The production process of flexible printed circuit boards is basically similar to that of rigid boards. For some operations, the flexibility of the laminate requires a different device and a completely different approach. Most flexible printed circuit boards use a negative method. However, there are some difficulties in the machining and coaxial processing of flexible laminates, and one of the major problems is the handling of the substrate. The flexible material is a different width of the web, so during the etching, the flexible laminate is conveyed using a rigid bracket.
In the production process, the processing and cleaning of flexible printed circuits are more important than the handling of rigid boards (Lexin, 1993). Improper cleaning or violation of the procedure may result in failure in the subsequent manufacture of the product, which is determined by the sensitivity of the material used in the flexible printed circuit, where the flexible printed circuit plays an important role in the manufacturing process. The substrate is affected by mechanical pressure such as baking wax, lamination and electroplating, and the copper foil is also susceptible to percussion and dents, while the extended part ensures maximum flexibility. The mechanical damage or work hardening of the copper foil will reduce the flexible life of the circuit.
During the manufacturing process, a typical flexible single-sided circuit must be cleaned at least three times, however, the multi-substrate needs to be cleaned 3-6 times due to its complexity. In contrast, rigid multi-layer printed circuit boards may require the same number of cleaning times, but the cleaning procedure is different, cleaning the flexible material need to be more careful. Even with very light pressure during the cleaning process, the spatial stability of the flexible material is affected and the panel is elongated 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 alkaline dye bath, thorough rinsing, micro etch and final cleaning. Damage to the film material often occurs during the panel shelves, when the shelves are removed from the tank, or when the shelves are removed, and the surface tension in the clear pool is broken.
The holes in the flexible plate are generally perforated, which leads to an increase in processing costs. Drilling is also possible, but this requires special adjustment of the drilling parameters to obtain uncoated hole walls. After drilling, remove the drilling dirt in a water cleaner with ultrasonic agitation.
It has been shown that large-scale production of flexible boards is cheaper than rigid printed circuit boards. This is because the flexible laminate allows the manufacturer to produce a circuit on a continuous basis, which begins with the laminate sheet and can directly produce the finished plate. For the manufacture of printed circuit boards and etching of a flexible printed circuit board of a continuous processing schematic diagram, all the production process in a series of sequential machines to complete. Screen printing may not be part of this continuous transfer process, which causes the interruption of the online process.
In general, welding in flexible printed circuits is even more important due to the limited heat resistance of the substrate. Manual welding requires sufficient experience, so if possible, wave soldering should be used. When welding flexible printed circuits, the following should be noted:
1) Since the polyimide has hygroscopicity, the circuit must be baked (at 250 ° F for 1 h) before welding.
2) The pad is placed in a large conductor area, such as the ground plane, power plane, or heatsink, and the heat sink area should be reduced, as shown in Figure 12-16. This limits the heat dissipation and makes welding easier.
3) When manually welding the pins in a dense place, try not to solder the adjacent pins continuously and move the welding back and forth to avoid local overheating.
The design and processing of flexible printed circuit information 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 the supplier, coupled with the scientific experience of processing experts, can produce high-quality flexible printed circuit boards.