In your message dated Wednesday 25, September 1996 you wrote :

> The Fab house that we use has recently asked us if they could use a black 
> oxide treatment on external layers of our designs. I know that this process 
> is used for internal layers but I want to know if any of you have used it 
> for external layers ? Their reason for using it is " To create better 
> adhesion for the solder mask and eliminate potential slivers ". To me, this 
> sounds more like a process problem. What do you think ?
> 
> To recap, do any of you use a black oxide coating on outer layers ?   If so,
>  why ?.   If not, why not ?
> 
> Thanks in advance for your help !
> 
> Lou Takach
> 
Hello Lou,

We used to black oxide treat outer layers 12-14 years ago mainly to improve 
solder mask adhesion on copper, and eliminate the need to brush. Brushing 
produces slivers due to undercut after etch which leaves a fragile track edge. 
These can lead to many invisible shorts after solder mask.

Oxide is a good cosmetic finish on pth circuits but does not look so good on 
multi-layer because the inner layers are also black and there is no contrast.

As soon as we put in pumice cleaning and improved the surface prep there were no 
adhesion problems and so we stopped using oxide. Although some of our customers 
had specified it as their preferred finish, most did not want it. 

It is easier to control than brushing and solder resist adhesion is excellent.
-- 
Paul Gould
EMail [log in to unmask]

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