Intermetallic growth of wire-bond at 175 degrees 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 ex amination of wire-bond and the other was without compound encapsulant used for the plane view examination of wire-bond interface. These samples were a ged 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 p hases. 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 phas e layer thickness increased to similar to6 mum and reached the steady state . A titanium-rich thin layer was also induced within the reacted phase laye r. Three ternary phases as AlAu2Ti, AlAuTi, and Al2Au2Ti are found in this titanium-rich layer. In particular, Al2Au2Ti could be a new phase.