High-performance sapphire metallization using a novel ZnO-B2O3-SiO2-CuO glass-based silver thick film pastes

Sapphire, with its superior optical and thermal properties, is an increasingly attractive high-performance substrate material for advanced LED packaging. However, its inherent surface characteristics-namely the absence of grain boundaries and strong chemical inertness-pose significant challenges for conventional metallization processes, severely limiting its broader application in electronic packaging. To address this critical issue, this study develops a novel silver conductive paste incorporating a custom-designed ZnO–B 2 O 3 –SiO 2 –CuO (ZBSC) glass frit as the inorganic binder. A robust silver thick film was successfully fabricated on a sapphire substrate via a thick-film metallization process. We systematically investigate the effect of sintering temperature on the film's microstructure and properties. The results demonstrate that the ZBSC glass exhibits excellent comprehensive performance and exceptional compatibility with the sapphire substrate. A key finding is the in-situ formation of a spinel CuAl 2 O 4 phase at the interface during sintering, resulting from a chemical reaction between the glass frit and the substrate. This interfacial reaction is crucial for achieving superior bonding. Optimized at a sintering temperature of 850 ℃, the silver film exhibits outstanding comprehensive performance: an ultra-low sheet resistance of 2.03 mΩ/□ and a high shear strength of 21.97 MPa. This performance is attributed to a dense, well-sintered silver microstructure with a continuous and complete conductive network, intimately bonded to the sapphire substrate. This work not only provides a high-performance solution for sapphire metallization but also offers new insights into the role of interfacial chemistry in thick-film technology. The proposed method represents a high-quality, reliable metallization technique with significant promise for advanced electronic packaging applications.