Etchback

When a hole is drilled during board fabrication, it can transfer resin from the base material (eg, FR4 core or prepreg) to cover the exposed edge of conductive material in the wall of a drilled hole. This is called resin smear. Etchback is a controlled chemical or plasma process that removes nonmetallic materials to a specific depth from the sidewalls of holes to remove resin smear and to expose additional internal conductor surfaces.

Virtually all military, aerospace, and space OEM require etchback. They call it out because they have test data (probably from the 70's and 80's) that shows that etchback is better than no etchback and more reliable than negative etchback. It wasn�t until the early 90's that plating materals and technology developed to a point that could change the data. During that time, equipment suppliers have reduced their engineering staffs. So, research into to etchback or not etchback unlikely to be funded. So, we expect the etchback requirement to never go away.

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