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April 2007

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Brian Ellis <[log in to unmask]>
Date:
Mon, 30 Apr 2007 11:22:56 +0300
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A generation or so ago (I stopped making PCBS in 1974!!!!!), we used to 
buy 5 µm cladded laminate. However, the 5 µm copper was plated onto an 
aluminium substrate before pressing and the laminate was delivered with 
the aluminium (as a guess, probably ~20 µm thick) to protect the fragile 
copper during the mechanical operations. Immediately before laminating 
the resist, we peeled off the aluminium, which we sold as scrap.

The barrel of the PTHS were only about 2-3 µm less than the tracks, 
because the etching fluid was replaced more slowly than the surface in 
the holes because of the capillary effect. We used a copper chloride 
etchant.

I don't know whether 5 µm (or 3 µm) laminate is offered today.

Brian

Adam Seychell wrote:
> 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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