In a message dated 7/25/00 6:28:39 AM US Eastern Standard Time,
[log in to unmask] writes:

<< Going through the data sheets on AVX's web site concerning capacitors (X7R
dielectric in particular), I find a note that 0402, 0504, and 0603 are for
reflow soldering only. >>
Graham,
     I have experienced problems with these specific components exhibiting
cracks due to thermal stress caused by wave soldering.  Although the defect
rate for these cracks can be reduced by raising the preheat schedule so that
the temperature delta on the caps between preheat and solder immersion is
less than 100 C, it will not completely eliminate the defects.  Further
study, including FEA, showed that the maximum stress point is actually the
thermal shock of hitting the second wave in a dual wave machine.  That stress
can be eliminated by adding heat to the board while it is between the waves,
so that the solder joints on these caps never drops below the liquidus point.
 Additional problems are encountered in attempting this process.  In the end,
it is better to confine these components to the top (reflowed) side of the
board by design, and prevent the opportunity for the problem.

Jon Moore

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################