1. Placing vias by the stiffener area or where the flex bends which can cause via cracking.
2. Not showing the overall thickness of the stiffener area. It is important that you show the x & y dimensions of the stiffener, show placement on the flex, and dictate whether the material is Kapton or FR4.
3. 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.
4. Bending a flex circuit 90 degrees. See “Minimum Bend Radii for Flex Circuits” chart for guidelines.
5. Not showing the stackup. (Should indicate base material, copper thickness, cover layer thickness, as well as stiffener material and thickness.)
6. Failing to indicate copper weight. When specifying copper weight, it is important that you state whether you are indicating base material copper or finished copper weight.
7. Having silkscreen nomenclature less than .008″ which can cause illegibility or placing silkscreen too close to exposed pad areas. Silkscreen should be no closer than .010″.
8. Not indicating the total thickness of the flex and tolerance.
9. Placing edge of trace closer than .015″ to edge of board.
10. Making hole opening on stiffener too small. Should be +.010″ over finished pad size.