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June 1998

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Subject:
From:
Jeff Hempton <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 26 Jun 1998 11:40:30 -0500
Content-Type:
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        Brett,
          There is some of your processing info missing that would help give you
a better answer.
1) Do you clean, and with what, after the hybrids are reflowed the first time?
2) Are you printing a thickfilm conductor or is this a thinfilm solderable on
ceramic. What type of conductor is it (i.e., Pt/Ag, Pt/Pd/Ag, etc??)?
3) What thickness is your ceramic?
4) Have you profiled?? Those ceramics soak a heck of a lot of heat, ya know.
  I have had some similar problems with a Pt/Pd/Au thickfilm conductor that was
printed over dielectric. The material was sensitive to shelf life, since the
platinum seemed to "oxidize" somewhat, but N2 storage helped.
  Also, I remember having similar problems when we were co-firing thickfilm
dielectrics and solderable conductors...the material that was burning off the
dielectric during firing was detrimental to the solderability of the conductor.
  Again, more process info could probably provide some better answers.
 Good Luck.

Jeff Hempton
United Technologies Electronic Controls

______________________________ Forward Header __________________________________
Subject: [TN] Pinholes in reflowed SMT
Author:  Brett Goldstein <[log in to unmask]> at Internet
Date:    6/26/98 9:51 AM


        I wonder if anyone out there can help me with this problem.  We've
been observing multiple pinholes in the solder joints of SMT
components (0603 and 0805 resistors and caps) that were reflowed in a
batch reflow oven.  These parts are being reflowed on ceramic
hybrids.  The process flow is to print solder paste on the hybrids,
reflow the solder paste, apply some paste flux, place the components,
and then reflow the hybrids again.  (We use this process because we
may manufacture 100 or so of the ceramic substrates at once, but then
place components on only a few per day.)  Any idea why we getting
these pinholes?

Thanks for your help.

Brett Goldstein
EVI, Inc.

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