Abstract: A finite element thermal analysis model of welded component for an aerospace electronic product was established in the cooling process,and the variation of the thermophysical parameters of the Si-Al shell and Pb-Sn solder with temperature was investigated. Taking the minimum first principal stress produced in LTCC substrate as the optimization object,the optimized cooling process parameters were obtained by the orthogonal test method. Simulation and experimental research on the reflow welding cooling process were carried out under the process parameters. The results showed that the overall deformation of LTCC substrate was a bulge from the bottom of the substrate to the inside of the shell,which was consistent with the inspected results. The maximum value of the first principal stress of LTCC substrate distributed at the corners of the substrate,but it was not big enough to cause crack. The welding quality of LTCC substrate could be effectively improved by the cooling process parameters proposed in this paper.