Address,
     
     There's been a lot of discussion lately on Tantalum caps.  I think all 
     of us have had one or more problems with these types of caps.  I like 
     to throw another out on the table.
     
     We're planning on minimizing the quantities of 0603 and 0805 tantalum 
     caps that are used on our PCMCIA.  We've tried several footprints to 
     minimize the amount of tombstoning to now avail (all lands being 
     square).  
     
     NOTE:  The tombstoning is problematic, but no show stopper.
     
     In our new design, we will be using ceramic 0402's quite extensively.  
     To better help the assembly process we're discussing the recommended 
     footprint.  I've recommend we continue using a SQUARE/RECTANGLE 
     footprint, since ceramic caps are symetrical, whereas tantalums are 
     not.  Our designers are considering using OVAL footprints to minimize 
     tombstoning.  They are referencing an article that was written in 
     EE-Times (12/16/96), that discussed Motorola's approach to minimizing 
     tombstoning to under 100ppm's.  Motorola noted many variables that 
     could effect the tombstoning even with OVAL land changes.  My thinking 
     on this is that a ROUND or OVAL footprint will have more surface 
     tension than a square land, assuming some paste volume is constant, 
     due to the surface area.  
     
     Are others using OVAL lands to minimize tombstoning or are you having 
     successes with using square lands?  Also is anyone using triangle 
     lands for 0402's?  Please advise.
     
     Thank you
     
     John Gulley 

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************