1 , the role and characteristics
PCB ( printed circuit board English abbreviation ) nickel-plated on the substrate coating as precious and base metals , for some single-sided printed circuit boards, also used as a surface layer . For some heavy-duty wear surface , such as switch contacts , contacts or plug is gold plated with nickel and gold as a substrate , can greatly improve the wear resistance. When used as a barrier layer of nickel can effectively prevent the diffusion of copper and other metals. Matte nickel / gold plating compositions are often used as an etch-resistant metal coating , and can adapt to the thermocompression bonding and brazing requirements , can be used as read- only nickel- ammonia type etching resist coating agent , without thermocompression also requested shiny coating PCB, usually light nickel / gold plating. Usually the thickness of the nickel plating layer not less than 2.5 micrometers, usually 4-5 micrometers.
PCB low stress nickel deposition layer, usually with a modified type of Watt nickel bath and a nickel sulfamate bath with a number of stress reducing additive to the plating .
We often say that the PCB matte nickel and nickel-plated bright nickel ( also known as low-stress nickel or semi-bright nickel ) , usually require meticulous coating uniformity , low porosity, low stress , and good ductility .
2 , nickel sulfamate ( Ni ammonia )
Amino acids are widely used as the nickel metal plating and printing plug contact hole plating film on the substrate . Internal stress of the deposited layer obtained low, high hardness , and has a very superior scalability. The one kind of agent is added to the stress in the bath , the resulting coating will be just a little stress . There are many different formulations sulfamate bath , a nickel sulfamate plating bath typical recipes in the following table . Since the stress in the coating is low, so widely used, but the poor stability of nickel sulfamate , the cost is relatively high.
3 watt nickel- modified ( S Ni )
W. Nickel modified formula, using nickel sulfate, nickel bromide or together with nickel chloride . Due to the internal stress , the selected mostly nickel bromide . It can produce a semi-bright , just a little stress, ductile coating ; and this coating is easily activated subsequent electroplating , the cost is relatively the end.
4 , the role of each component of the bath :
The nickel salt solution in the main primary salts, nickel salts is to provide the desired nickel and nickel metal ions , and plays the role of the conductive salt ─ ─ nickel sulfamate to nickel sulfate . Concentration of nickel plating with a slightly different different suppliers , nickel salt content changes allowing greater . Nickel salt content, use of higher cathodic current density , deposition rate , thick plating of nickel used at a high speed . But the concentration is too high will reduce the cathodic polarization , dispersion ability, but with the loss of a large bath . Nickel salt content is low low deposition rate , but the dispersion ability is very good, bright coating can be obtained crystalline detail .
