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A new thick film paste composition that eliminates the possible formation of free silver when exposed to high Pb, Pb-Sn solders is described. When reacted with Pb--Sn solder in the molten state, the ternary Au-Ag-Pd, while still subject to palladium depletion, is shown to yield an AgAu alloy. The resulting AgAu alloy is more resistant to sulfur corrosion than the pure silver it replaces. Studies revealed that with increasing Au content, the rate of sulfide attack decreased. In addition the type of corrosion also changed dependent upon temperature and sulfur concentration. At higher temperatures (125°C) and saturated sulfur concentrations (104ppb), a mixed Ag and Au sulfide forms, whereas at lower temperatures and lower sulfur concentrations (e.g., 30°C and 10 ppb) only silver sulfide forms. These results are discussed in relation to the noble alloying element protection model of Wagner.
Components, Hybrids, and Manufacturing Technology, IEEE Transactions on (Volume:5 , Issue: 4 )
Date of Publication: Dec 1982