GB1222969A - Plating process - Google Patents

Abstract

1,222,969. Successive electroless and electrolytic plating from the same bath. GEIGY (U.K) Ltd. May 31, 1968 [June 3, 1967], No. 25708/67. Headings C7B and C7F. Metal is deposited on to a substrate which is substantially free from grease and other contaminating material by immersing the substrate in an aqueous bath containing per litre 0.002 to 0.6 moles of a source of metal ions, 0.0015 to 6 moles of a complexing agent for said metal ions, and 0.002 to 2.5 moles of a reducing agent to effect electroless plating and thereafter while still immersed in the same bath effecting electroplating on to the substrate. Preferably the plating solution is agitated during the electroless plating stage which lasts for 10 to 40 minutes to produce a metal film of sufficient thickness to carry the electro-plating current without damage to the film and the specified range of proportions of the metal ions and of the reducing agent is maintained by periodic additions. The substrate may be a metal such as copper, nickel, steel, brass chromium, tin or silver or a non-metallic material such as glass, ceramic or a synthetic resin such as an epoxy, amide, vinyl, styrene, ethylene, propylene or acrylic polymer, which material is treated successively with acid solutions of stannous chloride and an acid noble metal salt e.g. palladium chloride before immersion in the plating bath. Preferably the metal complexing agent is in excess of that required to complex all the metal in the solution. Specified types of complexing agents are aminocarboxylic or polyaminopolycarboxylic acid or their alkali metal salts or alkylene or polyalkylene polyamines, while specified reducing agents are formaldehyde, alkali metal hypophosphites, alkali metal borohydrides or aminoboranes. In examples the substrate is stainless steel or sensitized activated ABS resin and the plating metal is copper or nickel. Reference is made to the subsequent electro-plating of copper with nickel or chromium. Preferred baths for copper contain copper sulphate, disodium EDTA, sodium hydroxide and formaldehyde together with either sodium cyanide and optionally thiourea, used at pH 12À1 to 12.7 and 23‹C., or with sodium cyanide or carbonate and mercaptobenzthiazole used at pH 11.8 to 12.4 at 50‹C., while for nickel the baths contain nickel chloride, disodium EDTA, sodium hypophosphite and lead chloride, used at pH 4.5 and 70 or 85‹ C. Reference is made to including arsenic in the nickel baths e.g. added as arsenate ions or arsenic pentoxide. To avoid electroless deposition on the anodes, which preferably are of the metal to be deposited, during the initial electroless step either the anodes are removed from the bath or they are made slightly anodic relative to inert cathodes. Reference is made to applying the invention to the deposition of silver, gold, cobalt, platinum or palladium.