What are the Different Electroplating Methods Used in PCBs?

Electroplating is the process of depositing a thin metal layer onto a surface with the help of an electric current. Electroplating circuit boards has many advantages, including the prevention of oxidation and extending longevity of the boards. There are four broad categories of electroplating methods in PCBs:

1. Finger Plating
2. Through-Hole Plating
3. Reel Linkage Selective Plating
4.  Brush Plating

Finger Plating

 Finger-Plating refers to the process of plating rare metals on board edge connectors, board edge bumps, or gold fingers to lower contact resistance and increase wear resistance. It is also known as "protruding partial plating".

The initial tin coating is taken off and rinsed with water. For applications where abrasion resistance must be high, gold and nickel are used. The board is then scrubbed while rinsing and submerged in sulfuric acid for activation. The actual metal plating is then carried out, starting with the protruding contact head. The removal of water and minerals comes next. The gold plating is then finished, cleaned, and dried.

Through-Hole Plating

 Through-hole plating is an adhesive conductor coating applied to the interior portions of the vias. This coating is a single layer that is electroplated and thermally cured.

The method of drilling holes through the board is known as through-hole drilling. This process generates heat because it passes through the copper plating and substrate on the board. The heat generated during this process melts the surrounding material around the holes, affecting component adhesion to the board's surface. Therefore, on the inner wall of each via, a specially formulated low viscosity ink is used to create a highly adherent, highly conductive film. This is followed by thermal curing to create a continuous film on the interior of all the hole's walls, which eliminates the need for additional chemical treatments and enables direct electroplating without further processing. This resin-based ink can easily bond to the majority of thermally polished hole walls due to its extremely strong adhesion. This process also gets rid of the etch back step.

Reel Linkage Selective Plating 

The reel linkage selective plating method is applied to transistors, connectors, and integrated circuits to increase contact resistance and corrosion resistance.

Batch welding must be used because it is very expensive to individually select each of the pins for this plating method, which can be either manual or automatic. 

The ends of the metal foil are typically die-cut, then mechanically or chemically cleaned, then certain materials, such as nickel, gold, silver, iridium, button metal, tin-nickel alloy, or copper-nickel alloy, are used. In the selective plating method, a portion of the metal copper foil plate that does not need to be plated is coated with a resist film first, and plating is then performed only on the selected copper foil portion.

Brush Plating

Brush plating is an electrode position technique in which only a selected portion of the PCB is immersed in an electrolyte solution during the plating process. A special anode (a chemically reactive anode, such as graphite) is wrapped in an absorbent material (cotton stick) and used to carry the plating solution to the desired location. This is frequently used to repair boards that have been damaged as well as boards that have been plated with gold and other precious metals.

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