What are PCB Stiffeners?

PCB Fabrication 
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Editorial Team - PCB Directory

Aug 17, 2020

When working with flexible PCBs there are times when we need certain parts of the flexible printed circuit board to be rigid. We do so by adding mechanical support to parts of the PCB. This mechanical support is called a PCB Stiffener.

Flexible PCBs have many advantages like the capability to bend, twist, and fold. However, it is challenging to add/solder components and interconnects to these boards. A PCB Stiffener can be used to make a part of the board more stable/rigid so that it becomes easier to add/solder components or interconnects to the stiffer parts of the board. PCB stiffeners are usually not an integrated part of the PCB. They are only used to provide mechanical support to certain parts of the board.

Other advantages of PCB stiffeners include the reinforcing of solder joints, an increase in abrasion resistance and better handling of the board for automated pick-and-place component placement and soldering.

PCB stiffeners are usually made from FR4, Polyimide or aluminum. The thickness of FR-4 stiffeners varies from 0.003"(0.08 mm) to 0.125" (3.18 mm). The polyimide stiffeners are available with a thickness of 0.005" (125μm), 0.001" (25μm), 0.002" (50μm), and 0.003" (75μm). Polyimide stiffeners are usually a low-cost alternative to FR-4 as they are punched on a die instead of routed with a drill bit. To get better rigidity and heat sinking properties, aluminum stiffeners are used.

How are PCB Stiffeners Attached to Flexible PCBs?

There are two main methods to attached PCB Stiffeners to a flexible PCB - Thermal Bonding and Pressure-Sensitive Adhesives (PSA). The properties and differences of each approach have been highlighted in the table below:

Thermal BondingPressure Sensitive Adhesives (PSA)
Stiffeners are attached to the flex PCB by using heat and pressure
Stiffeners are attached with the flex PCB by only using pressure
Stronger BondBong not as strong
Used in bonding in IPC class 3 product (Military application, Avionics etc.)Used in bonding in IPC class 2 product (TV, laptops, Consumer electronics etc.)
Higher CostLower Cost
Will cause significant damage to the circuit while removing from flex circuit.Usually removed without damaging circuit, if care is taken while removing.
Process take more timeProcess takes less time

 

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