Hi Larry

IPC-FC-250  "Performance Specification for Single and Double Sided Flexible
Printed Wiring"  would the equivalent performace specification. Though as the
title states it does not cover multilayer. The document defines and specifies
the performance testing and qualification requirements for each of the
different product classes of single- and double-sided flexible circuits. Like
all IPC specifications, inspection criteria and test methods are provided at
the back of the document.

Of additional benefit would be:

IPC-MF-150F Metal Foil for Printed Wiring Applications 

IPC-FC-231C Flexible Bare Dielectric for Use in Flexible Printed Wiring

IPC-FC-232C Adhesive Coated Films for Use as Cover Sheets for Flex Circuits
	
IPC-FC-241C Flexible Metal Clad Dielectrics for Use in Fabrication of
Flexible Printed Wiring
	
IPC-RF-245A Performance Specification for Rigid Flex Printed Boards
	
IPC-D-249 Design Standard for Flexible 1 and 2 Sided Printed Boards
	
IPC-FA-251 Assembly Guidelines for Single and Double Sided Flexible Printed
Circuits
	
IPC-D-273 Design Guidelines for Multilayer Flexible Printed Wiring 
(I believe this is still in development)
	
For the archive... 

MIL-STD-2118  Military Standard, Flexible and Rigid-Flex Printed Wiring for
Electronic Equipment

MIL-P-50884 Military Specification, Printed Wiring, Flexible and Rigid-Flex

One caviat... Make your reference call outs based on real need. Take the time
to review the specs before you call them out. Also there are some new
materials entering the market that are not covered yet. These specs can
provide some good boiler plate but your P.O. is the ultimate contolling
document.

Cheers!

J. Fjelstad