Flex PCB Stiffeners: Mechanical Design Benefits and Material Options

Each type of stiffener material provides different benefits depending on the requirements of a flexible circuit design. Common applications for stiffeners can help designers determine which material is best suited for the application while considering cost and the advantages of each option.

Supporting Component and Connector Areas

For supporting component or connector areas, stiffeners can be manufactured from polyimide, FR4, aluminum, and stainless steel. When narrowing down the choices, other design and manufacturing considerations should also be reviewed.

Polyimide or FR4 are the least expensive material options for this type of application. If greater rigidity is required and the stiffener will also serve as a carrier panel for assembly purposes, FR4 is the most common choice.

ZIF Connectors

Only polyimide stiffeners can be used for ZIF connector applications. The stiffener provides the necessary increased thickness at the connector contacts.

The stiffener can only be applied with thermally bonded flex adhesive and is attached before profiling the part outline. It is applied oversized to the part outline so that the stiffener and the part outline can be cut simultaneously. This helps achieve the tight dimensional tolerances required by ZIF connector specifications.

Additional Thickness and Strength

When increased thickness is required in a specific area, polyimide stiffeners are preferred.

Polyimide is also ideal when the flexible circuit board is expected to experience higher-than-normal wear and tear.

Thermal Transfer Management

For flexible circuits that generate excess heat that needs to be dissipated, aluminum stiffeners can be used.

Their heat-transfer capability allows heat to move from components to the back of the flexible circuit, where it can dissipate into the surrounding environment or the device enclosure.

Controlling Bend Locations

Some flex PCB designs require bend locations to be constrained to specific areas.

Polyimide is most commonly used for this purpose, although some applications may require FR4.

This can allow the circuit to better fit within the final product or equipment without the risk of damage, or facilitate the assembly process.

Cost Factors

Controlling cost is an important part of a flexible circuit design.

For stiffener materials, polyimide is generally the most cost-effective option. It can be fabricated using die cutting or laser cutting, which makes it easier to manufacture.

FR4 is also widely used and cost-effective. Its added rigidity creates a flat and stable surface, but it typically requires additional drilling and routing operations during manufacturing.

Aluminum and stainless steel are more costly. The materials themselves are more expensive and typically require more expensive machining operations.

The designer should evaluate the flexible circuit design requirements to determine the most suitable stiffener material for the application.

Flex Circuit Stiffener Applications

Stiffeners add functionality to a flex PCB by providing rigidity in specific areas for component support or by increasing the thickness of a localized area to meet a specific connector requirement.