flex circuits withstand harsh environmental conditions
When designing a flex circuit, it’s important to consider the environment that the finished product will be exposed to. For example, if the product will be used outdoors, it’s important that the circuit is able to endure extreme temperatures and that the copper traces can adequately disperse heat. Similarly, if the circuit will be used in a harsh industrial environment, it’s important that the circuit can withstand chemical and radiation exposure. Fortunately, the materials used in flex circuits are designed to withstand these types of conditions.
The primary material in flex circuits is a polyimide or similar type of flexible polymer that dissipates heat more effectively than the materials used in rigid PCBs, allowing flex circuit to withstand high temperatures without degradation. In addition, a protective layer is applied over the copper to prevent it from oxidizing during the manufacturing process.
Incorporating thorough design validation tests into the development cycle helps identify and resolve issues before moving to production, which minimizes challenges in achieving high-quality, rugged rigid-flex designs. This can include automated optical inspection (AOI) for defect detection, impedance testing for electrical characteristics validation, and thermal cycling analysis for reliability assessment.
Can flex circuits withstand harsh environmental conditions
It’s important to use pad fillets on flex circuits to improve etch yield and material strength, as well as to reduce the risk of tear damage to the flex substrate. This can be achieved by using a solder mask opening to define the pad fillet area, or by placing an opening in the top solder layer of the flex section.
The design of a flex circuit should also take into account the bending radius requirements of each trace and pad. For example, it is recommended that inside corners on flex circuits have a radius of greater than 1.5 mm to avoid tearing the flex substrate material. This is especially important when the flex circuits are terminated to a connector, as they may be subjected to tangential bending during installation.
Adding strengtheners to the ends of a flex circuit is another simple solution to mitigate tear damage. A bead of epoxy, acrylic, or hot-melt glue can be added to the end of a flex circuit to provide additional support and stability. However, it’s important to collaborate with the assembly engineers to ensure that these strengtheners don’t interfere with the flex circuit’s ability to bend. Additionally, dispensing and curing these chemicals can add significant labor to the assembly process.
Incorporating pre-assembly baking into the production process for both flex and rigid-flex circuits is critical to mitigating assembly defects, such as moisture-induced damage, that can be detrimental to overall quality and performance. This process ensures that all components and solder joints are free of moisture before the circuit boards are assembled, enabling them to withstand stringent environmental specifications.
In summary, flex circuits are increasingly being used in consumer and industrial applications where a combination of size, weight, and functionality is required. They offer a number of advantages over traditional rigid-rigid circuits, including a smaller form factor and improved signal integrity. Thorough design validation testing, including impedance and thermal cycling, along with robust quality control measures, can help ensure that a flex circuit can withstand harsh environmental conditions.
