Double-sided heat dissipation elastic crimping packaging structure of SIC MOSFET based on low-melting-point metal and foamed silver

Abstract

The invention relates to the technical field of power semiconductor packaging, in particular to an SIC MOSFET double-face heat dissipation elastic crimping packaging structure based on low-melting-point metal and foamed silver, which comprises a drain copper electrode and a source copper electrode which are oppositely arranged in the forward direction, a SiC MOSFET chip and a grid DBC substrate are arranged on the drain copper electrode, and a source of the SiC MOSFET chip is connected with the source copper electrode through a silver column; the grid electrode DBC substrate is provided with a grid electrode terminal, the grid electrode of the SiC MOSFET chip is connected with the grid electrode terminal through an aluminum bonding wire, the top of the grid electrode terminal is connected with the source electrode copper electrode, and the grid electrode terminal extends out of the module for external connection; liquid cooling radiators are respectively arranged on the back surfaces of the drain copper electrode and the source copper electrode; the drain electrode of the SiC MOSFET chip is connected with the drain electrode copper electrode through low-melting-point metal and foam silver. Elastic connection is achieved by adopting the foam silver and the low-melting-point metal, and meanwhile the advantages of thermal shock protection, physical shock resistance, chip thermal stress decoupling and the like are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of power semiconductor packaging, in particular to a double-sided heat dissipation elastic pressing packaging structure of a SIC MOSFET based on low-melting-point metal and foamed silver. Background Art

[0002] Silicon-based chips have a nearly 70-year history. Their mature, traditional wire-bonded packaging structure has been widely used in most silicon-based power devices on the market, and continues to be so today. Devices using traditional packaging have also demonstrated superior performance. However, the 21st century has seen the rapid development of third-generation semiconductor devices. Silicon carbide MOSFETs, a representative example, offer advantages over traditional silicon chips, including high-voltage and high-temperature resistance, high switching frequencies, and compact size.

[0003] The emergence of SiC MOSFETs has brought with it new requirements and standards for packaging structures. In traditional bonded packaging structures, the parasitic inductance introduced by the bonding wires has a significant impact on the high-frequency and high-voltage operating conditions of SiC devices. The single-sided heat dissipation of the DBC substrate structure cannot meet the high power density of SiC MOSFETs. The chip press-fit packaging structure, on the other hand, modularly connects the chip to the upper and lower electrodes by applying external mechanical pressure, replacing the traditional bonding wire connection method. This achieves high current carrying capacity, low thermal resistance, double-sided heat dissipation, and failure short-circuit characteristics, resulting in excellent electrothermal and mechanical performance and high reliability. Typical press-fit structures are broadly categorized as rigid and flexible. In rigid IGBT press-fit devices, the chip is press-fitted to the collector and emitter using rigid molybdenum sheets (Mo), silver washers, and copper plates, respectively. The gate is connected to the gate PCB via ejector pins. The overall package, including components such as the bracket and housing, requires constant pressure applied by an external fixture to ensure good contact between layers. Flexible press-fit devices, on the other hand, incorporate disc springs into the rigid structure. These disc springs, combined with emitter washers, silver / aluminum washers, and molybdenum sheets, compensate for thermal expansion during press-fitting, reducing process precision requirements and ensuring uniform pressure across the chip surface. The advantages of press-fit structures align with the high-voltage, low-loop impedance, low parasitic parameters, and high-temperature resistance requirements of SiC MOSFET packages, making them a promising approach for improving traditional packaging structures.

[0004] For example, CN111477683A discloses a packaging structure for a power MOSFET chip, comprising a MOSFET chip having a gate and source on its front side and a drain on its back side; a first conductor electrically connected to the drain on the back side of the MOSFET chip; a second conductor electrically connected to the source on the front side of the MOSFET chip via a press-fit package; a stress buffer zone is provided within the region occupied by the source on the front side of the MOSFET chip, and the edge of the second conductor in contact with the source is located within the region occupied by the stress buffer zone on the front side of the MOSFET chip; and the portion of the MOSFET chip corresponding to the stress buffer zone does not contain a cellular structure. By providing a stress buffer zone within the source region on the front side of the MOSFET chip and using a metal molybdenum conductor, the problem of chip stress non-uniformity in press-fit packaging is resolved, the chip's pressure resistance and reliability are improved, and the double-sided heat dissipation capability is retained.

[0005] Due to the characteristics and requirements of SiC MOSFET chips, the application of press-fit structures in SiC MOSFET chip packaging faces new challenges. SiC material is inherently hard but brittle, unable to withstand excessive mechanical stress. Using a rigid press-fit structure on SiC MOSFET chips can easily cause the chips to crack or even break. However, typical elastic press-fit structures use disc springs for connection, which only supports single-sided heat dissipation, limiting the performance of the SiC MOSFET chip and making it a suboptimal packaging solution. Summary of the Invention

[0006] In response to the problems in the prior art of limited chip performance and reduced packaging reliability due to the characteristics of SiC MOSFET, the present invention provides a double-sided heat dissipation elastic press-fit packaging structure of SIC MOSFET based on low-melting-point metal and foamed silver.

[0007] The present invention is achieved through the following technical solutions: A double-sided heat dissipation elastic press-fit packaging structure for a SIC MOSFET based on a low-melting-point metal and silver foam, comprising a drain copper electrode and a source copper electrode arranged in a forward-facing manner. A SiC MOSFET chip and a gate DBC substrate are provided on the drain copper electrode, and the source electrode of the SiC MOSFET chip is connected to the source copper electrode via a silver pillar. A gate terminal is provided on the gate DBC substrate, and the gate of the SiC MOSFET chip and the gate terminal are connected via an aluminum bonding wire. The top of the gate terminal is connected to the source copper electrode, and the gate terminal extends outside the module for external connection. Liquid-cooled radiators are respectively provided on the backs of the drain copper electrode and the source copper electrode. The drain electrode of the SiC MOSFET chip and the drain copper electrode are connected via the low-melting-point metal and the silver foam.

[0008] Preferably, part of the low melting point metal is embedded in the drain copper electrode, another part is embedded in the inner groove of the foamed silver, and the outer side of the foamed silver is embedded in the drain copper electrode.

[0009] Preferably, a first groove is formed on the drain copper electrode, and the low melting point metal is located in the first groove.

[0010] Preferably, a second groove is formed on the drain copper electrode, and the foamed silver is located in the second groove.

[0011] Preferably, the first groove and the second groove are concentrically arranged.

[0012] Preferably, the low melting point metal and the silver foam are concentrically arranged.

[0013] Preferably, the upper surfaces of the silver foam and the low-melting-point metal are flush.

[0014] Preferably, the low melting point metal is solid at room temperature and liquid when the SiC MOSFET chip is in operation.

[0015] Preferably, the foamed silver is porous elemental silver.

[0016] Preferably, the source electrode, the source copper electrode and the silver pillar of the SiC MOSFET chip are all connected by welding; the drain copper electrode, the gate terminal and the gate DBC substrate are all connected by welding.

[0017] An electronic device comprising the double-sided heat dissipation elastic press-fit packaging structure of the SIC MOSFET based on low-melting-point metal and foamed silver.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention presents a double-sided heat-dissipating elastic press-fit packaging structure for SiC MOSFETs based on a low-melting-point metal and silver foam. The silver foam provides elastic support, while the low-melting-point metal provides stress decoupling and a low-thermal-resistance heat dissipation path. The silver foam also absorbs and stores some of the low-melting-point metal, allowing the molten low-melting-point metal to provide a strong and reliable electrical and thermal connection between the chip and the drain copper electrode. This structure addresses the core issue of press-fitting SiC MOSFET chips, ensuring double-sided heat dissipation while providing a highly reliable elastic connection that decouples thermal stress from the chip.

[0019] The power circuit connections of this packaging structure are completed through welding and crimping. There are no bonding wires. It has a longitudinal power circuit. The loop current passes through the drain copper electrode, SiC MOSFET chip drain, SiC MOSFET chip source, silver pillar, and source copper electrode in sequence. The parasitic inductance of the power circuit is extremely small, the electric field is uniform, the current circuit is symmetrical, and the reliability of electrical and thermal connections are also improved.

[0020] The drain of the SiC MOSFET chip is connected to the drain copper electrode through a low-melting-point metal with good thermal conductivity. The source of the SiC MOSFET chip is connected to the source copper electrode through a silver column and a solder layer. The upper and lower copper electrodes are directly connected to the liquid cooling radiator. Both sides of the chip have low thermal resistance heat dissipation paths, which can achieve good double-sided heat dissipation effect.

[0021] Furthermore, low-melting-point metals have high thermal conductivity and excellent thermal conductivity, and their special phase change properties can also provide thermal shock protection.

[0022] Furthermore, the silver foam has a porous structure and can be deformed under relatively small pressure. The thermal stress between the chip drain and the drain copper electrode is completely decoupled during the packaging process and working state, and the silver foam (4) can provide elastic support for the chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of a double-sided heat dissipation elastic press-fit packaging structure of a SIC MOSFET based on a low-melting-point metal and foamed silver according to the present invention; Figure 2 yes Figure 1 Schematic diagram of the internal layout of the double-sided heat dissipation elastic press-fit packaging structure; Figure 3 yes Figure 1 Exploded view of the internal structure of the double-sided heat dissipation elastic press-fit package structure.

[0024] In the figure, 1. Drain copper electrode; 2. Source copper electrode; 3. Low-melting-point metal; 4. Silver foam; 5. SiC MOSFET chip; 6. Silver pillar; 7. Bonding wire; 8. Gate DBC substrate; 9. Gate terminal. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0026] The present invention discloses a double-sided heat dissipation elastic press-fit packaging structure for a SiC MOSFET based on a low-melting-point metal and silver foam. The structure comprises a drain copper electrode 1 and a source copper electrode 2 arranged in a forward-facing manner. A SiC MOSFET chip 5 and a gate DBC substrate 8 are disposed on the drain copper electrode 1. The source of the SiC MOSFET chip 5 is connected to the source copper electrode 2 via a silver pillar 6. A gate terminal 9 is disposed on the gate DBC substrate 8. The gate of the SiC MOSFET chip 5 is connected to the gate terminal 9 via an aluminum bonding wire 7. The top of the gate terminal 9 is connected to the source copper electrode 2, and the gate terminal 9 extends outside the module for external connection. Liquid-cooled heat sinks are respectively disposed on the backs of the drain copper electrode 1 and the source copper electrode 2. The source of the SiC MOSFET chip 5, the source copper electrode 2, and the silver pillar 6 are all connected by welding. The drain copper electrode 1, the gate terminal 9, and the gate DBC substrate 8 are all connected by welding.

[0027] The drain of the SiC MOSFET chip 5 is connected to the drain copper electrode 1 via a low-melting-point metal 3 and silver foam 4. Specifically, a first groove is defined on the drain copper electrode 1, in which the low-melting-point metal 3 is located. A second groove is defined on the drain copper electrode 1, in which the silver foam 4 is located. The first and second grooves are concentrically arranged, meaning that the low-melting-point metal 3 and the silver foam 4 are concentrically arranged. Part of the low-melting-point metal 3 is embedded in the drain copper electrode 1, while another part is embedded in the internal groove of the silver foam 4. The outer side of the silver foam 4 is embedded in the drain copper electrode 1, and the upper surfaces of the silver foam 4 and the low-melting-point metal 3 are flush.

[0028] The low-melting-point metal 3 transforms into a liquid at the normal operating temperature of the SiC MOSFET chip 5. For example, a high-purity indium-bismuth-tin alloy, with a melting point of 47°C, is solid at room temperature. This metal can be soldered to the chip drain and drain copper electrode 1. During operation, the SiC MOSFET chip 5 heats above the melting point of the low-melting-point metal 3. As the chip junction temperature rises, the low-melting-point metal 3 melts. This phase change helps control the temperature rise smoothly, providing some thermal shock protection for the chip. At the stable operating temperature of the chip, the low-melting-point metal 3 is in a liquid state. Its thermal conductivity is approximately 70 W / (m·K), its saturated vapor pressure is on the order of 10-6 Pa, and its boiling point is above 1000°C. This stable liquid state provides a low-resistance heat dissipation path, decoupling thermal stress caused by the mismatch in thermal expansion coefficients between the chip and drain copper electrode 1.

[0029] The silver foam 4 is porous foam-like high-purity elemental silver. Due to the high surface tension of the low-melting-point metal 3 in liquid state, the liquid metal does not tend to enter the gaps of the silver foam 4 with more fine structures. The porous structure of the silver foam 4 will constrain the liquid metal therein. At the same time, when the chip is affected by external vibration or pressure, the silver foam 4 will stabilize the connection between the liquid metal liquid surface and the chip drain. When the chip moves slightly downward, the excess liquid metal will be pressed into the pores of the silver foam 4. When the chip moves slightly upward, the liquid metal stored in the pores of the silver foam 4 will replenish the liquid surface.

[0030] The gate terminal 9 is connected to the DBC substrate and extends outside the module for external connection; the drain copper electrode 1 and the source copper electrode 2 are respectively connected to a liquid cooling radiator.

[0031] The invention also discloses an electronic device comprising the double-sided heat dissipation elastic pressing packaging structure of the SIC MOSFET based on the low-melting-point metal and foamed silver.

[0032] In one embodiment, the drain copper electrode 1 has a double-layer square groove for injecting low-melting-point metal 3 and mounting silver foam 4. The source copper electrode 2 has a circular groove for aligning and soldering silver pillars 6.

[0033] See also Figures 1 to 3 , Figure 1 A schematic diagram of a double-sided heat dissipation elastic press-fit packaging structure according to an embodiment of the present invention is shown; Figure 2 Draw Figure 1 Schematic diagram of the internal layout of the double-sided heat dissipation elastic press-fit packaging structure; Figure 3 Draw Figure 1 An exploded view of the internal structure of the double-sided heat dissipation elastic press-fit packaging structure. The overall packaging process implementation process is as follows: the gate DBC substrate 8 and the gate terminal 9 and the gate DBC substrate 8 and the drain copper electrode 1 are welded in advance, and then the foam silver 4 gasket is installed on the outer layer of the square groove of the drain copper electrode 1. After the low-melting-point metal 3 is melted, it is injected into the inner layer of the square groove of the drain copper electrode 1. The injection liquid level is flush with the square annular foam silver 4 installed on the outer layer. After assembling the chip on it, pressure is applied and wait for the low-melting-point metal 3 to cool and solidify. At this time, the bonding connection between the chip gate and the gate DBC substrate 8 is completed. Subsequently, the vacuum reflow process is applied to weld the silver column 6 and the source copper electrode 2 in sequence, and the process flow of this embodiment is completed.

[0034] The present invention presents a double-sided heat-dissipating elastic press-fit packaging structure for SiC MOSFETs based on low-melting-point metal and silver foam. By combining silver foam 4 with low-melting-point metal 3, the structure provides a flexible connection and press-fit structure with high electrical and thermal connection reliability, low parasitic parameters, and the advantage of double-sided heat dissipation. This solution not only fills the gap in current press-fit solutions for SiC MOSFET chips 5, but also offers lower thermal resistance and parasitic parameters, higher reliability, and better performance than existing SiC MOSFET packaging structures. This allows for the module to achieve higher switching frequencies and enhanced electromagnetic compatibility.

[0035] The press-fit packaging structure doesn't rely solely on mechanical pressure to ensure electrical and thermal connections. The combination of silver foam (4) and low-melting-point metal (3) ensures module reliability even under vibration. The interfaces are connected using welding or low-melting-point metal (3), minimizing contact thermal resistance and providing high-quality, highly reliable electrical and thermal connections. The main circuit contains no thin sheets or fine wires, minimizing parasitic inductance. Furthermore, the structure is compatible with deionized water liquid cooling systems with floating radiator potential, eliminating parasitic common-mode capacitance.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to impose any limitation on the technical solution of the present invention. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and replacements, and these modifications and replacements are also within the scope of protection covered by the claims.

Claims

1. A double-sided heat dissipation elastic press-fit packaging structure of a SIC MOSFET based on a low-melting-point metal and foamed silver, characterized in that: The invention comprises a drain copper electrode (1) and a source copper electrode (2) arranged in a forward direction relative to each other, a SiC MOSFET chip (5) and a gate DBC substrate (8) are arranged on the drain copper electrode (1), the source of the SiC MOSFET chip (5) is connected to the source copper electrode (2) through a silver column (6); a gate terminal (9) is arranged on the gate DBC substrate (8), the gate of the SiC MOSFET chip (5) and the gate terminal (9) are connected through an aluminum bonding wire (7), the top of the gate terminal (9) is connected to the source copper electrode (2), and the gate terminal (9) extends outside the module for external connection; liquid cooling radiators are respectively arranged on the backs of the drain copper electrode (1) and the source copper electrode (2); the drain of the SiC MOSFET chip (5) and the drain copper electrode (1) are connected through a low melting point metal (3) and foamed silver (4).

2. The double-sided heat dissipation elastic press-fit packaging structure of SIC MOSFET based on low-melting-point metal and foamed silver according to claim 1, characterized in that: Part of the low melting point metal (3) is embedded in the drain copper electrode (1), and another part is embedded in the internal groove of the foam silver (4). The outer side of the foam silver (4) is embedded in the drain copper electrode (1).

3. The double-sided heat dissipation elastic press-fit packaging structure of SIC MOSFET based on low-melting-point metal and foamed silver according to claim 2, characterized in that: A first groove is provided on the drain copper electrode (1), and the low melting point metal (3) is located in the first groove.

4. The double-sided heat dissipation elastic press-fit packaging structure of SIC MOSFET based on low-melting-point metal and foamed silver according to claim 3, characterized in that: A second groove is provided on the drain copper electrode (1), and the foamed silver (4) is located in the second groove.

5. The double-sided heat dissipation elastic press-fit packaging structure of SIC MOSFET based on low melting point metal and foamed silver according to claim 4, characterized in that: The first groove and the second groove are concentrically arranged, and the low melting point metal (3) and the foamed silver (4) are concentrically arranged.

6. The double-sided heat dissipation elastic press-fit packaging structure of SIC MOSFET based on low melting point metal and foamed silver according to claim 2, characterized in that: The upper surfaces of the foamed silver (4) and the low-melting-point metal (3) are flush.

7. The double-sided heat dissipation elastic press-fit packaging structure of SIC MOSFET based on low melting point metal and foamed silver according to claim 1, characterized in that: The low melting point metal (3) is solid at room temperature and is liquid when the SiC MOSFET chip (5) is in a working state.

8. The double-sided heat dissipation elastic press-fit packaging structure of SIC MOSFET based on low melting point metal and foamed silver according to claim 1, characterized in that: The foamed silver (4) is porous elemental silver.

9. The double-sided heat dissipation elastic press-fit packaging structure of SIC MOSFET based on low melting point metal and foamed silver according to claim 1, characterized in that: The source electrode of the SiC MOSFET chip (5), the source copper electrode (2) and the silver column (6) are all connected by welding; the drain copper electrode (1), the gate terminal (9) and the gate DBC substrate (8) are all connected by welding.

10. An electronic device comprising the double-sided heat dissipation elastic press-fit packaging structure of the SIC MOSFET based on low-melting-point metal and foamed silver according to any one of claims 1 to 9.

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