Flexible PCBs Can Be Used in Stretchable Batteries
When designing wearable devices that can be worn on the wrist, the ankle, or around the chest, a lot of consideration goes into the electronics and battery that will control and power those devices. But the spotlight also needs to shine on the PCBs that will make these devices work. And that’s where flex and rigid-flex circuit boards come into play.
Both rigid-flex and flex PCBs are designed to be able to be bent and twisted in ways that standard printed circuit boards cannot. And they’re used in products from smartwatches and fitness trackers to medical devices and more. They’re often used where a lot of dynamic bending, twisting, and movement will occur. But how do you ensure the reliability of these flexible traces in such conditions?
One important way is to choose the right flex pcbs substrate material. This is the base layer that the entire circuit is built on. And the most common choice is polyimide. It’s very flexible, incredibly tough, and heat resistant. This allows for a large amount of movement and a lot of solder reflow cycles without the occurrence of stress fatigue or delamination.
How Flexible PCBs Can Be Used in Stretchable Batteries
A second way to increase the durability of a flex PCB is to add stress relief holes to key locations on the board where a lot of flexing will occur. This is like the metal house that is added to some parts of rigid PCBs and will help prevent a failure at these points due to repeated flexing and bending.
The third way to make a flex PCB more durable is to use a thicker and more robust copper foil. This can be done by using rolling annealed (RA) copper foil rather than the normal electrodeposited copper foil. This type of copper is able to bend and stretch a lot more before fatigue cracking occurs, and it’s also springier in the z deflection direction – perfect for a flex circuit.
Stiffeners can also be used on a flex PCB to help with stability during dynamic bending and torsional movements. These are added to the edges of the flex-to-rigid joins on the circuit and offer mechanical reinforcement where a flex-to-rigid join may experience excessive stress or strain.
Another thing to consider when choosing a substrate for your flex circuit is the thickness of the foil and how it’s treated. Rolled and annealed foils are commonly used for flex circuits, but thicker films that are electroplated can be used as well.
Lastly, making sure the design of a flex circuit is optimized for its intended applications is important. This includes reducing and eliminating stress concentration points by using the appropriate pad shape, size, and spacing. By taking these steps, you can guarantee the longevity of your flex PCB and the performance of your wearable device.
To learn more about how flex and rigid-flex PCBs can benefit your next project, contact the Rocket-PCB team today. We’re your trusted partner and will help you take the lead when it comes to creating bespoke wearables.
