Do you avoid rigid flex design?

It is common to hear, “we avoid rigid flex”,  with the most common objection often being the learning curve to produce a good layout.  Today’s Quick Tip lists the benefits of using a rigid flex construction and situations where this technology makes good sense.

Rigid flex circuits are a hybrid construction consisting of rigid and flexible substrates laminated together into a single package.  They are electrically interconnected by means of plated-thru holes and can be solid flexible or loose leaf flexible construction,  with or without a stiffener.

When to use Rigid Flex vs. Flex

  • When stable area is needed for component mounting and packaging requires flex to fit or flex to install.
  • Used when components are mounted on both sides of the rigid and flex section.
  • Used to solve high-density packaging problems.
  • EMI/RFQ Shielding.
  • Dense Surface Mount Assembly.
  • Controlled impedance with shielding applications.
  • Used to connect rigid boards together.

Benefits of Rigid Flex:

  • Rigid-flex circuits offer enormous advantages in quality, especially with high vibration applications – eliminating connectors, mis-wiring and reducing assembly process steps.
  • Reliability of the assembly is proportionally increased due to the reduction of solder joints.
  • Weight reductions, due to the elimination of connectors and solder joints.
  • The performance of a rigid-flex is dramatically superior to a similar design with the rigid PCB’s and jumpers.  The connector leads and through holes required to join the jumper to the rigid PCB add parasitic inductance and capacitance to the circuitry.  The inductance of one net of the soldered jumper is in excess of 1.5nH, vs 0 of the same net in a rigid flex solution.  Speed, power and clarity of the signal is degraded by the use of the jumper/connector assembly.

Rigid-flex can be differentiated from multi-layer flex construction with stiffeners by having conductors on the rigid layers.  Plated thru holes extend through both the flexible and the rigid areas, with the exception of the blind and buried via construction.

We always recommend involving your supplier in the early stages of the flex or rigid flex design.  An experienced flex circuit engineer will be able to guide you to the correct material stack up and tolerances needed to ensure you receive the product you require.

Please contact us if you have any questions or would like additional information! 

Remember, designing and purchasing printed circuit boards does not have to be difficult!

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