Microstructure and Reliability Studies of Mixed Sn-Pb and Pb-Free BGA Soldering
Authors: Ken Kramer, Ph.D., Corey Nelson, Alok Sharan, Ph.D. Company: Micro Systems Engineering, Inc. Date Published: 9/28/2014
Abstract: Backward compatible mixed-alloy soldering has been carried out on area array packages with Pb-free bumps and eutectic SnPb soldering paste. Thermal fatigue reliability testing indicates reduced performance relative to pure SnPb or Pb-free solder joints. Microstructural studies show evidence of shrinkage voids within the Pb-rich eutectic phase regardless of the peak reflow temperature and level of mixing. There is inconsistent evidence of segregation of the Pb-rich eutectic phase to the pad surfaces. Underfill is recommended to mitigate the increased risks of mixed alloy soldering of area array.