Reliability of Au-Ge and Au-Si Eutectic Solder Alloys for High-Temperature Electronics

High-temperature electronics will facilitate deeper drilling, accessing harder-to-reach fossil fuels in oil and gas industry. A key requirement is reliability under harsh conditions for a minimum continuous operating time of 500 h at 300A degrees C. Eutectic solder alloys are generally favored due to their excellent fatigue resistance. Performance of Au-Ge and Au-Si eutectic solder alloys at 300A degrees C up to 500 h has been evaluated. Nanoindentation results confirm the loss of strength of Au-Ge and Au-Si eutectic solder alloys during thermal aging at 300A degrees C, as a result of grain coarsening. However, the pace at which the Au-Ge eutectic alloy loses its strength is much slower when compared with Au-Si eutectic alloy. The interfacial reactions between these eutectic solder alloys and the underbump metallization (UBM), i.e., electroless nickel immersion gold (ENIG) UBM and Cu/Au UBM, have been extensively studied. Spalling of Au3Cu intermetallic compound is observed at the interface between Au-Ge eutectic solder and the Cu/Au UBM, when aged at 300A degrees C for 500 h, while the consumption of ENIG UBM is nominal. Unlike the Au-Si solder joint, hot ball shear testing at high temperature confirmed that the Au-Ge joint on ENIG UBM, when aged at 300A degrees C for 500 h, could still comply with the minimum qualifying bump shear strength based on the UBM dimension used in this work. Thus, it has been determined that, among these two binary eutectic alloys, Au-Ge eutectic alloy could fulfill the minimum requirement specified by the oil and gas exploration industry.