There are two main types of gold plating processes used in the PCB and connector industries: electrolytic plating (hereinafter referred to as electroplating) and electroless plating.

Electroplating: Electroplating refers to the process of conducting an electrolytic reaction in a solution by the action of an external current to deposit a uniform and dense layer of metal or alloy on the surface of the substance to be coated. The principle of electroplating reaction is galvanic cell reaction. During electroplating, the anode undergoes oxidation reaction, dissolves and loses electrons, and metal atoms become cations; The cathode undergoes a reduction reaction, and the metal anion gains electrons to form a coating.

Electroless plating: A process method that does not rely on external power supply in aqueous solution, and only relies on the reducing agent in the plating solution to carry out chemical reduction reaction, so that metal ions are continuously reduced to metal atoms and deposited on the surface of the substrate to form a metal coating.
Typical is the PCB surface treatment process: ENIG (electroless nickel gold).

Comparison of Electroless Plating and Electroplating
The biggest difference between electroless plating and electroplating is that no external current is required. The thickness of the electroless plating layer is uniform and the pinhole rate is low.