PCB, which stands for Printed Circuit Board, utilizes nickel plating as the substrate plating for both precious metals and base metals. Additionally, nickel is often used as a surface layer for some single-sided printed boards. In applications where surfaces are subjected to heavy loads, such as switch contacts or plug gold, using nickel as the gold substrate plating can significantly enhance wear resistance. When used as a barrier layer, nickel effectively prevents diffusion between copper and other metals. A dumb nickel/gold composite coating is commonly utilized as an anti-etching metal coating, meeting the requirements of hot-press welding and brazing. Nickel is essential for anti-corrosive coatings in ammonia-containing etchants, particularly for PCBs that necessitate bright plating; light nickel/gold plating is typically employed. The thickness of the nickel plating layer is generally no less than 2.5 microns, typically ranging from 4-5 microns.
The deposited layer of low-stress nickel on PCBs is often plated using a modified Watt nickel plating solution or sulfamate nickel plating solutions with stress-reducing additives.
PCB nickel plating encompasses bright nickel and dumb nickel (also known as low-stress nickel or semi-bright nickel), requiring uniform and fine plating, low porosity, low stress, and excellent ductility.
Nickel sulfamate is extensively used as the substrate plating for metallized hole plating and printed plug contacts on PCBs. The deposited layer exhibits low internal stress, high hardness, and exceptional ductility. By adding a stress relief agent to the plating solution, the resulting plating layer becomes slightly stressed. There are various formulations of sulfamate baths available, with the typical formulations of nickel sulfamate baths outlined below. Despite the widespread use of low-stress coatings, nickel sulfamate’s stability is subpar and the cost is relatively high.
The modified Watt Nickel formula involves the use of nickel sulfate, along with the addition of nickel bromide or nickel chloride. Nickel bromide is primarily used due to its ability to reduce internal stress, producing a semi-bright, slightly internally stressed, and ductile coating. This coating is easily activated for subsequent electroplating, and is cost-effective.
1. Nickel sulfamate and nickel sulfate are the primary salts utilized in nickel plating solutions. These salts provide essential nickel metal ions and serve as conductive agents. The concentration of nickel plating solutions may slightly vary among suppliers, with significant differences in the allowable nickel salt content. Higher nickel salt concentrations allow for increased cathode current density and rapid deposition, commonly employed in high-speed thick nickel plating. However, excessively high concentrations can diminish cathodic polarization, reduce dispersion capability, and result in substantial solution loss. Conversely, lower nickel salt concentrations yield slower deposition rates but offer excellent dispersion properties, resulting in fine, lustrous crystalline coatings.
2. Boric acid functions as a buffer to maintain the pH of the nickel plating solution within an optimal range. Low pH values decrease cathode current efficiency, while high pH values lead to excessive H2 precipitation, causing rapid pH elevation near the cathode surface and the formation of Ni(OH)2 colloids, which increase coating brittleness. Additionally, Ni(OH)2 colloid adsorption on the electrode surface traps hydrogen bubbles, increasing coating porosity. Boric acid not only buffers pH but also enhances cathode polarization, improving plating solution performance and reducing “scorching” at high current densities. Moreover, boric acid enhances coating mechanical properties.
3. Except for sulfate-based nickel plating solutions employing insoluble anodes, soluble anodes are used in other nickel plating processes. Nickel anodes are prone to passivation during electrolysis, necessitating the addition of anode activators to ensure normal dissolution. Experimentation has identified chloride ions (Cl-) as optimal nickel anode activators. In nickel plating baths containing nickel chloride, the chloride not only serves as the primary and conductive salt but also acts as an anode activator. Solutions lacking nickel chloride or containing low concentrations require supplemental sodium chloride. Nickel bromide or nickel chloride is commonly employed as a stress relief agent to manage coating internal stress and impart a semi-bright appearance.
4. The primary additive component is the stress reliever, which enhances cathodic polarization, reduces coating internal stress, and can transition stress from tension to compression with varying concentrations. Commonly used stress relievers include naphthalenesulfonic acid, p-toluenesulfonamide, and saccharin. Adding a stress reliever to the plating solution produces a uniform, fine, semi-bright coating compared to coatings without one. Typically, stress relievers are added based on ampere-hour usage, with current general-purpose additives including anti-pinhole agents.
5. During electroplating, hydrogen precipitation on the cathode is inevitable, reducing cathodic current efficiency and potentially causing pinholes in the coating due to trapped hydrogen bubbles. To mitigate pinhole formation, small amounts of wetting agents such as sodium lauryl sulfate, sodium diethylhexyl sulfate, or sodium n-octyl sulfate should be added to the plating solution. These anionic surface-active substances adsorb onto the cathode surface, reducing interfacial tension between the electrode and solution and lowering the wetting contact angle of hydrogen bubbles, facilitating their departure from the electrode surface and preventing or minimizing pinhole formation in the coating.
The deposited layer of low-stress nickel on PCBs is often plated using a modified Watt nickel plating solution or sulfamate nickel plating solutions with stress-reducing additives.
PCB nickel plating encompasses bright nickel and dumb nickel (also known as low-stress nickel or semi-bright nickel), requiring uniform and fine plating, low porosity, low stress, and excellent ductility.
Nickel sulfamate is extensively used as the substrate plating for metallized hole plating and printed plug contacts on PCBs. The deposited layer exhibits low internal stress, high hardness, and exceptional ductility. By adding a stress relief agent to the plating solution, the resulting plating layer becomes slightly stressed. There are various formulations of sulfamate baths available, with the typical formulations of nickel sulfamate baths outlined below. Despite the widespread use of low-stress coatings, nickel sulfamate’s stability is subpar and the cost is relatively high.
The modified Watt Nickel formula involves the use of nickel sulfate, along with the addition of nickel bromide or nickel chloride. Nickel bromide is primarily used due to its ability to reduce internal stress, producing a semi-bright, slightly internally stressed, and ductile coating. This coating is easily activated for subsequent electroplating, and is cost-effective.
1. Nickel sulfamate and nickel sulfate are the primary salts utilized in nickel plating solutions. These salts provide essential nickel metal ions and serve as conductive agents. The concentration of nickel plating solutions may slightly vary among suppliers, with significant differences in the allowable nickel salt content. Higher nickel salt concentrations allow for increased cathode current density and rapid deposition, commonly employed in high-speed thick nickel plating. However, excessively high concentrations can diminish cathodic polarization, reduce dispersion capability, and result in substantial solution loss. Conversely, lower nickel salt concentrations yield slower deposition rates but offer excellent dispersion properties, resulting in fine, lustrous crystalline coatings.
2. Boric acid functions as a buffer to maintain the pH of the nickel plating solution within an optimal range. Low pH values decrease cathode current efficiency, while high pH values lead to excessive H2 precipitation, causing rapid pH elevation near the cathode surface and the formation of Ni(OH)2 colloids, which increase coating brittleness. Additionally, Ni(OH)2 colloid adsorption on the electrode surface traps hydrogen bubbles, increasing coating porosity. Boric acid not only buffers pH but also enhances cathode polarization, improving plating solution performance and reducing “scorching” at high current densities. Moreover, boric acid enhances coating mechanical properties.
3. Except for sulfate-based nickel plating solutions employing insoluble anodes, soluble anodes are used in other nickel plating processes. Nickel anodes are prone to passivation during electrolysis, necessitating the addition of anode activators to ensure normal dissolution. Experimentation has identified chloride ions (Cl-) as optimal nickel anode activators. In nickel plating baths containing nickel chloride, the chloride not only serves as the primary and conductive salt but also acts as an anode activator. Solutions lacking nickel chloride or containing low concentrations require supplemental sodium chloride. Nickel bromide or nickel chloride is commonly employed as a stress relief agent to manage coating internal stress and impart a semi-bright appearance.
4. The primary additive component is the stress reliever, which enhances cathodic polarization, reduces coating internal stress, and can transition stress from tension to compression with varying concentrations. Commonly used stress relievers include naphthalenesulfonic acid, p-toluenesulfonamide, and saccharin. Adding a stress reliever to the plating solution produces a uniform, fine, semi-bright coating compared to coatings without one. Typically, stress relievers are added based on ampere-hour usage, with current general-purpose additives including anti-pinhole agents.
5. During electroplating, hydrogen precipitation on the cathode is inevitable, reducing cathodic current efficiency and potentially causing pinholes in the coating due to trapped hydrogen bubbles. To mitigate pinhole formation, small amounts of wetting agents such as sodium lauryl sulfate, sodium diethylhexyl sulfate, or sodium n-octyl sulfate should be added to the plating solution. These anionic surface-active substances adsorb onto the cathode surface, reducing interfacial tension between the electrode and solution and lowering the wetting contact angle of hydrogen bubbles, facilitating their departure from the electrode surface and preventing or minimizing pinhole formation in the coating.
