Flex Circuit PCBs Impact Thermal
The design, fabrication and testing of flex circuit PCBs are a complex process. It’s essential that designers carefully plan the flex areas to minimize stress in order to ensure long product lifetimes. The quality of a flex circuit depends on a number of factors, including material selection and bending. In addition, signal integrity and electromagnetic interference (EMI) must be maintained.
The primary material used to create a flex circuit pcb is flexible polyimide or PET. This is combined with copper foil to create the electrical paths. Depending on the application, the base raw material can be single or double-sided. A single-sided flex circuit has a single layer of conductors, while a double-sided flex circuit has two layers. Single-sided flex circuits can be constructed with or without plated through holes. Those with through holes allow for connections to be made on both sides. Double-sided flex circuits can be fabricated with protective coverlayers on one, both or neither side.
Copper-plated traces are etched into the top and bottom of the substrate to complete the circuit. The pads and traces are then covered with a coverlay, which protects the underlying traces and pads from damage during the drilling and soldering processes. The coverlay is also useful for preventing oxidation and reducing the risk of shorts.
How Do Flex Circuit PCBs Impact Thermal Performance?
Unlike rigid circuit boards, flex circuits can be bended and twisted. This allows them to fit into small or irregularly shaped spaces, making them ideal for use in a wide variety of applications. But this flexibility comes with a price: the resulting changes in temperature can cause the circuits to overheat and fail.
In order to prevent this, a number of different strategies can be applied to flex circuits to dissipate the heat that they generate. For example, aluminum heat sinks can be easily laminated to flex circuits to disperse the heat and prevent it from building up within the components of the circuit board. Internal or external copper planes can also be added to distribute and dissipate the heat more effectively. In addition, thermally conductive pressure sensitive adhesives (PSA) are available to further dissipate the heat and reduce the risk of overheating.
It’s also important to keep in mind that the more a flex circuit is bended, the more likely it is to sustain damage. To avoid this, a flex circuit should be designed to bend no more than 90 degrees. The best way to achieve this is to balance the construction, ensuring that the neutral bend axis is near the center of the stack. This will minimize both the distances of destructive forces and the forces that emerge between overlapping conductive and dielectric layers. The conductive layers should be as thin as possible to increase the mechanical resilience of the circuit. In addition, careful consideration should be given to the placement of connectors between the rigid and flex sections in order to maintain proper transitional stresses.
