Interfacial Reactions in the Cu/Ga/Co and Cu/Ga/Ni Samples

To fundamentally understand the solid-liquid interdiffusion joining processes between a Cu electrode and Co and Ni barrier layers using a Ga solder, the interfacial reactions in the Cu/Ga, Co/Ga, Ni/Ga, Cu/Ga/Co and Cu/Ga/Ni samples have been systematically examined. The reaction phases at the Cu/Ga interface in the Cu/Ga, Cu/Ga/Co and Cu/Ga/Ni samples reacted at 200 degrees C, 350 degrees C and 500 degrees C are all the same, and are (3)-Cu9Ga4 and CuGa2, (2)-Cu9Ga4 and (1)-Cu9Ga4 respectively. No Co/Ga interfacial reaction phase was found in either the Co/Ga or Cu/Ga/Co samples reacted at 200 degrees C, and the reaction phase is CoGa3 when reacted at 350 degrees C and 500 degrees C. The reaction phase in the Ni/Ga couples reacted at 200 degrees C and 350 degrees C is the Ni3Ga7 phase while it is Ni2Ga3 at 500 degrees C. In the Cu/Ga/Ni samples, no Ni/Ga interfacial reaction phase is observed at 200 degrees C, and the Ni3Ga7 and Ni2Ga3 phases formed at 350 degrees C and 500 degrees C have 8.5 at.%Cu and 14.0 at.%Cu solubilities. The growth rates of the reaction phases have been determined, and the Ga consumption rates in the Cu/Ga/Co and Cu/Ga/Ni samples at 200 degrees C, 350 degrees C and 500 degrees C were calculated. It is observed that the consumption rates increase with the square root of the reaction time, and the consumption rate constants are 39.2 m/h(0.5) and 77.3 m/h(0.5), respectively.