What is Selective Gold Plating in PCB?

PCB Basics 
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Editorial Team

Oct 28, 2022

Selective Gold Plating in printed circuit boards refers to the deposition of gold layer on high-wear areas of  PCB like connectors and switch contacts to improve abrasion resistance and durability. The copper surface of the PCB is not directly electroplated with gold. The copper surface is first electroplated with nickel and then a thin layer of gold is electroplated onto nickel. Usually, this thin layer of gold is between 0.25 and 5 microns thick (0.00001"-0.0002") and nickel thickness is between 3 and 6 microns. 

Why is gold used in the selective plating process?

  • Least Reactive Element: Gold is one of the least reactive elements when it comes to corrosion. Unlike silver or copper, it does not react with oxygen and tends to retain its properties for a longer time. As a coating for preventing corrosion, gold is very stable in both industrial and natural settings. Gold-plated parts need not be replaced frequently resulting in a much longer lifespan.
  • Electrical and Thermal Properties: Gold is a popular contact metal in electronics because of its conductivity. It is a good conductor of heat and electricity. At 20 °C, gold has a low electrical resistivity of 0.022 micro-ohm m and high thermal conductivity of 310 W m-1 K-1. It is regarded as an ideal conductor due to its ability to maintain conductivity in variable environments.
  • Anti-Oxidation Property: Surface oxide formation is prevented by the anti-oxidation properties of gold. Additionally, gold creates a smooth finish that makes it possible for a strong bond to form with the mated surface.
  • Durability: Gold offers outstanding resistance to everyday wear and tear. It is a very resilient metal that tends to spread out rather than wear away.
  • High melting point: High melting point (1947°F) of gold provides excellent heat resistance. As a result, it can endure high temperatures without losing its qualities. For electrical products that frequently come into contact with high temperatures, gold provides improved protection against damage caused by excessive heat.
  • Application simplicity: The electroplating coating should be thin as thick coatings can impact PCB performance. Since Gold is among the highly malleable materials, creating a thin coating of gold is simple.
  • No fretting corrosion: Fretting corrosion is the term used to describe material deterioration at the point where two contacting surfaces meet. When exposed to corrosive media, small oscillatory movements could develop between them. Gold is not prone to fretting. As a result, prolonged rubbing or friction will not cause it to wear out. 

 

The selective gold plating makes the selected areas of PCB corrosion resistant, and durable and protects them from regular wear and tear. However Selective Gold plating is very expensive and the relatively poor solderability of gold makes it difficult to be applied in common solderable areas.

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