JP7834232B2 - Manufacturing method for semiconductor devices - Google Patents

Description

This disclosure relates to a semiconductor device manufactured using solder joints and a method for manufacturing the same.

Semiconductor devices, including power modules, require miniaturization, weight reduction, and high heat dissipation. While soldering offers superior thermal conductivity compared to thermal grease, the bonding process temperature and heat resistance temperature are nearly equal. Therefore, it is difficult to bond power modules to heat sinks or other components without melting the solder used for internal mounting (hereinafter referred to as "internal mounting solder"). In particular, with the recent restrictions on the use of high-temperature Pb solder due to environmental concerns, step soldering using melting point differences is becoming increasingly difficult.

Furthermore, semiconductor devices using SiC semiconductors as materials have high operating temperatures and excellent efficiency, making them highly likely to become the mainstream in the future. Therefore, semiconductor devices are also required to have package forms that are compatible with SiC semiconductors.

Japanese Patent Publication No. 2002-94242

To ensure proper heat dissipation in semiconductor devices, it is sometimes necessary to solder the bottom surface of the semiconductor device to the base plate. In particular, with transfer-molded semiconductor devices, there is a concern that if the internal solder of the semiconductor device remelts during the soldering process, its volume will expand, causing it to leak through gaps in the sealing resin. Therefore, soldering the semiconductor device to the base plate should generally be performed at a process temperature below the melting point of the internal solder.

Traditionally, the melting point of solder could be adjusted to some extent by increasing the proportion of lead (Pb) it contained. However, as mentioned above, the use of lead (Pb) solder is currently restricted. Furthermore, using biSn solder (melting point 139°C) allows for low-temperature soldering processes. However, biSn solder has low heat resistance and lower thermal conductivity compared to SnAgCu solder, so brittle fracture of the solder joint becomes a problem when using biSn solder.

Patent Document 1 discloses a technique for necking (connecting) the liquid phase of BiSn solder to a Cu core material. According to this technique, it is expected that the melting point of the solder will increase and its heat resistance will improve as Cu diffuses into the BiSn solder. However, the technique in Patent Document 1 concerns materials for filling through-holes, and does not take into account the problems of BiSn solder's low heat resistance and brittleness.

This disclosure was made to solve the above-mentioned problems, and aims to ensure the heat resistance and reliability of solder joints while lowering the temperature of the bonding process in the manufacturing of semiconductor devices.

A method for manufacturing a semiconductor device according to the present disclosure comprises the steps of (a) laminating a mixed solder paste, which is made by mixing first solder particles and second solder particles having a higher melting point than the first solder in a solvent, and the second solder between a first circuit element and a second circuit element, and (b) performing a solder joint between the first circuit element and the second circuit element by heating the mixed solder paste and the second solder to a temperature between the melting point of the first solder and the melting point of the second solder, wherein in 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.

The semiconductor device according to this 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 in which a second solder having a higher melting point than the first solder is diffused into the first solder, and a layer consisting of the second solder , wherein the first solder is a tin-based solder containing 10 wt% or more of bismuth .

According to this disclosure, it is possible to lower the temperature of the bonding process in the manufacturing of semiconductor devices while ensuring the heat resistance and reliability of the solder joints.

This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 1. This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 1. This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 1. This is the Bi-Sn equilibrium phase diagram. This is a conceptual diagram showing a modified example of the method for manufacturing a semiconductor device according to Embodiment 1. This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 2. This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 2. This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 2. This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 2. This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 3. This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 3. This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 3. This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 3. This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 3. This is a conceptual diagram showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 3. This is a conceptual diagram showing a method for manufacturing a power module as a semiconductor device according to Embodiment 4. This is a conceptual diagram showing a method for manufacturing a power module as a semiconductor device according to Embodiment 4. This is a conceptual diagram showing a method for manufacturing a power module as a semiconductor device according to Embodiment 4. This is a conceptual diagram showing a method for manufacturing a power module as a semiconductor device according to Embodiment 4. This is a conceptual diagram showing a method for manufacturing a power module as a semiconductor device according to Embodiment 4. This is a block diagram showing the configuration of a power conversion system to which the power conversion device according to Embodiment 5 is applied.

<Embodiment 1>
Figures 1 to 5 are conceptual diagrams showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 1. The bonding process will be explained with reference to these figures.

First, as shown in Figure 1, a laminated solder 30 is placed and superimposed between a ceramic substrate 10, which is a first circuit element, and a semiconductor element 20, which is a second circuit element. The laminated solder 30 has a configuration in which a first solder, BiSn solder 31, which is a tin (Sn)-based solder containing bismuth (Bi), is provided on both sides of a second solder, SnCu solder 32.

In this embodiment, the ceramic substrate 10 is made of an aluminum nitride substrate with Cu conductive layers formed on both sides, and has a size of 25 mm x 25 mm. The semiconductor element 20 is made of Si, with Ni/Au plating applied to the back surface as a metallization for soldering, and has a size of 13 mm x 13 mm x 0.4 mm. The multilayer solder 30 has a size 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. Note that the semiconductor element 20 may be made of a wide-bandgap semiconductor such as SiC, GaN, or diamond. The semiconductor device 20, which uses a wide-bandgap semiconductor as the semiconductor material, exhibits superior operation at high voltage, high current, and high temperature compared to semiconductor devices made of Si.

The SnCu solder 32 is not limited to the eutectic 99.3 wt% Sn-0.7 wt% Cu; it may also contain trace amounts of additive elements such as Ag. In SnCu solder 32 with added Ag, the eutectic point (217°C) is located at an Ag concentration of around 3%. If the melting point of the SnCu solder 32 is lowered too much, it becomes difficult to bond while preserving the layer of SnCu solder 32; therefore, it is desirable to keep the concentration of Ag added to the SnCu solder 32 to 1% or less.

Furthermore, small amounts of Ag, Sb, etc., may be added to the BiSn solder 31. However, since flexibility is lost if the amount of added elements increases, it is desirable that the concentration of elements added to the BiSn solder 31 be 1% or less.

With the laminated solder 30 sandwiched between the ceramic substrate 10 and the semiconductor element 20, the solder is heated using a hot plate 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 shown in Figure 2, the BiSn solder 31 on both sides of the laminated solder 30 melts, and a liquid phase 311 is generated between the ceramic substrate 10 and the laminated solder 30, and between the semiconductor element 20 and the laminated solder 30, thereby forming a solder joint. At this time, the SnCu solder 32 in the center of the laminated solder 30 gradually melts and diffuses into the liquid phase 311.

Further increasing the temperature until it reaches 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 as shown in Figure 3, a solder joint layer 33 with an alloy having a nearly uniform composition is formed between the ceramic substrate 10 and the semiconductor element 20.

In this embodiment, the final Bi composition ratio of the solder joint layer 33 is approximately 7 wt%. A solder joint layer 33 with such a low Bi composition ratio possesses high heat resistance and strength, ensuring the heat resistance and reliability of the solder joint.

Figure 4 is an equilibrium phase diagram of Sn-Bi. From the equilibrium phase diagram in Figure 4, it can be seen that the 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 will not be generated unless it is heated to above 200°C. Generally, the fluidity of the liquid phase of the solder cannot be ensured unless it is heated to a temperature about 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 it to 235°C to 245°C.

In contrast, in the bonding process of Embodiment 1, the BiSn solder 31 of the laminated solder 30 exhibits sufficient fluidity at 160°C to 170°C, enabling good bonding. Although it is ultimately necessary to heat to the solidus temperature of 200°C to make the solder bonding layer 33 uniform, bonding is possible at a lower temperature than when using BiSn solder with a Bi composition ratio of 7 wt% from the beginning (235°C to 245°C).

Furthermore, if heating is limited to a temperature lower than 200°C due to some constraint, bonding between the ceramic substrate 10 and the semiconductor element 20 is still possible even in the state shown in Figure 2. In this case, although the composition of the solder joint layer 33 will not be uniform, it is not expected that any major problems will arise in terms of the strength, heat conduction, and electrical conduction 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 about 12 wt% due to isothermal solidification. However, the bonding strength and elastic modulus of this portion are about twice as high as those of the SnCu solder 32. Therefore, if a solder joint layer 33 with a non-uniform composition (as shown in Figure 2) is formed, reliability evaluations such as temperature cycling will show that fatigue-related changes such as cracks and delamination will occur in the center (the SnCu solder 32 portion). Consequently, even when the bonding temperature is set to 180°C, it is considered that the same level of reliability as that of SnCu solder with a melting point of 229°C can be obtained.

The Bi composition ratio of the BiSn solder 31 applied to the front and back surfaces of the laminated solder 30 should be 10 wt% or more, but it is preferable that it be between 21 wt% and 57 wt%, which results in a solidus temperature of 139°C. Even if the Bi composition ratio of the BiSn solder 31 is lower than 57 wt%, a liquid phase can be generated at a low temperature of about 170°C. By minimizing the Bi composition ratio of the BiSn solder 31, the amount of scarce Bi used can be reduced.

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. Using SnAgCu solder can be expected to lower the melting point of the bonding process.

The laminated solder 30 may be a clad material formed by cold rolling, or it may be made by plating BiSn solder 31 onto a core material SnCu solder 32 and laminating them, or by solder wetting BiSn solder 31 onto a core material SnCu solder 32 and laminating them.

Furthermore, as shown in Figure 5, in the joining process, a layered solder 30 may be formed by supplying BiSn solder paste 312 (solder paste) to both sides of the SnCu solder 32. In this case, positioning and fixing of the components using adhesive properties becomes possible, and flux can be supplied simultaneously.

When heating with a hot plate, flux may be used to improve the wettability of the solder. Using a reduction reflow oven with formic acid is also effective.

<Embodiment 2>
Figures 6 to 9 are conceptual diagrams showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 2. The bonding process will be explained with reference to these figures.

First, as shown in Figure 6, BiSn solder 31 is placed between the semiconductor element 20, which has SnCu solder 32 pre-applied to its back surface, and the ceramic substrate 10, and then they are placed on top of each other.

In this embodiment as well, the semiconductor element 20 is made of Si, with Ni/Au plating applied to the back surface as a metallization for soldering, and has dimensions of 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.

With BiSn solder 31 and SnCu solder 32 sandwiched between the ceramic substrate 10 and the semiconductor element 20, the mixture is heated using a hot plate 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 shown in Figure 7, the BiSn solder 31 melts, a liquid phase 311 is generated between the ceramic substrate 10 and the SnCu solder 32, and a solder joint is formed. 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.

Further increasing the temperature until it reaches 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 as shown in Figure 8, a solder joint layer 33 with an alloy having a nearly uniform composition is formed between the ceramic substrate 10 and the semiconductor element 20.

In this embodiment as well, the final Bi composition ratio of the solder joint layer 33 is approximately 7 wt%, and, similar to Embodiment 1, the heat resistance and reliability of the solder joint can be ensured.

In Embodiment 1, two liquid phases 311 were generated by two layers of BiSn solder 31, but in Embodiment 2, one liquid phase 311 is generated by one layer of BiSn solder 31. Therefore, the thickness of one layer of BiSn solder 31 was set to 0.024 mm, which is twice that of Embodiment 1 (0.012 mm).

Increasing the thickness of a single BiSn solder 31 and thereby increasing the amount of liquid phase 311 generated can accommodate warping and surface irregularities of the semiconductor element 20 and ceramic substrate 10, improving bonding performance. However, it should be noted that if the thickness of the BiSn solder 31 is too large, the Bi composition ratio of the final solder joint layer 33 will increase, lowering the solidus temperature and making it difficult to ensure heat resistance.

Furthermore, if diffusion of SnCu solder 32 into the liquid phase 311 of BiSn solder 31 occurs during the bonding process, voids (gaps) are likely to form due to isothermal solidification and subsequent volume changes of the metal associated with solid-phase diffusion. In Embodiment 2, since SnCu solder 32 is supplied to the back surface of the semiconductor element 20 in advance, even if voids are formed, they will be located at a distance equal to the thickness of the SnCu solder 32 from the semiconductor element 20, which is the heat source, thus suppressing the deterioration of heat dissipation due to voids.

Furthermore, SnCu solder 32 has lower tensile strength and greater elongation compared to BiSn solder 31, resulting in superior reliability, including temperature cycling properties. Therefore, as in Embodiment 2, by placing SnCu solder 32 at the interface with the brittle semiconductor element 20, the reliability of the solder joint of the semiconductor element 20 is improved.

Furthermore, if heating is limited to a temperature lower than 200°C due to some constraint, bonding between the ceramic substrate 10 and the semiconductor element 20 is still possible even 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 not expected that any major problems will arise in terms of the strength, heat conduction, and electrical conduction of the bonding area. 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 about 12 wt% due to isothermal solidification. However, since fatigue-related changes such as cracks and delamination occur in the SnCu solder 32 portion, it is expected that reliability equivalent to that of SnCu solder can be obtained.

Furthermore, as shown in Figure 9, a BiSn solder paste 312 (solder cream) may be used instead of the BiSn solder 31. In this case, positioning and fixing of the components using adhesive properties becomes possible, and flux supply can also be performed simultaneously.

<Embodiment 3>
Figures 10 to 15 are conceptual diagrams showing the semiconductor element bonding process in the semiconductor device manufacturing method according to Embodiment 3. The bonding process will be explained with reference to these figures.

First, as shown in Figure 10, a mixed solder paste 331 is applied to the upper surface of the ceramic substrate 10, and the semiconductor element 20 is placed on top of it. This is then heated on a hot plate to melt the mixed solder paste 331, and as shown in Figure 11, a solder joint layer 33 is formed and soldering is performed.

As shown in Figure 12, the mixed solder paste 331 is a mixture in which BiSn solder particles 313 and SnCu solder particles 323 are dispersed in solvent 330. In this embodiment, the ratio of BiSn solder particles 313 to SnCu solder particles 323 in the mixed solder paste 331 is 12:88.

When this mixed solder paste 331 is heated to 160°C, as shown in Figure 13, the solvent 330 evaporates, the BiSn solder particles 313 with a melting point of 139°C melt, and a liquid phase 311 of BiSn solder is generated, forming a solder joint between the semiconductor element 20 and the ceramic substrate 10. When heated further to 180°C, as shown in Figure 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. Thereafter, this area gradually expands, and as shown in Figure 15, a uniform solder joint layer 33 is formed.

In this embodiment as well, the final Bi composition ratio of the solder joint layer 33 is approximately 7 wt%, and, as in Embodiment 1, the heat resistance and reliability of the solder joint can be ensured. Furthermore, in Embodiment 3, since the SnCu solder is supplied in a granular state (SnCu solder particles 323), the contact area of the BiSn solder with the liquid phase 311 is increased, and the diffusion of the liquid phase 311 is completed more quickly.

Furthermore, if heating is limited to a temperature lower than 200°C due to some constraint, bonding between the ceramic substrate 10 and the semiconductor element 20 is still possible even in the state shown in Figure 14. In this case, although the composition of the solder bonding layer 33 will not be uniform, as explained in Embodiment 1, it is considered that no major problems will arise in terms of the strength, heat conduction, and electrical conduction of the bonding area.

Furthermore, in Embodiment 1 or 2, the mixed solder paste 331 used in Embodiment 3 may be used instead of the BiSn solder paste 312. Using the mixed solder paste 331 makes it easier to control the temperature at which the liquid phase 311 of the BiSn solder is generated. For example, if there are variations in the temperature of the components during the heating process, the timing and duration of the generation of the liquid phase 311 can be adjusted by changing the mixing ratio of the mixed solder paste 331 depending on the location. In addition, the physical properties of the solder joint layer 33, such as heat resistance, strength, and flexibility, can be adjusted by changing the mixing ratio of the mixed solder paste 331.

<Embodiment 4>
Figure 16 is a conceptual diagram showing the semiconductor element bonding process in the manufacturing method of a power module as a semiconductor device according to Embodiment 4. The bonding process will be explained with reference to these figures.

First, as shown in Figure 16, an IGBT (Insulated Gate Bipolar Transistor) 21 and a diode 22 are joined to the ceramic substrate 10 using SnCu solder 32. At this time, a convex shape of SnCu solder 32 is formed on the main electrodes on the upper surfaces of the IGBT 21 and the diode 22. Then, BiSn solder paste 312 is supplied on top of the SnCu solder 32 on the IGBT 21 and the diode 22. In this embodiment, the ratio of SnCu solder 32 to 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; for example, MOSFETs may also be used.

Furthermore, 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 to it, and a signal terminal 63 inserted into it.

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

Furthermore, when heated to 200°C, as shown in Figure 18, the SnCu solder 32 diffuses into the liquid phase 311 of the BiSn solder, forming a solder joint layer 33 with an alloy composition that is almost uniform throughout.

Finally, as shown in Figure 19, the signal electrode of the IGBT 21 and the signal terminal 63 are connected 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, an epoxy resin in which alumina filler is dispersed can be used. With the above steps, the power module is completed. Figure 20 shows a top view of the power module shown in Figure 19 (the sealing resin 7 is not shown in Figure 20).

Furthermore, if heating is limited to a temperature lower than 200°C due to some constraint, bonding between the ceramic substrate 10 and the semiconductor element 20 is still possible even in the state shown in Figure 17. In this case, although the composition of the solder bonding layer 33 will not be uniform, as explained in Embodiment 1, it is considered that no major problems will arise in terms of the strength, heat conduction, and electrical conduction of the bonding area.

Furthermore, in Embodiment 5, the mixed solder paste 331 used in Embodiment 3 may be used instead of the BiSn solder paste 312. Using the mixed solder paste 331 makes it 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.

<Embodiment 5>
This embodiment applies the semiconductor devices described in Embodiments 1 to 4 above to a power converter. The application of the semiconductor devices described in Embodiments 1 to 4 is not limited to a specific power converter, but below, Embodiment 5 will describe the case in which the semiconductor devices described in Embodiments 1 to 4 are applied to a three-phase inverter.

Figure 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.

The power conversion system shown in Figure 21 consists 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 made up of various components; for example, it can be made up of a DC grid, a solar cell, a storage battery, or a rectifier circuit or AC/DC converter connected to an AC grid. Alternatively, the power supply 100 may be made up of a DC/DC converter that converts DC power output from a DC grid into a predetermined power.

The power converter 200 is a three-phase inverter connected between the power supply 100 and the load 300. It converts the DC power supplied from the power supply 100 into AC power and supplies the AC power to the load 300. As shown in Figure 21, the power converter 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.

Load 300 is a three-phase motor driven by AC power supplied from power converter 200. Note that load 300 is not limited to a specific application; it is a motor installed in various electrical devices, such as hybrid vehicles, electric vehicles, railway vehicles, elevators, or air conditioning equipment.

The details of the power converter 200 are described below. The main conversion circuit 201 is equipped with switching elements and freewheeling diodes (not shown), and by switching the switching elements, it converts the DC power supplied from the power supply 100 into AC power and supplies it to the load 300. There are various specific circuit configurations for the main conversion circuit 201, but the main conversion circuit 201 according to this embodiment is a two-level three-phase full-bridge circuit and can be composed of six switching elements and six freewheeling diodes antiparallel to each switching element. Each switching element and each freewheeling diode of the main conversion circuit 201 is composed of a semiconductor module 202 corresponding to any of the embodiments 1 to 4 described above. The six switching elements are connected in series in pairs to form upper and lower arms, and each upper and lower arm constitutes each phase (U phase, V phase, 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.

Furthermore, the main conversion circuit 201 includes a drive circuit (not shown) for driving each switching element. The drive circuit may be built into the semiconductor module 202, or it may be configured to be a separate drive circuit from the semiconductor module 202. The drive circuit generates a drive signal to drive the switching elements of the main conversion circuit 201 and supplies it to the control electrodes of the switching elements of the main conversion circuit 201. Specifically, according to the control signal from the control circuit 203, which will be described later, it outputs a drive signal to turn on the switching element and a drive signal to turn off the switching element to the control electrodes of each switching element. When the switching element is kept in the ON state, the drive signal is a voltage signal (ON signal) that is greater than or equal to the threshold voltage of the switching element, and when the switching element is kept in the OFF state, the drive signal is a voltage signal (OFF signal) that is less than or equal to the threshold voltage of the switching element.

The control circuit 203 controls the switching elements of the main converter 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 converter circuit 201 should be in the ON state based on the power to be supplied to the load 300. For example, the main converter circuit 201 can be controlled by PWM control, which modulates the on time of the switching elements according to the voltage to be output. Then, it outputs a control command (control signal) to the drive circuit of the main converter circuit 201 so that an ON signal is output to the switching elements that should be in the ON state at each point in time, and an OFF signal is output to the switching elements that should be in the OFF state. The drive circuit outputs an ON signal or an OFF signal as a drive signal to the control electrode of each switching element according to this control signal.

In the power conversion device according to this embodiment, semiconductor modules according to embodiments 1 to 4 are used as the switching elements and freewheeling diodes of the main conversion circuit 201, thereby improving reliability.

In this embodiment, an example of applying the semiconductor device according to Embodiments 1 to 4 to a two-level three-phase inverter has been described. However, the application of the semiconductor device according to Embodiments 1 to 4 is not limited to this, and it can be applied to various power conversion devices. In this embodiment, a two-level power conversion device is used, but a three-level or multi-level power conversion device may also be used. Furthermore, when supplying power to a single-phase load, the semiconductor device according to Embodiments 1 to 4 may be applied to a single-phase inverter. In addition, when supplying power to a DC load, it is also possible to apply the semiconductor device according to Embodiments 1 to 4 to a DC/DC converter or an AC/DC converter.

Furthermore, the power conversion device using the semiconductor device according to Embodiment 5 is not limited to cases where the load is an electric motor, but can also be used, for example, as a power supply for an electrical discharge machine, a laser processing machine, an induction heating cooker, or a non-contact power supply system, and can even be used as a power conditioner for a solar power generation system or an energy storage system.

Furthermore, it is possible to freely combine the various embodiments, and to modify or omit them as appropriate.

<Note>
The various aspects of this disclosure are summarized below as an appendix.

(Note 1)
(a) A step of layering a first solder and a second solder having a higher melting point than the first solder between a first circuit element and a second circuit element,
(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 point of the first solder and the melting point of the second solder,
A method for manufacturing a semiconductor device comprising the same equipment.

(Note 2)
In step (b) above, the second solder diffuses into the liquid phase of the first solder, and a solder joint layer made of an alloy with a uniform composition is formed.
A method for manufacturing a semiconductor device as described in Appendix 1.

(Note 3)
In step (b) above, 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.
A method for manufacturing a semiconductor device as described in Appendix 1.

(Note 4)
The first solder is a tin-based solder containing 10 wt% or more of bismuth.
A method for manufacturing a semiconductor device as described in any one of the appendices 1 to 3.

(Note 5)
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.
A method for manufacturing a semiconductor device as described in any one of the appendices 1 to 4.

(Note 6)
(a) A step of supplying a mixed solder paste between a first circuit element and a second circuit element, which is made by mixing first solder particles and second solder particles having a higher melting point than the first solder in a solvent,
(b) A step of soldering the first circuit element and the second circuit element by heating the mixed solder paste to a temperature between the melting point of the first solder and the melting point of the second solder,
A method for manufacturing a semiconductor device comprising the same equipment.

(Note 7)
In step (b) above, the second solder diffuses into the liquid phase of the first solder, and a solder joint layer made of an alloy with a uniform composition is formed.
The method for manufacturing a semiconductor device as described in Appendix 6.

(Note 8)
In step (b) above, 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.
The method for manufacturing a semiconductor device as described in Appendix 6.

(Note 9)
The first solder is a tin-based solder containing 10 wt% or more of bismuth.
A method for manufacturing a semiconductor device as described in any one of the appendices 6 to 8.

(Note 10)
A first circuit element and a second circuit element,
The first circuit element and the second circuit element are joined together, and the solder joint layer includes a layer in which the second solder, which has a higher melting point than the first solder, is diffused into the first solder,
A semiconductor device equipped with a semiconductor device.

(Note 11)
The layer in which the second solder has diffused into the first solder is formed over the entire solder joint layer.
The semiconductor device described in Appendix 10.

(Note 12)
The aforementioned solder joint layer includes a layer in which the second solder has diffused into the first solder, and a layer consisting of the second solder.
The semiconductor device described in Appendix 10.

(Note 13)
The first solder is a tin-based solder containing 10 wt% or more of bismuth.
A semiconductor device as described in any one of the appendices 10 to 12.

(Note 14)
A semiconductor device described in any one of Appendix 10 to Appendix 13, comprising a main conversion circuit that converts and outputs the input power,
A control circuit that outputs a control signal to the main conversion circuit to control the main conversion circuit,
A power conversion device equipped with this device.

10 Ceramic substrate, 20 Semiconductor element, 30 Multilayer solder, 31 BiSn solder, 311 Liquid phase, 312 BiSn solder paste, 313 BiSn solder particles, 32 SnCu solder, 323 SnCu solder particles, 33 Solder joint layer, 330 Solder, 331 Mixed solder paste, 4 Wire, 5 Case, 21 IGBT, 22 Diode, 61 Electrode plate, 62 External main terminal, 63 Signal terminal, 7 Encapsulation resin, 100 Power supply, 200 Power converter, 201 Main conversion circuit, 202 Semiconductor module, 203 Control circuit, 300 Load.

Claims (5)

(a) A step of layering a mixed solder paste, which is made by mixing first solder particles and second solder particles having a higher melting point than the first solder in a solvent, and the second solder between the first circuit element and the second circuit element,
(b) A step of soldering the first circuit element and the second circuit element by heating the mixed solder paste and the second solder to a temperature between the melting point of the first solder and the melting point of the second solder,
Equipped with,
In step (b) above, 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.
A method for manufacturing a semiconductor device. The first solder is a tin-based solder containing 10 wt% or more of bismuth.
A method for manufacturing a semiconductor device according to claim 1. The second solder mentioned above is a solder containing Sn and Cu.
A method for manufacturing a semiconductor device according to claim 1 or claim 2. The second solder has Ag added to it, and the concentration of Ag is 1% or less.
The method for manufacturing a semiconductor device according to claim 3. The laminated solder formed in step (a) has a configuration in which the mixed solder paste is provided on both sides of the second solder.
A method for manufacturing a semiconductor device according to claim 1 or claim 2.