Hello,
Probably Mupsil was a typo. Mapsil 213B is a silicone-based coating also
approved (at least by ESA) for space applications.
Regards,
Javier
On 11/11/21 5:56, Lux, Jim wrote:
On 11/10/21 5:31 PM, Gerhard Hoffmann wrote:
A customer of mine uses Solitane, another one Mupsil.
I just wrote down the names in case I might need it.
Probably more for coating boards in space apps, no idea
if it fits.
Am 10.11.21 um 23:40 schrieb Richard (Rick) Karlquist:
I am looking for help choosing a potting compound that
has the following properties:
_
Yeah, the solithane (that's the name we use) is more used to repair
conformal coatings, stake fasteners, stick wires down to the board,
glue components to the board so it will survive vibe (think tall
skinny things, with the vibe in the plane of the board). Fairly
fluid, cures fairly quickly, low outgassing, and most important for
space - someone else used it and it worked without causing a
disaster. There probably is a potting version of it, and I'll ask
one of the M&P folks at work tomorrow what they think about Rick's need.
I've not heard of Mupsil, but we use a lot of Nusil - silicone
elastomers, often with alumina particles in it, as a thermal bonding
material. Say you've got a box with a fairly flat surface that you
want to clamp to another fairly flat surface. The problem is that
tightening the fasteners deforms both surfaces (unless you've got a
zillion of them) so the thermal contact area is just around the
fastener, and there is a perhaps a gap everywhere else. Spaceflight
people hate "perhaps" so they say, ok, put a thermal gasket in there
(hey, many of us have used a mica washer and silicone grease between
part and heat sink, right?). You can get elastomeric thermal gaskets
from Chomerics and similar companies, but they actually have the same
problem with clamping force. You tighten the fasteners, but to get the
required clamping force over the WHOLE gasket, you need a lot of
fasteners, or a lot of force, and you're back to the deformation problem.
So the answer is "thermally conductive glue" - you slather a thin
layer on, tighten the fasteners, which then causes the alumina
particles to poke into the surfaces on both sides, and hey - good
thermal conductivity. Of course, if you need to take it off, you need
to get in there with a wire saw and that's "not fun".
I will say the nifty-est thermal connection was a sort of velvet made
of carbon fibers. Carbon fibers have very high thermal conductivity.
You bond that furry velvet to both surfaces, and when you put it
together, the fibers slide along each other and make good contact
along their length, and there's millions of them. You aren't depending
on clamping force - it's the springyness of the very stiff fibers that
provides the contact force, and as you can imagine, it can tolerate a
lot of misalignment and gaps.
The actual stuff was developed originally to make a very optically
absorbing black coating over wide bandwidths - all those fibers bounce
the light around. And as a laser load (instead of the proverbial stack
of razor blades. It was then was used to coat mannequin forms, for
displaying lingerie for Victoria's Secret, of all places, because it
was very rugged and didn't shed lint. There's a whole exotic trade
secret about how they make the velvet - there's some sort of
electrostatic technique to making the fibers stand on end while
they're bonded, and some other exotic trick to getting them all the
same length, and so forth. I kept trying to use it in space (it is
*so* much easier than glue, gaskets, or zillions of fasteners), but it
never took -> 1) nobody else had used it before and 2) everyone was
worried about little conductive fibers shedding and floating around
into places they shouldn't be. Again, in the space world, no matter
how tedious and painful, if it worked before, we can do it again.
thermally conductive glue may be a pain, but it's "known to work".
For those of you doing bolted joints.. thermal conductances are
around 0.1 to 1 W/K -
You want to google a chapter called "Mountings and Interfaces" by
Gluck and Baturkin - It's in Spacecraft Thermal Control Handbook
Volume 1. but there's tons of copies floating around the web, and it's
a great handbook reference for "just what is the thermal resistance
with a 4-40 screw through that TO-220 tab onto an aluminum chassis"
It's one of those references which everyone cites.
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