A single sided flexible circuit board construction is the base material with a polymide coverlay laminated to copper allowing access from one side only.
General specifications:

number of layer:1 to 12 layers
base material: PI, PET
thickness of base cooper:1/3OZ, 1/2OZ, 1OZ, 2OZ
finished board size: 230/480*no limit
board thickness:0.8mm(adhesiveless material) to 0.65mm
minimum holes:PTH 0.2mm
minimum trace width:0.1mm(4mil)
surface treatment:immersion tin, immersion gold, ENIG(electroless nickel immersion gold)
coverlay: 1/2mil-2mil