In a message dated 96-09-26 15:40:13 EDT, you write:

> I believe the advantage Persulfate has over peroxide sulfuric in 
>     removing residues is it's undercutting ability due to the nature of 
>     the etch.   At a previous job, I had used the Persulfate to do what 
>     you suggest. I also have learned that it is better to spend the 
>     resources trying to fix the residue problem than band-aid the problem 
>     with a more aggressive etch.  What I found was that unless you want to 
>     etch huge amounts of Copper to undercut the mask residue, the fix will 
>     work when the residues are mild, but fail when they get bad.
>     

The above is right on the money.  Look into developer/rinsing issues.  Some
of these soldermasks leave residues in the developer/rinse that are
essentially impossible to remove chemically, and will eventually clog
nozzles, etc.

Another approach that one of customers found, quite incidently, was that a
mildly alkaline (pH = 9-10) cleaner did a marvelous job of cleaning up the
surface before microetch, did not attack the mask, and allowed a minimal
microetch to give a thoroughly clean, and wettable surface.

Rudy Sedlak
RD Chemical Company
phone 415-962-8004
fax 415-962-0370

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