CERAMIC FLAT PACK ENCLOSURES FOR PRECISION QUARTZ CRYSTAL UNITS

摘要

Techniques in the design and development of ceramic flat pack enclosures for 20-MHz and 5-MHz precision crystal units are described. A raicrocircuit enclosure "or the 5-MHz crystal unitsronsists of an octagonal A1203 laminated ceramic frame with four conductive feed throughs. Metallized ceramic ledges are provided internally for thenmocompression bonding of resonator mounting clips and on the outside for attachment of electrical leads. Single layer A1203, ceramic covers are bonded to the frame after resonator plating. The 20-MHz ceramic enclosure is a square frame with similar covers and feedthroughs. Nickel electrobonding provides a low stress conductive bond between the gold-chromium resonator contacts and thin preformed nickel clips. Three enclosure sealing techniques are described: (1) gold-gold diffusion bonding;(2) bonding of alumina to aluminum;(3) tin-gold reaction braze. Bonds are made in all mer.al, dry pumped vacuum systems at temperatures up to 3000C. The gold-gold and alumina-aluminum bonds are pressed using forces up to 86 MPz (12,500 psi). Bond strength, vacuum integrity and thermal shock resistance are evaluated with ASTM tensile test buttons. Gold-gold diffusion bonds provided strengths in excess of 172 MPa (25.000 psi).