Flex and Rigid-flex PCB Designer’s Guide

Are you designing added cost into your product?  Laminate, construction finishes and design features can greatly affect price and delivery.  We work closely with our customers to recommend cost-effective stackups, efficient arrays and manufacturable features that will produce consistent and reliable yields. 

Circuit’s Designing Flex and Rigid-Flex Products for High Reliability Applications is a comprehensive presentation that includes: 

  • An Overview of Flex Benefits and Applications
  • The Basics
  • Design Considerations
  • Materials Properties
  • Documentation
  • Industry Standards and Specification

“Designers Tips” are featured throughout the presentation illustrating best practices for robust and reliable circuit design.  

Request a copy of Circuit’s Designer’s Guide

Flexible PCB properties and benefits

Flexible PCBs and hybrids offer designers many advantages over traditional FR4 rigid boards. The versatile shape and formability of flex enable 3D configurations and solve numerous problems for designers who are faced with fitting more electronics into smaller spaces. Polyimide-based material and copper (annealed copper rather than electroplated) properties provide significant advantages to the design such as quick heat dissipation and high shock and vibration resistance. Flex properties also enable designers to easily predict and control impedance and crosstalk. 

Weight and Size: Compared to rigid and round wire configurations, a flex design can save up to 75% in overall weight. Flex circuit boards can be as thin as 4 mils, enabling designers to solve intricate interconnection issues while reducing overall packaging size. 

Cost effective: Flex circuits are typically designed to eliminate board to board interconnects or board to wire connections which are the most common failure point in electronic assemblies. A rigid-flex hybrid can reduce BOM connector count, increase product reliability and provide ease of installation (or field replacement) often eliminating human error associated with wire configurations.

Durability: Able to bend and straighten up to 500 million times without a failure, flex circuits provide un-matched performance for applications with repetitive motion. Flexible circuit boards are also able to survive hostile environments due the characteristics of Polyimide KAPTON® such as: dimensional stability and dielectric strength.

Standard Flexible Circuit Materials

Circuits, LLC carries a broad range of adhesive based or adhesiveless copper clad constructions using a wide variety of base dielectrics. All Dupont Pyralux materials stocked at Circuits are Certified to IPC 4204/11.   

Need the datasheet?  Visit Dupont’s Pryalux site here.

Datasheet Description

Design Considerations from the Design Guide

Minimum Bend Radius 

  • For single and double sided flex the minimum bend radius should be 6 times the overall thickness.
  • For multilayer and rigid flex, the minimum bend radius should be 12 times the overall thickness.
  • Critical area is the inside of the bend where delamination, dielectric and conductor fractures can occur.
  • Failures in the compression area (inside of the bend) may go undetected until after the flex board is in service.
  • This is the most common mechanical failure mechanism for a flex board and it can happen with just one excessive fold of the board.
  • Elevated PCB temperature during bending is not recommended.

bend radius

Designer Tips

  • Even distribution of copper features in the bend area.
  • Power & ground planes on the outside of the bend and cross-hatched.
  • For border-line conditions there is no substitute for a mechanical mockup that can be destructively tested after bend.