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 degrees 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 Pd/sub 3/Sn/sub 2/, Pd/sub 2/Sn, Pd/sub 3/Sn, PdSn, Ag/sub 5/Sn, and Ag/sub 3/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.<
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