Low Temperature Ni/Sn/Ni Transient Liquid Phase Bonding for High Temperature Packaging Applications by Imposing Temperature Gradient

With regulations mandating industry toward Pb-free solders in all electronics, the development of interconnecting materials capable of withstanding harsh thermal conditions becomes one of the key technological elements for the development of next generation wide band-gap semiconductors. By reflowing Ni/Sn/Ni interconnects under temperature gradient, a new transient liquid phase (TLP) bonding process is proposed for high temperature packaging applications in this study. The evolution of the dominant Ni3Sn4 intermetallic compounds (IMCs) depends strongly on temperature gradient. The essential cause of such dependence is attributed to the different amounts of Ni atomic fluxes being introduced into the interfacial reaction between the new and conventional TLP bonding processes. Under the effect of temperature gradient, mass thermomigration of Ni atoms from the hot end toward the cold end promotes the total Ni atomic flux for interfacial reaction. As a result, the total growth of IMCs is significantly accelerated. The new TLP bonding process consumes limited cold end Ni substrate. The mechanism for the new TLP bonding process is discussed and experimentally verified in this study.