PCB Assembly Services - Screaming Circuits: Choosing Between Flex and Rigid-Flex


Choosing Between Flex and Rigid-Flex

You're in the middle of designing a very small wireless data collection. The size has made it a real challenge and you've always thought that you could get another important chip or two on the board if it could just bend it a bit. You can do that. The first step is to make a few choices.


You could have more than one rigid board with cables connecting them. That would work, but connectors do take up some space and may have the potential for coming loose in a high vibration setting or if dropped. Rigid flex is ideal for this type of an environment:

  • You can afford the extra cost
  • Some of the electronics components need the stiffness of a rigid board
  • The product size makes you break it into two or more smaller board
  • Your product needs to survive a rugged environment

"Rugged" in this case can mean that it will be handled a lot. It doesn't have to mean "strapped to the side of a jet engine." Cameras, phones and other hand carry devices of similar size (quick - name one that is not a camera or phone) often use rigid flex due to the amount of life-time handling and the potential to be dropped.

Pure flex is ideal if: Flex cable w components

  • All of your components are small and light weight, or there won't be much vibration
  • The end use packaging requires that there are multiple bends, twists or folds in the PCB
  • Or the device will be bending while in use
  • You need to take every possible fraction of a cubic mm out of the device

Flex can also make a nice a small interconnect cable, even with connectors.

  • Flex connectors tend to be lower in profile than cable connectors
  • Flex cables can fit through extremely tight areas - much smaller than can insulated wire cables
  • You can put components onto the flex cable (as shown on the flex cable in the image above)
  • They can bend and fold when assembled
  • They can reliable bend for the live of the device

If your project doesn't fit any of the above considerations, you are probably better off with a conventional rigid PC board. You will save money in both fab and assembly But if you need it, flex is a lot more accessible than it was just a few years ago. There is no need to avoid it.

If you are having us build your flex or rigid flex boards, check with your customer service rep to see what the additional time and cost will be. Check with your fab house for their design requirements, and check back in this blog periodically for advice on how to layout more reliable flex and rigid flex boards.

Duane Benson






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