Gerber Layout & Design Recommendations
Epec's engineering team offers full flex and rigid-flex circuit design services. During our application review and quoting process, we carefully examined specifications, materials and construction in order to minimize and eliminate any technical issues.
We also look for areas of opportunity for improving the design of your flex or rigid-flex circuit's reliability, functionality, and ensure there are no IPC design standard violations. Cost reductions are also identified to generate an accurate quote that is based on a manufacturable, reliable and cost effective design.
Radiused Corners within Flex Bend Areas
Having a radiused corner within and flex bend area reduces / eliminates stress concentrators and improves reliability.
Sharp corners in flex circuits can lead to stress concentration and potential cracking over time. Radiused corners distribute mechanical stress more evenly, enhancing durability and flexibility. Use smooth, rounded corners to reduce the risk of tearing and to improve the longevity of the circuit.
For a more in-depth look, see our blog post on flex and rigid-flex bend capabilities.
Preferred
Acceptable
Not Allowed
Staggered Layer to Layer Trace Positioning
Staggering your designs layer to layer trace positioning eliminates the "I-Beam" effect which improves the flexibility and reliability of your flex circuit.
Aligning traces directly on top of each other in multiple layers can create weak points and affect the flexibility of the circuit. Staggering trace positions across layers helps to balance the mechanical stress and prevents issues like delamination or cracking during bending.
Preferred
Not Recommended
Fillets & Teardrops
Proper fillets and teardrops eliminate stress concentrations and improves the reliability of the flexible PCB.
Fillets, or rounded joints, at the intersections of traces and pads prevent sharp angles that can be prone to cracking. Properly designed fillets ensure a smoother transition of stress, reducing the likelihood of failure in these critical areas.
Vias within Bend Areas
This is not recommended. Having vias within a bend area can cause a significant stress concentrator which may lead to breakage.
Stiffener & Coverlay Terminations
Proper stiffener and coverlay terminations prevent creation of significant stress concentrator within the flexible circuit board. See our blog post on flex circuit polyimide coverlay and soldermask considerations for more information.
Required
Not Allowed
Additional Design Considerations
Balanced Construction
Ensuring that the layers in a flex circuit are symmetrically arranged around the centerline prevents warping and mechanical imbalances. A balanced construction minimizes stress concentrations and enhances the overall performance and reliability of the circuit.
Controlled Impedance
For high-speed signal transmission, maintaining controlled impedance is crucial. This involves precise control over trace widths, spacing, and dielectric materials. Controlled impedance ensures signal integrity, reduces electromagnetic interference, and improves the performance of the circuit.
Adequate Bend Radius
The bend radius of a flex circuit should be carefully designed to avoid excessive stress. The minimum bend radius depends on the material thickness and the number of layers. Following recommended bend radius guidelines ensures that the circuit can withstand repeated flexing without damage.
Via Protection
Vias in flex circuits can be vulnerable to mechanical stress. Using teardrop shapes at via connections, reinforcing via areas with additional material, or incorporating via caps can protect these critical points and enhance the circuit’s durability.
FAQs
Why are radiused corners important in flex circuit design?
Radiused corners help distribute mechanical stress more evenly, reducing the risk of cracking and enhancing durability.
What is the benefit of staggered trace positioning?
Staggered traces prevent weak points and reduce the risk of delamination, improving the flexibility and reliability of the circuit.
How do fillets improve flex circuit performance?
Fillets provide smooth transitions at trace intersections, minimizing stress concentrations and reducing the likelihood of cracking.
Why is balanced construction crucial in flex circuits?
Balanced construction prevents warping and mechanical imbalances, ensuring consistent performance and reliability.
What is controlled impedance, and why is it important?
Controlled impedance maintains signal integrity and reduces electromagnetic interference, crucial for high-speed signal transmission.
How is the minimum bend radius determined?
The minimum bend radius depends on material thickness and layer count, ensuring the circuit can withstand repeated flexing.
What measures can protect vias in flex circuits?
Using teardrop shapes, reinforcing via areas, and incorporating via caps can protect vias from mechanical stress.
Best Practices for Optimal Flex Circuit Design
Implementing best practices in the design of flexible printed circuit boards is essential for achieving optimal performance and reliability. By adhering to guidelines such as using radiused corners, staggered trace positioning, proper fillets, balanced construction, controlled impedance, adequate bend radius, and via protection, you can significantly enhance the durability and functionality of your flex circuits. These design recommendations ensure that your circuits can withstand the mechanical stresses of their applications, providing long-lasting and efficient performance.
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