Ed -- If the tombstoning is consistently happening at the same locations, your problems may be design related. Look at the parts that have tombstoned and or skewed for large traces and ground plane connections. The smaller the parts the more sensitive they are to having the pads reflow at slightly different times. On 0201 and 0402 parts the routing should exit the ends of the pads where ever possible. Where this isn't possible traces should at least exit the part in basically the same direction to prevent surface tension differences between pads. Jeffrey A. McGlaughlin CID Sr. Designer Battelle Memorial Institute Columbus Ohio [log in to unmask] -----Original Message----- From: Edward S. Wheeler [mailto:[log in to unmask]] Sent: Tuesday, April 09, 2002 1:59 PM To: [log in to unmask] Subject: [TN] 0402 tombstone problem Hi folks, we are running a new board with 0402 parts on it. It seems that we are having a tombstone problem as well as a problem with parts not staying centered on the pads. We are currently using 20 mil square pads on the board, with 20 mils of spacing between them. Our stencil is 6 mils thick, laser cut and electro polished. The trapezoidal walled apertures are slightly reduced, 17 mils square, and centered on the pads. It appears the chip shooter is placing the parts perfectly. We are using eutectic solder paste with an OA flux, and reflowing the parts using the recommended profile. Are there any suggestions any of you might have concerning this size of a part? Is there a better stencil design, reflow profile, or pad design that could help us out? I would appreciate any suggestions. Thanks. Ed ---------------------------------------------------------------------------- ----- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/scripts/wa.exe?S1=technet Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or 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 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------