Abstract
Sn-0.7 wt.%Cu alloy is a promising Pb-free solder, and Ni is a commonly used barrier layer material. Sn-0.7 wt.%Cu/Ni couples are prepared and reacted at 250 °C. The interfacial reactions are examined, reaction mechanisms are proposed, and solder size effects upon the interfacial reactions are investigated. The Cu 6 Sn 5 phase forms and grows with longer reaction time in the initial stage. Then the Cu 6 Sn 5 phase layer fractures and part of the layer detaches. Microstructural analysis indicates that the detached and the attached layers have finer and larger grains, respectively, and the Cu 6 Sn 5 phase has a near hexagonal prism shape. The freshly exposed Cu 6 Sn 5 phase layer continues to grow and then the reaction layer thickness reaches a plateau. The Ni 3 Sn 4 phase forms and the Cu 6 Sn 5 phase layer disintegrates in the later stage of the reactions. The transition timing of the different stages is affected by the amounts of solder used. © 2005 Acta Materialia Inc. All rights reserved.