PCB Tech - Four special plating methods for circuit boards

There are four special electroplating methods in circuit board production, which are row electroplating equipment, through-hole electroplating, reel interlocking selective plating, and brush plating. This article introduces these four special methods in detail.

1. Finger row type electroplating equipment

In electroplating, it is often necessary to plate rare metals on board edge connectors, board edge protruding contacts or gold 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 the board edge connector with the inner plating layer of nickel. The gold fingers or the protruding parts of the board edge use manual or automatic electroplating technology. At present, the gold plating on the contact plug or gold finger has been plated. Replaced by lead and plated buttons.

2. Through hole plating

In through-hole plating, there are many methods to build a layer of plating layer on the hole wall of the substrate drilled hole, which is called hole wall activation in industrial applications. The commercial production process of its printed circuit boards requires multiple intermediate storage tanks, each of which has its own control and maintenance requirements.

Through hole plating is a necessary follow-up process of the drilling process. When the drill bit drills through the copper foil and the substrate below, the heat generated melts the insulating synthetic resin that constitutes most of the substrate matrix, the molten resin and other drilling debris It is piled up around the hole and coated on the newly exposed hole wall in the copper foil.

In fact, this is harmful to the subsequent electroplating surface. The molten resin will also leave a layer of hot shaft on the substrate hole wall. It shows poor adhesion to most activators, which requires the development of another A technology similar to stain removal and etch back chemistry: ink!

The ink is used to form a highly adhesive and highly conductive film on the inner wall of each through hole, so that there is no need to use multiple chemical treatment processes, only one application step, and then heat curing, it can be on all the hole walls. A continuous film is formed on the inside, which can be directly electroplated without further processing. This ink is a resin-based substance that has strong adhesion and can be easily bonded to the walls of most thermally polished holes, thus eliminating the step of etchback.

3. Selective plating with reel linkage

The pins and pins of electronic components, such as connectors, integrated circuits, transistors and flexible printed circuits, use selective plating to obtain good contact resistance and corrosion resistance.

This electroplating method can use manual electroplating production lines or automatic electroplating equipment. It is very expensive to select each pin separately, so batch welding must be used. In electroplating production, the metal foil is usually rolled to the required thickness. The two ends are punched, cleaned by chemical or mechanical methods, and then selectively used such as nickel, gold, silver, rhodium, button or tin-nickel alloy, copper-nickel alloy, nickel-lead alloy, etc. for continuous electroplating.

4. Brush plating

The last method is called "brush plating": it is an electrodeposition technique in which not all parts are immersed in the electrolyte during the electroplating process. In this kind of electroplating technology, only a limited area is electroplated, and it has no effect on the rest.

Usually, rare metals are plated on selected parts of the printed circuit board, such as areas such as board edge connectors. Brush plating is used more when repairing discarded circuit boards in electronic assembly workshops. Wrap a special anode (a chemically inactive anode, such as graphite) in an absorbent material (cotton swab), and use it to bring the electroplating solution to the place where electroplating is needed.