In the past, we specified starting foil thickness and finished thickness.  It was a legacy thing, no one knows where it came from.  Realizing that copper is copper, and the vendor knows their process requirements, we recently removed the foil requirement and specify only minimum or nominal finished copper thickness.  Save s a lot of emails.


And I agree with Grunde, the IPC document charts are informative beyond just specifying a requirement.  Maybe they could be reworked to be more clear, but keep the additional data.

Pete