Hi Kelly,
     
     Its not that uncommon, particularly with very fine pitch boards. 
     Better though to get the board vendor to do a compensation on the 
     artwork to allow for stress relief ( shrinkage ) on multi-layer 
     product. Problem with many stencils is you have to measure the batches 
     and tie this up with the production run tooling. I have currently got 
     panels of 4 layer boards in the shop 9 inches long, with 3 up on a 
     panel. The repeats are 4 thou out from data overall. I.E distance 
     between same pads on numbers 1 and 3  4 thou different.


______________________________ Reply Separator _________________________________
Subject: PCB vs. Paste Stencil Comp
Author:  [log in to unmask] at INTERNET
Date:    10/19/95 12:09 AM


From: Kelly Kovalovsky, PCB Quality Engineering                                
~     EMail:[log in to unmask]                                           
Subject: PCB vs. Paste Stencil Comp                                            
We have a fairly large circuit board that we are assembling. The card          
has fine pitch SMT at extreme ends. We have noticed a mismatch between         
the solder paste stencil and the printed circuit board. The circuit            
board features are actually closer together than the stencil.                  
     
My question to any card assembly site is whether it is common practice         
to compensate a solder paste stencil for shrinkage of a PCB?                   
     
IBM Microelectronics Division                                                  
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