Mounting and metallic brazing of crystal units, design history

In the early 1960´s while working in the Crystal Design Laboratory at Hewlett-Packard, Don Hammond, the manager, and the author began to look into a new mounting system for quartz crystals. Their goal was to design a package that could be cleaned by H₂ firing at elevated temperatures, baked at temperatures greater than 300°C, sealed while in vacuum with leak rates that were less than any container available at that time and be impervious to He diffusion. Cost was of secondary concern. The first crystal unit that they were to design the system for was for their LC cut temperature sensor operating over the range -50°C to +250°C. The unit was a 28 MHz 3rd OT unit that was required to fit into a package no larger than a TO-5 configuration and maintain its He integrity for the life of the product. The brazed mounting system described in this paper was a manageable process. Both HP and later Agilent Technologies put nearly 500,000 units in the field with this design. Its MTBF was greater than 1,000,000 hours with specifications that were always at the leading edge