Leif,
Wow interesting problem.
- 10% defect
- standard finish
- Active water wash solder paste
- new prob on old board
- placement good
- lead free process OK
- lot code specific? Undetermined.
- Try printing paste on bare laminate or glass, placing components and
running at hotter and hotter temperatures to see if there is a
difference. - Perhaps you can just run a slightly hotter leaded
profile.
- Sounds like you are already using a fairly active flux in your solder
paste.
- Running a different make of caps sounds good.
- Any change to that board design where you now have a massive internal
ground plane hooked to one of the tow pads of the caps in question?
Let us know how it turns out.
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leif Erik Laerum
Sent: Tuesday, May 20, 2008 1:05 PM
To: [log in to unmask]
Subject: [TN] 0402 capacitors turning
Technetters,
I am new to this group, but I have scanned the archives and there seems
to a lot of expertise available, so I thought I bring up an issue we are
battling with that I was hoping getting some suggested remedies for.
We have an issue where 0402 Capacitors are turning during reflow. They
are basically clocking beyond the 50% pad coverage rule. We can have as
much as 10% of the caps on one board do this. These are lead free caps
with matte tin termination. The vendor is of course claiming that it is
compatible with eutectic solder and a leaded process. We are using
Sn63Pb37 water soluble solder with an RTS profile.
The boards in question have been built for a while and this is a new
problem. The placement is perfect. The problem does not appear when we
use this same cap on our lead free assemblies.
Within a batch of, say 50 boards, the issue seem to vary with each reel
different. We have not narrowed it down to a specific date code yet, but
that experiment is next. These are all from the same vendor so we are
also planning to try a different vendors capacitors.
One idea I had was that there is some sort of out gassing that move
these caps, but we do not see any blow holes. I am not observing any
other obvious defects and the issue is exclusive to these caps.. The
easy answer is of course to go to a lead free assembly, but that is not
really an option at this point.
Could oxidized caps on the caps cause this. Would using a different
solder with an more aggressive flux be an idea? I have also thought of
reducing the aperture in the stencil to reduce the solder.
Any input would be highly appreciated.
--
Leif Erik Laerum
Quality Assurance Manager
Texas Memory Systems
[log in to unmask]
Tel: (713) 266-3200 x468
www.texmemsys.com
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