Warning - Some silicone rubbers are corrosive to copper. Often as they cure they exude acetic acid (smell 'em and see for yourself!) GE makes a variety of silicone rubber specifically adapted for use around copper circuit boards - use it in commercial products! I know this because I sat on top of a 100 foot tall hazardous waste tank in a gale (OK a stiff breeze )fixing the alarms, which had been coated with silicone rubber and were lousy with corrosion. We always sealed stuff like that with parafin wax - easy to remove with low temperature heat, noncorrosive, runs into all the cracks, not sticky or messy. Keeps the water out real nice. -----Original Message----- From: William K. Borsum To: PICLIST@MITVMA.MIT.EDU Date: Friday, October 22, 1999 7:55 PM Subject: Re: [OT] Bullet Proof Circuit... >While on the topic of protecting boards...... > >Does anyone know of a good, cheap, flexible, repairable coating and potting >material--preferably transparent?? > >I have used a variety of urethanes...most stick pretty tightly, but will >come off with a hot knife, the right solvent (which also dissolves the >PCB), and a lot of elbow grease. Not what I would call repairable--usually >end up doing more damage than gets fixed. Potted units are in effect >potted for life--and that's the problem. Great if you want a throw-away >device--but not if you've got a very expensive board you can't get to to >repair. > >Also tried silicone rubber--nice coating, transparent, cuts with an exacto >knife, and peels right off. Not good for thin coatings since it will peel >off with the slightest touch around the edges, but great for potting the >whole shebang. Also, NOT cheap. about $30 for a 1-Kilo kit. Not real >sure it will completely protect the circuit from water creeping in around >leads, etc. > >HINT & Kink for the day: you can de-bubble mixed silicone rubber by >putting the mixed material in the freezer overnite. Stuff stays liquid, >and does not cure, so the bubbles have plenty of time to make their way to >the top and pop. Let it come up to room temperature away from moisture >however--in a baggie works well on those really humid days. Stuff will >then go through its normal pot life of several hours, then cure overnite at >room temperature, or a few hours at 50 degC. > >Kelly > >William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems > & San Diego, California, USA