Special flexible printed-circuit board (FPCB)
design recommendations include:
- Fabricate per IPC-6013.
- Use material of flexible
copper clad per IPC 4204/11 (Define polyimide and
copper thickness per product application).
- Finish: All exposed copper is
electroless Ni immersion gold (ENIG) per IPC
4556.
- Solder mask per IPC
SM840.
- Use a laser to create the
cutout for light sensing for better accuracy and
to avoid affecting the soldering pad dimension.
Other options, such as punched cutouts, are
possible. See the Section 8.2.1.2.1 for further discussions, ranging from the
implications of the device to cutout region size
and alignment. The full design must be considered,
including the tolerances.
To assist the handling of the very thin flexible
circuit, design and fabricate a fixture to hold
the flexible circuit through the paste-printing,
pick-and-place, and reflow processes. Contact the
factory for examples of such fixtures.