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Manufacturing flexible circuit board process

Shenzhen Inno Circuit Co.,Ltd | Updated: Jun 20, 2018

Manufacturing flexible circuit board process

The production process of a flexible printed circuit board (also called FPC) is basically similar to that of a rigid board. For some operations, the flexibility of the laminate requires different devices and completely different processing methods. Most flexible printed circuit boards use a negative method. However, some difficulties arise in the machining and co-axial processing of flexible laminates. One major problem is the handling of the substrate. Flexible materials are webs 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 the flexible circuit board is more important than the rigid board processing. Improper cleaning or operation in violation of the regulations may cause failures in the subsequent manufacture of the product. This is due to the sensitivity of the materials used in the flexible printed circuit. 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. The copper foil is also susceptible to knocking and dents, while the extended portion ensures maximum flexibility. Mechanical damage or work hardening of the copper foil will reduce the flexible life of the circuit.

During manufacturing, typical flexible single-sided circuits are cleaned at least three times. However, multiple substrates need to be cleaned 3 - 6 times due to its complexity. In contrast, a rigid multi-layer printed circuit board may require the same number of cleanings, but the cleaning procedure is different, and more care needs to be taken when cleaning flexible materials. Even with light pressure during the cleaning process, the space stability of the flexible material can be affected and can cause the panel to stretch in the z or y direction, depending on the bias of the pressure. Chemical cleaning of flexible circuit boards 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 pull-up, when the tank is agitated, when the shelves are removed from the pool or when there is no stack, and the surface tension is destroyed in the clearing pond.

Holes in flexible boards are generally punched, which leads to increased processing costs. Drilling is also possible, but this requires special adjustment of the drilling parameters to obtain a smear-free hole wall. After drilling, drilled dirt was removed in a water cleaner with ultrasonic agitation.

It has been demonstrated that the mass production of flexible circuit boards (FPC circuit boards) is less expensive than rigid printed circuit boards. This is because flexible laminates allow manufacturers to produce circuits on a continuous basis, starting with the laminate web and directly producing the finished board. To manufacture a printed circuit board and etch a continuous process schematic of a flexible printed circuit board, all production processes are performed in a series of sequential machines. Screen printing may not be part of this continuous transfer process, which caused interruptions in the online process.

In general, soldering in flexible printed circuits becomes more important due to the limited thermal resistance of the substrate. Manual welding requires sufficient experience, so if possible, wave soldering should be used. When soldering flexible printed circuits, the following should be noted:

1) Because polyimide is hygroscopic, the circuit must be baked before soldering (1 h at 250°F).

2) The 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 manually soldering pins in dense places, try not to continuously solder adjacent pins and move the solder back and forth to avoid local overheating.

Information on flexible printed circuit design and processing can be obtained from several sources, but the best sources of information are always the producers/suppliers 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.

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