I agree with the below comments and would add: The thicker the resist viscosity and coating weight, the greater the possibility of bubble retention. The lower the temperature, generally the thicker the viscosity. Fast stirring will fold air into the system so stir as slowly as possible but long enough for complete mixing. It's generally best to stand before use to let trapped air come out over a period of an hour or so. Perhaps more to the point... Talk to your supplier. LPISM suppliers have tech support staff to whom problems like this are bread and butter. Viscosity control is sensible even just before use in cases where little mixed mask is used per shift (some masks thicken on storage) but this might not be the whole answer. Part of the job of formulating LPISM's involves additives to reduce bubbling, reticulation etc. Your supplier will know about bubbling and should be able to help. He might even be able to recommend a minor change in resist (viscosity, thinning solvent etc) to meet your particular requirements. Bob Courtney Coates Circuit Products ______________________________ Reply Separator _________________________________ Subject: FW: Ink preparation mixing bubbles Author: [log in to unmask] at Internet Date: 07/05/96 10:56 My experience with bubbling has been that the viscosity of the ink is most critical. Mixing will always inject air as does forcing the ink through a screen. The key factors are; how viscous is the ink (It's hard to get bubbles out of peanut butter.), how thick is your coating (thicker coatings are harder to get the bubbles back out of), and how long do you allow product to sit for de-bubbling before tack-dry at what temperature. We had a rash of bubbling problems recently when one of our two suppliers sent in some thicker than normal ink. We're looking at incoming inspection for viscosity.