John, The LPI tenting process creates an air cavity in the Via holes. When you heat up the gas, it wants to expand. Sometimes the pressure is more than the LPI can take, and the LPI lifts. Other causes such as partially cured LPI and moisture in the boards can be reduced through baking, but the basic PV=nRT problem will remain. Try clipping the LPI 2-3 mil larger than the hole size. This will allow the via hole to get solder coated, and still cover the surface copper pads. If you need the vias tented for SMT / Wave solder processes, then plug the vias from the solder side AFTER HASL. This keeps solder off the SMT side of the boards (ie under the smt components), avoids air cavities, and lets all your copper to be solder coated. **** Please note that the assembly processing dictates **** the best soldermask tenting design. There is no **** "One Size Fits All" soldermask tenting solution. If you got some more questions,.... you have my E-mail address! -- George Franck Principal Product Engineer Raytheon E-Systems Falls Church Va On Apr 30, 8:32am, LANmark Circuits,Inc. wrote: > Subject: RE: FAB- LPISM ...We've been battling a problem with LPI covering (tenting) larger vias (>.020). ...There is a tendency for the mask to lift around these holes, particularly in ...ground planes, at HAL. We've been drying the panels after scrub in a heated ...board dryer and a quick bake in the oven. We are using Dynachem Epic mask. ... ...Any input would be appreciated. ... ...John Gordon ...LANmark Circuits ...LANmark Circuits,Inc. ...400 Crown Point Circle ...Grass Valley,Ca. 95945 ...(916)272-7280(voice) ...(916)272-7017(fax) ... ...************************************************************** ************* ...* TechNet mail list is provided as a service by IPC using SmartList v3.05 * ...************************************************************** ************* ...* To subscribe/unsubscribe send a message <to: [log in to unmask]> * ...* with <subject: subscribe/unsubscribe> and no text in the body. * ...************************************************************** ************* ...* If you are having a problem with the IPC TechNet forum please contact * ...* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ...************************************************************** ************* ... ... ... >-- End of excerpt from LANmark Circuits,Inc. *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************