Brazing Sealing and Extreme High Frequency (EHF) Wave Transmittance of Aluminum Nitride Ceramic Microwave Window

AlN ceramics are commonly used as high-power microwave window materials. In order to achieve effective connection between AlN ceramics and copper substrates, a self-configured Ag-28Cu-3Ti ternary active brazing filler metal was selected for brazing experiments. The brazed samples were subjected to characterizations, including nondestructive testing, gas tightness, microstructure, dielectric property and mechanical strength. It is showed the brazed samples had no obvious solder joint defects, cracks, bubbles and so on, with a helium leakage rate of 3.76×10^-8 Pa·m³·s^-1. The interface composition of the brazed joint was AlN/TiN/CuTi/Cu+Ag/Cu, while local segregation of Ti was observed. After brazing, the dielectric properties met the requirements for applications. According to dielectric loss and standing wave factor, optimal operating frequency range of the devices was 98.8-108.0 GHz. Average shear strength of the AlN sealing piece was 185.7 MPa, which met the strength requirements.