| 摘要 |
In an electroless coating process of forming a bi-metal coating on a metal base such as copper or copper-based alloys a first layer of Pt, Rh, Pd or Ru is applied, then a cover coating of gold. The first coating is deposited from a solution of the metal chloride, or bromide, or in the case of palladium, the sulfamate. The first coating solution contains 0.05-50 g./1. of metal, the coating temperature being 15-100 DEG C. With a solution of the bromide of Pt, Pd and Rh the solution should contain 0.5-20% free HBr and 1% of free HBr in the case of Ru. The solution of the chlorides should contain 20% of free HCl. The copper substrate is cleaned in ammonium persulphate or in acid, washed in water, immersed in the first coating solution, preferably palladium sulfamate, and then coated with gold by immersion at 80-90 DEG C. in a solution containing 5 gms. KAu(CN)2, 20 gms. ammonium citrate, 25 gms. ethylenedinitrilo tetra-acetic acid, water 1 litre, with a pH of 4-12 adjusted by the addition of NH4OH. Specification 872,785 is referred to. |
