Research On Preparation Of High Thermal Conductivity And Low Expansion SiC/Al Composite For IGBT Substrate

With the development of IGBT module towards the direction of high integration and high stability,the thermal performance of its packaging materials is put forward increasingly higher requirements.SiC/Al composites with high SiC volume fraction(SiC>50 vol.%)have attracted much attention in the field of IGBT module packaging(substrate)due to their high thermal conductivity,low thermal expansion coefficient,light weight and low cost.The preparation processes of this new electronic packaging material have become an important issue in the world.In this paper,IGBT substrate materials with high thermal conductivity and low expansion coefficient is studied.The substrate material was prepared by vacuum pressure infiltration method:based on the systematic research of the molding technology for simple shape SiC preform,the 3DP printing technology for complex shape SiC preform is proposed and studied,which solves the technical problem of the prefabrication of complex shape SiC preform;and the vacuum pressure infiltration process was also systematically studied,which infiltrated Al liquid into the SiC preform to prepare the high volume fraction SiC/Al composites.The influence of process parameters on the thermophysical properties of the composites was obtained,which provides technical and theoretical support for the preparation of IGBT substrate materials with high thermal conductivity and low expansion.The main results are as follows:(1)The influence of molding processes on volume fraction and pore characteristics of SiC preform was studied,and the preform with simple shape and excellent performance was prepared.The influence of different proportions of 100 ?m and 12 ?m SiC particles on the SiC preform was obtained:the introduction of small SiC particles leads to the decrease of the pore size of the preform,and the volume fraction of SiC can be controlled between 56%and 72%;The relationship model between the content of NH4HCO3 and the porosity of SiC preform was established:Y=27.04+0.398X,and it was found that NH4HCO3 can be used as a "pore bridge" to improve the connectivity of pores in preform;The influence of NH4H2PO4 on the pore characteristics of the preform was obtained,and the result shows that the optimal amount of NH4H2PO4 was 5%.(2)The influence of 3DP printing processes on the formability of the SiC preform was studied.The preform with complex shape and clear outline was prepared.The binder and its content were determined and optimized:furan resin was used as binder for low temperature environment,NH4H2PO4 was used as binder for high temperature environment,and the optimal amount of NH4H2PO4 was 9 vol.%.The influence of printing layer thickness on the formability of SiC preform is obtained:when the thickness of printing layer is 0.2 mm,the phenomenon of "layer error" is easy to form in the preform,and the phenomenon gradually decreases with the increase of the thickness of printing layer,and 0.24 mm is the ideal thickness of printing layer.(3)The influence of vacuum pressure infiltration processes on the infiltration behavior of liquid A1 was studied.SiC/Al composites with good interfacial bonding and complete infiltration were prepared.The influence of Si and Mg on the infiltration behavior of liquid Al was obtained:The Al-12Si-Mg alloy with high Si content is selected,which has good fluidity,the prepared composites have less pores,and the interface reactions were well controlled;the addition of Mg can improve the wettability between SiC and Al.When the Mg content is about 1 wt.%,the result of Al liquid infiltration is the best.Otherwise,the infiltration of liquid Al will be hindered when the Mg content is more than 1 wt.%,resulting in the decrease of the density of the composites.The influence of infiltration pressure on the infiltration behavior of liquid Al was clarified:With the increase of infiltration pressure,the Al liquid is filled more fully and the density of the composite increases.(4)The effects of SiC volume fraction and infiltration pressure on the thermophysical properties and mechanical properties of the composites were studied,and the SiC/Al composites with excellent properties were obtained.The results show that the increase of SiC volume fraction and infiltration pressure are beneficial to the thermophysical properties and flexural strength of SiC/Al composites.The thermal conductivity of high volume fraction SiC/Al composites is sensitive to its porosity.Based on the H-J model,a new calculation model,Kd=K?+K0-Ka,is established.Combined with the porosity of the composites,the model can achieve a good prediction of the thermal conductivity of high volume fraction SiC/Al composites.Based on the research above,the optimal preparation process of the composite was determined,and the microstructure of the composite was uniform,the interfacial reaction was well controlled,the thermal conductivity of the composite was 177 W/(m·k),the thermal expansion coefficient was 11.9×10-6/K and the bending strength was 334 MPa,which meet the performance requirements of IGBT substrates well.