Mil-C-14550B

Electrodeposited Copper on Metallic Surfaces
Thickness
Class 0 .001-.005 inch For heat treatment stop off shield
Class 1 .001 inch For carburizing shield, printed circuit board
plated through holes
Class 2 .0005 inch As undercoating for Nickel and other metals
Class 3 .0002 inch To prevent metal migration into tin layer to poison
solderability
Class 4 .0001 inch Same as .0002 inch