Flexible and reliable design of printed circuit board

- Feb 10, 2017-

Flexible printed circuit boards can be classified according to the type of bending encountered during assembly and use. There are two types of design, which are discussed below:

1.static design

Static design refers to the bending or folding of the product during the assembly process, or the bending or folding of the product during use. Single side, double sided and multilayer circuit board, can achieve the static design of folding. Generally, for most of the design of double sided and multi substrate, the minimum bending radius should be ten times the thickness of the whole circuit. More layers of the circuit (eight or more) will become very hard, it is difficult to bend them, so there will be no problems. Therefore, for a double sided circuit that requires a tight bend radius, all copper traces on the same side of the substrate film should be set in the folded area. By removing the coating on the opposite surface, the folded region is approximated to a single side circuit.

2.dynamic design

The dynamic circuit is designed for repeated bending of the entire life cycle of a product, for example, a printer and a disk drive cable. In order to make the dynamic circuit achieve the longest bending life cycle, the relevant part should be designed as a single side circuit, and the copper on the central axis. The central axis is a theoretical plane, which forms the central layer of the material of the circuit. By using the same thickness in both sides of the copper substrate and the coated film, copper foil will be accurately placed in the center position, and in bending or bending during the pressure minimum.

The need for high dynamic bending cycles and high density multi layer complexity design can now be achieved by using the opposite sex (Z axis) binder to connect a double-sided or multilayer circuit to a single circuit. Bending occurs only in a single side assembly, the dynamic bending area outside the multi layer independent region, which is not threatened by bending, can install complex wiring and components required.

Although flexible printed circuits are expected to meet all the needs of bending, bending and the application of some special circuits, but in these applications, a large part of the bending or bending failure. Flexible materials are used in the manufacture of printed circuit boards, but the flexible material itself does not guarantee the reliability of the circuit when it is bent or bent, especially in dynamic applications. A number of factors can improve the reliability of forming or repeated bending of printed flexible printed circuit boards. In order to ensure the reliable operation of the finished circuit, all of these factors must be considered in the design process. Here are some tips for adding flexibility:

1) in order to improve the dynamic flexibility, the circuit board with two or more layers should be selected.

2) minimum bending number is recommended.

3) wire should be staggered to avoid I micro spotlight effect, wire path to orthogonal to bending.

4) do not place the pad or through hole in the bend area.

5) do not place any ceramic parts near any bend area, so as to avoid the coating layer is discontinuous, the plating layer is discontinuous or other stress concentration occurs. It should be ensured that there is no distortion in the finished assembly. Distortion may cause undue stress on the outer edge of the circuit. Any irregularities or irregularities in the blanking process may result in the breakdown of the circuit board.

6) the thickness and width of the conductor should be kept constant in the bend area. There should be a change in the plating or other coating to prevent the neck from contracting.

7) a narrow cut is made in the flexible printed circuit, allowing different wooden brackets to bend in different directions. Although this is an effective means to maximize the efficacy, but the incision is easy to cause tearing and crack extension, this problem can be made by a drill in the end to prevent incision, using the rigid plate or a thick piece of flexible material or PTFE to reinforce these areas (Finstad, 2001). Another method is to make the incision as wide as possible, and making a complete semicircle in the incision at the end. If it is not reinforced, the circuit cannot be bent at a distance of 1I2in from the end of the notch.

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