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
-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Monday, December 02, 2002 8:35 PM
To: [log in to unmask]
Subject: [TN] Solderpaste life...
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- --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------
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