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 are 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 9.2.1.2.1 for further discussion 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.