"Dorothy M. Lush" wrote: > On Thu, 10 May 2001 07:59:58 -0500, Jason Gregory <[log in to unmask]> > wrote: > > >OK, guys, here's one. > >Why is it so important for local fiducials to be placed near diagonal > corners of BGA's. The keyword here is "SO". I've performed studies in the > past detailing the natural tendency of BGA's to self-align during reflow. > It's even lead to me to work on a patent concerning a BGA rework preform. > What I'm wondering is....ssop's, tssops, qfp's, etc. have greater impact on > placement quality when misplaced. And they do not self-align!!! I do, > however, understand that BGA's balls are not easily seen once placed (you > can only see the edges). But my point that I'm getting to is.....wouldn't > you want local fiducials more at the parts that will not "self-correct" > themselves during reflow than at the parts are more forgiving? Just > wondering. > > > > > >Jason Gregory > >Software Specialist - NPI Group > >SCI Systems/Plant 2 > >13000 S. Memorial Pkwy. > >Huntsville, AL. 35803 > >(256) 882-4107 x3728 > >[log in to unmask] > > > >--------------------------------------------------------------------------- > ------ > >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 the following message: SET > Technet NOMAIL > >Search previous postings at: www.ipc.org > On-Line Resources & Databases > > E-mail 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 > >--------------------------------------------------------------------------- > ------ > > Jason, > > Global and local fiducials are a requirement of the machines that place > them. You need to design/layout fiducials for ALL the machinery in all the > locations and countries that your PCB will be loaded from prototype to full > production. Global fiducials will have a error tolerance per length so any > distance over 12 inches should have another global fiducial inserted > between them including fiducials that are diagonally opposite. Global > fiducials are also used on the stencil for solder printing. On Fuji > machines a fiducial is good for 2 inches in the X and Y direction so every > 4 inches is recommended for local-to-local-to global fiducials. Chip > placement machines do not refer to local fiducials as often as IC placing > machines. But Fuji does not make all placement machines. Every time a > placement machine resets itself it is to a fiducial and if it has to go to > the global ones then it is sometimes a longer distance than to a local one. > > The convenience of giving every fine pitch part and/or BGA its own > fiducials is in the layout library hence no thinking and you cannot forget > to do it. It is definitely not necessary to have two fiducials diagonally > opposite for every part with modern equipment butn we all don't have modern > equipment. > > Dorothy Lush > Manufacturing Engineer > > --------------------------------------------------------------------------------- > 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 the following message: SET Technet NOMAIL > Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 > --------------------------------------------------------------------------------- Jason , Here we use local fiducials for all fine pitch components be it ssop's, tssops, qfp, ... and all BGA's . And as you pointed out it is crucial to have them (fiducials) for better placement. -- Shahed Safavi-Bayat PCB Designer, C.I.D. Harris, Microwave Communication Division 3 Hotel de Ville, Dollard-Des-Ormeaux, QUE, H9B 3G4 Canada