Abstract: Vacuum projection welding process was applied to MEMS package,which could improve yield rate and cut the cost.According to vacuum projection welding process,a thermal-electric-stress coupled field model was established,and the result of projection collapse and nugget growth process was discussed,which showed that the projection collapse occurred in the first half of part-time,then metal around project was melt and final welding nugget was formed.Based on this analysis,the effect of projection tendon angle on welding quality was studied,and the result showed that fine welding quality was achieved when projection tendon angle is 60°.Simulation results agreed with the tensile test results after welding.