PCB Technical - About the special PCB circuit board plating method

This article mainly introduces 4 special plating methods in circuit board welding.

The first type, finger row 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 technique is called finger row plating or protruding part plating. Gold is often plated on the protruding contacts of the board edge connector with the inner plating layer of nickel. The gold finger or the protruding part of the board edge is 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 is as follows:

1) Strip the coating to remove the tin or tin-lead coating on the protruding contacts

2) Rinse with washing water

3) Scrubbing with abrasives

4) The activation is diffused in 10% sulfuric acid

5) The thickness of nickel plating on the protruding contacts is 4 -5μm

6) Clean and demineralize water

7) Gold penetration solution treatment

8) Gold plated

9) Cleaning

10) Drying

The second type, through-hole plating

There are many ways to build a layer of electroplating layer 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. This requires the development of a class of similar de-staining and etch-back chemical technologies.

A method more suitable for PCB prototyping 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 etchback.

The third type, reel linkage type selective plating

The pins and pins of electronic components, such as connectors, integrated circuits, transistors, and flexible FPCs, 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 like 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 plate that does not need to be electroplated, and electroplating only on the selected copper foil part.

The fourth type, 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 PCB 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.