Ceramic metallization enables the joining of ceramics to other ceramics or metals via eutectic or pure metal alloy brazing processes. Ever since the advent of ceramic-to-metal brazing in the 1930s, the brazing industry has relied primarily on hand application for the refractory metallization pastes needed to create the braze seal. For a complex joint, skilled technicians (artists, really) painstakingly apply the paste using a variety of methods, typically a paint brush, pen or spray. Operators will often spend several minutes on individual parts to ensure that the applied paint meets all the dimensional, positional and thickness requirements needed for a hermetic joint.
For complex parts in quantities of up to 50-100, hand painting by skilled operators is an efficient process. For high-volume, simple parts, where automation could provide multiple benefits, hand painting is still the norm in our industry. Although semi-automation tools such as rotating fixtures are often used to process parts more quickly, each operator has their own application technique, which leads to high part-to-part variability in film thickness, quality, uniformity, and application time. Ideally, a single coat is applied; however, the paint must be free of voids and pinholes so that the subsequent Ni plating required for brazing is uniform and light tight. This may require two coats due to the inconsistent nature of hand application.