Power module, method for manufacturing a power module, and power conversion device

Abstract

The objective is to provide a technology that can suppress the decrease in reliability of wire bonding caused by solder splashes that occur during soldering between the main electrode and electrode plate of a semiconductor device. [Solution] The power module 202 comprises a semiconductor element 2 having a main electrode 17 and a wire bonding pad 9 on its upper surface, an electrode plate 81 soldered to the main electrode 17, and a signal terminal 83 wire-bonded to the wire bonding pad 9. A solderable metal is formed on the outermost surface of the main electrode 17, and a layer 16 mainly composed of Al is formed on the outermost surface of the wire bonding pad 9.

Description

Technical Field

[0001] The present disclosure relates to a power module, a method for manufacturing a power module, and a power conversion device.

Background Art

[0002] With the increasing environmental problems, power modules are becoming more and more popular in all scenarios of electric energy generation, transmission, and regeneration. In particular, high reliability is required for power modules mounted on transportation equipment such as electric vehicles. Therefore, instead of the conventional wire bonding, a structure in which a copper electrode plate is used for soldering to the main electrode of a semiconductor element is becoming more and more popular.

[0003] While solder is used for joining the main electrode and the electrode plate in a semiconductor element, wire bonding is often used for wire bonding pads such as gate electrodes. Therefore, there has been a concern that solder splashing (in other words, solder balls) from the joint portion between the main electrode of the semiconductor element and the electrode plate adheres to the wire bonding pad, causing a decrease in the reliability of wire bonding.

[0004] In order to solve such problems, for example, Patent Document 1 describes a technique in which a bent portion is formed at the tip of a lead (corresponding to an electrode plate) that is solder-joined to the main electrode of a semiconductor element, and solder splashing is suppressed at the bent portion.

[0005] Further, Patent Document 2 describes a technique in which a groove portion is provided between the solder-joining electrode and the wire-joining electrode, and the solder splashing is received at the groove portion.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] However, in the technology described in Patent Document 1, there is a gap on the underside of the bent portion, which means that solder balls may pass through this gap. Therefore, there was a problem in that the deterioration of wire bonding reliability could not be suppressed. Similarly, in the technology described in Patent Document 2, there was also a problem in that the deterioration of wire bonding reliability could not be suppressed.

[0008] Therefore, the present disclosure aims to provide a technology that can suppress the decrease in reliability of wire bonding caused by solder splashes that occur during soldering between the main electrode and the electrode plate of a semiconductor device. [Means for solving the problem]

[0009] The power module according to this disclosure comprises a semiconductor element having a main electrode and a wire bonding pad on its upper surface, an electrode plate soldered to the main electrode, and a lead frame wire-bonded to the wire bonding pad, wherein the solderable metal is formed on the outermost surface of the main electrode, and a layer mainly composed of Al is formed on the outermost surface of the wire bonding pad. [Effects of the Invention]

[0010] According to this disclosure, since solder and Al do not bond, even if solder adheres to the wire bonding pad, it does not bond, and the solder adhering to the wire bonding pad can be easily removed. Therefore, a decrease in the reliability of wire bonding can be suppressed. [Brief explanation of the drawing]

[0011] [Figure 1] This is a top view showing the power module according to Embodiment 1 with the sealing resin removed. [Figure 2]Cross-sectional view of the power module according to Embodiment 1. [Figure 3] Top view of the semiconductor element included in the power module according to Embodiment 1. [Figure 4] Cross-sectional view of the semiconductor element included in the power module according to Embodiment 1. [Figure 5] Cross-sectional view showing the manufacturing method of the power module according to Embodiment 1. [Figure 6] Cross-sectional view showing the manufacturing method of the power module according to Embodiment 1. [Figure 7] Cross-sectional view showing the manufacturing method of the power module according to Embodiment 1. [Figure 8] Cross-sectional view showing the manufacturing method of the power module according to Embodiment 1. [Figure 9] Cross-sectional view showing the manufacturing method of the power module according to Embodiment 1. [Figure 10] Cross-sectional view showing the manufacturing method of the power module according to Embodiment 1. [Figure 11] Cross-sectional view showing the manufacturing method of the power module according to Embodiment 1. [Figure 12] Top view of the semiconductor element included in the power module according to Embodiment 2. [Figure 13] Top view showing an example of the wire bonding pad of the semiconductor element in Embodiment 2. [Figure 14] Top view showing another example of the wire bonding pad of the semiconductor element in Embodiment 2. [Figure 15] Top view showing still another example of the wire bonding pad of the semiconductor element in Embodiment 2. [Figure 16] Block diagram showing the configuration of the power conversion system to which the power conversion device according to Embodiment 3 is applied.

Mode for Carrying Out the Invention

[0012] Embodiment 1. Embodiment 1 will be described below with reference to the drawings. FIG. 1 is a top view showing the state of the power module 202 according to Embodiment 1 excluding the encapsulating resin 11. FIG. 2 is a cross-sectional view of the power module 202 according to Embodiment 1.

[0013] As shown in FIGS. 1 and 2, the power module 202 includes a base plate 6, a ceramic substrate 1, semiconductor elements 2 and 3, an electrode plate 81 including a main terminal 82, a signal terminal 83 as a lead frame, a wire 10, a case 8, and an encapsulating resin 11.

[0014] The base plate 6 is a plate member made of metal such as Cu or Al, formed in a rectangular shape in a top view.

[0015] The ceramic substrate 1 is joined to the upper surface of the base plate 6 via solder 5. The ceramic substrate 1 has a base material 1a, a surface conductor layer 1b, and a back surface conductor layer 1c. The base material 1a is a plate member made of aluminum nitride, formed in a rectangular shape in a top view. A copper-made surface conductor layer 1b is provided on the upper surface of the base material 1a, and a copper-made back surface conductor layer 1c is provided on the lower surface of the base material 1a. The size of the base material 1a is 40 mm in width, 20 mm in depth, and 0.5 mm in thickness. The sizes of both the surface conductor layer 1b and the back surface conductor layer 1c are 37 mm in width, 17 mm in depth, and 0.8 mm in thickness. Note that the base plate 6 and the ceramic substrate 1 are not limited to being separate members, and a substrate-integrated base plate may be used.

[0016] The semiconductor element 2 is an IGBT (Insulated Gate Bipolar Transistor), and is joined to the upper surface of the surface conductor layer 1b via solder 4. The semiconductor element 2 is made of silicon, and the size of the semiconductor element 2 is 13 mm in width, 13 mm in depth, and 0.2 mm in thickness. Also, the semiconductor element 3 is a diode, and is joined to the upper surface of the surface conductor layer 1b via solder 4. The semiconductor element 3 is made of silicon, and the size of the semiconductor element 3 is 10 mm in width, 13 mm in depth, and 0.2 mm in thickness.

[0017] Furthermore, the semiconductor elements 2 and 3 are not limited to silicon, but may be composed of wide-bandgap semiconductors such as SiC. Also, the semiconductor elements 2 and 3 are not limited to IGBTs and diodes, but may be MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), IGBTs with integrated diodes, or MOSFETs with integrated diodes. In addition, although it has been explained that the semiconductor elements 2 and 3 are bonded to the upper surface of the surface conductor layer 1b via solder 4, the invention is not limited to this, and they may be bonded to the upper surface of the surface conductor layer 1b by sintered bonding of Ag or Cu.

[0018] Case 8 is made of, for example, PPS (Polyphenylenesulfide) resin and is formed in a rectangular frame shape when viewed from above. Case 8 is fitted to the peripheral edge of the upper surface of base plate 6. The electrode plate 81 and signal terminal 83 are integrally formed with case 8 by insert molding. One end of electrode plate 81, the main terminal 82, protrudes upward from case 8. Similarly, one end of signal terminal 83 protrudes upward from case 8.

[0019] The main electrodes 17, provided on the upper surfaces of the semiconductor elements 2 and 3, are joined to the other end of the electrode plate 81 via solder 7. The electrode plate 81 is made of copper and has a thickness of 0.64 mm. The signal terminal 83 is also made of copper and has a thickness of 0.64 mm. The solders 4, 5, and 7 are composed of 96.5% tin, 3% silver, and 0.5% copper.

[0020] The wire bonding pad 9 provided on the upper surface of the semiconductor element 2 is connected to the signal terminal 83 by an aluminum wire 10 (0.2 mm in diameter). The wire 10 may be made of a metal other than aluminum. Furthermore, the size of each component is not limited to the above.

[0021] The inside of case 8 is filled with a sealing resin 11 made of epoxy resin, and the inside of case 8 is insulated and sealed. Note that the sealing resin 11 is not limited to epoxy resin, but may be made of a gel such as silicone or a transfer mold.

[0022] Furthermore, in the power module 202, the case 8 is fitted to the base plate 6, and insulation is ensured by the sealing resin 11 filled inside the case 8. However, a structure in which the circuit is formed with a lead frame without using the case 8 and sealed with a transfer mold is also possible. However, in the case of a transfer mold, lead cutting and lead molding will be necessary.

[0023] Alternatively, instead of the ceramic substrate 1, semiconductor elements 2 and 3 may be soldered to a heat spreader or lead frame, and an insulating sheet may be placed underneath before performing transfer molding.

[0024] Next, the structure of the semiconductor element 2 as an IGBT, which is a feature of this invention, will be described. Figure 3 is a top view of the semiconductor element 2 provided in the power module 202 according to Embodiment 1. Figure 4 is a cross-sectional view of the semiconductor element 2 provided in the power module 202 according to Embodiment 1. Note that the termination region 12 is simplified in Figure 4.

[0025] As shown in Figures 3 and 4, when the wire bonding pad 9 is a gate pad, the region of the semiconductor substrate 13, which is the base material of the semiconductor element 2, is formed in the order of an SiO2 layer 14, a polysilicon layer 15, and then an Al-based layer 16 is formed on top of that. When the main electrode 17 is an emitter electrode, the region of the main electrode 17 is formed in the order of an Al-based layer 16, and then a Ni plating layer 18 and an Au plating layer 19 are formed on top of that. On the upper side of the semiconductor substrate 13, a SiN layer 20 and a polyimide layer 21 are formed in the order of a terminal region 12 and between the main electrode 17 and the wire bonding pad 9. On the back side of the semiconductor substrate 13, an Al-based layer 16, a Ti layer 22, a Ni plating layer 18, and an Au plating layer 19 are formed in that order.

[0026] The outermost surface of the wire bonding pad 9 does not have a Ni plating layer 18 or Au plating layer 19 that can bond with the solder 7 (see Figure 2). Instead, a layer 16 mainly composed of Al that does not bond with the solder 7 is formed. As a result, even if solder splatters (in other words, solder balls) generated when soldering the electrode plate 81 to the main electrode 17 of the semiconductor element 2 adhere to the wire bonding pad 9, they will not bond. Therefore, solder balls adhering to the wire bonding pad 9 can be easily removed. This makes it possible to provide a power module 202 that does not impair the reliability of wire bonding.

[0027] Although it is stated that a Ni plating layer 18 and an Au plating layer 19 are formed on the main electrode 17, the Au plating layer 19 can be omitted as long as the electrode plate 81 can be joined with the solder 7 placed on the semiconductor elements 2 and 3. Alternatively, a Cu plating layer or an Ag plating layer may be formed instead of the Ni plating layer 18. In other words, it is sufficient if at least one of the Ni plating layer 18, Cu plating layer, or Ag plating layer is formed.

[0028] Next, a method for manufacturing the power module 202 according to Embodiment 1 will be described. Figures 5 to 11 are cross-sectional views showing the method for manufacturing the power module 202 according to Embodiment 1.

[0029] As shown in Figure 5, a step is taken to prepare a semiconductor substrate 13 that will become the semiconductor element 2 as an IGBT. Structures such as a transistor (not shown), a termination region 12 (see Figure 4), and a wire bonding pad 9 (see Figure 4) are formed on the semiconductor substrate 13. Similarly, it is necessary to prepare another semiconductor substrate 13 that will become the semiconductor element 3 as a diode, but since the semiconductor element 3 can be obtained from this semiconductor substrate 13 by conventional methods, the manufacturing of the semiconductor element 3 will not be explained. The semiconductor substrate 13 is a wide-bandgap semiconductor such as silicon or SiC.

[0030] Next, a step is performed to form a layer 16 mainly composed of Al on the back surface of the semiconductor substrate 13 and in the area on the top surface of the semiconductor substrate 13 that will become the main electrode 17 and wire bonding pad 9.

[0031] Next, as shown in Figure 6, a step is performed to form an insulating film on the Al-based layer 16 in the region that will become the wire bonding pad 9. More specifically, a Ti layer 22 is formed on the back side of the semiconductor substrate 13, and a SiN layer 20 and a polyimide layer 21 are formed on the front side of the semiconductor substrate 13. At this time, the SiN layer 20 is formed in all areas except the region that will become the main electrode 17, and the polyimide layer 21 is formed in all areas except the region that will become the main electrode 17 and the wire bonding pad 9. In other words, of the Al-based layer 16 on the front side of the semiconductor substrate 13, nothing is on the region that will become the main electrode 17, and the SiN layer 20 is formed on the region that will become the wire bonding pad 9.

[0032] Next, as shown in Figure 7, the main electrode 17 is formed by forming a solderable metal film on the Al-based layer 16 in the region that will become the main electrode 17. More specifically, the main electrode 17 is formed by forming Ni plating 18 and Au plating 19 on the Al-based layer 16 on the front and back sides of the semiconductor substrate 13.

[0033] Next, as shown in Figure 8, a step is performed to form the wire bonding pad 9 by removing the insulating film formed in the region that will become the wire bonding pad 9 using a laser. More specifically, the wire bonding pad 9 is formed by removing the SiN layer 20 using a laser.

[0034] Next, as shown in Figure 9, the semiconductor element 2 obtained through the above steps is soldered to the ceramic substrate 1 together with the semiconductor element 3, thereby mounting the semiconductor elements 2 and 3 onto the ceramic substrate 1.

[0035] Next, as shown in Figure 10, the electrode plate 81 is soldered to the metal film of the main electrode 17. More specifically, the back surface conductive layer 1c of the ceramic substrate 1 is soldered to the base plate 6 to which the case 8 is attached, and then the electrode plate 81 is soldered to the Au plating 19 (see Figure 7) of the main electrode 17.

[0036] Finally, as shown in Figure 11, after performing the step of wire bonding the signal terminals 83 to the wire bonding pad 9, the semiconductor elements 2 and 3 are resin-sealed with the sealing resin 11.

[0037] Furthermore, immediately before the wire bonding process, an air-blowing step may be performed to remove solder balls generated during the soldering process.

[0038] Furthermore, although a SiN layer 20 is formed on the region that will become the wire bonding pad 9, a polyimide layer 21 may be formed instead of the SiN layer 20 if it functions as a mask for the Al-based layer 16 during plating and can be removed by laser. Alternatively, both the SiN layer 20 and the polyimide layer 21 may be formed.

[0039] As described above, in Embodiment 1, the power module 202 comprises a semiconductor element 2 having a main electrode 17 and a wire bonding pad 9 on its upper surface, an electrode plate 81 soldered to the main electrode 17, and a signal terminal 83 wire-bonded to the wire bonding pad 9. A solderable metal is formed on the outermost surface of the main electrode 17, and a layer 16 mainly composed of Al is formed on the outermost surface of the wire bonding pad 9. Specifically, the solderable metal includes at least one of Ni, Ag, or Cu.

[0040] Furthermore, the manufacturing method for the power module 202 includes the steps of: preparing a semiconductor substrate 13 to be a semiconductor element 2; forming a layer 16 mainly composed of Al on the upper surface of the semiconductor substrate 13 in the region that will become the main electrode 17 and the wire bonding pad 9; forming an insulating film on the layer 16 mainly composed of Al in the region that will become the wire bonding pad 9; forming the main electrode 17 by forming a solderable metal film on the layer 16 mainly composed of Al in the region that will become the main electrode 17; forming the wire bonding pad 9 by removing the insulating film formed in the region that will become the wire bonding pad 9 with a laser; mounting the semiconductor element 2 obtained through all of the above steps onto a ceramic substrate 1; soldering an electrode plate 81 to the metal film of the main electrode 17; wire bonding a signal terminal 83 to the wire bonding pad 9; and resin encapsulating the semiconductor element 2. Specifically, the insulating film contains at least one of SiN or polyimide.

[0041] Therefore, since solder 7 and Al do not bond, even if solder balls, which are part of solder 7, adhere to the wire bonding pad 9, they do not bond, and the solder balls adhering to the wire bonding pad 9 can be easily removed. This suppresses a decrease in the reliability of wire bonding.

[0042] Furthermore, the manufacturing method for the power module 202 includes a step of using air blowing to remove solder balls generated during soldering, immediately before the wire bonding step. Therefore, in the wire bonding step, the solder balls are removed from the surface of the wire bonding pad 9 and do not hinder the wire bonding.

[0043] Furthermore, when the semiconductor substrate 13, which is a semiconductor wafer, is returned to processes such as photolithography or etching after plating, there is a concern about contamination, and there is a problem in that the processes and equipment cannot be shared with the processes before plating. In contrast, in Embodiment 1, since the SiN layer 20 is removed with a laser, the only changes from the existing process are a change in the mask used when forming the SiN layer 20 and the addition of a laser device.

[0044] Furthermore, while it is possible to avoid forming the Ni plating layer 18 and Au plating layer 19 on the wire bonding pad 9 by using sputtering, considering that Ni dissolves into the solder during soldering, sputtering has a lower film deposition rate than plating, resulting in reduced productivity. Therefore, the manufacturing method shown in Figures 5 to 11 is more productive than the method using sputtering.

[0045] Embodiment 2. Next, Embodiment 2 will be described. Figure 12 is a top view of the semiconductor element 2 provided in the power module 202 according to Embodiment 2. Figure 13 is a top view showing an example of the wire bonding pad 9 of the semiconductor element 2 in Embodiment 2. Figure 14 is a top view showing another example of the wire bonding pad 9 of the semiconductor element 2 in Embodiment 2. Figure 15 is a top view showing yet another example of the wire bonding pad 9 of the semiconductor element 2 in Embodiment 2. In Embodiment 2, the same reference numerals are used for components that are the same as those described in Embodiment 1, and their descriptions are omitted.

[0046] As shown in Figure 12, in Embodiment 2, a solderable metal is formed in the area of ​​the wire bonding pad 9 other than the area to be wire-bonded. Specifically, openings 23 are provided in positions where wire bonding is not actually performed, such as the four corners of the wire bonding pad 9, and a solderable metal is formed in the openings 23 instead of the Al-based layer 16. Since the openings 23 are areas that are not wire-bonded, the reliability of the wire bonding is not affected even if solder balls are bonded to the openings 23. Furthermore, by utilizing the openings 23, the electrical characteristics of the semiconductor device 2 can be confirmed even before the SiN layer 20 is removed with a laser.

[0047] The openings 23 may be provided at two diagonal locations on the wire bonding pad 9, as shown in Figure 13, or along the two short sides of the wire bonding pad 9, as shown in Figure 14. Alternatively, since the joint of the wire 10 in the wire bonding pad 9 is elliptical, the openings 23 may be provided in the portion excluding the elliptical shape, as shown in Figure 15.

[0048] Next, we will describe only the parts of the manufacturing method for the power module 202 according to Embodiment 2 that differ from Embodiment 1.

[0049] In Embodiment 1, as shown in Figure 7, Ni plating 18 and Au plating 19 were formed on the Al-based layer 16 on the front and back surfaces of the semiconductor substrate 13. In other words, a process was carried out to form an insulating film on the Al-based layer 16 in the region that would become the wire bonding pad 9. In contrast, in Embodiment 2, an insulating film was formed on the portion of the Al-based layer 16 excluding a part of the region that would become the wire bonding pad 9 (the portion excluding the four corners of the wire bonding pad 9 in Figure 12), and then a solderable metal film was formed on a part of the Al-based layer 16 in the region that would become the wire bonding pad 9 (the four corners of the wire bonding pad 9 in Figure 12).

[0050] Furthermore, in Embodiment 1, as shown in Figure 8, before the process of mounting the semiconductor element 2 onto the ceramic substrate 1, a process of forming the wire bonding pad 9 was carried out by removing the insulating film formed in the region that would become the wire bonding pad 9 using a laser. In contrast, in Embodiment 2, since the electrical characteristics of the semiconductor element 2 can be confirmed using the semiconductor element 2 alone, it is possible to carry out the process of forming the wire bonding pad 9 after the process of mounting the semiconductor element 2 onto the ceramic substrate 1 and immediately before the wire bonding process.

[0051] In Embodiment 2, a solderable metal is formed in the portion of the wire bonding pad 9 other than the area to be wire-bonded.

[0052] Furthermore, the manufacturing method for the power module 202 according to Embodiment 2 includes the steps of: preparing a semiconductor substrate 13 to be a semiconductor element 2; forming an Al-based layer 16 on the upper surface of the semiconductor substrate 13 in areas that will become the main electrode 17 and wire bonding pad 9; forming an insulating film on the portion of the Al-based layer 16 excluding a part of the area that will become the wire bonding pad 9, and then forming a solderable metal film on a part of the Al-based layer 16 in the area that will become the wire bonding pad 9; forming the main electrode 17 by forming a solderable metal film on the Al-based layer 16 in the area that will become the main electrode 17; mounting the semiconductor element 2 obtained through all of the above steps onto a ceramic substrate 1; soldering an electrode plate 81 to the metal film of the main electrode 17; forming a wire bonding pad 9 by removing the insulating film formed in the area that will become the wire bonding pad 9 with a laser; wire bonding a signal terminal 83 to the wire bonding pad 9; and resin encapsulating the semiconductor element 2.

[0053] Therefore, the electrical properties of the semiconductor device 2 cannot be confirmed until the SiN layer 20 is removed. However, solderable metal is formed in the parts of the wire bonding pad 9 other than the area to be wire-bonded, and conductivity can be established in the exposed solderable metal parts. As a result, the electrical properties of the semiconductor device 2 can be confirmed even before the SiN layer 20 is removed.

[0054] Embodiment 3. This embodiment applies the power module 202 according to Embodiments 1 and 2 described above to a power converter. The application of the power module 202 according to Embodiments 1 and 2 is not limited to a specific power converter, but below, as Embodiment 3, we will describe the case in which the power module 202 according to Embodiments 1 and 2 is applied to a three-phase inverter.

[0055] Figure 16 is a block diagram showing the configuration of a power conversion system to which the power conversion device according to Embodiment 3 is applied.

[0056] The power conversion system shown in Figure 16 consists of a power supply 100, a power converter 200, and a load 300. The power supply 100 is a DC power supply and supplies DC power to the power converter 200. The power supply 100 can be composed of various components, for example, a DC grid, a solar cell, or a battery, or it may be composed of a rectifier circuit or AC / DC converter connected to an AC grid. Alternatively, the power supply 100 may be composed of a DC / DC converter that converts DC power output from a DC grid into a predetermined power.

[0057] 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 16, 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.

[0058] Load 300 is a three-phase electric motor driven by AC power supplied from power converter 200. Note that Load 300 is not limited to a specific application; it is an electric motor installed in various electrical devices, such as hybrid vehicles, electric vehicles, railway vehicles, elevators, or air conditioning equipment.

[0059] The details of the power converter 200 are described below. The main conversion circuit 201 is equipped with switching elements (not shown) and freewheeling diodes (not shown). 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. At least one of each switching element or each freewheeling diode of the main conversion circuit 201 is composed of a power module 202 corresponding to either embodiment 1 or 2 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.

[0060] 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 power module 202, or it may be configured as a separate drive circuit from the power 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.

[0061] 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. The control circuit then 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.

[0062] In the power conversion device according to this embodiment, the power module 202 according to Embodiments 1 and 2 is used as the switching element and freewheeling diode of the main conversion circuit 201, thereby improving reliability.

[0063] In this embodiment, an example of applying the power module 202 according to Embodiments 1 and 2 to a two-level three-phase inverter has been described. However, the application of the power module 202 according to Embodiments 1 and 2 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 power module 202 according to Embodiments 1 and 2 may be applied to a single-phase inverter. In addition, when supplying power to a DC load, the power module 202 according to Embodiments 1 and 2 can also be applied to a DC / DC converter or an AC / DC converter.

[0064] Furthermore, the power conversion device to which the power module 202 according to Embodiments 1 and 2 is applied is not limited to cases where the load is an electric motor, but can also be used, for example, as a power supply for electrical discharge machining equipment, laser processing equipment, induction heating cookers, or contactless power supply systems, and can even be used as a power conditioner for solar power generation systems or energy storage systems.

[0065] Furthermore, it is possible to freely combine each embodiment, or to modify or omit each embodiment as appropriate.

[0066] The various aspects of this disclosure are summarized below as an appendix.

[0067] (Note 1) A semiconductor element having a main electrode and a wire bonding pad on its upper surface, An electrode plate to be soldered to the main electrode, The system comprises the wire bonding pad and the lead frame to be wire-bonded, The solderable metal is formed on the outermost surface of the main electrode. A power module in which a layer mainly composed of Al is formed on the outermost surface of the wire bonding pad.

[0068] (Note 2) The power module according to Appendix 1, wherein the solderable metal includes at least one of Ni, Ag, or Cu.

[0069] (Note 3) The power module according to Appendix 1 or Appendix 2, wherein the portion of the wire bonding pad other than the area to be wire-bonded has the solderable metal formed thereon.

[0070] (Note 4) The process of preparing a semiconductor substrate that will become a semiconductor device, A step of forming a layer mainly composed of Al in the region that will become the main electrode and wire bonding pad on the upper surface of the semiconductor substrate, A step of forming an insulating film on the layer mainly composed of Al in the region that will become the wire bonding pad, The process of forming the main electrode by forming a solderable metal film on the Al-based layer in the region that will serve as the main electrode, A step of forming the wire bonding pad by removing the insulating film formed in the region that will become the wire bonding pad using a laser, A step of mounting the semiconductor element obtained through all of the above steps onto a substrate, A step of soldering an electrode plate to the metal film of the main electrode, The process of wire bonding the lead frame to the aforementioned wire bonding pad, The process of encapsulating the semiconductor element with resin, A method for manufacturing a power module, comprising the following features.

[0071] (Note 5) The method for manufacturing a power module according to Appendix 4, wherein the insulating film comprises at least one of SiN or polyimide.

[0072] (Note 6) A method for manufacturing a power module according to Appendix 4 or 5, further comprising a step of using air blowing to remove solder balls generated during the soldering process, immediately before the wire bonding step.

[0073] (Note 7) The process of preparing a semiconductor substrate that will become a semiconductor device, A step of forming a layer mainly composed of Al in the region that will become the main electrode and wire bonding pad on the upper surface of the semiconductor substrate, A step of forming an insulating film on the portion of the Al-based layer in the region that will become the wire bonding pad, excluding a portion thereof, and then forming a solderable metal film on the portion of the Al-based layer in the region that will become the wire bonding pad, The process of forming the main electrode by forming the solderable metal film on the layer mainly composed of Al in the region that will serve as the main electrode, A step of mounting the semiconductor element obtained through all of the above steps onto a substrate, A step of soldering an electrode plate to the metal film of the main electrode, A step of forming the wire bonding pad by removing the insulating film formed in the region that will become the wire bonding pad using a laser, The process of wire bonding the lead frame to the aforementioned wire bonding pad, The process of encapsulating the semiconductor element with resin, A method for manufacturing a power module, comprising the following features.

[0074] (Note 8) A power module described in any one of Appendix 1 to Appendix 3, and 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. [Explanation of Symbols]

[0075] 2 semiconductor element, 9 wire bonding pad, 13 semiconductor substrate, 16 Al-based layer, 17 main electrode, 19 Au plating layer, 20 SiN layer, 81 electrode plate, 83 signal terminal, 200 power converter, 201 main conversion circuit, 202 power module, 203 control circuit.

Claims

1. A semiconductor element having a main electrode and a wire bonding pad on its upper surface, An electrode plate to be soldered to the main electrode, The system comprises the wire bonding pad and the lead frame to be wire-bonded, The solderable metal is formed on the outermost surface of the main electrode. A power module in which a layer mainly composed of Al is formed on the outermost surface of the wire bonding pad.

2. The power module according to claim 1, wherein the solderable metal comprises at least one of Ni, Ag, or Cu.

3. The power module according to claim 1, wherein the portion of the wire bonding pad other than the area to be wire-bonded has the solderable metal formed thereon.

4. The process of preparing a semiconductor substrate that will become a semiconductor device, A step of forming a layer mainly composed of Al in the region that will become the main electrode and wire bonding pad on the upper surface of the semiconductor substrate, A step of forming an insulating film on the Al-based layer in the region that will become the wire bonding pad, The process of forming the main electrode by forming a solderable metal film on the Al-based layer in the region that will serve as the main electrode, A step of forming the wire bonding pad by removing the insulating film formed in the region that will become the wire bonding pad using a laser, A step of mounting the semiconductor element obtained through all of the above steps onto a substrate, A step of soldering an electrode plate to the metal film of the main electrode, The process of wire bonding the lead frame to the aforementioned wire bonding pad, The process of encapsulating the semiconductor element with resin, A method for manufacturing a power module, comprising the following features.

5. The method for manufacturing a power module according to claim 4, wherein the insulating film comprises at least one of SiN or polyimide.

6. The method for manufacturing a power module according to claim 4, further comprising a step of using air blowing to remove solder balls generated during the soldering process, immediately before the wire bonding step.

7. The process of preparing a semiconductor substrate that will become a semiconductor device, A step of forming a layer mainly composed of Al in the region that will become the main electrode and wire bonding pad on the upper surface of the semiconductor substrate, A step of forming an insulating film on the portion of the Al-based layer in the region that will become the wire bonding pad, excluding a portion thereof, and then forming a solderable metal film on the portion of the Al-based layer in the region that will become the wire bonding pad, The process of forming the main electrode by forming the solderable metal film on the layer mainly composed of Al in the region that will serve as the main electrode, A step of mounting the semiconductor element obtained through all of the above steps onto a substrate, A step of soldering an electrode plate to the metal film of the main electrode, A step of forming the wire bonding pad by removing the insulating film formed in the region that will become the wire bonding pad using a laser, The process of wire bonding the lead frame to the aforementioned wire bonding pad, The process of encapsulating the semiconductor element with resin, A method for manufacturing a power module, comprising the following features.

8. A power module according to any one of claims 1 to 3, comprising a main conversion circuit that converts and outputs 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.

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