TIN-NICKEL ALLOY PLATING

摘要

Tin-nickel may be electroplated directly on basis metals such as steel, copper, and brass as well as on an undercoat of copper or nickel on zinc die castings. The alloy is an intermetallic compound of ～65% tin and 35% nickel. Tin-nickel alloy plating offers a replacement or an alternative to decorative chromium plating for a number of indoor and outdoor applications because of its attractive faint rose-pinkish color, which gives it a very pleasant appearance. The alloy is resistant to corrosion and tarnish and has good contact and wear resistance. Its hardness lies between those of nickel and chromium. It has excellent frictional resistance and the ability to retain an oil film on its surface. Tin-nickel alloy plating solutions have deep throw so that where there is a problem in plating chromium in deep recesses, tin-nickel is an alternative. Because of these properties, as well as a number of others, tin-nickel alloy has found its use in light engineering fields and in the printed circuit board manufacturing industry as an excellent etch resist and as a substitute for gold. Table I gives the bath composition and operating conditions for a fluoride-based bath. The solution pH can be adjusted by additions of ammonium hydroxide (to raise) and ammonium bifluoride (to lower). The total fluoride content should be at least as high as the total tin content (both stannous plus stannic). The solution operates at 65℃ (150℉), 2-4 V, and a cathode current density of 25 A/ft~2 (2.8 A/dm~2). Agitation is not necessary for thin deposits but mechanical agitation may be necessary for thick deposits. Continuous filtration is necessary to remove the suspended matter.