Adeodato

It is about a hundred years since I did this, so what I say is certainly
out of date! Our preferred method was to clean the board with a good hot
(55°C) agitated DI water wash with 10% IPA, followed by a single DI
rinse at 85°C, followed by a 30°C dilute sodium persulfate (not
ammonium) etch to remove c. 2 um of copper followed by 3 DI rinses.
Oxide-free drying was done by successive pure IPA (to remove the gross
water) and toluene displacement, followed by placing in a walk-in oven
with filtered air at 30°C for 5 hours minimum.. This produced a residual
ionic contamination of < 0,3 ug/cm2 eq. NaCl, where the then MIL-P-55110
suggested a max of about 1,3-1,5 ug/cm2 eq. NaCl depending on your
interpretation. Solderability was excellent. We did this with both dry
film and liquid screened masks. Do NOT use abrasives or brushing of any
sort: you smear epoxy onto the copper and implant abrasives into the
copper, causing a certain dewetting (see my book for full details).

Brian


Adeodato Vigano wrote:

>  TechNet,I would like to hear the Forum's opinions about pre-cleaning
> before soldermask (both Dry Film and LPI), in particular about the
> methods based on chemical rather than mechanical action.We are
> evaluating an "oxide replacement" chemistry versus different microetch
> chem-clean systems.  The microetch would be our preference because
> running thick panels through our oxide replacement equipment may
> result in damage to the line, of course we are getting good results
> from the oxide replacement chemistry but we are not getting consistent
> results from the chem-cleaning process.Also I would like to know what
> other PCB manufacturers are doing when they are not using mechanical
> scrubbing methods.Any suggestions regarding chemistry and/or process
> parameters would be greatly appreciated.Thanks in advanceadeodato
> viganocompunetics, inc.  -  pcb divisionphone: 412.858.6115fax:
> 412.858.8060email: [log in to unmask]

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