Thermal Reliability Analysis Of High Temperature Resistant Microsystem Package

The third-generation semiconductors represented by Si C and Ga N have the characteristics of large band gap,high critical breakdown voltage,high thermal conductivity,and high carrier saturation drift velocity.They have high application value in the fields of aerospace exploration,aviation equipment and deep well drilling,electronic devices in these fields are often in a high temperature environment,accompanied by corrosive gases,and usually require high temperature resistant air-tight packaging.This thesis was mainly focused on the reliability of high temperature microsystem packaging.Firstly,the nanosilver solder for high-temperature packaging was studied,and the micro morphology and structure of nanosilver solder were analyzed,and the modeling method of three-dimensional porous material was established;the temperature field distribution of porous silver model was calculated by finite element method,and the effect of porosity on the thermal conductivity of porous nanosilver was studied.Aiming at the mechanical behavior of nanosilver solder,the finite element prediction model of Young's modulus of porous nanosilver was established,and the variation characteristics of Young's modulus with porosity were studied.The accuracy of prediction was verified by nanoindentation experiment,and the microstructure and macro mechanical properties of porous nanosilver were correlated.Secondly,for indium,a thermal interface material commonly used in electronic packaging,the effects of contact surface roughness,contact pressure and interface medium on the thermal contact resistance between copper and indium were studied.The fractal method was used to establish the surface profile with different surface roughness,and the contact model was established by importing the finite element software.The temperature field of the model was calculated by loading different pressures,and the contact thermal resistance was calculated by Fourier law.The effect of air and grease in the interface gap on the thermal resistance of copper in contact was studied by setting different interface thermal conductivities to simulate the heat transfer characteristics of the contact interface medium.Finally,according to the working environment of the high temperature devices,the structure design and packaging material selection were completed.The ceramic substrate was used as the packaging basis,and the Kovar alloy cap was welded on the ceramic substrate by Au80Sn20 solder to form an air tight cavity.A three-dimensional model of the package structure was established to calculate the thermal stress of each package interconnection position in high temperature environment,and to verify the thermal reliability of the design.By simulating the temperature cycling test conditions,the inelastic strain damage accumulation process of welding was studied,and the cycle life was predicted by the CoffinManson mathematical model.The chip placement process was simulated,and the welding deformation and residual thermal stress of different solder were compared to verify the reliability of the process.According to the parameters of Au80Sn20 solder thickness and metal layer thickness of ceramic substrate,the gas tight welding process was optimized and analyzed,and finally the parameter optimization design was realized.The thesis carried out reliability evaluation and life prediction for high temperature resistant packaging,and studied the properties of high temperature resistant interconnection materials and contact thermal resistance,which has certain reference significance for high temperature resistant packaging of electronic devices.