Electro-thermo-mechanical Design Of SiC MOSFET Modules With Multiple Chips In Parallels

The package volume of SiC power module is decreasing,while the power is increasing,which leads to a great thermal-flux increase of power module.The longterm reliability of SiC modules should be concerned,especially a SiC module with double-sided packaging structure.It was believed that more significant thermomechanical stresses could easily cause fatigue failure of die attachment.Moreover,the current size of SiC MOSFET chips is small and the flow capacity is limited by the manufacturing process and product yield.However,in industrial applications,multiple chips in parallels are often required for SiC MOSFET power module with very large power rating.Therefore,unbalanced current is inevitable as well as uneven distribution of temperature and stress.However,there are few reports on the design optimization of temperature and stress of the double-sided multi-chip SiC MOSFET module.It was because it was complex to design uniform temperature and stress because of complex coupling effects.Consequently,this paper aims to study how to design uniform temperature and stress distribution of a double-sided multi-chip SiC MOSFET module based on electro-thermo-mechanical coupling.Firstly,the influence of thicknesses of sintered silver,buffer and liner on temperature and stress distribution of a double-sided SiC MOSFET module using multiphysical fields coupling by ANSYS WORKBENCH.It is found that the maximum temperature of sintered silver attachment rises with the increase of its thickness,while the peak equivalent stress decreases.The equivalent stress of the silver silver attachment of the double-sided SiC module with a buffer can be decreased by 15%.The maximum temperature of the sintered silver attachment is first increased and then decreased with the increase of the buffer thickness,while the peak equivalent stress of the sintered silver attachment is decreased monotonically with the increase of the buffer thickness.The maximum temperature of the sintered silver attachment is first decreased and then reach saturation,while the peak equivalent stress of the sintered silver attachment is increased monotonically with the increase of the liner thickness.Secondly,a response surface optimization method is used to optimize the design of multiple variables to reduce the temperature and stress levels of the chips and the sintered silver attachment and improve the reliability of the SiC MOSFET module.It is also glad to see the parasitic parameters decreased slightly after optimization.Then a modified Coffin-Manson equation is used to predict the fatigue life of the sintered silver attachment of the double-sided SiC modules.Finally,heat spreader is optimized by the response surface optimization.The maximum temperature and stress of the chip are decreased after the optimization.In order to further improve the uniformity of the temperature and stress,we propose increasing the radiator area locally.At the same time,the results show that the average temperature of the chip decreased by about 3? and the average stress decreased by about 7 MPa.