Electrolytic Ni-Au (Nickle-Gold) is a health care PCB finish that is composed of a layer of Gold, plated over a base of electroplated nickel. The purity of gold used for plating categorizes the finish as Hard Gold (99.6% purity) or Soft Gold (99.9% purity). Hardness is achieved by adding non-noble metallic elements alloyed with Gold deposit like Cobalt, Nickel or Iron, which enhances its durability

Hard Gold has a hardness between 130 to 200 HK25, whereas Soft Gold has a hardness of 20 to 90 HK25. Gold has good electrical conductivity, tarnish resistance, solderability after storage, and etch resistance.

This finish is usually applied to highly wear-prone areas like edge connectors, Gold fingers, keypads, contacts, etc. The typical plating thickness of a health care PCB gold finger is around 300 micro-inches. At this thickness, hard gold can survive up to 1000 thermal cycles before wear-through. Quality of hard Gold finish is verified by performing a thickness and tape adhesion test.

The Hard Gold finish is more lustrous or brighter than that of Soft Gold. Additionally, due to reduced hardness, the Soft Gold plating is more prone to scratching. For these reasons, hard gold plating is recommended over soft gold to fulfill visible interconnect applications. The choice of hard Gold or soft Gold also depends upon the type of application. When hard gold is used for military applications, the minimum thickness should be 50 to 100 micro-inches. Non-military applications require 25 to 50 micro-inches thickness.