The copper foil materials used for FPC flexible circuit boards are mainly divided into two types: rolled copper and electrolytic copper. It is a conductor layer bonded to the insulating material of the cover film and is etched into the required pattern through various processes. Electrolytic copper foil is deposited on a bright stainless steel roll by an acid copper plating solution to form a uniform copper film, which is obtained by continuous stripping and winding; calendered copper foil is obtained by using copper ingots or copper blocks of a certain thickness. Repeated rolling and annealing process to form the required thickness of copper foil.
The copper atomic structure of the rolled material is irregular and layered strong crystals, which are not easy to form cracks after heat treatment, and the copper foil material has good bending performance; while the electrolytic copper foil material shows a columnar crystal structure in the thickness direction. It is easy to crack and break; similarly, when the cross-section of the high elongation electrolytic copper foil material that has undergone special processing such as heat treatment is observed, although columnar crystals are still the main form, layered crystals are formed in the copper layer and are not easy to break when bent.
After testing, the flexibility of rolled copper foil is 4 times that of ordinary electrolytic copper foil, but its price is also more expensive. Therefore, for products that do not require high flexibility (such as key boards, module boards, 3D static flexible circuits, etc.), you can choose to use high elongation electrolytic copper foil instead of rolled copper foil materials. Of course, the reliability requirements are relatively high. Under circumstances (such as sliding phone panels, folding mobile phone panels, etc.), it is better to use rolled copper foil materials.
Most FPC flexible circuit board products require high bending performance, which leads to the preference of most manufacturers for calendering materials. In fact, there are also many blind selection factors. The above mentioned calendering materials have their own characteristics, and they also have many The shortcomings are inside and should be applied appropriately.