Crimping type power semiconductor module packaging framework based on carbon reinforced metal matrix composite material cushion block

Abstract

The invention belongs to the technical field of composite materials, and discloses a crimping type power semiconductor module packaging framework based on a carbon reinforced metal matrix composite material cushion block, and the framework is characterized in that in a crimping type power semiconductor module, upper and lower electrode plates of a chip need to be led out through the cushion block so as to realize electrical connection with an external circuit. The carbon-reinforced metal-based composite material is used for replacing a traditional molybdenum material to serve as a cushion block material, the performance requirements of high electric conduction and heat conduction of the power semiconductor module can be met, fretting wear of the surface of a power chip can be reduced, and the reliability of the power module is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to but is not limited to the technical field of composite materials, and particularly relates to a press-in type power semiconductor module packaging architecture based on a carbon-reinforced metal matrix composite pad. BACKGROUND

[0002] Packaging is an indispensable key link for power semiconductor devices, and its importance runs through multiple dimensions such as performance play, reliability guarantee, application adaptation, and cost control, directly affecting the performance and service life of the devices in power electronic systems.

[0003] At present, there are two packaging forms for power semiconductor modules, namely welding and press-in. Welding type devices form electrical connection between internal chips and external electrodes through bonding wires, and have lower production cost, so they are the most widely used devices at present. However, they have problems such as insufficient power density, solder layer peeling, bonding wire fracture, and single-sided heat dissipation, making it difficult to meet the needs of high power levels. Press-in type IGBT devices form electrical connection between internal chips and external electrodes by applying pressure, and can realize multi-chip parallel press-in packaging. Compared with welding type IGBT devices, press-in type IGBT devices realize electrical contact between chips and electrodes through pressure instead of solder (such as tin, silver solder), avoiding the fatigue failure problem of solder under thermal cycling in welding type modules, and integrating chips, buffer layers, electrodes, and heat sinks, which takes into account electrical performance and heat dissipation efficiency. At the same time, due to its special structural design, press-in modules are easy to scale chip parallel packaging and series use, and have the advantages of low thermal resistance, double-sided heat dissipation, and short-circuit failure. Therefore, press-in type devices have important applications in high-voltage direct current transmission and high-power power drive.

[0004] The commonly used press-in method is divided into two types, namely rigid press-in and elastic press-in. So-called rigid press-in is to realize electrical connection between chips and external electrodes through rigid pads (Cu\Mo, etc.), and the pads are processed into shapes suitable for chip plates, and the tolerance requirements for surface roughness and flatness of the pads are very strict to ensure good point contact and uniform pressure distribution. At present, the mainstream form of elastic press-in is the ABB press-in type IGBT device (referred to as "StakPak"), which is a single-sided heat dissipation structure. It uses a disc spring instead of a lead terminal to connect the emitter of the chip based on the traditional welding and potting type device, realizing the press-in connection of the device.

[0005] The simplified structure of a common rigid press-in module (omitting the gate circuit part) is as follows Figure 1As shown, the electrodes at both ends of the chip are directly connected to the external circuit through mechanical pressure connection, and the gate is also connected to the copper-clad PCB through the spring contact pin, and then connected to the external driving circuit through the copper-clad PCB. The resistance of the chip gate circuit is embedded in the spring contact pin, so that each chip corresponds to a gate resistance. SUMMARY

[0006] In view of the problems existing in the prior art, the present application provides a crimping type power semiconductor module packaging architecture based on a carbon reinforced metal matrix composite pad.

[0007] The present application is implemented in a crimping type power semiconductor module packaging architecture based on a carbon reinforced metal matrix composite pad, which comprises: a metal electrode, a gasket, a pad, a power chip, and a metal electrode.

[0008] In the crimping type power semiconductor module, the upper and lower plates of the power chip need to be led out through the pad to realize electrical connection with the external circuit.

[0009] Further, the pad is made of carbon reinforced metal matrix composite material.

[0010] In combination with the above technical solutions and the technical problems solved, the technical solution to be protected by the present application has the following advantages and positive effects:

[0011] In the crimping type power module, the pad is the core component connecting the chip, the electrode and the external pressure system, and its design directly affects the pressure distribution, thermal management, electrical contact stability and long-term reliability of the module. The core principle of the crimping type module is to form an ohmic contact between the chip and the electrode through external axial pressure, and the pad is the "bridge" of pressure transmission, and its primary function is to convert the external concentrated pressure into uniformly distributed surface pressure to ensure that each chip bears consistent pressure.

[0012] The crimping type module will experience severe temperature cycling in working conditions, and if the thermal expansion coefficients of the chip and the pad are greatly different, thermal stress will easily occur. The pad can effectively alleviate this "thermal mismatch" through material selection and structural design. Currently, in order to match the thermal expansion coefficient of the chip, metal molybdenum is generally selected as the pad material, but the thermal conductivity of molybdenum is low, which affects the heat dissipation efficiency of the module,

[0013] Fretting wear failure is one of the main packaging failure modes of crimping type devices. Fretting wear refers to a composite form of wear caused by small amplitude oscillation of the surfaces of two materials pressed against each other. In actual working conditions, the crimping device is affected by alternating stress, relative sliding occurs between the contact surfaces, leading to fretting wear, which causes the roughness of the contact surface, the contact resistance and the contact thermal resistance to rise, and then causes fretting wear failure, so the selection of the pad is very important.

[0014] Carbon materials are very high-quality materials with high thermal conductivity, low thermal expansion coefficient, high strength, and wear resistance. Metal materials, such as copper and aluminum, are widely used in industry due to their good electrical conductivity and thermal conductivity, excellent friction and wear resistance, and ductility. Carbon-reinforced metal matrix composites are a new type of material formed by carbon-based reinforcement phases (such as carbon fibers, carbon nanotubes, graphene, carbon cloth, etc.) and metal or alloy matrices (such as aluminum, magnesium, copper, titanium, etc.) through a composite process. They have both the high strength and high thermal conductivity of carbon materials and the toughness and electrical conductivity of metals, making them irreplaceable in the fields of aerospace, electronic packaging, new energy, and high-end equipment.

[0015] By controlling the structure, content, and spatial distribution of carbon materials in the metal, carbon-reinforced metal matrix composites with excellent thermal conductivity and suitable thermal expansion coefficients are born.

[0016] Therefore, replacing traditional molybdenum materials with carbon-reinforced metal matrix composites as pad materials can not only meet the performance requirements of high electrical conductivity and thermal conductivity of power semiconductor modules, but also reduce the fretting wear on the surface of power chips and improve the reliability of power modules.

[0017] The choice of pad has a very significant impact on the performance of crimped power modules. Currently, in the selection of pad materials for crimped power modules, a trade-off between high thermal conductivity and suitable thermal expansion coefficient is needed. If a copper pad with high thermal conductivity is chosen, although it can enhance the heat dissipation capacity of the power module, the difference in thermal expansion coefficient between copper and the power chip is large, which can easily cause fretting wear during long-term power cycling and lead to module failure. If a molybdenum pad with a thermal expansion coefficient more matched to the power chip is chosen, although it can alleviate the fretting wear problem on the contact surface between the chip and the pad, the low thermal conductivity of molybdenum is not conducive to heat dissipation of the power chip. Therefore, carbon-reinforced metal matrix composite pads have unparalleled advantages over other pads, with higher thermal conductivity than copper and a more matched thermal expansion coefficient with the chip, successfully achieving a win-win in both aspects. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a simplified structure diagram of a typical rigid crimp module provided by an embodiment of the present application;

[0019] Figure 2 is a thermal simulation result of a crimp module provided by an embodiment of the present application: (a) carbon-reinforced metal matrix composite pad; (b) molybdenum pad;

[0020] In the figure: 1, metal electrode; 2, gasket; 3, pad; 4, power chip; 5, metal electrode. DETAILED DESCRIPTION

[0021] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0022] The existing compression type power module adopts Cu / Mo / AlSiC metal or metal matrix composite as a pad, and realizes the electrical-thermal connection of the upper and lower electrode plates of the chip through external pressure. However, under long-term thermal cycle / power cycle, there are three common pain points: first, the micro rough peak contact between the pad and the electrode / chip metallization layer leads to the increase of contact resistance with oxidation and fretting wear, and generates hot spots; second, the high stiffness of the pad and the thermal expansion mismatch of the chip (Si, SiC, GaN) easily form stress concentration and cracks at the edge / passivation layer of the chip; third, the traditional isotropic thermal conductive material is difficult to balance "longitudinal low thermal resistance + in-plane uniform temperature", and uneven current / distribution pressure occurs when the large chip is connected in parallel, which further amplifies the junction temperature gradient and aging rate difference.

[0023] To solve the above bottleneck, the core idea of using "carbon reinforced metal matrix composite (C-MMC)" as a pad is proposed: using anisotropic graphite fiber / graphite sheet / three-dimensional carbon foam as a reinforcing framework, the C-MMC is obtained by directional laying and Cu or Ag pressure infiltration forming, which has the functions of "thick direction high thermal conductivity, in-plane high diffusion, and overall medium elastic modulus". By vertically arranging high thermal conductivity carbon + metal continuous phase in the thick direction (z direction), the thermal resistance of the chip-electrode is significantly reduced; by laying sheet-shaped graphite / graphene layers in the in-plane (x-y direction), a uniform temperature network is formed to suppress the temperature difference between the parallel chips. The low density and compressibility of the carbon framework can also provide "flexible cushioning" during compression to reduce thermal cycle stress and warping transmission.

[0024] For interface failure, a "graded interface engineering" pad skin is proposed: a microporous plastic metal surface layer (such as a silver / copper microporous sintered layer or a microporous Ni-P / Ag composite layer formed by chemical replacement) is prepared at both ends of the C-MMC, which can reversibly flow under compression load, filling the micro gaps on the mating surface to obtain a low and stable contact resistance; a thin layer system (TiW / Cu / Ni, etc.) for diffusion barrier and wetness enhancement is arranged below it to inhibit the interdiffusion of Cu to the chip metallization layer and the formation of brittle intermetallic compounds. The "soft-hard-soft" graded skin not only ensures repeatable assembly, but also delays interface oxidation and fretting wear, significantly improving long-term contact reliability.

[0025] To further equalize pressure and current, the internal topology of the pad employs a "zoning-micropillar-step thickness" approach: a hybrid zone of high-porosity carbon foam and high metal filling ratio is arranged in the expected hot spot / current-dense area to enhance local thermal and electrical conductivity; a more compliant micropillar array and thinned steps are set in the edge area to adaptively adjust the contact stiffness throughout the entire chip surface, transforming the external single clamping force into a near-uniform surface pressure; radial graphite heat dissipation fins are introduced into the pad surface, forming a dual-channel thermal path of "rapid heat dissipation in the thickness direction + rapid temperature equalization in the surface" in conjunction with the electrode heat dissipation channels. This integrated geometry-material design can flatten the temperature field and suppress thermal crosstalk and current preemption between parallel chips.

[0026] Considering the mechanical drift during assembly and service, this invention proposes introducing a "constant force" coupling element (a combination of disc spring / shape memory alloy ring / constant force spring sheet) into the electrode-pad system. This allows the clamping force to automatically compensate for temperature and creep, maintaining it within the target range over a long period. Simultaneously, a solid lubrication anti-fretting coating (such as a graphene-like / carbon-based solid lubricating layer + a thin noble metal coating) is applied to the pad surface to reduce fretting wear during thermal-mechanical cycles. Combined with edge stress-relief grooving and milling chamfering, this effectively suppresses shear peaks at the interface between the chip's metallization and passivation layers, extending power cycle life.

[0027] Unlike existing improvements that merely replace the pad substrate (Cu, Mo, AlSiC) or simply add a heat-conducting sheet, the innovation of this solution lies in the synergy of "materials-interface-structure-mechanics-thermal": ① Using an orientably designable C-MMC pad, it simultaneously achieves multi-physical coupling performance of low thermal resistance in thickness, in-plane temperature uniformity, and compliant buffering within the same volume; ② Through a hierarchical skin of malleable microporous metal + diffusion barrier, it achieves long-term stability of the press interface with "self-compliant low Rc + anti-oxidation and anti-micromotion"; ③ By combining geometric optimization of partitioned micropillars / stepped thickness with constant force clamping, it achieves continuous pressure and current equalization of large-area parallel chips under manufacturing tolerances and service drift. The combination of the above features is not a direct splicing of existing technologies, but can reduce hot spots and stress concentration from the source, and improve the efficiency and reliability of the press module in high-temperature, high dI / dt and high heat flux density scenarios, possessing outstanding substantial characteristics and significant progress.

[0028] Depend on Figure 1 As can be seen, the present invention provides a press-fit power semiconductor module packaging architecture based on carbon-reinforced metal matrix composite material pads, the architecture including: metal electrode 1, pad 2, pad 3, power chip 4, and metal electrode 5;

[0029] In this press-fit power semiconductor module, the upper and lower plates of the power chip 4 need to be led out through the pad 3 to achieve electrical connection with the external circuit.

[0030] The pad 3 is made of carbon-reinforced metal matrix composite material.

[0031] Particular applications or related products of the present application.

[0032] (1) Westcode Press Pack IGBT

[0033] (2) Toshiba IEGT

[0034] (3) ABB StakPak

[0035] (4) CRRC Press Pack IGBT Module

[0036] For example, if the ratio of copper and diamond is controlled, the thermal expansion coefficient of the pad block is 4ppm / ℃ (close to the thermal expansion coefficient of SiC), and the thermal conductivity is about 800W / mK. For molybdenum pad block, the thermal expansion coefficient is 5ppm / ℃, and the thermal conductivity is 138W / mK. It can be seen that in any aspect, the performance of the new carbon reinforced metal matrix composite pad block is better than that of the molybdenum pad block.

[0037] In order to verify the improvement of the carbon reinforced metal matrix composite on the performance of the module, the press-pack modules composed of copper-diamond pad blocks and molybdenum pad blocks are respectively simulated, and the model is as shown in Figure 2 Figure 2 (a) is the thermal simulation result of the copper-diamond pad block module, Figure 2 (b) is the thermal simulation result of the molybdenum pad block module. Two physical fields of solid and fluid heat transfer and turbulent flow are selected, the material parameters of each part are set, the chip heat rate is 200W, and the fluid flow rate of the upper and lower heat sinks is 2L / min. The junction temperature of the chip during stable operation of the copper-diamond pad block and copper pad block press-pack modules is simulated respectively. From the simulation result, it can be seen that under the condition that other conditions are completely the same, the junction temperature of the molybdenum pad block press-pack module during stable operation is 100.37℃, and the junction temperature of the copper-diamond pad block press-pack module during stable operation of the chip is 88.06℃. The junction temperature during stable operation of the chip is greatly reduced, which shows that the copper-diamond can obviously improve the thermal performance of the module. At the same time, since the thermal expansion coefficient of the copper-diamond pad block is more close to SiC, the fretting wear caused by thermal expansion and contraction during the operation of the chip is smaller, and the long-term reliability of the module is also higher.

[0038] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any modification, equivalent replacement and improvement made by any person skilled in the art within the technical range disclosed by the present application, as long as it is within the spirit and principle of the present application, should be covered within the protection scope of the present application.​

Claims

1. A press-fit power semiconductor module packaging architecture based on carbon-reinforced metal matrix composite material pads, characterized in that, The packaging architecture includes at least: an upper metal electrode, a lower metal electrode, a pad, a spacer, and a power chip; the upper and lower electrodes of the power chip are led out in the thickness direction through the spacer and form a detachable electrical and thermal connection with the upper and lower metal electrodes, respectively; the spacer provides a low thermal resistance channel in the thickness direction and a uniform temperature diffusion channel in the plane to suppress the temperature difference and current unevenness between parallel chips.

2. The packaging architecture according to claim 1, characterized in that, The pad is a carbon-reinforced metal matrix composite material, which includes a carbon-reinforced skeleton and a continuous metal phase. The carbon-reinforced skeleton is arranged in a thickness orientation to improve the thickness thermal conductivity, and graphite sheets are laid between the in-plane layers to improve the in-plane thermal diffusion capacity. The continuous metal phase is either copper or silver.

3. The packaging architecture according to claim 1, characterized in that, The pad has a graded interface layer on both ends. The graded interface layer includes a malleable microporous metal surface layer and a diffusion barrier layer from the outside to the inside. The malleable microporous metal surface layer has a thickness of 5 μm to 80 μm and a porosity of 5% to 35%. The diffusion barrier layer includes at least one of a titanium-tungsten layer, a copper layer and a nickel layer, with a total thickness of 0.2 μm to 3 μm.

4. The packaging architecture according to claim 1, characterized in that, The pad adopts a partitioned and stepped thickness structure in the plane: the metal filling ratio of the thermally conductive area in the center of the chip is higher than that of the edge area. The edge area is provided with a micropillar conformal structure and a thinning step to adjust the local contact stiffness. Radial heat dissipation ribs are provided in the plane to guide heat from the center of the chip to the electrode heat dissipation channel.

5. A carbon-reinforced metal matrix composite material pad, characterized in that, This pad is used for press-fit power semiconductor modules and features anisotropic thermal conductivity and a moderate modulus of elasticity. Its thickness thermal conductivity is not less than 300 W·m. -1 K-1, in-plane thermal conductivity not less than 200 W·m -1 ·K-1, with a linear expansion coefficient of 3ppm·K-1 to 9ppm·K-1 and an elastic modulus of 50GPa to 120GPa.

6. The pad according to claim 5, characterized in that, The pad has a high metal-filled zone facing the chip working area and a compliant zone facing the edge. The volume fraction of the high metal-filled zone is not less than 70%, and the compliant zone is provided with a carbon foam microporous network to improve the compressing compliance and reduce edge stress concentration.

7. The pad according to claim 5, characterized in that, The pad has a solid lubricating anti-fretting coating and a precious metal coating layer on both ends of its surface. The solid lubricating anti-fretting coating is a carbon-based coating with a thickness of 50 nm to 500 nm, and the precious metal coating layer is either silver or gold with a thickness of 50 nm to 500 nm.

8. A method for assembling a press-fit power semiconductor module, characterized in that, Includes the following steps: S1, placing a carbon-reinforced metal matrix composite pad between the upper electrode and the upper metal electrode and between the lower electrode and the lower metal electrode of the power chip; S2, applying a target clamping force to the upper and lower metal electrodes through a constant force clamping assembly, the target clamping force being 1kN to 30kN; S3, under the target clamping force, completes the microplastic flow of the graded interface layer to fill the micro gaps, stabilizes the electrical connection resistance, and forms a thick-to-low thermal resistance channel.

9. The assembly method according to claim 8, characterized in that, Before step S1, the end face of the pad is roughened and sintered with microporous metal. The roughening parameters make the surface arithmetic mean roughness 0.2μm to 1.5μm, and the surface pore diameter after sintering is 0.2μm to 2μm, so as to facilitate the formation of stable low contact resistance in step S3.

10. A constant force clamping assembly, characterized in that, This component is used to maintain a constant clamping force for a press-fit power semiconductor module. It includes an elastic element and a compensation element. The elastic element is a disc spring stack, and the compensation element is either a shape memory alloy ring or a constant force spring sheet. The component maintains a clamping force fluctuation of no more than ±10% within the range of -40°C to 175°C, and automatically compensates for load creep to maintain a stable contact state between the pad and the electrode as described in claim 1.

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