Introduction of nickel plating process for multilayer PCB circuit board
1, function and characteristics
Multilayer PCB circuit board (is the English printed Circuie board printed circuit board abbreviation) on the nickel-plated as the precious metals and base metal substrate coating, on some PCB single-sided circuit boards, also often used as a surface layer. multilayer PCB For heavy load wear of some surface, such as switch contact, touch piece or plug gold, nickel as a gold substrate coating, can greatly improve wear resistance. When used as a barrier layer, nickel can effectively prevent the diffusion of copper and other metals. The matte nickel/gold composite coating is often used as an etching-resistant metal coating, multilayer PCB and can adapt to hot-pressing welding and brazing requirements, only read nickel can be used as a corrosion-resistant coating of ammonia-like etching, without the need for hot-pressing welding and require the plating layer of bright multilayer PCB circuit boards, usually the use of light nickel/gold plating. Nickel plating thickness is generally not less than 2.5 microns, usually using 4-5 microns.
Multilayer PCB circuit board low stress nickel deposition layer, usually with the modified type of W-ni plating solution and has the effect of reducing the stress of some of the additives of the amino acid nickel plating bath.
We often say that multi-layer PCB circuit board Nickel-plated with nickel and matte nickel (also known as low stress nickel or half bright nickel), usually requires a uniform coating, low porosity, low stress, good ductility characteristics
2, amino sulfonic acid nickel (ammonia nickel)
Ni-amino-sulfonic acid nickel is widely used as a substrate coating on metal-plated holes and printed plugs. multilayer PCB The obtained deposition layers have low internal stress, high hardness and excellent ductility. A stress inhibitor is added to the bath and the coating will be slightly stressed. There are many different formulations of amino sulfonate plating solution. Because of the low stress of the coating, it has been widely used, but the stability of the amino-sulfonic acid nickel is poor and its cost is relatively high.
3, Modified W-ni (nickel sulfide)
The modified W-ni formula is nickel sulfate, together with the addition of nickel bromide or nickel chloride. Because of the internal stress, most of the nickel bromide is used. It can produce a half bright, slightly internal stress, a good ductility of the coating, and this coating for subsequent plating is very easy to activate, the cost is relatively bottom.
4, the role of various components of the bath:
Main salts of ── amino sulfonic acid nickel and nickel sulfate are the main salts in nickel solution, and nickel salts provide nickel metal ions for nickel plating and play the role of conductive salts. multilayer PCB The concentration of nickel plating liquid varies slightly with the supplier, and the allowable content of nickel salt varies greatly. The nickel salt content is high, can use the high cathode current density, the deposition speed is quick, commonly used as the high speed thick nickel. But the concentration is too high to reduce the cathode polarization, dispersion capacity is poor, and the loss of the plating solution is large. Nickel salt content low deposition speed, but the dispersion is very good, can obtain crystallization of fine bright coating.