Experimental Investigations on Vertical Ultrasonic Assisted Low Temperature Sintering Process

The low temperature joining technology is an important joining technique for high power electronic components. In this process, a substrate and an electronic component are sintered with silver paste by pressure and temperature at approx. 250 °C. The industry often uses a batch process for this technique. Some disadvantages, however, lead to a limited use of this technique. During the process, high pressure and high process temperature have to be applied for a long process time (several minutes). As a consequence, for many components the conventional sintering technique cannot be used. In this work, ultrasonic assisted low temperature joining process is proposed and investigated. The additional ultrasound energy can substitute a part of the thermal energy and the external heating energy can be thus greatly decreased. In this way, temperature sensitive components can be protected from high temperatures. In addition the vertical ultrasound excitation can better compact the sintered material. Finally, the porosity of the connection layer decreases and the strength and the conductivities of the connection increase. The shear strength could even be doubled with very short process times. The joining process is performed as a single placement, which provides for higher positioning accuracy and better control over the process. The ultrasonic assisted low temperature joining process and the connected components will be presented. The results of the investigations and potentials of the introduction of ultrasound will be emphasized. In particular, a comparison is drawn between the ultrasound assisted and the conventional low temperature joining technology. Here the focus is on the mechanical strength of the connection.