How to Assemble a PCB Stiffener
Assemble a PCB Stiffener
The pcb stiffener provides structural support for a flexible circuit board, improving its mechanical stability and reliability. They are a necessary addition to many flex PCB designs, especially those that have complex layouts or require a high level of insertions (e.g. ZIF connectors).
Depending on the design, stiffeners can be fabricated from various materials, including FR4 glass epoxy, plastics, and metals. Each material offers advantages and disadvantages, and the optimal choice depends on the design constraints of a given enclosure or form factor, assembly considerations, manufacturing costs, and EMI shielding requirements.
Stiffeners can be bonded to the FPC substrate using acrylic, epoxy, or polyimide adhesives. This can be done either during lamination or afterward. A common method is to use heat and pressure to attach the pcb stiffener, though some CMs also offer a pressure-sensitive adhesive option.
How to Assemble a PCB Stiffener
Another way to install a stiffener is to fasten it in place using screws or rivets that pass through clearance holes in the FPC substrate and into tapped holes in the stiffener. This method offers greater stability and supports reworkability, but it may require the use of special tools for inspection, rework, and repairs.
The most cost-effective type of stiffener is made from the same laminate material as the FPC substrate and can be bonded with the same process as the base FPC layer. It offers a great balance between cost and rigidity, and it is ideal for a broad range of applications. Another benefit is its resistance to corrosion and moisture. However, a drawback is the fact that it can absorb moisture and solvents from the air, which can cause copper to be torn away from solder pads.
In order to ensure the best performance, a stiffener should be designed and fabricated with the same care that goes into the FPC itself. Several key factors should be considered, including how much stress the stiffener will be subject to, the amount of lateral force it will be required to bear, and its thickness. A good contract manufacturer should be able to help a designer determine the ideal thickness and material for their specific application.
For flex circuits with plated-through hole (PTH) components, it is important to position the stiffener on the same side as the components. This allows for easier access during the reflow and pick-and-place assembly processes. The stiffener should be positioned to overlap the exposed coverlay by at least 0.762 mm to relieve stress and provide additional wear resistance.
A pcb stiffener is an excellent way to prevent the bending and warping of a flexible circuit board during assembly. It is an inexpensive insurance policy against mechanical failure in the event of dynamic stresses. Combined with careful handling and adherence to industry standards, stiffeners can significantly improve the quality and durability of a flex PCB. For the best results, be sure to consult with your CM early in the design process to optimize quality and cost.