The production process of flexible printed circuit board is basically similar to that of rigid board.For some operations, the flexibility of the laminate requires a different device and a completely different treatment.Most flexible printed circuit boards use negative methods.However, there are some difficulties in the mechanical processing and coaxial processing of flexible laminates.Flexible materials are coils of different widths, so the transfer of flexible laminates requires the use of rigid brackets during etching.
In the production process, the processing and cleaning of flexible printed circuits is more important than that of rigid plates (Lexin, 1993).Incorrect cleaning or improper operation may lead to failure in product manufacturing, which is due to the sensitivity of materials used in flexible printed circuit, which plays an important role in manufacturing process.The base plate is affected by mechanical pressure such as paraffin, lamination and electroplating, and 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 should be cleaned at least three times during manufacturing, whereas a multi-substrate circuit should be cleaned 3-6 times due to its complexity.In contrast, rigid multilayer printed circuit boards may require the same number of times of cleaning, but the cleaning process is different and the flexible material needs to be cleaned more carefully.Even under extremely light pressure in the cleaning process, the space stability of the flexible material will be affected, and the panel will be stretched in the z or y direction, depending on the pressure deflection.Chemical cleaning of flexible printed circuit board should pay attention to environmental protection.The cleaning process includes alkaline dyeing bath, thorough rinsing, micro-etching and final cleaning.Damage to the membrane material often occurs during the mounting of the panel, during the stirring of the pool, during the removal of the shelves from the pool or without them, and in the clearing of the surface tension.
Holes in flexible plates are generally punched, which leads to higher processing costs.Drilling is also possible, but this requires special adjustment of the drilling parameters to obtain unpainted bore walls.After drilling, remove the hole contamination in a water cleaner with ultrasonic stirring.
Mass production of flexible panels has proved cheaper than rigid printed circuit boards.This is because flexible laminates enable manufacturers to produce circuits on a continuous basis, a process that starts with the laminates sheet and directly generates the finished sheet.A continuous process diagram for manufacturing printed circuit boards and etching flexible printed circuit boards, all production processes are completed in a series of sequentially placed machines.Screen printing may not be part of this continuous transmission process, which results in the interruption of the online process.
Usually, due to the limited thermal resistance of the substrate, welding in flexible printed circuit is more important.Manual welding requires sufficient experience, so crests should be used if possible.When welding flexible printed circuit, the following items should be noted:
1) because polyimide has hygroscopicity, before welding circuit must be baked (in the 250 ° F for 1 h).
2) the solder pad is placed in a large conductor area, such as the ground layer, power supply layer or radiator, and the heat dissipation area should be reduced, as shown in figure 12-16.This limits heat emissions and makes welding easier.
3) when manual welding pins are performed in dense places, try to avoid continuous welding of adjacent pins and move welding back and forth to avoid local overheating.
Information on flexible printed circuit design and processing can be obtained from several sources, however the best source of information is always the producer/supplier of processed materials and chemicals.High quality flexible printed circuit boards can be produced from the information provided by suppliers and the scientific experience of processing experts.