Let me put it simply: The smooth surface of copper foil refers to the non-rough side of the copper foil, which should be flat, shiny, without spots, scratches, oxidation, or unevenness.
When it comes to electrolytic copper foil (the most commonly used type), it is divided into several major steps: liquid treatment, electroplating, roller surface treatment, water washing, drying, post-processing, and operation. In simple terms, without using complicated jargon.
I. Electrolyte Base (Electroplating Raw Material Water)
1. Copper ions should not fluctuate greatly. Too little copper leads to a thin and foggy coating; too much copper causes bumps to form.
2. The acid level should not be too high or too low: too high acid results in a hard coating and easy formation of stripes; too low acid leads to the growth of particles and burrs.
3. Impurities are the biggest killers of a smooth surface: too much iron, zinc, nickel, oil stains, and sediment in the water will make the smooth surface gray, with spots, and pinholes.
The simple explanation: The electroplating solution must be clean. Regularly filter and remove impurities. Do not bring oil stains into it.
4. Additives (brighteners, leveling agents): Not all additives are needed in larger quantities for better brightness. Insufficient additives result in a dull coating; excessive additives can cause brittleness, stripes, and defect spots. Always add them in a stable proportion.
II. Electroplating Parameters (Current, Temperature, Speed)
1. Current density: Too low current leads to a loose and non-glossy coating; too high current causes the edges to burn, form bumps, and have spots.
2. Liquid temperature: High temperature accelerates the reaction, but it also makes the crystal grains larger and the surface foggy; too low temperature leads to the formation of particles and burrs. The temperature should be stable, without sudden changes in temperature.
3. Belt speed: Fast speed results in a thinner coating and shorter electroplating time; too slow speed leads to a thicker coating, rough crystal grains, and a non-glossy surface. The speed and current must be matched.
III. Cathode Roll (Most Critical! The smooth surface is the side that contacts the roll)
?? The smooth surface of the electrolytic copper foil = the side that comes into contact with the cathode roll. The shape of the roll determines the shape of the copper foil's smooth surface!
1. The roll surface itself has scratches, spots, pits, and polishing patterns. These will appear as marks on the copper foil.
2. If the roll is not clean, it may be coated with copper powder, accumulate dirt, or oxidize. The smooth surface of the copper foil will have spots and impressions.
3. If the roll is polished well and the roughness is controlled properly: It is not always better to be overly smooth. A mirror-like roll is prone to sticking the copper foil and causing difficulties in removing it; a too rough roll will make the smooth surface of the copper foil visible with roll patterns. Find the appropriate roughness, and regularly polish, grind, and maintain it.
4. The roll should be cooled evenly: Uneven temperature differences on both sides of the roll result in inconsistent brightness on both sides of the copper foil and stripes.
IV. Water Washing and Drying (Many people tend to overlook this)
After electroplating, if the acid solution is not washed clean:
Residual acid, salts, and additives crystallize → After drying, the smooth surface will have watermarks, fog spots, and color changes due to oxidation in the later stage.
1. Multiple stages of water washing, using pure water, with appropriate water pressure, and without causing water splashes to create watermarks.
2. The drying temperature should not be too high, and local overheating should be avoided. The hot air should be uniform, and unclean hot air can also cause spots.
V. Surface Post-Treatment (Preventing Oxidation while Ensuring Gloss)
Passivation and anti-oxidation treatment:
Inconsistent concentrations, pH values, and temperatures of the solution can easily cause the smooth surface to become dull, have rainbow colors, and have a foggy appearance.
Do not overdo the passivation treatment for rust prevention; a thick film on the surface will make the smooth surface dull.
VI. Environment and Operations
1. The workshop has a lot of dust and oil in the air, which will form spots on the wet copper foil surface.
2. The guide rollers and idler rollers are not clean, with copper shavings, causing scratches on the smooth surface.
3. Inconsistent tension causes the copper foil to shake, resulting in uneven current distribution and dark and light stripes.