PCB Fabrication

Four main methods of electroplating methods in circuit boards

by:A-TECH      2021-03-20
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 requires rare metals to be plated on the board edge connector, board edge protruding contact or gold finger to provide lower contact resistance and higher wear resistance. This technology is called For 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 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. Washing water, rinsing, scrubbing, scrubbing and activation, immersion in 10% sulfuric acid, nickel plating on the protruding contacts, thickness For 4-5μm cleaning and removing mineral water, gold penetration solution treatment, gold plating cleaning and drying 2. Through-hole plating has a variety of methods to build a layer of plating that meets the requirements on the hole wall of the substrate drilled hole, which is called in industrial applications In order to activate the hole wall, the commercial production process of its printed circuit 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 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. The reel linkage type selects the pins and pins of the electronic components, such as connectors, integrated circuits, transistors and flexible printed circuits, etc., 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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