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There are four main methods of electroplating in circuit boards: finger-type electroplating, through-hole electroplating, roller-type selective plating, and brush plating.
Here is a brief introduction:
1
Finger-type Electroplating
This method requires rare metals to be plated on the edge connectors, protruding contacts, or gold fingers of the board to provide lower contact resistance and higher wear resistance. This technique is known as finger-type electroplating or protruding part electroplating. Gold is often plated on the protruding contacts of edge connectors with a nickel underlayer. Gold fingers or protruding parts of the board are plated using manual or automatic electroplating techniques. Currently, gold plating on contact plugs or gold fingers has been replaced by nickel plating, lead plating, or tin plating.
The process of finger-type electroplating is as follows:
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Remove the coating to eliminate tin or tin-lead coating on the protruding contacts
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Wash with water
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Scrub with abrasive
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Activate by immersing in 10% sulfuric acid
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Plate nickel with a thickness of 4-5μm on the protruding contacts
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Wash to remove mineral water
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Gold penetration solution treatment
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Gold plating
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Wash
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Dry
2
Through-Hole Electroplating
There are various methods to establish a compliant electroplating layer on the walls of drilled holes in the substrate, known in industrial applications as hole wall activation. The commercial production process of printed circuit boards requires multiple intermediate tanks, each with its own control and maintenance requirements. Through-hole electroplating is a necessary subsequent process after drilling. When the drill passes through the copper foil and the underlying substrate, the heat generated causes the insulating synthetic resin that constitutes most substrate matrices to melt. The melted resin and other drilling debris accumulate around the holes, coating the newly exposed hole walls in the copper foil, which is detrimental to subsequent electroplating surfaces. The melted resin also leaves a thermal axis on the substrate hole walls, which exhibits poor adhesion to most activators, necessitating the development of a class of technologies similar to stain removal and etching chemical actions.
A method more suitable for prototype production of printed circuit boards is to use a specially designed low-viscosity ink to form a high-adhesion, high-conductivity coating on the inner walls of each through-hole. This eliminates the need for multiple chemical treatment processes, requiring only one application step, followed by thermal curing, to form a continuous coating on all inner hole walls, which can be directly electroplated without further treatment. This ink is a resin-based material with strong adhesion, allowing it to easily bond to most thermally polished hole walls, thus eliminating the etching step.
3
Roller-Type Selective Plating
The pins and connectors of electronic components, such as connectors, integrated circuits, transistors, and flexible printed circuits, use selective plating to achieve good contact resistance and corrosion resistance. This electroplating method can be performed manually or automatically. Selective plating of each pin individually is very expensive, so batch soldering must be used. Typically, the ends of metal foils rolled to the required thickness are punched, cleaned using chemical or mechanical methods, and then selectively electroplated with materials such as nickel, gold, silver, rhodium, tin-nickel alloy, copper-nickel alloy, or nickel-lead alloy. In the selective plating method, a resistive film is first applied to the parts of the copper foil that do not require plating, and electroplating is only performed on the selected copper foil portions.
4
Brush Plating
Another method of selective plating is called “brush plating.” It is an electro-deposition technique where not all parts are immersed in the electrolyte during the electroplating process. In this electroplating technique, only limited areas are electroplated, while the remaining parts are unaffected. Typically, rare metals are plated on selected areas of the printed circuit board, such as edge connectors. Brush plating is more commonly used in electronic assembly workshops for repairing discarded circuit boards. A special anode (an inert chemical reaction anode, such as graphite) is wrapped in an absorbent material (like a cotton swab) to deliver the electroplating solution to the areas requiring plating.
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