Intermetallic growth of wire-bond at 175°C high temperature aging

Abstract

Two types of samples were applied in this wire-bond evaluation work for an Al-pad diffusion process. One was finished product for the cross-section examination of wire-bond and the other was without compound encapsulant used for the plane view examination of wire-bond interface. These samples were aged at 175 C in air from 0 h to 1008 h. It is found that the normal product which was ready on board existed ∼1 μm Au₂Al and Au₅Al₂ phases. The Au₂Al phase was then transformed to Au₅Al₂ phase in a 4 ∼ 72 h aging period. The Au₄Al phase formed along with the Au₅Al₂ phase in 72 h to 240 h aging period showing some porosity within the reacted phases. The total phase thickness increased to ∼4μm after 240 h aging. The Au₄Al phase became the major phase after 336 aging h. The reacted phase layer thickness increased to ∼6 μm and reached the steady state. A titanium-rich thin layer was also induced within the reacted phase layer. Three ternary phases as AlAu₂Ti, AlAuTi, and Al₂Au₂Ti are found in this titanium-rich layer. In particular, Al₂Au₂Ti could be a new phase.