Flexible PCB Boards Be Folded
The answer to “Can flexible PCB boards be folded?” depends on your product design and assembly process requirements. If the circuit is going to be static and will only be flexed once or twice in the lifetime of your product – for example, an ultrasound device held by the hand – then you have more freedom to choose layers, copper thickness, surface finish types and other fabrication and assembly options.
However, if the flexible pcb board will be repeatedly bent and subjected to mechanical shocks or vibrations – like automotive products for example – then you’ll want to limit the number of bends, choose rigid-flex technology, specify a maximum allowed bending radius, design for plated vias (or buried via holes) and consider using stiffeners where necessary.
The flex circuit may require special dielectric materials to support the bending movement and maintain flexibility. A common material used in flex circuits is polyimide film, usually with an acrylic or hot-melt adhesive attached. Stiffeners, which are rigid dielectric materials such as aluminum or FR4, can also be added to the flex circuit to improve rigidity and stability. They help relieve stress and balance weight, and they increase abrasion resistance and heat dissipation.
Can Flexible PCB Boards Be Folded?
Trace routing: Try to route traces perpendicular to the bending direction and use wider traces in the bend areas to distribute stress over a larger area. In addition, avoid transition layers in the bending area and avoid overlapping traces where possible. Via placement: Use teardrop or fillet shaped vias rather than square and round ones, as the latter can crack under stress. Also, use large annular rings to connect a via and copper trace to reduce stress concentration points.
Folding area clearance: To prevent flex circuit damage during manufacturing and assembly, you’ll need to leave plenty of clearance around the bending area. This will allow you to remove the stiffener if necessary and will avoid overstressing the traces, vias or components.
The assembly process for a flex circuit can be complex and requires careful coordination between the PCB designer, the fabricator, and the assembler. For example, you’ll need to carefully specify assembly steps in the fabrication drawings and provide detailed instructions for each step. You’ll also need to carefully collaborate on the choice of assembly fixtures and fluid dispensing methods. Using automated fluid dispensing is helpful, but it can add extra steps and cost to the process.
You’ll also need to consider the types of coverlays, flexible solder masks, stiffeners and surface finishes that are suitable for a flex circuit. You’ll probably need to choose a specialized type of surface finish that provides a good soldering surface and resists copper oxidation. You should discuss these with your manufacturer to ensure they have the capabilities to produce a high-quality flex circuit for you. To get the best quality and value, you should work with a turnkey PCB manufacturer that offers full-service design, fabrication, and assembly.