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PCB Circuit Board Electroplating Nickel Process Analysis

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PCB circuit board with nickel plating as a precious metal and base metal substrate plating, for some PCB single-sided circuit board, also commonly used as a surface layer. pcb circuit board nickel plating process has what effect? What are the advantages? The following one to understand.

With regard to heavy load wear and tear of some of the appearance, such as switch contacts, contacts or plug gold, nickel is used as a gold backing plating layer, which can greatly advance the wear resistance. When used as a barrier layer, nickel can effectively avoid laxity between copper and other metals. Dumb nickel / gold combination plating is often used as a resist etching metal plating, and can adapt to the requirements of hot press welding and brazing, only read as long as the nickel can be used as a resist plating containing ammonia etchant, and do not need to be hot press welding and require a bright coating PCB multilayer circuit boards, the general choice of light nickel / gold plating. Nickel plating thickness is generally not less than 2.5 microns, generally choose 4-5 microns.

PCB circuit board low-stress nickel precipitation layer, generally with a modified type of watt nickel plating solution and some sulfamic acid nickel plating solution with the effect of decreasing the stress of the increasing agent to plating system.

We often say that the PCB multilayer circuit board nickel plating has bright nickel and matte nickel (also known as low-stress nickel or semi-glossy nickel), generally requires uniform plating exhaustive, low porosity, low stress, good ductility characteristics.

Nickel Sulfamate (Ammonia Nickel)        

Nickel sulfamate is widely used as a substrate coating on metallized hole plating and printed plug contacts. The precipitated layer obtained has low internal stress, high hardness, and extremely excellent ductility. By adding a stress relieving agent to the plating solution, the resulting layer will be slightly stressed. There are a number of different formulations of sulfamate plating solutions, and a typical sulfamate nickel plating solution formulation is shown in the table below. Because of the low stress of the plated layer, it has gained wide application, but nickel sulphamate has poor unrestability and its cost is relatively high.

Modified Watts Nickel (Sulfur Nickel)

Modified Watt nickel formula, choose nickel sulfate, together with participation in nickel bromide or nickel chloride. Nickel bromide is mostly chosen because of the internal stress. It can produce a semi-bright, slightly internal stress, good ductility of the coating; and this coating for the subsequent plating is easy to activate, the cost is relatively low.

Advantages of nickel plating process for pcb circuit boards

The main salt - nickel sulfamate and nickel sulfate for the main salt in the nickel solution, nickel salt is the primary supply of nickel plating nickel metal ions required and also plays the role of conductive salt effect. The concentration of nickel-plating solution varies slightly with different suppliers, and the promised content of nickel salt changes greatly. Nickel salt content is high, can use higher cathodic current density, fast buildup, commonly used for high-speed plating of thick nickel. But the concentration is too high will decrease the cathodic polarization, disorganization ability is poor, and the loss of the plating solution out of the band is large. Nickel salt content of low accumulation rate is low, but the disorganization is very good, can obtain the crystallization of exhaustive bright plating.       

PCB -41

Buffer - boric acid is used as a buffer to maintain the pH value of nickel-plating solution within a certain range. Practice has confirmed that when the nickel-plating liquid PH value is too low, will make the cathode current efficiency; and PH value is too high, due to the continuous separation of H2, so that the cathode around the exterior of the liquid layer of the PH value of the rapid increase, resulting in the natural generation of Ni (OH) 2 colloid, Ni (OH) 2 in the plating of the interference, so that the brittleness of the plating increased, together with Ni (OH) 2 colloid adsorption in the electrode exterior, will also form Hydrogen bubbles in the electrode appearance of the stay, so that the porosity of the plating layer increases. Boric acid is not only PH buffer effect, and he can advance the cathodic polarization, and then improve the function of the plating solution to reduce the "burning" phenomenon in the high current density. The presence of boric acid is also conducive to improving the mechanical function of the plating layer.

Anode activator - In addition to sulfate-type nickel plating solution using insoluble anode, other types of nickel plating process are selected soluble anode. The nickel anode is easy to passivate in the process of electrification, in order to ensure the normal dissolution of the anode, in the plating solution to participate in a certain amount of anode activator. Through experiments, it is found that CI-chloride ion is the best nickel anode activator. In the nickel plating solution containing nickel chloride, nickel chloride, in addition to being the main salt and conductive salt, also plays the effect of anode activator. In the nickel plating solution that does not contain nickel chloride or its content is low, it is necessary to increase a certain amount of sodium chloride according to the actual situation. Nickel bromide or nickel chloride is also commonly used as a stress reliever to adhere to the internal stress of the plating layer, and endowed with the plating layer with a semi-glossy appearance.

Increasing agent - the primary component of the increasing agent is stress relieving agent, stress relieving agent participation, improve the cathodic polarization of the plating solution, reduce the internal stress of the plating layer, with the change of the concentration of stress relieving agent, it can make the plating layer internal stress by tensile stress change to compressive stress. Commonly used additives are: naphthalene sulfonic acid, p-toluene sulfonamide, saccharin and so on. Compared with the nickel plating layer without stress relieving agent, the plating solution with the participation of stress relieving agent will obtain uniform and detailed plating layer with semi-brightness. Generally, the stress relieving agent is added by ampere per hour (now the general-purpose combination of special additives includes anti-pinhole agent, etc.).

Moisture agent - in the electroplating process, the cathode on the separation of hydrogen is unavoidable, the separation of hydrogen not only reduces the cathode current efficiency, and due to the hydrogen bubbles in the electrode appearance of the stay, but also will make the plating layer flooded with pinholes. The porosity of the nickel plating layer is relatively high, in order to reduce or avoid the occurrence of pinholes, should be to the plating solution to participate in a few humidifying agents, such as sodium dodecyl sulfate, sodium diethylhexyl sulfate, sodium n-octyl sulfate, etc., which is a kind of anionic type of appearance of the active substance, can be adsorbed on the cathode appearance, so that the electrode and the interfacial tension between the solution decreases, the hydrogen bubble in the electrode on the humid contact angle decreases, and then the negative gas bubbles can easily detach from the electrode appearance, avoiding or alleviating the occurrence of pinholes in the plating layer.

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