Analysis of residual stress after reflow soldering of QFN package

Abstract

The finite element analysis model of residual stress after reflow soldering of QFN lead-free solder joints is established in this paper, and the residual stress after reflow soldering was analyzed under thermal structural coupling conditions. With the solder joint height, lead pitch, chip thickness and PCB thickness as design factors, 9 solder joints model of QFN with different levels combination were designed and the maximum residual stress values of the 9 solder joints model of QFN were obtained by simulation analysis. And carried out the range analysis for structural parameters of the QFN solder joints model. The results show that the residual stress of QFN solder joints is unevenly distributed. The maximum residual stress appears in the contact point between the solder joints and the chip and farthest from the chip center. The order of the influence for residual stress after reflow soldering from large to small is solder joint height, chip thickness, PCB thickness and lead pitch. Provides theoretical guidance for controlling residual stress after reflow soldering of QFN.