Thermal Cycle Reliability and Failure Mechanisms of CCGA and PBGA Assemblies With and Without Corner Staking

Abstract

Area array packages (AAPs) with 1.27 mm pitch have been the packages of choice for commercial applications; they are now starting to be implemented for use in military and aerospace applications. Thermal cycling characteristics of plastic ball grid array (PBGA) and chip scale package assemblies, because of their wide usage for commercial applications, have been extensively reported on in literature. Thermal cycling represents the on-off environmental condition for most electronic products and therefore is a key factor that defines reliability. However, very limited data is available for thermal cycling behavior of ceramic packages commonly used for the aerospace applications. For high reliability applications, numerous AAPs are available with an identical design pattern both in ceramic and plastic packages. This paper compares assembly reliability of ceramic and plastic packages with the identical inputs/outputs (I/Os) and pattern. The ceramic package was in the form of ceramic column grid array (CCGA) with 560 I/Os peripheral array with the identical pad design as its plastic counterpart. The effects of the following key parameters on reliability of both CCGA and PBGA assemblies were investigated:(1) thermal cycle ranges, -50degC/75degC, -55degC/100degC, and -55degC/125degC; (2) corner staking on failure mechanisms for two thermal cycle profiles, -55degC/125degC and -50degC/75degC; (3) package interchangeability, i.e., using PBGA package on CCGA pad design with a larger pad. Packages were assembled on polyimide boards and their daisy chains were continuously monitored. Optical photomicrographs were taken at various thermal cycle intervals to document damage progress and behavior. Representative samples along with their cross-sectional photomicrographs at higher magnification, taken by scanning electron microscopy and analyzed by energy dispersive X-ray, are also presented. The inspection documents were used to determine crack propagation and failure analyses for packages with and without corner staking. In assemblies with corner staking adhesive, a transition in failure from corner columns to center columns was observed when maximum temperature in thermal cycling profiles changed. This is a new failure mechanism not reported on in literature. Finite element analysis (FEA) was used to predict such global failure mode changes. FEA findings are also presented.