close
Choose Your Site
Global
Social Media
Views: 1411 Author: Ruqinba Publish Time: 2026-09-18 Origin: Site
In the processing and post-treatment of copper and copper alloys, the passivation process is a critical step to ensure corrosion resistance and maintain consistent surface appearance. However, in actual production, issues such as reddening/discoloration, blotchiness, and BTA white spots repeatedly occur. These problems not only lower yield rates but also delay delivery schedules.
Below, we break down the three most common failures in copper passivation, identify their root causes, and provide actionable, ready-to-implement solutions.
Irregular red patches or an overall uneven red/oxidized color appear on the workpiece surface. The surface loses its uniform luster, and its fingerprint resistance and anti-tarnish capabilities drop significantly.
Improper Alkaline Degreasing: Alkaline degreasing requires precise control over alkalinity, temperature, and time to ensure complete oil removal, full surface wetting, and zero alkaline residue. If adding a small amount of amine-based complexing agent, strictly adhere to the principle: "a small amount helps, but residue causes harm." Strictly control the dosage, choose mild, easy-to-rinse formulations for copper, and strengthen water rinsing (warm running water recommended, pure water if necessary). Always verify via a small trial to confirm no reddening or blotchiness before moving to the next process.
Over-Pickling Exposes the Substrate: High acid concentration or excessive time during pre-treatment pickling over-corrodes the copper oxide layer and base metal. Fresh copper substrate is exposed to air, causing rapid oxidation and reddening.
Overly Acidic Passivation Bath: A low pH in the passivation solution creates an acidic environment that damages the protective film. It can even corrode the base metal, causing copper ions to dissolve and oxidize.
Excessive Treatment Time: Soaking workpieces beyond the recommended process window makes the passivation film overly thick or eroded, creating film defects that trigger oxidation and discoloration.
Excessive Copper Ion Accumulation: Over long-term use, copper ion concentration continuously rises. This disrupts the passivation reaction balance, leading to a loose, uneven film layer and subsequent reddening.
Strictly control acid concentration and pickling time during pre-treatment. Rinse immediately with pure water to avoid over-corroding the copper substrate.
Test the bath pH regularly and adjust it to the required process range to prevent acid damage to the film.
Control passivation processing time precisely using timers, standardized rack travel speeds, or automated controls.
Purify the passivation bath regularly or replace it based on production batches to keep copper ion concentration within reasonable limits.
Irregular color depth across the workpiece surface creates a blotchy appearance. Localized areas show uneven film thickness, and significant color variations occur within the same batch.
Incomplete Degreasing & Uneven Oil Distribution: Inadequate pre-treatment degreasing leaves residual oil that forms an isolation barrier. This prevents contact between the passivation fluid and the copper substrate, leaving oiled areas without a complete passivation film.
Overlapping Workpieces & Uneven Chemical Contact: Poor rack design causes workpieces to stack or touch. Areas in contact cannot touch the passivation solution, preventing normal film formation and causing localized color differences.
Insufficient Agitation & Uneven Bath Concentration: A lack of circulation or agitation in the passivation tank leads to an uneven distribution of active ingredients. Different parts of the workpiece contact varying chemical concentrations, resulting in uneven film growth rates and blotchiness.
Optimize pre-treatment and strengthen the degreasing step. Incorporate ultrasonic cleaning or add pure water rinses after degreasing to ensure no oil residue remains.
Redesign racking using point-contact or hollowed-out designs. This prevents workpieces from touching and ensures all surfaces receive full chemical exposure.
Add circulation filtration or air agitation systems to the passivation tank. This maintains consistent chemical concentration throughout the bath.
White spots or crystalline substances appear on the workpiece surface. The surface feels rough to the touch, and traces remain even after wiping, compromising visual cleanliness.
Excessive BTA Concentration: High concentrations of Benzotriazole (BTA) exceed solubility limits. Undissolved BTA precipitates on workpiece surfaces, forming white crystalline spots.
Low Operating Temperature: When the bath temperature drops below process standards, BTA solubility decreases. Previously dissolved BTA precipitates out of solution and adheres to the workpiece.
Incomplete Rinsing & Chemical Residue: Inadequate post-passivation rinsing leaves chemical residues. As moisture evaporates, BTA components precipitate into white crystals.
Excessive Drying Temperature: High drying temperatures rapidly evaporate residual surface moisture before BTA can re-dissolve, leaving behind crystalline white spots.
Regularly test BTA concentration in the passivation bath and keep it within process parameters.
Maintain bath temperature between 20°C and 30°C to prevent BTA precipitation due to cold temperatures.
Enhance post-passivation rinsing using multi-stage countercurrent rinsing or pure water spraying to eliminate chemical residues.
Keep drying temperatures below 60°C and utilize low-temperature hot-air drying to evaporate moisture slowly without forming BTA crystals.
While these issues seem like minor operational oversights, they stem directly from bath formulation stability. High-quality copper passivation additives stabilize bath pH, manage BTA solubility, and optimize film uniformity—eliminating reddening, blotchiness, and white spots at the source.
Shenzhen Ruqinba Group has specialized in copper surface treatment for years. To address pain points in copper and copper alloy passivation, we developed specialized copper passivation additives that stabilize bath composition and enhance film uniformity and corrosion resistance.
If your passivation line is struggling with these challenges, contact us today for a customized chemical and process solution.
