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Quad flat no-lead (QFN) package is manufactured in a molded array format that maximizes product throughput. However, the excessive warpage and stress induced by thermal mismatch among different materials may affect the assembly processes due to the large matrix of the molded strip. In this study, both experimental and modeling works are resorted to analyze the warpage and wire sweep of QFN molded strip. Effect of QFN package size is investigated so as to provide the relation between warpage and metal to mold compound ratio. Design guideline for optimum metal to mold compound ratio can be obtained. Nonlinear large deformation finite element analysis has been performed to investigate the impact of die size and mold compound material properties on the warpage and stress induced. Thermal loading is applied to simulate the cooling process after molding. For wire sweep analysis, a design of experiment is performed by using three factors, i.e. transfer time, transfer force, and two types of mold compound. The results show that the new mold compound induced lower die stress but slightly higher wire sweep than current material.
Date of Conference: 10-12 Dec. 2007