Tools and Tips

Flexible Printed Circuit Board

Common Mistakes Made with Flex Printed Circuit Board

Flexible Printed Circuit Board
  • Placing vias outside the stiffener area or where the flex bend which can cause via cracking at the time of manufacturing Flexible PCB.
  • Not providing proper stiffener information. It is important that you show the x & y dimensions of the stiffener, show location of the stiffener, and dictate the type of stiffener material - FR-4, Kapton, Ceramic, etc.
  • Failing to state a tolerance on the overall thickness of the stiffener area. The tolerance specified should not be less than +/- 10% of the overall thickness in this area.
  • Bending a flex circuit tighter than is recommended. See “Minimum Bend Radii for Flex Circuits” chart for guidelines.
  • Not showing the material stack up.(Should indicate base material, copper thickness, cover layer thickness, as well as stiffener material and thickness.)
  • The Flexible PCB Manufacturer need to take care of the traces routed on top of each other on adjacent layers. Traces should be staggered on the adjacent layers to avoid "I-beam" effect which could cause trace fracture.
  • Having silkscreen nomenclature less than .007” which can cause illegibility or placing silkscreen too close to exposed pad areas. Silkscreen should be no closer than .010”.
  • Designing without correct pad geometries. Teardrops and tie downs are important to add to pad geometries to avoid stress fractures and assembly issues.
  • Placing edge of feature closer than .010" to edge of board.
  • Making hole size on stiffener too small. Should be +.020” over finished hole size.

Flexible Circuit - Application Drivers

  • Reduction in package size required
  • Reduction in package weight sought
  • Decrease in assembly time sought
  • Need to reduce assembly costs
  • Requirement for assembly error reduction
  • Increased system reliability sought
  • More than 25 point to point wire needed
  • Dynamic flexure of circuitry required
  • Controlled impedance signal transmission required
  • Lower inductance cabling needed
  • Improved heat dissipation capability
  • Airflow improvement inside "box" required
  • 3-Dimensional packaging scheme sought
  • Compliant substrate for surface mounting
  • Desire to improve product appearance