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 degreesC in air from 0 h to 1008 h. It is found that the normal product which was ready on board existed similar to1 mum Au2Al and Au5Al2 phases. The Au2Al phase was then transformed to Au5Al2 phase in a 4 similar to 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 similar to4 mum after 240 h aging. The Au4Al phase became the major phase after 336 aging h. The reacted phase layer thickness increased to similar to6 mum 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.