The neutral bend axis of the flex circuit board may not be exactly in the middle of the circuit stack. Proper handling of the flex circuit board may help prevent dents and breaks in the flex PCB.

Flexible PCBs are as much as mechanical devices as there are electrical devices. The conductors should be arranged so that the entire circuit functions reliably and adequately. Unlike traditional rigid printed circuit boards (rigid PCBs), flexible PCBs can be bent, bent and twisted to fit the final assembly. When bent beyond a certain point, this bending can severely strain the circuit, causing the flex PCB to break and dent.

The flexibility of flex circuits offers designers a range of options that rigid PCBs lack. Even though flex circuits are ideal for bending and twisting, that doesn't mean that flex copper traces will never crack. Like all materials, there are limits to the type and strength of stress that copper can withstand.

There are various challenges. When dynamic bending is required (continuous flexing of the product as it is in use), or in applications where circuits need to be folded into tight spaces within a multi-lane enclosure, precision and care must be maintained to avoid breakage

Considerations for optimizing flex circuit flex and bend.

Understanding Stress Points and Bend Radius

You need to understand the design problems of bending, folding and bending - understand the physics of bending. For single-sided flex circuit bending, the copper layer will eventually crack if extended or compressed beyond the bend radius or stress point. Always make sure you operate within these parameters.

Neutral axis

For dynamic flex applications, single-sided (one layer copper circuit) is recommended. This provides room for the copper to move at the center of the structure with an equivalent thickness. With this configuration, the copper layer is neither compressed nor tensioned during dynamic bending or flexing.

Thinner is better

The thinner the layer, the smaller the inner bend radius and therefore the less stress on the outer layer. For applications that require frequent bending, thinner copper and thinner dielectric layers are preferred.

H-beam design

An H-beam configuration means that the other side of the copper or dielectric directly overlaps each other. This type of structure becomes stronger in the folded area. Due to the compression layer of the inner layer, the outward extension force is significantly increased. To eliminate this problem, traces on opposite sides should be staggered.

Sharp bends or folds

Many flex circuit boards are folded as part of a design kit. A well-constructed circuit can easily withstand first folds, twists, or creases. However, wrinkled circuits should not be folded frequently, as the copper will eventually crack. This is not recommended under any circumstances. To avoid this problem, some design considerations are provided. For example, flexible circuit boards with rounded corner traces are designed for this purpose.

Additional considerations to avoid trace cracking on flex circuits include:

Use solder or solder-coated paths for traces

Use RA (roll annealed) copper or electrodeposited copper (ED) with grain orientation

Covers areas where the polyimide film is bent or bent,

Use stiffeners on the bottom and overlays on the top.