Hi Neil,
No such standard exists or can exist, because [drum roll]—'It depends!'
It depends on thicknees of the layers [each one individually], the modulus of
elasticity [of each layer—from this the location of the neutral plane is
determined], and the ductility of each metallic layer [use IPC-TM-650, 2.4.2.1
"Flexural Fatigue and Ductility, Foil,” or ASTM E 796 “Standard Test Method
for Ductility Testing of Metallic Foil”].
Having all of this, you can determine the minimum sustainable bend radius.
You can find the methodology in IPC-D-330, Section 6.2.1.2 “Flexibility
Considerations in the Design of Flexible Printed Wiring” [most likely
out-of-print] or in the upcoming book by Joseph Fjelstad Flexible Circuit Technology, 4th
edition.
Werner
Future workshops:
Reliability Issues with Lead-Free Soldering Processes, June 17, London
Interconnect Failures and Design for Reliability for PCB PTHs, June 17,
London
Pb-Free Soldering Processes—Survival, Quality, Reliability, August 18,
Orlando
Reliability Issues with Lead-Free Soldering Processes, September 22,
Schaumburg
Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture,
ENIG), September 22, Schaumburg
**************
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favorites at AOL Food.
(http://food.aol.com/dinner-tonight?NCID=aolfod00030000000001)
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