Jim, What are the pads and gap dimensions? We usually see tombstoning on wrong/marginal foot print design no matter what is the trace width. It does of course contribute to the imbalance but with a correct design it does not have any influence. Mickey -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of James Verrette Sent: Tuesday, May 16, 2006 11:53 PM To: [log in to unmask] Subject: Re: [TN] 0402 Experience and Pitfalls Hi Kerry, How much of an improvement in tombstoning did you see with ENIG vs. HASL when the traces going to the parts were balanced? I have always heard of trace imbalance as the major reason for tombstoning, but I guess the solder volume imbalance makes sense too. If the HASL can range in thickness from .1 mil to 1.5 mils (number I've seen somewhere correct me if I'm wrong), that can create a significant difference is solder volume with a 5 to 6 mil stencil. Typically, how much difference in solder volume is required to tombstone an 0402 part? I guess that would depend on part height, mass, etc. -Jim ________________________________ From: [log in to unmask] [mailto:[log in to unmask]] Sent: Friday, May 12, 2006 10:09 AM To: TechNet E-Mail Forum; James Verrette Subject: Re: [TN] 0402 Experience and Pitfalls Hi Jim, I saw that when I used HASL originally, I could not guarentee that I would have the same deposition of solder on each Pad during the HASL process. This left me with 2 pads that had different deposition of solder on them. This imbalance caused me to see more tombstoning of the 0402 devices during relflow. When I switched to ENIG (bad topic to mention today), which has a more planar surface, the tombstoning was minimized. Let me know if you need more info. I ran a pretty good DOE on 0402's back in 98. We also looked at the weight of traces going into the pads. Both factors will affect tombstoning. The RF boards we were running were 3.5" x 3.5 " with 250 (0402"s) on both side. Kerry McMullen Principal New Product Mfg. Engineer LTX Corporation 50 Rosemont Road Westwood, MA 02090-2306 (T) 781-467-5468 James Verrette <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 05/12/2006 09:06 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to James Verrette <[log in to unmask]> To [log in to unmask] cc Subject Re: [TN] 0402 Experience and Pitfalls Kerry, Please elaborate on your recommendation, Do not use HASL finish. What specific problems occur with 0402s on HASL finished PCBs and what aspect of the HASL finish causes them? Typically HASL is avoided for things like BGAs fine pitch large pin count packages because of the relatively poor uniformity compared to other finishes, but I would not think that this is a concern for a two pin device. Jim Verrette Electrical Engineer ------------------------------ Date: Wed, 10 May 2006 09:11:26 -0400 From: Kerry McMullen <[log in to unmask]> Subject: Re: 0402 Experience and Pitfalls Hi Ryan, Approach them the way you would a 0603 DOE. The biggest thing I saw that keeps tombstoning to a minimum is to keep a large area gap between the pads, and also try to balance the trace widths that come into the pads. I use a .006 thk stencil with rectangular pads and 1:1 aperature openings. Also, do not use HASL finish. I stay away from glue. I could go on, but lets see what everyone else says. Kerry McMullen Principal New Product Mfg. Engineer LTX Corporation 50 Rosemont Road Westwood, MA 02090-2306 (T) 781-467-5468 --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- ________________________________________________________________________ _____ Scanned by Sanmina-SCI eShield ________________________________________________________________________ _____ _____________________________________________________________________________ Scanned by Sanmina-SCI eShield _____________________________________________________________________________ --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------