Sintered Ag joints on copper lead frame TO220 by pressure sintering process with improved reliability and bonding strength

Abstract

In recent years silver sinter materials have attracted rising attention as interconnect materials in the power electronic devices mainly due to the requirement for devices with longer lifetime, higher efficiency, lower manufacturing cost and the most important is devices that do not contain lead. Silver sintering process are generally classified as pressure and nonpressure sintering process based on the presence or absence of applied pressure during sintering process. Non-pressure sintering process is the common process for lead frame TO220 application. Silver sinter paste is usually dispensed on the lead frame and followed by die placement. Subsequently, non-pressure sintering process is performed in a programmable oven under nitrogen or air atmosphere. Typical non-pressure sintering profile takes approximately 4 hours to complete. The porosity of sinter layer obtained by non-pressure sintering process is higher than the porosity of sinter layer obtained by pressure sintering process. It is known that thermal and electrical conductivities are strongly related to the porosity of sinter layer. Thermal and electrical conductivities increase with increasing density of silver sintered joints. The porosity of sinter layer can be decreased by applying pressure during sintering process. The main focuses of this study are to increase the bonding strength of silver sintered joints on TO220 lead frame and to shorten the total process time.