Flexible Circuits vs. Traditional Printed Circuit Boards  “Mechanical Considerations”

Flexible Circuits vs. Traditional Printed Circuit Boards “Mechanical Considerations”

October 15, 2014 in Design Tips

Flexible circuits are usually considered for a product when a mechanical designer encounters interference or connectivity issues using a traditional printed circuit board. Other reasons exist for the decision to use flexible circuits that include overall weight, the “smaller is better” requirements we all face today and the ability to replace two or more circuit boards with connection cables with one circuit. Once the decision is made we must address the mechanical characteristics of the flexible circuit compared with the traditional printed circuit board.

In order for a flexible circuit design to be fully compatible it must be able to carry all the pertinent electronic components and solve the mechanical issues encountered. The inherent flexible nature of these circuits, cause many to question the reliability and robustness of this type of design. It’s understandable given the flexible circuit’s small footprint in the overall printed circuit industry. There just isn’t as much information available as there is for traditional printed circuit boards. Let’s look at a few concerns and address them one at a time.

  • Can we attach all of the components associated with our design on a flexible circuit?

Yes! Any component that can be soldered reliably to a printed circuit board can also be soldered reliably to a flexible circuit. There are some exceptions that require special attention, for instance, a ball grid array or chip on board. These components rely on a very consistent flat surface to be soldered correctly. There are several options available to allow these tedious components to be soldered to a flexible circuit. Some are permanent and some are temporary and are in place only during the assembly process. But all components may be soldered to a flexible circuit.

  • Can a flexible circuit be bent or formed to fit into tight places with components attached?

Yes! The solder joint on a flexible circuit is surprisingly fragile. If the circuit is designed correctly to keep the solder joints away from the bend areas a fully functional circuit may be assembled, cleaned, tested and then bent or formed into place without any ill effects. Contract manufacturers experienced in flexible circuit assembly can guide you through the methods typically used to protect those fragile areas and create a robust electronic assembly that is flexible and able to conform to your unique mechanical design.

  • Can a flexible circuit assembly handle excessive vibration in an application?

Yes! Flexible circuits are used regularly in high vibration applications. They are commonly found in airplanes, automobiles, trains etc. These are applications that experience high levels of vibration and must function as intended. Again, when designed correctly flexible circuit assemblies will provide a robust and reliable product even when subjected to high vibration.

  • Can a flexible circuit be mounted with traditional hardware?

Yes! Typically a flexible circuit would be designed with a rigid stiffener that is made of FR4 or G10 (materials used to fabricate traditional printed circuit boards), laminated to it in the mounting areas to afford the use of screws, washers and nuts. In this way, they are mechanically similar to a traditional printed circuit board. You may permanently mount portions of the flexible circuit assembly and leave other portions as is so that it may be bent or formed in to the tight constraints of the application that warranted the flexible design to begin with.

There are many other scenarios that can be addressed, but the takeaway message should be that you can trust the mechanical nature of a flexible circuit assembly to perform well in any application. It requires some expert design and assembly assistance, but in the end, your flexible circuit assembly will be robust and reliable.

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