There are four special plating methods in the production of PCB. They are row plating, through-hole plating, coil-driven selective plating and brush plating.
1. Finger row electroplating
Rare metals are often plated on edge connectors, edge protruding contacts or golden fingers to provide lower contact resistance and higher wear resistance. This technology is called finger-row electroplating or protruding part electroplating.
In electroplating, gold is often plated on the protruding contacts of plate-edge connectors with inner nickel coating. Manual or automatic plating technology is used for the protruding parts of gold finger or plate edge. At present, the gold plating on contact plugs or gold finger has been replaced by lead plating and button plating.
2. Through-hole plating
In through-hole plating, there are many ways to build a layer of electroplating on the hole wall of the drill hole on the substrate, which is called hole wall activation in industry I application. The commercial production process of printed circuit requires many intermediate storage tanks, each of which has its own control and maintenance requirements.
Through-hole electroplating is a necessary follow-up process in the drilling process. When the drill bit drills through the copper foil and the underlying substrate, the heat generated melts the insulating synthetic resin which constitutes the majority of the substrate substrate. The melted resin and other drilling fragments accumulate around the hole and coat on the newly exposed hole wall in the copper foil.
In fact, this is harmful to the subsequent electroplating surface. The melted resin will also leave a layer of hot axes on the pore wall of the substrate. It shows bad adhesion to most activators, which requires the development of another technology similar to the decontamination and corrosion chemical effect: ink.
Ink is used to form a high adhesion, high conductivity love film on the inner wall of each through hole, so it does not need to use multiple chemical treatment processes, only one application step, followed by thermal curing, can form a continuous love film on the inner wall of all through holes, and it can be directly electroplated without further treatment. This ink is a resin-based material, which has a strong adhesion and can be easily bonded to most hot-polished pore walls, thus eliminating the step of backetching.
3. Selective plating of coil wheel linkage type
Bows, feet and pins of electronic components, such as connectors, integrated circuits, transistors and flexible printed circuits, are selectively plated to obtain good contact resistance and corrosion resistance.
This plating method can be manually plated production line or automatic plating equipment. It is very expensive to select plating for each pin separately. Therefore, batch welding must be adopted. In the plating production, the two ends of the gold residence foil which is rolled to the required thickness are usually punched and cut, and cleaned by chemical or mechanical methods. Then, continuous electroplating such as nickel, gold, silver, rhodium, button or tin-nickel alloy, copper-nickel alloy, nickel-lead alloy is selected.
4. Brush plating
The last method is called "brush plating": it is an electrodeposition technique in which not all parts of the plating process are immersed in the electrolyte. In this electroplating technology, only a limited area is electroplated without any effect on the rest.
Normally, rare metals are plated on selected parts of printed PCB, such as edge connectors. Brush plating is used more in repairing waste PCB in electronic assembly workshop. A special anode (an inactive anode, such as graphite) is wrapped in an absorptive material (cotton rod) to carry the electroplating solution to where it is needed.