[time-nuts] Re: Potting compound advice needed
I forgot to mention that it can be removed nicely with hot air, and has the very nice property that you can solder things that are coated just in case you should make a misteak. it is soft. I did not know the epsilon or tand. Don On 2021-11-11 17:49, Lux, Jim wrote: On 11/11/21 4:00 PM, djl wrote: I've used, wait for it, beeswax as a potting compound. Gouda cheese comes coated with it (some has paraffin, get the best,) in a lovely red. I also found out some years ago that Catholic churches use pure beeswax for large (not votive) candles and may give you the stubs. Nice, clean white. Or, dear ol' Amazon has a huge assortment for around $1.00 / oz, in various stages of "purification". For expensive beeswax with some unknown sticky additives, use toilet mounting rings... (good also for preserving dry milsurp gunstocks, according to Anvil.) 73, Don Beeswax, if perfectly dry, and no carbon residue, is pretty good RF wise - at 1 MHz, epsilon is around 2.5, tan d is around 0.01 which is ok, but not great. You could mix it with microballoons to lower epsilon and dissipation. It does shrink and, of course, it's pretty soft. Pointing back to a previous suggestion 3M DP270 - that's 3.5 epsilon and 0.018 tan d, but at 1kHz. The graph in the datasheet does show pretty constant 0.020 up to 1 MHz. http://www.emesystems.com/pdfs/parts/DP270.pdf At least it's available in less than a gallon quantities. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. The whole world is a straight man. -- Dr. Don Latham AJ7LL PO Box 404, Frenchtown, MT, 59834 VOX: 406-626-4304 ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Potting compound advice needed
On 11/11/21 4:00 PM, djl wrote: I've used, wait for it, beeswax as a potting compound. Gouda cheese comes coated with it (some has paraffin, get the best,) in a lovely red. I also found out some years ago that Catholic churches use pure beeswax for large (not votive) candles and may give you the stubs. Nice, clean white. Or, dear ol' Amazon has a huge assortment for around $1.00 / oz, in various stages of "purification". For expensive beeswax with some unknown sticky additives, use toilet mounting rings... (good also for preserving dry milsurp gunstocks, according to Anvil.) 73, Don Beeswax, if perfectly dry, and no carbon residue, is pretty good RF wise - at 1 MHz, epsilon is around 2.5, tan d is around 0.01 which is ok, but not great. You could mix it with microballoons to lower epsilon and dissipation. It does shrink and, of course, it's pretty soft. Pointing back to a previous suggestion 3M DP270 - that's 3.5 epsilon and 0.018 tan d, but at 1kHz. The graph in the datasheet does show pretty constant 0.020 up to 1 MHz. http://www.emesystems.com/pdfs/parts/DP270.pdf At least it's available in less than a gallon quantities. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Potting compound advice needed
I've used, wait for it, beeswax as a potting compound. Gouda cheese comes coated with it (some has paraffin, get the best,) in a lovely red. I also found out some years ago that Catholic churches use pure beeswax for large (not votive) candles and may give you the stubs. Nice, clean white. Or, dear ol' Amazon has a huge assortment for around $1.00 / oz, in various stages of "purification". For expensive beeswax with some unknown sticky additives, use toilet mounting rings... (good also for preserving dry milsurp gunstocks, according to Anvil.) 73, Don On 2021-11-11 15:00, Gregory Beat via time-nuts wrote: Rick - Look at 3M Scotch-Weld Epoxy Potting Compound DP270. https://www.3m.com/3M/en_US/p/d/b40066438/ I purchase from McMaster-Carr (Midwest pickup window is 2 miles from house). This is what I have used, since it is rated for -65° to 350° F and safe with copper (potting electronics, transformers, etc.) *** Date: Wed, 10 Nov 2021 14:40:53 -0800 From: "Richard (Rick) Karlquist" Subject: [time-nuts] Potting compound advice needed To: time and frequency measurement T 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 ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. The whole world is a straight man. -- Dr. Don Latham AJ7LL PO Box 404, Frenchtown, MT, 59834 VOX: 406-626-4304 ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Potting compound advice needed
Rick - Look at 3M Scotch-Weld Epoxy Potting Compound DP270. https://www.3m.com/3M/en_US/p/d/b40066438/ I purchase from McMaster-Carr (Midwest pickup window is 2 miles from house). This is what I have used, since it is rated for -65° to 350° F and safe with copper (potting electronics, transformers, etc.) *** Date: Wed, 10 Nov 2021 14:40:53 -0800 From: "Richard (Rick) Karlquist" Subject: [time-nuts] Potting compound advice needed To: time and frequency measurement T 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 ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Potting compound advice needed
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. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Potting compound advice needed
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 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-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Potting compound advice needed
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 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-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Potting compound advice needed
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: ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Potting compound advice needed
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 Sent: Wednesday, November 10, 2021 7:37 PM To: Discussion of precise time and frequency measurement Cc: Brooke Clarke 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. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Potting compound advice needed
On 11/10/21 4:37 PM, Brooke Clarke via time-nuts wrote: Hi Jim: Be careful with RTVs. Some out gas acid that attacks metal, even gold plated metal. Guess how I know that. Oh yes.. one definitely needs to read the data sheets.. RTV12 is 2 part. Most 2 part RTVs don't use acid. And the one part that cure in an oven at 70C, likewise. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[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. 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. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Potting compound advice needed
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. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
