Industrial copper foil can be commonly classified into two main categories: rolled copper foil (RA copper foil) and electrolytic copper foil (ED copper foil). Rolled copper foil, with its superior ductility and other properties, was used in early flexible circuit board manufacturing processes. Electrolytic copper foil, on the other hand, has the advantage of lower manufacturing costs compared to rolled copper foil.
(1) Rolled Copper Foil
Rolled copper foil is a raw foil (also called rough foil) made by repeatedly rolling copper plates, followed by roughening treatment as required.
Due to limitations in the processing technology of rolled copper foil, its width is difficult to meet the requirements of rigid copper-clad laminates, so rolled copper foil is rarely used in rigid copper-clad laminates. Because rolled copper foil has greater folding endurance and elasticity coefficient than electrolytic copper foil, it is suitable for flexible copper-clad laminates.
The copper purity of rolled copper foil (99.9%) is higher than that of electrolytic copper foil (99.8%), and its rough surface is smoother than that of electrolytic copper foil, both of which are beneficial for the rapid transmission of electrical signals. Therefore, in recent years, rolled copper foil has been used abroad as a substrate for high-frequency, high-speed signal transmission and fine-wire printed circuit boards. Its use in printed circuit board substrates for audio equipment can also improve sound quality. It is also used in "metal sandwich panels" made to reduce the coefficient of thermal expansion (TCE) of multilayer circuit boards with fine wires and high layer counts.
(2) Electrolytic Copper Foil
Electrolytic copper foil is made by first dissolving copper to form a solution, then electrodepositing the copper sulfate electrolyte under direct current in a specialized electrolytic device to form a raw foil. The raw foil then undergoes a series of surface treatments, including surface treatment, heat-resistant layer treatment, and anti-oxidation treatment, according to requirements.
Electrolytic copper foil differs from rolled copper foil in that the two sides of the electrolytic copper foil have different crystal morphologies. The side in contact with the cathode roller is relatively smooth and is called the glossy surface; the other side exhibits a rough crystalline structure with uneven surfaces and is called the rough surface.
Because electrolytic copper foil has a columnar crystalline structure, its strength and toughness are inferior to those of rolled copper foil. Therefore, electrolytic copper foil is mostly used in the production of rigid copper-clad laminates, which are then used to manufacture rigid printed circuit boards.
