I too had the same experience Brooke. Back in the late 70's I built a TVRO station and saved up enough money for two GaAs FETs for an LNA. Used RTV to seal it. Sadly it died. Upon taking it apart to troubleshoot I found just about everything was green. 73 - Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 848-245-9115 -----Original Message----- From: Brooke Clarke via time-nuts <time-nuts@lists.febo.com> Sent: Wednesday, November 10, 2021 7:37 PM To: Discussion of precise time and frequency measurement <time-nuts@lists.febo.com> Cc: Brooke Clarke <brooke@pacific.net> Subject: [time-nuts] Re: Potting compound advice needed 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.

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:

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.

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. > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe > send an email to time-nuts-leave@lists.febo.com > To unsubscribe, go to and follow the instructions there.

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. > > Thanks in advance > > Rick Karlquist N6RK After consulting the experts at work, what they use for this kind of thing (HVPS, high power RF, etc.) is: https://www.elantas.com/pdg/products/tooling-composites-materials/gel-encapsulants-sealants.html Elantas EN-11 (Conap) Casting, Potting and Molding Compound. epsilon of 2.9 @ 1 MHz 610 V/mil breakdown tan d of 0.009 at 1 MHz 8 hour cure at 80C, more than a week at 25C. 50 min pot life your challenge may be finding it in small quantities - a casual search shows gallon cans at just under $200, and I'm not sure that you don't need to buy a part a and a part b.