Improvement in thermal reliability of a flip chip interconnection system joined by Pb-free solder and Au bumps

The failure mechanism and improvement in the thermal reliability were studi ed of a new dip chip interconnection system using Au bumps on Si chips and Sn bumps on substrates. The thermal reliability of this hip chip depended o n the diffusion behaviour at the Au/Sn bonded interface. Kirkendall voids, which were formed at the Au/Sn bonded interface, induced cracks and impaire d the reliability. By the addition of Ag into the Sn bumps, the reliability was improved, due to the formation of an Ag concentrated layer at the Au/S n bonded interface which acted as a barrier to Au-Sn further interdiffusion and suppressed the Kirkendall voiding. The AuSn phase grew faster than the other Au-Sn intermetallic compounds did at the Au/Sn bonded interface afte r annealing. Activation energy for AuSn growth was 29.3 kJmol(-1).