Best thermal interface material - Page 1
Forum section: electronics / projects

author: Zeranin
author_rank: Regular Contributor
timestamp: April 28, 2016, 02:16:37 am
content: I’m interested in the highest performance, thermally conductive, electrically insulating, thermal interface material. In other words, I want an electrically insulating film or sheet, with the lowest thermal resistance. The application is spelled out in the Metrology thread PCR versus TCR, but that is not directly relevant to this thread.As I have spent some time searching for the best material, I thought I might as well share my findings with you, and am also interested to hear of what products others have found, and how well they performed.I have ordered an 18” x 18” sheet of 0.003” thick Tpcm 580 Series Phase Change Material, part number Tcpm583, manufactured by Laird Technologies, priced at US $49.81 from Digikey.The phase change softening temperature is 50 DegC, so at or above this temperature the material softens and flows, filling the microscopic irregularities of the components it is in contact with. I’ll be operating at only 35 DegC, but presumably I can initially heat to ~60 DegC so as to get the material to flow, and then it’s OK to operate at 35 DegC and still achieve the thermal specs?In general, I have found that although the modern ‘rubbery’ thermal interface sheet materials have impressively high thermal conductivity of 1.5 to 5.0 W/mK, the manufacturers usually make the sheets so thick (eg 0.5 to 2 mm) that the overall thermal resistance is quite poor, no better than the traditional approach of using a thin (say 0.05mm) sheet of Polyimide (Kapton) sheet with thermal grease.That said, the TCPM583 product that I have ordered promises very high performance indeed, with a claimed thermal conductivity of 3.8 W/mK, but wonderfully thin at only 0.076mm (0.003”).In my application of providing a thermal interface from zeranin foil to a constant-temperature heatsinking plate, the dissipated power is 25W, and the zeranin area is about 270 cm^2.The formula for calculating the temperature across the thermal interface is :-dT = PL/(CA) wheredt is the temperature difference in DegCP is the power passing thru the interface, in WL is the length (thickness) of the interface, in metersA is the surface area of the interface, in m^2C is the thermal conductivity of the interface material, in W/mKIn practice, the result is worse because of the two pressure-dependent contact interfaces, so I’ll assume that in practice the effective thermal conductivity is only half of the published value of 3.8 W/mK. Plugging in all the numbers, we get:dT = 25 x 0.076E-3 / (1.9 x 270E-4) = 0.037 DegCHmm. Hard not to be impressed by that. The 0.06mm thick PVC film that I am using now results in a temperature rise of ~0.25 DegC, about 6.7 times higher! It seems like a no-brainer. If I want the best thermal performance I can get (I do), then Ineedto use this high-tech TCPM583 thermal interface material. I’ll report back as to how well it works in practice.PS. The data sheet also gives thermal resistance values at different pressures, that should account for the contact interfaces, but the values given seem like nonsense. I have contacted Laird but received no response. I’ll talk about that in another post, and maybe someone else can make sense of the published thermal resistance data.

author: Marco
author_rank: Super Contributor
timestamp: April 28, 2016, 02:38:53 am
content: How about bopet? They make some very thin films for thermal transfer tapes (4.5 micron).

author: BravoV
author_rank: Super Contributor
timestamp: April 28, 2016, 02:44:09 am
content: Quote from: Zeranin on April 28, 2016, 02:16:37 amFew years ago bought from ebay, Shin-Etsu top tier thermal pads, looks like they're industrial excess stock from an Israeli's seller (its gone now).Mine is TC-80BG , with thermal conductivity -> 7.3 W /m-K (with 0.8 mm thickness) , and with dielectric breakdown voltage at 12 Kilo Volt. Currently the TC-BG series is the top performer thermal pad series from Shin Etsu.Detail spec here ->High-hardness Thermal Interface Silicone Rubber

author: Zeranin
author_rank: Regular Contributor
timestamp: April 28, 2016, 02:52:35 am
content: Quote from: BravoV on April 28, 2016, 02:44:09 amYes, I have seen thermal conductivities as high as 8 W/mK BUT .....There are 2 problems with your pads. Firstly they are much too small, as I need 350mm x 120mm.More importantly though, the thickness makes them only mediocre. At 0.8mm, they are 11.9 times thicker than my Tcpm-583 product, but conductivity is only 1.9 times better, so overall the Tcpm-583 wins by a factor of x6.3, which makes your pads very mediocre indeed by comparison. That's the problem with so much of what's out there.

author: Fsck
author_rank: Super Contributor
timestamp: April 28, 2016, 03:01:10 am
content: sarcon XR-m and XR-um will get you to 17W/m*K and 0.3mm thickness but to a max size of 300mmx200mm. if you can have a high enough mounting pressure (like, silly high ), you can get some pretty crazy results. they're also silly expensive.

author: Zeranin
author_rank: Regular Contributor
timestamp: April 28, 2016, 03:02:44 am
content: Quote from: Marco on April 28, 2016, 02:38:53 amI know from long, bitter experience that if you make the film too thin, then even the tiniest spec of dust or whatever will puncture the film on assembly, and you electrical isolation is lost. Even worse, it may seem OK initially, and then fail totally or partially after the equipment passes to the customer. In practice, about 37 micron (0.037mm) is about the thinnest that is practical. I'ts a bit like a condom, thinner is better, up to a point ...

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: April 28, 2016, 03:04:21 am
content: http://www.americanberyllia.com/BerylliumOxideProducts.html

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 28, 2016, 03:41:06 am
content: Quote from: Alex Eisenhut on April 28, 2016, 03:04:21 amdon't wast time with aluminum heat sinks with these your just insulating at that point

author: Zeranin
author_rank: Regular Contributor
timestamp: April 28, 2016, 04:00:08 am
content: Quote from: Alex Eisenhut on April 28, 2016, 03:04:21 amYes, Beryllium Oxide is extraordinary stuff, being an electrical insulator, but with thermal conductivity between that of aluminium and copper. If I could use it in my one-off application I would.

author: Zeranin
author_rank: Regular Contributor
timestamp: April 28, 2016, 04:05:22 am
content: Quote from: Fsck on April 28, 2016, 03:01:10 amGotta be impressed with the 17 W/mK, but not available in the size I need. At 0.3mm thick, it comes out to same performance as the cheap and readily available Tpcm-583 product that I have ordered. However, in practice I suspect that the phase change material wins because of better conformance to the surface, especially at moderate pressure of 50kPa in my application.

author: Zeranin
author_rank: Regular Contributor
timestamp: April 28, 2016, 04:13:24 am
content: At the end of the day, it is not the thermal conductivity that matters, but the thermal resistance per unit area, when clamped between two surfaces at a given pressure, for example in units of (DegC-cm^2)/W.This is listed for the Laird Tpcm-580 series, except it appears to be wrong. Here is the email I sent to Laird, explaining why the thermal resistance data makes no sense to me. Find the data sheet on the Laird website, and if anyone else can make sense of the thermal resistance data, then please explain it to me.Hello,We are interested in your Tpcm 580 series thermally conductive sheet phase change materials. Your data sheet specifies a thermal conductivity of 3.8 W/mK, which sounds reasonable.The data sheet also lists the thermal resistance at contact pressures of 10,20,50 psi, and this is the data that we need to evaluate the product for our application.Unfortunately, the thermal resistance data appears wrong. Firstly, for example at 50 psi, the thermal resistance is listed as 0.08 DegC-cm/W, for all thicknesses from 0.003" up to 0.016". Surely that cannot be correct, as we would expect the thermal resistance to increase very significantly when the thickness changes from 0.003" to 0.016".Also, the listed thermal resistances are not consistent with the listed thermal conductivity of 3.8 W/mK. For example, the thermal resistance for the 0.25mm thick product is listed as 0.08 DegC-cm2/W at 50 PSI. From this, we can calculate the thermal conductivity, from the formula :-c = PL/AdT whereC is the thermal conductivity in W/mKP is the power in wattsL is the material thickness (m)A is the material area (m^2)dT is the temperature difference across the material, in DegCTherefore, for the 0.25mm thick material listed as 0.08 DegC-cm2/W, we calculate the corresponding thermal conductivity as :-c = 1.0 x 0.00025 / (0.01x0.01x0.08) = 31.25 W/mKThis implied thermal conductivity of 31.25 W/mK is grossly inconsistent with the listed value of 3.8 W/mK, and in fact is much higher than is possible for a flexible, electrically-insulating sheet, again suggesting that there is something seriously wrong with the listed thermal resistance of 0.08 DegC-cm2/W.Please help us to understand the listed thermal resistances, that appear to be wrong for the reasons given above.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 28, 2016, 05:07:23 am
content: What sort of budget do you have? A sheet of diamond will have very high thermal conductivity and a very high price to match.Maybe you could space the surfaces a millimeter or two apart, seal them together with epoxy, and have some arrangement to circulate nonconductive coolant in that space?

author: Zeranin
author_rank: Regular Contributor
timestamp: April 28, 2016, 05:21:05 am
content: Quote from: NiHaoMike on April 28, 2016, 05:07:23 amDiamond is too brittle, but a previous project did use a temperature-controlled circulation system similar to as you describe, but I wanted to get away from all that wet mess and complexity by using Peltiers this time around. At this stage the project is essentially complete, and a major re-design not practical. It's pretty much OK as is, but if I can squeeze a bit more performance just by improving the thermal interface material, then it's worth doing.

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 28, 2016, 06:27:35 am
content: Have you considered a copper heat spreader plate? You can solder the power device (or bolt with no isolation) to the copper plate to get a really low junction-plate thermal resistance. Then place the isolation between the large spreader plate and the heatsink. This is often how RF power amp power devices are thermally coupled to the heatsink.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 28, 2016, 06:39:37 am
content: What levels of isolation do you need? Is it only for extra low voltage DC, or are you building a device with components to be cooled at mains voltage? If so, you would want more specs from Laird.

author: AndyC_772
author_rank: Super Contributor
timestamp: April 28, 2016, 08:17:41 am
content: This any help?http://www.tglobaltechnology.com/product-range.html#who_we_are

author: Zeranin
author_rank: Regular Contributor
timestamp: April 28, 2016, 08:19:50 am
content: Quote from: Richard Head on April 28, 2016, 06:27:35 amYes, I often do that for power semis and it's very effective, but in this case the device is 350x100mm, so it already has a large surface area. The application is unusual and full details are in the Metrolgy PCR vs TCR thread, but the bottom line is that I needs a 350x100mm sheet/film with the lowest possible thermal resistance.

author: Zeranin
author_rank: Regular Contributor
timestamp: April 28, 2016, 08:21:15 am
content: Quote from: Siwastaja on April 28, 2016, 06:39:37 amElectrical isolation is for only 1.6V DC.

author: Zeranin
author_rank: Regular Contributor
timestamp: April 28, 2016, 08:32:16 am
content: Quote from: AndyC_772 on April 28, 2016, 08:17:41 amYes, an impressive selection of thermal management products - thanks for that. I looked through, but found nothing with a better combination of thermal conductivity (3.8 W/mK) and small thickness (0.076mm) than the product I ordered.

author: Marco
author_rank: Super Contributor
timestamp: April 28, 2016, 08:46:28 am
content: Not on the market, but Litecool has some amazing (unbelievable?) claims for theirBlack X dielectric.QuotePS. from the look of it probably just pyrolitic graphite and not actually an electrical insulator ... what you'd really want is a PGS-insulator-PGS sandwich.

author: mzzj
author_rank: Super Contributor
timestamp: April 28, 2016, 09:49:30 am
content: Quote from: Zeranin on April 28, 2016, 08:21:15 amWas your heatsink made of copper plate or something?If aluminum then I would consider hard anodizing. 0,02mm thick, high thermal conductivity and good for plenty of voltage. Just watch out for sharp cornersOkay, then your problem is getting your shunt foilreallyflat and smooth. And you still probably need some sort of thermal grease.

author: Zeranin
author_rank: Regular Contributor
timestamp: April 28, 2016, 10:47:12 am
content: Quote from: mzzj on April 28, 2016, 09:49:30 amThe heatsinking plate is 450x500x12mm thick aluminium, with Peltier modules on the underside, driven from a PID temperature controller so as to keep the plate at constant temperature within 0.1 DegC. The 0.3mm thick zig-zag zeranin sheet is then clamped down onto this constant temperature plate with a 12mm thick copper plate, with electrically insulating film between. You are right. In principle I could anodize the aluminium plate, and without doubt I would still need thermal grease, but the grease layer would get squeezed out to an very thing layer indeed, really just filling in surface roughness and microscopic hollows. As now, the zeranin sheet needs to have all edges carefully sanded so there are no rough edges, corners or protrusions of any sort. I would be nervous that the zeranin might cut though the very thin oxide layer, but it might be fine, hard to say.I researched the thermal conductivity of typical anodized aluminium layers, and it's not particularly good, falling in the range of 0.5 to 1.6 W/mK, quote :-Measured thermal conductivities of (aluminium anodized) oxide layers produced using different electrolytes were as follows; 1.31–1.62 W m?1 K?1 for oxalic acid, 0.53–1.01 W m?1 K?1 for sulfuric acid and 0.82–1.12 W m?1 K?1 for mixed acid ....If we assume a conductivity of around 1.2 W/mK, then this is around 3 times less than the phase-change material that I ordered, that has a thickness of 0.076mm. If the oxide layer is 0.025mm, then the overall thermal resistance would be similar, with the anodizing layer 3 times as thin, but having a thermal conductivity 3 times less.Thank you for your suggestion, It certainly appears to be a viable approach attaining low thermal resistance. In practice, it's not going to be practical to anodize that plate at this stage, as it is part of a complicated mechanical assembly that I do NOT want to disassemble and re-assemble at this stage. I'll try the 0.076mm phase change material that I ordered and see how it performs, as doing this is cheap and easy. My suspicion is that this will be about as good as it gets.

author: Zeranin
author_rank: Regular Contributor
timestamp: May 03, 2016, 02:08:05 am
content: There is a wise old saying, that if something appears too good to be true, then it probably is. As it turns out, the Laird Tcpm-583 thermal interface product that I ordered is utterly useless, being merely an expensive and inferior alternative to thermal grease.Despite being an electrical insulator, this material (as it turns out) is apparently not intended to provide electrical isolation, though nowhere do Laird actually say this. The ‘film’ is supplied between 2 transparent protective plastic sheets. To use the material, you peel off the top plastic sheet, then press the sticky surface of the grey ‘thermal interface material’ onto one surface. Then you peel off the other protective plastic sheet, and finally, press your second surface down onto the tacky grey material. The interface ‘film’ has no mechanical strength or integrity whatsoever. I tried a 25mm square test sample of the material, clamped between 2 metal surfaces and heated to 65 DegC, and just as predicted, a few 10’s of volts was enough to break down the film, with the 2 metal surfaces thereafter shorted together. Oh, and once assembled, you can’t get the surfaces apart again, another great ‘feature’ of the product.Apparently, the purpose of this material is simply to provide good thermal contact between two metal surfaces, but provide no electrical isolation. That being so, it is difficult to comprehend why they make the material electrically insulating in the first place, as better thermal conductivity can be obtained by using thermal grease loaded with microfine copper or silver particles. Furthermore, a metal-loaded grease will provide a thinner interface, as the excess grease is squeezed out under pressure, while with the Laird product you are lumbered with the thickness of the thermal interface material, 0.003” in this case, and much thicker again for most of their Tcpm-580 products. No thanks.In summary, what we have here is an expensive and inferior alternative to a high-quality, metal-loaded thermal grease. I am extremely unimpressed with both the product and the company. As described in detail in a previous posting, the published thermal resistance specifications are nonsense. I sent two emails to Laird, to 2 different enquiry email addresses, seeking clarification, and still have received no reply to either. Their documentation, product, and customer service are all complete rubbish as far as I am concerned, and I won’t be buying anything from Laird again. I am seriously unimpressed.My conclusion from all of this, is that the only advantage of the modern thermal interface materials is ease of use. Sure, some of the modern insulating interface materials have quite good thermal conductivity (W/mK), but in order to get useable mechanical integrity and electrical isolation, the thickness is so great that the resultant thermal resistance is at best as good, and generally inferior, to the old-fashioned approach of using a thin film of Kapton or similar, with thermal grease. My original plan was to use the thermally conductive grade of Kapton, known as ‘Kapton MT’, and it looks like that would still be the best solution. The only reason that I didn’t do it that way in the first place was because I could not obtain a sample sheet of Kapton MT bigger than A4 size, which is too small.Other suggestions that in principle might work well are 0.3mm thick Sarcon XR-m (but not available in size that I need) and hard anodizing the aluminium heatsinking plate, but not practical to do that at this late stage.Maybe I need to spend $500 or so on to get the minium order quantity of 37 mictron Kapton MT. At least I would have plenty left over for the next job.

author: Marco
author_rank: Super Contributor
timestamp: May 03, 2016, 08:54:41 pm
content: You get a bit stiffed on small orders (60$ winding fee) but youcan get it in smaller quantities.

author: Zeranin
author_rank: Regular Contributor
timestamp: May 03, 2016, 10:51:37 pm
content: Quote from: Marco on May 03, 2016, 08:54:41 pmUseful information. Thanks. I'll probably get some, and report back as to how it performed.Edited update. The customer is happy to pay for the Kapton MT, so I'lldefinitelyorder some, and report back how it performed.

author: mikerj
author_rank: Super Contributor
timestamp: May 04, 2016, 07:26:22 am
content: Quote from: Zeranin on May 03, 2016, 02:08:05 amIt's far from inferior, you'd know this if you'd ever used thermal grease in a production enviroment!Quote from: Zeranin on May 03, 2016, 02:08:05 amThe magic words you overlooked were "Phase change". If it turns into a liquid, how can it be expected to provide electrical isolation?Quote from: Zeranin on May 03, 2016, 02:08:05 amWhy would you want a conductive liquid oozing out of your thermal interface when the material changes phase? Doesn't sound like a good idea to me.Quote from: Zeranin on May 03, 2016, 02:08:05 amFor your application it's clearly not suitable, but just a small amount of research would have told you that. These phase change materials are an excellent solution for providing a high performance thermal interface in a production environment. We use this almost exclusively on our TEC cooled laser assemblies and have yet to find anything that provides the same combination of performance, ease of use and cleanliness.

author: Zeranin
author_rank: Regular Contributor
timestamp: May 04, 2016, 12:53:32 pm
content: Quote from: mikerj on May 04, 2016, 07:26:22 amIn a production environment, where speed of assembly and ease of use are important, I can see the benefits of a phase-change thermal interface material such as this, yes. For one-off applications, where the highest possible performance is required, then probably not, and not suitable if electrical isolation is required, as we agree.Your description of a phase change material simply as a liquid at higher temperatures is not correct. The material that I bought was unusually thin, but often these phase change thermal interface materials are quite thick, a significant fraction of a mm, and if the material literally turned to liquid rather than just softening, you would have one heck of a mess that would make thermal grease look very clean by comparison.Why would you want a conductive liquid oozing out of your thermal interface when the material changes phase? Doesn't sound like a good idea to me.This statement of yours makes no sense, and contradicts your claims of phase-change thermal interface materials being clean and mess free. Here you seem to be arguing that a phase change material should not be electrically conductive, because who would want a conductive liquid oozing out of your thermal interface when the material changes phase!! Does you magic PC material ooze out of the interface when hot, or doesn't it? If it doesn't then why should it not be electrically conductive, if the metallic particles used provided better thermal conductivity. I stand by what I said on that point.The magic words you overlooked were "Phase change". If it turns into a liquid, how can it be expected to provide electrical isolation?As I said, it does not literally turn into a liquid in the normal sense, or it would squirt out of the interface, and make one awful mess. Also, some of these phase change interface materials are so damned thick, and remembering that they don't literally turn to soup, that they may well be OK for providing electrical isolation. I'll agree with you though, that the 0.003" tick product that I bought was totally unsuitable for purpose.Did you see my posting questioning the published thermal resistances? Canyoumake head or tail of that data from Laird? Do you think that a competent and responsible company might have responded to my query by now? I remain unimpressed, but your reply does restore some balance.

author: M. András
author_rank: Super Contributor
timestamp: May 05, 2016, 07:23:21 pm
content: Quote from: Jady Zeng on May 05, 2016, 03:54:32 amis that what you call test results?

author: Zeranin
author_rank: Regular Contributor
timestamp: May 06, 2016, 10:26:22 am
content: Jady Zeng, are you still there?I did look at your website, and your 9000 series thermal pad material may be of interest, with a thermal conductivity of up to 5 W/mK.Your posting from memory mentioned a thermal conductivity of 1700 W/mK. Which of your products has this amazingly high thermal conductivity, and how is this even possible, given that copper is from memory only around 400 W/mK ?

author: mikerj
author_rank: Super Contributor
timestamp: May 06, 2016, 04:42:53 pm
content: Quote from: Zeranin on May 04, 2016, 12:53:32 pmYes it does ooze out a little bit, and that should be completely obvious. If you place a viscous liquid under pressure between two surfaces and what would you expect to happen? That said "liquid" is possibly not the correct term for it, but it's not solid and does flow under pressure when hot. When it has cooled it quite strongly bonds the device to the heatsink, to re-work the part you need to get the heatsink hot enough to reflow the material.It doesn't contradict my claim that it's mess free because the material is in it's solid state during assembly, unlike grease. Even during re-work, after reflowing the material it's very easy to clean up, it can just be scraped it off with a plastic scraper and the surface cleaned with IPA. It doesn't smear around and contaminate everything like the white grease does.Presumably you agree that conductive material oozing out from your device when the device undergoes phase change is probably not a good idea? The thermal interface formed is so thin after the phase change process (at least in our application) that improving the already good thermal conductivity would have negligible benefits.

author: Marco
author_rank: Super Contributor
timestamp: May 06, 2016, 05:14:05 pm
content: Quote from: Zeranin on May 06, 2016, 10:26:22 amPresumably Pyrolytic graphite ... generally an excellent heat spreader, not necessarily good through thickness thermal conductors (although perhaps you could orient the structure for that as well). Also conductive.

author: Marco
author_rank: Super Contributor
timestamp: May 06, 2016, 08:11:49 pm
content: Just curious, if you had to do it again would you design the resistors according to the available insulators instead of the other way around?Something like thisis probably the best large dielectric thermal conductor you can find before the cost gets ridiculous.

author: Zeranin
author_rank: Regular Contributor
timestamp: May 06, 2016, 11:51:39 pm
content: Quote from: Marco on May 06, 2016, 08:11:49 pmNow you have got me quite excited. Someone else suggested Beryllium Oxide, which is even better at 280 W/mK vesus 170 W/mK for the Aluminium Nitride sheets in your link. I'm not likely to be able to get a sheet of either in the size I need, 120 x 400mm, so I rejected the whole idea of using ceramics.But now you have got me thinking. For US$108, I can get 5 of your Al Nitride sheets, each 120x120x0.38mm But hey, my electrical isolation requirement is for only 2 volts, so I should be able to butt the sheets together, and simply rely on the 0.38mm separation for electrical isolation between the zeranin sheet and constant temperature heatsinking plate. Anyone got an objection to that?Then I need to consider thermal performance, as 0.38mm thickness of Al Nitride is10 times thickerthan the 0.038mm thick Kapton MT that I was planning to use. That is where most of the trendy rubbery and phase change materials come unstuck, because by the time you make them thick enough to give electrical isolation, their overall thermal performance is usually worse than the traditional approach of using Kapton with thermal grease.But the incredibly high thermal conductivity of Al Nitride changes the game. The 'thermally conductive' grade of Kapton, known as Kapton MT, has a thermal conductivity of 0.46 W/mK, versus 170 W/mK for Al Nitride, a ratio of 370!! OK, so I lose a factor of x10 on account of the 0.38mm thickness, but gain a factor of 370 on thermal conductivity, so overallI gain by a factor of 37!!Using Al Nitride looks like a no brainer, doesn't it? I'm excited.It is also notable that the thermal coefficient of expansion of Al Nitride (5ppm/K) is very low compared to most metals such as aluminium (22ppm/K). Long story on the PCR vs TCR thread on Metrology Forum, but the root of my problem stems from the expansion coefficient of the aluminium substrate onto which the resistive zeranin foil is bonded. If I could bond the zeranin instead onto an Al Nitride substrate, then in principle I could reduce my root problem by a factor of x4, then gain by another substantial factor on account of the high thermal conductivity relative to the Kapton sheet that is no longer required. The sky is the limit when using Al Nitride when designing from the ground up, but in my case the zeranin is already bonded to an aluminium substrate on one side, so I'll need to be satisfied with a mere improvement of x37. I can live with that.Of course, I won't actually get a x37 improvement, because the overall thermal resistance will be dominated by the thermally greased contact interfaces on either side of the Al Nitride, but I should still do very significantly better than using Kapton MT.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: May 07, 2016, 01:30:12 am
content: But now you have got me thinking. For US$108, I can get 5 of your Al Nitride sheets, each 120x120x0.38mm But hey, my electrical isolation requirement is for only 2 volts, so I should be able to butt the sheets together, and simply rely on the 0.38mm separation for electrical isolation between the zeranin sheet and constant temperature heatsinking plate. Anyone got an objection to that?So long as, when pressure is exerted, the sheets cannot spread. They must stay abutted (if that's a word).Is there uneven pressure? Vibration, too, can cause creep. Certainly sounds doable.

author: Zeranin
author_rank: Regular Contributor
timestamp: May 07, 2016, 02:16:46 am
content: Quote from: RandallMcRee on May 07, 2016, 01:30:12 amI would argue that you could have a mm or so gap between adjacent sheets, and it should be fine. A 0.38mm spacing is more than enough for a maximum of 2 volts. Spark-over occurs at about 1000V/mm, so the 0.38 spacing will be good for 380V before spark-over, and thus perfectly OK for anything less than say 50V, with plenty of margin. Anyone got an objection to that?