A few years back (Long, long ago.....) No, just kidding! 
     I've built initial prototypes out of DFSM as high as .004" thick 
     (DryFilm that is). The goal was to have solder paste thickness'
     to yield a higher volume of reflowed solder. Two problems came
     up. 
                1: DFSM is not gaining a lot of popularity lately.
                   Due to many issues. The majority of the parts I see
                   are moving towards LPI. DFSM conforms with the shape
                   of the outerlayer circuitry. This can greatly 
                   contribute to gasketing issues during solder
                   paste application. LPI provides higher          
                   productivity therefore it is more economical.
                   Some (past) DryFilms are no longer available.
     
                2: LPI provides better image resolution. Finer features
                   are capable. This is associated with the thickness.
                   Most assemblers are controlling that solder paste
                   thickness by stencil thickness. LPI provides a more
                   planar surface for paste application. (Its' applied
                   fully wet as opposed to a (dry) film.)
     
     My thoughts anyways......
     
     I'm sure others will join in to.
     
     Groovy

______________________________ Reply Separator _________________________________
Subject: ASSY: Solder Paste Volume
Author:  [log in to unmask] at SMTPLINK-HADCO
Date:    10/30/96 10:31 AM


     Address,
     
     Is anyone applying solderpaste to PCBAs with an aperture to stencil 
     ratio of 1.33?  I have some .012 pitch QFPs with random opens.  The 
     problem is either related to the device handling (bent leads that are 
     not visual or automatically inspected prior to assy) in the wafer 
     prior to pick and place or the soldepaste volume on the land.  Past 
     rules have been to have a ratio of 1.6 or greater, does this still 
     apply?  Has anyone used Dryfilm S/M versus LPI to increase solderpaste 
     volume on the lands?
     
     Please advise.
     

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************


***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************