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What is the difference between 'start copper' and 'finish copper'? If the specified requirement is of '2 oz / 70 um Copper thickness', will that be start copper thickness or finish copper thickness?

A little confused with the terms there. Will be grateful for help!

Thanks!

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    \$\begingroup\$ (1) Before and after through hole plating, which adds copper to the outer layers as well as plating the vias and holes. (2) Normally start, but confirm with your PCB vendor to be sure. \$\endgroup\$ – Brian Drummond May 5 '18 at 14:24
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    \$\begingroup\$ It can be 1+1 or 0.5 + 1.5 electroplated \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 5 '18 at 17:55
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If you just require 70 µm without specifying more, the manufacturer will likely ask what it is you really want. The good ones at least will ask.

I typically specify the starting copper thickness, and then require the final thickness to follow IPC class 2. On my PCB specifications I write clearly that the number is the starting thickness.

The standard starting copper thickness are 12, 18, 35 and 70. On inner layers the final thickness is smaller due to cleaning processes and on outer layers it is thicker due to plating.

Minimum final thickness for IPC class 2 are

enter image description here

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If you require 70um of copper, that will be the finish copper thickness of your board.

The manufacturer will start with a base copper thickness of 35um and in the finishing process (plating of outer layers) reach the requested 70um thickness.

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