Temperature cycling effects between Sn/Pb solder and thick film Pd/Ag conductor metallization

Thermal cycling effects on solder joints between thick-film mixed bonded conductor and Sn/Pb solder are investigated. Microstructural evolution of the interfacial morphology, elemental, and phase distribution are probed with the aid of electron microscopy and X-ray diffraction. Microstructural analysis reveals the formation of intermetallic compounds Pd₃Sn, Pd₂Sn, Pd₃ Sn₂, PdSn, Pd₃Pb, Ag₅Sn, and Ag ₃Sn, after thermal cycles from -55 to +125°C. A transverse crack is observed across the joint from the conductor/substrate interface to the conductor/solder interface, which results in the failure of the joint. The microstructural analysis and stress analysis reveal that the transverse crack is initiated by the microcracks at the glass-penetrated region of the substrate and propagates under a tensile stress due to the solder shrinkage. An appropriate joint geometry and a materials system with good interface strength and with negligible thermal expansion mismatch are important in the enhancement of the life time for the solder joints in thick-film microelectronics