INTERMETALLIC FORMATION ON THE FRACTURE OF SN/PB SOLDER AND PD/AG CONDUCTOR INTERFACES

Intermetallic formation between thick film mixed bonded conductor and Sn/Pb solder is investigated. Microstructural evolution of the interfacial morphology, elemental and phase distribution is probed with the aid of electron microscopy and X-ray diffraction. There exists mechanical interlocking between conductor and substrate. Penetration of a Bi element into the substrate is observed. A decrease in adhesion strength occurs when the sample is aged at 130°C for a long period of time. Microstructural analysis reveals the segregation of Pb-rich and Sn-rich phases in aged samples and formation of intermetallic compounds Pd3Sn2, Pd2Sn, Pd3Sn2, PdSn, Ag5Sn, and Ag3Sn. It is argued that conductor swelling caused by tin diffusion into the conductor film and volume change resulting from the intermetallic formation are major factors in the degradation of the peel strength. © 1990 IEEE