The Flex PCB stiffener refers to a stiffener attached to the back of the FPC when a widget such as a connector is attached to the FPC.
From the point of view of reinforcing materials, various materials, including metals and resins, can be provided depending on the application.
FPC（Flexible Printed Circuit）it is a soft and flexible structure. This is the biggest feature of FPC, but due to its soft structure, when connecting a small part such as a connector to an FPC, it is necessary to place a reinforcing plate on the back side of the electronic component to which the connector is attached.
But why do you want to put a stiffener? There are three main reasons for this. 1 solder resist off measure 2 solder pad drop countermeasure As shown in the right side of Figure 1, when the connector mounted on the FPC is inserted and removed, the FPC is soft, so external force is applied to the terminal portions of some connectors. As a result, the welded portion may fall off directly. Similarly, since the copper foil portion (pad) of the FPC may also easily fall off from the underlying structure, the base portion. This is where the mat falls off.
In either case, as shown in the left part of Fig. 1, as long as a sufficiently stiff reinforcing plate is placed on the FPC, it is possible to prevent the force from being concentrated on the terminal portion, and the solder/pad can effectively prevent the falling off.
3 Anti-substrate warpage countermeasures during reflow soldering
If the reinforcing plate is not attached during reflow soldering, the FPC will bend and the correct soldering may not be possible.
At the same time, even if it is difficult to weld, the mounting portion sometimes bends, which causes the mounting failure. (parts fall off)
In order to keep the mounting surface flat and securely mounted, the reinforcing plate is essential.