Label：PCB Production, Plating Methods, Through-hole Plating
Jan 22, 20213220
There are four main types of plating methods in PCB (Printed Circuit Board) production: finger-plated plating, through-hole plating, reel linkage selective plating and brushing plating.
Here's a brief introduction:
1. Finger-plated plating
Rare metals need to be plated on the board edge connectors, board edge joint or gold fingers to provide lower contact resistance and higher abrasive resistance. This technique is known as finger-plated or protruding partial plating. Gold is often plated on the inner nickel coating of board edge connectors’ protruding contact head. The gold finger or the board edge protruding partial use the manually or automatically plated technology. The gold that plated on the contact head or gold finger has been replaced by rhodanise, lead plating and plating button.
The process of finger-plating plating is as follows:
a. Strip the coating to remove the tin or the tin-lead coating of the protruding contact head.
b. Rinse with water
c. Scrub with abrasive
d. Activated immersion in 10% sulfuric acid
e. Plate nickel on the protruding contact head, and the thickness is 4-5μm
f. Clean and remove mineral water
g. Gold permeation solution treatment
h. Gold plating
2. Through-hole plating
There are a number of ways to create a desirable layer of plating on the walls of the substrate borehole. This is referred to as hole wall activation in industrial applications, and its printed circuit production process requires multiple intermediate storage tanks, each having its own control and maintenance requirements. Through-hole plating is a necessary manufacturing process for the drilling process. When the drill bit drills through the copper foil and the substrate below it, the heat generated causes the insulating synthetic resin constituting most of the base of the substrate to melt. And the molten resin and other drilled fragments heap up around the holes and apply to the newly exposed hole walls of the copper foil, which is in fact detrimental to the subsequent plating surface. The molten resin also leaves a hot axis on the hole walls of the substrate.
It exhibits poor adhesion to most activators, which requires the development of techniques for stain removal and etch back chemistry.
One method that is more suitable for prototype PCB production is to use a specially designed low viscosity ink to form a highly adherent, highly conductive film on the inner wall of each via. This eliminates the need for multiple chemical treatments, requires only one application step, followed by thermal curing to form a continuous film on the inside of all the walls of the hole, which can be directly electroplated without further processing. This ink is a resin-based material that has a very strong adhesion and can be bonded to most thermally polished hole walls without any effort. Thus eliminates the step of etch back.
3.Reel linkage selective plating
Pins and contact pins for electronic components, such as connectors, integrated circuits, transistors, and flexible printed circuits, are all choose selectively plated for good contact resistance and corrosion resistance. This plating method can be either manual or automatic, and it is very expensive to individually select each of the pins, so batch welding must be used. Usually, the ends of the metal foil which are flattened to the required thickness are die-cut, chemically or mechanically cleaned, and then selectively used like nickel, gold, silver, iridium, button or tin-nickel alloy, copper-nickel alloy, nickel-lead alloy to continuous plate. In this plating method, first, a portion of the metal copper foil plate which is not required to be plated is coated with a resist film, and plating is performed only on the selected copper foil portion.
Another method of selecting plating is called "brushing plating". It is an electrode position technique in which not all parts are immersed in the electrolyte during the plating process. In this plating technique, only a limited area is plated. While there is no impact on the rest. Typically, rare metals are plated on selected portions of the printed circuit board, such as board edge connectors. Brush plating is used more often in the electronics assembly shop to repair waste boards. A special anode (chemically reactive anode, such as graphite) is wrapped in an absorbent material (cotton stick) that is used to bring the plating solution to where it is needed.