Electroless Ni/Au Plating Overview The Under-Bump-Metallization (UBM) is an integral part of all bumping processes. This layer is typically deposited by physical vapor deposition (PVD), electroplating, or electroless plating. The choice between these three UBM technologies is often dictated by cost and reliability. PVD and electroplating techniques require both high vacuum and photolithography steps and are therefore considered high cost operations. The electroless nickel/gold process technology is a simple wet chemical process that is self-patterning thus leading to lower costs in relation to its total capital investment and operational costs.