Reaction Diffusion in the Au-Cu-Pb-Sn System at Low Temperature
The microstructure of a Cu 3 Au v. Pb-5wt%Sn diffusion couple was examined in the as-dipped and annealed conditions. The as-dipped couple showed no reaction between the solder and the base metal. The couple developed intermediate layers of two intermetallic phases upon annealing for 289 hours at 169°C. These phases were identified as phi and eta’ which are contained in the Au-Cu-Sn ternary system. No phases containing significant amounts of Pb formed, indicating that even at low concentrations in a Pb-Sn solder, Sn is the active chemical specie in the solder for the Au-Cu-Pb-Sn system. The microhardness of the eta’ phase was found to be equal to that of Cu 3 Sn, which forms in the absence of Au in the Cu base metal. However, the the phi phase was harder, and therefore the presence of Au in the base metal may adversely affect the thermal fatigue resistance of the solder joint.
Solder Sealing Semiconductor Packages
After a comparison of current common sealing systems, a review of the development and properties of metal sealing alloys is presented. Development stages leading to a new laminated composite system for seal alloy preforms is described and results are presented of differential thermal analysis (d.t.a.) scans showing reflow characteristics. Also described are the solderability and aging properties of a nickel alloy plated seal lid which together with the alloy constitute a totally new hermetic seal system. Mention is also made of a composite gold plating scheme Currently in development, designed to meet the new updated corrosion requirements of MIL-STD-883.
The Au-Pb-Sn ternary system
Abstract Thermal analysis, metallography, microhardness and X-ray techniques have been used to determine the AuSn-Pb-Sn partial-ternary system. A ternary quasiperitectic reaction, liquid + AuSn/aiPb + AuSn2, occurs at 275°C. A second ternary quasiperitectic reaction, liquid + AuSn2/aiPb + AuSn4, occurs at 208°C and is followed by a ternary eutectic reaction, liquid/aiPb + Sn + AuSn4, at 177°C.