Common problems and troubleshooting methods for nickel electroplating

Nickel plating is currently the most commonly used plating method for electroplating, as it is widely used and many people will not eliminate all common faults. In this issue, we will talk about common problems and troubleshooting methods for nickel plating. Nickel plating has evolved from ordinary nickel plating (dark nickel) to full bright nickel plating, and the brighteners used for nickel plating have also evolved from inorganic brighteners to fourth generation organic brighteners. The fully bright nickel plating bath currently used in the electroplating industry is basically watt type, and its formula and process specifications are basically the same except for concentrated brighteners. When nickel plating malfunctions, the process execution should be checked, the cause of the malfunction analyzed, and resolved.
2. Causes of faults and troubleshooting methods
2.1 Process imbalance
2.1.1 Insufficient brightness of the coating
2.1.1.1 Causes
(1) There is too little brightener, the main salt content is too low, the anode plate is too short and too few, and the deposition rate and migration rate of nickel ions cannot reach a balance, resulting in insufficient brightness of the coating.
(2) The pH and temperature are too high. At this point, the main salt is easily hydrolyzed into Ni (OH) 2 precipitation, and some Ni (OH) 2 is mixed in the coating, resulting in insufficient brightness of the coating.
(3) After acidic copper plating, the parts were not cleaned. At this point, there is an alkaline film on the surface of the part (copper layer), and nickel deposits on the film layer, causing the coating to not achieve mirror gloss.
2.1.1.2 Exclusion methods
(1) Supplement the main brightener, and correspondingly, supplement the auxiliary brightener. Adjust the main salt and other components according to the process requirements, and add anode nickel plates.
(2) Adjust the pH with dilute sulfuric acid and lower the temperature to the process specifications.
(3) After acidic copper plating, the parts should be thoroughly cleaned, and if necessary, dilute sulfuric acid can be used to remove the film.
2.1.2 The nickel plating layer is orange peel like
2.1.2.1 Causes
When the pH of the plating solution is too high and the wetting agent is excessive, the wetting agent is prone to react with Ni2+, generating insoluble compounds that randomly adsorb (or precipitate) on the surface of the parts, resulting in uneven coating thickness.
2.1.2.2 Exclusion methods
Add a small amount of activated carbon to absorb some of the wetting agent, filter, and then adjust the pH to the process specifications with dilute sulfuric acid.
2.1.3 Nickel layer is prone to burning
2.1.3.1 Causes
There is too little main salt in the plating solution, the temperature is too low, the pH is too high, and the current density is too high. During the process of nickel deposition, the amount of Ni2+lost needs to reach a dynamic balance with the amount of Ni2+migrating near the cathode. However, due to the scarcity of main salts and the low temperature, very low concentrations of Ni2+can only slowly migrate to the vicinity of the cathode for discharge deposition under low temperature conditions. At the same time, a high pH results in the formation of light green Ni (OH) 2 precipitates that are slightly soluble in water, resulting in less Ni2+in the plating solution. Under the action of high current density, the positive and negative ions near the cathode cannot reach equilibrium, causing the coating to burn.
2.1.3.2 Exclusion methods
According to the analysis report, supplement the main salt, increase the temperature of the plating solution, adjust the pH to the process specification with dilute sulfuric acid, filter the plating solution, and adjust the current density appropriately.
2.1.4 Coating peeling and foaming
2.1.4.1 Causes
(1) The presence of Zn2+and N03- impurities in the plating solution not only causes black stripes and other phenomena in the coating, but also increases the internal stress of the coating, causing brittle cracking of the nickel layer and ultimately powdery detachment.
(2) Saccharin is the main component in light aids. When adding too much saccharin as a self formulated light aid, it can increase the internal stress of the nickel layer, resulting in peeling and detachment of the nickel layer.
(3) Poor pre-treatment before plating. There are residual oxide scales and other debris on the surface of the parts, causing the nickel layer to peel and blister.
2.1.4.2 Exclusion methods
(1) When removing Zn2+, corrugated iron sheet can be used as the cathode and electrolyzed at a rate of 0.2-0.4A/dm2 under stirring conditions until it is completely removed; When removing N03-, first adjust the pH to 1-2, then use a large area anode and a small area cathode to electrolyze at a current density greater than 1.4-dm2 for 1-2 hours, and then decrease to 0.2A/dm2 to continue electrolysis until the coating is normal.
(2) When there is too much saccharin, dilute the plating solution with water, and supplement the corresponding amount of main salt, boric acid, and main brightener. Alternatively, 2-3 mL/L.H202 (W=30%) can be used to decompose saccharin and other brighteners, and then the plating solution can be heated to 60-80 ℃ under stirring conditions to remove excess H202. Then, 2-3 g/L electroplated grade activated carbon can be added, stirred for 0.5 hours, allowed to stand for 2-3 hours, filtered, supplemented with NiS04 and H3B03 according to the analysis report, and the pH adjusted. Finally, the main and auxiliary brighteners can be added according to the requirements of the new tank.
(3) Strengthen the pre-treatment work of parts, and strictly prohibit residual oxide skin and oil stains on the surface of parts.
2. There are pinholes and pits on the I.5 nickel layer
2.1.5.1 Causes
(1) There is too little wetting agent. The hydrogen bubbles generated by the electrode action are prone to stay on the surface of the cathode, and Ni2+continuously discharges and deposits around the hydrogen bubbles. The nickel layer gradually thickens: when the nickel layer is too thick for the hydrogen bubbles to withstand, the bubbles will automatically rupture. The bubble area without the deposited nickel layer will have pits, such as pinholes or pits.
(2) There is air inside the pump. A plating bath with discontinuous filtration. The pump on the filter is mobile and always contains a certain amount of air. When the filter is used, the residual air in the pump is not completely removed, and this air enters the plating layer as bubbles with the operation of the pump, causing the same malfunction as when there is too little wetting agent.
(3) There are organic impurities such as animal glue and oil stains inside the coating. These non conductive organic impurities will adhere to the surface of the part, and Ni2+cannot discharge and deposit on it; In areas where organic impurities are not adhered, the coating continues to deposit and thicken. In this way, concave pinholes or pits are formed.
(4) After adjusting the plating solution with a wetting agent, there are still spots on the coating, so it is necessary to consider whether the Fe3+content is too high. Fe3+forms a colloidal form in the plating solution, which is difficult to filter out. When it adheres to the surface of the part, the coating becomes pitted.
2.1.5.2 Exclusion methods
(1) Using Hull cell test data as the basis for supplementing wetting agents. Alternatively, a lead wire ring with a diameter of 90-100 mm and a handle can be gently lifted in parallel from the plating solution. When the liquid film inside the ring is intact and unbroken, the wetting agent content is normal. There is too little wetting agent, and there is no liquid film formed inside the circle; Too much makes it difficult for the liquid film to disappear.
(2) Before filtering the plating solution, the air inside the pump should be removed with filtrate or deionized water.
(3) When removing organic impurities, first use 2-3 mL/L of H202 to oxidize the organic impurities in the solution; Then, under stirring conditions, 2-3 g/L of powdered activated carbon is added to the solution and heated to 60-70 ℃. Stir for 0.5 hours and let stand for 3, 4 hours or overnight. Finally, filter and try plating.
(4) Remove Fe3+impurities. Heat the plating solution to 60-70 ℃, then add 0.5-1.0g/L lead sulfate dissolved in hot water and stir for 1 hour. Then add 2-5g/L activated carbon and continue stirring for 1 hour; Adjust the pH to 6 and let it stand for 4 hours or overnight; Filter and then conduct low current electrolysis for 0.5 hours; Finally, add brightener and try plating.