Krishna, Bottom side SMT components are held on by solder tension during the second phase of reflow. First check you have good and acceptable solder fillets for the first reflow. A lot of cases, there are insufficient solder tension to hold components during the second reflow mainly due to small SMT lands to form adequate solder fillets. Redesigning SMT lands and patterns solve components falling off during the second reflow. Also, you may need to adjust the second reflow profile (different from the first reflow profile) for an optimum reflow time. I would say minimize the second reflow time to 30s and not to exceed 210'c peak temp. The best way to prevent components falling off is "print-glue-pick'n place-reflow the first side" and "print-pick'n place-reflow the second side". And keep large and heavy components on top side for the second reflow. regards Matthew Park >>> Krishna Kalyan <[log in to unmask]> January 6, 1998 7:15 am >>> Hello : Happy New Year to all of you. I am a process engineer trying to resolve the falling of a bottom side surface mount component during second pass of forced convection reflow. I am beginning to feel that the solderability of the component leads is getting reduced after the first pass of reflow and that is causing the part to fall. If any of you have had similar experiences, could you please share ? Your suggestions are welcome. Krishna Kalyan ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com ############################################################## 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. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ############################################################## ############################################################## 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. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ##############################################################