EFFECT OF INTERFACIAL FACTORS ON FATIGUE LIFETIME OF LEAD-FREE DIE-ATTACH SOLDER JOINT

摘要

Pb-5Sn solder has been widely used for die-attachment in the field of power devises from the point of its high joint reliability and high melting temperature. Recently, because of the harmful effect of lead on the environment and the human health, Sn-8.5Sb and Sn-3.5Ag have been demonstrated if they can be used as a die-attach solder instead of Pb-5Sn. So it is important to estimate the reliability of Sn-8.5Sb and Sn-3.5Ag solder joints relative to Pb-5Sn. In power devise packages, die-attached solders are deformed by shear stress caused by the mismatch of thermal expansion coefficients between Si die and Cu substrate. Thermal cycling test is a popular method to examine reliability of solder joint. But this method takes a lot of time. So the authors have used an isothermal fatigue-test equipment to apply shear stress to Pb-5Sn, Sn-8.5Sb and Sn-3.5Ag solder joints. It was found that the fatigue lifetime was affected by not only solder compositions, but also interfacial factors due to soldering temperatures and electroplated Au layer on Ni coated Cu substrate.