Why are thermal jumpers so expensive? - Page 1
Forum section: electronics / beginners

author: Faringdon
author_rank: Super Contributor
timestamp: April 26, 2024, 07:40:23 pm
content: Hi,Why are these Al Nitride thermal jumpers (SIZE 0603) So expensive (42p each in volume of 1000's.)https://www.vishay.com/docs/60157/thjp.pdfI mean, an SMD FET with a copper pour could have that copper pour coupled to an 0603 NTC (via a thermal jumper) and temperature regulation of the FET getdone very directly like that. This could pave the way for the SMD FET revolution in SMPS's (ousting of thru hole TO220 FETS)Also, this aluminium nitride , has W/mk of 170, thats great considering alu is 240, and the best gap pad is around 7W/mk.So why arent people using this aluminium nitride for SMPS enclosures? (rather than plastic)

author: jpanhalt
author_rank: Super Contributor
timestamp: April 26, 2024, 08:27:10 pm
content: Is $0.39 in small quantities "so expensive." Why settle for second rate? BN sheets can easily have double the W/mK. Make your own. Get a life.

author: artag
author_rank: Super Contributor
timestamp: April 26, 2024, 08:35:12 pm
content: I guess they're really hard to knit when they're so small

author: tooki
author_rank: Super Contributor
timestamp: April 27, 2024, 01:52:46 am
content: Quote from: Faringdon on April 26, 2024, 07:40:23 pmThey're a niche product without much competition. That alone means they can charge whatever they want. I suspect they aren’t made in huge quantities, so economies of scale aren’t there.Quote from: Faringdon on April 26, 2024, 07:40:23 pmUhhh… PCBs, even with multilayer copper pour, are terrible heatsinks compared to, well, heatsinks. Even so, with modern low-Rds(on) MOSFETs that don’t need much cooling to begin with, we are seeing more and more SMD versions. They can also be coupled to heatsinks.You may even have heard of these things called “CPUs”. They’re these so-called “computer chips” that form the “electronic brain” of your computer. Most of these have been surface-mounted for years and years now (since most computers now are laptops, which don’t normally use socketed chips). And these cyber-cerebra often dissipate a lot of heat, which we manage to remove despite not being in TO-220 packages.Quote from: Faringdon on April 26, 2024, 07:40:23 pmSo you want your chargers to be enclosed in a very expensive ceramic? That sounds like a grand idea… /sOr you could use, ya know, aluminum, and just insulate it. There are thermal pads with very much higher W/mK than 7. I bought one on DigiKey with 1600W/mK.

author: coppercone2
author_rank: Super Contributor
timestamp: April 27, 2024, 02:03:04 am
content: they are superior materials but they are difficult to make and expensive, some require a long heat treat process (72 hours glowing)ceramic is expensive when its performance ceramics. when we have 1$ / megawatt hour electricity they will be really cheapYou know, guaranteed not to crack for no reason, because ceramic.I think high performance 3d metal printing bringing down the cost of acceptable mold making (maybe) will cut some of the price off ceramic (press before sinter). then the other part is high efficiency furnaces and cheap electricity. I think the cost already went down some because of high end robotic inspection equipment for doing QC on that side of things.mold making is like a giant problem. They need to be made of the toughest materials, require inspection and are very precise (to deliver pressure properly and uniformly)AlN is synthesized by the carbothermal reduction of aluminium oxide in the presence of gaseous nitrogen or ammonia or by direct nitridation of aluminium. The use of sintering aids, such as Y2O3 or CaO, and hot pressing is required to produce a dense technical-grade material.[citation needed]Hot pressing. That means what, inconel molds and monel plumbing? $$$that is the kinda tech aliens will have lolpushing investment into big AlN manufacture for low priced materials would be interesting. That is maybe how you do high voltage power converters that are simple, reliable and efficient. liquid cooled AlN heatsinks come to mind. But nothing stops big AlN air heat sinks if their cheap. Direct air cool is best, particularly if you can put a giant ass radiator on it and not need a fan. that would be infrastructure . No stupid heat spreaders and paste layers and pressure, just a honking big ass piece of AlN. Combined with some silver asteroids to get rid of all this god damn copper

author: dietert1
author_rank: Super Contributor
timestamp: April 27, 2024, 06:14:23 am
content: Somewhat similar and a possible replacement could be a high resistance SMD resistor, like this:https://www.digikey.de/de/products/detail/vishay-beyschlag-draloric-bc-components/MCA1206MD1005BP100/11196602.Price is similar, too: 33 cents in 1000s.Regards, Dieter

author: tszaboo
author_rank: Super Contributor
timestamp: April 27, 2024, 08:35:26 am
content: Quote from: coppercone2 on April 27, 2024, 02:03:04 amYou do realize that this is just a resistor without the resistance coating? Albeit, a specific Al nitride one.All the processes that you describe are already solved for high quantities.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 27, 2024, 09:02:19 am
content: The cheap resistors are likely an easier to handle ceramic than the high thermal conductivty AlN. So they look like resistors, but a different material.A bit point is the small quatety for a niece product with little competition. They probably get a lot cheaper once you look for millions of them.AFAIK AlN ceramic is used for ceramic knifes, though the requitements on the material could be a little different.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: April 27, 2024, 10:28:53 am
content: Next question:What are the most common ceramics used for SMT resistors?It looks like AIN is a fairly common ceramic for thick film stuff.

author: tooki
author_rank: Super Contributor
timestamp: April 27, 2024, 10:44:16 am
content: Quote from: dietert1 on April 27, 2024, 06:14:23 amNonsense.If you look at the datasheet, those resistors are made on Al2O3ceramic, which is a very different material (aluminum (III) oxide, commonly called alumina) from aluminum nitride. Alumina ceramic has thermal conductivity 2-10 times worse than aluminum nitride. Sure, either is better than the FR-4 PCB substrate, but they aren’t substitutes for thermal jumpers.

author: tooki
author_rank: Super Contributor
timestamp: April 27, 2024, 10:45:26 am
content: Quote from: Kleinstein on April 27, 2024, 09:02:19 amNope. They’re zirconia (zirconium dioxide).

author: tooki
author_rank: Super Contributor
timestamp: April 27, 2024, 11:09:40 am
content: Quote from: Doctorandus_P on April 27, 2024, 10:28:53 amAlN only used on very high-power ones. Most are alumina, and cheaper ones unspecified “ceramic”.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: April 27, 2024, 11:34:46 am
content: I did a bit of poking before I posted, and did find AIN in high power SMT resistors, but was not sure about the "common" small resistors.These higher power resistors also seem to be around 50ct, (or much more expensive for high accuracy ones) so similarly priced to these thermal jumpers.

author: tooki
author_rank: Super Contributor
timestamp: April 27, 2024, 11:52:34 am
content: Quote from: Doctorandus_P on April 27, 2024, 11:34:46 amRight. (And that agrees with my own poking around.) But that’s a very different statement than:Quote from: Doctorandus_P on April 27, 2024, 10:28:53 amOn the contrary, I’d describe the situation as “AlN is an exotic ceramic used for some specialty resistors.”

author: coppercone2
author_rank: Super Contributor
timestamp: April 27, 2024, 03:19:58 pm
content: uh read the process it requires hot pressed glowing for a long time while chemicals act on it.you don't have bulk processes, its sintered into the shape you want. No one machines ceramic tiny parts. And you don't just sinter AlN powder. You get other materials that you press and react while under pressure to form the AlN. There is some AlN powder and then there is elemental aluminum and the reactants that work in pressure in the mold (possibly with action of gas) to make the part you want. Its like sintering advanced

author: tooki
author_rank: Super Contributor
timestamp: April 27, 2024, 05:27:57 pm
content: As I understand it, SMD chip resistors are made in strips, with all steps done in strip form, and then as a final step the strips are snapped or sawed apart.

author: coppercone2
author_rank: Super Contributor
timestamp: April 28, 2024, 02:55:12 am
content: strips are better but its still a tiny thin part for making in a chemical pressure moldalso with heaters something that raises cost alot is temperature. The cost sky rockets over ~1400C (as soon as you go more then nichrome and kanthal give)then you start having ceramic heating elements. and then you need to control offgassing from heaters too, and it actually needs power electronics. its not in the same league as cheap stuff like porcelain (still expensive for quality). Geometrically stable chemically inert mold at 1500C. I wonder how long those last.I think alumina you can press then heat. which makes it much cheaper, since you are not baking it under pressurealso, AlN comes in a bunch of different grades. the ones with the best thermal conductivity probobly are the worst processes. IIRC the performance of the cheap one is very poor for thermal conductivity, if you are after those 'nice' numbers

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 28, 2024, 11:41:35 am
content: Mind, Al2O3 isn't bad, it's just not as good as metal (or AlN or BeO, lol). That's still good enough for a lot of things.You can get ceramic (I think more generic porcelain) heatsinks, it might not be great but it's better than air, and might be used to just take a few to tens of degrees off an IC or whatever. There were also... maybe they're still available somewhere, but someone made extruded/HIP Al2O3 heatsinks. ... Aha, here they were:https://www.ohmite.com/wc-series-heatsink/also CA series (now discontinued?), and also Wakefield CE-OMNI-38, so I guess there is one surviving  line across two mfgs (or maybe they're both from a common source and selling as brands, who knows).Main thing is, plopping hunks of ceramic around a design isn't going to do much unless there's good thermal contact between everything. An SMT chip can't be very big to still be a chip, which makes AlN great for it, and the solder is good thermal contact. Al2O3 is good, but not great, and the low aspect ratio of a chip hurts more; it would have to be more cubic to do a comparable job.Or insulator plates and such, but they have to be fairly thick for strength, which somewhat defeats the purpose. Not to mention the plates themselves might not be very smooth, and heatsinks are rarely very planar, so you still need a generous dose of grease to fill everything in.I suppose a potting compound filled with Al2O3 sand would be pretty effective (not to mention, torture to excavate). A lot of thermal potting compounds are basically that, or ZnO or other ceramics, and they do pretty well overall.Tim