Properties of High-Speed Gold Electrodeposits Applied to Ceramic Electronic Packages

In this study, the Ni diffusion barrier characteristics of a relatively high-speed (> 8 mA/cm²) gold deposit electroplated upon electrodeposited Ni in an in-line, conveyorized system were correlated with the Au layer's microstructural characteristics, including surface morphology, texture (preferred orientation), crystallite size, and microstrain. Depositing the Au upon a Ni surface which had been recrystallized by heat-treatment (sintering) achieved, in the as-plated condition, the microstructural features important to good diffusion barrier performance (large grain/crystallite size, lower defect density). If deposited on heat-treated Ni, the Au deposit contained relatively large grains and had a slightly preferred 〈111〉 orientation. It was a better Ni diffusion barrier than the finergrained Au deposited on unsintered Ni. The latter Au deposit had a slightly preferred 〈100〉 orientation. In addition to larger grain size, the Au deposited on sintered Ni contained larger crystallites or sub-grains and a lower degree of nonuniform microstrain. The lower density of grain boundaries and defects limited the extent of Ni diffusion to, and oxidation on, the gold surface during heat testing in air at 450 °C for 5 min. Annealing the Au deposited on an unsintered Ni surface at 335 °C slightly improved the diffusion barrier performance by increasing crystallite size and apparently reducing defect density. Further improvement was obtained using a 450 °C anneal. Diffusion that occurred during annealing, however, limited the extent to which annealing improved the performance.