[cms_heading title=”SHORT CHECKLIST FOR DESIGNING RELIABLE FLEX CIRCUITS:” font_size_title=”28″]


  • Route traces perpendicular to bend line
  • Traces must be evenly spaced across the bend area, wide & uniform, and staggered on adjacent layers
  • Sharp angles should be avoided
  • Traces should always come out perpendicular to the rigid edge, when transitioning to the flexible region
  • Cross-hatch ground and plane layers, especially in the bend area
  • Number of layers at the bend area should be kept at a minimum
  • Flex layers can be separated (loose-leaf) for multilayer construction to increase flexibility
  • Mechanical slots, slits or ICT custom hinge design can be used to increase flexibility
  • No vias or PTH should be placed in the flex region, unless used for shielding or away from bend region
  • Use RA copper grain direction for dynamic flexing or tight bend radius
  • Conductors should be close to neutral axis, especially for dynamic application
  • Minimize the dielectric thickness to reduce stress on the conductors
  • Follow minimum bend radius rules


  • Tear-drop all pads and tie-down all unsupported pads
  • Pad size should be large enough for selective plating the holes
  • All vias should be in the stiffened/rigid area
  • Stiffener holes should be at least 20 mils larger than finished hole size
  • Gang open the coverlay wherever possible
  • Use LPI/Coverlay combo for fine pitch components such as BGA, CSP, etc.
  • Allow for possible squeeze out of the adhesive onto the pads


  • Radius all inside corners. Additionally copper trace can be used as tear stop
  • Use holes at the end of slits or slots as tear stop
  • Use epoxy bead in the rigid to flex transition area
  • Use appropriate stiffener thickness and material to support solder joints
  • Keep vias, holes and SMT features at least 25 mils away from the board edge
  • Vias on rigid-flex should be minimum 50 mils away from the rigid-to-flex transition edge
  • Never have edge of coverlay opening and edge of stiffener right on top of each other


  • Take into account stress due to environment such as Temperature, Vacuum, Vibration, Bends, etc.