Low-temperature low-pressure die attach with hybrid silver particle paste

New types of die attach pastes comprising micron-sized Ag particles hybridized with submicron-sized Ag particles were considered as lead-free die attach materials for SiC power semiconductors. Micron-sized Ag particles in alcohol solvent were prepared by mixing the die attach paste with submicron-sized Ag particles. The alcohol vaporizes completely during sintering and no residue exists in the bonding layer. The Ag layer has a uniform porous structure. The electrical resistivity of the printed tracks decreases below 1 x 10(-5) Omega cm when sintered above 200 degrees C. When sintered at 200 degrees C for 30 min, the average resistivity reaches 5 x 10(-6) Omega cm, which is slightly higher than the value obtained by using Ag nanoparticle paste. A SiC die was successfully bonded to a direct bonded copper substrate and the die-shear strength gradually increases with the increase in bonding temperature up to 300 degrees C. The Ag die attach bond layer was stable against thermal cycles between -40 degrees C and 300 degrees C. (C) 2011 Elsevier Ltd. All rights reserved.