Effects of bonding pressures on microstructure and mechanical properties of silver–tin alloy powders synthesized by ball milling for high-power electronics packaging

Abstract

Silver (Ag) sintering is widely adopted as a die attach method for power electronics packaging. However, oxidation, massive grain growth, and increasing porous structure occur in sintered Ag joints at high temperatures, resulting in decreasing mechanical properties of the die attachment in power devices. To solve the problems of sintered Ag joints, a novel die attach material consisting of silver–tin (Ag–Sn) alloy particles is developed in this study. Ag–Sn alloy powders were newly fabricated by high-energy ball milling technique. The microstructural evolutions of the Ag–Sn alloy joints bonded at different pressures were systematically analyzed. With increasing high-temperature storage time at 300 °C, the reactions between sintered Ag–Sn alloy joints and Cu substrates increased, which resulted in the formation of Cu3Sn or Ag-rich diffusion layer. The relationships between microstructures and the formation of each phase were discussed. In addition, the robust sintered Ag–Sn alloy joints exhibited low porosity without pore coarsening and limit oxidation at high temperatures, indicating a dense and stable microstructure of sintered Ag–Sn alloy joints. As a result, high bonding strength did not deteriorate even after high-temperature storage for 2000 h. It is concluded that the novel Ag–Sn alloy paste produced by high-energy ball milling has long-term high-temperature reliability to be used as a die attach material for the power electronics packaging, thus enabling high-power devices to have higher operating temperatures and thermal stability.