Selection of Electrolyte Composition for Bright Nickel Plating of Resistive Element Contact Pads

A number of electrolytes to obtain nickel coatings on a graphite substrate of resistive elements that offer good adhesion, strong shine, sufficient wear resistance, and thickness uniformity have been tested. The operating conditions of electrolytes have been determined, the appearance of coatings have been examined, and internal stresses have been estimated. It has been found that if a product to be coated has a cylindrical form, it is necessary to apply coatings with internal compressive stresses σ = 0–70 MPa. The throwing power and current efficiency of test electrolytes have been studied. It has turned out that the coating thickness uniformity can be achieved if the throwing power of the electrolyte falls into the interval 70–90%. The throwing power of sulfuric acid electrolyte is in the range 20–30%. Because of this, it is suggested that the cylindrical shape of the anode copy that of the resistor (cathode). Such a method is known as the artificial technique for increasing the throwing power, which proved to be very efficient in plating from sulfuric acid electrolytes. Based on a laboratory setup, an industrial technology of bright nickel plating on resistive elements of different rating values has been developed.