Cleaning of fine tungsten wire before gold electroplating

Abstract

This paper examines some issues related to the gold plating of fine tungsten wires. The key properties of tungsten are described that determined the choice of that material for manufacturing reflector curtains. Available information sources are considered which recommend cleaning of tungsten wires before electroplating. The paper gives a brief overview of electrolytes used in gold electroplating, as well as achievable gold plating rates. The authors offer a review of literature on existing electrochemical treatment machines for fine metal wires. It is shown that the high-rate cleaning (which only takes a few seconds) of tungsten wire can be more efficient when using alternating or reverse current. Thus, the best performance was achieved when a 50 Hz current was applied at the solution temperature of 60 oC (the solution contained 180 g/l NaOH) and the average current density of 180 A/dm2 for 3–4 sec. A similar cleaning performance was achieved when the same alkaline solution and the same solution temperature were used, but when reverse current was applied at the average density of 20 A/dm2 for 5 sec, with cathodic and anodic pulses having different lengths: 0.2 sec for the anodic one and 0.8 sec for the cathodic one. It was found that the above conditions for pre-treatment and alkaline cleaning of fine tungsten wires are associated with minimal alteration of the mechanical properties of such wires caused by hydrogen pick-up.