Au-Sn bonding metallurgy of TAB contacts and its influence on the Kirkendall effect in the ternary Cu-Au-Sn system

The authors summarize work done on different Au-Sn-Cu and Au-Cu metallurgies in the inner lead bond (ILB) area. The influence of Kirkendall-pore formation in the Cu-Au-Sn system as a degradation mechanism is shown. This effect together with the formation of a new type of ternary intermetallic compound is observed during thermal aging in contacts with a direct interface between the eutectic 80/20 Au-Sn alloy and copper. The zeta-phase (Au/Sn 90/10) acts like a diffusion barrier, which inhibits the pore formation associated with copper diffusion. The composition of the ternary intermetallic compounds, their growth constant, and their activation energy were determined. The possibility of increasing the contact reliability by producing a reliable Au-Sn metallurgy during the ILB-process is shown