Nickel, element symbol Ni, atomic weight 58.7, density 8.88g/cm3, electrochemical equivalent of Ni2+1.095g/ah. Nickel coatings for printed circuit boards are divided into semi-bright nickel (also known as low-stress nickel or dumb nickel) and bright nickel. It is mainly used as the bottom layer of the gold plating on the surface of the board or the plug. It can also be used as the surface layer according to the IPC-6012 (1996) standard. The thickness of the coating is not less than 2~2.5μM. Nickel plating should be uniform and fine, with low porosity and good ductility. Low-stress nickel should be suitable for brazing or pressure welding.

Some common problems and solutions of PCB nickel plating:

1) Coating burn
Possible causes of coating burns include insufficient boric acid, low metal salt concentration, low operating temperature, high current density, high pH or insufficient stirring.

2) Low deposition rate
Low pH or low current density will result in low deposition rate.
If the copper coating is not activated to remove the oxide layer, the adhesion between copper and nickel is poor, and peeling of the coating may occur. If the current is interrupted, it may cause the nickel coating to peel itself; if the temperature is too low, it may also peel off.

3) The coating is fragile and the weldability is poor
When the coating is bent or worn to a certain degree, it usually shows the brittleness of the coating, which indicates the presence of organic or heavy metal pollution. Excessive additives will increase the amount of organic matter and decomposition products in the paint. This is the main source of organic pollution and can be treated with activated carbon. Heavy metal impurities can be removed by electrolysis and other methods.

4) Dark coating and uneven color
Dark coating and uneven color indicate metal contamination. Since copper plating is usually performed first, followed by nickel plating, the introduced copper solution is the main source of contamination. It is important to minimize the amount of copper solution on the hanger. In order to eliminate the metal pollution in the battery, corrugated steel plate is used as the cathode, and the current density is 0.12-0.50a/dm2. Poor pretreatment, poor primer, low current density, low main salt concentration, and poor conductive contact all affect the color of the coating.

5) The coating blisters or flakes
Poor pretreatment, long shutdown time, organic impurities are contaminated, current density is too high, temperature is too low, pH is too high or too low, and the impact of impurities is serious.

6) Anode passivation
The anode area is too small and the current density is too high.

7) Pit (pinhole)
Acne marks are the result of organic pollution. Big pits usually indicate oil pollution. If the mixing is not good, the bubbles will not be discharged, which will form spots. Wetting agents can be used to reduce their effects. We usually refer to small pitting as pinholes. Poor pretreatment, metal impurities, too low boric acid content and too low bath temperature will cause pinholes. Therefore, the maintenance of the plating solution and the strict control of the process are the key.

8) Rough (burr)
Roughness means that the solution is dirty and can be corrected after complete filtration; if the pH is too high, hydroxide precipitates are easily formed and should be controlled. If the current density is too high, the anode slime and the impure water added will be impure and the impurities will become rough (burr).

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