PCB Flex Circuits

A circuit board generates a significant amount of heat in its normal operation. If this heat is not dissipated, it can damage components and lead to a variety of problems. This includes overheating, which can cause components to fail in their function, as well as thermal stress, which can cause the board itself to break down or degrade over time. To prevent this from happening, PCB manufacturers need to consider various design and layout guidelines when they produce flex circuits.

These guidelines include the stackup of layers, as well as the size and shape of traces. For example, if there is too much copper between two conductive elements, it can create a short and increase the chance of failure. This is why it’s important to carefully analyze the traces in your designs and follow guidelines for their positioning.

Another consideration is the choice of material for the base of the flex. A good option is polyimide, which is incredibly tough, highly tolerant of solder reflow cycles and thermal cycling, and a relatively stable material in terms of its coefficient of expansion. This makes it a great choice for both rigid and pcb flex. In addition, it has a lower thermal conductivity than traditional network epoxy resins, which means that the boards will be less prone to overheating and thermal stress.

Thermal Considerations for PCB Flex Circuits

In addition to the aforementioned material selection, it is also essential to ensure that adequate ventilation is in place for the PCB assembly. This will ensure that hot air pockets are not able to form, and that there is a constant flow of cold air across the entire surface area of the circuit board.

Because flex circuits are generally thinner than 2-layer FR4 rigid boards, they have an inherent capability to dissipate heat more efficiently due to their larger surface-to-volume ratio. Furthermore, there are additional strategies that can be implemented to help manage this heat, such as localized external or internal copper planes, aluminum heat sinks, and thermally conductive pressure sensitive adhesives.

Additionally, when designing a flex circuit, it is a good idea to use higher grade Rolling Annealed (RA) copper foil rather than un-annealed. This is because RA copper can be stretched significantly before fatigue cracking occurs, which is a good thing for flex circuits that will be bending and moving on a regular basis.

There are a number of other important thermal considerations for PCB flex, such as the placement of high-power components. These should be distributed throughout the circuit board to avoid creating specific hotspots, and it’s a good idea to use metal-plating holes and keep component leads short to improve heat transfer. Lastly, it’s also worth considering adding ground flood to the top and bottom layers of the circuit board to increase its overall resistance to heat. This will improve the ability of the flex circuit to dissipate heat effectively and reduce the risk of failure in its application.