HI I have plated heavy copper boards for years ( up to 20 oz of copper)
I have not had problem with plating only one oz when the outer layers are
3-10 oz , there is no issue with thermal expansion , other then one study
showed a vastly improved resistance to via cracking if there is 3 oz or
greater of copper in the hole. seems the expansion forces of FR4 is not as
strong as 3-4 oz of copper in the holes. I have a book on heavy copper and
survivability studied of heavy copper in the hole. its available at
megadawn.com.

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