Michael, Generally speaking, we do not allow via barrels to be put under any compression. However, when clamping FR-4 the compression is localized around the bearing surfaces and the pwb returns to a relatively stress-free state rather quickly depending on the geometry, composition, and loading of the clamped joint. You must determine the via keepout area for your paticular application but outside this area you should have no via reliability concerns. Mike 0000000000000000000000000000000000000000000000000000 Mike McNulty Lockheed Martin GES Moorestown NJ Phone:(609)722-7323 Fax:(609)722-2207 [log in to unmask] 0000000000000000000000000000000000000000000000000000 Dear Scholars, I would like to know if there is information available, or opinions that address this subject of torque. September 20, 1995 Our design engineers have requested a torque specification for a circuit board. This is a two layers board, FR-4 material, thickness 0.062", and copper is 2oz. This torque requirement is due to a mechanical assembly operation. We are inserting a threaded SCR through the circuit board, where we will secure this device with a lock washer and nut. This assembly operation is very similar to your (IPC'S) description on page 10, fig. 2-10 of the "Acceptability of Electronic Assemblies," the only difference is there is no insulating washer. I do have the torque specification for the part being assembled which is 22 Lb.in (US-units), and I found no problems with this pressure. Still the design engineer is requiring the torque specification for the FR-4 product. Can you please assist me in qualifing this torque requirement. My first concers are, could an assembler tighten this part tight enough to crush the barrels or feed-throughs. "I will answer that myself," if no constraints are given, sure with a big enough vise or lever damage would occur. Sincerely your, Medar Inc, Michael Cussen