adminflex circuit design handle prolonged exposure to vibration
One of the most challenging aspects of flex circuit design is finding ways to balance electrical requirements with mechanical constraints. The bending and unbending of a flex PCB can cause the copper layers to crack or tear if not carefully planned, resulting in malfunctions or failures. Fortunately, there are several things that can be done to help mitigate these problems.
Using a stiffener between the rigid and flex circuit design PCBs is one way to increase their durability. This can be accomplished by adding a bead of epoxy, acrylic or hot-melt around the edges where the flex circuit exits the rigid board. However, this adds steps to the fabrication and assembly process, increasing cost. Alternatively, using a stronger adhesive on the flex PCB side can improve durability without increasing assembly time.
Another way to increase the durability of a flex circuit is to stagger traces across adjacent layers. Doing so reduces stress on the flex substrate, as it prevents them from being pushed against each other. This is particularly important for dynamic designs that undergo repeated bending and unbending throughout their lifecycle.
How do flex circuit design handle prolonged exposure to vibration?
When designing a flex PCB, it’s essential to avoid placing any pads or vias on bend lines. This is because the mechanical strain from a flex PCB tends to concentrate on a single line of the circuit, known as a bend line. Prolonged exposure to this stress can weaken these areas of the flex PCB, reducing their lifespan.
It’s also important to avoid overlapping traces on a flex PCB, as this increases tension in the circuit during bending. This can lead to I-beaming and eventually break the copper traces, causing shorts and other circuit failures. To prevent this, designers should plan to use a hatched copper polygon instead of a solid pour for ground planes on a flex PCB.
Similarly, it’s essential to avoid sharp-angled corners in a flex circuit. While this is standard practice for PCB design on a rigid PCB, it’s not advisable for a flex PCB, as these corners may cause the flex circuit to tear. Instead, designers should use rounded corners that have radii greater than 1.5 mm to avoid tearing the flex substrate material.
Finally, avoiding discontinuities such as holes, cut-outs and slits in the bend area of the circuit is crucial to maintaining its durability. These will introduce stress points to the copper that can weaken the trace and eventually result in failures during assembly and soldering. Instead, designers should plan to transition gradually from wide to narrow traces in the bend area, as this will decrease the stress and minimize damage.
Flex circuits are integral to modern electronics, but integrating their electrical and mechanical requirements can be a challenge. By following these dos and don’ts, engineers can maximize the functionality of a flex circuit and reduce the risk of failure. Whether dealing with static or dynamic flex designs, following IPC guidelines and industry standards can help ensure the reliability of a flex circuit.
