Hi
Steve.
I work
in a low-volume high mix shop as well with similar lot sizes. We also use
both NC and OA.
I'll
tell you what we do (but then I'll have to kill ya).
We use
350g jars. We open the jar and label it with the date that is 5 days
out.
We
place all the paste on the stencil. Use the paste until the next
job. Transfer that paste
to the
next stencil, or, put it in a jar between change-overs. We use the stuff
for 5 days or until the paste starts
getting stiff and we start seeing various printing issues such as dog
earing or clogging. Periodically we'll add a
little
new stuff to make it last just a tad longer.
But,
How long you use your paste is dependent on a number of variables including past
type, container, environmental conditions the paste sees on the stencil, amount
of paste you dispense and the size of the apertures. We have some boards
with just chip caps and we can use older paste with no problems. Try to
get that same paste through a 20mil pitch aperture on a dry day and forget
it.
Also,
your customers may or may not have their opinions about you using "old"
paste. I have found that paste manufacturers spec their paste in
extremely conservatively. This covers their butts from a processing
standpoint (i.e.: keeps complaining SMT process engineers off their
tails) and also increases usage/sales.
-Carrie
Hi all!
Hope everybody had
a good thanksgiving holiday (our USA members anyway), but have a question
about solderpaste life.
We are a low-volume, high mix shop, and we may
run 5-20 assemblies, then switch over to another assembly. The solderpaste
between these switch-overs may change from a high activity OA to a low
activity no-clean depending on the requirements called out on the assembly
drawing.
In the past, we have chosen the path, that once solderpaste is
opened, it is either used, or scrapped. But looking closely at this policy,
we're throwing a lot of paste away, and maybe we shouldn't.
It's no
small change, when I've looked at how much we throw away...just wondering now,
and I understand the issues of using very old solderpaste, and mixing fresh
with new, but does anybody have any guidelines of when they throw paste away,
or put it back in the jar to reuse?
I'm about to write some procedures
concerning this. I don't think that once the jar, or container is opened, it
needs to be consumed all at once, or scrapped. I do think solderpaste is a bit
more robust than that (but you might have a hard time for the vendors to say
that...hehehe....sorry Mike!). I do think that if good control is maintained,
solderpaste can perform as advertised, whether it has been opened previously
or not...
Just curious if anybody else has encountered this issue...and
adressed it.
-Steve Gregory-
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