System in Package (SiP) Assembly and Reliability

This paper presents assembly challenges and reliability evaluation of 2.5D (aka, System in Package [SiP]) in fine pitch ball grid array (FPGA). The SiP test vehicles were configured with centrally located integrated circuits (IC) surrounded by eight chip scale packages (CSPs). The ICs and CSPs with either tin-lead (SnPb) or SAC305 balls were assembled onto a fine pitch ball grid array (FPGA) interposer for subsequent assembly into a hybrid configuration. Mix assembly becomes a challenging task and required to be characterized by X-ray for solder-joint quality and by Shadow Moire analysis for warpage characterization. Acceptable assemblies were then subjected to thermal cycling between -40 degrees C and 125 degrees C for reliability evaluation and failure mechanisms assessment. The paper presents details of design, characterization by X-ray and Moire, as well as reliability behavior of the SiP due to thermal cycling exposures. Failure analyses results also presented covering evaluation by optical, scanning electron microscopy (SEM), X-sectioning, and dye-and-pry methods.