Selective gold plating of base layer-coated substrate to allow gold and aluminium wire bonding to same substrate

摘要

A process for gold coating of a substrate (1) bearing a base layer (2), in order to form gold-coated first contact areas (2a-c) and gold-free second contact areas (3a-c), involves temporarily covering the second contact areas and then placing the substrate in an exchange gold plating bath. The novelty is that the gold bath has an electrolyte which causes no gold deposition on the base layer (2). Preferably, the base layer is a chemical nickel layer (2) and the gold bath is a reductive gold plating bath, the electrolyte of which preferably contains 0.1-20 g/l potassium, sodium or ammonium gold(I) cyanide or gold(III) cyanide, 0.1-25 g/l free potassium, sodium or ammonium cyanide, 0.1-50 g/l potassium, sodium or ammonium sulphite, 0.01-10 g/l aromatic nitro compound, 1-100 g/l free alkali, 1-50 g/l complex former(s) selected from hydroxycarboxylic acids, phosphonic acids, nitriloacetic acids and ethylenediamineacetic acids and 0.1-50 g/l borane and/or boranate reducing agent.