>From jamesp Tue Nov  5 11:47:33 1996
To: [log in to unmask]
Subject: re: Surface Mount Land Patterns
Content-Length: 1003

Gary,

Thanks for the "X" info. This "X" column of information is probably the only
information in the spec that we habitually ignore, being that we have found
it characteristically excessive in the width dimension. We have found that the
wider pads tend to allow skewing during reflow. We have been assuming the
strength in the Sn pedestal and toe/heel fillet as the primary region of concern
for solder formation. I'm not sure if this is wise, but we have made our
assumptions for "X" dims : nom. +.005 and not being concerned as much about
a side fillet. What is your opinion about this? Is there possibly another
mechanism for skewing that we didn't think of? For long term reliability
reasons we are trying to minimize temp exposures from rework as much as possible
The numbers have improved, but haven't neccessarily determined the direct
causes for the skewing.

                         Thanks in advance,
                           James Patten
                           TRW Space Electronics

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