Discussion on copper foil for FPC flexible circuit board

The copper foil materials used for FPC flexible circuit boards are mainly divided into two types: calendered copper and electrolytic copper. It is a conductive layer bonded to the insulating material of the covering film, and is etched into the required patterns through various processing processes. Electrolytic copper foil is obtained by precipitation of acidic copper plating solution on a bright stainless steel roller to form a uniform copper film, which is continuously peeled and rolled; Calendering copper foil is the process of using a certain thickness of copper ingots or blocks to form the required thickness of copper foil through repeated rolling and annealing.



The copper atomic structure of the calendering material exhibits irregular layered strong crystals, which are resistant to recrystallization after heat treatment, so it is not easy to form cracks. The copper foil material has good bending properties; The electrolytic copper foil material exhibits columnar crystalline structure in the thickness direction, which is prone to crack and fracture when bent; Similarly, when observing the cross-section of highly ductile electrolytic copper foil material subjected to special processing such as heat treatment, although it is still dominated by columnar crystals, layered crystals are formed in the copper layer and are not easily broken when bent.



The bending property of rolled copper foil is four times that of ordinary electrolytic copper foil, but its price is also relatively expensive. Therefore, for products with low flexibility requirements (such as key boards, module boards, 3D static flexible circuits, etc.), it is possible to choose to replace the calendered copper foil material with high ductility electrolytic copper foil. Of course, when reliability requirements are relatively high (such as slide phone boards, folding phone boards, etc.), it is better to use the calendered copper foil material.



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 many blind selection factors. As mentioned above, calendering materials have their own characteristics, but they also have many shortcomings, which should be appropriately applied.