[log in to unmask] a écrit :

> Hi Arnaud,
> You do not give much of a description of your flex circuit. Thickness? 
> Layer count? History? Bookbinder folds? Are you sure you have RA 
> copper? It may be rolled, but not annealed and thus have high 
> ductility in one direction and not the other. One way to determine 
> that is to do an X-section--long needle-like grains are an indication 
> opf insufficient annealing. Are there any unassembled circuits left? 
> You could used IPC TM  2.4.3.2 “Flexural Fatigue and Ductility, 
> Flexible Metal-Clad Dielectrics.”
>
> Regards,
> Werner Engelmaier
> Engelmaier Associates, L.C.
> Electronic Packaging, Interconnection and Reliability Consulting
> 7 Jasmine Run
> Ormond Beach, FL 32174 USA
> Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
> E-mail: [log in to unmask], Website: www.engelmaier.com
>
Werner,

I already detailed the flex buid-up, but it's true it was a long time 
ago: it consists of a 50µm polyimide core with two 35µm RA copper layers 
covered by an adhesive of 50µm and a coverlay of 25µm.
A cross section of the copper traces followed by a chemical etching 
showed a granular copper structure characteristic of a RA copper.
The design has already been pointed out and will be considered, but I 
would like to ensure there is no manufacturing problem.  I do not have 
unassembled circuits, so my intention is to perform some comparative 
hardness measurements on cross sectioned assembled boards as it was 
discussed.

Arnaud

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