Mouser sells aluminum oxide ceramic insulators for $0.91 each. Some dude on eBay has 100 mica insulators for $9. Whenever something is that much cheaper, and on eBay instead of Mouser, I worry a bit about quality, so I wanted to check if it made much difference?
Mica has gone out of fashion to some extent, but I'd be a bit wary of some fly by night dude on ebay selling some potentially shonky non-branded parts.
At least with a distributor you can trace their origin so you know what you're buying.
At least with a distributor you can trace their origin so you know what you're buying.
I have likely used those eBay insulators (not sure of your seller in question, but all eBay products probably come from the same original distributor) on 5 DIY amp builds and 10 amp repairs without an issue. They are brittle like any mica insulator, so just make sure you take a good look at them for cracks or chips prior to installing. To date, not had any issues with using them.
EDIT: bought from eBay seller "HIFIIC" and they were $9 for 100, so likely exactly what you are asking about
EDIT: bought from eBay seller "HIFIIC" and they were $9 for 100, so likely exactly what you are asking about
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I have bought the Mouser ones and cheaper ones from eBay. The ones from Mouser are thick and sturdy. The cheaper ones are thin and break easily and don't tolerate high tightening torque. I've cracked them while screwing the part to the heatsink.
Of course all the different thermal pads available today have got different heat transfer characteristics - their thermal conductivity, and some need heatsink compound to ensure good thermal transfer, some don't.
You seem to be under the flawed idea that "cheap" is a Technical Parameter.
It´s NOT.
Read 10000 manuals and datasheets, you won´t find it there.
In this case, only relevant one is Thermal Resistance , period; have you checked that to influence your choice?
Guess not.
I personally prefeer the gray insulting gum which with a very little of silicon grease can take large termal transfering area particularly with TO 247 and TO220.
I sincerelly unknow what this mayerial is, but I used one of them to isolate the collector of a carbonized horizontal output transistor in a Samsung monitor of the CRT era until the entire set was replaced by a flat unit, so several years of no problem under such an exigent service. The transistor itself was OK but the bakelite-like compound covering entirelly it was punched in one very humid day.
I sincerelly unknow what this mayerial is, but I used one of them to isolate the collector of a carbonized horizontal output transistor in a Samsung monitor of the CRT era until the entire set was replaced by a flat unit, so several years of no problem under such an exigent service. The transistor itself was OK but the bakelite-like compound covering entirelly it was punched in one very humid day.
Alumina has conductivity of about 70 W/K/m, mica has only 0.7W/K/m
You can calculate how good a thermal insulator is by calculating its thermal conductance from the bulk conductivity and thickness and area:
Bulk conductivity (in W/K/m) * area (in m^2) / thickness (in m) = conductance (in W/K)
For instance alumina 1cm^2 and 0.3mm thick gives 23W/K,
mica 1cm^2 and 0.02mm thick gives only 3.5W/K
Or in short alumina is so much better than mica than it can be much thicker and still out-perform mica.
SoaDMTGguy:
I bought these a while back to replace Keratherm pads that failed in my F5T monoblocks: 150 PCS/Lot TO 247 Al2O3 0.635mm *17mm*22mm Alumina Ceramic Plate With Hole|lot lot|plate ceramic - AliExpress
They've been working fine for the past year or so and seem substantial. Yes, you'll need a thermal paste as well, but I suspect these pads will stand the test of time.
Regards,
Scott
I bought these a while back to replace Keratherm pads that failed in my F5T monoblocks: 150 PCS/Lot TO 247 Al2O3 0.635mm *17mm*22mm Alumina Ceramic Plate With Hole|lot lot|plate ceramic - AliExpress
They've been working fine for the past year or so and seem substantial. Yes, you'll need a thermal paste as well, but I suspect these pads will stand the test of time.
Regards,
Scott
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I always used mica, I was very happy with them , and I never used ceramic ones , my question is if I can drill holes and if I can adjust size /cut them,
Thanks
Thanks
On a very related subject, I prefer the spring loaded device clamps rather than using the device hole, gives a better clamp pressure centrally where it matters rather than just clamping one end of the device.
Doesn’t need a special heat sink with slots either.
Also is continuously putting the same pressure on.
Example THFM1 | Heatsink Retaining Spring for use with TO-218, TO-220, TO-247, TO-264 | RS Components
Doesn’t need a special heat sink with slots either.
Also is continuously putting the same pressure on.
Example THFM1 | Heatsink Retaining Spring for use with TO-218, TO-220, TO-247, TO-264 | RS Components
Attachments
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Laser Cutting Alumina Ceramic | CMS Laser - YouTube
AFAIK, waterjet cutters are usually used for alumina cutting.
The first question is "What is the capacity of your heatsink?" If it stays nice and cool, any thermal pad will work. If it gets toasty then the thermal resistance of the insulator matters.
Some thin pads may be made from materials that have higher bulk thermal resistance, but the issue is the actual thermal resistance in use.
The other issue that gets often overlooked is the voltage breakdown. Normally not an issue as most devices are running at relatively low voltages, but not always the case. I have seen applications where the voltage across the insulator can exceed 1,500 volts.
Personally I use mica pads with a filled thermal grease. I have replaced failed semiconductors that used the thermal silicone pads and were held in place by plastic drive rivets, MADE it through the warranty period!!!
Some thin pads may be made from materials that have higher bulk thermal resistance, but the issue is the actual thermal resistance in use.
The other issue that gets often overlooked is the voltage breakdown. Normally not an issue as most devices are running at relatively low voltages, but not always the case. I have seen applications where the voltage across the insulator can exceed 1,500 volts.
Personally I use mica pads with a filled thermal grease. I have replaced failed semiconductors that used the thermal silicone pads and were held in place by plastic drive rivets, MADE it through the warranty period!!!
Possibly, using diamond or carbide boron tools. Ceramic pads are hard but brittle, so there is a need to be gentle and careful with the forces applied. A better idea is to use some high-quality silicon thermal pads because they can be cut easily,