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: from 2021 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 456662835

• Final Report Year: 2025

Final Report Abstract

Silver compound sintering is an important joining process in the current production of high-performance electronic components. The advantages of the joining process are high electrical and thermal conductivity, and high mechanical strength. However, high process pressures, high temperatures, long process times (> 30 minutes) and large fluctuations in the resulting strength of the joints limit the use of this joining technology for single-chip assembly. The project focuses on researching the impact of ultrasound (US) and alloying elements (especially tin) on the silver sintering process. The central working hypothesis is, that alloying elements and ultrasound can overcome the mentioned limitations of classic silver sintering. In the course of the project, the test bench was first extended resulting in a test stand with a semiautomatic pick-and-place system, optimized force control and an optimized ultrasonic sonotrode that reduces process-related fluctuations. Furthermore, heterogeneous sinter pastes containing the metallic alloying element tin were developed. The positive influence of the alloying element on the quality of the joint was confirmed by increasing shear strengths with increasing tin content up to an optimum at 27.5 at%. Optimized process parameters (250 °C process temperature, 180 s process time, 20 MPa process pressure) with specific working flow for sintering processes without the use of ultrasound allowed for joints with high shear strengths of over 60 MPa. By using ultrasound, the process time could be reduced by a factor of 3 to 60 s with unchanged joint quality (porosity, shear strength, thermal and electrical conductivity), so that efficient single-chip assembly is feasible. The expected additional temperature increase through the use of ultrasound was determined during the joining process using specially designed and in House made thin-film sensors. Only small temperature changes of up to 7 °C were measured. This leads to the conclusion, that the proven positive effect of the ultrasonic energy cannot be attributed to a thermal effect. Finally, with the help of the research data obtained in the project, empirical models were created that describe the energy flow in the joining process and the parameter influences on the joint quality.

Publications

• Investigations on Silver Sintering using an Ultrasonic Transient Liquid Phase Sintering Process. 2021 IEEE 23rd Electronics Packaging Technology Conference (EPTC), 288-291. IEEE.
  Hadeler, Steffen; Seefisch, Henning; Ottermann, Rico; Long, Yangyang; Dencker, Folke; Wurz, Marc Christopher & Twiefel, Jens
  
• Influence of Microscale Tin Particles on Mechanical Properties of Silver Sintering Joints with Reduced Processing Parameters. 2023 IEEE 73rd Electronic Components and Technology Conference (ECTC), 676-681. IEEE.
  Hadeler, Steffen; Long, Yangyang; Ottermann, Rico; Dencker, Folke; Twiefel, Jens & Wurz, Marc Christopher
  
• Measurement of the Ultrasound Induced Temperature Change in an Ultrasonic Assisted Silver Sintering Process. 2023 IEEE SENSORS, 1-4. IEEE.
  Hadeler, Steffen; Long, Yangyang; Twiefel, Jens & Wurz, Marc Christopher