Low-Temperature Sinterable Cu@Ag Paste with Superior Strength Driven by Pre-Heating Process

Abstract

To preserve the structural integrity of power semiconductor devices, ensuring a reliable connection between wide-bandgap (WBG) chips and their substrates at temperatures above 200 °C is crucial. Therefore, easily processable chip-attach materials with high bonding strengths at high temperatures should be developed. Herein, we determined the optimal pre-heating conditions of chip-attach materials to achieve highly reliable WBG semiconductor devices. Sintering with silver-coated copper (Cu@Ag) particle paste was investigated as a model system for chip attachment in electric power devices. After printing the paste onto a direct-bonded ceramic substrate and placing the Si chip on the paste, the pre-heating process was conducted at 50 and 70 °C for different periods of time. Finally, the samples were sintered at a pressure of 9 MPa at 250 °C in an N2 atmosphere for 1 h. The quality of the obtained Cu@Ag joints significantly varied depending on the pre-heating temperature and time. When Cu@Ag joints were pre-heated at 50 °C, more reliable and reproducible bonding was achieved than at 70 °C. In particular, high-quality sintered joints were obtained with a pre-heating time of 4 min. However, after excessive pre-heating time, cracks and voids were generated impacting negatively the performance of the sintered joints.