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 [log in to unmask] ______________________________ 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