Journal of SMT Article


Author: Tong Yan Tee et al.
Company: STMicroelectronics
Date Published: 4/1/2004   Volume: 17-2

Abstract: The warpage induced after the post mold cure (PMC) process is critical for matrix TFBGA (thin fine pitch BGA), because it affects the solder ball attach process and also the subsequent package singulation process. In this paper, comprehensive warpage analysis is performed on matrix TFBGA by means of experimental warpage measurement, real-time shadow moiré measurement with temperature profile, material characterization of mold compound viscoelastic properties, and finite element modeling of package warpage with consideration of chemical shrinkage and viscoelasticity effects.

Accurate temperature and time dependent viscoelastic material properties are required for the mold compound materials because the curing profile and cooling rate during PMC are important. Shadow moiré measurements show that the block warpage reaches the maximum value, around the Tg of mold compound, rather than at the room temperature after the PMC or reflow cooling. The validated 3D viscoelastic finite element model explains that the observation from shadow moiré is due to the global CTE mismatch between mold compound and substrate materials.

The effect of chemical shrinkage during molding and PMC is significant, too. Additionally, the sensitivities of mold compound and substrate material properties to block warpage are also studied. The finite element model developed can be a useful warpage predicting tool for future design of matrix BGA.

Key words: TFBGA, warpage, viscoelastic, modeling, shadow moiré, chemical shrinkage.

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