Nickel plating is often used on PWBs to increase wear resistance and to prevent diffusion between copper and other plated metals. The nickel plating is often present in through holes as well as on the surface, such as when the entire PWB panel is nickel/gold plated or when press fit pins are used for assembly. When the plated through holes are evaluated by microsectioning, it often becomes apparent that the nickel plating is not uniform. It tends to be much thinner in the middle of the hole than on the surface of the board, and may not meet minimum thickness requirements. This paper will evaluate the effect of various plating parameters and chemical additives on through hole plating uniformity. Data will be presented comparing direct current and pulse plating. This paper will also evaluate how the addition of chemical additives to increase throwing power affects the intrinsic stress and grain structure of the nickel. Tests include plating PWBs having through holes of varying diameters and aspect ratios with nickel in thicknesses up to 100 mils. Nickel thickness and uniformity are evaluated both by microsection and X-ray fluorescence measurement techniques.
展开▼
