ROGER HELD wrote: > > 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 We often observe barrel cracking in small vias after thermal shock. This is a fairly common failure mechanism, and is observed particularly after thermal shock and not thermal stress (solder float). I don't have any data to offer, but since you asked for opinions, I doubt the trapped gas is the problem. I'd be more concerned about the copper ductility, and plating quality. -- John Moylan Delsen Testing Laboratories, Inc. 1024 Grand Central Ave. Glendale, CA 91201 Phone: 818 247 4106 FAX 818 247 4537 email: [log in to unmask] URL: http://www.primenet.com/~delsen/ Delsen Testing Laboratories, Inc. is an independent testing laboratory primarily engaged testing advanced materials.