Abstract

PBGA packages are very sensitive to humidity, moisture-induced failures such as popcorn crack and delamination during moisture preconditioning and reflow soldering are major concerns for the lifetime and reliability of PBGA packages. In this paper, a continuous experiment up to 1500h at JEDEC Level 1 was executed in a constant temperature-humidity chamber to characterize the moisture absorption behavior of EMC (Epoxy molding compound). At the same time, an approximate fitting method called Dual-Fickian was applied to better describe and simulate the moisture diffusion process during moisture preconditioning. Besides, the CHS (coefficients of hygroscopic swelling) of five EMC materials at four different temperatures were characterized. The correlation of CHS with temperature and its relationship with the Tg (Glass Transition Temperature) were examined. On this basis, a simplified PBGA package model was established and the coupling effects of thermal stress, hygroscopic swelling stress, and vapor pressure on this package in the reflow environment were quantitatively analyzed with FEM simulation. Furthermore, a tentative optimal structure design was proposed to release the layered stress and improve the reliability of the package.

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