[time-nuts] TAPR TICC boxed (input protection)

David davidwhess at gmail.com
Sat Apr 8 11:58:31 EDT 2017


On Fri, 7 Apr 2017 01:06:17 -0400, you wrote:

>Another thing to watch out for if you need very low leakage, is if the
>package is transparent.  All junctions are photodiodes.
>
>Maybe it's less of a problem now with SMTs, than it was with glass body
>diodes or translucent transistor packages.
>
>Andy

I got caught by this once.  We had a design which had to use hermetic
parts and this happened with the diodes used for input protection
during development and testing.  Luckily I noticed within a few
minutes that the apparent drift coincided with the angle that I was
observing the circuit leading to the discovery that my desk lamp was
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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