Surface driving stress-assisted rapid and large area silver porous sheet bonding for power electronics packaging

This study introduces a novel rapid die attach and large-area substrate bonding technology based on an Ag porous sheet with ultra-fine grain structure and surface-driven stress. The Ag porous sheet is fabricated using Ag particles with a high dislocation density, processed via a hot-pressing method without the addition of any organic solvents. The high dislocation density of the Ag particles promotes neck growth during the fabrication of the Ag porous sheet. Additionally, surface polishing alters the grain structure to ultra-fine grains, which generates surface-driven stress. A shear strength of 82.1 MPa was achieved for the SiC dummy chip / Cu substrate joint using this Ag porous sheet, with a bonding time of only 1 min at 250°C. Furthermore, large-area (30 mm × 30 mm) Cu die-to-Cu substrate bonding was successfully achieved using the Ag porous sheet, with a short heating time of 3 min at 250°C. The bonding interface exhibited a bonding ratio of over 85% for the large-area bonding. The rapid bonding mechanism was discussed and analyzed based on the surface stress and grain structure of the Ag porous sheet, validated through electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), and finite element analysis (FEA). The use of this Ag porous sheet offers a highly efficient process with significant potential for a wide range of SiC power device applications in high-temperature and high-power electronics.