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Help fixing a cracked/ detached "ceramic heat-pad".

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Dan R. Hansen:

--- Quote from: thm_w on March 23, 2022, 12:34:17 am ---Can you link the item page?

Seller is just making up an excuse for why they don't want to ship to your country. There may be various legitimate reasons, shipping cost too high, current delay too long, etc.
Definitely not radioactive. Unless the product specifically is advertised as such.

--- End quote ---

I do actually believe the seller, because I could track the package, and it stopped in the airport, where it got delayed and rejected. It had been through many checkpoints before that, so I think it is safe to say, that they did in fact ship the item.
How, there were some "fuckery" going on before that. It was sold as free Fedex shipment included. But it ended of beign shipped with AliExpress "Premium" shipping.

I was not happy about it, at all. But there is practically nothing I could do about it. In the end though, the seller actually refunded all of the money the received from the transaction. AliExpress however, did fuck me over by keeping the mandatory VAT, that they were required to charge at the checkout. Fucking scumbags... :P
Last time I bought a unit like this, the seller didn't include the proper paperwork and documentation, resulting in me having to pay VAT twice. AliExpress dispute "judges" didn't understand the problem, and kept referring me to the rule, saying that seller is not responsible for extra fees beign applied by other governments...


--- Quote from: BrokenYugo on March 23, 2022, 01:37:05 am ---You mostly only see beryllium oxide insulators, as I understand, in RF transistors, ancient magnetrons, etc. And with warnings at that in anything remotely modern. I wouldn't expect it in this case, but I am about as far from an expert as you can get.

--- End quote ---

Well, it is cell tower equipment and the unit are made for outputting 56.1A, at 53.5 volts, so I assume the mosfets do need some insanely good heat transfer, which Beryllium pads are, if I understand correctly?
And it seems like Beryllium pads are a good choice since it never dries out, because it is a hardened ceramic, which I believe is a plus in always on equipment that must not fail often, being blasted with air from al kinds of environments and conditions.

https://great-ceramic.com/beryllium-oxide-beo-ceramics/

RoGeorge:
It happened to me a couple of times to get fake tracking numbers, so following that number might be irrelevant.

Since there is a piece of chipped material, and if you are still curious about the ceramic material, you may try to identify the material, for example by its density.  I have no experience doing that, found it by searching for "identify beryllium oxide":  https://www.eevblog.com/forum/chat/beryllium-oxide-vs-alumina-is-there-a-way-to-identify/

Dan R. Hansen:

--- Quote from: RoGeorge on March 23, 2022, 12:02:31 pm ---It happened to me a couple of times to get fake tracking numbers, so following that number might be irrelevant.

Since there is a piece of chipped material, and if you are still curious about the ceramic material, you may try to identify the material, for example by its density.  I have no experience doing that, found it by searching for "identify beryllium oxide":  https://www.eevblog.com/forum/chat/beryllium-oxide-vs-alumina-is-there-a-way-to-identify/

--- End quote ---

I know they give you false tracking number, but this one doesn't fit the usual pattern. It does seem legit. Times and dates match, and a package is actually being sent to my destination. Seller also offered to send the package again with DHL, free of charge, after granting me a full refund.
It doesn't fit the usual shady pattern.

Gyro:

--- Quote from: Dan R. Hansen on March 23, 2022, 09:39:10 am ---...
Well, it is cell tower equipment and the unit are made for outputting 56.1A, at 53.5 volts, so I assume the mosfets do need some insanely good heat transfer, which Beryllium pads are, if I understand correctly?
And it seems like Beryllium pads are a good choice since it never dries out, because it is a hardened ceramic, which I believe is a plus in always on equipment that must not fail often, being blasted with air from al kinds of environments and conditions.

https://great-ceramic.com/beryllium-oxide-beo-ceramics/

--- End quote ---

It's not Beryllium. If it was, there would be big bold warning labels on the heatsink / enclosure. Beryllium was only ever used in small quantities in the packages of specific RF semiconductor. There is some debate as to whether it was ever used in industrial magnetrons or other high power tubes (certainly not consumer).

Alumina and Beryllium still require thermally conductive grease (or maybe adhesive in this case) to fill the microscopic voids caused by surface irregularities on the semiconductor packages and also the surface machining of the heatsink. They are not a 'dry' solution. They are no different to Mica in this respect - the grease can still dry out. They just have higher voltage withstand than Mica or silicone pads [EDIT: and better RF properties).

richard.cs:

--- Quote from: Gyro on March 23, 2022, 12:56:33 pm ---It's not Beryllium. If it was, there would be big bold warning labels on the heatsink / enclosure. Beryllium was only ever used in small quantities in the packages of specific RF semiconductor. There is some debate as to whether it was ever used in industrial magnetrons or other high power tubes (certainly not consumer).

--- End quote ---

I agree beryllia is very unlikely here as it seems to be a pretty modern device, but it didn't used to be that rare. It was certainly once possible to buy beryllia semiconductor mounting washers similar to (but thermally better than) the alumina ones available today (https://www.mascera-tec.com/product/to247-to220-al2o3-alumina-ceramic-wafer). I have an RF load with a BeO resistor in, specifically this resistor: https://www.richardsonrfpd.com/docs/rfpd/RFP-150-50TCGF.pdf. The thermal path is BeO but the top cover is alumina, it's obsolete and replaced by an all-alumina part, but only in the early 2000s (from memory).

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