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May 1998

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Subject:
From:
Kathy Palumbo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 13 May 1998 09:11:52 -0700
Content-Type:
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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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