Sintered Ag Joints on Copper Lead Frame TO220 by Pressure Sintering Process with Improved Reliability and Bonding Strength

Inhalt:
In recent years, silver sinter materials have attracted rising attention to use 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 non-pressure sintering process based on the presence or absence of applied pressure during the sintering process. Non-pressure sintering process is the common process for lead frame TO220 application. Ag sinter paste is usually dispensed on the lead frame and the die is then placed on the deposited paste. Subsequently, the non-pressure sintering process is performed in a programmable oven under nitrogen or air atmosphere. The total non-pressure sintering process takes approximately 4 hours and the porosity of sinter layer after non-pressure sintering process is much higher than the porosity of sinter layer obtained by pressure sintering process. It is well known that the thermal and electrical conductivities are strongly related to the porosity of sinter layer [1]. Thermal and electrical conductivities increase with increasing density of sintered Ag joints. Lower porosity leads to higher reliability and stronger bonding of sintered Ag 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 sintered Ag joints on TO220 lead frame and to shorten the total process time.