In a message dated 6/1/98 8:31:18 AM Pacific Daylight Time, [log in to unmask]
writes:

<<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

 ############################################################# >>

Chris,

       I can understand your problem trying to think of what to do if your pot
were to fail in between sample intervals...I mean you're right, who wants to
think of the logistical nightmare it would be trying to recall everything one
has built over the last 30-days? Makes the hair on the back of my neck stand-
up just thinkin' about it...

       But to look at things realistically, how would that ever happen if
you're paying close attention to the results of the samples you're submitting,
and have some sort of idea of the volume of PCB's that have run across the
wave in those 30-day periods. It's been my experience that wave solder pots
don't suddenly go wacko over a 30-day period unless something unusual happens.
You can spot trends taking place in your analysis over time, and then have an
idea of what happens to your pot based on the volumes you run over a thirty
day period. You should also be able to see what happens when you run a lot of
gold plated boards vs. HASL, OSP, etc., then be able to have some sort of idea
what it might take to throw your pot out.

      That's something that you need to get a history on anyway, because the
volume of solder that your machine holds is most likely going to be different
than the pot I have, and will be affected differently in the percentage of
different metal introduced than my pot for a given volume of boards waved.

      So, I guess in a nutshell you need to get to know your solder pot,
become familiar with it's make-up, and watch what it eats
(GRIN)...establishing a baseline, and then monitoring things should keep
everything under control.

      What you might want to tell the next auditor so he has a "warm fuzzy",
is that you've established a baseline, you monitor it once a month, and then
explain to him that it's very, very rare for a pot to go out of limits because
you're monitoring it once a month.

      For the times that you find yourself waving a majority of boards that's
different from the normal mix of boards you wave (such as all gold or all OSP
boards), you may want to increase to testing to twice a month during those
production conditions.

      One other time that I can think of that might warrant a special analysis
is if you start having defects that you're not used to seeing. There are
certain types of defects that can be contributed to, or caused by a
overabundance, or lack of, certain metals. So that's another way you can
explain how closely you monitor your wave, by watching how current product is
running.

      I've never had a pot go bad on me except for one time, it got low on
tin. The reason I had that was because the operator I had turned the chip wave
on all the time whether there was SMT on the bottom or not (a bad habit he
picked-up somewhere), and he didn't use the care he needed to when cleaning
the dross out of the pot...my recycler was giving me a lot for my dross
though! But that's what was eating the tin.

      I've seen the gold level get close a couple of times in the past when
the boards were being plated with a lot thicker gold than what's used today,
but that's all I've ever seen.

                                        I hope this helps a little...

                                             -Steve Gregory-

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