Electrolytic Ni-Au PCB Finish

What is Nickle-Gold Finish? What is Hard Gold? What is Soft Gold?

PCB Fabrication PCB Surface Finishes 
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Editorial Team - PCB Directory

Apr 25, 2020

Electrolytic Ni-Au (Nickle-Gold) is a 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 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.

Advantages of Electrolytic Ni-Au PCB Finish

  • Durable and offers long-shelf life (12+ months)
  • Suitable for repetitive use
  • Unlike ENIG, its thickness can be varied by controlling the plating cycle duration

Disadvantages of Electrolytic Ni-Au PCB Finish

  • Inadequate bonding ability: Not suitable to apply on solderable areas because of hard Gold’s poor solderability (due to the addition of Nickel, Iron, Cobalt, and other non-noble metals)
  • Not suitable for sensitive joining applications
  • Not good for wire bonding and results in bad solder joints
  • Expensive and requires extra processing cost
  • RoHS Compliant
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