GB922098A - Electrolytic gold plating - Google Patents

Abstract

922,098. Electrodeposition of gold. WESTERN ELECTRIC CO. Inc. July 7, 1960 [July 28, 1959], No. 23739/60. Drawings to Specification. Class 41. Metallic surfaces, such as made of copper, brass, nickel or its alloys, e.g. " Kovar " (Registered Trade Mark), zinc, zincated aluminium or lead-tin solder-dipped cooper, are electrolytically gold plated, such as for printed copper circuitry or ornamental purposes, by immersing them in a bath of cyanide-free aqueous solution containing gold citrate (tribasic aurous citrate), the concentration of gold preferably being from 1 to 50 g/l., and in which the surfaces are biased cathodic with respect to an immersed electrode, which may be an insoluble anode of stainless steel, gold or carbon. The solution may be made initially of sodium and/or potassium gold cyanide, e.g. 20 g/l. of commercial NaAu(CN) 2 , with citric acid and/or a salt thereof such as of ammonium, potassium or sodium, e.g. 20-100 g/l. of anhydrous (NH 4 ) 2 HC 6 H 5 O 7 ), and boiled to drive off all hydrocyanic acid. Alternatively, the cyanide-free solution may be made using other aurous salts such as AuCl, AuBr, AuI, Au 2 O, Au 2 S and AuOH. The plating is preferably carried out in a bath of temperature at least 45‹ C. using a current density of at least 1 amp/sq. ft., and with a solution of pH at least 4, and not more than 8 for plating adhesively bonded, e.g. through phenol formaldehyde containing a vinyl compound, copper circuits; the pH may be controlled by the addition to the solution of HCI, H 2 SO 4 , KOH, NaOH or NH 4 OH. The solution may also be prepared by anodic dissolution using a gold anode and chloride ions, e.g. HCl or NH 4 Cl. Up to 100 g/l. of a conducting salt such as ammonium sulphate and up to <SP>1</SP>/10 g/l. of an additive to reduce grain size may be added. For hardness, alloys of gold, such as Au-Pt, Au-Rh and Au-Ag, may be plated whereby the alloying ingredients, generally less than 2%, are added to the solution in the form of diamino nitrite (for platinum), sulphate (for rhodium) or cyanide (for silver).