Bill,

Like yourself, I too am doing a solder paste evaluation, and am nearing
completion.  To answer your question on age or freshness of paste, it may
not be an issue, but you may want to get all fresh samples and evaluate
them fairly, and if you desire, let them sit for a month or so to evaluate
their performance with age.  That's what I did, but did not notice any
performance difference with age.  I have heard that when paste sits in its
container at room temperature, the solder tends to settle towards the bottom, but I have
not seen evidence of this.  I have had paste sit at my desk for 3 months
and it performed great, though your environment will likely be different
than mine.

 As far as whether or not you should make a science project out of this, I
would say "yes", by all means.  If you don't, you probably won't choose a
"bad" solder paste, but you might not choose the "best" for your needs. By
the way, I used a fractional factorial DOE checking for response variables
such as wetting, bridging, solder balls and other items that you
mentioned.  I found that all the pastes I tried were very good, but there
was one (EFD 576D) that was exceptional with regards to eliminating solder
balls, or more correctly, solder "beads", which for us is a sporadic and
troublesome problem.  Good luck, and I hope to hear more of your
evaluation.

Howard Watson
Manufacturing Engineer
AMETEK/Dixson




"Mengers, William D." <[log in to unmask]>
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06/21/01 06:55 AM
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Fellow Techies,

We are getting ready to do a somewhat "extensive" solder paste evaluation
for an SMT operation.  What to do seems fairly straight forward using
"standard" tests (wetting, solder ball, slump, etc.), but a concern I have
is age and relative age of the different pastes we are testing.  In
practice, we generally use paste within three months of the date
manufacture, so the paste we use is anywhere from one to three months old.
Manufacturers claim good performance for the paste until expiration of
shelf
life, but I suspect there could be a difference in performance between
fresh
paste and 6 month old paste.  Maybe not for all pastes, but probably for
some.  My question is, at what age should we test the paste, and does it
matter (significantly?) if some pastes are fresh and others are close to 6
months old, or am I sweating the small stuff by even being concerned about
this?

The pastes we will be testing are no-clean formulations, eg. Alpha LR737,
UP
78N, Omnix 5000, Indium NC-SMQ92J, AIM NC 251, Heraeus SC3401HTP, Kester
Easy Profile 256, and Qualitek 691A.

Do we really need to make a science project out of this or should we just
go
with something that is popular for the type of application we have and see
if it works on our hardware as long as it meets the standard (J-Std) we
are
using?

Any ideas?  Thanks for any responses you give.

Bill Mengers
Process Engineer
Northrop Grumman Corp.
Baltimore, Md.

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