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For an FPC made out of Kapton (polyimide), what are the:
I'm looking for the "lowest common denominator" that any competent fab should be able to handle. Thanks!
There are no standard design rules, each manufacturer, unfortunately, has their own design rules. These are dictated by how tightly controlled they run their processes. Even if they use the same machines and processes it will vary a little. Vias in FPC (which are small) are not an issue unless you expect to flex the cable lots and PTH parts should be fine as well as long the parts are mounted (the body supplies some rigidity). SMT devices can be an issue as the rigid body combined with flexing generates large stresses on the pads and can pull the pads off.
Have run PTH, SMT and wire bonds onto FPC and rather than use rigid flex (which is a good option) we used FR-4 (and some times ceramic) stiffeners on the backside to prevent flexing in that region (no traces, just 
).
I'm no expert on Flex PCB's but a board house I've used in the past has the following specifications listed for flex boards and flex rigid boards material PI, PET, PEN, FR-4
:
Minimum trace Width / Min Clearance:
Inner: 0.5oz: 4/4mil, 1oz: 5/5mil,2oz: 5/7mil
Outer: 1/3oz-0.5oz: 4/4mil, 1oz: 5/5mil, 2oz: 5/7mil
Min Hole Ring
Inner: 0.5oz: 4mil , 1oz: 5mil,2oz: 7mil
Outer: 1/3oz-0.5oz: 4mil, 1oz: 5mil,2oz: 7mil
Min Hole Size and Tolerance
Min hole: 8mil
Tolerance: PTH±3mil, NPTH±2mil
Minimum distance from a drill hole to the edge of the FPC : Not listed ??
Minimum distance from a drill hole to a trace: Apply Minimum trace Width / Min Clearance rule
