According to the number of layers of conductive copper foil, it is divided into single-layer board, double-layer board, multi-layer board, double-sided board, etc.
The structure of a single-layer board: The flexible board of this structure is the
flexible board with the simplest structure. Usually the substrate + transparent glue + copper foil is a set of bought raw materials, and the protective film + transparent glue is another bought raw material. Firstly, the copper foil needs to be etched and other processes to obtain the required circuit, and the protective film is drilled to expose the corresponding pads. After cleaning, the two are combined by rolling method. The exposed pad part is then protected by gold or tin plating. In this way, the slab is ready. Generally, it is also stamped into a small circuit board of corresponding shapes. There are also those that do not use a protective film and print a solder mask directly on the copper foil, which will be cheaper, but the mechanical strength of the circuit board will be worse. Unless the strength is not high, but the price needs to be as low as possible, it is best to apply a protective film.
The structure of the double-layer board: When the circuit is too complex, the single-layer board cannot be routed, or the copper foil is required for ground shielding, the double-layer board or even the multi-layer board needs to be selected. The most typical difference between multilayer boards and single-layer boards is the addition of a via structure to connect the layers of copper foil. Mostly, the first processing process of substrate + transparent glue + copper foil is to make vias. Drill holes in the substrate and copper foil first, and after cleaning, plating a certain thickness of copper, the vias are ready. After that, the production process is almost the same as that of a single-layer board.
Double-sided structure: There are pads on both sides of the double-sided board, which are mainly used for connection with other circuit boards. Although it is similar in structure to a single-layer board, the manufacturing process is very different. Its raw material is copper foil, protective film + transparent glue. First, drill holes in the protective film according to the requirements of the pad position, and then paste the copper foil, etch out the pad and lead, and then paste another drilled hole of the protective film.
