Creep analysis of solder bumped direct chip attach (DCA) on microvia build-up printed circuit board with underfill

Abstract

The creep analysis of solder-bumped flip-chip on microvia build-up printed circuit board (PCB) with underfill encapsulant subjected to thermal cycling conditions are presented. Emphasis is placed on the effects of the conventional PCB's additional microvia build-up circuits on the solder joint reliability of the direct chip attach (DCA) assembly. The 62Sn-36Pb-2Ag solder joints are assumed to obey the Garofalo-Arrhenius steady-state creep constitutive law. The shear stress and shear creep strain hysteresis loops, shear stress history, and shear creep strain history at the corner solder joint, and the von Mises stress and effective plastic strain in the microvia are presented for a better understanding of the thermal-mechanical behaviors of the solder bumped flip chip on build-up PCB with microvia circuits. It is found that, due to the very large thermal expansion mismatch among the silicon chip, solder joints, underfill encapsulant, build-up resin, electroplated copper microvia, and the FR-4 epoxy glass PCB, the stress and strain in the solder joints are higher than those of a DCA on a conventional PCB.