Summary of flexibility and reliability design of PCB

1. Static design

Static design refers to the bending or folding that the product encounters only during assembly, or the bending or folding that rarely occurs during use. Like single-sided, double-sided and multi-layer boards, the static design of the fold can be successfully achieved. In general, for most double-sided and multi-substrate designs, the bend radius of the fold should be at least ten times the thickness of the entire circuit. More layers of circuits (eight layers or more) can become very hard and it is difficult to bend them, so there is no problem. Therefore, for a double-sided circuit that requires a strict bending radius, all copper traces are placed on the same side of the substrate film in the folded region. The folded area is approximated to a single-sided circuit by removing the film on the opposite side.

2. Dynamic design

Dynamic circuits are designed for repeated bending throughout the life of the product, such as cables for printers and disk drives. In order for the dynamic circuit to achieve the longest bending life cycle, the relevant part should be designed as a single-sided circuit with copper on the central axis. The central axis refers to a theoretical plane that is at the center of the material that makes up the circuit. By using a substrate film and film of the same thickness on both sides of the copper, the copper foil will be accurately centered and subjected to minimal stress during bending or bending.

Multi-layer complexity designs that require high dynamic bending cycles and high densities can now be achieved by connecting double-sided or multilayer circuits to single-sided circuits using anisotropic (z-axis) adhesives. Bending occurs only in the case of single-sided assembly. Outside the dynamic bending area is a multi-layer independent area, which is not subject to bending and can be installed with complicated wiring and required components.

Although flexible printed circuits are expected to meet all applications requiring bending, bending, and some special circuits, in these applications, a large portion of bending or bending is a failure. Flexible materials are used in the manufacture of printed circuit boards, but the flexible materials themselves do not guarantee the reliability of the circuit function when bent or bent, especially in dynamic applications. Many factors can improve the reliability of forming or repeating bending of printed flexible printed circuit boards. To ensure reliable operation of the finished circuit, all of these factors must be considered during the design process. Here are some tips for adding flexibility:

1) In order to improve dynamic flexibility, circuits with two or more layers should be selected for plating.

2) It is recommended to keep the minimum number of bends.

3) The wires should be staggered to avoid the type I micro-cluster effect. The wire paths should be orthogonal to facilitate bending.

4) Do not place pads or through holes in the bend area.

5) Do not place ceramic devices near any bend areas to avoid discontinuities in the coating, discontinuities in the plating, or other stress concentrations. There should be no distortion in the finished assembly. Distortion can cause stress that should not be present at the outer edge of the circuit. Any burrs or irregularities that occur during the blanking process can cause the board to rupture.

6) Factory forming processing should be the first choice.

7) The thickness and width of the conductor should remain constant in the bend area. There should be variations in plating or other coatings to avoid neck-to-neck shrinkage.

8) Make a long and narrow cut in the flexible printed circuit that allows different wooden supports to bend in different directions. Although this is an effective means of maximizing efficacy, the incision is prone to tearing and the extension of the breach. This problem can be prevented by making a drill hole at the end of the incision, using a rigid plate or a thick piece of flexible material or PTFE. Ethylene to strengthen these areas (Finstad, 2001). Another method is to make the slit as wide as possible and to make a complete semicircle at the end of the slit. If it cannot be reinforced, the circuit cannot be bent at a distance of 1I2in from the end of the slit.