Three practical examples of failure analysis of brazed ceramic-to-metal joints for rugged, hermetically sealed vacuum devices are presented. Manufacture of vacuum devices at PTC involves the joining of metallized Al 2O 3 ceramic to F15 alloy. Failures were observed as gas leakage into the vacuum envelope and subsequent failure in the operation of the vacuum devices. In each case, the vacuum leaks were isolated to the braze joint and failure analysis was performed to determine the cause of the failure. Methods of analysis included isolation of the gas leak to the braze joint, metallographic analysis, scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM/EDS) and stylus profiler measurements. Causes of failure were determined to be related to: 1) deviations from ideal geometry in the joined parts, 2) the composition of the F15 alloy, and 3) materials issues at the ceramic joint interface.