Fabrication Processes

Pre-baking prior to assembly for flex and rigid-flex applications is extremely critical due to the hydroscopic nature of flexible PCB materials. We offer the following suggestions:

  • Hand Soldering
  • Surfaces to be soldered need to be clean
  • Bake circuits at 250°F (121°C) for 1 hour
  • Remove enough units from the oven that can be soldered within 2 hours.
  • Allow to cool to the touch (if the units are not soldered within 2 hours, they should be re-baked or placed in a desiccant after removing from the oven).
  • Apply Flux (a rosin type flux like Kester 185 works well).
  • Use Acid Brushes to apply flux; area to be soldered should covered by the flux.
  • A soldering iron (something like a MetCal unit set at 700°F) with a 700°F #2 solder tip should apply the right amount of heat.
  • Soldering tip held on the pad/component lead while applying the solder.
  • A solder joint forms in 3-5 seconds.
  • Minimize the dwell time
  • Longer dwell time causes solder to "run under" the covercoat or delaminate.
  • Remove flux using an appropriate flux remover (a vapor degreaser works well).
  • The solder joint should a have a nice uniform fillet with no voids or dewetting.
  • Pre-bake for 45 minutes at 250°F
  • Rigid-Flex with 2 layer flex
  • Pre-bake for 3 hours at 300°F
  • Rigid-Flex with Multilayer Flex
  • Pre-bake for 4 hours at 325°F