Low-Temperature Direct Bonding of Sputtered Nanocrystalline Ag Film for Power Electronic Packaging: Bonding Mechanism, Thermal Characteristics, and Reliability

Nanocrystalline metal films are emerging as die-attach materials for power electronic packaging owing to their organic-free nature and capacity for low-temperature bonding. In this study, we proposed magnetron-sputtered nanocrystalline Ag (Nano-Ag) film as a die-attach material for power device packaging. Low-temperature direct bonding of Nano-Ag films was achieved at 200 °C in air, utilizing the thermal instability of Nano-Ag. Significant grain growth in Nano-Ag films facilitated the interfacial voids shrinkage, ultimately enabling high-quality bonding of Nano-Ag films. The SiC/Nano-Ag/direct-bonding copper (DBC) bonding structure demonstrated exceptional reliability after the thermal aging and harsh thermal cycling shocks, maintaining a high shear strength of 76.9 MPa after aging at 250 °C for 500 h. The thermal resistance (R_th) measurement revealed that the Nano-Ag film die-attach layer exhibited a low R_th of 0.10 K/W, representing a reduction of 37.5% than the Ag nano-paste. Furthermore, the SiC devices using Nano-Ag film as die-attach material showed excellent electronic property and power cycling reliability, achieving a power cycling life of 19 240 cycles at a temperature swing of 150 °C. These results indicate that this organic-free and dense Nano-Ag film is a promising die-attach material for enhancing the electronic property, thermal performance, and power cycling reliability of power modules.