Interesting thought ----- Original Message ----- From: Jac Kroeker <[log in to unmask]> To: <[log in to unmask]> Sent: Wednesday, April 10, 2002 12:42 PM Subject: Re: [TN] 0402 tombstone problem > Hi TN assemblers; > Having followed this thread, I haven't seen any body point a finger at the > board finish as a cause of tombstoneing. I always thought that HASL or > poorly HASSLED boards contributed to tombstoneing. We went to immersion > White Tin years ago in order to make our boards more manufacturable. Is > there a comment from the assembly community about tombstoning and the > topography of the bare board? > Jac Kroeker > Omni Graphics Ltd. > www.omnigraph.com > > At 11:16 AM 04/10/2002 -0400, you wrote: > >Hi Dan, > > > >can you give the exact dimensions of the round land pattern? > > > >Thanks, > >Ioan > > > > > -----Original Message----- > > > From: Dan R. Johnson [SMTP:[log in to unmask]] > > > Sent: Wednesday, April 10, 2002 10:22 AM > > > To: [log in to unmask] > > > Subject: Re: [TN] 0402 tombstone problem > > > > > > Steve, > > > I use round pads to decrease pad size (increase circuit density). A side > > > benefit seems to be less chance of skew, I don't have numbers on > > > tombstoning/drawbridging, but product hasn't yelled. I have also been > > > tinkering with the idea of other geometries just haven't come across the > > > right application yet. > > > Dan > > > > > > ----- Original Message ----- > > > From: [log in to unmask] <mailto:[log in to unmask]> > > > To: [log in to unmask] <mailto:[log in to unmask]> > > > Sent: Tuesday, April 09, 2002 8:12 PM > > > Subject: Re: [TN] 0402 tombstone problem > > > > > > I just heard something not too long ago, that round pads for 0402's > > > are the way to go. > > > > > > Never heard of that before, but just recently received a board for > > > quote that uses round pads for the 0402 components...anybody else ever > > > heard of this? > > > > > > Guess I'll find out how it works inna little while, while pondering > > > why a round pad would work better than a square pad.... > > > > > > -Steve Gregory- > > > > > > > > > > > > > > > Edward, > > > > > > When we do everything correct on 0402 and 0201 and still > > > have components > > > standing-up, we often look to the component terminations and > > > find poor > > > plating. > > > > > > Good luck > > > Dave Fish > > > > > > ----- Original Message ----- > > > From: "Edward S. Wheeler" <[log in to unmask]> > > > To: <[log in to unmask]> > > > Sent: Tuesday, April 09, 2002 10:59 AM > > > 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 > > > > > > > > ======================================================== > Omni Graphics Ltd. 2 - 12760 Bathgate Way, Richmond BC, Canada V6V 1Z4 > Tel 604-276-9717 Fax 604-276-2514 > [log in to unmask] www.omnigraph.com > ======================================================== > > -------------------------------------------------------------------------- ------- > 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 > -------------------------------------------------------------------------- ------- > --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------