The production process of
flexible circuit boards is basically similar to rigid plate production. For these operations, the flexibility of laminates requires different devices and completely different processing methods. Most flexible printed circuit boards adopt negative methods. However, there are some difficulties in the mechanical processing and coaxial processing of flexible laminates. One of the main problems is the treatment of substrates. Flexible materials are coils of different widths, so rigid brackets are needed for the transmission of flexible laminates during etching.
In the production process, the processing and cleaning of flexible printed circuit is more important than that of rigid board (Lexin, 1993). Improper cleaning or violation of regulations may lead to failure in subsequent product manufacturing, which is due to the sensitivity of materials used in flexible printed circuits, and flexible printed circuits play an important role in the manufacturing process. Substrate is affected by mechanical pressure such as wax drying, lamination and electroplating. Copper foil is also susceptible to impact and dents. The extension part ensures maximum flexibility. The mechanical damage or work hardening of copper foil will reduce the flexible life of the circuit.
During manufacturing, a typical flexible one-sided circuit needs to be cleaned at least three times. However, due to its complexity, multi-substrates need to be cleaned three to six times. In contrast, rigid multilayer printed circuit boards may require the same number of cleaning times, but different cleaning procedures require more care when cleaning flexible materials. Even under very light pressure during cleaning, the spatial stability of flexible materials will be affected, and the panel will be elongated in Z or Y direction, depending on the bias of pressure. The chemical cleaning of flexible PCB should pay attention to environmental protection. The cleaning process includes alkaline bath, thorough rinsing, micro etching and final cleaning. Damage to membrane materials often occurs in the process of panel mounting, when stirring in the pool, removing the shelf from the pool or not erecting the shelf, and the destruction of surface tension in the clearing pool.
The holes in flexible plates are usually punched, which results in higher processing cost. Drilling is also acceptable, but it requires special adjustment of drilling parameters to obtain non smeared hole walls. After drilling, remove the borehole contaminants in the ultrasonic agitator water purifier.
It has been proved that the large-scale 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. This process starts with laminated sheet coils and directly generates finished sheets. In order to produce printed circuit boards and etch a continuous processing schematic of flexible printed circuit boards, all production processes are performed in a series of sequential placement machines. Screen printing may not be part of this continuous transmission process, which results in interruption of online processes.
In general, due to the limited heat resistance of substrate, welding in flexible printed circuit is more important. Manual welding requires sufficient experience, so if possible, wave soldering should be used. When welding flexible printed circuit, we should pay attention to the following matters:
1. When the pad is placed on a large conductor area, such as the ground layer, the power supply layer or the radiator, the heat dissipation area should be reduced, as shown in Fig. 12-16. This limits heat dissipation and makes welding easier.
2 Because polyimide is hygroscopic, the circuit must be baked before welding (lasting for 1 hour at 250 degrees F).
3) When manual welding pins are carried out in dense areas, it is necessary to avoid continuous welding of adjacent pins and move welding back and forth to avoid local 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 processing materials and chemicals. Through the information provided by suppliers and the scientific experience of processing experts, high quality flexible printed circuit boards can be produced.
