ROGER, WHAT YOU ARE SEEING IS A THE RESULT OF AN UNSUPPORTED PLATED THROUGH HOLE. WITH OUT A SOLDER PLUG OR A COMPONENT LEAD IN THE HOLE TO CONSTRAIN THE LAYERS THE VIAS WILL TEND TO SHEAR IN THE CENTER OF THE BOARD. QUESTIONS I HAVE FOR YOU ARE; ARE THERE PADS ON EVERY LAYER FOR THE VIA? THIS WILL HELP ENSURE GOOD PLATING FROM THE FABRICATOR. WHY IS THE VIA TENTED? IS THE SOLDER MASK RELIEF NOT LARGE ENOUGH TO CLEAR IT? I WORKED FOR A COMPANY THAT BUILT DOWN HOLE SENSORS FOR THE OIL FIELD INDUSTRY. WE SAW TEMP CHANGES FROM -20C (DECK OF AN ARTIC DRILL RIG) TO 150C (DOWN HOLE). WE USED PADS ON EVERY LAYER, SOLDER PLUGGED, AND FINALY A SMALL LEAD SOLDERED IN THE VIA HOLE. WE EVENTUALY DID AWAY WITH VIA HOLES (WE USED ONLY THROUGH HOLE COMPONENTS). HOPE THIS HELPS. ROB BUTTERWORTH SR PWB DESIGNER ADC VIDEO SYSTEMS MERIDEN, CT 06450 [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: FAB: Barrel Cracking due to Air Entrapment Author: [log in to unmask] at internet-mail Date: 6/6/96 12:49 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