Not sure about any formal standard but we use our
light tables to evaluate e-copper panels...tilting the panel at a slight degree
so the light reflects off the hole wall, and looking down on the panel at an
angle gives a good indication of where there are voids...
Keep in mind, as far as I know this is one of those
"quick-look" inspections...when, or if anything is observed it will or must lead
to a more thorough evaluation, i.e. magnification, etc...
Franklin