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 <davidwh...@gmail.com>
To: Discussion of precise time and frequency measurement <time-nuts@febo.com>
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.
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