Flexible and Reliable Design of Flexible Circuit Board During Factory Processing (Part 1)

Factory produced flexible circuit board can be classified according to the type of bending encountered during assembly and use. There are two design types, which are discussed as follows:

1. Static design 　　

Static design refers to the bending or folding that the product encounters only during the assembly process, or the bending or folding that rarely occurs during use. Single-sided, double-sided, and multi-layer circuit boards can successfully achieve a folded static design. Generally, for most double-sided and multi-substrate designs, the minimum folding radius should be ten times the thickness of the entire circuit. Circuits with more layers (eight layers or more) will become very rigid and it is difficult to bend them, so there will be no problems. Therefore, for double-sided circuits that require a strict bending radius, all copper traces should be placed on the same surface of the substrate film in the folding area. By removing the film on the other side, the folded area approximates a single-sided circuit. 　　

2. Dynamic design 　　

The design of the dynamic circuit is aimed at the repeated bending during the entire life cycle of the product, such as the cables of printers and disk drives. In order to achieve the longest bending life cycle of the dynamic circuit, 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, which is in the center layer of the material that constitutes the circuit. By using the same thickness of the substrate film and film on both sides of the copper, the copper foil will be accurately placed in the center and the pressure on the copper foil will be minimized during bending or bending.

Multi-layer complex designs that require high dynamic bending cycles and high density can now be achieved by using an anisotropic (z-axis) adhesive to connect double-sided or multilayer circuits to single-sided circuits. Bending only occurs in single-sided assembly. The dynamic bending area is a multi-layer independent area. It is not endangered by bending and can install complex wiring and required components.