flex cable simulation
I have had a similar design challenge. I went about it in the following manner:
You can cope with the trace widths if the width/distance ratio is kept both in the flex and the rigid board. If the signal are very high frequency, you will need to make sure that the connector can handle them. Generally speaking; If you have 1ns rise time and 2 inches of trace length - then you have a problem!
I know that Mentor Expedition can make differential timing controlled routing, and I think that Cadence Allegro can do it too.
(BTW: I have designed 800MBit/s LVDS repeaters using a cad system with no differential routing capabilities at all, so If you are careful it can be done)
I did NOT use a ZIF connector. The design was for a hand held unit. ZIF connectors have a tendency to slide out as the unit gets worn. Instead I designed the flex cable with a stiffener at the end and used a HiRose miniature type board2board connector.
The flex cable was designed as a multi layer cable, using two sides as VCC and GND respectively. I got a good ground plane for the high frequency signals, and a wide conductor for the supply voltage. Do a calculation and you will be surprized about the voltage drop.
Have a meeting with the flex cable manufacturer and ask him to supply you with their design rules and constraints. There are a number of different manufacturing technologies, each with pro's and con's.
Some flex manufacturers are happy to do the design work for you just to get it right the first time!
Since the design of flex cables is much a mechanical design work involving many rounded arcs and tapers, some folks prefer using a mechanical drafting package (such as AutoCAD) together with a DXF2Gerber translator (e.g. Artwork Conversion Software, Inc.) (I do not work for them, but I am using this software myself).
Bypass capacitors should be placed close to the components that are to use them as high frequency charge supplys in such a way that the loop fomed by the circuit and the capacitor becames as small as possible.
Double sided assemblies cost $$$. Bear that in mind.