Hi Alex-
     
     I don't use any given set of rules but more a rule of thumb. The more 
     layers the PWA contains the easier it is to not drop the components 
     off the backside/bottom side. My thermal characterization runs have 
     shown that the board inner layers absorb the reflow heat thus keeping 
     the PWA surface from heating up over the 183C mark - i.e. the more 
     inner layers easier to keep parts in place. The PWA thickness has an 
     effect too but not nearly as influential as the number of inner 
     layers. Have fun.
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]
     


______________________________ Reply Separator _________________________________
Subject: # of Layers?
Author:  [log in to unmask] at ccmgw1
Date:    12/10/96 5:50 PM


    Dave/ Rockwell Collins
Can you elaborate more on the response you gave concerning  "SMT 
components on both sides of PCB"
  << some assemblies are hard to do both sides due to design issues (# of 
 layers)>>
 What is the rules you use as far the # of layer is concerned?
Thank you Dave
     
     
Alex Basauri
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Trimble Navigation LTD
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Sunnyvale, CA 94086
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(408) 481-6077 Fx
     
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