Well, the purpose of gold is actually refers to the characteristics of gold:

1. Extremely strong resistance to oxidation;

2. Excellent conductivity.

BTW, the difference between hard gold, soft gold and flash gold on the circuit board, which lies in the composition of the layer of gold that is finally plated.

Soft Gold: Pickling → Electroplating Nickel → Electroplating Pure Gold

Hard Gold: Pickling → Electroplating Nickel → Pre-Gold Plating → Electroplating Gold Nickel or Gold Alloy

Flash Gold: Fast Gold Plating. In fact, it is a procedure of “pre-gold plating” for electroplating hard gold, which uses a relatively large current and a thin solution containing gold. The first layer in the nickel layer is denser, then a pretty thin layer of gold is used for subsequent electroplating of gold-nickel or gold-cobalt alloys.