Pb-Sn Alloy Microstructure: Potential Reliability Indicator for Interconnects

Investigation of the microstructure and chemistry of Pb-Sn alloy interconnects by scanning electron microscopy (SEM) and X-ray microanalysis shows that certain physical and chemical characteristics of the Pb-rich and Sn-rich phases are indicative of crack formation during temperature cycling. Those solder alloy interconnects that crack when temperature cycled exhibit significantly different microstructure patterns compared with solder interconnects that do not crack. Energy dispersive X-ray (EDX) data indicate that cracking is more pronounced when impurities such as Al, Au, or W are inadvertently introduced into the alloy material.