something like this?
https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=14&ved=0ahUKEwj5tM-l27PTAhVI4oMKHaApAJkQFghNMA0&url=http%3A%2F%2Fwww.springer.com%2Fcda%2Fcontent%2Fdocument%2Fcda_downloaddocument%2F9788847023352-c2.pdf%3FSGWID%3D0-0-45-1346469-p174130084&usg=AFQjCNGJcriQkGhNIrmY0lNGoCq2L5hC0g&sig2=3cfY23JS4IKkJY6WJzJLeg&cad=rja

> Hi all,
>    We have been working on an issue with a flex circuit that has failed
> during some vibe testing. The copper is just .5oz. and when looking at
> the cross section, the copper has some definite cracks that became
> opens to the circuit, but in the areas that don't have the cracks, the
> copper looks like gravel on a driveway. It looks like crushed gravel
> and seems to me to look work hardened  and very grainy. The copper
> should have been RA type and I wouldn't think it should look like it
> does, but maybe someone can say for sure? I may be able to provide some
> pictures off the forum, I need to confirm that first. Thanks in
> advance.
> Later...
>
> Scott Decker - Senior Analyst, Drafting & Design Services CID+ -
> Electronic Systems Center
> UTC AEROSPACE SYSTEMS
> 3445 S. 5th Street, Suite 170, Phoenix, AZ 85040 U.S.A.
> Tel: 602 308 5957  FAX: 602 243 2347
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