High-dielectric-property homogeneous polymer coating suitable for medium-voltage SIC power module and application of high-dielectric-property homogeneous polymer coating

Abstract

The invention relates to the technical field of power semiconductor packaging, in particular to a high-dielectric-property homogeneous polymer coating suitable for a medium-voltage SIC power module and application, the polymer coating is prepared from a solution formed by dissolving dicyclohexyl-3, 4, 3 ', 4'-tetracarboxylic dianhydride and 2, 2 '-dimethyl-[1, 1'-biphenyl]-4, 4 '-diamine in chloroform, and the polymer coating is prepared from a high-dielectric-property homogeneous polymer coating suitable for the medium-voltage SIC power module and a high-dielectric-property homogeneous polymer coating suitable for the high-dielectric-property homogeneous polymer coating suitable for the medium-voltage SIC power module. The dielectric constant of the polymer coating is 4.52 under 1kHz, the dielectric constant of the polymer coating is 3.94 under 100kHz, and the breakdown field strength of the polymer coating is 700kV / mm. The coating is verified through electric field simulation, the maximum electric field intensity in the silica gel can be reduced to 43% or below of the original maximum electric field intensity through the coating with the thickness of 80 microns, and partial discharge can be effectively restrained; meanwhile, compared with an uncoated sample, the partial discharge initial voltage (PDIV) is averagely improved by 101%, and the insulation requirement of a 15kV medium-voltage module is met.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of power semiconductor packaging, in particular to a high-dielectric-property homogeneous polymer coating suitable for a medium-voltage SIC power module and application. BACKGROUND

[0002] Medium-voltage (MV) silicon carbide (SiC) power devices are increasingly widely used in power grids, high-voltage pulse power supplies and other fields, but their power modules face the contradiction between high insulation voltage and high power density, and new types of insulating materials are urgently needed to alleviate the contradiction. The electric field in the power module is concentrated at the three-phase point (the intersection of the copper layer, the ceramic layer and the insulating medium) of the direct bonding copper substrate (DBC), and traditional solutions such as changing the geometry of the DBC substrate, the size of the electrode or using a nonlinear dielectric have problems such as high engineering complexity, thermal mismatch or complex preparation process.

[0003] Among existing insulating materials, the nonlinear dielectric needs to be doped with fillers, which can easily lead to increased solution viscosity, bubble formation and increased loss. For example, CN110938288A discloses a SiC@SiO2 core-shell structure nano-filler / epoxy resin-based composite material and a preparation method thereof. The composite material is doped with 5wt.% SiC@SiO2 core-shell structure nano-filler, the SiC@SiO2 core-shell structure nano-filler has a core layer of nano-SiC particles, and a shell layer of SiO2 with a thickness of 6nm is coated outside the core layer. By doping the SiC@SiO2 core-shell structure nano-filler in the epoxy resin, the breakdown strength and conductivity characteristics of the nonlinear insulating material are improved.

[0004] Therefore, it is of great significance to develop a high-dielectric-property homogeneous polymer coating suitable for a medium-voltage SiC power module to improve the insulation performance and power density of the module. SUMMARY

[0005] In view of the problem in the prior art that the nonlinear dielectric needs to be doped with fillers, which can easily lead to increased solution viscosity, bubble formation and increased loss, the application provides a high-dielectric-property homogeneous polymer coating suitable for a medium-voltage SIC power module and application.

[0006] The application is implemented by the following technical solutions: A high-dielectric-property homogeneous polymer coating suitable for a medium-voltage SIC power module, the polymer coating is prepared from a solution of dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride and 2,2'-dimethyl-[1,1'-biphenyl]-4,4'-diamine dissolved in chloroform, the dielectric constant of the polymer coating is 4.52 at 1kHz and 3.94 at 100kHz, and the breakdown field strength is 700kV / mm.

[0007] Preferably, the polymer coating is prepared by dissolving the dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride and 2,2'-dimethyl-[1,1'-biphenyl]-4,4'-diamine in chloroform to obtain a mixed solution, and then coating and curing the mixed solution to obtain the polymer coating.

[0008] Preferably, the total mass fraction of the dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride and 2,2'-dimethyl-[1,1'-biphenyl]-4,4'-diamine in the mixed solution is 15%.

[0009] The application of a high-dielectric-property homogeneous polymer coating suitable for a medium-voltage SIC power module in a medium-voltage power module.

[0010] Preferably, the polymer coating is coated on the triple-point edge region of the DBC substrate.

[0011] Preferably, the polymer coating on the DBC substrate is formed by dissolving the dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride and 2,2'-dimethyl-[1,1'-biphenyl]-4,4'-diamine in chloroform to obtain a mixed solution, and then coating and curing the mixed solution.

[0012] Preferably, the viscosity of the mixed solution is 300.

[0013] Preferably, the curing includes first curing and second curing, wherein the temperature of the first curing is 70℃, and the holding time is 60min; the temperature of the second curing is 260℃, and the holding time is 60min.

[0014] Preferably, the thickness of the polymer coating is 80±1μm.

[0015] Preferably, the module can withstand a 12kV DC bus voltage.

[0016] Compared with the prior art, the application has the following beneficial effects: The application discloses a high-dielectric-property homogeneous polymer coating suitable for a medium-voltage SIC power module, which is a single homogeneous insulation material coating, has the advantages of simple process and good compatibility, and has uniform internal structure and performance distribution, so that the coating can provide stable electrical performance at each position, reduces the risk of electrical failure caused by local performance difference, and can improve the stability and reliability of the module. The dielectric constant is 4.52 at 1 kHz and 3.94 at 100 kHz. The higher dielectric constant means that the polymer coating can store more electric energy under the action of an electric field, which helps to improve the capacitance performance of the medium-voltage SIC power module, thereby enhancing the energy storage and regulation capability of the module in a circuit, making the module more stable when dealing with voltage fluctuations, and improving the overall circuit performance.

[0017] The breakdown field strength reaches 700 kV / mm, indicating that the polymer coating has excellent insulation performance and can withstand a high electric field strength without being broken down, which provides reliable electrical insulation protection for the medium-voltage SIC power module, effectively prevents insulation failure problems caused by excessively high electric field, improves the safety and reliability of the module, and prolongs the service life of the module.

[0018] The application of the high-dielectric-property homogeneous polymer coating suitable for a medium-voltage SIC power module in a medium-voltage power module applies the polymer coating to the three-phase point edge area of the DBC substrate, because the three-phase point edge area is usually the part where electrical stress is concentrated and insulation problems are prone to occur. Coating the polymer coating with high dielectric performance in this area can effectively enhance the insulation strength of this area, reduce the risk of partial discharge and insulation breakdown, improve the overall insulation performance of the medium-voltage SIC power module, and make it work stably under higher voltage environment, meeting the requirements of the power module in the medium-voltage power system. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The preparation flowchart of the polymer coating on the DBC substrate in the application.

[0020] Figure 2 The DBC substrate structure and three-phase point cross-sectional schematic diagram in the embodiment of the application (A: DBC plate structure diagram; B: metallographic microscope observation diagram; C: overall structure schematic diagram of the module).

[0021] Figure 3 The electric field simulation result comparison in the embodiment of the application (A: simulation condition setting schematic diagram; B: electric field distribution diagram around the three-phase point without coating; C: electric field distribution diagram around the three-phase point with coating).

[0022] Figure 4A: Sampling point electric field intensity changes with coating thickness; B: Metallographic observation figure of coating thickness controlled at 80 pm after process stabilization.

[0023] Figure 5 For the PDIV data comparison of the coating and without coating in the partial discharge test in the embodiment of the application.

[0024] Figure 6 For the 15kV module packaging process and double pulse test waveform (A: new coating process step; B: double pulse test waveform under 12kV bus voltage) in the embodiment of the application. DETAILED DESCRIPTION

[0025] The application will be further described in detail below with specific embodiments, which are an explanation but not a limitation of the application.

[0026] The application discloses a high-dielectric-property homogeneous polymer coating suitable for a medium-voltage SIC power module, referring to Figure 1 , comprising the following steps: The application further discloses application of the high-dielectric-property homogeneous polymer coating suitable for a medium-voltage SIC power module in a medium-voltage power module, by coating the coating on the edge of the three-phase point of the DBC substrate, reducing the electric field intensity in the silicon gel, improving the partial discharge inception voltage (PDIV), and solving the contradiction between insulation and power density of the medium-voltage power module.

[0027] EMBODIMENT A high-dielectric-constant and high-dielectric-strength polymer coating for slowing down the electric field of a 15kV SiC MOSFET power module is prepared, and a power module is made for test, including a DBC substrate, a SiC MOSFET chip, a gate terminal, a direct-current positive and negative terminal and an alternating-current terminal, and the structure of the power module with the coating is as follows: The DBC substrate has a size of 40mm*36mm, the upper and lower copper layers have a thickness of 0.3mm, the middle aluminum oxide ceramic layer has a thickness of 1mm, the distance between the direct-current positive (DC+) and negative (DC-) terminals and the alternating-current (AC) terminal is 2mm, the polymer coating is coated on the edge of the three-phase point of the DBC substrate, the coating area covers the junction area of the copper layer and the ceramic layer, and the silicon gel is filled on the surface of the coating during module packaging. The module adopts a conventional welding and wire bonding process, the silicon gel is filled, and a complete packaging structure is formed.

[0028] The polymer coating material is prepared by dissolving dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride and 2,2'-dimethyl[1,1'-biphenyl]-4,4'-diamine in chloroform solvent in a certain proportion, and the mass fraction of the two substances is controlled at about 15%. After adjusting the solution viscosity to 300, the solution is uniformly applied to the triple point edge area (copper layer-ceramic layer-silicon gel junction position) of the DBC substrate using a coating process. After coating, the substrate is subjected to two-stage curing treatment: first at 70°C for 60 minutes and then at 260°C for 60 minutes, thereby forming a uniform 80μm thick polymer coating.

[0029] By adding solvents to the coating solution, the viscosity of the solution can be adjusted from high to low. Apply the solution with different viscosities to the substrate and let the solution level out. After leveling, different thicknesses of coatings can be obtained after curing due to the different viscosities of the solutions. Through repeated experiments, it is determined that when the solution viscosity is 300, the specified 80μm can be achieved.

[0030] The coated DBC substrate and 15kV SiC MOSFET chip are bonded by soldering and wire bonding to form a half-bridge module structure. During the module packaging process, the coating process only adds the coating and curing steps to the traditional module packaging process, and is compatible with the remaining processes.

[0031] Reference Figure 3 Through electric field simulation verification, the 80μm coating can reduce the maximum electric field strength in the silicon gel to less than 43% of the original, which can effectively suppress partial discharge.

[0032] Reference Figure 4 , Figure 4 (A): When the thickness increases to 80μm, the electric field strength in the silicon gel is reduced to less than 43% of the original. As the thickness continues to increase, the rate of decline in the electric field strength in the silicon gel slows down significantly.

[0033] Figure 4 (B): Observed by metallographic microscope, the coating thickness at the triple point is 79.12 microns, i.e. the thickness of the coating can be controlled around 80 microns.

[0034] Reference Figure 5 The completed module is subjected to partial discharge test, which shows that the PDIV of the sample with a coating thickness of 80μm is increased by an average of 101% compared with the uncoated sample, meeting the insulation requirements of 15kV medium voltage modules.

[0035] Reference Figure 6 In the double pulse test (DPT), the coating preparation only needs to add one coating process in the traditional module packaging process, and the module using the coating can withstand 12kV DC bus voltage, verifying the insulation reliability and process compatibility of the coating.

[0036] The above only describes the preferred embodiments of the present application, and does not use any restriction on the technical solutions of the present application. Those skilled in the art should understand that the technical solutions can be modified and replaced in several simple ways without departing from the spirit and principles of the present application, and these modifications and replacements also belong to the protection scope covered by the claims.

Claims

1. A high dielectric performance homogeneous polymer coating suitable for medium voltage SIC power modules, characterized in that, The polymer coating is prepared from a solution of dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride and 2,2'-dimethyl-[1,1'-biphenyl]-4,4'-diamine dissolved in chloroform, and has a dielectric constant of 4.52 at 1 kHz, 3.94 at 100 kHz, and a breakdown field strength of 700 kV / mm.

2. A high dielectric performance homogenous polymer coating suitable for medium voltage SIC power modules according to claim 1, characterized in that, The polymer coating is prepared by dissolving dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride and 2,2'-dimethyl-[1,1'-biphenyl]-4,4'-diamine in chloroform to obtain a mixed solution, and then coating and curing the mixed solution to obtain the polymer coating.

3. A high dielectric performance homogenous polymer coating suitable for medium voltage SIC power modules according to claim 2, characterized in that, The total mass fraction of dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride and 2,2'-dimethyl-[1,1'-biphenyl]-4,4'-diamine in the mixed solution is 15%.

4. Use of the homogeneous polymer coating with high dielectric properties suitable for medium voltage SIC power modules according to any one of claims 1 to 3 in a medium voltage power module.

5. Use according to claim 4, characterized in that, The polymer coating is coated on the triple point edge area of the DBC substrate.

6. Use according to claim 5, characterized in that, The polymer coating is formed on the DBC substrate by dissolving dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride and 2,2'-dimethyl-[1,1'-biphenyl]-4,4'-diamine in chloroform to obtain a mixed solution, and then coating and curing the mixed solution to form the polymer coating on the DBC substrate.

7. Use according to claim 6, characterized in that, The viscosity of the mixed solution is 300.

8. Use according to claim 6, characterized in that, The curing includes first curing and second curing, wherein the temperature is 70°C and the holding time is 60 min during the first curing, and the temperature is 260°C and the holding time is 60 min during the second curing.

9. Use according to claim 6, characterized in that, The thickness of the polymer coating is 80±1 μm.

10. Use according to claim 6, characterized in that, The module can withstand a DC bus voltage of 12 kV.

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