The Features to FPC

Advantage
(1) Can be freely bent, coiled, folded, may request any arrangements in accordance with the spatial layout, and can be moved and scaled in three-dimensional space, so as to achieve integration of the components assembly and wires connection.

(2) The use of flexible PCB board can greatly reduce the volume and weight of the electronic products.

(3) FPC itself has good heat resistance and weldability, and easy to be packed with low comprehensive cost advantages. The design of Flex-Rigid PCB also make up the shortage of carrying capacity of Flexible base material to components in a certain extent.

2.Disadvantage
(1)High initial cost
Due to Flexible PCB is designed and manufactured for special applications, so start cost for circuit design, circuit layout is relatively higher. Unless there is special demands to apply for flexible PCB, usually FPC is not adopted for small qty demands.

(2)Difficult repair and modification for flexible PCB
Once Flexible PCB finished, if need to be double modified, should be started from the base drawing and Light painting program, so it is not easy for changing. Because there is a cover lay on FPC surface, before repairing, cover lay should be taken off first, and must be redone with cover lay after repair, this is difficult job.

(3)Limitation on size to FPC
Under the condition that the flexible PCB is not very popular, FPC usually made by intermittent method process, thus with restrictions on the size of production equipment, flexible PCB can't be made very long and wide.

(4)Improper operation easily cause damage to FPC
Improper operation taken by worker will cause the damage to flexible circuit and the soldering and rework need to be runed by specially trained operator.

Economy of FPC
If the circuit design is relatively simple, and the total volume is not big, and with appropriate space, the traditional way for internal connection is too much cheaper. If the circuit is complex, and there’s special requirement on electrical or mechanical performance, flexible circuits is a better design option. When the size and performance of the application beyond the ability of rigid PCB, flexible circuit board is the most economical. On a thin film can be made with 5 mil vias and 12 mil pads 3 mil line width and space of flexible circuits. Therefore, mounting chips directly onto the film is more reliable. These films may be protective, and cured at high temperatures, get higher glass transition temperature. Flexible material is more saving on cost compared to rigid material, the reason is out of  connector.

Structure of FPC
According to the conductive copper foil layer division, FPC is divided into single layer board, double layer plate, and multi-layer FPC. Single layer plate structure: the structure of flexible plate is the simplest structure of flexible plate. Usually base material + cellophane tape, copper foil is a set of purchased raw materials, protective film + cellophane tape is another purchased raw material. First of all, the copper foil need to be done with etching process to get the needed circuit, protective film need to be done with drilling to reveal the corresponding pad. After cleaning, then use rolling method to combine the two parts. Then to do with gold plating or plating tin on the uncovering part as protection. Then, the large sheet is ready. Generally, the bog sheet should be punched into several unit pieces with required shape an outline. Also some FPC has no requirement on protective film and directly print solder mask onto the copper foil, this way can low down a lot on cost. However, this will weaken the mechanical strength of the FPC. Unless the strength requirement is not high and the price also should be low as far as possible. But it is best to stick the protective film. Double layer FPC structure: when circuit of the circuit is too complex, single plate can’t meet the demand or in need of copper foil for grounding shield, will need to use double layer FPC or multilayer FPC. The most typical difference between multilayer and single layer FPC is there’s vias to connect the copper in every layer. The first process to multilayer FPC is making vias. First do drilling on the base material and copper foil, then cleaning and then plating with a certain thick copper, then vias finished. After above, the later process is the same as single layer FPC. Double layer FPC structure: There are pads on both top and bottom layers. Double layer FPC is mainly used to be connected with other board. Though the structure is similar as single layer FPC, however, big difference on process. It’s raw material is protective film + cellophane tape.   First do drilling on the film according to the pad location, then stick the copper foil, when the pad and circuit come out then stick another film which already with vias. Then finished.