Microstructural evolution in Sn/Pb solder and Pb/Ag thick film conductor 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. A decrease in adhesion strength occurs when the sample is aged at 130°C for long periods for time. Microstructural analysis reveals the formation of intermetallic compounds Pd₃Sn, Pd₂Sn, Pd₃Sn₂, PdSn, Pd₃Pb, Ag₅Sn, and Ag₃Sn. A possible mechanism of adhesion loss for the conductor is described. In the initial stage, the fracture interface is located where the Pd₃Pb exists, which is near the solder. However, the fracture takes place within the solder after aging. It is argued that volume change of the conductor film resulting from the intermetallic formation and incoherency between the compounds due to grain growth are major factors in the degradation of the peel strength