The process of FPC circuit board manufacturing
Flexible printed circuit board production process is basically similar to rigid plate production process. For some operations, the flexibility of the laminate requires different devices and completely different processing methods. Most flexible printed circuit boards adopt a negative approach. However, some difficulties arise in the machining of the flexible laminate and in the coaxial processing. A major problem is the handling of the substrate. Flexible materials are webs of different widths so the delivery of flexible laminates requires the use of rigid brackets during etching.
Flexible PCB handling and cleaning are more important than handling rigid boards during manufacturing (Lexin, 1993). Improper cleaning or off-specification operations can lead to subsequent failure in product manufacture due to the sensitivity of the material used in the flexible printed circuit, which plays an important role in the manufacturing process. The substrate is subject to mechanical stresses such as waxing, lamination and electroplating. Copper foil is also susceptible to percussion and dents, while the extension ensures maximum flexibility. Mechanical damage or work hardening of copper foil will reduce the flexible life of the circuit.
A typical flexible single-sided circuit needs to be cleaned at least three times during manufacture, however, the multi-substrate needs to be cleaned 3 to 6 times due to its complexity. In contrast, Rigid multilayer printed circuit boards may require the same number of cleanings, but the cleaning process is different and care needs to be taken when cleaning the flexible material. Even with extremely light pressure during cleaning, the spatial stability of the flexible material can be affected and the panel can elongate in the z or y direction, depending on the pressure bias. Flexible printed circuit board chemical cleaning should pay attention to environmental protection. The cleaning process includes a basic dye bath, thorough rinsing, micro-etching and final cleaning. Damage to the film material often occurs during panel mounting, agitation in the pool, removal of the shelf from the pool or unpinning, and destruction of surface tension in the clear pool.
The holes in the flexible board are generally punched, which leads to the increase of the processing cost. Drilling is also possible, but this requires special adjustment of the drilling parameters to obtain a non-smear wall. After drilling, remove the bored dirt in the ultrasonic agitator water cleaner.
It has been demonstrated that mass production of flexible boards is cheaper than rigid printed circuit boards. This is because flexible laminates enable manufacturers to produce circuits on a continuous basis, starting with the laminate web and directly producing the final product. To produce a printed circuit board and etch a flexible printed circuit board schematic diagram of a continuous process, all the production process in a series of machines placed in order to complete. Screen printing may not be part of this continuous transfer process, which creates an interruption in the online process.
In general, soldering in flexible printed circuits is even more important due to the limited heat resistance of the substrate. Manual welding requires sufficient experience, so wave soldering should be used if possible. When soldering flexible printed circuits, you should note the following:
1) Because polyimide is hygroscopic, the circuit must be baked (at 250 ° F for 1h) before soldering.
2) Solder pads are placed in large conductor areas such as ground planes, power planes, or heat sinks, and the heat sink area should be reduced, as shown in Figure 12-16. This limits heat dissipation and makes welding easier.
3) When performing manual soldering on pins in a crowded place, try not to continuously solder adjacent pins and move the soldering back and forth to avoid overheating.
Information on the design and processing of flexible printed circuits can be obtained from several sources, but the best source of information is always the producer / supplier of materials and chemicals. Through the information provided by suppliers, coupled with the scientific experience of processing experts, can produce high-quality flexible printed circuit board.