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.
Alloy phase diagrams
These proceedings collect papers presented at a symposium on alloy phase diagrams. Topics include: Crystal phase transformations; order-disorder transformations; crystal lattices; metallic glasses; metastable states; solubility; binary alloy systems; and alloys of iron, tantalum, silicon, aluminum, germanium, palladium, copper, and nickel.
Barrier Layers Against Diffusion
SummaryTests have been carried out on copper and brass substrates which have been electroplated with a number of different barrier layers and then with an excess of matt tin. These samples have been heat treated to simulate accelerated storage and operation periods and observations made on the resulting intermetallic compound layers between the substrate and the tin coating. The results indicate the suitability of each barrier layer for altering the rate of growth of substrate-tin intermetallics and also the ability of the barrier to inhibit the diffusion of, specifically, zinc to the surface of the coating. On the basis of lowest barrier/coating reaction rates, iron appears by far the best choice for a barrier layer.