Effects of Pretreatment and Ag Coating Processes Conditions on the Properties of Ag-Coated Cu Flakes

To elucidate the effects of a pretreatment process on the uniformity of Ag electroless plating on Cu flakes, pretreatment time was mainly considered with a mixed solution of 0.15 M ammonium hydroxide and 0.0375 M ammonium sulphate. Optical inspection of Ag-coated Cu flakes determined that the optimal pretreatment time is 120 s. Repetition of the sequence in which Ag plating was done immediately after the pretreatment of 120 s clearly enhanced the plating uniformity. Scanning electron microscopy revealed that holes were formed irregularly on some Cu flakes during the period from the as-dropping of an Ag precursor solution to 5 min. The hole formation was judged to be due to continuous removal of Cu on the local surfaces by the repetitive formation and elimination of Cu2O or Cu(OH)(2) layers. However, the increase of the amount of Ag coating suppressed the hole creation and increasingly enhanced the antioxidant property.