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April 2007

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Subject:
From:
Adam Seychell <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Adam Seychell <[log in to unmask]>
Date:
Mon, 30 Apr 2007 18:08:34 +1000
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I am trying to get a basic understanding on the "semi additive" process. 
 From what I understand, the copper base foil begins at 5um, and circuit 
traces are electroplated to a desired thickness. Unlike conventional 
"pattern plating" , there is no metal etch resist, but instead the 
entire panel is etched just enough to remove the 5um copper base copper, 
leaving the relatively thicker traces still in tack.
My question is, what steps are involved in obtaining the 5um copper base  ?

The thinnest copper cladding I can find is 18um (1/2oz) which suggests 
to me people are deposited 5um of electroless copper on blank PCB 
insulating material.

If this is the case then will any of the direct metalization systems be 
usable ? Due to the plating propagation effect with direct metalization, 
there would be excessive variations in copper thickness over the whole 
panel.
The only alternative I can see is to take standard 18um copper clad and 
carefully etch down to 5um. The resulting 5um copper clad laminate could 
then be used with direct metalization systems, however hole walls will 
not have a 5um base, and therefore the hole wall plating finishes up 
being 5um thinner than traces.


regards,

Adam Seychell

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