Hi If anybody gets into this sort of thing in the future — There are black / optical blocking die coat materials out there. They are silicone based and quite stable. We used a *lot* of the stuff on watch modules after it was discovered that the watch died when exposed to a heavy dose of sunlight (right through the LCD and into the chip … poof!!)
Bob > On Apr 9, 2017, at 1:10 PM, David <[email protected]> wrote: > > I have run across the conductive carbon filled plastic problem before. > > We did not actually use just paint. We took black mastic electrically > insulating tape, dissolved it in thinner, and painted the parts with > it. It dried to form a pliable black coating. > > On Sat, 8 Apr 2017 17:49:01 +0000 (UTC), you wrote: > >> You need to be careful how you paint the package black. My first >> electronics job was in a place that made, among other things, mass >> spectrometers. We made very high input impedance electrometers for the mass >> specs using TO-5 can mosfet transistors. One batch was found to be very >> photo sensitive through the glass/ceramic lead interface. Someone had the >> idea to spray paint the bottom of the package with black paint. Not a good >> idea. The black paint, likely loaded with carbon, decreased the electrometer >> input impedance by many orders of magnitude. Considering that our >> electrometers had an input impedance of 1E-12 to 10E-15, even a fingerprint >> made a huge difference. The carbon filled black paint was practically a >> short. >> Maybe an overcoat with silicone or some other type of low leakage sealant, >> then the black paint? >> >> Tom >> >>> From: David <[email protected]> >>> To: Discussion of precise time and frequency measurement >>> <[email protected]> >>> Sent: Saturday, April 8, 2017 10:00 AM >>> Subject: Re: [time-nuts] TAPR TICC boxed (input protection) >>> >>> On Fri, 7 Apr 2017 01:06:17 -0400, you wrote: >>> >>> ....controlling the offset voltage. >>> >>> We ended up painting the diodes black after soldering. >>> >>> I have also heard of it happening with metal TO-18 packages through >>> the lead interface under the package. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
