Die-Attach Bonding with Etched Micro Brass Metal Pigment Flakes for High-Power Electronics Packaging

Sinter pastes for rapid and low-temperature die-attach bonding are developed to enable sintering under a nitrogen atmosphere. First, microscale brass metal pigment flakes are stirred in hydrochloric acid to selectively etch zinc from the alloy composition, creating surface modifications. A binder mixture of alpha-terpineol and polyethylene glycol 600 (PEG600) is used to prepare the sinter paste. The surface modifications provide accelerated material transport, leading to improved sintering capabilities even at low sintering temperatures (<= 275 degrees C). A bulk-like sintered microstructure with <10% porosity is achieved with a low solid content of 60 wt % in the paste formulation due to improved coarsening and densification behavior as a result of the surface modifications. PEG 600 is observed to be effective in reducing the copper oxides in situ during the sinter process. A shear strength of 30 MPa is achieved while sintering with 10 MPa bonding pressure at 275 degrees C for just 1 min, which is comparable to the performance of sintering under the same bonding conditions with commercially available silver pastes. The characterization of the flakes involved in the etching phenomenon and the influence of sintering parameters on the development of the microstructure are discussed in detail.