Flexible pcb design compare
As a rule, flexible circuits have lower layer counts than rigid PCBs. This is due to the fact that the copper foil used in flex is thinner and more conductive, so there’s less copper per layer. Also, flex circuits don’t need as many ground plane layers or shielding areas.
This makes them lighter and smaller than rigid boards, which saves space on the product assembly floor. For this reason, flex circuits are used in wrist-watches and other small electronic products where space is at a premium. During the manufacturing process, flex circuits may experience high tensile stress or torsional deformations, which is why they must be made using materials that are both durable and lightweight. A common choice is polyimide, which can be made into a variety of thicknesses and is very durable.
In addition, the material must be able to withstand the high-temperature heat required for soldering. The underlying substrate should also be able to handle high-temperature processes. For this reason, manufacturers often use adhesiveless PI, which is a thermally-resistant film that can be laminated to the copper without an adhesive. This can reduce cost and increase reliability.
How do Flexible pcb design compare to rigid PCBs?
Another consideration when designing a flexible pcb design is the amount of solder that needs to be added. Because the copper foil is so thin, adding too much solder can weaken the circuit. To combat this, designers should make sure that the pads are large enough to accommodate a proper amount of solder and that the traces have appropriate transitional fillets at their end caps to improve the strength of these connections.
Flex circuits can have through-hole pads that are anchored to the underlying substrate with plating, anchoring stubs, and reduced coverlay access openings. This can help ensure that the pads don’t break due to bending. However, it also prevents the pads from being as dense as they could be on a rigid PCB. To address this, flex designers should consider using larger footprints for SMT components or designing their traces to avoid crossing through the SMT pad.
A common mistake that flex designers make is routing corners in the bend area of their circuits. This can lead to EMI and create stress points that can make or break the flex circuit. To avoid these problems, it’s important to avoid sharp corners and use rounded edges whenever possible.
Another issue with flex circuits is their ability to transfer signals between rigid and flex sections of the board. This is a critical design requirement, and can be accomplished with signal routing or through a stiffener. Stiffeners can be made of a variety of materials, but most manufactures use a dielectric stiffener on the flex-to-rigid termination sections of a flex circuit.
While it is possible to make a rigid-flex circuit with a stiffener, it adds cost to the production panel and can introduce manufacturing challenges. As a result, it’s best to incorporate them into the flex circuit early in the design stage.
