Flex PCB Design Tips and Tricks

Flexible printed circuit boards (Flex PCB) are a type of printed circuit board that is made from a flexible material, such as polyimide. FPCBs are used in a wide variety of applications, including consumer electronics, medical devices, and automotive electronics.

flex PCB from jlcpcb

Designing FPCBs can be challenging, as there are a number of unique considerations that must be taken into account. In this article, we will discuss some of the most important flex PCB design tips and tricks.

The outline of a flex PCB refers to the final shape of the board. When designing the outline, it is important to consider the following:

• The outline layer must be unique. Typically, this layer is represented by GM1 or GKO.

• Non-metallic hole annuli or slot frames should also be placed on the outline layer.

• The outline layer should not contain any miscellaneous lines.

• The FPC outline cannot have internal right angles or sharp corners. It must also be closed, and cannot be open.

Outline design example 1

Outline design example 2

Outline design example 3

Outline design example4

Outline design example 5

Ground Copper Design for Flex PCB

The ground copper design is another important consideration for flex PCBs. When designing the ground copper, it is important to avoid large areas of copper, as this can reduce the flexibility of the board. It is also important to design the ground copper in a grid pattern, with a line width of 0.2mm and spacing of 0.2mm.

Ground Copper Design Example 1

Issue: Bubbles during lamination

Cause: Large areas of ground copper with few openings in the solder mask can trap air, which can react with the copper surface during lamination, causing oxidation spots.

Solution: Add solder mask openings or change to a grid copper design.

Ground Copper Design Example 2

Issue: Reduced flexibility

Cause: Large areas of ground copper can reduce the flexibility of the board.

Solution: Design the ground copper in a grid pattern, with a line width of 0.2mm and spacing of 0.2mm.

Ground Copper Design Example 3

Issue: Misalignment of components or insufficient solder during SMT

Cause: Ground copper covering between IC pads or gold finger pads can result in several pads connecting together.

Solution: Do not cover excess copper between pads.

Ground Copper Design Example 4

Issue: Solder bridging and short circuits during soldering

Cause: Thick traces or ground copper on component pads can decrease the spacing between pads.

Solution: Avoid designing thick traces or ground copper on similar pads.

Flex PCB Soldering Gold Finger Design

Soldering gold fingers are used to connect flex PCBs to other components. When designing soldering gold fingers, it is important to consider the following requirements

• Soldering fingers must have pads designed on both the top and bottom layers.

• The lengths of the pads on the upper and lower layers need to be staggered by 0.5mm, and the corresponding solder mask openings should also be staggered by more than 0.5mm.

• The solder mask needs to cover the pad by 0.5mm (this can be achieved by extending the pad).

• Design half-holes at the front of the gold fingers; also design a hole on the finger pad, with an inner diameter of 0.3mm and an outer diameter of 0.5mm.

• The through-holes on the pads need to be staggered and should not be aligned in a single row.

Additional Tips

In addition to the tips discussed above, there are a few other things to keep in mind when designing flex PCBs:

• Use a flexible material that is appropriate for the application.

• Consider the bend radius of the flex PCB.

• Use a solder mask that is compatible with the flexible material.

• Test the flex PCB thoroughly before using it in a production environment.

• By following these tips, you can design flex PCBs that meet your specific needs and requirements.

By following these tips, you can design flex PCBs that meet your specific needs and requirements.