Why is the plating thickness on my product non-uniform?

Electroplating is an electrochemical process wherein the metal deposited on a substrate is supplied through the bath chemicals, containing the metal of interest under the application of a direct electric voltage across the anodic and cathodic sides of the plating cell. The generated current through the bath is an ionic current flow, and the current in the external circuit is electronic. Both are direct currents. Direct current always seeks the path of least resistance from the anode (metal source) to the cathode (work piece). The geometric shape of the work piece can shorten the distance to the anode, and thus decrease the electrical resistance (the resistance of the plating solution is directly proportional to the linear distance between anode and cathode). The least resistant path will carry more current and thus deposit more metal. The classic example of this phenomenon is a sharply pointed object (i.e. a rod) with the ends pointing at the anodes.  The ends will have dramatically more plating than the center of the piece.

Often the shape of a part will restrict the ionic movement over its surface and thus, metal deposition. Dead end holes limit effective solution exchange within the hole, that is they have very little plating if any within the hole.

Electrodeposits are notorious for being non-uniform. Awareness of this property helps the design engineer to build his product such that functional surfaces will not receive diminished coating thickness.  Reference the Design for Plating Guide available within the white papers section of the Technical Library for additional information on how part design affects electrolytic plating distribution and why they appear non-uniform.