What we found was an issue with smaller parts in general. IF traces
come out of the same side of the component, instead of the ends, the
solder cools at different rates and turns the parts. We had issues with
turning and parts that we at about a 45 degree angle (like there was
something under the component). 
  We had board with this issue which we could not figure out for over 1
year. We happened to have a consultant in talking about designs and he
mentioned this issue. We went back to the board and found out that is
what the problem was. It was actually on a SOD-123 part rather than a
0402 but similar issue I would bet.

Dan

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leif Erik Laerum
Sent: Tuesday, May 20, 2008 12:05 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


---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------