The impact of temperature on microstructure and mechanical properties of Kovar/Al2O3 joints using Bi-B-Zn-Si glass solder

In the realm of electronic packaging advancements, the utilization of metal to ceramic joints has garnered significant attention. This manuscript details the development of a specific glass solder with excellent wettability and a thermal expansion coefficient of 8.1 × 10 −6 °C −1 , comprising 35Bi 2 O 3 -30B 2 O 3 -15ZnO-20SiO 2 (mol.%). This design achieves reliable connection of the Al 2 O 3 ceramics and Kovar alloy in an atmospheric environment. The interface reaction between the glass solder, Al 2 O 3 ceramics, and oxidized Kovar alloy resulted in the formation of ZnAl 2 O 4 particles and Bi spheres at the joints. The enhancement in joint shear strength was primarily attributed to the nanoscale, dispersed ZnAl 2 O 4 particles. However, the presence of microscale Bi spheres, with a lower elastic modulus than the glass solder, initiated cracks during shear deformation, thereby compromising the integrity of the joint. Optimization of brazing temperatures enabled control over the ZnAl 2 O 4 and Bi sphere phases within the joints, yielding a peak shear strength of 51.7 ± 8.9 MPa at 650 °C. This study highlights the achievement of high-performance metal-ceramic bonding through tailored interface reactions and optimized joint microstructures.