Black or brown oxide will provide better bonding strength than Cu surface
due to it's topography.  However it is cupric oxide that is black, CuO and
cuprous, brown Cu2O.  Cupric is is the original, sensitive to an acid
attack,demonstrated by the pink ring, cuprous is the reduced one, more
resistant to an acid attack.  Some of the newer theories claim that brown
oxide actually contains fully reduced Cu.

Regards,

Paul

>Olson, Jack C wrote:-
>>I was under the impression that black oxide provided more "tooth" for
>>bonding copper to the substrate material.  Recently I was told is was just
>>to protect the surface during handling. Since I can't find it in Coombs
>>Handbook, can anyone briefly explain?
>Hi Jack
>You are right, the reason for oxide treat of copper foil is to improve
>the bond strength. It makes handling more difficult as it is easily
>marked. Early oxides were cuprous and readily attacked by acids. They
>could also be quite thick and hence led to pink ring phenomenon around
>holes. Nowadays the norm is to reduce the oxide coating to cupric by
>post treatment. This is impervious to acid attack and is also much
>thinner which prevents pink ring formation.
>There are alternative finishes but, as far as I know, none of them give
>higher bond strengths than reduced oxide.
>Paul Gould
>[log in to unmask]
>Teknacron Circuits Ltd
>Fax: 1983 865141
>Tel: 1983 866531
>
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