Effect of Palladium Thickness and Extended Isothermal Aging on the Reliability of Solder Interconnects Formed on ENEPIG Surface Finish

Abstract

Surface finishes for copper on printed wiring boards play an important role in the reliability of electrical interconnects. Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG), developed in the mid-1990s to alleviate the "black-pad" problem created by Electroless Nickel/Immersion Gold (ENIG) surface finish, has gained interest for critical system applications. This thesis investigates the effect of palladium layer thickness and extended isothermal aging on the reliability of both tin-lead and tin silver copper solder interconnects under temperature cycling, vibration cycling, and drop loading conditions. Chip array ball grid array (CABGA) packages soldered onto ENEPIG-finished PCBs are subjected to the three previously listed conditions. Reliability and failure analyses are conducted to determine the overall effect of palladium layer thickness and isothermal aging on the reliability of these solder interconnects.