The study of failure mechanism and chip warpage for DCA components

Abstract

Encapsulation of Direct Chip Attach (DCA) devices helps reduce the impact of the thermal stress that results from the mismatch in the coefficient of thermal expansion (CTE) between the silicon chip and the substrate. In the encapsulated DCA assembly, the warpage of chip was observed due to the CTE mismatch between the silicon chip and the encapsulant/substrate. During the cooling stage of the curing for underfill, the encapsulant and the silicon die shrink at different rates and result in concave warpage of the chip. This scenario has been an issue which may degrade the package reliability or even assembly yield. Also, the adhesion of the encapsulant to the chip and the board coating are essential to the reliability of the package. Studies the adhesion characteristics of an encapsulant to a DCA package. The quality of the encapsulation was inspected using a Scanning Acoustic Microscope (SAM). The various delamination mechanisms were then studied. Comparisons were made between samples assembled by different materials used, such as chip passivation layer, encapsulant materials and fluxes. Finally, the effect of encapsulant pre-cure and annealing on the chip warpage was explored.