PCB Technical - Four main methods of electroplating in circuit boards

Four main methods of electroplating in circuit boards

There are four main electroplating methods in circuit boards: finger row electroplating, through-hole electroplating, reel-linked selective plating, and brush plating.

Here is a brief introduction:

1. Finger row electroplating

Rare metals need to be plated on the 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. 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 are manually or automatically plated. At present, the gold plating on the contact plug or gold finger has been plated or leaded., Instead of plated buttons.

The process of finger row electroplating is as follows:
Stripping the coating to remove the tin or tin-lead coating on the protruding contacts
Rinse with washing water
Scrub with abrasives
Activation is diffused in 10% sulfuric acid
The thickness of nickel plating on the protruding contacts is 4-5μm
Clean and demineralize water
Gold penetration solution treatment
Gilded
Cleaning
drying

2. Through hole plating

There are many ways to build a layer of electroplating layer that meets the requirements on the hole wall of the substrate drilled hole. This is called hole wall activation in industrial applications. The commercial production process of its printed circuit requires multiple intermediate storage tanks. The tank 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 underneath, the heat generated melts the insulating synthetic resin that constitutes most of the substrate matrix, the molten resin and other drilling debris It accumulates around the hole and is 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 hole wall of the substrate, which exhibits poor adhesion to most activators, which requires the development of a class of similar decontamination and etch-back chemical technologies.

A more suitable method for prototyping printed circuit boards is to use a specially designed low-viscosity ink to form a high-adhesion, high-conductivity film on the inner wall of each through hole. In this way, there is no need to use multiple chemical treatment processes, only one application step, followed by thermal curing, can form a continuous film on the inner side of all the hole walls, which can be directly electroplated without further treatment. This ink is a resin-based substance that has strong adhesion and can be easily adhered to the walls of most thermally polished holes, thus eliminating the step of etch-back.

3. Selective plating with reel linkage

The pins and pins of electronic components, such as connectors, integrated circuits, transistors, and flexible printed circuits, all use selective plating to obtain good contact resistance and corrosion resistance. This electroplating method can be manual or automatic. It is very expensive to selectively plate each pin individually, so batch welding must be used. Usually, the two ends of the metal foil that is rolled to the required thickness 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. In the electroplating method of selective plating, first coat a layer of resist film on the part of the metal copper foil board that does not need to be electroplated, and electroplating only on the selected part of the copper foil.

4. Brush plating

Another method of selective plating is called "brush plating". It is an electrodeposition technique, and 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 there is 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.

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