Semiconductor device

Abstract

A semiconductor device constituting an upper and lower arm circuit of one phase is provided with joint parts (80, 81) connected via solder (104). Each of a plurality of solders electrically connected to the main electrode of the semiconductor element contains Cu and Sn. Each of the solder connection objects has an Ni layer. The solder (104) contains Cu and Sn, and the joint parts (80, 81) have Ni layers (801, 811). The particle size of the solder (104) is smaller than the particle size of the solder to which the collector electrode is to be connected.

Description

[0001] Cross-referencing of related applications

[0002] This application is based on Japanese Patent Application No. 2022-140168, filed in Japan on September 2, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This specification relates to semiconductor devices. Background Technology

[0004] Patent Document 1 discloses a semiconductor device comprising a semiconductor element constituting an upper arm circuit and a semiconductor element constituting a lower arm circuit. The contents of prior art documents are incorporated herein by reference as descriptions of technical elements thereof.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2016-92166 Summary of the Invention

[0008] The aforementioned semiconductor device includes a connector conductor that connects a conductor to the main electrode on the low-potential side of the semiconductor element constituting the upper arm and a conductor to the main electrode on the high-potential side of the semiconductor element constituting the lower arm via solder. The solder joint area of ​​the connector conductor is relatively small. In Patent Document 1, a Ni layer is provided on the connector conductor to suppress electromigration (EM) propagation at the solder joint area. EM is short for Electromigration.

[0009] In the process of promoting carbon neutrality and the advancement of electric vehicles, there is a demand for further miniaturization and high current in semiconductor devices. That is, further improvements are needed to enhance the lifespan of semiconductor diodes (EMs). From the above perspective, or from other perspectives not mentioned, further improvements are required for semiconductor devices.

[0010] This disclosure is made in view of such issues, with the aim of providing a semiconductor device capable of improving EM lifetime.

[0011] A disclosed semiconductor device comprises: a plurality of semiconductor elements, each having signal pads and an upper electrode serving as a main electrode on its upper surface, and a lower electrode serving as a main electrode on its lower surface, opposite to the upper surface in the thickness direction; the lower electrode having an area significantly larger than that of the upper electrode when viewed in planar view in the thickness direction; and a plurality of conductors electrically connected to the main electrode via solder; the plurality of semiconductor elements including a first semiconductor element and a second semiconductor element, the first semiconductor element constituting the upper arm of an upper and lower arm circuit, the second semiconductor element constituting the lower arm of the aforementioned upper and lower arm circuit, the first semiconductor element and the second semiconductor element being arranged in a direction orthogonal to the thickness direction such that their upper surfaces are on the same side in the thickness direction; the plurality of conductors including a first upper conductor, The system comprises a first lower conductor, a second upper conductor, a second lower conductor, and a connector conductor. The first upper conductor is connected to the upper electrode of the first semiconductor device via a first upper solder. The first lower conductor is connected to the lower electrode of the first semiconductor device via a first lower solder. The second upper conductor is connected to the upper electrode of the second semiconductor device via a second upper solder. The second lower conductor is connected to the lower electrode of the second semiconductor device via a second lower solder. The connector conductor connects the first upper conductor and the second lower conductor via a relay solder. Each solder contains Cu and Sn. Each solder has a Ni layer on its bonding surface. The particle size of at least one of the first upper solder, the second upper solder, and the relay solder is smaller than the particle size of the first lower solder and the second lower solder.

[0012] In a structure where the upper electrode is smaller than the lower electrode and has a connector conductor, the current density in the first upper solder, the second upper solder, and the relay solder is higher than the current density in the first lower solder and the second lower solder. According to the disclosed semiconductor device, at least one of the first upper solder, the second upper solder, and the relay solder with high current density has a smaller particle size than the first lower solder and the second lower solder. This slows down the disappearance of the Ni layer caused by EM (Effective Microstructure). As a result, a semiconductor device capable of improving EM lifetime can be provided.

[0013] The various technical solutions disclosed in this specification employ different technical means to achieve their respective purposes. The reference numerals within parentheses in the claims and their items illustratively indicate the correspondence with portions of the embodiments described later, and are not intended to limit the scope of the technology. The purposes, features, and effects disclosed in this specification will become clearer with reference to the following detailed description and accompanying drawings. Attached Figure Description

[0014] Figure 1 This is a diagram showing the schematic structure of a vehicle drive system using the semiconductor device of the first embodiment.

[0015] Figure 2This is a plan view showing the semiconductor device of the first embodiment.

[0016] Figure 3 It is along Figure 2 A sectional view along line III-III.

[0017] Figure 4 It is along Figure 2 A cross-sectional view along line IV-IV.

[0018] Figure 5 It is a plan view with the sealed solid part omitted.

[0019] Figure 6 This is a plan view that omits the heat sink on the emitter electrode side.

[0020] Figure 7 This is a diagram showing the output current and return current.

[0021] Figure 8 It is Figure 3 The enlarged sectional view of region VIII.

[0022] Figure 9 It is a magnified cross-sectional view of the area near the solder joint surface of the connector.

[0023] Figure 10 This is a sectional view representing a reference example.

[0024] Figure 11 This is a reference diagram illustrating the mechanism of EM progression.

[0025] Figure 12 It is a plan view representing a variation.

[0026] Figure 13 This is an enlarged cross-sectional view of the area near the solder joint surface of the connector in the semiconductor device of the second embodiment.

[0027] Figure 14 This is a plan view showing the heat sink, including the connector portion, in the semiconductor device of the third embodiment.

[0028] Figure 15 It is Figure 14 The image shows the region XV magnified.

[0029] Figure 16 This is a cross-sectional view showing the solder joint structure of the connector in the semiconductor device of the fourth embodiment.

[0030] Figure 17 This is a sectional view representing a modified example. Detailed Implementation

[0031] Hereinafter, several embodiments will be described based on the accompanying drawings. Additionally, there are instances where repeated descriptions are omitted by assigning the same reference numerals to corresponding constituent elements in each embodiment. Where only a portion of the structure is described in each embodiment, the structures of other previously described embodiments can be applied to the other parts of that structure. Furthermore, not only combinations of structures explicitly shown in the descriptions of each embodiment, but also structures of multiple embodiments can be partially combined with each other, even without explicit description, as long as no particular obstacle arises in the combination.

[0032] The semiconductor device in this embodiment is applied, for example, to a power conversion device for a mobile body driven by a rotary electric motor. Examples of mobile bodies include electric vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), flying vehicles such as electric helicopters or drones, ships, construction machinery, and agricultural machinery. Hereinafter, examples of its application to vehicles will be described.

[0033] (First Embodiment)

[0034] First, based on Figure 1 The general structure of the vehicle's drive system 1 is described.

[0035] <Vehicle drive system>

[0036] like Figure 1 As shown, the vehicle's drive system 1 includes a DC power supply 2, an electric generator 3, and a power conversion device 4.

[0037] DC power supply 2 is a DC voltage source composed of rechargeable and discharging secondary batteries. Examples of secondary batteries include lithium-ion batteries and nickel-metal hydride batteries. Electric generator 3 is a three-phase AC rotating electric motor. Electric generator 3 functions as the vehicle's driving force, i.e., an electric motor. During regeneration, electric generator 3 functions as a generator. Power conversion device 4 performs power conversion between DC power supply 2 and electric generator 3.

[0038] <Power Conversion Device>

[0039] Next, based on Figure 1 The circuit structure of the power conversion device 4 is described below. The power conversion device 4 includes a power conversion circuit. For example... Figure 1 As shown, the power conversion device 4 includes a smoothing capacitor 5 and an inverter 6 as a power conversion circuit.

[0040] The smoothing capacitor 5 primarily smooths the DC voltage supplied from the DC power supply 2. The smoothing capacitor 5 is connected to the P-line 7, which is the high-potential side of the power line, and the N-line 8, which is the low-potential side of the power line. The P-line 7 is connected to the positive terminal of the DC power supply 2, and the N-line 8 is connected to the negative terminal of the DC power supply 2. The positive terminal of the smoothing capacitor 5 is connected to the P-line 7 between the DC power supply 2 and the inverter 6. The negative terminal of the smoothing capacitor 5 is connected to the N-line 8 between the DC power supply 2 and the inverter 6. The smoothing capacitor 5 is connected in parallel with the DC power supply 2.

[0041] Inverter 6 is a DC-AC conversion circuit. Inverter 6, under switching control by a control circuit (not shown), converts DC voltage to three-phase AC voltage and outputs it to the electric generator 3. The electric generator 3 is then driven to produce a specified torque. During regenerative braking of the vehicle, inverter 6, under switching control by the control circuit, converts the three-phase AC voltage generated by the electric generator 3, which is subjected to the rotational force from the wheels, back to DC voltage and outputs it to line P 7. Thus, inverter 6 performs bidirectional power conversion between the DC power supply 2 and the electric generator 3.

[0042] Inverter 6 is configured with three-phase upper and lower arm circuits 9. The upper and lower arm circuits 9 are sometimes referred to as legs. Each upper and lower arm circuit 9 has an upper arm 9H and a lower arm 9L. The upper arm 9H and lower arm 9L are connected in series between the P-line 7 and the N-line 8, with the upper arm 9H on the P-line 7 side. The connection point between the upper arm 9H and the lower arm 9L is connected to the corresponding phase winding 3a of the generator 3 via the output line 10. Inverter 6 has six arms. At least a portion of each of the P-line 7, N-line 8, and output line 10 is constructed, for example, by conductive components such as busbars.

[0043] Each arm comprises an IGBT 11 as a switching element and a diode 12 for return current. IGBT is short for Insulated Gate Bipolar Transistor. In this embodiment, an n-channel IGBT 11 is used. The diode 12 is connected in anti-parallel to the corresponding IGBT 11. In the upper arm 9H, the collector of the IGBT 11 is connected to the P-line 7. In the lower arm 9L, the emitter of the IGBT 11 is connected to the N-line 8. Furthermore, the emitters of the IGBT 11 in the upper arm 9H and the collectors of the IGBT 11 in the lower arm 9L are interconnected. The anode of the diode 12 is connected to the emitter of the corresponding IGBT 11, and the cathode is connected to the collector.

[0044] The power conversion device 4 may also include a converter, which serves as a power conversion circuit. The converter is a DC-DC conversion circuit that converts DC voltage into different DC voltage values. The converter is located between the DC power supply 2 and the smoothing capacitor 5. The converter may be configured, for example, with a reactor and the aforementioned upper and lower arm circuits 9. With this configuration, step-up and step-down voltage conversion is possible. The power conversion device 4 may also include a filter capacitor to remove power supply noise from the DC power supply 2. The filter capacitor is located between the DC power supply 2 and the converter.

[0045] The power conversion device 4 may also include a drive circuit for switching elements that constitute the inverter 6, etc. Based on the drive command from the control circuit, the drive circuit supplies a drive voltage to the gate of the corresponding IGBT 11. By applying the drive voltage, the drive circuit drives the corresponding IGBT 11, i.e., performs turn-on drive and turn-off drive. Sometimes the drive circuit is referred to as a driver.

[0046] The power conversion device 4 may also include a control circuit for switching elements. The control circuit generates drive commands to operate the IGBT 11 and outputs them to the drive circuit. The control circuit generates drive commands based on torque requests input from a higher-level ECU (not shown) and signals detected by various sensors. These various sensors include, for example, current sensors, rotation angle sensors, and voltage sensors. The current sensor detects the phase current flowing into the windings 3a of each phase. The rotation angle sensor detects the rotation angle of the rotor of the electric generator 3. The voltage sensor detects the voltage across the smoothing capacitor 5. The control circuit outputs, for example, a PWM signal as the drive command. The control circuit may be configured with a processor and memory. ECU is short for Electronic Control Unit. PWM is short for Pulse Width Modulation.

[0047] Semiconductor Devices

[0048] Next, based on Figures 2-6 The general structure of the semiconductor device 20 will be described. Figure 2 This is a plan view showing the semiconductor device 20. Figure 2 This is a top plan view of semiconductor device 20. Figure 3 It is along Figure 2 A sectional view along line III-III. Figure 4 It is along Figure 2 A cross-sectional view along line IV-IV. Figure 5 It is relative to Figure 2 The diagram of solid 30 is omitted. Figure 6 It is relative to Figure 5 The diagram of the heat sink 50 on the emitter electrode 42 side is omitted.

[0049] For a portion of the elements constituting a semiconductor device, the end of the marking is given an "H" to indicate the upper arm 9H side and an "L" to indicate the lower arm 9L side. For convenience, common markings are given to the other parts of the elements in the upper arm 9H and the lower arm 9L.

[0050] Hereinafter, the thickness direction of the semiconductor element (semiconductor substrate) is defined as the Z direction. A direction orthogonal to the Z direction is defined as the X direction. A direction orthogonal to both the Z and X directions is defined as the Y direction. Unless otherwise specified, the shape observed from the Z-direction plane, in other words, the shape along the XY plane defined by the X and Y directions, is defined as a planar shape. Furthermore, sometimes the observation from the Z-direction plane is simply represented as a planar observation.

[0051] like Figures 2-6 As shown, the semiconductor device 20 includes a sealing solid 30, a semiconductor element 40, heat sinks 50 and 60, conductive spacers 70, connectors 80-82, and external connection terminals 90. The semiconductor device 20 also includes bonding wires 97 and solder 100. The semiconductor device 20 constitutes the upper and lower arm circuits 9 of one phase described above.

[0052] Encapsulating solid 30 encapsulates a portion of other elements constituting semiconductor device 20. The remainder of the other elements is exposed outside encapsulating solid 30. Encapsulating solid 30 is made of resin, for example. An example of resin is epoxy resin. Encapsulating solid 30 is formed, for example, by transfer molding. Such encapsulating solid 30 is sometimes referred to as an encapsulating resin body, molding resin, resin molded body, etc. Encapsulating solid 30 can also be formed using gel, for example. The gel is filled (configured) in the opposing regions of heat sinks 50 and 60, for example.

[0053] like Figures 2-4 As shown, the sealing solid 30 is generally rectangular in shape. The sealing solid 30, as the surface forming the outer contour, has a surface 30a and a back surface 30b opposite to surface 30a in the Z direction. Surface 30a and back surface 30b are, for example, generally flat surfaces. Furthermore, it has side surfaces 30c, 30d, 30e, and 30f connected to surface 30a and back surface 30b. Side surface 30c is the surface from which the main terminals 91 to 93 of the external connection terminals 90 protrude. Side surface 30d is the surface opposite to side surface 30c in the Y direction. Side surface 30d is the surface from which the signal terminal 94 protrudes. Side surfaces 30e and 30f are the surfaces from which the external connection terminals 90 do not protrude. Side surface 30e is the surface opposite to side surface 30f in the X direction.

[0054] Semiconductor element 40 includes a semiconductor substrate 41, an emitter electrode 42, a collector electrode 43, and a pad 44. Semiconductor element 40 is sometimes referred to as a semiconductor chip. The semiconductor substrate 41 is formed with vertically shaped elements using silicon (Si) or wide-bandgap semiconductors with a wider bandgap than silicon as materials. Examples of wide-bandgap semiconductors include silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), and diamond.

[0055] The vertical element is configured such that the main current flows in the thickness direction (Z direction) of the semiconductor substrate 41 (semiconductor element 40). In this embodiment, the vertical element is an IGBT 11 and a diode 12 forming one arm. The vertical element is an IGBT connected in anti-parallel with the diode 12, i.e., an RC-IGBT. RC is short for Reverse Conducting. The vertical element is a heat-generating element that heats up when energized. A gate electrode (not shown) is formed on the semiconductor substrate 41. The gate electrode, for example, is formed in a trench structure.

[0056] The semiconductor substrate 41 is generally rectangular in shape. An emitter electrode 42, one of the main electrodes, is disposed on one side of the semiconductor substrate 41. A collector electrode 43, the other main electrode, is disposed on the back side of the semiconductor substrate 41. One side of the semiconductor substrate 41 is the side 30a of the main surface of the semiconductor substrate 41 that is the side of the sealing solid 30 in the thickness direction. The back side of the semiconductor substrate 41 is the side 30b of the main surface of the semiconductor substrate 41 that is the back side of the sealing solid 30 in the thickness direction.

[0057] With the IGBT 11 turned on, current (main current) flows between the main electrodes, namely between the emitter electrode 42 and the collector electrode 43. The emitter electrode 42 also serves as the anode electrode of the diode 12. The collector electrode 43 also serves as the cathode electrode of the diode 12. The collector electrode 43 is formed almost entirely on the back side of the semiconductor substrate 41. The emitter electrode 42 is formed on a portion of one side of the semiconductor substrate 41. That is, in planar view, the collector electrode 43 has a larger area than the emitter electrode 42. The emitter electrode 42 corresponds to the upper electrode, and the collector electrode 43 corresponds to the lower electrode.

[0058] The emitter electrode 42 has a Ni layer formed using a material primarily composed of Ni (nickel). In this embodiment, the emitter electrode 42 has an Al layer formed using a material primarily composed of Al (aluminum) and a Ni layer stacked on top of the Al layer. The collector electrode 43 also has an Al layer and a Ni layer, similar to the emitter electrode 42.

[0059] Pad 44 is a signal electrode. Pad 44 is formed on one side of the semiconductor substrate 41 in a region different from the region where the emitter electrode 42 is formed. Pad 44 is formed in the Y direction at an end opposite to the region where the emitter electrode 42 is formed. Pad 44 is arranged in the Y direction alongside the emitter electrode 42. The number of pads 44 is not particularly limited. Pad 44 includes at least a pad for the gate electrode.

[0060] As an example, the semiconductor device 40 has five pads 44. Specifically, the pads are used for: gate electrode, emitter potential detection, cathode potential detection of a temperature-sensing diode (not shown) included in the semiconductor device 40, anode potential detection of the temperature-sensing diode, and current sensing. The five pads 44 are arranged along the X direction.

[0061] The semiconductor device 20 includes two semiconductor elements 40. Specifically, it includes a semiconductor element 40H constituting the upper arm 9H and a semiconductor element 40L constituting the lower arm 9L. Semiconductor element 40H is sometimes referred to as the first semiconductor element, the upper arm element, etc. Semiconductor element 40L is sometimes referred to as the second semiconductor element, the lower arm element, etc. Semiconductor elements 40H and 40L are of the same specifications, i.e., common components. Semiconductor elements 40H and 40L are arranged in the X direction. Semiconductor elements 40H and 40L are arranged in approximately the same position in the Z direction. Semiconductor elements 40H and 40L are arranged such that their emitter electrodes 42 are located on the same side in the Z direction.

[0062] Heat sink 50 is electrically connected to emitter electrode 42, providing wiring functionality. Similarly, heat sink 60 is electrically connected to collector electrode 43, providing wiring functionality. Heat sinks 50 and 60 provide heat dissipation functionality to dissipate heat generated by semiconductor element 40. Therefore, heat sinks 50 and 60 may be referred to as wiring components, conductive components, heat dissipation components, etc. Heat sinks 50 and 60 are configured to sandwich semiconductor element 40 in the Z direction. Heat sinks 50 and 60 are configured to be at least partially opposed to each other in the Z direction. In planar view, heat sinks 50 and 60 contain semiconductor element 40 internally.

[0063] Heat sinks 50 and 60 are metal plates made of metals with good electrical conductivity, such as Cu or Cu alloys. The metal plates are provided, for example, as part of a lead frame. Heat sinks 50 and 60 have a Ni layer formed on their surface through plating or similar processes. Heat sinks 50 and 60 have a Ni layer at least at the solder joint surfaces.

[0064] As a wiring component, a substrate with metal bodies disposed on both sides of an insulating substrate such as ceramic or resin can be used instead of heat sinks 50 and 60. In this case, the metal body on the semiconductor element 40 side is equivalent to a conductor bonded by solder, i.e., an upper conductor or a lower conductor. The metal body on the semiconductor element 40 side has a Ni layer on its surface.

[0065] Heat sink 50 has a facing surface 50a that serves as the side of semiconductor element 40 and a back surface 50b that is the side opposite to the facing surface 50a. Similarly, heat sink 60 also has a facing surface 60a and a back surface 60b. The back surfaces 50b and 60b of heat sinks 50 and 60 are exposed from the encapsulating solid 30. The back surfaces 50b and 60b are sometimes referred to as heat dissipation surfaces, exposed surfaces, etc. The back surface 50b of heat sink 50 is substantially coplanar with one surface 30a of encapsulating solid 30. The back surface 60b of heat sink 60 is substantially coplanar with the back surface 30b of encapsulating solid 30.

[0066] The semiconductor device 20 includes two heat sinks 50. Specifically, it includes a heat sink 50H constituting the upper arm 9H and a heat sink 50L constituting the lower arm 9L. The heat sink 50H corresponds to the first main body portion of the first upper conductor, and the heat sink 50L corresponds to the second main body portion of the second upper conductor.

[0067] like Figure 5 As shown, heat sinks 50H and 50L are roughly rectangular in shape. Heat sinks 50H and 50L are arranged in the X direction. Figure 3 and Figure 4 As shown, heat sinks 50H and 50L have approximately the same thickness and are positioned approximately at the same location in the Z direction. In planar view, heat sinks 50H and 50L enclose the corresponding semiconductor element 40 and conductive spacer 70. On the opposing surfaces 50a of each heat sink 50H and 50L, grooves 51 are formed to collect overflowing solder. The grooves 51 surround the solder joint in the opposing surfaces 50a. The grooves 51 are, for example, formed in a ring shape. The back surfaces 50b of the heat sinks 50H and 50L exposed from the encapsulating solid 30 are arranged in the X direction.

[0068] The semiconductor device 20 includes two heat sinks 60. Specifically, it includes a heat sink 60H forming the upper arm 9H and a heat sink 60L forming the lower arm 9L. The heat sink 60H corresponds to the first lower conductor, and the heat sink 60L corresponds to the second lower conductor.

[0069] like Figure 6 As shown, heat sinks 60H and 60L are roughly rectangular in shape. Heat sinks 60H and 60L are arranged in the X direction. Figure 3 and Figure 4As shown, heat sinks 60H and 60L have approximately the same thickness and are positioned approximately at the same location in the Z direction. In planar view, heat sinks 60H and 60L enclose corresponding semiconductor elements 40. The back surfaces 60b of the heat sinks 60H and 60L exposed from the encapsulating solid 30 are aligned in the X direction.

[0070] A conductive spacer 70 is positioned between the semiconductor element 40 and the heat sink 50 in the Z direction. The conductive spacer 70 provides a spacer function to ensure a predetermined distance between the semiconductor element 40 and the heat sink 50. For example, the conductive spacer 70 ensures the height of the corresponding signal terminal 94 used to electrically connect the pad 44 of the semiconductor element 40. The conductive spacer 70 is located midway through the conductive and thermally conductive path between the emitter electrode 42 of the semiconductor element 40 and the heat sink 50, providing wiring and heat dissipation functions. The conductive spacer 70, together with the heat sink 50, constitutes the upper conductor.

[0071] The conductive spacer 70 is a metal component made of a metal with good electrical and thermal conductivity, such as Cu. The conductive spacer 70 is sometimes referred to as a terminal, terminal block, or metal block. The conductive spacer 70 has a Ni layer formed on its surface through plating or other processes. The conductive spacer 70 has a Ni layer at least at the solder joint surface. In this embodiment, the conductive spacer 70 is a generally rectangular columnar body with a planar shape and approximately the same size as the emitter electrode 42 when viewed in planar view.

[0072] The semiconductor device 20 includes two conductive spacers 70. Specifically, it includes a conductive spacer 70H constituting the upper arm 9H and a conductive spacer 70L constituting the lower arm 9L. The conductive spacer 70H corresponds to the first spacer portion of the first upper conductor, and the conductive spacer 70L corresponds to the second spacer portion of the second upper conductor.

[0073] Connectors 80-82 connect the elements constituting the upper and lower arm circuits 9. Connectors 80-82 also connect the elements constituting the semiconductor device 20. Connectors 80-82 are metal components made of a metal with good electrical and thermal conductivity, such as Cu. Connectors 80-82 have a Ni layer formed on their surface through plating or other processes. Connectors 80-82 have a Ni layer at least at the solder joint surfaces.

[0074] like Figure 3 and Figure 6 As shown, the connector 80 is connected to the heat sink 60L. The thickness of the connector 80 is thinner than that of the heat sink 60L. The connector 80 is connected to the opposing surface (side surface) opposite to the heat sink 60H, for example, in a state that is substantially coplanar with the opposing surface 60a of the heat sink 60L. The connector 80 has two bends, thus presenting a generally crank-like shape in the ZX plane. The connector 80 is covered by a sealing solid 30.

[0075] The connector portion 80 can be connected to the heat sink 60L either by being integrally formed as a continuous component, or it can be connected as a separate component by a joint. In this embodiment, the connector portion 80 is integrally formed with the heat sink 60L as part of the lead frame. The Ni layer is integrally formed with respect to the heat sink 60L and the connector portion 80.

[0076] like Figure 3 , Figure 4 and Figure 5 As shown, connectors 81 and 82 are connected to the corresponding heat sinks 50. Connector 81 is connected to heat sink 50H. Connector 82 is connected to heat sink 50L. The thickness of connectors 81 and 82 is thinner than that of the corresponding heat sinks 50. Connectors 81 and 82 are covered by a sealing solid 30.

[0077] The connectors 81 and 82 can be connected to the heat sink 50 either by being integrally formed or by being connected as separate components through a joint. In this embodiment, the connectors 81 and 82 are integrally formed with respect to the corresponding heat sinks 50H and 50L. The connectors 81 and 82 extend in the X direction from the opposing sides of the heat sinks 50H and 50L. The Ni layer is integrally formed with respect to the heat sink 50H and the connector 81. The Ni layer is integrally formed with respect to the heat sink 50L and the connector 82.

[0078] As an example, the heat sink 50H including the connector portion 81 and the heat sink 50L including the connector portion 82 are common components. The configuration of the heat sink 50H including the connector portion 81 and the heat sink 50L including the connector portion 82 is centrally symmetrical about the Z-axis. Solder is present between the opposing surfaces of the connector portion 80 and the connector portion 81, forming a solder joint. Figure 5 As shown, connectors 81 and 82 are positioned between heat sinks 50H and 50L in a planar view. Connectors 81 and 82 are arranged in the Y direction between heat sinks 50H and 50L.

[0079] At the mating surfaces of joint portions 81 and 82, a groove 83 is formed to collect overflowing solder. The groove 83 is formed in an annular shape to surround the solder joint. The groove 83 is formed, for example, by pressure processing. Joint portions 80 and 81 correspond to joint conductors and the first joint conductor. Joint portion 82 corresponds to the second joint conductor.

[0080] External connection terminal 90 is a terminal used to electrically connect semiconductor device 20 to external devices. External connection terminal 90 is formed using a highly conductive metal material such as copper. External connection terminal 90 is, for example, a substrate. External connection terminal 90 is sometimes referred to as a lead. External connection terminal 90 includes main terminals 91, 92, and 93 and signal terminals 94. Main terminals 91, 92, and 93 are external connection terminals 90 that are electrically connected to the main electrodes of semiconductor element 40.

[0081] like Figure 5 and Figure 6 As shown, the main terminal 91 is electrically connected to the collector electrode 43 of the semiconductor element 40H. The main terminal 91 is also electrically connected to the positive terminal of the smoothing capacitor 5. The main terminal 91 is sometimes referred to as a P-terminal, a high-potential power supply terminal, etc. The main terminal 91 is connected to the collector electrode 43 of the semiconductor element 40H via the heat sink 60H. The main terminal 91 is connected to one end of the heat sink 60H in the Y direction. The thickness of the main terminal 91 is thinner than that of the heat sink 60H. The main terminal 91 is connected to the heat sink 60H, for example, in a manner substantially coplanar with the opposing surface 60a. The main terminal 91 can be connected to the heat sink 60H either by being integrally formed or by being connected as a separate component via a bonding process.

[0082] In this embodiment, the main terminal 91 is integrally provided with the heat sink 60H as part of the lead frame. The main terminal 91 extends from the heat sink 60H in the Y direction and protrudes outward from the side 30c of the sealing solid 30. The main terminal 91 has a bend in the middle of the portion covered by the sealing solid 30 and protrudes from near the center in the Z direction in the side 30c.

[0083] like Figure 5 and Figure 6 As shown, the main terminal 92 is electrically connected to the emitter electrode 42 of the semiconductor element 40L. The main terminal 92 is also electrically connected to the negative terminal of the smoothing capacitor 5. The main terminal 92 is sometimes referred to as an N-terminal, a low-potential power supply terminal, etc. The main terminal 92 is connected to the emitter electrode 42 of the semiconductor element 40L via the connector 82, the heat sink 50L, and the conductive spacer 70L. The main terminal 92 extends in the Y direction and protrudes from the same side 30c as the main terminal 91 beyond the sealing solid 30.

[0084] The main terminal 92 has a connecting portion 920 near one end in the Y direction, which connects to the connector portion 82. A portion of the main terminal 92, including the connecting portion 920, is covered by a sealing solid 30, while the remaining portion protrudes from the sealing solid 30. The plate thickness of the connecting portion 920 is thicker than the portion protruding from the sealing solid 30. The plate thickness of the connecting portion 920 is, for example, approximately the same as that of the heat sink 50L. The main terminal 92 also has a bent portion, similar to the main terminal 91, protruding from near the center in the Z direction in the side surface 30c. The main terminal 92 has a Ni layer on its surface, formed by plating or the like. The main terminal 92 has a Ni layer at least at the solder joint surface of the connecting portion 920.

[0085] The main terminal 93 is connected to the connection point between the upper arm 9H and the lower arm 9L. The main terminal 93 is electrically connected to the emitter electrode 42 of the semiconductor element 40H and the collector electrode 43 of the semiconductor element 40L. The main terminal 93 is also electrically connected to the winding 3a of the corresponding phase of the electric generator 3. The main terminal 93 is sometimes referred to as an output terminal, AC terminal, or O terminal. The main terminal 93 is electrically connected to the emitter electrode 42 of the semiconductor element 40H via the heat sink 60L, connectors 80 and 81, heat sink 50H, and conductive spacer 70H. The main terminal 93 is also connected to the collector electrode 43 of the semiconductor element 40L via the heat sink 60L.

[0086] The main terminal 93 is connected to one end of the heat sink 60L in the Y direction. The thickness of the main terminal 93 is thinner than that of the heat sink 60L. The main terminal 93 is connected to the heat sink 60L, for example, in a manner that is substantially coplanar with the opposing surface 60a. The main terminal 93 can be connected to the heat sink 60L either by being integrally disposed continuously, or by being disposed as a separate component and connected by a joint.

[0087] In this embodiment, the main terminal 93 is integrally provided with the heat sink 60L as part of the lead frame. The main terminal 93 extends from the heat sink 60L in the Y direction and protrudes from the same side 30c as the main terminal 91 beyond the sealing body 30. The main terminal 93 also has a bend, similar to the main terminal 91, and protrudes from near the center in the Z direction in the side 30c. The three main terminals 91 to 93 are arranged in the X direction in the order of main terminal 91, main terminal 92, and main terminal 93.

[0088] Signal terminals 94 are electrically connected to corresponding pads 44 of semiconductor element 40. In this embodiment, signal terminals 94 are electrically connected to pads 44 via bonding wires 97. Signal terminals 94 extend in the Y direction and protrude from the side 30d of encapsulation solid 30 to the outside. Semiconductor device 20 has 5 signal terminals 94 for each semiconductor element 40, that is, a total of 10 signal terminals 94. The plurality of signal terminals 94 are arranged in the X direction. For example, the signal terminals 94 are configured as lead frames common to heat sink 60 and main terminals 91 to 93.

[0089] Additionally, the semiconductor device 20 includes suspension leads 95. The heat sink 60 (60H, 60L), connector 81, main terminals 91-93, and signal terminals 94 form a lead frame as a common component. The lead frame is a shaped strip with varying thicknesses locally. The signal terminals 94, before cutting, are supported by the suspension leads 95 via tie rods (not shown). Unnecessary parts of the lead frame, such as the tie rods and outer frame, are cut (removed) after the encapsulating solid 30 is formed.

[0090] Semiconductor device 20 includes a plurality of solders 100 for connecting elements. Solders 100 include solders 101H, 101L, 102H, 102L, 103H, 103L, 104, and 105. Solder 101H is located between the emitter electrode 42 of semiconductor element 40H and the conductive spacer 70H, bonding the emitter electrode 42 to the conductive spacer 70H. Solder 102H is located between the conductive spacer 70H and the heat sink 50H, bonding the conductive spacer 70H to the heat sink 50H. Solders 101H and 102H correspond to a first upper solder. Solder 103H is located between the collector electrode 43 of semiconductor element 40H and the heat sink 60H, bonding the collector electrode 43 to the heat sink 60H. Solder 103H corresponds to a first lower solder.

[0091] Solder 101L is positioned between the emitter electrode 42 of the semiconductor element 40L and the conductive spacer 70L, bonding the emitter electrode 42 to the conductive spacer 70L. Solder 102L is positioned between the conductive spacer 70L and the heat sink 50L, bonding the conductive spacer 70L to the heat sink 50L. Solder 101L and 102L correspond to the second upper solder. Solder 103L is positioned between the collector electrode 43 of the semiconductor element 40L and the heat sink 60L, bonding the collector electrode 43 to the heat sink 60L. Solder 103L corresponds to the second lower solder.

[0092] Additionally, solders 101H and 101L are sometimes referred to as component-on-solder. Solders 102H and 102L are sometimes referred to as spacer-on-solder. Solders 103H and 103L are sometimes referred to as component-below-solder.

[0093] Solder 104, together with connectors 80 and 81, electrically connects heat sink 50H and heat sink 60L. In this embodiment, solder 104 is located between connector 80 connected to heat sink 60L and connector 81 connected to heat sink 50H, connecting connectors 80 and 81. Solder 104 is equivalent to relay solder, the first relay solder. Solder 105, together with connector 82, electrically connects heat sink 50L to main terminal 92. In this embodiment, solder 105 is located between connector 82 connected to heat sink 50L and connection portion 920 of main terminal 92, connecting connector 82 to main terminal 92. Solder 105 is equivalent to second relay solder.

[0094] Multiple solders 100 contain Cu and Sn respectively. Solder 100, as an example, contains Cu, Bi, Sb, etc., with the remainder being a multi-element lead-free solder composed of Sn. The thickness of each solder 100 is, for example, approximately 100 μm.

[0095] As described above, in the semiconductor device 20, a plurality of semiconductor elements 40 constituting the upper and lower arm circuits 9 of one phase are encapsulated by an encapsulating solid 30. The encapsulating solid 30 integrally encapsulates a portion of each of the plurality of semiconductor elements 40, a portion of each of the heat sinks 50 and 60, a conductive spacer 70, connectors 80 to 82, main terminals 91 to 93, and a portion of each of the signal terminals 94.

[0096] Semiconductor element 40 is disposed between heat sinks 50 and 60 in the Z direction. Semiconductor element 40 is sandwiched between opposing heat sinks 50 and 60. This allows heat from semiconductor element 40 to be dissipated to both sides in the Z direction. Semiconductor device 20 forms a two-sided heat dissipation structure. The back surface 50b of heat sink 50 is substantially coplanar with one surface 30a of encapsulating solid 30. The back surface 60b of heat sink 60 is substantially coplanar with the back surface 30b of encapsulating solid 30. Since the back surfaces 50b and 60b are exposed, heat dissipation is improved.

[0097] Alternatively, an Au layer can be deposited on the Ni layer through plating or other processes. Au, for example, inhibits Ni oxidation and improves wettability with the solder. Since Au diffuses into the solder during soldering, it exists in the state before bonding but not in the state after bonding.

[0098] <Output Current and Return Current>

[0099] Next, based on Figure 7 The output current and return current are explained. Figure 7 The diagram illustrates, as an example, the output current and return current related to the semiconductor element 40H on the upper arm 9H side. Figure 7 In the diagram, the output current is represented by a dashed arrow, and the return current is represented by a single-dot dashed arrow.

[0100] The output current (main current) flows when the IGBT operates. The output current on the upper arm 9H side flows from the main terminal 91 through the IGBT 11 of the semiconductor element 40H and the main terminal 93 to the electric generator 3. Specifically, as... Figure 7 As indicated by the dashed arrow, the flow path is: main terminal 91 (P terminal) → heat sink 60H → semiconductor element 40H (IGBT11) → conductive spacer 70H → heat sink 50H → connector 81 → connector 80 → heat sink 60L → main terminal 93 (O terminal).

[0101] The return current flows when the diode operates. The return current on the upper arm 9H side flows in the opposite direction to the output current, that is, from the main terminal 93 through the diode 12 of the semiconductor element 40H and the main terminal 91 to the DC power supply 2 side. Specifically, as... Figure 7As shown by the arrow with a single dotted line, the flow path is: main terminal 93 (O terminal) → heat sink 60L → connector 80 → connector 81 → heat sink 50H → conductive spacer 70H → semiconductor element 40H (diode 12) → heat sink 60H → main terminal 91 (P terminal).

[0102] The same applies to the lower arm 9L side. Output current flows via the path: main terminal 93 → IGBT 11 of semiconductor element 40L → main terminal 92. Return current flows via the path: main terminal 92 → diode 12 of semiconductor element 40L → main terminal 93.

[0103] <Joint structure and solder particle size>

[0104] Next, based on Figures 8-10 The joint structure and solder particle size are explained. Figure 8 This is a cross-sectional view showing the bonding structure of the connector portions 80 and 81 of the semiconductor device 20 in this embodiment.

[0105] Figure 8 It will be Figure 3 The enlarged sectional view of region VIII, represented by a single-dotted line. For convenience, in... Figure 8 The diagram omits the wire sheet 120. Figure 9 This is a cross-sectional view showing the wire strip 120 disposed on the surface of the connector portion 80. Figure 9 For convenience, alloy layer 110 has been omitted. Figure 10 This is a sectional view representing a reference example. Figure 10 Corresponding to Figure 8 In the reference example, the markings of each element are set such that an 'r' is appended to the end of the markings of the associated elements of the semiconductor device 20.

[0106] like Figure 8 As shown, the connector 80 has a Cu-based base material 800 and a Ni layer 801 disposed on the base material 800. Similarly, the connector 81 also has a Cu-based base material 810 and a Ni layer 811 disposed on the base material 810. As an example, the Ni layers 801 and 811 are NiP films formed by an electroless plating method. The Ni layers 801 and 811 are Ni films containing P.

[0107] Semiconductor device 20 includes an alloy layer 110 between a Ni layer 801 and a solder 104, and an alloy layer 111 between the Ni layer 801 and the solder 104. The alloy layers 110 and 111 are sometimes referred to as IMC. IMC is short for Intermetallic Compound. The alloy layers 110 and 111 are formed during solder bonding. The alloy layers 110 and 111 contain Ni, Cu, and Sn. For example, the composition of the alloy layers 110 and 111 is (Ni-Cu)3Sn4.

[0108] Semiconductor device 20 also includes P-rich layers 802 and 812. P-rich layer 802 is formed on the surface of Ni layer 801. P-rich layer 812 is formed on the surface of Ni layer 811. P-rich layers 802 and 812 are formed by diffusion of a portion of the Ni in Ni layers 801 and 811 towards the solder 104 side during bonding. P-rich layers 802 and 812 are layers richer in P than Ni layers 801 and 811 (NiP). The composition of P-rich layers 802 and 812 is, for example, Ni3P.

[0109] like Figure 9 As shown, at least one of the connector portions 80 and 81 has a plurality of wire strips 120 at the solder joint surface. The wire strips 120 are small portions of the bonding wire. Sometimes the wire strips 120 are referred to as protrusions or raised bonding portions. The wire strips 120 are disposed within the solder 104. The plurality of wire strips 120 are distributed dispersedly within the solder 104. By appropriately setting the height of the wire strips 120, a minimum thickness of the solder 104 can also be ensured. The plurality of wire strips 120 are fixed (jointed) to one of the opposing surfaces constituting the solder joint, namely the first opposing surface, and protrude toward the other opposing surface, namely the second opposing surface. As an example, in this embodiment, wire strips 120 are provided at the solder joint surface of the connector portion 80. The wire strips 120 are provided, for example, at a predetermined spacing.

[0110] The surface of the connector portion 80, which has a wire sheet 120, is irregularly shaped. Solder 104 begins grain growth from the wire sheet 120 as it solidifies. Adjacent grains collide to form grain boundaries 106. The grains grow from the corner of the wire sheet 120, for example, the upper corner. Therefore, the grain size of solder 104 is, for example, smaller than the grain size of solders 103H and 103L. As described above, the thickness of solder 104 is approximately 100 μm. The grain size of solder 104 is smaller than its thickness, i.e., 100 μm.

[0111] exist Figure 10In the comparative example shown, no wire strips are provided at the solder joint surfaces of the connector portions 80r and 81r. That is, the particle size of the solder 104 is not controlled. Other structures are the same as those of the semiconductor device 20 of this embodiment. In this case, the particle size of the solder 104r is approximately 100 μm. The number of solder 104r grains is one or two in the thickness direction (Z direction) of the solder 104.

[0112] In this embodiment, no wire strip 120 is provided for solders 103H and 103L among the multiple solders 100. The particle size of solders 103H and 103L is similar to... Figure 10 The comparative examples shown are equivalent. The particle size of solder 103H and 103L is larger than that of solder 104 with wire sheet 120.

[0113] <em>

[0114] Next, based on Figure 11 Explain EM (electromigration). Figure 11 This is a reference diagram illustrating the mechanism of EM progression. In Figure 11 The labeling of each element is also set by appending an 'r' to the end of the labeling of the associated elements of the semiconductor device 20. In the example shown in the reference figure, with Figure 10 The structure shown is the same, without particle size control of the solder 104r. Other structural aspects are the same as those of the semiconductor device 20 in this embodiment.

[0115] Figure 11 The 1st indicates the initial stage before power is applied. An alloy layer 110r exists between the Ni layer 801r and the solder 104r. In addition, a P-rich layer 802r is formed on the surface of the Ni layer 801r.

[0116] Figure 11 The 2nd, 3rd, and 4th indicate the application of output current. The dashed arrows indicate the direction of electron (e-) flow. Figure 11 As shown in Figure 2nd, with the movement of electrons, Cu and other metals in the alloy layer 110r move (diffuse) towards the junction 81r side. Specifically, Cu and other metals ionize and move towards the junction 81r side. Thus, the alloy layer 110r gradually thins, as... Figure 11 It disappeared as shown in the 3rd diagram.

[0117] If alloy layer 110r disappears, then as follows Figure 11 As shown in Figure 3, with the movement of electrons, the Ni in the Ni layer 801r moves towards the junction 81r side (diffusion), the Ni layer 801r decreases, and the P-rich layer 802r increases. Next, as... Figure 11 As shown in Figure 4, the Ni layer 801r disappears, and the P-rich layer 802r reaches the base material 800r. That is, the P-rich layer 802r replaces the Ni layer 801r.

[0118] After the P-rich 802r layer reaches the base material 800r, further penetration leads to decreased adhesion, such as the formation of porosity. Furthermore, cracks can originate along the interface from these porosity points. Additionally, cracks may also form within the P-rich 802r layer itself.

[0119] As described above, in structures where solder particle size is not controlled (refer to...) Figure 10 In this process, the solder 104r has a relatively large particle size. There are fewer grain boundaries in the Cu migration path. Therefore, the Cu in the alloy layer 110r moves easily as electrons migrate.

[0120] Furthermore, while an example of output current is shown, the same applies to the case of return current. When a return current is applied, firstly, the alloy layer 111r on the connector 81r side disappears, and then the P-rich layer 812r replaces the Ni layer 811r. After the P-rich layer 812r reaches the base material 810r, further passage will result in decreased adhesion, such as the formation of porosity and cracks. Due to the large particle size of the solder 104r, the Cu in the alloy layer 111r easily moves with the movement of electrons.

[0121] On the other hand, the structure of this embodiment (refer to...) Figure 8 In the process, the particle size of solder 104 at the joint of the high current density connectors 80 and 81 is smaller than that of solders 103H and 103L where the particle size is not controlled. Therefore, as electrons move, the Cu in alloy layers 110 and 111 is difficult to move. That is, alloy layers 110 and 111 are difficult to disappear. The time taken for alloy layers 110 and 111 to disappear is longer. Consequently, the time it takes for Ni layers 801 and 811 to become P-rich layers 802 and 812 and begin to decrease is later. The time taken for Ni layers 801 and 811 to disappear is longer.

[0122] <Summary of Implementation Method 1>

[0123] In planar view, the area of ​​the collector electrode 43, which serves as the main electrode on the high-potential side, is larger than the area of ​​the emitter electrode 42, which serves as the main electrode on the low-potential side. Furthermore, due to the miniaturization of the semiconductor device 20, it is difficult to increase the area of ​​the solder joints of the connectors 80 and 81, and the solder joint of the connector 82. Therefore, for the semiconductor device 20 constituting the upper and lower arm circuits 9 of a single phase, the current density of solders 101H, 101L, 102H, 102L, 104, and 105 becomes higher than the current density of solder 103H and 103L. That is, EM (emergence potential) easily develops at the joints of solders 101H, 101L, 102H, 102L, 104, and 105 among the multiple solders 100. EM is difficult to develop at the joints of solders 103H and 103L among the multiple solders 100.

[0124] As an example, in this embodiment, the particle size of solder 104 (relay solder, first relay solder) is smaller than that of solders 103H and 103L (first lower solder and second lower solder). There are more grain boundaries 106 between the solder objects. The grain boundaries 106 hinder the movement of Cu. Therefore, as electrons move, the Cu in alloy layers 110 and 111 is difficult to move. This allows for a longer time until alloy layers 110 and 111 disappear. Furthermore, it allows for a longer time until Ni layers 801 and 811 disappear. Based on the above, EM lifetime can be improved.

[0125] Regarding the current density of the semiconductor device 20, that is, the current density of the energized path connected to the main electrode, it is highest, for example, in the solder joint of the connectors 80 and 81. In this embodiment, by reducing the particle size of the solder 104, the EM lifetime can be improved.

[0126] Furthermore, the effect of the particle size of solder 104 has been confirmed through prototype testing. It has been confirmed that by reducing the particle size of solder 104, the disappearance of alloy layers 110 and 111 is slowed down, meaning that the EM process can be slowed down. At this time, Ni layers 801 and 811 are formed by electroless NiP plating. The composition of alloy layers 110 and 111 is (Ni-Cu)3Sn4.

[0127] In this embodiment, the connector portion 80 has a plurality of wire strips 120 at the solder joint surface. The solder 104 solidifies starting from the wire strips 120. The wire strips 120 are the starting points for solidification. By providing the wire strips 120, the particle size of the solder 104 is reduced, thereby improving the EM lifespan.

[0128] <Variation Example>

[0129] The example shown is of a wire strip 120 being provided on the mating head 80, but it is not limited to this. The wire strip 120 may also be provided at the solder joint surface of the connector 81. In this case, the solder 104 solidifies and becomes smaller, starting from the wire strip 120. Alternatively, both the mating heads 80 and 81 may each have a wire strip 120. That is, at least one of the connected objects needs to be provided.

[0130] Solder 104 is shown as an example of a small-particle solder with a small particle size, but it is not limited to this. As a small-particle solder, at least one of the multiple solders 100 other than solders 103H and 103L can be used.

[0131] For example, solder 105 can be made into small-particle solder. By providing multiple wire strips 120 at the solder joint surface of the connector portion 82 and / or the connection portion 920 of the main terminal 92, the particle size of solder 105 can be smaller than that of solder 103H and 103L. As a result, EM propagation can be suppressed at the joint of solder 105.

[0132] For example, solders 101H and 101L can be made into small-particle solders. By providing multiple wire strips 120 at the solder joint surfaces of the emitter electrode 42 and / or the conductive spacer 70, the particle size of solders 101H and 101L can be smaller than that of solders 103H and 103L. This suppresses EM propagation at the joint of solders 101H and 101L. This is effective in miniaturizing the semiconductor device 40.

[0133] For example, solders 102H and 102L can be made into small-particle solders. By providing multiple wire strips 120 at the solder joint surfaces of the conductive spacer 70 and / or heat sink 50, the particle size of solders 102H and 102L can be smaller than that of solders 103H and 103L. This suppresses EM propagation at the joints of solders 102H and 102L. Similar to the miniaturization of solders 101H and 101L, this is also effective for miniaturizing the semiconductor device 40.

[0134] The configuration of multiple wire strips 120 is not specifically limited. For example, it can also be as follows: Figure 12 As shown, multiple wire strips 120 are disposed in the solder joint surface of the conductive spacer 70, overlapping with the center of the semiconductor element 40. Higher temperatures and higher current densities lead to greater EM (emergence precipitates). By disposing of wire strips 120 in the overlapping portion near the center of the element in planar view, reliably miniaturized particles can be formed in the higher-temperature regions. This suppresses EM progression. Alternatively, multiple wire strips 120 can be disposed in the solder joint surface of the conductive spacer 70 at the four corners overlapping with the emitter electrode 42. The lower temperature at the corners facilitates solder solidification. This promotes miniaturization.

[0135] Figure 12 The arrangement of the wire sheet 120 shown is not limited to the conductive spacer 70. Regarding the emitter electrode 42, it can be located either near the center of the component or at the four corners. Regarding the heat sink 50, it can be located either in the portion overlapping with the center of the component or in the portion overlapping with the four corners.

[0136] The example shown is of a semiconductor device 20 having a conductive spacer 70, but it is not limited to this. A protrusion providing a spacer function may also be provided on the heat sink 50 instead of the conductive spacer 70. In this case, the heat sink 50 is equivalent to an upper conductor. An upper solder is placed between the emitter electrode 42 and the heat sink 50, bonding the emitter electrode 42 and the heat sink 50. To refine the upper solder, multiple wire strips 120 may be provided at the solder joint surfaces of the emitter electrode 42 and / or the heat sink 50.

[0137] The example shown is of a semiconductor device 20 having a connector 82, but it is not limited to this. The heat sink 50L, the connector 82, and the main terminal 92 can also be provided continuously and integrally. That is, the semiconductor device 20 can also be a structure without solder 105.

[0138] This illustration shows an example where the semiconductor device 20 has two connectors 80 and 81 for connecting the upper arm 9H and the lower arm 9L, but it is not limited to this. It may also have only one of the connectors 80 and 81. For example, it may have only connector 80, configured such that connector 80 is connected to the heat sink 50H via solder 104. It may also have only connector 81, configured such that connector 81 is connected to the heat sink 60L via solder 104.

[0139] (Second Implementation)

[0140] This embodiment is a variation based on the prior embodiment, and the description of the prior embodiment can be referenced. In the prior embodiment, multiple wire sheets are provided as the starting point for solidification. Alternatively, an uneven oxide film formed by laser irradiation can be provided instead.

[0141] <Uneven Oxide Film>

[0142] Figure 13 This is a cross-sectional view of the uneven oxide film 803 provided on the surface of the connector portion 80 in the semiconductor device 20 of this embodiment. Figure 13 Corresponding to Figure 9 .exist Figure 13 For convenience, the P-rich layer 802 and the alloy layer 110 are omitted.

[0143] As described above, the connector 80 has a base material 800 and a Ni layer 801 disposed on the surface of the base material 800. Figure 13 As shown, the connector portion 80 also has a rough oxide film 803 disposed on the Ni layer 801. By irradiating the Ni layer 801 with a laser, the rough oxide film 803 is dispersed and formed at multiple locations on the solder joint surface of the connector portion 80.

[0144] The 803 undulating oxide film is a film of oxide with Ni as the main component. For example, in the composition of the 803 undulating oxide film, 80% is Ni₂O₃, 10% is NiO, and 10% is Ni.

[0145] The recesses 801a on the surface of the Ni layer 801 are formed by irradiation with a pulsed laser. One recess 801a is formed for each pulse. Through laser irradiation, the surface portion of the Ni layer 801 melts, vaporizes, and evaporates to form a rough oxide film 803. The rough oxide film 803 is an oxide film derived from the Ni layer 801. The rough oxide film 803 is a film of oxide of the metal (Ni), the main component of the Ni layer 801. The rough oxide film 803 is formed by mimicking the irregularities on the surface of the Ni layer 801 with recesses 801a. On the surface of the rough oxide film 803, irregularities are formed at a spacing finer than the width of the recesses 801a. That is, very fine irregularities (roughened areas) are formed.

[0146] The pulsed laser pulses are tuned so that the energy density is greater than 0 J / cm². 2 And 100J / cm 2 The pulse width must be less than 1 μs. To meet this requirement, YAG lasers, YVO4 lasers, fiber lasers, etc., can be used. For example, in the case of a YAG laser, the energy density is 1 J / cm². 2 That's all. In the case of non-electrolytic Ni plating, even at 5J / cm... 2 The Ni layer 801 can also be processed on the left and right sides.

[0147] <pores>

[0148] Compared to metal films, oxide films (803 rough-surface oxide films) have lower solder wettability. Because of the fine irregularities on the surface of the 803 rough-surface oxide film, the contact area with the solder is smaller, and some of the solder becomes spherical due to surface tension. That is, the contact angle is larger, resulting in lower solder wettability.

[0149] As mentioned above, the uneven oxide film 803 has low wettability for solder 104. Therefore, as Figure 13 As shown, pores 121 are formed in such a way that they cover the uneven oxide film 803. Pores 121 are formed around the uneven oxide film 803. In the semiconductor device 20, a plurality of pores 121 are present near the solder joint surface of the connector portion 80. Other structural features are the same as those described in the prior embodiment.

[0150] <Summary of Implementation Method 2>

[0151] The structure described in this embodiment achieves the same effects as the structure described in the prior embodiment. Specifically, the solder 104 contains multiple pores 121 caused by the uneven oxide film 803. During solidification, the solder 104 undergoes grain growth starting from the pores 121. The pores 121 are the starting points for solidification. By providing the uneven oxide film 803 and, moreover, by providing the pores 121, the particle size of the solder 104 is made smaller than that of the solders 103H and 103L, thereby improving the EM lifetime.

[0152] <Variation Example>

[0153] This illustration shows an example of providing the uneven oxide film 803 on the connector portion 80, but it is not limited to this. It can be provided on conductors other than the heat sink 60 that are the conductors to be connected. For example, the uneven oxide film can also be provided on the solder joint surface of the connector portion 81. The uneven oxide film can also be provided on each of the connector portions 80 and 81. The uneven oxide film can also be provided on the solder joint surface of the heat sink 50. The uneven oxide film can also be provided on the solder joint surface of the conductive spacer 70.

[0154] The configuration of the uneven oxide film is not particularly limited. It can also be dispersed at a specified interval. For example... Figure 12 As shown, the heat sink 50 and the conductive spacer 70 can be located in the part that overlaps with the center of the component, or they can be located in the part that overlaps with the four corners.

[0155] (Third Implementation)

[0156] This embodiment is a variation based on the prior embodiment, and the description of the prior embodiment can be referenced. In the prior embodiment, the solder particle size is reduced by providing wire sheets or an uneven oxide film. Alternatively, unevenness can be provided at the inner peripheral end of the groove that collects overflowing solder.

[0157] Figure 14 This is a plan view showing the heat sink 50H including the connector portion 81 in the semiconductor device 20 of this embodiment. Figure 14 This is a plan view seen from the opposite side 50a. Figure 15 It will be Figure 14 The region represented by the dashed line in the image is magnified (XV). Figure 15 The text indicates that the solder 104 is disposed on the connector portion 81. Figure 15 In the text, only a portion of the grain boundary 106 is shown.

[0158] Similar to the prior embodiment, the connector 81 is provided continuously and integrally with respect to the heat sink 50H. For example... Figure 14 As shown, the heat sink 50H has a groove 51. Furthermore, the connector 81 has a groove 83. (As...) Figure 15 As shown, in planar view, the inner peripheral end 830 of the groove 83 has a continuous concave-convex shape. The connector portion 81 has a concave-convex portion 831 at the inner peripheral end 830 of the groove 83. As an example, the concave-convex portion 831 is provided along the entire length of the groove 83.

[0159] The solder 104 begins to grow grains during solidification from the recess and / or protrusion of the uneven portion 831 located at the inner peripheral end 830 of the groove 83. Because growth begins from the uneven portion, the grains in the solder 104 become smaller. Other structural aspects are the same as those described in the prior embodiment.

[0160] <Summary of the Third Implementation>

[0161] The structure described in this embodiment achieves the same effects as the structure described in the prior embodiment. Specifically, the inner peripheral end 830 of the groove 83 that contains overflowing solder 104 has a continuous uneven shape. During solidification, the solder 104 grows grains starting from the unevenness of the inner peripheral end 830. The uneven portion 831 is the starting point for solidification. By making the inner peripheral end 830 of the groove 83 uneven, the particle size of the solder 104 is smaller than that of the solders 103H and 103L, thereby improving the EM lifetime.

[0162] This illustrates an example where the protrusion 831 extends along the entire length of the groove 83, but it is not a limitation. The protrusion 831 may be provided in at least a portion of the entire length of the groove 83. By making at least a portion of the inner peripheral end 830 of the groove 83 into a protrusion shape, the particle size of the solder 104 can be made smaller than the particle size of the solders 103H and 103L.

[0163] Furthermore, when the heat sink 50H including the connector portion 81 and the heat sink 50L including the connector portion 82 are common components, the connector portion 82 also has a protrusion 831 at the inner peripheral end 830 of the groove 83. In this case, the solder 105 can also be made smaller.

[0164] <Variation Example>

[0165] This illustration shows an example of providing the protrusion 831 in the groove 83, but it is not limited to this. The protrusion may also be provided at the inner circumferential end of the groove 51 of the heat sink 50. It may also be provided at the inner circumferential end of the groove 51 of the heat sink 50H, or at the inner circumferential end of the groove 51 of the heat sink 50L. The protrusion may also be provided on both the groove 51 and the groove 83.

[0166] (Fourth implementation)

[0167] This embodiment is a variation based on the prior embodiment, and the description of the prior embodiment can be referenced. In the prior embodiment, the particle size of the solder is reduced by carefully designing the solder joint. Alternatively, the particle size of the solder can also be reduced by carefully designing the solder.

[0168] Figure 16 This is a cross-sectional view showing the bonding structure of the connectors 80 and 81 in the semiconductor device 20 of this embodiment. Figure 16 Corresponding to Figure 8 .

[0169] like Figure 16 As shown, conductive balls 122 are added to the solder 104. The balls 122 are mainly composed of Ni or Cu. Such balls 122 are sometimes called Ni balls or Cu balls. By appropriately setting the diameter of the balls 122, for example, the minimum thickness of the solder 104 can be guaranteed.

[0170] With the presence of the ball 122, the solder 104 undergoes grain growth starting from the ball 122 during solidification. Because it starts from the ball 122, the grains of the solder 104 are smaller compared to the structure without the ball 122. Other structures are the same as those described in the prior embodiment.

[0171] <Summary of Implementation Method 4>

[0172] The structure described in this embodiment achieves the same effects as the structure described in the prior embodiment. Specifically, spheres 122 are added to the solder 104. During solidification, the solder 104 undergoes grain growth starting from the spheres 122. The spheres 122 are the starting points for solidification. By providing the spheres 122, the grain size of the solder 104 is made smaller than that of the solders 103H and 103L, thereby improving EM lifetime.

[0173] Furthermore, the effect of ball 122 has been confirmed through trial production. It has been confirmed that by adding ball 122, the particle size of solder 104 becomes smaller. In addition, it has been confirmed that the disappearance of alloy layers 110 and 111 is slowed down, that is, the progress of EM is slowed down. At this time, Ni layers 801 and 811 are formed by electroless NiP plating. The composition of alloy layers 110 and 111 is (Ni-Cu)3Sn4.

[0174] <Variation Example>

[0175] Solder 104 can also be made into a multi-layered structure, so that the occupancy rate of spheres 122 per unit volume varies depending on the layer. Figure 17 In the example shown, solder 104 has a first layer 104a and a second layer 104b. The first layer 104a is the layer on the side of the joint portion 80, and the second layer 104b is the layer on the side of the joint portion 81. Figure 17 Corresponding to Figure 16 .exist Figure 17 For convenience, grain boundary 106 has been omitted.

[0176] exist Figure 17 In the example shown, the occupancy rate of spheres 122 in layer 104a is higher than that in layer 104b. Layer 104a contains more spheres 122 than layer 104b. This structure allows for a smaller particle size in layer 104a while simultaneously reducing the particle size in layer 104b. Therefore, in structures where EM (Effect Micrometer) readily advances through the output current, EM lifetime can be improved.

[0177] Alternatively, in the first layer 104a and the second layer 104b, the diameters of the balls 122 can be made different, so that the occupancy rate of the balls 122 in the first layer 104a is higher than that in the second layer 104b. The quantity and diameter of the balls can also be different.

[0178] It is also possible to make the occupancy rate of spheres 122 in the second layer 104b higher than that in the first layer 104a. If such a structure is made, it is possible to further reduce the particle size of the second layer 104b while reducing the particle size of the first layer 104a. As a result, in a structure where EM progresses easily through the return current, the EM lifetime can be improved.

[0179] The two-layer structure of solder 104 can be achieved, for example, by configuring two layers of solder foil with different ball content. Alternatively, three layers of ballless solder foil can be stacked, such that the amount and / or diameter of the balls 122 disposed between the solder foils are different. The number of layers of solder 104 is not limited to two layers. It can also be three or more layers.

[0180] This illustrates an example of arranging ball 122 in solder 104, but is not limited thereto. Ball 122 may be arranged in at least one of the plurality of solders 100 other than solders 103H and 103L.

[0181] (Other implementation methods)

[0182] The disclosure in this specification and accompanying drawings is not limited to the illustrated embodiments. The disclosure includes the illustrated embodiments and variations thereof as known to those skilled in the art. For example, the disclosure is not limited to the combination of parts and / or elements shown in the embodiments. The disclosure can be implemented in a wide variety of combinations. The disclosure may have additional portions that can be added to the embodiments. The disclosure includes forms in which parts and / or elements of an embodiment are omitted. The disclosure includes substitutions or combinations of parts and / or elements between one embodiment and other embodiments. The scope of the disclosure is not limited to the description of the embodiments. It should be understood that certain technical scopes of the disclosure are indicated by the description in the claims, and also include all modifications in the meaning and scope equivalent to the description in the claims.

[0183] The disclosures in the specification and drawings are not limited by the claims. The disclosures in the specification and drawings include the technical ideas described in the claims, but also encompass a wider range of technical ideas. Therefore, it is possible to extract a variety of technical ideas from the disclosures in the specification and drawings without being bound by the claims.

[0184] When referring to an element or layer as "above," "connected," "linked," or "combined," there are cases where it is directly above, connected to, linked to, or combined with other elements or layers, and cases where there are intermediate elements or layers. Conversely, when referring to an element as "directly above," "directly connected to," "directly linked to," or "directly combined" with other elements or layers, there are no intermediate elements or layers. Other terms used to describe relationships between elements should be interpreted in the same way (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.). As used in this specification, the term "and / or" includes any and all combinations relating to one or more of the associated listed items.

[0185] The spatially relative terms "inner," "outer," "back," "lower," "lower," "upper," and "higher," etc., are used here to facilitate the description of the relationship of one element or feature relative to other elements or features, as illustrated in the diagram. Spatially relative terms can imply different orientations of the device in use or operation, in addition to the orientation depicted in the diagram. For example, if the device in the diagram is inverted, the element described as "lower" or "directly lower" to other elements or features is oriented "upper" to other elements or features. Therefore, the term "lower" can encompass both upper and lower orientations. The device may also be oriented in other directions (90 degrees or rotated in other directions), and the spatially relative descriptors used in this specification are explained accordingly.

[0186] The vehicle's drive system 1 is not limited to the structure described above. For example, an example with one electric generator 3 is shown, but it is not limited to this. Multiple electric generators may also be included. An example with an inverter 6 as a power conversion unit is shown, but it is not limited to this. For example, it may be configured to have multiple inverters. It may also be configured to have at least one inverter and a converter. It may also only have a converter.

[0187] The switching element is not limited to IGBT11. For example, a MOSFET can also be used. MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. In the case of an n-channel MOSFET, the source electrode is equivalent to the upper electrode, and the drain electrode is equivalent to the lower electrode. In the case of a MOSFET, the diode used for return current can be either a parasitic diode (body diode) or an external diode.

[0188] This illustrates an example where the semiconductor device 20 has only one semiconductor element 40 constituting each arm, but it is not limited to this. The semiconductor device 20 may also have multiple semiconductor elements 40 constituting each arm. That is, multiple semiconductor elements 40H may be connected in parallel to form an arm 9H, and multiple semiconductor elements 40L may be connected in parallel to form an arm 9L.

[0189] This illustration shows an example where the back surfaces 50b and 60b of heat sinks 50 and 60 are exposed from the encapsulating solid 30, but it is not limited to this. It is also possible to have a structure where at least one of the back surfaces 50b and 60b is covered by the encapsulating solid 30. It is also possible to have a structure where at least one of the back surfaces 50b and 60b is covered by an insulating component (not shown) different from the encapsulating solid 30. It is also possible to have a structure where the semiconductor device 20 does not have the encapsulating solid 30.

[0190] This illustrates an example of a semiconductor device 20 having a sealing solid 30, but it is not limited to this. It is also possible to make a structure in which the sealing solid 30 is excluded.

[0191] (The disclosure of technological ideas)

[0192] This specification discloses several technical ideas described in the following list of items. Several items are described by selectively referencing an antecedent in a subsequent item in a multiple dependent form. Furthermore, several items are described by referring to another multiple dependent form of an item in a multiple dependent form. Several technical ideas are defined by these items described in multiple dependent forms.

[0193] <Technical Idea 1>

[0194] A semiconductor device includes: a plurality of semiconductor elements (40), each having signal pads and an upper electrode serving as a main electrode on its upper surface, and a lower electrode serving as a main electrode on its lower surface, opposite to the upper surface in the thickness direction, having an area significantly larger than that of the upper electrode when viewed in planar view in the thickness direction; and a plurality of conductors (50, 60, 70, 80, 81, 82, 92) electrically connected to the main electrode via solder; the plurality of semiconductor elements includes a first semiconductor element (40H) and a second semiconductor element (40L), the first semiconductor element constituting the upper arm (9H) of an upper and lower arm circuit (9), and the second semiconductor element constituting the lower arm (9L) of the upper and lower arm circuit; the first semiconductor element and the second semiconductor element are arranged in a direction orthogonal to the thickness direction such that their upper surfaces are on the same side in the thickness direction; the plurality of conductors includes a first upper conductor (50H, 70H), a first lower conductor (60H), and a second upper conductor (40L). The first upper conductor (50L, 70L), the second lower conductor (60L), and the connector conductors (80, 81) are connected to the upper electrode of the first semiconductor device via a first upper solder (101H, 102H). The first lower conductor is connected to the lower electrode of the first semiconductor device via a first lower solder (103H). The second upper conductor is connected to the upper electrode of the second semiconductor device via a second upper solder (101L, 102L). The lower conductor is connected to the lower electrode of the second semiconductor element via the second lower solder (103L), and the connector conductor connects the first upper conductor and the second lower conductor via the relay solder (104); each solder contains Cu and Sn; the connection objects of each solder have Ni layers (801, 811); the particle size of at least one of the first upper solder, the second upper solder, and the relay solder is smaller than the particle size of the first lower solder and the second lower solder.

[0195] <Technological Ideas 2>

[0196] The semiconductor device as described in Technical Concept 1 includes a first upper conductor having a first main body portion (50H) and a first spacer portion (70H) between the upper electrode of the first semiconductor element and the first main body portion; a second upper conductor having a second main body portion (50L) and a second spacer portion (70L) between the upper electrode of the second semiconductor element and the second main body portion; a first upper solder being located between the upper electrode of the first semiconductor element and the first spacer portion, and between the first spacer portion and the first main body portion; and a second upper solder being located between the upper electrode of the second semiconductor element and the second spacer portion, and between the second spacer portion and the second main body portion.

[0197] <Technological Idea 3>

[0198] In the semiconductor device described in technical concept 1 or technical concept 2, the connector conductor is a first connector conductor that connects the first upper conductor and the second lower conductor via a first relay solder, which is the relay solder; the plurality of conductors include a main terminal (92) and a second connector conductor (82) that connects the second upper conductor and the main terminal via a second relay solder (105); the particle size of the second relay solder is smaller than that of the first lower solder and the second lower solder.

[0199] <Technological Ideas 4>

[0200] The semiconductor device according to any one of technical ideas 1 to 3 has a starting point for solidification to reduce the particle size inside the small solder particles, which are solder particles with a smaller particle size than the first lower solder and the second lower solder, or on the surface of the solder particles to be joined.

[0201] <Technological Idea 5>

[0202] In the semiconductor device described in Technical Concept 4, the starting point is a plurality of wire strips (120) disposed within the small solder particles and fixed to the surface of the object to be joined by the small solder particles.

[0203] <Technological Ideas 6>

[0204] As described in technical concept 4, the semiconductor device, which is the connection target of the aforementioned small solder particles, has a Ni-based, continuously uneven oxide film (803) on the Ni layer; the starting point is a pore (121) covering the aforementioned uneven oxide film.

[0205] <Technological Ideas 7>

[0206] The semiconductor device described in technical concept 4 has a groove (83) for receiving overflowed solder as the conductor to which the small solder particles are connected; the inner peripheral end of the groove is continuously concave and convex; the starting point is the concave part and / or convex part of the inner peripheral end of the groove.

[0207] <Technological Ideas 8>

[0208] The semiconductor device described in technical concept 4 includes a conductive ball (122) added to the aforementioned small-particle solder; the aforementioned starting point is the aforementioned ball.

[0209] <Technological Ideas 9>

[0210] In the semiconductor device described in Technical Concept 8, the aforementioned sphere contains Ni or Cu.< / em>

Claims

1. A semiconductor device, characterized in that: have: A plurality of semiconductor elements (40) having a signal pad and an upper electrode as a main electrode on the upper surface, and having a lower electrode as a main electrode having a larger area than the upper electrode when viewed in a planar manner from the plate thickness direction, on the lower surface opposite to the upper surface in the plate thickness direction; as well as A plurality of conductors (50, 60, 70, 80, 81, 82, 92) electrically connected to the main electrode via solder; The plurality of semiconductor elements include a first semiconductor element (40H) and a second semiconductor element (40L), the first semiconductor element constituting an upper arm (9H) of an upper and lower arm circuit (9), the second semiconductor element constituting a lower arm (9L) of the upper and lower arm circuit, the first semiconductor element and the second semiconductor element being arranged in a direction orthogonal to the plate thickness direction in such a manner that the upper surfaces are on the same side in the plate thickness direction; The plurality of conductors include a first upper conductor (50H, 70H), a first lower conductor (60H), a second upper conductor (50L, 70L), a second lower conductor (60L), and a connector conductor (80, 81), wherein the first upper conductor is connected to the upper electrode of the first semiconductor element via a first upper solder (101H, 102H), the first lower conductor is connected to the lower electrode of the first semiconductor element via a first lower solder (103H), the second upper conductor is connected to the upper electrode of the second semiconductor element via a second upper solder (101L, 102L), the second lower conductor is connected to the lower electrode of the second semiconductor element via a second lower solder (103L), and the connector conductor connects the first upper conductor and the second lower conductor via a relay solder (104); Each solder contains Cu and Sn; The connection objects of each solder respectively have Ni layers (801, 811); A particle size of at least one of the first upper solder, the second upper solder, and the relay solder is smaller than a particle size of the first lower solder and the second lower solder.

2. The semiconductor device according to claim 1, wherein The first upper conductor has a first main body portion (50H) and a first spacer portion (70H) interposed between the upper electrode of the first semiconductor element and the first main body portion; The second upper conductor has a second main body (50L) and a second spacer (70L) interposed between the upper electrode of the second semiconductor element and the second main body. The first upper solder is interposed between the upper electrode of the first semiconductor element and the first spacer portion, and between the first spacer portion and the first main body portion; The second upper solder is interposed between the upper electrode of the second semiconductor element and the second spacer portion, and between the second spacer portion and the second main body portion.

3. The semiconductor device according to claim 1, wherein: The joint conductor is a first joint conductor that connects the first upper conductor and the second lower conductor via a first relay solder serving as the relay solder. The plurality of conductors include a main terminal (92), and a second joint conductor (82) connecting the second upper conductor and the main terminal via a second relay solder (105); The particle diameter of the second relay solder is smaller than the particle diameters of the first lower solder and the second lower solder.

4. The semiconductor device according to any one of claims 1 to 3, wherein A solidification starting point for reducing the particle size is provided inside the small-particle solder, which is solder having a smaller particle size than the first lower solder and the second lower solder, or on a surface of a connection target of the small-particle solder.

5. The semiconductor device according to claim 4, wherein: The starting point is a plurality of wire pieces (120) which are arranged in the small solder particles and fixed to the surface of the connection object of the small solder particles.

6. The semiconductor device according to claim 4, wherein: The conductor as the connection object of the small solder particles has a concavoconvex oxide film (803) with Ni as the main component and a continuously concavoconvex surface on the Ni layer; The starting point is a hole (121) covered by the uneven oxide film.

7. The semiconductor device according to claim 4, wherein: The conductor as a connection target of the small solder particles has a groove (83) for accommodating overflowing solder; The inner peripheral end of the groove is in a continuous concave-convex shape; The starting point is a concave portion and / or a convex portion at the inner peripheral end of the groove.

8. The semiconductor device according to claim 4, wherein: Adding conductive balls (122) to the above-mentioned small solder particles; The starting point is the ball.

9. The semiconductor device according to claim 8, wherein: The above-mentioned balls contain Ni or Cu.

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