Chris:
Solder purity maintenance is a process control requirement, with the primary
intent of ensuring good looking (and therefore reliable) solder joints. The
J-Std states that "If contamination exceeds the limits of Table 5-1,
intervals between the analyses, replacement or replenishment shall be
shortened". Clearly, what they want you to do is keep your process in
control and minimize rework. They don't want you to give a month's worth of
boards the death sentence.
It is quite correct that pots do not suddently jump out of limits, and any
serious drift in the wrong direction will declare itself in the form of
gray, grainy, or otherwise homely looking solder joints.
Our business is mostly military, and we have seen auditors who think they
have a gotcha with the "containment" question. A common sense explanation
of "process control" usually works. We explain that we also do periodic
checks of our static mats, soldering irons, and many other things. Spec
limits are quite strict, and are designed that way so that serious problems
are rare. Failures do happen, but they are monitored and controlled, and we
use the information to continuously improve our processes. Soldering irons
(and solder pots) are tools, not test instruments used to accept product.
If the resistance to ground of an iron tip is found to be slightly over high
limit, it is not looked at as an indictment of every board that has been
soldered since the last test.
Joe Kane
Lockheed Martin Control Systems
> ----------
> From: Chris_Smith[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;Chris_Smith
> Sent: Monday, June 01, 1998 8:46 AM
> To: [log in to unmask]
> Subject: [TN] Solder Sample Testing?
>
> Ladies & Gentlemen,
> I am currently working on a schedule for solder pot sampling. The
> pots will be tested every 30 days and two samples will be taken from
> each pot. This way if one test happens to fail, we can send the
> other
> sample to verify the test. The problem I have ran into is what to do
> if it fails. In a recent customer audit I was asked what kind of
> containment would we have if the test failed? Since we are using the
> ANSI/J-STD-001A there are clearly defined limits that must be met.
> It
> is my understanding that when you test the solder you are testing for
> the last 30 days. The problem I have is this. If I test the pot on
> 1-1-98 and it passes I'm fine. But when I test again on 2-1-98 and
> it
> fails I have a huge problem. Since the last day I can prove the
> solder was within limits was Jan, 1 that makes everything suspect bad
> material to that date. I can't write the procedure to recall
> everything for the last 30 days, I need a different solution. If you
> have any information on how your company handles this please let me
> know. Please keep in mind, that we must meet the ANSI-STD and any
> element out of range is considered a failure to our customer,
> regardless if the solder integrity is affected or not.
>
> Thanks
> Chris Smith
> Manufacturing Engineer
>
>
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