| Abstract |
| To suppress Ag dewetting from around 200 ℃ in Ag-coated Cu (Cu@Ag) flakes, Ag and Ni-coated Cu (Cu@Ni@Ag) flakes were fabricated by successive Ni and Ag electroless plating. The Ni bath type was an important consideration to induce differences in the Ag dewetting and resultant Cu oxidation. An acid Ni bath contained succinic acid as a complexing agent and sodium hypophosphite as a reductant, and an alkaline Ni bath contained sodium citrate as a complexing agent and sodium hydroxide as a pH adjuster as well as sodium hypophosphite. A hydrazine-based Ni bath contained sodium citrate, sodium hydroxide, and hydrazine hydrate as a reductant. The acid Ni bath provided amorphous coatings with a P content of approximately 10 wt%. The Cu@Ni@Ag flakes started the Ag dewetting and Cu oxidation at 350 ℃, together with the formation of the Ni3P phase. Meanwhile, the alkaline Ni bath created Ni-5 wt% P amorphous Ni coatings, which transformed into a crystalline phase after heating at 350 ℃. The Ag shell was dewetted at 450 ℃, which caused oxidation of the flakes. Finally, the hydrazine-based Ni bath formed crystalline coatings without P, which induced rapid mixing with the core Cu. The Ag shells on the mixed Cu-Ni alloy showed repressed dewetting behavior, and thus the dewetting and oxidation temperature was the highest, such as 500 ℃. Enhancing the high oxidation resistance at approximately 300 ℃ will enable the use of Cu@Ni@Ag flakes as a low-cost filler material in conductive pastes, especially for long-time or hightemperature curing.
(Received 3 February, 2023; Accepted 4 July 2023) |
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| Key Words |
| Cu flake, Ni plating, Ag plating, Ag dewetting, flakes oxidation |
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