There is also a wealth of information on flexible circuits from Technet's sponsor, the IPC. Below is a large sampling also including some standards related to HDI which often uses flex circuit technology.
Best to all,
Joe
2223 - Sectional Design Standard for Flexible Printed Boards
4202 - Flexible Base Dielectricsfor Use in Flexible Printed Circuitry
4203 - Adhesive Coated Dielectric Films for Use as Cover Sheets for Flexible Printed Circuitry and Flexible Adhesive Bonding Films
4204 - Flexible Metal-Clad Dielectrics for Use in Fabrication of Flexible Printed Circuitry
6013-K - Qualification & Performance Specification for Flexible Printed Boards & Amendment 1
6202 - IPC/JPCA Performance Guide Manual for Single- and Double-Sided Flexible Printed Wiring Boards
FA-251 - Guidelines for Assembly of Single- and Double-Sided Flex Circuits
FLEX-CO-99 - IPC National Conference Flexible Circuits Volume I & II - Denver, CO 1999
FLEX-TX-00 - IPC 6th Annual National Conference on Flexible Circuits: A Technology Comes of Age
New FLXCSP03-K - "Flex and Chips" - IPC International Conference on Flexible Circuits and Chips Scale Packaging - Hard Copy & CD-ROM
M-102 - Flexible Circuits Compendium
PAS-62123 - Performance Guide Manual for Single & Double Sided Flexible Printed Wiring Boards
PAS-62249 - Qualification and Performance Specification for Flexible Printed Boards
A-31 - Flexible Raw Material Test Pattern - Film Format
TMRC-01F - 2001 Market for Flexible Printed Circuit Boards
2315 - Design Guide for High Density Interconnects & Microvias
New 2226 - Sectional Design Standard for High Density Interconnect (HDI) Boards