the heat dissipation base 330 in the longitudinal direction (for example, between the third and fourth insulating layers 323 from the positive Y side), or only in the center and near the center of the heat dissipation base 330 in the longitudinal direction (for example, between the second and third insulating layers 323 from the positive Y side, or between the fourth and fifth insulating layers 323 from the positive Y side). Alternatively, the solder resist R may be wider in the center and near the center of the heat dissipation base 330 than in other areas.

[0062] <Other Embodiments> Figure 12 is a cross-sectional view (corresponding to the II-II cutting line in Figure 1) showing the wiring board 120, etc., in another embodiment.

[0063] In this embodiment, the solder resist R is omitted, and the dimensions of each part of the wiring board 120 are slightly different, but otherwise it can be constructed in the same manner as the semiconductor module 1 of the above-described embodiment. Therefore, explanations of overlapping matters will be omitted.

[0064] The wiring board 120 shown in Figure 12, like the wiring board 20 described above, has a rectangular shape in plan view and includes a first conductor layer 121, a second conductor layer 122, and an insulating layer 123. The number of wiring boards 120 is not particularly limited; it may be four as shown in Figure 1, two as shown in the first modified example in Figure 10, or six as shown in the second modified example in Figure 11.

[0065] In this embodiment, in a cross-section (cross-section in Figure 12) passing through the corner of the insulating layer 123 in a plan view and the corner of the second conductor layer 122, the distance (length L3) from the second conductor layer 122 to the periphery of the insulating layer 123 (for example, the corner in the diagonal direction D) is less than or equal to the thickness (length L2) of the bonding material S between the second conductor layer 122 and the heat dissipation base 30. Therefore, similar to the embodiment described above, in the above cross-section, the distance (length L1) from the second conductor layer 122 to the periphery of the bonding material S on the second surface 123b of the insulating layer 123 is also less than or equal to the thickness (length L2) of the bonding material S between the second conductor layer 122 and the heat dissipation base 30.

[0066] In order to shorten the length L3 in this way, it is possible to reduce the size of the insulating layer 123 so that its periphery is closer to the second conductor layer 122, or to enlarge the second conductor layer 122 so that it is closer to the periphery of the insulating layer 123. By enlarging the second conductor layer 122, the heat dissipation of the semiconductor element 10 can be improved.

[0067] Other length relationships are the same as in the embodiment described above, but in particular, the distance (length L3) from the second conductor layer 122 to the periphery (e.g., corner) of the insulating layer 123 is shorter than in the embodiment described above, which makes it difficult to secure the insulating distance, as the bonding material S spreads over the outer surface of the insulating layer 123.

[0068] From this perspective, it is particularly beneficial that, in the cross-section of Figure 12, the distance in plan view from the second conductor layer 122 to the periphery of the bonding material S in the heat dissipation base 30 (length L4) is shorter than the distance from the first conductor layer 121 to the periphery of the first surface 123a of the insulating layer 123 (length L5), and that the distance from the first conductor layer 121 to the periphery of the first surface 123a of the insulating layer 123 (length L5) is longer than the distance from the second conductor layer 122 to the periphery of the second surface 123b of the insulating layer 123 (length L3).

[0069] In the other embodiments described above, in the cross-section of Figure 12 (a cross-section passing through the corner of the insulating layer 123 in a plan view and the corner of the second conductor layer 122), the distance (length L3) from the second conductor layer 122 to the periphery of the insulating layer 123 (for example, the corner in the diagonal direction D) is less than or equal to the thickness (length L2) of the bonding material S between the second conductor layer 122 and the heat dissipation base 30.

[0070] Therefore, similar to the embodiment described above, in the cross-section of Figure 12, the distance (length L1) from the second conductor layer 122 to the periphery of the bonding material S on the second surface 123b of the insulating layer 123 can be made less than or equal to the thickness (length L2) of the bonding material S between the second conductor layer 122 and the heat dissipation base 30. Therefore, when the bonding material S is cooled, even if the insulating layer 123, which has a relatively small coefficient of thermal expansion, is pulled by the bonding material S and the second conductor layer 122, which have relatively large coefficients of thermal expansion, the stress concentrated at the boundary between the bonding material S and the second conductor layer 122 in the insulating layer 123 can be relieved. Thus, this embodiment also makes it possible to suppress the occurrence of cracks C in the insulating layer 123 of the wiring board 120.

[0071] The semiconductor module according to the present invention is not limited to the embodiments described above, and may be modified, substituted, or transformed in various ways without departing from the spirit of the technical idea. Furthermore, if the technical idea can be realized in a different way by technological advancements or other derived technologies, it may be implemented by that method. Accordingly, the claims cover all embodiments that may fall within the scope of the technical idea.

[0072] For example, as in other embodiments, the distance (length L3) from the second conductor layer 122 to the periphery (e.g., corner) of the insulating layer 123 in the cross-section of Figure 12 is less than or equal to the thickness (length L2) of the bonding material S between the second conductor layer 122 and the heat dissipation base 30, and a solder resist R may be provided as in one embodiment. Furthermore, the heat dissipation bases 30, 230, and 330 are formed by bending a flat base plate by press working or the like so that the lower surface becomes a convex curved surface, and the upper surface to which the wiring boards 20 and 120 are joined is formed to become a concave curved surface, but the heat dissipation bases 30, 230, and 330 in the present invention are not limited to such shapes.

[0073] The following are some of the inventions described in the specification and drawings of this application.

[0074] <Note 1> Semiconductor elements and A wiring board on which the aforementioned semiconductor elements are mounted, The system comprises a heat dissipation base joined to the wiring board by a bonding material, The wiring board comprises an insulating layer, a first conductor layer provided on the first surface of the insulating layer facing the semiconductor element, and a second conductor layer provided on the second surface of the insulating layer facing the heat dissipation base. In a cross-section passing through the corner of the insulating layer in a plan view and the corner of the second conductor layer, the distance from the second conductor layer to the periphery of the bonding material on the second surface is less than or equal to the thickness of the bonding material between the second conductor layer and the heat dissipation base. A non-joined portion is provided around the joining material in the heat dissipation base. The wettability between the bonding material and the second conductor layer, and between the bonding material and the heat dissipation base, is greater than the wettability between the unbonded portion and the bonding material. In the aforementioned cross-section, the distance in the plan view from the second conductor layer to the non-joined portion is less than or equal to the distance from the second conductor layer to the periphery of the insulating layer on the second surface. A semiconductor module characterized by the following features.

[0075] <Note 2> Semiconductor elements and A wiring board on which the aforementioned semiconductor elements are mounted, The system comprises a heat dissipation base joined to the wiring board by a bonding material, The wiring board comprises an insulating layer, a first conductor layer provided on the first surface of the insulating layer facing the semiconductor element, and a second conductor layer provided on the second surface of the insulating layer facing the heat dissipation base. In a cross-section passing through the corner of the insulating layer in a plan view and the corner of the second conductor layer, the distance from the second conductor layer to the periphery of the insulating layer on the second surface is less than or equal to the thickness of the bonding material between the second conductor layer and the heat dissipation base. A semiconductor module characterized by the following features.

[0076] <Note 3> The circuit board comprises multiple such circuit boards, The corner of the insulating layer is adjacent to another insulating layer. A semiconductor module as described in Appendix 1 or 2, characterized by the above.

[0077] <Note 4> In the aforementioned cross-section, the distance in the plan view from the second conductor layer to the periphery of the bonding material on the heat dissipation base is shorter than the distance from the first conductor layer to the periphery of the insulating layer on the first surface. A semiconductor module characterized by any one of the appendices 1 to 3.

[0078] <Note 5> In the aforementioned cross-section, the distance in plan view from the second conductor layer to the periphery of the bonding material on the heat dissipation base is longer than the distance between the insulating layer and the heat dissipation base in the thickness direction of the bonding material. A semiconductor module characterized by any one of the appendices 1 to 4.

[0079] <Note 6> In the cross-section, the distance from the first conductor layer to the periphery of the insulating layer on the first surface is longer than the distance from the second conductor layer to the periphery of the insulating layer on the second surface. A semiconductor module characterized by any one of the appendices 1 to 5.

[0080] <Note 7> The bonding material covers the second conductor layer and is in contact with the insulating layer. A semiconductor module characterized by any one of the appendices 1 to 6.

[0081] <Note 8> The wettability between the non-joined portion and the joining material is lower than the wettability between the insulating layer and the joining material. A semiconductor module as described in Appendix 1, characterized by the features described herein. [Industrial applicability]

[0082] As described above, the present invention has the effect of suppressing the occurrence of cracks in the insulating layer of a wiring board, and is particularly useful for industrial or electrical inverter devices. [Explanation of symbols]

[0083] 1,2,3 Semiconductor Modules 10 Semiconductor devices 20 Wiring board 21 First Conductor Layer 22 Second Conductor Layer 23 Insulating layer 23a 1st page 23b 2nd side 30 Heat dissipation base 31 Fastening hole 40 cases 41 Hollow part 50 Sealing material 120 Wiring board 121 First Conductor Layer 122 Second Conductor Layer 123 Insulating layer 123a 1st page 123b 2nd side 223,323 insulating layer 230,330 Heat dissipation base 231,331 Fastening hole C Crack D Diagonal direction P intermediate position R Solder Resist Ra Longitudinal wide section Rb Short-side wide section S Bonding material W1 Main current wiring W2 control wiring

Claims

1. Semiconductor elements and A wiring board on which the aforementioned semiconductor elements are mounted, The system comprises a heat dissipation base joined to the wiring board by a bonding material, The wiring board comprises an insulating layer, a first conductor layer provided on the first surface of the insulating layer facing the semiconductor element, and a second conductor layer provided on the second surface of the insulating layer facing the heat dissipation base. In a cross-section passing through the corner of the insulating layer in a plan view and the corner of the second conductor layer, the distance from the second conductor layer to the periphery of the bonding material on the second surface is less than or equal to the thickness of the bonding material between the second conductor layer and the heat dissipation base. A non-joined portion is provided around the joining material in the heat dissipation base. The wettability between the bonding material and the second conductor layer, and between the bonding material and the heat dissipation base, is greater than the wettability between the unbonded portion and the bonding material. In the aforementioned cross-section, the distance in the plan view from the second conductor layer to the non-joined portion is less than or equal to the distance from the second conductor layer to the periphery of the insulating layer on the second surface. A semiconductor module characterized by the following features.

2. Semiconductor elements and A wiring board on which the aforementioned semiconductor elements are mounted, The system comprises a heat dissipation base joined to the wiring board by a bonding material, The wiring board comprises an insulating layer, a first conductor layer provided on the first surface of the insulating layer facing the semiconductor element, and a second conductor layer provided on the second surface of the insulating layer facing the heat dissipation base. In a cross-section passing through the corner of the insulating layer in a plan view and the corner of the second conductor layer, the distance from the second conductor layer to the periphery of the insulating layer on the second surface is less than or equal to the thickness of the bonding material between the second conductor layer and the heat dissipation base. A semiconductor module characterized by the following features.

3. The circuit board comprises multiple such circuit boards, The corner of the insulating layer is adjacent to another insulating layer. A semiconductor module according to claim 1 or 2, characterized in that it is as described above.

4. In the aforementioned cross-section, the distance in the plan view from the second conductor layer to the periphery of the bonding material on the heat dissipation base is shorter than the distance from the first conductor layer to the periphery of the insulating layer on the first surface. A semiconductor module according to claim 1 or 2, characterized in that it is as described above.

5. In the aforementioned cross-section, the distance in plan view from the second conductor layer to the periphery of the bonding material on the heat dissipation base is longer than the distance between the insulating layer and the heat dissipation base in the thickness direction of the bonding material. A semiconductor module according to claim 1 or 2, characterized in that it is as described above.

6. In the cross-section, the distance from the first conductor layer to the periphery of the insulating layer on the first surface is longer than the distance from the second conductor layer to the periphery of the insulating layer on the second surface. A semiconductor module according to claim 1 or 2, characterized in that it is as described above.

7. The bonding material covers the second conductor layer and is in contact with the insulating layer. A semiconductor module according to claim 1 or 2, characterized in that it is as described above.

8. The wettability between the non-joined portion and the joining material is lower than the wettability between the insulating layer and the joining material. The semiconductor module according to claim 1, characterized in that it is a semiconductor module.

Images