Glass ceramic contg. thallous oxide to lower softening temp. - so semiconductors contg. gold bonding wires can be encapsulated

摘要

Glass ceramic, esp. for the encapsulation of semiconductor elements, and contg. by wt. 2.5-2.5% SiO2, 7.5-10% B2O3, 70-80% PbO, 10-15% ZnO, 0.5-1.5% F less an equiv. amt. of O2. The material also contains 2.3 mole % Tl2O; the mole ratios PbO:ZnO:B2O3 are 2:1:1; the mole ratios PbF2:Tl2O:SiO2 are 2:1:1; and the mole. ratio-(PbO+ZnO+B2P3):(PbF2+Tl2O+SiO2) is between 8:1 and 10:1. Conventional glass ceramics have transformation point (T) 327-375 degrees C., so the solding or encapsulating temp. is >400 degrees C. But Au and Si form eutectic at 378 degrees C so semiconductors using Au bonding wires cannot be encapsulated. Encapsulation at ca. 350 degrees C. i.e. below the Au-Si eutectic m.pt. is permitted.