Kathy:
Was the thickness of the silver deposit the same as required of the gold immersion process?
And if so, did it meet your requirements of consistent 5u to 7u thickness?
Palumbo wrote:
> Nicolas,
>
> I have been doing the same exact analysis. I have already looked at the
> Gold Immersion, and the OSP coating, and am now analyzing the Silver
> Immersion coating.
>
> For our application we found that the Gold Immersion coating would not be
> acceptable due to our suppliers not being able to hold the thickness of the
> gold deposit to our requirement of 5u" to 7u" consistently. We would like
> to see the deposit at this thickness to prevent gold embrittlement, and
> oxidation of the nickel plate under coat.
> When the gold deposits were above the 7u" thickness our solder joints failed
> lead pull tests. When the gold deposit thickness was under 5u" the boards
> failed solderability testing after steam age.
>
> Then we analyzed the OSP coating. For our application the coating was not
> acceptable due to the copper ring that was left around every solder joint
> that was not printed one to one. We have more 2500 stencils that would have
> to have the apertures opened up in order to print one to one at a cost of
> about $500K. This was not feasible for us. We also had problems with the
> special storage and handling that was required.
>
> Currently, we are now looking at the Silver Immersion coating. We ran a lot
> of 250 pieces of our most difficult double sided product. We experienced an
> increase in our first pass yield from 95% to 99.3%. We then ran another lot
> sample of 2500 pieces of the same product, and had the same exact results.
> There was excellent wetting characteristics on every solder joint. There
> were no special handling or storage requirements needed. The stencils did
> not have to be changed, and the boards could be treated exactly as if they
> were hot air solder leveled. I sent two completed samples out for
> Temperature cycling (-20 degrees C to +80 degrees C for 20 cycles), and then
> retested them. They both passed test. Both samples are now being shock
> tested and Vibration tested. They will then be retested. Then a lead pull
> test will be done, and then cross sectioning of various solder joints.
>
> A lot of people love the OSP coating, and a lot love the gold immersion
> coating. I think everyone has a unique process and product and what may
> work for me may not work for you. I think everyone should go through their
> own qualification process when making a major change like this. I can
> provide you with my lab reports if you want for reference, but you should
> really try all the different coatings out yourself. Anyway, hope this
> helps, and good luck!
>
> Thanks,
>
> Kathy Palumbo
> > ----------
> > From: Nicolas van der Heyden[SMTP:[log in to unmask]]
> > Sent: Wednesday, May 13, 1998 6:27 AM
> > To: [log in to unmask]
> > Subject: [TN] HASL alternatives
> >
> > To All,
> > We are now making a comparison between different alternatives to HASL. The
> > chosen alternative will have to meet the following criterias criterias.
> >
> > - flat coating
> > - compatible with No-clean process and mixed technology
> > - resistant to 2-3 reflow (multiple heat cycle)
> > -and MINIMUM 1 year shelf life (storage before assembly)
> >
> > These are the alternatives we think can meet our needs:
> >
> > * OSP
> > - Benzimidazole (?)
> >
> > * IMMERSION
> > - Silver
> > - Bismuth
> > - Au-Ni
> > - Palladium
> >
> >
> > Q: Wich one do you think could be the best meet to our criterias ?
> >
> > Q: And what would be its advantage(s) compared to the others ?
> >
> > Q: OTHERS ? (is anyone using other coating alternative )
> >
> >
> > Thanks for all for your help
> >
> >
> > Nicolas van der Heyden
> >
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--
Have a Golden Day,
Paul Anderson
Amherst Systems Inc
[log in to unmask]
716-631-0610 x190
716-631-0629 (fax)
http://www.amherst.com/
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