A multitude of things can be added to a “simple” single or double sided flexes to enhance form, fit and function. Mechanical stiffeners bonded to one or both sides can be designed to match virtually any thickness requirement, and bonding of metal heatsinks is just as easy. Sections of the circuit board can be designed to work as a heater or easily shielded from electro-magnetic interference without adding another copper layer. What will your design require? There is a good chance that we have seen the right (and the wrong) way of answering those questions.