Formation of a highly conductive thick film by low-temperature sintering of silver paste containing a Bi2O3-B2O3-ZnO glass frit

A new Pb-free Ag paste containing a Bi2O3-B2O3-ZnO glass frit was developed for Al2O3 substrate metallization. First, Bi2O3-B2O3-ZnO glass frits with various compositions and glass transition temperatures (Tg) of 322 °C–440 °C were synthesized by using a traditional melt-quenching method. Then, silver pastes containing different contents of the glass frit were sintered on an Al2O3 substrate at temperatures ranging from 450 °C to 600 °C. The glass frit content and the sintering temperature had significant impacts on the electrical resistivity and shear strength of the product. The experimental results indicated that the silver film formed from the paste containing 7 wt.% glass frit and sintered at 600 °C for 15 min had a low electrical resistivity of 2.5 μΩ cm and a high strength of 28.5 MPa. These properties resulted from the formation of a stable glass network that supported the Ag network. Furthermore, ZnAl2O4 was observed to form close to the interface of the Al2O3 substrate, which could improve the shear strength. Moreover, the Bi-based glass frit could be a suitable substitute for Pb-based glass frits in the preparation of environmentally friendly silver pastes for forming thick Ag films on Al2O3 substrates.