High Density Printed Circuit Board

How does immersion gold work?

Process of PCB chemical immersion gold:
Hole-Degreasing-Washing-Micro-etching-Washing-Activation-Washing-Nickel-Washing-Gold-Washing-Drying.

Hole: Use hydrochloric acid or thiourea to deactivate the remaining palladium in the non-conducting holes to prevent it from being deposited with nickel and gold.

Degreasing: Use acidic degreasing agent to remove mild grease and oxides on the copper surface to clean the copper surface and increase wettability.

Washing: Washing in countercurrent after removing the oil tank.

Micro-etching: Acidic sodium persulfate etching solution is used to roughen the copper surface and increase the precision of the copper and chemical nickel layer.

Activation: In the electrochemical sequence, copper is behind nickel, so the copper surface must be activated before electroless nickel plating can be carried out. The PCB industry mostly uses the method of producing a replacement palladium layer on the copper surface to activate it. The activator is generally two kinds of sulfuric acid type and hydrochloric acid type. Nowadays, sulfuric acid type palladium is used to activate the night, and the effect is more ideal.

Nickel Immersion: Under the activation of palladium, nickel ions are deposited on the surface of bare copper under the reducing conditions of sodium hypophosphite. When nickel deposits cover the palladium catalytic crystals, the autocatalytic reaction will continue until the required nickel layer thickness.

Immersion gold: After the buile-up printed board surface is plated with a nickel layer and placed in the gold tank, the nickel surface is attacked by the tank solution to dissolve nickel ions, and the two electrons thrown out are obtained by gold cyanide ions and gold is deposited on the nickel surface Floor.
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