Wettability of Al2O3 by Liquid Cu as Influenced by Additives and Partial Transient Liquid-Phase Bonding of Al2O3

The effect of additions (Cr, Ni and 80Ni·20Cr alloy) on the wetting characteristics of liquid Cu on Al2O3 has been studied using a sessile drop method in a vacuum at 1150°C. Through the use of microdesigned multilayer Cu/80Ni·20Cr/Cu interlayers, PTLP (Partial Transient Liquid-Phase) bonding of Al2O3 has been achieved in a vacuum at 1150°C.80Ni·20Cr alloy and Cr additions reduced the contact angle of liquid Cu on an Al2O3 substrate. For Cu with 10 mass%80Ni·20Cr alloy and with 6 mass%Cr added, contact angles decreased with time reaching values of ≤90° and ≤70°, respectively, at the end of the measurements. From SEM and EPMA observations, dissolution of the additions occurred, and thereby introduced Ni and Cr into liquid Cu droplets. The uniform distribution of Ni throughout the Cu droplet and the segregation of Cr at the Cu droplet/Al2O3 interface were observed in the solidified specimen.The average strength for Cu/80Ni·20Cr/Cu interlayer bonded Al2O3 was 137 MPa with a standard deviation of ±33 MPa. Failure of these samples occurred along the Al2O3/interlayer interface. From SEM and EPMA observations, some dissolution of 80Ni·20Cr core layer into liquid Cu film and the diffusion of liquid Cu into 80Ni·20Cr core layer occurred, however, because of the thicker Cu layers used, homogenization was incomplete.The results demonstrate that at the bonding temperature, the dissolution of Cr into liquid Cu film improved the wettability of liquid Cu film on Al2O3 and facilitate the formation of reliably strong joint of PTLP bonded Al2O3 using Cu/80Ni·20Cr/Cu interlayer.