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March 2000

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 7 Mar 2000 11:37:35 +0200
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Pete

Lest I be accused of spamming, I'll send you the title by a private e-mail. Although I
have no experience of the problem, I could well imagine that it may be difficult to
weld a gold or aluminium wire onto an implanted carborundum particle from a brushing
process :-) However, as the particles are much smaller than the weld diameter, it may
be that you would not notice the reduction of pull strength. However, as the
carborundum is less malleable than the gold plating, it may be that there would be a
mechanical effect whereby the pressure on the metal-to-metal parts would be reduced
while that of the metal-to-inclusion would increase, but this is off the top of my
head. I don't think that the substrate material would have a significant effect.

Brian

Pete Nemcik wrote:

> Hi Brian
> Can you share with me the title of your book? I am very interested.
> Also, would this abrasive implanted contamination affect wire bonding? I
> would imagine that the effect of these particles imbedded into the gold
> would interfere with proper bonding of the wire (especially if the
> substrate is Teflon filled with ceramic filler).
> Thanks in advance
> Pete
> > -----Original Message-----
> > From: Brian Ellis [SMTP:[log in to unmask]]
> > Sent: Tuesday, February 29, 2000 5:54 AM
> > To:   [log in to unmask]
> > Subject:      Re: [TN] Surface prep before soldermask
> >
> > 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 out of date!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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