Let me contribute my observations on thickness.

The quality manual here says (written by me) that boards will be built to 
class A tolerances in the latest revision of IPC-D-300, unless otherwise 
specified by the customer.

That said, I have questioned IPC about the meaning of "thickness".  David 
Bergman and Lisa Williams did some investigating and thinking and advised 
me that thickness was to be measured over plated copper, but before 
solder resist application.  They also told me that the committee 
responsible for D-300 planned on expanding upon the present statement on 
baords thickness in the standard, to direct the user to specify board 
thickness in any areas of importance.

Lou Hart


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