PCB Assembly Services - Screaming Circuits: Afraid of designing with Flex? Three reasons you might want to try

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Afraid of designing with Flex? Three reasons you might want to try

Until fairly recently the use of flexible PC board material (flex) was considered only for specialized or exotic applications. As tends to happen with advanced technology, the "mainstream" has caught wind of flex. With so many Internet of Things (IoT) and compact wearable device being built, flex and rigid flex is starting to look like an appropriate technology.

First - don't the terms "rigid" and "flex" contradict each other? Well, yes and no. In our application it means "rigid boards connected to flex boards", not rigid boards that are flexible. The image below, shows a pure flex circuit board on the left and a common type of rigid-flex board on the right.

Flex and rigid-flex from PrintedCircuits.com

images courtesy of Printedcircuits.com

Designing with flex is not too terribly different than designing with conventional rigid materials, but it is a bit more complex and typically costs more; both in fab and assembly. Sounds great - more complex and more expensive. Just what I like with my dinner. Give that, why would one choose such a thing? Here are the three most common applications.

1. Packaging with irregular contours

Some applications require that the flex board bend once when being installed in a device. A good example of that would be a camera. There is little spare space in a modern camera. Often the circuit needs bend around the lens or conform to the surface of a prism or battery. Flex or rigid-flex construction is ideal for this application.

2. Applications with motion

Other applications require the board to flex in application. The electrical connection to an ink jet print head is a common example of this, as is the hinge section of a laptop computer. A properly designed and constructed flex board will reliably move as needed for the life of the deice and will not deform or creep side to side as a more conventional wire cable would.

3. Non-bendy applications where space is critical

The third common use for flex and rigid-flex doesn't necessarily involve movement at all. In modern mobile and wearable devices, sometimes the difference in thickness between even the thinnest rigid printed circuit board and a flex board is enough to keep the device within its size and weight specifications. A cell phone would be a good example of this. Rigid flex might be used when there is enough room of a thin PCB and the rigidity of the PCB is required, but board to board wire cabling would be too thick. Flex between the boards can save a lot of room over the cable.

You may not have need to use one of the flex technologies today, but if you are designing for very compact devices, you may want to consider if it would better serve your design than would conventional rigid PC board construction.

Duane Benson
Tastes filling. Less great

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