Impact of ingressed moisture and high temperature warpage behavior on the robust assembly capability for large body PBGAs

Abstract

The critical interplay of ingressed moisture, peak reflow temperature, package materials, and the resultant warpage behavior is shown to directly affect the board mount assembly capability of large body size plastic ball grid array (PBGA) packages. Thermal shadow Moire measurements are used to characterize package warpage demonstrating that the amount of ingressed moisture can significantly impact the high temperature warpage response for PBGAs. Board mount assembly experiments using both dry and moisture ingressed 37.5 nun PBGAs reveal warpage to be a function of both higher ingressed moisture content and higher peak reflow temperatures and can cause solder ball shorting. The effect of package construction using varying mold compound types is shown to significantly affect the total warpage response and found to directly impact board assembly performance. Higher peak reflow temperature capability, as required for Pb-free, is shown to be strongly dependent on the package warpage characteristics. Traditional moisture sensitivity level (MSL) classification requirements, as determined by package delamination and popcom response, must be modified to include an assessment of package warpage at peak reflow temperatures for larger body size PBGAs.