Abstract: Among the third-generation wide-band semiconductors, Si₃N₄ ceramics have become the most promising insulating thermal dissipation substrate material due to its combination of high strength and high thermal conductivity. According to the multi-criteria decision-making method (junction temperature, thermal resistance, coefficient of thermal expansion (CTE) mismatch, etc.), thermal-stress coupling simulation is used to investigate the comprehensive effects of replacing different solder layers and substrate materials on the thermal characteristics and reliability of the module when combined with Si₃N₄ ceramic layer. The results show that the optimal combination of nano-silver solder layer and CuW substrate is the one that combines with Si₃N₄ ceramic layer with good thermal characteristics and reliability. Temperature cycling simulation is used to verify the optimized model, and the results show that the average stress of the optimized model is decreased by 16.6%, and the average first principal strain is reduced by 10.2%. This conclusion is a reference for the reliability evaluation of Si₃N₄ ceramic substrate when it is used in combination with other components as a whole.