|Metal Holders -
Commonly used metal holders HC-types are through-hole devices available with either leads or pins. HC holders are into a circuit. The various metal holder are standardized and identified in the MIL specification MIL-H-10056. Metal holders, regardless of the seal-type are comprised of a cover and a base that contains the quartz plate and the mechanical and electrical interface for the plate. The cover and base also have a flange that serves as the point of contact for sealing purposes.
HC-types are sealed by resistance welding or cold-welding the cover to the base. The atmosphere internal to the crystal is typically dry nitrogen for resistance welding and a vacuum for cold-welding.
Resistance welding is accomplished by placing the cover and base in a fixture inside a nitrogen chamber, then passing an electric current through the package causing the flange area to fuse together from the heat that is generated.
Cold-welding has only a distant resemblance to welding A more accurate term is compression welding. The cover and base is placed in a heated die which also acts as a vacuum chamber. The atmosphere is pumped out of the die and at that point hydraulic rams squeeze the flanges together under tons of pressure essentially fusing them together and obliterating the boundary between flange and cover.
Leaded metal holders, HC-types sometimes include the attachment of top wires, ground wires, clips or tabs and lead cropping and forming. Solderability requirements may also require pre-tinning of the leads accomplished by solder dipping.
METAL HOLDERS- "HC" TYPES:
HIGH-PRECISION COLD-WELD METAL HOLDERS:
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