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During the pre-treatment process of the foam copper, it turned black without being dried properly. This might be due to surface oxidation or the reaction between the residual chemicals and the copper. Here are some solutions that can be attempted:
Optimize the cleaning process
Increase the number and duration of cleaning steps: When using acetone, 1M hydrochloric acid, deionized water, and ethanol for cleaning, appropriately increase the number and duration of each step. For example, extend the cleaning time from 5 - 10 minutes to 15 - 20 minutes to ensure that all impurities and residual chemicals on the surface are thoroughly cleaned.
Use ultrasonic cleaning: In the deionized water cleaning step, an ultrasonic cleaning instrument can be used. Ultrasonic cleaning can generate cavitation effects, more effectively removing the tiny impurities in the pores and on the surface of the foam copper. Generally, let it run for 15 - 30 minutes, with the temperature controlled at 30 - 50℃.
Control the cleaning environment
Avoid prolonged exposure to the air: During the cleaning process, minimize the time the foam copper is exposed to the air. As oxygen in the air can react with copper, causing the surface to turn black. You can protect it in the cleaning equipment by filling it with inert gases (such as nitrogen) or operate it in a glove box.
Control the temperature and purity of the cleaning solution: Ensure that the quality and purity of acetone, hydrochloric acid, deionized water, and ethanol meet the requirements. Also, control the temperature of the cleaning solution within an appropriate range. Generally, a normal temperature or slightly above normal (20 - 30℃) is suitable. Avoid excessively high temperatures that accelerate the oxidation reaction.
Improve the drying method
Choose an appropriate drying temperature and time: The drying temperature should not be too high or too low. Generally, a temperature range of 60 - 80℃ is suitable. Adjust the drying time according to the size and thickness of the foam copper to ensure complete drying. For smaller-sized foam copper, dry for 1 - 2 hours; for larger-sized ones, extend it to 2 - 3 hours.
Use vacuum drying: The vacuum environment can lower the boiling point of water, making the drying process more efficient and reducing the contact between oxygen and the surface of the foam copper, thereby reducing the possibility of oxidation. Place the foam copper in a vacuum drying box and dry it under a vacuum pressure of 0.08 - 0.1MPa. Surface treatment
Passivation treatment: After cleaning and drying, the foam copper can be subjected to passivation treatment to form a protective film on the surface, preventing further oxidation. For example, passivation can be carried out using a benzotriazole (BTA) solution. The foam copper can be immersed in a 0.1 - 0.5% BTA solution for 10 - 30 minutes, and then removed and dried.
Coating protective layer: A layer of organic or inorganic protective layer, such as a polymer coating or oxide coating, can be applied to the surface of the foam copper to isolate it from air and moisture. The choice of coating material and coating method can be made according to specific application requirements.
