PCB plating has several methods
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:
01
Finger row plating
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 of coating to remove tin or tin-lead coating on protruding contacts
Rinse with washing water
Scrub with abrasive
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
02
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 is accumulated 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 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 more suitable method for prototyping printed circuit boards is to use a specially designed low-viscosity ink to form a highly adhesive and highly conductive 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 and subsequent thermal curing can form a continuous film on the inside 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.
03
Reel linkage type selective plating
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 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 board that does not need to be electroplated, and electroplating only on the selected copper foil part.
04
Brush plating
“Brush plating” is an electrodeposition technique, in which not all parts are immersed in the electrolyte. 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 shops. 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.
5. Manual wiring and processing of key signals
Manual wiring is an important process of printed circuit board design now and in the future. Using manual wiring helps automatic wiring tools to complete the wiring work. By manually routing and fixing the selected network (net), a path that can be used for automatic routing can be formed.
The key signals are wired first, either manually or combined with automatic wiring tools. After the wiring is completed, the relevant engineering and technical personnel will check the signal wiring. After the inspection is passed, the wires will be fixed, and then the remaining signals will be automatically wired. Due to the existence of impedance in the ground wire, it will bring common impedance interference to the circuit.
Therefore, do not randomly connect any points with grounding symbols during wiring, which may produce harmful coupling and affect the operation of the circuit. At higher frequencies, the inductance of the wire will be several orders of magnitude larger than the resistance of the wire itself. At this time, even if only a small high-frequency current flows through the wire, a certain high-frequency voltage drop will occur.
Therefore, for high-frequency circuits, the PCB layout should be arranged as compactly as possible and the printed wires should be as short as possible. There are mutual inductance and capacitance between the printed wires. When the working frequency is large, it will cause interference to other parts, which is called parasitic coupling interference.
The suppression methods that can be taken are:
① Try to shorten the signal wiring between all levels;
②Arrange all levels of circuits in the order of signals to avoid crossing over each level of signal lines;
③The wires of two adjacent panels should be perpendicular or cross, not parallel;
④ When signal wires are to be laid in parallel in the board, these wires should be separated by a certain distance as much as possible, or separated by ground wires and power wires to achieve the purpose of shielding.
6. Automatic wiring
For the wiring of key signals, you need to consider controlling some electrical parameters during wiring, such as reducing distributed inductance, etc. After understanding what input parameters the automatic wiring tool has and the influence of input parameters on the wiring, the quality of the automatic wiring can be obtained to a certain extent Guarantee. General rules should be used when automatically routing signals.
By setting restriction conditions and prohibiting wiring areas to limit the layers used by a given signal and the number of vias used, the wiring tool can automatically route the wires according to the engineer’s design ideas. After setting the constraints and applying the created rules, the automatic routing will achieve results similar to the expected results. After a part of the design is completed, it will be fixed to prevent it from being affected by the subsequent routing process.
The number of wiring depends on the complexity of the circuit and the number of general rules defined. Today’s automatic wiring tools are very powerful and can usually complete 100% of the wiring. However, when the automatic wiring tool has not completed all signal wiring, it is necessary to manually route the remaining signals.
7. Wiring arrangement
For some signals with few constraints, the wiring length is very long. At this time, you can first determine which wiring is reasonable and which wiring is unreasonable, and then manually edit to shorten the signal wiring length and reduce the number of vias.