Manufacturing Printed Flexible Circuits
Printed flexible circuits (PFC) enable products to be smaller and lighter. They are found in virtually all modern electronic devices, including mobile consumer electronics like tablets, smart phones and laptop computers. The flexible PCBs in these products provide interconnects between the rigid circuit boards that house the primary components and the connectors to the device components.
Unlike rigid PCBs, which are typically built on copper clad polyimide substrates, flex circuits are made from thin film laminates. Copper traces are bonded to these dielectric layers, which can vary in thickness from.0005’’ to.010’’. The traces are then coated with gold or solder for conductivity and environmental durability.
Flex circuits are available in sheets or in rolls, which offer the flexibility to be cut into a specific size and shape. This design flexibility is a major benefit of the technology, providing designers with a wider range of design options. In addition, it can also help to reduce manufacturing costs by reducing material waste from cutting and trimming the circuits into individual components.
There are a number of key challenges in manufacturing printed flexible circuits, however. Despite the benefits they bring to product design, these challenges make it important for designers to understand the limitations and constraints of flex circuits as they move forward in their adoption of this emerging technology.
While it may be tempting to design an entire assembly, and then add in a flex circuit to meet connections between the various elements, this approach can create issues that may cost more in the long run. For example, if the circuit requires very tight bends that are well beyond the flex circuit’s ability to stretch, it may not withstand the stress and could be prone to failure. The same is true of designing a circuit with too many layers for its size, which can lead to high costs.
Key Challenges in Manufacturing Printed Flexible Circuits
The thinness and flexibility of a flex circuit provides significant advantages, but it can be challenging to achieve the required performance levels in all applications. For example, high speed signals may require thicker layers, sensitive signals may require shielding and thermal expansion considerations might impact reliability.
The transition between the rigid and flexible portions of a flex circuit is often the source of mechanical stresses, signal integrity problems and electromagnetic interference (EMI). The choice of materials used for both the rigid and flexible sections is critical. In addition, determining how the circuit will be bent during use is essential.
Unlike rigid PCBs, which have a fixed shape at the point of production, flex circuits are often more susceptible to damage during secondary manufacturing operations such as storage, handling, paste printing, assembly, reflow and inspection. A strong focus on DFX principles, appropriate training and the implementation of inline inspection at critical points are all critical to avoiding these quality issues.
Using a contract manufacturer with a proven track record of producing a wide variety of products that incorporate flex circuitry can help to mitigate some of these challenges. SigmaTron International produces a wide range of flex and hybrid products at its facility in Acuna, Mexico, which includes a large fab area dedicated to the production of flex circuits.