Flex Circuit PCBs Be Used in Wearable Technology
A flex circuit PCB is an electrical circuit that combines copper conductors with insulators and support materials. The most common insulator is polyimide film, which can be coated with various surface finishes. These surfaces can provide a solderable surface, prevent copper oxidation and reduce the chances of I-beaming or delamination over time.
These coatings can also help insulate and protect the conductors from damage caused by moisture or heat. The surface finish on a flex PCB is important because it can affect the conductor’s performance and longevity. There are several different types of surface finishes available, including electroless nickel immersion gold (ENIG), which is used on about 80% of all boards. This type of finish provides a thin, silvery-colored layer that prevents copper from oxidizing and improves the strength of the bond between copper and polyimide.
Unlike standard rigid flex circuit pcb, which have a fiberglass or metal base, flex circuits have a flexible polymer substrate. The most common flex circuits are made with polyimide (PI) film, which is thermosetting and stays flexible after heating. However, standard PI does not have good resistance to humidity or tears, so it’s important to choose upgraded PI films for use in a flex circuit.
Can Flex Circuit PCBs Be Used in Wearable Technology?
The thickness of the PI substrate and the number of layers determine how much a flex circuit can bend. To maximize bending capabilities, choose a thinner PI substrate and keep the layer count low. Conductors should be routed to avoid stress points that can damage them when the circuit is bent. In multi-layer flex circuits, stagger the traces on both sides of the board to minimize stress.
In addition to the aforementioned material features, a flex circuit must have good thermal stability and abrasion resistance. This is because it will likely be exposed to high temperatures and extreme environmental conditions, such as temperature swings, humidity, moisture, and vibration.
The best way to ensure that a flex circuit can withstand these conditions is by using an advanced PCB CAD tool that’s optimized for rigid-flex design. This tool will automatically generate a fabrication drawing with all the necessary layers and material specifications for a rigid-flex or a rigid-flex printed circuit board, which is crucial for accurate manufacturing.
For example, the tool will automatically include a relief slot and large corner radius in the corners of the flex to prevent stress cracking. It will also include pad fillets to improve etch yield and material strength, and staggered traces to eliminate stress in the bend area. Finally, the CAD software will also enable designers to select a material that’s compatible with your circuit’s operating environment. For example, a material that is plated with a copper alloy can resist corrosion and abrasion, while a polyimide-based material can withstand high temperatures.
