Investigations on Silver Sintering using an Ultrasonic Transient Liquid Phase Sintering Process

Silver sintering is a very important state-of-the-art joining process in the production of high-performance electronic components, as conventional assembly and connection technology is reaching its limits, especially due to the increasing requirements of e-mobility. Silver sintering is particularly suitable for today's high-performance electronic components such as IGBTs or diodes. However, the silver compound sintering process is not yet widely used. This is due to the very high process pressures, the high process temperatures, long process times and fluctuations in the strength of the joint. This work shows the potential and preliminary results on the optimization of silver compound sintering by using ultrasound in the joining zone and by adding low melting alloy partners to reduce the required sintering temperature. This generates a completely new process which is introduced by the authors as Ultrasonic Transient Liquid Phase Sintering (UTLPS). Without ultrasound, the shear strength of pure silver sintering joints increases as the temperature and process duration increase. When ultrasonic vibration is applied, for selected process parameters, the shear strength could be improved from 6 MPa to 12 MPa with the increasing of ultrasonic power. The addition of low-melting point alloy partners reduces the required sintering temperature. The combination of the addition of the alloying element indium and the application of ultrasonic vibration leads to an increase in shear strength with a maximum value of about 20 MPa.