Low-Temperature and Low-Pressure Die Bonding Using Thin Ag-Flake and Ag-Particle Pastes for Power Devices

The operating temperature of new-generation power semiconductors is expected to exceed 150 $^{\circ}{\rm C}$ . To develop a low heat-resistant die-attachment technology that can be processed at relatively low temperatures, four Ag filler-based die-bonding materials are investigated. They include Ag micrometer-particles, Ag nanoparticles, Ag micrometer-flakes, and Ag nano-thick-flakes, and are mixed with a solvent to formulate into pastes. These Ag pastes are printed onto three types of substrate, bare Cu and Cu with Au and Ag finishes, and then the bonding experiments are carried out at temperatures of 160 $^{\circ}{\rm C}$ –220 $^{\circ}{\rm C}$ for 60 min. At 200 $^{\circ}{\rm C}$ and 220 $^{\circ}{\rm C}$ , the die bonding onto the Cu substrate with Ag finish using the Ag micrometer-flake paste is found to have an excellent shear strength of 36.0 and 39.1 MPa while the die bonding using the other three pastes all have shear strengths below 20 MPa. This can be explained in terms of the bonded interface area formed with the Ag micrometer-flake paste, which is significantly larger than those formed with the other three Ag pastes. Therefore, the Ag micrometer-flake paste promises to provide sufficient die-bonding strength at low temperatures.