Hi Jim:
Be careful with RTVs. Some out gas acid that attacks metal, even gold plated
metal. Guess how I know that.
--
Have Fun,
Brooke Clarke
https://www.PRC68.com
axioms:
1. The extent to which you can fix or improve something will be limited by how
well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------
On 11/10/21 2:40 PM, Richard (Rick) Karlquist wrote:
I am looking for help choosing a potting compound that
has the following properties:
1. Good for 5,000VAC @ 1 MHz
2. Low RF losses.
3. Low permittivity is preferred
4. Low tempco of permittivity is a want.
5. Something I can implement in my home shop
without access to a vacuum pump etc. is a want.
What about curing? Is temperature cure (put it in an oven) ok? or do you need
room temp cure?
Silicones are usually pretty good, RF wise. But you need to check the filler
and exact composition.
I found a two component silicone that has epsilon 2.5 used for RF potting,
15kV/mm breakdown.
https://vitrochem.com/wordpress/wp-content/uploads/2020/10/Two-Component-Condensation-Silicone.pdf
they say nothing about the dissipation.
Aha. RTV12 from Momentive - clear - epsilon 3.0, tan d (at 1kHz) is 0.001, 400 V/mil - This stuff is pretty common,
but I can't find any higher frequency permittivity info, which is odd. Someone somewhere probably built something and
measured it.
Diallyl Pthalate is what they use in connectors - it's a thermosetting resin
with good electrical properties.
https://www.cosmicplastics.com/products/dap/
Picking the first one in the list 224 DAP - 360 V/mil, so for your 5kV, you'd need ~14 mils. (most plastics are in
this range)
Epsilon is kind of high 3.5, tan D is 0.01? Is that good enough for you dissipation wise? There's lots of kinds with
various fillers.
A common way to reduce epsilon and tan d is to mix in microspheres.
Some epoxies are also good. Rogers not only makes laminates for circuitboards they also produce the epoxy from which
they are made
We use tons of arathane and solithane at JPL (both are urethanes), but I don't know if we pot RF circuits in araldite.
Huntsman makes the "ara???" materials
https://huntsman-pimcore.equisolve-dev.com/Documents/US_2019_High_Performance_Components_Selector_Guide.pdf
one thing is that we store this stuff at -80C, but I don't know if that's after mixing or if it's shipped that way (in
dry ice).
masterbond.com -> give them a call or email
EP110F80-1 is a 2 part epoxy with e=2.69@1MHz, so it's probably reasonably low
loss.
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