Ed --

If the tombstoning is consistently happening at the same locations, your
problems may be design related.  Look at the parts that have tombstoned and
or skewed for large traces and ground plane connections. The smaller the
parts the more sensitive they are to having the pads reflow at slightly
different times. On 0201 and 0402 parts the routing should exit the ends of
the pads where ever possible. Where this isn't possible traces should at
least exit the part in basically the same direction to prevent surface
tension differences between pads.

Jeffrey A. McGlaughlin CID
Sr. Designer
Battelle Memorial Institute
Columbus Ohio
[log in to unmask]



-----Original Message-----
From: Edward S. Wheeler [mailto:[log in to unmask]]
Sent: Tuesday, April 09, 2002 1:59 PM
To: [log in to unmask]
Subject: [TN] 0402 tombstone problem


Hi folks, we are running a new board with 0402 parts on it. It seems that
we are having a tombstone problem as well as a problem with parts not
staying centered on the pads. We are currently using 20 mil square pads on
the board, with 20 mils of spacing between them. Our stencil is 6 mils
thick, laser cut and electro polished. The trapezoidal walled apertures are
slightly reduced, 17 mils square, and centered on the pads. It appears the
chip shooter is placing the parts perfectly. We are using eutectic solder
paste with an OA flux, and reflowing the parts using the recommended
profile.

Are there any suggestions any of you might have concerning this size of a
part? Is there a better stencil design, reflow profile, or pad design that
could help us out? I would appreciate any suggestions.

Thanks.

Ed

----------------------------------------------------------------------------
-----
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
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 delivery of Technet send e-mail to [log in to unmask]: SET
Technet NOMAIL
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/scripts/wa.exe?S1=technet
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
----------------------------------------------------------------------------
-----

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
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 delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL
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
---------------------------------------------------------------------------------