Microstructural evolution in Sn/Pb solder and Pd/Ag thick film conduction metallization

Intermetallic compound formation between thick-film mixed bonded conductor and Sn/Pb solder is investigated. Microstructural evolution of the interfacial morphology, and elemental and phase distribution are probed with the aid of electron microscopy and X-ray diffraction. Mechanical interlocking between the conductor and the substrate is shown to exist. Penetration of Bi element into the substrate is observed. Decrease in adhesion strength occurs when the sample is aged at 130°C for a long period of time. Microstructural analysis reveals the formation of the intermetallic compounds Pd₃Sn, Pd₂ Sn, Pd₃Sn₂, PdSn, Pd₃Pb, Ag₅ Sn, and Ag₃Sn. The grain growth of the compounds after aging is also observed. It is argued that conductor swelling caused by tin diffusion into the conductor film and volume change caused by the intermetallic formation are the major reasons for the degradation of the peel strength