Warpage measurements of laminate based BGA packages at elevated temperatures and comparison with real board assembly behaviour

Abstract

This paper is about warpage of laminate substrate based BGAs and fine pitch BGAs at lead-free board assembly reflow temperatures using shadow moire technique. Various constructions (e.g. single die devices and multi chip modules) and different die and package sizes as well as different molding compound materials were considered in this study. A simple model for predicting high temperature warpage for single die devices based on the distance between package corner and die corner was developed. The comparison of the warpage results with and without moisture soaking according JEDEC MSL 3 did not exhibit a significant influence on high temperature warpage. The shadow moire test results at elevated temperatures are compared with solder joint height distributions measured in cross sections after real lead-free board assembly. A clear correlation of the solder joint height distributions with the package warpage status at 170°C during cooling phase was found. This is much lower than the mominal solidification temperature of lead-free solder. This study helps to understand the influencing factors of BGA warpage and its role for board assembly.