Improvement of Mechanical Endurance of Bellows for Variable Vacuum Capacitor

A variable vacuum capacitor(VVC) is mainly used for impedance matching in semiconductor wafer and display panel manufacturing, where plasma load is required, due to its high dielectric strength and stability. As usage in these fields steadily increases, very long service life and reliability are required for VVCs. Among the internal components of the VVC, the bellows is manufactured by bending a thin metal sheet, making it structurally the most vulnerable part in terms of lifetime. Because a mechanical endurance of over 100,000 cycles is required, the bellows’ lifetime usually determines the lifetime of VVCs. In particular, the bellows is responsible not only for operation and maintaining vacuum tightness, but also for current carrying. Therefore, materials with high thermal conductivity are used for carrying high-frequency currents, or plating is applied to STS316L material. In this study, the mechanical endurance of the bellows used in VVCs was first tested under various plating conditions. After designing, analyzing, and manufacturing the bellows, they were plated with different solutions, and mechanical endurance tests were conducted. It was confirmed that the bellows showed the longest service lifetime when Au- plating was applied. However, due to increased manufacturing costs and management issues with Au-plating, VVCs were manufactured using bellows plated with copper, which showed the next best durability. Finally the mechanical endurance test of VVCs confirmed that the target service life requirement was met.