As you probably know, there are at least three keys to preventing
Tombstoning of 0402's.
These are pad design, accurate placement, and most important a solder
profile that results in the solder at both ends becoming molten at the same
time.

Doing a second side reflow probably puts the last item at risk.  It could
be very difficult to obtain simultaneous reflow of the solder on the first
side when soldering the second.

Recommendation,  put all the difficult parts to solder, like 0402's on the
last side to be soldered.

Good Luck




"Marsico, James" <[log in to unmask]>@IPC.ORG> on 04/12/2000 07:40:45
AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to "Marsico, James" <[log in to unmask]>

Sent by:  TechNet <[log in to unmask]>


To:   [log in to unmask]
cc:
Subject:  [TN] DOUBLE SIDED SMT REFLOW


Hello TechNet:

We've just ran our first production board designed with double sided SMT
components.  Everything worked well (bottom side components actually stayed
on!) except for one thing.  During the second reflow operation, some of the
0402s on the bottom tombstoned.  These all soldered fine the first time
around.  My first thought is to raise the heat slightly, but I thought I'd
check with you guys/girls first.  Any recommendations?

Thanks,
Jim M.

##############################################################
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
##############################################################

##############################################################
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
##############################################################