Protecting Flexible Printed Circuits From Mechanical Stress
Flexible Printed Circuits From Mechanical Stress
A flexible printed circuit, or FPC, is a conductive circuit board that has a thin substrate and is designed to flex or bend. It may contain surface mount devices (SMDs) or terminals for connecting to other components. FPCs are used in a variety of electronic applications. The conductive pathways on the board are typically made of copper foil and may also include dielectric layers that are backed by protective solder mask. This combination creates a strong, durable structure that can withstand mechanical stress. However, the substrate and solder can still be vulnerable to damage from mechanical stress.
To protect a flexible printed circuit from mechanical stress, it is important to understand the construction and manufacturing processes. The first step is to decide how much flexing is necessary. It is possible to produce a flex PCB that only needs to be bent once, but repeated bending or creasing will crack the copper traces and can damage the substrate.
Manufacturers can reduce the risk of this by carefully planning the design and establishing the bend radius characteristics in the early stages of production. This helps them to select the best material and ensure that the copper foil can withstand the intended number of flex cycles.
Protecting Flexible Printed Circuits From Mechanical Stress
Another important factor to consider is how a flex circuit will be handled once it has been completed. Often, a flex circuit will need to be folded or creased when it is being shipped or stored, and the circuit should be able to support this without fracturing. The flex circuit can be reinforced with a rigid stiffener that is adhered to the base, or if it will not be folding, an epoxy bead can be placed at the transition between the rigid and flex sections to provide strain relief.
The final factor that should be taken into consideration is how a flex circuit will be assembled and reflow soldered. This can be done either by using an automated fluid dispensing machine, or by hand. The assembly process will put a great deal of stress on the joints, and it is important that this stress is evenly distributed throughout the joint. The best way to achieve this is by properly filling all the through-hole pads in a flex circuit, using anchoring stubs, and reducing coverlay access openings where possible.
A flex PCB should also be carefully inspected during the assembly process to check for any signs of moisture, scratches, or other damages. It should then be sealed and wrapped before it is shipped to prevent moisture from entering the traces and weakening them. It is also crucial to use a high-quality adhesive for the final layer of the PCB, such as Ecobond 45/15 from Henkel Loctite. The glue will not only act as a strain reliever, but it will also be able to withstand the reflow soldering temperatures. By following these tips, a flex circuit can be protected from mechanical stress and will be able to perform well under any conditions.