What is electrolytic copper foil?

The process flow of electrolytic copper foil has four main process stages.

1.  Solution making (in the solution-making tank, copper material is made into copper sulfate solution with sulfuric acid, which is made into electrolytic solution)
2.  Raw foil manufacturing (in an electrolyzer, raw foil is produced by an electrochemical reaction)
3.  Surface treatment (In the surface treatment machine, the raw foil is surface treated to form a roughening layer, heat-resistant layer, anti-oxidation layer, etc.)
4.  Cutting, winding, and inspection.

The key to the manufacture of electrolytic copper foil is in the raw foil and surface treatment.

Raw foil

• The raw foil machine mainly consists of cathode rollers, anode plates, slots, a winding mechanism, and a DC power supply system. Under the action of direct current, copper ions are reduced and precipitated from the chemical cell to the cathode surface. The copper solution is continuously injected into the electrolytic cell, the cathode rollers are rotated, and the copper foil is continuously peeled off from it. By controlling various process parameters and adjusting the rotation speed of the cathode rollers, different thicknesses of raw foil can be obtained. Raw foil manufacturing is a key process in the production of copper foil for making its semi-finished products. It determines most of the quality properties of the electrolytic copper foil and largely determines the quality of the surface treatment in the subsequent process. The production of high-level, high-quality raw foil depends mainly on the quality of the dissolved copper system and the process control conditions for the manufacture of dust foil (current density, concentration, temperature, circulation, cathode roll speed of the electrolyzer, etc.), the surface quality of the cathode roll, the composition and the number of additives, etc. The morphology and mechanical properties of copper can be controlled by using various types of additives, mainly gelatin, fibrin, and hydrochloric acid.

Surface treatment

• The surface and processing process mainly includes three aspects, such as roughing layer treatment, heat-resistant layer treatment, and anti-oxidation layer treatment. These surface treatments are done on a single surface treatment machine. The roughening layer (also called tumor treatment) and heat-resistant layer treatment are done on the rough side of the dust foil, and the anti-oxidation layer treatment is done on both sides of the dust foil. The roughening layer treatment of the day is to increase the bond between the copper foil and the insulating substrate. If only the roughening layer treatment is available, its corrosion resistance and ion migration resistance are relatively poor, and it is easy to produce rust and spots when manufacturing circuit boards, and even short circuits. Therefore, the roughening layer of the coating and then coated with two or even three alloy coating called heat-resistant layer treatment. The anti-oxidation layer treatment, in addition to the treatment of anti-oxidant, generally has to be treated with a silane coupling agent to improve the bonding between the rough surface of the copper foil and the resin of the base material. With the increase of PCB's requirement for heat resistance of copper clad board, the anti-high temperature oxidation resistance of copper foil is also becoming an important property. In short, the surface treatment technology of electrolytic copper foil has become one of the important technologies for a copper foil manufacturer.

Electrolytic copper foil is produced by the electrolysis of copper using electrochemical principles. The main factors that affect its varying crystalline organization are:

1. Copper and sulfuric acid concentration of the electrolyte, additive type.
2. Temperature and flow rate of the electrolyte.
3. The current density in electrolysis, etc.

In recent years, the quality of electrolytic copper foil has been improved and new varieties have been introduced, often by improving the electrolytic conditions to achieve finer and higher-strength crystalline grains. The original copper foil, whether calendered or electrolyzed, is generally subjected to surface treatment. The surface treatment includes roughing layer treatment, heat-resistant layer treatment, and anti-oxidation layer treatment of copper foil, etc., and is done in successive steps on the same surface treatment machine. The surface treatment process of copper foil differs considerably from company to company but should include a pre-treatment process, a shoeing process, and a heat and oxidation treatment.