Interfacial Reactions Between Sn-3.8 Ag-0.7cu Solder And Ni-W Alloy Films

In this study, interfacial reactions between Ni-W alloy films and Sn-3.8Ag-0.7Cu solder have been investigated. Ni-Wa lloys films with tungsten content in the range of 5.0 - 18.0 at. % was prepared on copper substrate by electrodeposition in ammonia citrate bath. Solder joints were prepared on the Ni-Wc oated substrate at a reflow temperature of 250 degrees C. The solder joint interface was investigated by cross-sectional scanning electron microscopy, energy dispersive X-ray spectroscopy and electron back scatter diffraction. It has been observed that a (Cu, Ni)(6)Sn-5 layer formed on the Ni-W alloy film after reflow. The thickness of the ( Cu, Ni)(6)Sn-5layer was found to decrease with the increase of tungsten content in the Ni-W film. An additional layer with a bright appearance was also found to form below the (Cu,Ni)(6)Sn-5 layer. The bright layer was identified to be a ternary phase containing Sn, Cu, Wand Ni. The bright layer is found to be amorphous and is suggested to have formed through solid state amorphization caused by anomalously fast diffusion of Sn into Ni-W film.