Solder joint formation simulation and reliability study of quad flat no lead package

Abstract

Based on the minimal energy principle, the shape prediction models of the 0 . 5 mm pitch, 16 pin quad flat no lead (QFN) package solder joints were developed. The influence of the process parameters including the pad length, the pad width and the stand-off on the solder joint shape of QFN was studied. Utilising the surface coordinate exported from the QFN solder joint shape prediction models, finite element analysis (FEA) models were set up and then the non-linear FEA of the QFN solder joints under thermal cycles was performed by ANSYS. The stress-strain distribution within the solder joints and the maximum strain range of the solder joint were determined. The thermal fatigue life of the QFN solder joint was calculated based on the maximum strain range and the Coffin-Manson equation. The results show that the process parameters influence the QFN solder joint shape distinctly, and the QFN solder joint with different pad lengths, pad widths and stand-offs has various stress-strain distributions and fatigue life. The QFN solder joint with a pad length of 0 . 7 mm, a pad width of 0 . 28 mm and a stand-off of 0 . 125 has a fatigue life of 252 cycles under thermal cycles.