Circuit Board Stiffener Affect PCB Flexibility
A circuit board stiffener is used to increase the rigidity of a flexible printed circuit board (FPC). They are a great way to protect the flex circuit from damage and improve the performance of the PCB. They also provide a smooth transition between the flexible and rigid areas of the board. Stiffeners are often made from FR4, PI, or aluminum and they can be cut by laser machines to match the design of the FPC. They are then bonded to the circuit with a special adhesive or thermally bonded. There are three types of stiffeners: FR4, a woven glass fiber laminate filled with epoxy, PI, a polyimide material, and aluminum. Each has its own pros and cons.
Flex PCBs are designed to bend, but bending them too much can cause the circuit to break or even rip. A circuit board stiffener adds rigidity to specific parts of the flex PCB and prevents the board from bending too far. Stiffeners are also useful when mounting Plated Through Hole (PTH) connectors to the board. The stiffener provides a hard region where the PTHs can be mounted and reduces stress on them, which increases reliability.
The choice of a circuit board stiffener depends on the type of flex PCB and application. FR-4 stiffeners are popular because they are made from the same laminate material as the flex PCB and so blend seamlessly. They offer cost-effective rigidity and support the flex circuit during pick-and-place and reflow assembly processes. They are also ideal for applications that require a solid conductive surface and can be easily applied to plated through holes.
How Does a Circuit Board Stiffener Affect PCB Flexibility?
FR-4 and PI are both great choices for FPCs that need to be inserted into ZIF connectors. They are easy to apply and form a strong bond, protecting the connection pads from stress and damage during insertion. Kapton is another common form of polyimide used in stiffeners. It is particularly preferred when a flex PCB needs to be inserted into ZIF connectors with multiple insertions, as it can absorb and retain moisture, which is important in these situations.
Other materials, such as aluminum and stainless steel, are used for stiffeners in flex circuits that need increased heat dissipation or robustness. They are more expensive than FR4 or PI, but they can be used in applications where the added rigidity is worth the higher cost.
A flex PCB stiffener also makes the flex circuit easier to handle, helping it to avoid mishandling accidents that could damage or rip the board. Stiffeners are especially important for thinner flex circuits, as they are more susceptible to damage from handling.
The number of layers in a flex PCB determines its rigidity, and the stiffener’s thickness plays an important role in how thick it is. Thicker stiffeners are more rigid than thinner ones, and they can be a good option for applications where the flex circuit will be subjected to high temperatures or heavy loads.