The surface of the circuit board has several processes: Bare PCB (surface without any treatment), Rosin board, OSP (organic solder preservative, slightly better than rosin), HASL (a tin, lead free tin), gold plating, ENIG(Electroless Nickel/Immersion Gold), which is more common. We briefly introduce the difference between gold plating and ENIG.

ENIG is a method of chemical deposition, and a layer of coating is formed by chemical oxidation-reduction reaction. The thickness of the deposit is thicker, which is one of the chemical nickel, gold and gold layer deposition methods, which can reach a thicker gold layer.

Gold plating uses the principle of electrolysis, also known as electroplating. Most other metal surface treatments are plated.

In the actual product applications, 90% of the gold boards are the ENIG, because the poor weldability of the gold-plating is his fatal flaw, but also a direct cause of many companies to abandon the gold-plating process.

ENIG of printed circuit surface is stable color, good brightness, good coating and good weldability. Basically can be divided into four stages: pretreatment (degreasing, micro corrosion, activation, after immersion), immerse nickel, immerse gold, end treatment (waste gold washing, DI washing, drying). The thickness of ENIG is between 0.025-0.1um.

Gold used in circuit board surface treatment, because the conductivity of gold is strong, good oxidation resistance, long life, general applications such as key board, finger board, etc. The fundamental difference between gold plating and ENIG is gold plating is hard gold (hard wearing), ENIG is soft gold (not hard wearing).
Difference between gold plating and ENIG:

    * As the circuit board processing requirements are higher and higher, the line width and spacing have reached below 0.1mm. Gold plating is easy to produce gold wire short circuit. The ENIG only has nickel gold on the pad, so it is not easy to produce a gold wire short circuit.
    * The crystal structure is more dense of ENIG compare gold plating, so it is difficult to produce oxidation.
    * The ENIG only has nickel gold on the pad compare gold plating. In the skin effect, the signal transmission is in the copper layer, which will not affect the signal.
    * ENIG and gold plating crystal structure is not the same, It required thicker gold for ENIG than gold plating,and the gold will be golden yellow than gold plating,which is recognition method of ENIG and gold plating,the gold is slightly pale of gold plating like nickel color.
    * ENIG and gold plating crystal structure is different,ENIG is easier to weld, will not cause welding bad. The     stress of the ENIG is easier to control, and it is more conducive to the processing of the bonding products. At the same time, it is because the gold deposit is more soft than the gold plating. Therefore, the gold finger of ENIG is not wearable (the disadvantages of the ENIG).
    * The ENIG only has nickel gold on the pad. Therefore, the solder mask on the line is more firmly integrated with the copper layer. It will not affect the spacing when it is compensated.
    * For higher requirements of flatness PCB, generally used ENIG, ENIG generally does not appear black pad phenomenon after assembly. The flatness and longevity life of ENIG is better than gold plating.

So most factories now use ENIG process to produce gold PCB. But the ENIG process is more expensive than the gold plating process (higher gold content), so there are still a large number of low-priced products using gold plating process (such as remote control board, toy board).