Hi Earl,
Dogbone tensile elongation testing is adequate for quality control purposes,
but it does not give you the material ductility. There are a number of
reasons for this, all discussed in IPC-TR-484, Results of IPC Copper Foil
Ductility Round Robin Study.
If you want to do  any engineering predictions of the behavior of foils (flex
circuits, innerlayer separation) you need the ductility. For standard tensile
test samples the elongation is reasonably close to the ductility,  nut for
foil sampes it is not. Just thick of the aspect ratios: cross-section 500:1
width:thickness, 2000:1 gage length:thickness; ductility needs to include the
plastic deformation--you can not get this for foil with tensile tests.
That is why the efforts were made to develop alternatives--various bulge and
flex testers.

Werner

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