In printed circuit boards, copper is used to interconnect components on the substrate. Although it is a good conductor material for forming the pattern of the conductive path of the printed circuit board, if it is continuously exposed to the air, it will easily lose its luster due to oxidation and corrosion and lose its solderability. So, various technologies must be used to protect copper printed wiring, vias and plated through holes. These technologies include organic coatings, oxide films and electroplating.
The application of organic coatings is very simple, but due to changes in its concentration, composition and curing cycle, it is not suitable for long-term use. It may even cause unpredictable deviations in solderability. The oxide film can protect the circuit from corrosion, but cannot maintain solderability. Electroplating or metal coating processes are standard operations to ensure solderability and protect circuits from corrosion, and play an important role in the manufacture of single-sided, double-sided and multilayer printed circuit boards. In particular, plating a layer of solderable metal on printed wiring has become a standard operation to provide a solderable protective layer for copper printed wiring.
In electronic equipment, the interconnection of various modules usually requires the use of a printed circuit board socket with spring contacts and a printed circuit board with matching connection contacts. These contacts should have a high degree of wear resistance and very low contact resistance, which requires a layer of rare metal plating on them, of which the most commonly used metal is gold. In addition, other coated metals can be used on printed circuits, such as tin plating, electroplating, and sometimes copper can also be plated in certain printed areas.
Another type of coating on copper traces is an organic coating, usually a solder mask. Use screen printing technology to cover a layer of epoxy resin film where welding is not required. This process of applying a layer of organic solderability preservatives does not require electronic exchange. When the circuit board is immersed in the electroless plating solution, the nitrogen-resistant compound will stay on the bare metal surface and will not be absorbed by the substrate.
The precise technology required by electronic products and the strict requirements of environmental and safety adaptability have made considerable progress in the practice of electroplating. This is clearly reflected in the manufacturing of high-complexity, high-resolution multi-substrate technology.
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