Hi Joyce - You are going to have to give a better explanation of why you
believe that a bright and shiny joint is a reflection (pun intended!) of
good solder joint functionality before I become a believer! There is a very
large body of data (Klein Wassink, Steen, Lea, Tench) that demonstrates the
appearance of a solder joint is an extremely poor indicator of solder joint
quality and reliability. Solder alloy, solder joint cooling rate, type of
flux, and the type of cleaning chemistry used in your assembly processes
are just a few of the possible sources for making a solder joint dull in
appearance. Pb oxide is less stable than Sn oxide - but the conversion of
Pb oxide to Sn oxide is measured in minutes and not hours. You can use
either SERA technology or Auger technology to watch the conversion in real
time. The oxide states of solder joints play a minimal role in any
electromigration issues on assemblies - the potential to form a battery and
transport ions are the driving forces by several orders of magnitude in
relation to solder joint oxide. I do agree with you on the process
indicator aspects - if you were getting a shiny appearance and suddenly the
solder joints become dull in appearance then something changed in the
process which should be investigated.
Dave Hillman
Rockwell Collins
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joyce <[log in to unmask]> on 08/03/99 03:44:51 PM
Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
to joyce <[log in to unmask]>
To: [log in to unmask]
cc:
Subject: Re: [TN] Culture Changing...any ideas?
Steve,
Sorry, I have to agree with your QA for the dull solder joints... If you
analyse the joint surface (XPS), it would be Pb rich oxide, which is
unstable compare to the Sn rich oxide surface under RH condition.... The
best cost saving you can do is to eliminate the idle time and get the
assembly running as smooth as possible...(you are going to tell me to "go
to
hell", I know). Based on my experience, the best products are produced
with
full running of assembly line with minimum idle time (nobody take extra
long
lunch or coffee break, therefore, not "happlily" forgot some steps...). I
AGREE with you that process indicator is not necessary required rework, but
required investigation!(and documentation of why such an incidence
occur...warning: not going to make you very popular). If you find out that
process is not optimized (can not minimize the idle time...for example),
such an inherited process is not easy to fix...Usually, it is caused by
rush
(cost/time saving) of initial design of process (extreme case, no
consideration of process flow at all)...In that case, you have a "career
opportunity" on your hand...No easy fix in near future but work one station
at the time and use your "Roberts University" output and ask for the God
(who ever you think will listen) to help you too...by the way, if you have
trouble for class 2, boy oh boy...(I think I should stoppppp....)
jk
>One of the things that I've noticed since I've been here, is that there is
>that everything is looked at through MIL-SPEC shaded glasses...and I've
found
>that boards we were building under IPC 610 class-II standards were being
>touched-up un-neccessarily. Things that are maybe only a process
indicator,
>but acceptable, are being reworked. For one example, dull solder joints
that
>were caused because an active OA flux was left on longer than it should
have
>been before cleaning has made the joints look dull. QA won't accept the
board
>until all the solder joints are sparkling. I'll fix the problem about the
>operators leaving the flux on too long before washing the board, but you
>still don't need to touch every joint up! But I sure couldn't convince QA
of
>that...and so on it goes.
>
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