TEMPERATURE CYCLING EFFECTS BETWEEN SN/PB SOLDER AND THICK-FILM PD/AG CONDUCTOR METALLIZATION

Thermal cycling effects on solder joint 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, Pd3Sn2, PdSn, Pd3Pb, Ag5Sn, and Ag3Sn, after thermal cycles from -55 to + 125-degrees-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.