Hello all,

To add some data regarding this case, all the failures correspond to
trace cracking at a fold line. Most cracks locate at a pad to trace
junction on an "arm" of the flex board, but one trace next to the holes
is also cracked at the fold line. All the junctions are filleted and the
base copper is RA. The cracks occur during integration. The "arms" of
the flex board has waves (i.e. other folding lines).
I am wondering whether these waves are normal, or if they are due to a
poor design, a poor copper ductility or a poor flexure of the polyimide
material, or....

Any insight will be welcome.

Best regards.


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