A small and thin IGBT module packaging structure, an assembling method and a functional circuit

Abstract

The application discloses a small and thin IGBT module packaging structure and an assembling method thereof. The structure comprises a substrate for functional circuit layout, insulation and heat dissipation of IGBT; and an outer frame assembled with the substrate for mounting, fixing, mechanical support and isolation protection, an embedded electrode pin, two ends of the electrode pin respectively extending out of the outer frame, one end serving as an external connection end for connection with an external circuit, and the other end serving as an internal connection end for electrical connection with the functional circuit; the electrode pin is electrically connected with the functional circuit through a bonding wire, and the bonding wire is directly connected with the electrode pin. The bonding mode of the bonding wire and the electrode pin of the packaging structure adopts direct bonding on the upper surface of the pin, realizes electric and thermal shunting of the pin, reduces the area of the metal layer, reduces the solder layer resistance heating link, and avoids the overall failure of the module caused by the solder layer stress failure.

Description

Technical Field

[0001] This invention belongs to the field of power semiconductor device packaging, and in particular relates to a small ultra-thin IGBT module packaging structure, assembly method and functional circuit. Background Technology

[0002] IGBTs (Insulated Gate Bipolar Transistors) are core devices for power conversion and control, widely used in consumer electronics, industrial control, new energy power generation, smart grids, locomotive traction, and electric vehicle transportation. Their applications range from tens of watts to tens of megawatts in power electronics and continue to expand with technological advancements, placing higher demands on device performance, reliability, miniaturization, high integration, flexibility, and low cost. In practical applications, several IGBT chips and supporting auxiliary components need to be integrated and packaged together according to typical power electronic circuit topologies to form various power modules to meet different application requirements. The packaging of power modules is crucial, playing roles in mechanical support and protection, electrical connection, thermal coupling and power distribution, insulation, and heat dissipation. Related data shows that packaging costs account for approximately 40% of the cost structure of power modules, while at least 25% of device failures are caused by packaging.

[0003] Currently, IGBT packages include: 1. Typical IGBT module packaging structure containing a copper substrate, such as... Figure 1 As shown, it includes a metal substrate 12, a ceramic backing plate 13, a side frame 14, a busbar electrode 15, and a tube cover 16, etc. Components 17 are distributed on the ceramic backing plate 13; its heat dissipation structure and thermal resistance network are as follows: Figure 2 As shown. Combined with Figure 1 , 2 As shown, this packaging structure suffers from problems such as complex side frame mounting process, large size, high thermal resistance, high cost, and complicated installation and use.

[0004] 2. Substrate-less small IGBT modules use grid-distributed pins connected to the PCB by soldering or pressing, which reduces the size to some extent (its height can be as low as 12mm). However, it has problems such as high process requirements, many production steps, weak mechanical strength, high stress on the DBC substrate, reduced reliability, and still relatively high cost.

[0005] In summary, current typical IGBT modules with copper substrates have good mechanical strength but high thermal resistance. Existing small substrate-free IGBT modules have low thermal resistance, but the stress on the pins is entirely borne by the DBC substrate, resulting in weak mechanical strength and insufficient reliability. They are also large in size, with typical IGBT modules measuring approximately 152x62x21mm and small substrate-free IGBT modules measuring approximately 62x35x12mm. Existing technologies have complex structures, high process requirements, and many production steps, resulting in high costs. Summary of the Invention

[0006] To address the technical problems existing in the prior art, the present invention aims to provide a small, ultra-thin IGBT module packaging structure with good mechanical strength and high reliability.

[0007] To achieve the objectives of this invention, the small, ultra-thin IGBT module packaging structure provided by this invention includes: Substrate, used for functional circuit layout, insulation, and heat dissipation of IGBTs; and The outer frame is assembled with the substrate for mounting, mechanical support, and isolation protection. It has embedded electrode pins, with each end of the electrode pin extending out of the outer frame. One end serves as an external connection terminal for connecting to an external circuit, and the other end serves as an internal connection terminal for electrically connecting to the functional circuit. The electrode pins are electrically connected to the functional circuit via bonding wires, and the bonding wires are directly connected to the electrode pins.

[0008] In some embodiments, the encapsulation structure provided by the present invention further includes a cover plate that serves a protective function. The cavity formed by the substrate and the outer frame is filled with a flexible encapsulating adhesive for insulation and isolation of moisture and dust. The cover plate is directly bonded to the filled flexible encapsulating adhesive, and a gap is left between the cover plate and the outer frame so that the cover plate can move with the expansion and contraction of the flexible encapsulating adhesive.

[0009] In some embodiments, the substrate includes a first metal layer, a second metal layer, and an insulating layer mounted between the first metal layer and the second metal layer. The first metal layer is etched with a circuit layout to provide independent soldering areas for each component constituting the functional circuit and the electrode pins, so that all soldering can be completed at once.

[0010] In some embodiments, a solder layer for electrical connection and heat conduction is provided on the substrate for soldering the electrode pins and components constituting the functional circuit. Heat from the electrode pins is conducted to the substrate through the solder layer. Existing typical substrate-based IGBT modules have pins isolated from both the substrate and the substrate, resulting in ineffective heat dissipation. Figure 1 , 2 As shown.

[0011] In some implementations, the components constituting the functional circuit are connected by bonding wires.

[0012] In some embodiments, the outer frame is provided with integrally formed resilient mounting holes for providing screw mounting positions with external heat sinks and applying preset pressure, enabling quick, reliable, and low-cost installation with screws.

[0013] The second objective of this invention is to provide an IGBT functional circuit, which includes IGBT transistors Q1, Q2, Q3, Q4, Q5, and Q6, a sampling resistor R Shunt, and a thermistor RTH for temperature detection. The IGBT transistors Q1 to Q6 constitute a three-phase full-bridge voltage source inverter circuit. After a DC voltage is input, the switching states of the IGBT transistors Q1 to Q6 are controlled to convert them into three-phase AC voltages with variable frequency and amplitude, which are output from output terminals U, V, and W, respectively. A sampling resistor R Shunt is connected in series with each output to detect the output current.

[0014] In some embodiments, a freewheeling diode FRD is connected between the collector and emitter of each of the IGBT transistors Q1 to Q6. The freewheeling diode FRD is connected in anti-parallel with the IGBT transistor to provide a freewheeling circuit for the inductive load after the IGBT transistor is turned off.

[0015] A third objective of this invention is to provide an assembly method for the small, ultra-thin IGBT module packaging structure provided by this invention, the method comprising: Step 1: Etch the substrate to form a circuit layout, providing independent soldering areas for each component and electrode pin that constitute the functional circuit; Step 2: Embed the electrode pins into the outer frame, and extend both ends of the electrode pins out of the outer frame. One end serves as an external connection terminal for connection with external circuits, and the other end serves as an internal connection terminal for electrical connection with the functional circuit. Step 3: Assemble the outer frame with the substrate, so that the electrode pins are located in the corresponding soldering areas on the substrate, and then place each component constituting the functional circuit in the corresponding soldering areas on the substrate and solder it. Step 4: Use bonding wires to bond the components and electrode pins according to the circuit topology. The bonding method between the bonding wires and the electrode pins is that the bonding wires are directly bonded to the upper surface of the electrode pins. Step 5: Fill with flexible encapsulating adhesive; Step 6: Assemble the cover plate and cure the flexible sealing adhesive.

[0016] In some embodiments, before assembling the cover plate, a flexible encapsulating adhesive is first poured in to form an isolation layer, and then the cover plate is directly bonded to the flexible encapsulating adhesive with a gap between the cover plate and the outer frame so that the cover plate can move as the flexible encapsulating adhesive expands and contracts.

[0017] The technical effects achieved by adopting the technical solution of this invention include at least the following: 1) The bonding method of the packaging structure provided by the present invention is to directly bond the bonding wire to the electrode pin on the upper surface of the pin. Compared with the existing small substrate-free IGBT module, which uses the bonding wire to bond to the metal layer soldered to the electrode pin, the current is shunted for the heat of the pin and the area of ​​the metal layer is reduced. The current passes directly through the electrode pin and the bonding wire without flowing through the solder layer or the metal layer, which reduces the heat generation of the solder layer resistance and avoids the failure of the whole module due to the stress failure of the solder layer.

[0018] 2) The packaging structure provided by this invention embeds the electrode pins into the outer frame, ensuring the shape stability of the pins. The outer frame bears the main mechanical stress, reducing the stress on the substrate, improving the reliability of the module and extending its lifespan.

[0019] 3) The encapsulation structure of this invention is filled with flexible encapsulating adhesive (which may be silicone gel) and covered with a cover plate to achieve electrical insulation and isolate moisture and dust. The cover plate and the outer frame are directly bonded to the flexible encapsulating adhesive without a snap-fit ​​structure, which can effectively reduce the volume. Because there is a suitable gap between the cover plate and the outer frame, the cover plate can expand and contract with the flexible encapsulating adhesive without the need for reserved space, which greatly reduces the contact area between the encapsulating adhesive and the air. In the prior art, the cover plate and the outer frame are snap-fit ​​or fixed assembly, and there is a shrinkage space between the cover plate and the encapsulating adhesive. During use, the encapsulating adhesive expands and contracts with temperature changes, which produces a breathing effect and increases the probability of contact with moisture and dust.

[0020] 4) All welding connections can be completed in one go. Compared with the existing technology that requires more than two welding processes, this reduces the number of processes, lowers the process requirements, and effectively reduces costs. In particular, the existing small substrate-free IGBT module mesh pin arrangement is difficult to weld and has high process requirements. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings: Figures 1-2 This is a schematic diagram of a typical IGBT module packaging structure, heat dissipation structure, and thermal resistance network described in this invention. Figure 3This is a schematic diagram of the packaging structure of the small ultra-thin IGBT module provided by the present invention; Figure 4 This is a schematic diagram of the pin bonding connection method in the small ultra-thin IGBT module packaging structure provided by the present invention; Figure 5 The circuit diagram of the IGBT functional circuit provided by the present invention. Detailed Implementation

[0022] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make the invention more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art.

[0023] Please refer to Figure 3 As shown, the small, ultra-thin IGBT module packaging structure provided by the present invention includes: The substrate, used for the functional circuit layout including IGBTs, includes a first metal layer 5, a second metal layer 6, and an insulating layer 4 assembled between the first metal layer 5 and the second metal layer 6. The first metal layer 5 is etched with a circuit layout to provide independent soldering areas for each component and electrode pin constituting the functional circuit. Each component and electrode pin constituting the function is placed in the corresponding soldering area, and all soldering can be completed in one step with solder, without the need for more than two soldering processes; or the substrate can be directly made of DBC ceramic copper-clad laminate. The outer frame 2 is assembled with the substrate and has embedded electrode pins 3. The two ends of the electrode pins 3 extend out of the outer frame 2. One end serves as an external connection terminal for connecting to external circuits. The electrode pins can be soldered to the PCB to complete the circuit construction. The other end serves as an internal connection terminal for electrical connection to functional circuits to realize functional lead-out. Cover plate 1 is used to assemble with the substrate to form an encapsulation structure.

[0024] like Figure 4 As shown, electrode pin 3 is electrically connected to the functional circuit via bonding wire 9. The bonding wire 9 is directly soldered to the upper surface of electrode pin 3, realizing direct connection between the electrode pin 3 and the bonding wire 9.

[0025] The cover plate 1 and the outer frame 2 are connected by a snap-fit ​​connection, creating a space between the cover plate 1 and the outer frame 2 for the injection of flexible encapsulant 10. The flexible encapsulant 10 forms an isolation layer, achieving electrical insulation and isolating moisture and dust. This structure can also achieve the purpose of this solution, but it results in a relatively large encapsulation structure volume. To reduce the volume of the encapsulation structure, another structure of this solution is to inject flexible encapsulant 10 (which can be silicone gel) between the cover plate 1 and the substrate. The cover plate 1 is directly bonded to the flexible encapsulant, and a gap is reserved between the cover plate 1 and the outer frame 2. Because there is a gap between the cover plate 1 and the outer frame 2, the cover plate 1 can expand and contract with the flexible encapsulant 10 without the need for reserved space, greatly reducing the contact area between the encapsulant and the air, and effectively reducing the volume of the encapsulation structure.

[0026] To facilitate assembly, the outer frame 2 of this disclosure is provided with an integrally formed (low cost) elastic mounting hole, which can be installed quickly, reliably and at low cost by screws; and the elastic mounting hole applies a preset pressure between the substrate and the external heat sink to reduce thermal resistance (a thermal interface material needs to be coated between the substrate and the external heat sink).

[0027] The functional circuit described in this disclosure can be any circuit composed of IGBT chips 7, such as a switching circuit, a bridge drive circuit, an amplifier circuit, etc. More specifically, the functional circuit described in this disclosure includes at least a number of IGBT chips 7 and a freewheeling diode FRD8 matching the number of IGBT chips 7; or the functional circuit described in this disclosure includes at least a number of IGBT chips 7, a freewheeling diode FRD matching the number of IGBT chips 7, a thermistor, and a sampling resistor. For example... Figure 5 The diagram shows a topology circuit diagram of a three-phase full-bridge voltage source inverter. It can convert the DC voltage at the input terminals (HV+ and HV-) into a three-phase AC voltage at the output terminals (U, V, and W) with variable frequency and amplitude by controlling the switching state of the IGBT. The thermistor RTH in the diagram is used to detect the module temperature, the sampling resistor RShunt is used to detect the output current, and the freewheeling diode FRD is connected in anti-parallel with the IGBT chip to provide a freewheeling circuit for the inductive load after the IGBT is turned off.

[0028] The packaging structure disclosed herein is assembled using the following method: Step 1: Etch the substrate to form a circuit layout to provide independent soldering areas for each component and electrode pin 3 that constitute the functional circuit, for soldering the electrode pin 3 and each component that constitutes the functional circuit. Step 2: Embed the electrode pin 3 into the outer frame 2, and make both ends of the electrode pin 3 extend out of the outer frame 2 respectively; Step 3: Assemble the outer frame 2 with the substrate, so that the electrode pins 3 are located in the corresponding soldering area on the substrate, and solder each component constituting the functional circuit to the corresponding soldering area on the substrate according to the circuit topology. Solder layers 11 are formed between the components and the substrate and between the electrode pins 3 and the substrate, respectively. The heat of the components and electrode pins 3 is transferred to the substrate through the solder layers 11. Step 4: Using bonding wire 9, bond each component and electrode pin 3 according to the circuit topology. The bonding method between bonding wire 9 and electrode pin 3 is as follows: Figure 4 As shown, it is directly bonded to the upper surface of electrode pin 3; Step 5: Fill with flexible encapsulating adhesive; Step 6: Assemble cover plate 1 and cure the flexible sealing adhesive.

[0029] Before assembling the cover plate 1, the flexible encapsulating adhesive 10 is first poured in to form an isolation layer. Then, the cover plate 1 is directly bonded to the flexible encapsulating adhesive 10, and a gap is left between the cover plate 1 and the outer frame 2 so that the cover plate can move with the expansion and contraction of the flexible encapsulating adhesive 10.

[0030] In this scheme, the bonding wire 9 and the electrode pin 3 are bonded by direct bonding, which realizes the electrothermal current shunting of the pin and reduces the area of ​​the metal layer. The current passes directly through the electrode pin 3 and the bonding wire 9 without flowing through the solder layer 11, reducing the solder layer resistance heating link and avoiding the overall failure of the module due to the stress failure of the solder layer. The heat of the electrode pin is conducted to the substrate through the solder layer.

[0031] In this design, the electrical pathways between the components constituting the functional circuit, and between the components and the electrode pins, are formed by the first metal layer of the substrate, the solder layer, and the bonding wires. The bonding wires complete the connection between the upper surfaces of the components and the pins. When the electrode pins are embedded in the outer frame, they can also be directly placed in the outer frame molding mold and molded together with the outer frame during the outer frame molding process. This simplifies the assembly method and makes the connection between the outer frame and the electrode pins more robust.

[0032] The packaging structure provided by this invention is small in size (the volume can be reduced to 50x30x8mm), ultra-thin, substrate-free, with pins embedded in the outer frame and directly bonded to the bonding wires. It has low thermal resistance, mechanical stability, good heat dissipation, and good mechanical strength. The cover plate and the outer frame are fitted with a gap, and the cover plate is tightly bonded to the flexible encapsulating adhesive for better isolation performance. The overall structure is simple, with fewer processes, low cost, and high reliability.

[0033] This disclosure has been described with reference to the foregoing embodiments; however, these embodiments are merely examples for implementing this disclosure. It must be noted that the disclosed embodiments do not limit the scope of this disclosure. On the contrary, any changes and modifications made without departing from the spirit and scope of this disclosure are within the scope of patent protection of this disclosure.

Claims

1. A small, ultra-thin IGBT module packaging structure, characterized in that, The structure includes: Substrate, used for functional circuit layout, insulation, and heat dissipation of IGBTs; and The outer frame is assembled with the substrate for mounting, mechanical support, and isolation protection. It has embedded electrode pins, with each end of the electrode pin extending out of the outer frame. One end serves as an external connection terminal for connecting to an external circuit, and the other end serves as an internal connection terminal for electrically connecting to the functional circuit. The electrode pins are electrically connected to the functional circuit via bonding wires, and the bonding wires are directly connected to the electrode pins. The functional circuit includes IGBTs Q1, Q2, Q3, Q4, Q5, and Q6, a sampling resistor R Shunt, and a thermistor RTH for temperature detection. IGBTs Q1 to Q6 form a three-phase full-bridge voltage source inverter circuit. After a DC voltage is input, the switching states of IGBTs Q1 to Q6 are controlled to convert them into three-phase AC voltages with variable frequency and amplitude, which are output from output terminals U, V, and W, respectively. A sampling resistor R Shunt is connected in series with each output to detect the output current.

2. The small, ultra-thin IGBT module packaging structure according to claim 1, characterized in that, The structure also includes a protective cover plate. The cavity formed by the substrate and the outer frame is filled with a flexible encapsulating adhesive for insulation and isolation of moisture and dust. The cover plate is directly bonded to the filled flexible encapsulating adhesive, and a gap is left between the cover plate and the outer frame so that the cover plate can move as the flexible encapsulating adhesive expands and contracts.

3. The small, ultra-thin IGBT module packaging structure according to claim 1, characterized in that, The substrate includes a first metal layer, a second metal layer, and an insulating layer assembled between the first metal layer and the second metal layer. The first metal layer is etched with a circuit layout to provide independent soldering areas for each component constituting the functional circuit and the electrode pins, so that all soldering can be completed at once.

4. The small, ultra-thin IGBT module packaging structure according to claim 1, characterized in that, The substrate is provided with a solder layer for electrical connection and heat conduction, which is used for soldering the electrode pins and components constituting the functional circuit.

5. The small, ultra-thin IGBT module packaging structure according to claim 1, characterized in that, The components constituting the functional circuit are connected by bonding wires.

6. The small, ultra-thin IGBT module packaging structure according to claim 1, characterized in that, The outer frame is provided with an integrally formed elastic mounting hole for providing a screw mounting position with an external heat sink and applying a preset pressure.

7. The small, ultra-thin IGBT module packaging structure according to claim 1, characterized in that, A freewheeling diode FRD is connected between the collector and emitter of each of the IGBT transistors Q1 to Q6. The freewheeling diode FRD is connected in anti-parallel with the IGBT transistor to provide a freewheeling circuit for the inductive load after the IGBT transistor is turned off.

8. The assembly method of the small ultra-thin IGBT module packaging structure according to any one of claims 1-7, characterized in that, The method includes: Step 1: Etch the substrate to form a circuit layout that provides independent soldering areas for each component and electrode pin that constitute the functional circuit. Step 2: Embed the electrode pins into the outer frame, and extend both ends of the electrode pins out of the outer frame. One end serves as an external connection terminal for connection with external circuits, and the other end serves as an internal connection terminal for electrical connection with the functional circuit. Step 3: Assemble the outer frame with the substrate, so that the electrode pins are located in the corresponding soldering areas on the substrate, and then place each component constituting the functional circuit in the corresponding soldering areas on the substrate and solder it. Step 4: Use bonding wires to bond the components and electrode pins according to the circuit topology. The bonding method between the bonding wires and the electrode pins is that the bonding wires are directly bonded to the upper surface of the electrode pins. Step 5: Fill with flexible encapsulating adhesive; Step 6: Assemble the cover plate and cure the flexible sealing adhesive.

9. The assembly method according to claim 8, characterized in that, Before assembling the cover plate, a flexible encapsulating adhesive is first poured in to form an isolation layer. Then, the cover plate is directly bonded to the flexible encapsulating adhesive, with a gap left between the cover plate and the outer frame so that the cover plate can move as the flexible encapsulating adhesive expands and contracts.

10. An IGBT functional circuit for the small, ultra-thin IGBT module packaging structure according to any one of claims 1-7, characterized in that, The circuit includes IGBTs Q1, Q2, Q3, Q4, Q5, and Q6, a sampling resistor R Shunt, and a thermistor RTH for temperature detection. IGBTs Q1 to Q6 form a three-phase full-bridge voltage source inverter circuit. After a DC voltage is input, the switching states of IGBTs Q1 to Q6 are controlled to convert them into three-phase AC voltages with variable frequency and amplitude, which are output from output terminals U, V, and W, respectively. A sampling resistor R Shunt is connected in series with each output to detect the output current.

11. The functional circuit of the IGBT according to claim 10, characterized in that, A freewheeling diode FRD is connected between the collector and emitter of each of the IGBT transistors Q1 to Q6. The freewheeling diode FRD is connected in anti-parallel with the IGBT transistor to provide a freewheeling circuit for the inductive load after the IGBT transistor is turned off.

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