ENIG (Electroless Nickel Immersion Gold) is a process used for surface treatment of circuit boards. It is generally referred to as "nickel immersion gold plate" or "electroless gold plate" for short. It is currently widely used in circuit boards installed in mobile phones. Above, some BGA carrier boards will also use ENIG.

Compared with electroplated nickel gold, this kind of nickel immersion gold does not need to be energized on the circuit board during the process of the circuit board factory, nor does it need to pull a wire on each pad to be electroplated to be plated with nickel. Gold, so its manufacturing process is relatively simple, and the output is more than multiple, so the production cost is relatively cheap.

However, ENIG surface treatment also has its shortcomings and problems. For example, the welding strength is low, and it is easy to generate black pads, which is often criticized.

The production process of chemical nickel gold is roughly as follows:

Pretreatment → degreasing → water washing → pickling → water washing → micro-etching → water washing → pre-dipping (H2SO4) → activation (Pd catalyst) → water washing → chemical nickel (Ni/P) → water washing → immersion gold plating → gold recovery → water washing → drying

Pre-treatment: The purpose is to brush or sandblast to remove oxides on the copper surface and roughen the copper surface to increase the subsequent adhesion of nickel and gold.

Micro-etching: sodium persulfate/sulfuric acid to remove the oxide layer on the copper surface and reduce the depth of groove marks caused by brushing during pretreatment. Too deep brush marks often become an accomplice of the immersion gold attacking the nickel layer.

Activation: Since the copper surface cannot directly initiate the electroless nickel deposition reaction, a layer of palladium (Pd) must be applied to the copper surface as a catalyst for the electroless nickel deposition reaction. Using the principle that Cu is more active than Pd, palladium ions are reduced to palladium metal and attached to the copper surface.

Chemical nickel: Ni/P, its main function is to prevent migration and diffusion between copper and gold, and as an element that chemically reacts with tin to form IMC during subsequent welding.

Dip gold plating: The main purpose of gold is to protect and prevent the oxidation of the nickel layer. Gold does not participate in chemical reactions during the soldering process. Too much gold will hinder the strength of the solder, so gold only needs to cover the nickel layer to make it difficult Oxidation is sufficient, if COB (Chip On Board) wiring is to be used, it is another matter, because the gold layer must have sufficient thickness.