Low-Porosity Pressureless Sintering of a Novel Ag Paste for Die-Attach
Authors: Sihai Chen, Guangyu Fan, Xue Yan, Chris LaBarbera, Lee Kresge, and Ning-Cheng Lee, Ph.D. Company: Indium Corporation Date Published: 9/28/2014
Abstract: A novel nano-Ag sintering paste C has been developed for a pressureless sintering process under air. Paste C was sintered at 250°C (C1) and 280°C (C2), respectively; C1 showed a slightly higher porosity but higher shear strength after aging at 250°C for 840 hours. Both C1 and C2 exhibited a microstructure much more stable than the control solder 92.5Pb/5Sn/2.5Ag, which suffered both IMC spalling after thermal aging and voiding. Ag migration toward the DBC to form a dense layer of AgCuNi(Au) was observed for all nano-Ag pastes that were studied, with C1 and C2 being more moderate in the migration rate. The Ag migration could be attributed to the tendency of Ag to form an alloy with Au, with abundant Ni and Cu at the DBC side, and appeared to be affected by the chemistry of nano-Ag paste. A liquid to liquid thermal shock test from -45°C to 240°C was attempted, and was considered too harsh for the die/DBC system employed in this study.