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

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.