Hi Frank, I have had a lot of board assemblies with over 1,000 of those little guys per board. I used the .012 air gap for my footprints with .020 pads with no tombstoning. I have found that those 0402's that do tombstone is due to pad to pad imbalance due to the amount of traces going into the pads. Those you have to deal with the layout and designer to address. Hope this helps, Kerry Frank Kimmey <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 05/06/2005 01:05 PM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Frank Kimmey <[log in to unmask]> To [log in to unmask] cc Subject [TN] 0402 issues This question is for Assembly Process Engineering types. Our designs are suffering from 0402 tombstoning. The best feedback I am receiving from our Asian CM is this is caused by footprints. As I am a Designer and not a Process Engineer I have been tasked with asking some experts. So, here we go: We are in the process of redesigning some PCBs that use 0402 chip parts (Rs and Cs). Our CM is requesting we deviate from our IPC-782 footprints. At present IPC782 and 7351 both recommended .016" gap between lands. Our CM is requesting reduction to .012" Comments? Also, we use flooded ground pours due to RF performance and there fore end up with unequal land sizes (one copper defined pad and one soldermask defined pad +.004 in X and Y size) depending on device connections. What would be your concerns over this design style? Do we need to equalize land sizes at the cost of time in design (literally thousands of parts per board) or can this be relatively compensated for with assembly process (paste, profile, fixturing, etc.)? Any help is appreciated Thanks, FNK Frank N Kimmey CID+ Principal PCB Designer Powerwave Technologies Inc Office 916-941-3159 Fax 916-941-3195 Cellular 916-804-2491 --------------------------------------------------- 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 -----------------------------------------------------