When To Use Stiffeners In Your Flex PCB Design

Stiffeners can be used to reinforce the areas where components will be assembled, but not where the board will flex. If your board requires stiffeners on both sides of the flex, it may require two laminations. Also keep in mind that stiffeners require their own prepreg lamination cycle, and certain stiffener materials require an additional lamination cycle as well. They add thickness to your board, and impact both cost and manufacturing time. However, there are certain cases where stiffeners are required.

Flex-only PCBs can withstand fewer components than rigid-flex. The rigid part of rigid-flex can also be as complex as a traditional rigid PCB. Stiffeners are occasionally laminated the same time as the coverlay.

Stiffener Materials
Stiffeners are typically made of FR-4 or Kapton. Kapton is often used when the end of the flex must be thickened and inserted into a ZIF connector. However, the use of Kapton requires a separate lamination cycle. FR-4 stiffeners can be done within the same lamination cycle.

Route And Retain With Stiffeners For Flex PCBs
When routing and retaining arrays, the same material as the stiffener will simply be extended into the array. This rigidizes the array.

Stiffeners Are Required When:

    • Components are near or in an active, or dynamic, flex zone
    • Component size and weight will import stress onto the flex
    • A large number of SMT pads make planarity critical
    • Connectors that require repeated insertions or assemblies require a stiffener, or something to help alleviate the stress of pads.

Stiffeners Are Not Required When:

    • Small “static” components do not exert a large amount of strain on the flex of the PCB.
    • There are no components in the flex region.

Want to learn more about flexible PCBs? Click here to download our Flex Design Guide.

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