Hi Roger;
 
 I also agree with Jon Moylan of Delsen Laboratories.  The only other thing 
 that I could add is that you might also want to check the elongation and 
 thickness of the copper in the via hole wall.  If the copper properties are 
 not optimal, anything under .0007" thickness could start to show increased 
 rates of failure at the test parameters you are using.
 
 Hope this helps.
 
 Greg Schroeder
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______________________________ Reply Separator _________________________________
Subject: FAB: Barrel Cracking due to Air Entrapment
Author:  [log in to unmask] at SMTPLINK-HADCO
Date:    6/6/96 6:34 PM


     To TechNet,
 
     I have had a problem with a sample PCB evaluation and I hope someone 
     can help me with some supporting data.
 
     The problem is that the evaluation board had a shear crack in the 
     barrel of a 12mil small via hole after 100 cycles of thermal shock. 
     What we discovered is that the hole had been plugged on both sides 
     with soldermask (not my idea).  We feel like the expansion of the 
     trapped air eventually caused the barrel to shear.  What I need is 
     some confirming data to show that the theory is correct.
 
     In the past, we had some boards which were plugged on both sides with 
     mask (but not thermal shocked).  The resultant after reflow was that 
     one side of the plug popped (outgassing) and that the barrel did not 
     crack.  Was the difference in resultants due to the cycling at lower 
     temperature (-65C ~ +125C) vs. short term exposure at high temp (270C 
     for ~7 secs.)?
 
     Any opinions or sources of data would be greatly appreciated.  Thanks 
     in advance for all your responses.
 
     Roger Held
     Hitachi Computer Products (America), Inc. 
     [log in to unmask]
     (405) 360-5500 x142