Design references for flex circuit stiffeners

Most expereneced PCB designers are expert in rigid PCB design but not good at flex PCB design, such as stiffeners for flex circuit board.

Firstly, the PCB designers should have complete knowledge about stiffeners, such as:
What is the flex PCB stiffeners
The purpose of stiffeners
Stiffener’s common usage application

How to correctly design stiffeners for flex PCB

For flex PCB circuits, stiffeners are a common and important requirement in many types of designs. Stiffeners provide a mechanical function for the flexible area and are not part of the electrical requirements of the overall part(This is not important but necessary part).

So,for correct stiffeners design,it is necessary for designer to specify:

  • Exact area on the flex PCB board that need a mechanical function suport
  • The material of the stiffeners: Such as, FR4,PI,Steel material,etc
  • The thickness of the stiffeners: 0.1mm,0.15mm…0.8mm,1.0mm,etc

In above 3 pictures is the exact design from customer (Pictures can be magnified by clicking):

The first picture is the top circuit side review,which we can see there are some SMD components on the bottom (down side).

The second picture is the stiffeners (yellow area) designed by customer for SMD components which be assembled on opposite side of top,the design is nearly correct,but there are some SMD PADs on bottom side (down side),which be covered by stiffeners which is a mistake if keep original design

The third picture is the modified design for stiffeners (blue area) which was canceled the bottom stiffeners on the area which have SMD components (in the picture 2).Now they are correct and can move to manufacturinng process(picture 3).

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