Intermetallic formation on the fracture of Sn/Pb solder and Pd/Ag conductor interfaces

Intermetallic formation between a thick-film mixed bounded conductor and Sn/Pb solder is investigated. The 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 the element Bi 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, Pd ₂Sn, Pd₃Sn, PdSn, Ag₅Sn, and Ag₃ Sn. 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