Hello Ron,

The tombstoning problems that I've encountered have been
primarily with 0603 and 0402 caps/resistors.  Two simple
fixes I did in the past have been:

1) to shorten the center to center dimension of the
component pad design.  You said that you centered the
component terminal on the pad leaving .025" of the pad
exposed on each side of the cap.  If you bring in the pads so
that only .010"-.015" of the pad is exposed on each side of
the cap, you should see a significant improvement.
2) Make sure both pads of the component are balanced as
far as incoming trace size.  Also, avoid having one pad being
a part of a ground plane.  This will insure even heating of both
sides of the component.

The above advice is assuming:
1) there are no solderability issues with the components
themselves.
2) Your reflow profile is correct (i.e. your 1st zone ramp rate
is less than or equal to 2 deg/min and your above liquidus
between 30-60 sec).

Regards,

Michael Campos
Process Engineer
MC Assembly & Test
Melbourne, FL
[log in to unmask]

>>> RON MOWBRAY <[log in to unmask]>
12/17/96 03:02pm >>>
   I would greatly appreciate any help I can get in reference to
tombstoning of plastic film caps.  My pad design for each
terminal is .060" X .050". The .060" dimension is for width of
the cap.  Each terminal is centered on the .050", leaving
.025" of the pad exposed on each side of the cap. We have
to run the parts perpendicular to the direction of travel
through the reflow because it is critical to the design. Please
reply if anyone has experience with this.  Thanks.

***************************************************************************
* TechNet mail list is provided as a service by IPC using
SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message
to:           *
* [log in to unmask] with <subject: unsubscribe> and
no text.        *
***************************************************************************
* If you are having a problem with the IPC TechNet forum
please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at
[log in to unmask]      *
***************************************************************************



***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************