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July 1998

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From:
Bev Christian <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 27 Jul 1998 15:52:00 -0400
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Yves,
What an interesting question.
> -   Once the solderability has been tested on one of these "old" lots, for
> how long do you consider the test results valid?  i.e. I may have some
> devices with date codes that are 24 months old where I verified their
> solderability 1 month (or choose any time period for the example) ago.
> Should I re-verify solderability again prior to releasing them for
> assembly?
>
Usually we get asked to do solderability testing of "old" components because
there was a part shortage and the buyers have only been able to scrounge
parts through a distributor.  The number of parts received are usually not
all that was needed, but there are enough to get the plant through until a
regular supplier can send new components.  In this case there are no parts
left over to sit around, so your scenario does not come up.

You'll note I said usually.  I am sure the situation has come up, but if it
has, it has never been brought to my attention before.  The way our internal
spec (my site) reads, it should be retested irrespective of when it was
tested last.  This of course makes little sense if it was just tested
yesterday!

I think the problem you are going to have as far as getting a definitive
answer from fellow Techneters is that there are no industry numerical
standards for solderability, other than the 95% coverage for dip and look
testing in the US Mil specs.  This is an issue that I believe the IPC
solderability committees are just going to start addressing.  Wetting
balance testers have now made it into the specs as valid test methods, with
no pass/fail criteria and adding that criteria will be the next hurdle.
Once that is done, then there is at least a faint hope of being able to
correlate oxide thickness to the solderability results and then calculate
how much life the parts have left before they have to be junked, retinned or
ROSA treated.  Of course I have said nothing about the presence or organics,
the surface roughness of the surface to be soldered, etc.

And, folks, a fellow Norteler did not set me up for this little soapbox
oration!

regards,
Bev Christian

> ----------
> From:         Trudell, Yves [WSC:W460:EXCH]
> Sent:         Monday, July 27, 1998 2:31 PM
> To:   [log in to unmask]
> Subject:      [TN] Solderability test - period of validation
>
> Technetters, the following question is vague, and I'm sure that I'll get a
> lot of "it depends" type of answers, but that's fine as long as the
> responses contain some examples of guidelines that are followed.
> -   The solderability on many devices must be verified prior to assembly
> if
> the devices have surpassed a certain date code limit.
> So, here's the question:
> -   Once the solderability has been tested on one of these "old" lots, for
> how long do you consider the test results valid?  i.e. I may have some
> devices with date codes that are 24 months old where I verified their
> solderability 1 month (or choose any time period for the example) ago.
> Should I re-verify solderability again prior to releasing them for
> assembly?
>
> I'm looking for any guidelines that are used or considered in such
> situations. I understand that storage conditions are likely the main
> variable and that a general guideline is not likely.  Any case-specific
> examples would be greatly appreciated.
>
> Yves Trudell
> Nortel, Wireless Networks Calgary
> Quality System Engineering
>
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