Nickel plating is used as the substrate coating for precious metals and base metals on PCB (the abbreviation of Printed Circuie Board). It is also commonly used as a surface layer for some single-sided printed boards. For some surfaces that are heavily worn, such as switch contacts, contacts, or plug gold, using nickel as a backing layer of gold can greatly improve wear resistance. When used as a barrier, nickel is effective in preventing diffusion between copper and other metals. Dumb nickel/gold combination coatings are often used as etching-resistant metal coatings, and can meet the requirements of hot-press welding and brazing. Only nickel can be used as a corrosion-resistant coating for ammonia-based etchants without hot-press welding. PCBs with bright plating are also required, usually with bright nickel/gold plating. Nickel plating thickness is generally not less than 2.5 microns, usually 4-5 microns.
PCB low-stress nickel deposits are usually plated with modified Watts nickel baths and some nickel sulfamate baths with stress-reducing additives.
PCB nickel plating includes bright nickel and matt nickel (also known as low stress nickel or semi-bright nickel), which usually require uniform and meticulous plating, low porosity, low stress and good ductility.
Nickel sulfamate is widely used as a substrate coating on metallized hole plating and printed plug contacts. The obtained deposited layer has low internal stress, high hardness and excellent ductility. Add a stress reliever to the bath and the resulting coating will be slightly stressed. There are a variety of sulfamate baths with different formulations. The typical nickel sulfamate bath formula is shown in the table below. Due to the low stress of the coating, it is widely used, but the stability of nickel sulfamate is poor, and its cost is relatively high.
Modified Watts Nickel formulation using nickel sulfate, along with the addition of nickel bromide or nickel chloride. Due to internal stress, nickel bromide is mostly used. It can produce a semi-bright, slightly internal stress, good ductility coating. And this coating is easy to activate for subsequent electroplating, and the cost is relatively low.
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