Providing pressure relief beside stiffeners helps to stop stress risers from taking place at flex-to-rigid shift. Tearing of the flex PCB or breaking of the copper at the shift factor could take place much more easily if the procedure is omitted from the design or manufacturing process. One or both of the following techniques should be used for flex PCB.

SPHERICAL STIFFENER EDGES AT TRANSITION

In areas where the flex circuits egresses from the border of the support, the stiffener edges need to be rounded or offered with a radius at the edge to prevent a point of focused anxiety. Conversely, breaking the side of the rigid support with a documents or sandpaper at the transition edge prior to assembly can supply a comparable advantage.

FILLET TRANSITION EDGE OF STIFFENER

Filleting of the change edge of a stiffener with a resistant adhesive or epoxy is an additional common approach of pressure alleviating flex PCB circuits. The small grain of an appropriate polymer will give a straightforward ways of transitioning strain from the support to the flex PCB circuits. Figure 7-28 shows the two approaches.

STRESS RELIEF FOR UNSUPPORTED FLEX circuits

Strain relief should additionally be provided for when mounting the completed flex PCB or assembly. The adhering to methods can be made use of for this function:

– Break or radius sharp sides of any type of retaining bars or clamps that may be made use of to hold the flexible circuits in place.
– Use a reduced modulus, elastomeric product in between the limiting bar as well as the flex PCB.
– Bond the circuits to the assembly housing making use of a double-backed adhesive foam material or easy pressure-sensitive adhesive.