Thoroughly remove oil, oxides and other impurities on the surface of the workpiece, using organic solvents to remove oil and alkaline solution combined treatment, and control the pickling time to avoid excessive corrosion.
Author: Anna
Methods to ensure the uniformity of plating layer
I. Optimization of pre-plating treatment
1. Surface cleaning and leveling
Thoroughly remove oil, oxides and other impurities on the surface of the workpiece, using organic solvents to remove oil and alkaline solution combined treatment, and control the pickling time to avoid excessive corrosion.
Reduce surface roughness by mechanical polishing or chemical polishing to ensure uniform current distribution.
2. Reasonable mounting and stress relief
Select the mounting method according to the shape of the workpiece to avoid gas retention in blind holes or recessed parts and optimize the current distribution.
Annealing or tempering of high stress workpieces (such as machined or heat-treated parts) to reduce the abnormal distribution of current in the plating process.
II. Precise control of process parameters
1. Current Density and Distribution Adjustment
Short treatment with inrush current (2-3 times of normal current) is used in the initial stage to improve the plating coverage of complex parts.
Adjust the current density according to the shape of the workpiece to avoid over-thickness or over-thinness caused by edge effect.
2. Cathode-Anode Distance and Layout
Reduce the difference in cathode-anode spacing and use profiled anodes (e.g., use ring anodes for bolt-type parts) to improve current uniformity.
Compensate for plating deposition in low current density areas by adjusting anode position or adding auxiliary anodes.
3. Temperature and Stirring Management
Control the bath temperature at 45-65°C to prevent temperature fluctuations from affecting the deposition rate.
Use mechanical or air agitation to enhance the fluidity of the plating solution and reduce the concentration polarization phenomenon.
III. Plating solution composition and additives management
1. Plating solution uniformity guarantee
Regularly test the concentration of the main salt (nickel sulfate, nickel chloride), replenish the consumed components, and filter to remove suspended particles.
Add boric acid to stabilize the pH value (3.0-4.5) to avoid coarse crystallization of the plated layer due to pH fluctuation.
2. Application of functional additives
Use brightening agents (e.g. saccharin) to refine the grain size, and work with leveling agents to improve the surface uniformity of the plated layer.
For specific needs (such as high sulfur nickel layer), optimize the ratio of additives to enhance the performance of the coating.
IV. Equipment and auxiliary measures
1. Shielding and protection technology
Use shielding board or insulating tape for high current density areas (e.g. edges) to inhibit localized over-thickening.
Coat the non-plating area with protective layer to reduce the waste of plating solution and abnormal deposition of plating layer.
2. Dynamic process design
For double-sided large area ratio pads (e.g., PCBs), use a patchwork structure design and cover insulating boards to balance plating solution contact density.
Periodic reversal of current or rotate the workpiece to reduce local plating solution aggregation.
V. Inspection and Maintenance
1. Process monitoring and adjustment
Regularly measure the plating thickness (e.g. X-ray fluorescence method) with tolerance control within ±10%.
Verify the plating bonding force by thermal shock test or bending test, and adjust the process parameters in time.
2. Equipment and plating solution maintenance
Clean anode plate regularly to ensure dissolution uniformity.
Use activated carbon to treat aging additives to maintain the activity of plating solution.
Conclusion: The uniformity of plating layer should be realized through pre-plating treatment, process parameter regulation, bath management and equipment optimization, focusing on current distribution optimization, shaped anode design, dynamic stirring technology and periodic inspection and maintenance.