Hi John -
     
     Let me throw another angle at you - the width of your conductors will 
     influence your solder wetting even if you have good solderability or 
     acceptable heat transfer! FM Hosking's paper "Parametric Study on the 
     Solderability of Etched PWB Copper" in the SMI 96 proceedings (page 
     671) might be helpful. He has done some interesting work on how 
     roughness, temperature, flux, etc (many variables) can impact wetting. 
     I'll bet that the influence of copper thickness can be pulled out of 
     his equations or maybe one of the listed references could be helpful. 
     Good Luck.
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: ASSY: DSN: Conductor to Land ratio
Author:  [log in to unmask] at ccmgw1
Date:    11/15/96 12:57 PM


     Address,
     
     We use .020 pitch devices extensively in our designs, 12mil lands with 
     8mil spacings.  The conductors widths coming from these lands are 
     8mils (2.1 Cu thk; .0007 foil and .0014 plating).  In addition to 
     other varibles, I believe the 8mil cond width is robbing much needed 
     heat for solderability.  The 8mil cond width is out of context for 
     such lands and FPT devices.
     
     Q: How much influence does the conductor really have on the wetting of 
        the land in reflow (No heavy copper planes in the 8 layer lay-up)?
     
     Q: Is there a test that can be conducted to determine the amount heat  
        absorbed by the land.
     
     I am in the process of convincing Hardware Design to reduce the 
     conductor width for the reason above, in addition to buying real 
     estate.
     
     Please advise.
     
     John Gulley 
     [log in to unmask]
     972-578-3928
     
     
     
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