Semiconductor device, power conversion device, and method for manufacturing semiconductor device

Abstract

A first solder and a second solder having a higher melting point than the first solder, are laminated between a first circuit element and a second circuit element. Solder joining of the first circuit element and the second circuit element is performed by heating the first solder and the second solder to a temperature between the melting point of the first solder and the melting point of the second solder. During the solder joining, a solder joint layer, in which a portion of the second solder diffuses into a liquid phase of the first solder and the second solder partially remains, is formed.

Description

Semiconductor device, power conversion device, and method of manufacturing the semiconductor device

[0001] The present disclosure relates to a semiconductor device manufactured using solder bonding and a method for manufacturing the same.

[0002] Semiconductor devices, including power modules, are required to be small and lightweight, and have high heat dissipation properties. While solder joints have superior thermal conductivity compared to thermal grease, the joining process temperature and heat resistance temperature are nearly equal, making it difficult to join a power module to a heat sink or the like without melting the solder used for internal mounting of the power module (hereinafter referred to as "internal mounting solder"). In particular, the use of high-temperature Pb solder has been restricted in recent years due to environmental concerns, making step soldering, which utilizes differences in melting points, increasingly difficult.

[0003] In addition, semiconductor devices using SiC semiconductors as their material have a high operating temperature and excellent efficiency, so they are likely to become mainstream in the future. Therefore, semiconductor devices are also required to have a package form that is compatible with SiC semiconductors.

[0004] Japanese Patent Application Laid-Open No. 2002-94242

[0005] In order to ensure the heat dissipation of a semiconductor device, it may be necessary to solder the bottom surface of the semiconductor device to a base plate. In particular, in the case of a transfer mold type semiconductor device, if the internally mounted solder of the semiconductor device remelts when soldering the semiconductor device to the base plate, its volume may expand, causing the internally mounted solder to leak through gaps in the sealing resin. Therefore, the soldering between the semiconductor device and the base plate must basically be performed at a process temperature below the melting point of the internally mounted solder.

[0006] In the past, the melting point of solder could be adjusted to some extent by increasing the proportion of Pb contained in the solder, but as mentioned above, the use of Pb solder is currently restricted. Furthermore, the use of BiSn solder (melting point 139°C) allows for a low-temperature soldering process. However, because BiSn solder has low heat resistance and lower thermal conductivity than SnAgCu solder, brittle fracture of the solder joint becomes a problem when BiSn solder is used.

[0007] The above-mentioned Patent Document 1 discloses a technique for necking (connecting) the liquid phase of BiSn solder to a Cu core material. This technique is expected to increase the melting point of the solder and improve heat resistance by diffusing Cu into the BiSn solder. However, the technique of Patent Document 1 relates to a material for filling through holes, and does not take into account the problems of BiSn solder's low heat resistance and brittleness.

[0008] The present disclosure has been made to solve the above-mentioned problems, and aims to ensure the heat resistance and reliability of solder joints while reducing the temperature of the joining process in the manufacture of semiconductor devices.

[0009] The method for manufacturing a semiconductor device according to the present disclosure includes: (a) a step of stacking a first solder and a second solder having a melting point higher than that of the first solder between a first circuit element and a second circuit element; and (b) a step of soldering the first circuit element and the second circuit element by heating the first solder and the second solder to a temperature between the melting points of the first solder and the second solder, wherein in the step (b), a portion of the second solder diffuses into the liquid phase of the first solder, forming a solder joint layer in which the second solder partially remains.

[0010] The semiconductor device according to the present disclosure comprises a first circuit element and a second circuit element, and a solder joint layer that joins the first circuit element and the second circuit element and includes a layer of first solder in which a second solder having a melting point higher than that of the first solder has diffused, and a layer made of the second solder.

[0011] According to the present disclosure, it is possible to lower the temperature of the bonding process in the manufacture of semiconductor devices while ensuring the heat resistance and reliability of the soldered joints.

[0012] 1 is a conceptual diagram showing a bonding process of semiconductor elements in a manufacturing method of a semiconductor device according to a first embodiment. FIG. 2 is a conceptual diagram showing a bonding process of semiconductor elements in a manufacturing method of a semiconductor device according to a first embodiment. FIG. 3 is a Bi—Sn equilibrium diagram. FIG. 4 is a conceptual diagram showing a modification of the manufacturing method of a semiconductor device according to the first embodiment. FIG. 5 is a conceptual diagram showing a bonding process of semiconductor elements in a manufacturing method of a semiconductor device according to a second embodiment. FIG. 6 is a conceptual diagram showing a bonding process of semiconductor elements in a manufacturing method of a semiconductor device according to a second embodiment. FIG. 7 is a conceptual diagram showing a bonding process of semiconductor elements in a manufacturing method of a semiconductor device according to a third embodiment. FIG. 8 is a conceptual diagram showing a bonding process of semiconductor elements in a manufacturing method of a semiconductor device according to a third embodiment. FIG. 9 is a conceptual diagram showing a bonding process of semiconductor elements in a manufacturing method of a semiconductor device according to a third embodiment. FIG. 10 is a conceptual diagram showing a bonding process of semiconductor elements in a manufacturing method of a semiconductor device according to a third embodiment. Fig. 10 is a conceptual diagram showing a method for manufacturing a power module as a semiconductor device according to embodiment 4. Fig. 11 is a conceptual diagram showing a method for manufacturing a power module as a semiconductor device according to embodiment 4. Fig. 12 is a conceptual diagram showing a method for manufacturing a power module as a semiconductor device according to embodiment 4. Fig. 13 is a conceptual diagram showing a method for manufacturing a power module as a semiconductor device according to embodiment 4. Fig. 14 is a block diagram showing a configuration of a power conversion system to which a power conversion device according to embodiment 5 is applied.

[0013] 1 to 5 are conceptual diagrams showing a bonding process of semiconductor elements in a method for manufacturing a semiconductor device according to a first embodiment. The bonding process will be described with reference to these figures.

[0014] 1, a laminated solder 30 is placed between a ceramic substrate 10 as a first circuit element and a semiconductor element 20 as a second circuit element, and they are stacked together. The laminated solder 30 is configured such that BiSn solder 31 as a first solder, which is a tin (Sn)-based solder containing bismuth (Bi), is provided on both sides of SnCu solder 32 as a second solder.

[0015] In this embodiment, the ceramic substrate 10 is made of an aluminum nitride base material with Cu conductor layers formed on both sides and measuring 25 mm x 25 mm. The semiconductor element 20 is made of Si, with Ni / Au plating on the backside as soldering metallization, measuring 13 mm x 13 mm x 0.4 mm. The laminated solder 30 is made of 13 mm x 13 mm x 0.176 mm. The BiSn solder 31 has a composition ratio of 57 wt% Bi-43 wt% Sn, a melting point of 139°C, and a thickness of 0.012 mm. The SnCu solder 32 has a composition ratio of 99.3 wt% Sn-0.7 wt% Cu, a melting point of 229°C, and a thickness of 0.21 mm. The semiconductor element 20 may also be made of a wide bandgap semiconductor such as SiC, GaN, or diamond. The semiconductor element 20 using a wide band gap semiconductor as the semiconductor material is superior to a semiconductor element made of Si in terms of operation at high voltage, large current, and high temperature.

[0016] The SnCu solder 32 is not limited to the eutectic 99.3 wt% Sn-0.7 wt% Cu, but may contain trace amounts of additive elements such as Ag. SnCu solder 32 with added Ag has a eutectic point (217°C) at an Ag concentration of about 3%. If the melting point of SnCu solder 32 drops too low, it becomes difficult to bond the SnCu solder 32 while leaving the layer of SnCu solder 32 intact, so it is desirable to keep the concentration of Ag added to SnCu solder 32 at 1% or less.

[0017] A small amount of Ag, Sb, etc. may also be added to the BiSn solder 31. However, if the amount of the additive element increases, flexibility is lost, so the concentration of the element added to the BiSn solder 31 is preferably 1% or less.

[0018] With the laminated solder 30 sandwiched between the ceramic substrate 10 and the semiconductor element 20, a hot plate is used to heat the laminated solder 30 to a temperature between the melting point of the BiSn eutectic solder 31 (139°C) and the melting point of the SnCu solder 32 (229°C), for example, 160°C. As a result, as shown in Figure 2, the BiSn solder 31 on the front and back of the laminated solder 30 melts, and liquid phases 311 are generated between the ceramic substrate 10 and the laminated solder 30 and between the semiconductor element 20 and the laminated solder 30, forming soldered joints. At this time, the SnCu solder 32 in the center of the laminated solder 30 gradually melts and diffuses into the liquid phase 311.

[0019] When the temperature is further increased to a temperature close to the melting point of the SnCu solder 32 (229°C), for example 215°C, the melting and diffusion of the SnCu solder 32 is completed, and a solder joint layer 33 made of an alloy with a substantially uniform composition is formed between the ceramic substrate 10 and the semiconductor element 20, as shown in Figure 3.

[0020] In this embodiment, the final Bi composition ratio of the solder joint layer 33 is approximately 7 wt %. The solder joint layer 33 with a low Bi composition ratio has high heat resistance and strength, and can ensure the heat resistance and reliability of the solder joint.

[0021] 4 is a Sn—Bi equilibrium diagram. From the equilibrium diagram in FIG. 4, it can be seen that a solder joint layer 33 with a Bi composition ratio of approximately 7 wt % has a liquidus temperature of approximately 220°C and a solidus temperature of approximately 200°C. In other words, in order to perform a joint using BiSn solder with a Bi composition ratio of 7 wt % from the beginning, the liquid phase does not occur unless the solder is heated to 200°C or higher. Generally, the fluidity of the liquid phase of the solder cannot be ensured unless the solder is heated to a temperature approximately 20°C to 30°C higher than the liquidus temperature of the solder. Therefore, in order to perform a solder joint using BiSn solder with a Bi composition ratio of 7 wt % from the beginning, it is necessary to heat the solder to 235°C to 245°C.

[0022] In contrast, in the joining process of the first embodiment, the BiSn solder 31 of the laminated solder 30 exhibits sufficient fluidity at 160° C. to 170° C., enabling good joining. Although it is necessary to heat the solder joining layer 33 to its solidus temperature of 200° C. to ultimately make it uniform, joining is possible at a lower temperature than the temperature (235° C. to 245° C.) required when using BiSn solder with a Bi composition ratio of 7 wt % from the beginning.

[0023] If heating is limited to temperatures below 200°C due to some constraint, bonding between the ceramic substrate 10 and the semiconductor element 20 is possible even in the state shown in Figure 2 . In this case, although the composition of the solder joint layer 33 is not uniform, it is believed that no significant problems will arise in terms of the strength, thermal conductivity, electrical conductivity, etc. of the joint. For example, if the bonding temperature in the bonding process of this embodiment is set to 180°C, the Bi composition ratio of the liquid phase 311 is expected to be approximately 12 wt% due to isothermal solidification. However, the bonding strength and elastic modulus of this portion are approximately twice as high as those of the SnCu solder 32. Therefore, if a solder joint layer 33 with an inhomogeneous composition (as shown in Figure 2 ) is formed, when reliability evaluations such as temperature cycles are performed, fatigue-related changes such as cracking and peeling will occur in the center (the SnCu solder 32 portion). Therefore, even when the bonding temperature is set to 180°C, it is believed that reliability equivalent to that of SnCu solder with a melting point of 229°C can be obtained.

[0024] The Bi composition ratio of the BiSn solder 31 provided on the front and back surfaces of the laminated solder 30 may be 10 wt% or more, but is preferably 21 wt% or more and 57 wt% or less, at which point the solidus temperature is 139° C. Even if the Bi composition ratio of the BiSn solder 31 is lower than 57 wt%, it can generate a liquid phase at a low temperature of about 170° C. By keeping the Bi composition ratio of the BiSn solder 31 to the minimum necessary, the amount of scarce Bi used can be reduced.

[0025] The SnCu solder 32 provided in the center of the laminated solder 30 may be replaced with another solder material having a higher melting point than the BiSn solder 31, for example, SnAgCu solder with a composition ratio of 96.5Sn-3Ag-0.5Cu. When SnAgCu solder is used, a lower melting point can be expected in the joining process.

[0026] The laminated solder 30 may be a clad material formed by cold rolling, or may be a laminated material in which BiSn solder 31 is plated onto a core material SnCu solder 32, or a laminated material in which BiSn solder 31 is solder-wetted onto a core material SnCu solder 32.

[0027] 5, in the joining process, a BiSn solder paste 312 (cream solder) may be supplied to both sides of the SnCu solder 32 to form a laminated solder 30. In this case, the adhesiveness can be utilized to position and fix the components, and flux can be supplied at the same time.

[0028] When heating using a hot plate, flux may be used to improve the wettability of the solder. It is also effective to use a reduction reflow furnace using formic acid.

[0029] 6 to 9 are conceptual diagrams showing a bonding process of semiconductor elements in a method for manufacturing a semiconductor device according to a second embodiment. The bonding process will be described with reference to these figures.

[0030] First, as shown in FIG. 6, the semiconductor element 20, on the rear surface of which the SnCu solder 32 has been previously applied, and the ceramic substrate 10 are superimposed with the BiSn solder 31 disposed between them.

[0031] In this embodiment, the semiconductor element 20 is made of Si, has Ni / Au plating on the back surface as a metallization for soldering, and measures 13 mm x 13 mm x 0.4 mm. The thickness of the SnCu solder 32 is 0.176 mm, and the thickness of the BiSn solder 31 is 0.024 mm.

[0032] With the BiSn solder 31 and SnCu solder 32 sandwiched between the ceramic substrate 10 and the semiconductor element 20, a hot plate is used to heat the substrate to a temperature between the melting point of the BiSn eutectic solder 31 (139°C) and the melting point of the SnCu solder 32 (229°C), for example, 160°C. As a result, as shown in Fig. 7, the BiSn solder 31 melts, creating a liquid phase 311 between the ceramic substrate 10 and the SnCu solder 32, forming a soldered bond. At this time, the SnCu solder 32 on the back surface of the semiconductor element 20 gradually melts and diffuses into the liquid phase 311.

[0033] When the temperature is further increased to a temperature close to the melting point of the SnCu solder 32 (229°C), for example 215°C, the melting and diffusion of the SnCu solder 32 is completed, and a solder joint layer 33 made of an alloy with a substantially uniform composition is formed between the ceramic substrate 10 and the semiconductor element 20, as shown in Figure 8.

[0034] In this embodiment, the final Bi composition ratio of the solder joint layer 33 is about 7 wt %, and similarly to the first embodiment, the heat resistance and reliability of the solder joint can be ensured.

[0035] In the first embodiment, two liquid phases 311 are generated by two layers of BiSn solder 31, but in the second embodiment, one liquid phase 311 is generated by one layer of BiSn solder 31. Therefore, the thickness of one BiSn solder 31 is set to 0.024 mm, which is twice that of the first embodiment (0.012 mm).

[0036] Increasing the thickness of one BiSn solder 31 and increasing the amount of liquid phase 311 generated improves bonding properties and accommodates warpage and surface irregularities of the semiconductor element 20 and ceramic substrate 10. However, it should be noted that if the thickness of BiSn solder 31 is too large, the Bi composition ratio of the final solder bonding layer 33 will be high, lowering the solidus temperature and making it difficult to ensure heat resistance.

[0037] Furthermore, if diffusion of the SnCu solder 32 into the liquid phase 311 of the BiSn solder 31 occurs during the joining process, voids (air gaps) are likely to occur due to changes in the volume of the metal caused by isothermal solidification and subsequent solid-phase diffusion. In the second embodiment, since the SnCu solder 32 is supplied in advance to the back surface of the semiconductor element 20, even if voids occur, they will occur at a position far away from the semiconductor element 20, which is the heat source, by the thickness of the SnCu solder 32, and therefore deterioration of heat dissipation due to voids is suppressed.

[0038] Furthermore, SnCu solder 32 has superior reliability, including temperature cycle resistance, because it has lower tensile strength and greater elongation than BiSn solder 31. Therefore, by disposing SnCu solder 32 at the interface with the brittle semiconductor element 20 as in the second embodiment, the reliability of the solder joint of semiconductor element 20 is improved.

[0039] If heating is only possible up to a temperature lower than 200°C due to some constraint, the ceramic substrate 10 and the semiconductor element 20 can still be bonded in the state shown in Figure 7. In this case, although the composition of the solder bonding layer 33 will not be uniform, it is believed that no major problems will arise in terms of the strength, thermal conductivity, or electrical conductivity of the bonded portion. For example, if the bonding temperature in the bonding process of this embodiment is 180°C, the Bi composition ratio of the liquid phase 311 is thought to be about 12 wt% due to isothermal solidification, but changes due to fatigue, such as cracking and peeling, will occur in the SnCu solder 32, and therefore reliability equivalent to that of SnCu solder can be obtained.

[0040] 9, a solder paste 312 (cream solder) of BiSn solder may be used instead of the BiSn solder 31. In this case, it becomes possible to position and fix the components by utilizing the adhesiveness, and it becomes possible to supply flux at the same time.

[0041] 10 to 15 are conceptual diagrams showing a bonding process of semiconductor elements in a method for manufacturing a semiconductor device according to a third embodiment. The bonding process will be described with reference to these figures.

[0042] First, as shown in Fig. 10, mixed solder paste 331 is applied to the upper surface of ceramic substrate 10, and semiconductor element 20 is placed thereon. This is heated on a hot plate to melt mixed solder paste 331, and as shown in Fig. 11, solder bonding is performed by forming solder bonding layer 33.

[0043] 12, mixed solder paste 331 is obtained by dispersing BiSn solder particles 313 and SnCu solder particles 323 in solvent 330. In this embodiment, the ratio of BiSn solder particles 313 to SnCu solder particles 323 in mixed solder paste 331 is 12:88.

[0044] When this mixed solder paste 331 is heated to 160°C, as shown in Fig. 13, the solvent 330 evaporates, and the BiSn solder particles 313, which have a melting point of 139°C, melt to generate a liquid phase 311 of BiSn solder, thereby forming a solder joint between the semiconductor element 20 and the ceramic substrate 10. When further heated to 180°C, as shown in Fig. 14, the SnCu solder particles 323 diffuse into the liquid phase 311 of BiSn solder, forming a solder joint layer 33 with a high Bi concentration. This portion then gradually expands, and as shown in Fig. 15, a uniform solder joint layer 33 is formed overall.

[0045] In this embodiment, too, the final Bi composition ratio of solder joint layer 33 is approximately 7 wt %, and the heat resistance and reliability of the solder joint can be ensured, as in embodiment 1. Furthermore, in embodiment 3, since the SnCu solder is supplied in a particulate state (SnCu solder particles 323), the contact area of ​​the BiSn solder with liquid phase 311 is increased, which also has the effect of quickly completing the diffusion of liquid phase 311.

[0046] If heating is only possible up to a temperature lower than 200° C. due to some constraint, it is possible to bond ceramic substrate 10 and semiconductor element 20 in the state shown in Fig. 14. In this case, the composition of solder bonding layer 33 will not be uniform, but as explained in the first embodiment, it is thought that this will not cause any major problems in terms of the strength, thermal conductivity, electrical conductivity, etc. of the bonded portion.

[0047] Furthermore, in the first or second embodiment, the mixed solder paste 331 used in the third embodiment may be used instead of the BiSn solder paste 312. The use of the mixed solder paste 331 makes it easier to adjust the temperature at which the liquid phase 311 of the BiSn solder is generated. For example, if the temperature of components varies during a heating process, the timing and time at which the liquid phase 311 is generated can be adjusted by changing the mixing ratio of the mixed solder paste 331 depending on the location. Furthermore, the physical properties of the solder joint layer 33, such as heat resistance, strength, and flexibility, can also be adjusted by adjusting the mixing ratio of the mixed solder paste 331.

[0048] 16A and 16B are conceptual diagrams showing a bonding process of semiconductor elements in a manufacturing method of a power module as a semiconductor device according to embodiment 4. The bonding process will be described with reference to these drawings.

[0049] First, as shown in FIG. 16 , an IGBT (Insulated Gate Bipolar Transistor) 21 and a diode 22 are joined to a ceramic substrate 10 with SnCu solder 32. At this time, convex SnCu solder 32 is formed on the main electrodes on the upper surfaces of the IGBT 21 and the diode 22. Then, a BiSn solder paste 312 is applied onto the SnCu solder 32 on the IGBT 21 and the diode 22. In this embodiment, the ratio of the SnCu solder 32 to the BiSn solder paste 312 is adjusted to 88:12. Note that the semiconductor elements mounted on the semiconductor device are not limited to IGBTs and diodes, and may be, for example, MOSFETs.

[0050] The case 5 is positioned and bonded to the outer edge of the ceramic substrate 10. The case 5 has an external main terminal 62, an electrode plate 61 connected thereto, and a signal terminal 63 inserted therein.

[0051] Then, when the semi-finished power module is heated to 160°C, the BiSn solder paste 312 melts and a liquid phase 311 is generated, as shown in Figure 17, and the SnCu solder 32 on the top surface of the IGBT 21 and diode 22 is joined to the electrode plate 61.

[0052] When the solder is further heated to 200° C., the SnCu solder 32 diffuses into the liquid phase 311 of the BiSn solder, forming a solder joint layer 33 that is an alloy with a substantially uniform composition throughout, as shown in FIG.

[0053] Finally, as shown in Fig. 19, the signal electrode of the IGBT 21 is connected to the signal terminal 63 using an aluminum wire 4, and the inside of the case 5 is filled with sealing resin 7 to insulate and seal the IGBT 21, diode 22, etc. As the sealing resin 7, for example, epoxy resin with alumina filler dispersed therein can be used. This completes the power module. Fig. 20 shows a top view of the power module shown in Fig. 19 (the sealing resin 7 is not shown in Fig. 20).

[0054] If heating is only possible up to a temperature lower than 200° C. due to some constraint, it is possible to bond ceramic substrate 10 and semiconductor element 20 in the state shown in Fig. 17. In this case, the composition of solder bonding layer 33 will not be uniform, but as explained in the first embodiment, it is thought that this will not cause any major problems in terms of the strength, thermal conductivity, electrical conductivity, etc. of the bonded portion.

[0055] Also in the fifth embodiment, the mixed solder paste 331 used in the third embodiment may be used instead of the BiSn solder paste 312. By using the mixed solder paste 331, it becomes easier to adjust the temperature at which the liquid phase 311 of the BiSn solder is generated and the physical properties of the solder joint layer 33.

[0056] Fifth Embodiment In this embodiment, the semiconductor device according to any of the above-described first to fourth embodiments is applied to a power conversion device. Although the application of the semiconductor device according to any of the first to fourth embodiments is not limited to a specific power conversion device, the following will describe a case where the semiconductor device according to any of the first to fourth embodiments is applied to a three-phase inverter as the fifth embodiment.

[0057] FIG. 21 is a block diagram showing the configuration of a power conversion system to which the power conversion device according to this embodiment is applied.

[0058] The power conversion system shown in Fig. 21 is composed of a power supply 100, a power conversion device 200, and a load 300. The power supply 100 is a DC power supply and supplies DC power to the power conversion device 200. The power supply 100 can be composed of various components, such as a DC system, a solar cell, or a storage battery, or it may be composed of a rectifier circuit connected to an AC system or an AC / DC converter. The power supply 100 may also be composed of a DC / DC converter that converts DC power output from a DC system into a predetermined power.

[0059] The power conversion device 200 is a three-phase inverter connected between the power source 100 and the load 300, and converts DC power supplied from the power source 100 into AC power and supplies the AC power to the load 300. As shown in Fig. 21 , the power conversion device 200 includes a main conversion circuit 201 that converts DC power into AC power and outputs it, and a control circuit 203 that outputs a control signal to the main conversion circuit 201 to control the main conversion circuit 201.

[0060] The load 300 is a three-phase electric motor driven by AC power supplied from the power conversion device 200. The load 300 is not limited to a specific application, but is an electric motor mounted on various electrical devices, and is used as an electric motor for, for example, a hybrid vehicle, an electric vehicle, a railroad car, an elevator, or an air conditioning device.

[0061] The power conversion device 200 will be described in detail below. The main conversion circuit 201 includes switching elements and freewheel diodes (not shown). The switching elements convert DC power supplied from the power source 100 into AC power, which is supplied to the load 300. The main conversion circuit 201 can have a variety of specific circuit configurations. The main conversion circuit 201 according to this embodiment is a two-level, three-phase full-bridge circuit, which can be configured with six switching elements and six freewheel diodes connected in anti-parallel to each switching element. Each switching element and freewheel diode of the main conversion circuit 201 is configured using a semiconductor module 202 corresponding to any one of the first to fourth embodiments described above. Two of the six switching elements are connected in series to form upper and lower arms, which constitute each phase (U phase, V phase, and W phase) of the full-bridge circuit. The output terminals of each upper and lower arm, i.e., the three output terminals of the main conversion circuit 201, are connected to the load 300.

[0062] The main conversion circuit 201 also includes a drive circuit (not shown) that drives each switching element, but the drive circuit may be built into the semiconductor module 202, or may be provided separately from the semiconductor module 202. The drive circuit generates drive signals that drive the switching elements of the main conversion circuit 201 and supplies them to the control electrodes of the switching elements of the main conversion circuit 201. Specifically, in accordance with control signals from a control circuit 203 (described later), the drive circuit outputs to the control electrodes of each switching element a drive signal that turns the switching element on and a drive signal that turns the switching element off. To maintain a switching element in the on state, the drive signal is a voltage signal (on signal) that is equal to or greater than the threshold voltage of the switching element, and to maintain a switching element in the off state, the drive signal is a voltage signal (off signal) that is equal to or less than the threshold voltage of the switching element.

[0063] The control circuit 203 controls the switching elements of the main conversion circuit 201 so that the desired power is supplied to the load 300. Specifically, it calculates the time (on time) that each switching element of the main conversion circuit 201 should be in the on state based on the power to be supplied to the load 300. For example, the main conversion circuit 201 can be controlled by PWM control, which modulates the on time of the switching elements according to the voltage to be output. The control circuit 203 then outputs a control command (control signal) to a drive circuit included in the main conversion circuit 201 so that an on signal is output to a switching element that should be in the on state at each time point, and an off signal is output to a switching element that should be in the off state at each time point. In accordance with this control signal, the drive circuit outputs an on signal or an off signal as a drive signal to the control electrode of each switching element.

[0064] In the power conversion device according to this embodiment, the semiconductor modules according to the first to fourth embodiments are applied as the switching elements and free wheel diodes of the main conversion circuit 201, thereby achieving improved reliability.

[0065] In the present embodiment, an example has been described in which the semiconductor device according to any one of the first to fourth embodiments is applied to a two-level three-phase inverter, but the application of the semiconductor device according to any one of the first to fourth embodiments is not limited to this, and the semiconductor device can be applied to various power conversion devices. In the present embodiment, the two-level power conversion device is described, but a three-level or multi-level power conversion device may also be used, and when power is supplied to a single-phase load, the semiconductor device according to any one of the first to fourth embodiments may be applied to a single-phase inverter. Furthermore, when power is supplied to a DC load or the like, the semiconductor device according to any one of the first to fourth embodiments can also be applied to a DC / DC converter or an AC / DC converter.

[0066] Furthermore, the power conversion device to which the semiconductor device according to the fifth embodiment is applied is not limited to the case where the load described above is an electric motor, but can also be used, for example, as a power supply device for an electric discharge machine, a laser processing machine, an induction heating cooker, or a contactless power supply system, and can also be used as a power conditioner for a solar power generation system, a power storage system, etc.

[0067] It is possible to freely combine the embodiments, and to modify or omit the embodiments as appropriate.

[0068] <Supplementary Notes> Various aspects of the present disclosure will be summarized below as supplementary notes.

[0069] (Supplementary Note 1) A method for manufacturing a semiconductor device, comprising: (a) a step of stacking a first solder and a second solder having a melting point higher than that of the first solder between a first circuit element and a second circuit element; and (b) a step of heating the first solder and the second solder to a temperature between the melting points of the first solder and the second solder, thereby soldering the first circuit element and the second circuit element.

[0070] (Supplementary Note 2) The method for manufacturing a semiconductor device according to Supplementary Note 1, wherein in the step (b), the second solder diffuses into the liquid phase of the first solder, and a solder joint layer made of an alloy having an entirely uniform composition is formed.

[0071] (Supplementary Note 3) The method for manufacturing a semiconductor device according to Supplementary Note 1, wherein in the step (b), a portion of the second solder diffuses into the liquid phase of the first solder, forming a solder joint layer in which the second solder partially remains.

[0072] (Supplementary Note 4) The method for manufacturing a semiconductor device according to any one of Supplementary Note 1 to Supplementary Note 3, wherein the first solder is a tin-based solder containing 10 wt % or more of bismuth.

[0073] (Appendix 5) The method for manufacturing a semiconductor device according to any one of Appendices 1 to 4, wherein the second solder is pre-formed on the first circuit element, and step (a) is performed by sandwiching the first solder between the second solder on the first circuit element and the second circuit element.

[0074] (Supplementary Note 6) A method for manufacturing a semiconductor device, comprising: (a) a step of supplying a mixed solder paste between a first circuit element and a second circuit element, the mixed solder paste being obtained by mixing particles of a first solder and particles of a second solder having a melting point higher than that of the first solder in a solvent; and (b) a step of heating the mixed solder paste to a temperature between the melting points of the first solder and the second solder, thereby soldering the first circuit element and the second circuit element.

[0075] (Supplementary Note 7) The method for manufacturing a semiconductor device according to Supplementary Note 6, wherein in the step (b), the second solder diffuses into the liquid phase of the first solder, and a solder joint layer made of an alloy having an entirely uniform composition is formed.

[0076] (Appendix 8) The method for manufacturing a semiconductor device according to Appendix 6, wherein in the step (b), a part of the second solder diffuses into the liquid phase of the first solder, and a solder joint layer in which the second solder partially remains is formed.

[0077] (Supplementary Note 9) The method for manufacturing a semiconductor device according to any one of Supplementary Note 6 to Supplementary Note 8, wherein the first solder is a tin-based solder containing 10 wt % or more of bismuth.

[0078] (Supplementary Note 10) A semiconductor device comprising: a first circuit element and a second circuit element; and a solder joint layer that joins the first circuit element and the second circuit element and includes a layer in which a second solder having a melting point higher than that of the first solder is diffused into a first solder.

[0079] (Supplementary Note 11) The semiconductor device according to Supplementary Note 10, wherein a layer in which the second solder is diffused into the first solder is formed over the entire solder joint layer.

[0080] (Supplementary Note 12) The semiconductor device according to Supplementary Note 10, wherein the solder joint layer includes a layer in which the second solder is diffused into the first solder, and a layer made of the second solder.

[0081] (Supplementary Note 13) The semiconductor device according to any one of Supplementary Note 10 to Supplementary Note 12, wherein the first solder is a tin-based solder containing 10 wt% or more of bismuth.

[0082] (Supplementary Note 14) A power conversion device comprising: a main conversion circuit having the semiconductor device according to any one of Supplementary Note 10 to Supplementary Note 13, which converts input power and outputs the converted power; and a control circuit which outputs a control signal for controlling the main conversion circuit to the main conversion circuit.

[0083] 10 ceramic substrate, 20 semiconductor element, 30 laminated solder, 31 BiSn solder, 311 liquid phase, 312 BiSn solder solder paste, 313 BiSn solder particles, 32 SnCu solder, 323 SnCu solder particles, 33 solder joint layer, 330 solvent, 331 mixed solder paste, 4 wire, 5 case, 21 IGBT, 22 diode, 61 electrode plate, 62 external main terminal, 63 signal terminal, 7 sealing resin, 100 power supply, 200 power conversion device, 201 main conversion circuit, 202 semiconductor module, 203 control circuit, 300 load.

Claims

1. (a) laminating a mixed solder paste, which is obtained by mixing particles of a first solder and particles of a second solder having a melting point higher than that of the first solder in a solvent, and the second solder between a first circuit element and a second circuit element; (b) heating the mixed solder paste and the second solder to a temperature between a melting point of the first solder and a melting point of the second solder to solder the first circuit element and the second circuit element; Equipped with In the step (b), a part of the second solder diffuses into the liquid phase of the first solder, and a solder joint layer in which the second solder partially remains is formed. A method for manufacturing a semiconductor device.

2. The first solder is a tin-based solder containing 10 wt % or more of bismuth. The method for manufacturing a semiconductor device according to claim 1 .

3. The second solder is a solder containing Sn and Cu. The method for manufacturing a semiconductor device according to claim 1 or 2.

4. The second solder contains Ag, and the concentration of Ag is 1% or less. The method for manufacturing a semiconductor device according to claim 3 .

5. The laminated solder formed in the step (a) has a configuration in which the mixed solder paste is provided on both sides of the second solder. The method for manufacturing a semiconductor device according to claim 1 or 2.

6. a first circuit element and a second circuit element; a solder joint layer that joins the first circuit element and the second circuit element and includes a layer in which a second solder having a melting point higher than that of the first solder is diffused into a first solder, and a layer made of the second solder; Equipped with The first solder is a tin-based solder containing 10 wt % or more of bismuth. Semiconductor device.

7. The second solder is a solder containing Sn and Cu. The semiconductor device according to claim 6.

8. The second solder contains Ag, and the concentration of Ag is 1% or less. The semiconductor device according to claim 7.

9. A main conversion circuit having the semiconductor device according to any one of claims 6 to 8, which converts input power and outputs the converted power; a control circuit that outputs a control signal for controlling the main conversion circuit to the main conversion circuit; A power conversion device comprising: