Optimisation of the ultrafast high sintering process for NanoCu particles bonding

• Main Author: Koh, Clifford Sin Yuen
• Other Authors: Gan Chee Lip
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Materials::Electronic packaging materials
• Online Access: https://hdl.handle.net/10356/157120
• Institution: Nanyang Technological University

To support the harsh environment of power electronics, such as high operating temperature, and high current density, the advancement in package and assembly technology of the modules is critical. The objective of this study is to develop an optimised ultrafast high temperature sintering (UHS) process for the preparation of sintered nano-copper particles (NanoCu) to act as a replacement for nano-silver ones (NanoAg) as an interconnect material. NanoCu is a potential candidate as it has similar thermal, electrical, and mechanical properties but with advantages of lower costs and better electromigration resistance as compared to NanoAg. The UHS process is a newly developed sintering technique with high potential in the field of sintering. In this study, the NanoCu paste was first analysed using thermo-analytical techniques to determine its thermal properties. The preparation of sintered NanoCu joints was done using UHS with varying sintering dwell times from 30 to 50 seconds with 10 second intervals. After which, the joints underwent mechanical and microstructural evolution evaluation using die shear test and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX) respectively. The results were compared amongst the different dwell times as well as with standard reflow sintered NanoCu joints. The average die shear strength of the NanoCu joints obtained for 30s, 40s, and 50s dwell time are 49.13 MPa, 38.24 MPa, and 54.04 MPa respectively. For the microstructural evolution, three observations were made. First, the different sintering times had similar mode of failure. Second, the sintered NanoCu layer demonstrated good bonding between the die/substrate interface with lower evaporation channels formed at higher sintering dwell times. Third, non-uniform diffusion of sputtered Ag to sintered Cu layer was observed, changing the bonding interface to Cu-Ni in some regions. Upon comparison with reflow sintered joints, UHS was determined to be superior with higher shear strengths obtained due to larger sintering necks and long-range interconnection between particles. These results suggest the high potential of utilising UHS process as a novel die-attach sintering technique for NanoCu paste as an interconnect material in power electronics.