Fundamental Investigation into the Mechanisms of Ultrasonic Assisted Single-Component and Multi-Component Low Temperature Sintering for the Assembly of Power Electronic Components

• Applicants: Dr.-Ing. Jens Twiefel; Professor Dr.-Ing. Marc Christopher Wurz
• Subject Area: Microsystems ; Joining and Separation Technology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 456662835

Today's demands on power electronics have increased significantly, especially due to e mobility, so that the connection properties of proven processes such as soldering or bonding no longer meet future requirements. Especially the electrical and thermal conductivity as well as the increased process temperatures are challenges. As a result, silver compound sintering has become increasingly important in recent years. Here, a substrate and a chip are connected by a sintered intermediate layer of silver. Compared to traditional compounds, the properties of silver compound sintering are many times better. Why is this process not yet widely used? The reason are the high values of pressure and temperature required for the process. The process times are significantly longer than with other methods, so that currently only a batch process is economical; however, this leads to irregular joint qualities. This is where our research project comes in. We were able to show that in single chip assembly, the introduction of ultrasound into the bonding layer has a significantly positive effect on the formation of the bond, so that the process temperature, pressure and times were reduced. In addition, the process was extended by an alloying partner to form a new type of multi-component, ultrasonic-assisted process, which is introduced as Ultrasonic Transient Liquid Phase Sintering (UTLPS). Here, we were able to show first positive effects, too. The guiding questions for this research project are: Which mechanisms have a positive effect on the formation of compounds when using ultrasound? Is the diffusion process accelerated by ultrasound analogous to wire bonding? For this purpose, micro- and nanoscale sintering pastes will be developed first. Subsequently, the experimental investigation of the parameter influences on the joint quality will be carried out to enable a separation from the ultrasonic influence parameters. These are mainly the vibration amplitude, the power and the duration of the ultrasound. After the optimal ultrasonic direction (horizontal or vertical) has been determined, the time profile of the process is analyzed. Porosity and mechanical strength are measured to evaluate the joints and supplemented with other analysis methods. The investigations are performed on passive test chips and on active components (diode, IGBT, NTC). Here, the ultrasonic influence on the quality of the connection and the durability as well as possible damage to the components are examined. The research project is concluded with the model-based description of the mechanisms of ultrasonic assisted silver compound sintering. By answering the key questions, silver compound sintering will be significantly improved. This opens up this bonding technology for many more applications.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Jörg Wallaschek