Ultrasonic-assisted silver sintering for accelerated interconnects fabrication in power electronic devices

Due to its excellent electro-mechanical properties and high remelting temperature, Ag particle sintering becomes a popular approach to create reliable die-substrate interconnections in high-performance power electronic devices. The long processing time of this technique, however, leads to a low packaging efficiency, especially when batch sintering is not applicable. In this study, a novel ultrasonic-assisted sintering (UAS) method is proposed, where ultrasonic vibration was applied during the thermo-compression stage of conventional Ag micro-particle sintering (CS) to accelerate individual sintering processes. The shear test results showed that ultrasonic-assisted sintering between diode die and DBC substrate was successfully accomplished and compared with conventional sintering technique, the sintering speed was increased by three times. Microstructure investigations demonstrated a faster densification process in UAS than in CS. It is assumed that the acoustoplastic effect greatly promoted the plastic deformation of Ag particles and enlarged the contact areas among Ag particles, especially at the early stage of thermo-compression; as vibration introduced more crystal defects, the diffusion activation energy was significantly reduced, leading to a faster diffusion process and denser joints. The ultrasonic-induced friction was considered to be limited while particle rearrangement, cavitation or recrystallization during UAS were unlikely to occur. Preliminary thermal aging and thermal shock tests revealed no measurable differences between the mechanical reliability of CS and UAS joints. This process could greatly elevate the packaging efficiency of power electronic industry.