| Nelson Pass |
Here's some information that some of you may find interesting.
At Pass Labs we use Bergquist Silpads for thermally conductive
insulators on TO3P (Plastic packages) but not on the TO3
packages because they tend to shear and fail with the TO3.
This is not the case with the TO3P because of the smaller single
hole and the transistor's plastic insulation around the mounting
hole.
We've been happy with the Silicone pads in this application as
they are less messy and perform nearly as well as the
traditional Mica and thermal goo. As far as I can make out,
they have lower thermal impedance than claimed. However this
is assuming a certain degree of smoothness of the metal, which
is simply the flat surface of an anodized extrusion, and has a
somewhat polished look to the finish.
More recently with the First Watt product, the heat sink has
been bead blasted to make it more spiffy, and you'd think that
the slight dullness of the surface wouldn't make a difference.
In fact it made quite a bit of difference with the silicone pads -
apparently something like another 50% thermal resistance, and
I ended up using Mica and goo. The figures I get are 1.5 deg C
per watt with mica, and 2.1 with silicone. This is obtained by
running the devices at 20 watts and measuring the temperature
of the top of the case versus the heat sink right next to the
device.
If we take the ratings of the device itself, we see internally we
can expect .83 deg/watt, and so we see that Mica and goo
end up about 1/2 the total thermal resistance. If your surface
is not flat and polished, and/or you're pushing on the power
ratings of the device, consider good old messy mica and goop.
:cool: |
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| Netlist |
Interesting,
I never bothered measuring the difference but it seems obvious to me that the good old grease is doing a much better job especially with non flat surface. I really don’t mind working with it. Whenever I open an amp and see the grease sticking out of the transistor surface (Peavey is a nice example) I always consider it as good craftsmanship. Perhaps that’s only my conservative opinion. ;)
I recall reading something about thermal isolation that had the best of both worlds. Must have been an old Elector magazine.
It appeared to be some kind of silpad that had the ability to become softer when heat was applied. The principle was to burn in the transistor or mosfet or whatever had to be isolated and after a period of time turn on the screws to tighten the contact with the heatsink.
/Hugo :) |
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| Nelson Pass |
I forgot to mention it, but I believe goop may be even more
crucial to thermal coupling for insulated plastic packages like
some of the chip amp packages.
By the way, we use Thermalloy's "Thermalcote" (a fine Texas
company), although the computer crowd raves about "Arctic
Silver" (if you can afford it) :cool: |
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| anatech |
Hi Nelson,
I agree with your assessment as I've found the same thing. When repairing an amp with a rough heatsink I smooth it with 600 grit sandpaper and a milled block (flat). It does make a difference. Yes, you can see the differential temperature drop with a thermocouple thermometer.
Aluminum chips from the heatsink can pierce the sil pads :bawling: , so watch for that. Same goes for solder balls.
-Chris |
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| wrenchone |
| Nelson, which silpads were you using? the better ones are filled with boron nitride and are supposed to be equivalent to an alumina insulator, though they still may fall short of mica and goop on a bead-blasted surface. It may be Chomerics rather than Berquist that makes this particular silpad variation. A lot of times I put a thin film of goop on a silicone insulator anyway just to hold it in place while I'm trying to assemble things - best of both worlds... |
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| lumanauw |
There is a metal insulator. I saw it in Rockford Fosgate car amp. The insulator is a metal sheet, but somehow it doesnt conduct electricity. What is this called? Who sells them?
Also I wonder where to buy insulator sheet that is not small-cut. In size of A4 paper or bigger. Where to buy this un-cut insulator? The one I saw is like plastic, with yellow or orange color. Not mica, not that greyish-rubber like insulator. |
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| Nelson Pass |
Anodizing is a pretty good insulator, but I'd still use goop.
:cool: |
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| kevin gilmore |
The metal insulators are heavily anodized aluminum. I got
a whole bunch of them they are very old. Dynaco 400's
used this insulator plus the goo on both sides. A good deep
scratch would make them conductive.
I would like to buy some of those large sheet silicone insulators
too. |
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| Nelson Pass |
When I googled "silpad" to look up some specs, I
saw sheets for sale.
BTW, an Exacto (tm) blade slices them like butter. :cool:
P.S. anyone who would like to buy a roll or two of the
TO3 insulators should email me. ;) |
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| lumanauw |
My English is not good. Is GOOP = silicon paste, white like your toothpaste? Anyone knows what's its chemical name?
Where to buy this GOOP and sheet insulators (the one that is like paper, not the stiff mica) |
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| highbias |
I can absolutely assure you that sandblasting a surface would increase its thermal resistance as I've also done this before and had to go back and finish machine on a mill that blasted(pun intended!) surface. What some may think by sandblasting the heatsinks mounting surface would be that its flatter and smoother... but not true! Blasting alumnium creates a pebbled/ textured finish that can be most uneven in itself since most blasting is done by hand, not cnc. It will definately prevent good contact between two parts because of all the tiny raised almost microscopic dings in the metal. Its great for decorative purposes though and the resulting matte finish is very nice looking after anodizing although its a champ at holding dust and lint and a pain to clean easily.
To lower the thermal resistance in the surface of an alumnium sink one should finish grind that alumnium surface on a surface grinder to a very good, almost mirror like finish. If you are the patient type that has lots of time to spare this can also be done by crefully drawfiling with a flat file across the surface. In doing this you would lower the thermal resistance quite a bit and the sil pads would be even more effevtive.
Mark |
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| Nelson Pass |
I like to think of bead blasting as creating a fractal surface
which in fact has a larger surface area than described by
the square of it's boundary dimensions. Kind of like the coast
of England or the fabric of space at the sub-atomic scale.
And then I like to smear goop on it. :cool: |
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| vpharris |
| quote: | | Is GOOP = silicon paste, white like your toothpaste? Anyone knows what's its chemical name? |
Yes; Nelson was making funny by calling it "goop." It's probably usually called "heat sink compound" or "thermal grease"
| quote: | | Where to buy this GOOP and sheet insulators (the one that is like paper, not the stiff mica) |
Here's one page from the Digi-Key catalog:
http://dkc3.digikey.com/PDF/T042/0564.pdf |
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| ARAD |
In addition to a flat cooling surface, it helps to 'clean' the mounting surface of the transistors as well. Very often, the plastic around the edges is just a tiny bit higher then the metal surface. I use 600 or 800 sandpaper (wet) and polish the entire mounting surface of the transistor to the point that the copper underneath the plating shines just before mounting the devices.
Regards,
Andreas |
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| JacekPlacek |
Hi !
Why nobody consider utilizing pads made of alumnium oxide ?
They are the best. Much better than mentioned one mica and silikon. I utilize them
without problems with transistors when one looses over 40W.
Regards
Jacek |
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| joensd |
| quote: | | the grease sticking out of the transistor surface |
If you have the possibility after mounting the transistor to apply so much pressure that the grease that´s too much will be squeezed away, that´s OK.
Usually you shouldn´t use more than you need.
It obviously is only effective filling the mountain-like surface.
A whole layer of it won´t do any good.
When I repair TV´s for example there are only cheap clamps that hold the transistor. Applying too much of that goopy stuff isn´t a good thing and I can assure you that I did it wrong in the beginning.:devilr:
Jens - used to overgoop transistors and send them to semiconductor-heaven |
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| Netlist |
| quote: | Originally posted by joensd
When I repair TV´s for example there are only cheap clamps that hold the transistor. Applying too much of that goopy stuff isn´t a good thing and I can assure you that I did it wrong in the beginning.:devilr:
|
Couldn't agree more...it's artwork. ;)
/Hugo |
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| Andypairo |
| quote: | Originally posted by JacekPlacek
Hi !
Why nobody consider utilizing pads made of alumnium oxide ?
They are the best. Much better than mentioned one mica and silikon. I utilize them
without problems with transistors when one looses over 40W.
Regards
Jacek |
The problem is their availability (and probably cost).
Do you have a reasonably-priced source?
Cheers
Andrea |
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| Damon Hill |
In addition to surface finish, the holes for TO-3 devices may
have to have the edges beveled on the mounting side to
prevent shearing of the silicon insulators. Because of that,
I've usually used mica or thin plastic insulators which have
a better shear strength. Berquist comes to mind for
insulators. I'm not fond of the mess that thermal compounds
make, so I'd like to avoid their use too.
Beryllium oxide insulators used to be popular, but there
may be restrictions on their use now; aluminum oxide is
nearly as good. You want radical? How about diamond/
silicon carbide composites? Gotta find the link for this,
but it's a real product!
Popular among CPU overclockers, Artic Silver, a non-conducting silver paste might also be helpful. Instructions caution that
it will increase capacitive coupling, if that's an issue; they
also have non-silver products and other enhancements in
the form of variable-size particles that pack more tightly to
increase thermal conductivity.
Another possibility is simply increasing the thickness of the
heatsinking anodizing and mounting the device directly, using
only conductive compound without an insulator. This is
risky but probably gives the best thermal results short of
direct metal-to-metal contact and an electrically isolated
heatsink. You'll need to consult your heatsink supplier to
see what special needs they can accomodate; it may be
easier than you think.
And, what everybody else said, too. :) |
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| anatech |
I can't help but think what happens in real life. Generally, assemblers just want to stick the transistor on the heatsink quickly. That's where sil pads come in. Grease and mica take too long, but are great in service (where many techs overtighten & cut through sil pads). Using metal oxide as your insulator turns the unit into "factory service only". Or let the destruction begin!
On a DIY level you can get esoteric if you want. In manufacturing I'd suggest keeping device dissipation within reasonable limits by speading the power around more outputs.
-Chris |
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| HBarske |
I was wondering if nobody here has ever heard of Kapton insulators. This is a sort of plastics often used for voice coil formers on speakers. I just collected some thermal data from the German company "Fischer Elektronik", they manufacture insulators of a lot of materials. Given a TO-247 footprint, these are the thermal resistances I have found:
Mica: 0,4 K/W
Silicone: 0,4 - 0,96 K/W
Aluminum oxide: 0,3 K/W
Kapton: 0,07K/W
I use Kapton insulators for many years now, and I have a lot less problems then before. |
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| anatech |
Yup, that's the yellow film commonly used in car amps. It seems to work fine as well. I seem to remember it rips easily, but is otherwise resistant to damage. It is also used with heatsink compound (grease).
With any film you want to make sure nothing sharp "pokes" through to ruin your day.
-Chris |
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| highbias |
Nelson Pass said:
"I like to think of bead blasting as creating a fractal surface
which in fact has a larger surface area than described by
the square of it's boundary dimensions. Kind of like the coast
of England or the fabric of space at the sub-atomic scale."
No argument on that theory... I've just found by experience that better intimate contact is more efficient. Perhaps you can tell me why???
Damon Hill said:
"Another possibility is simply increasing the thickness of the
heatsinking anodizing and mounting the device directly"
This can easily be done by having the sinks hard coat anodized instead of a simple anodize. Any standard hard coating process will penetrate the metal a ten thousandth as well as build up another tenth on the surface, there are some other hard coat process that build up even more thickness up to .003 or so. Hard coating is also far more fade resistant , scratch resistant and very color stable over long time periods. Standard anodize even when properly sealed will eventually fade out to a bluish or bronze or some other color, partly on its own and partly from exposure to light. Hard coating anodize is one of the toughest coatings known to man and can be literally diamond hard. Normal dielectric strength of standard hard coating is about 2kv. So..... I have yet to have my Aleph 2's done and am seriously considering just hard coating the sinks and chassis parts black and throwing the insulators away. I haven't yet thought of a reason not to do it this way.
Mark |
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| Magura |
| quote: | Originally posted by Netlist
I recall reading something about thermal isolation that had the best of both worlds. Must have been an old Elector magazine.
It appeared to be some kind of silpad that had the ability to become softer when heat was applied. The principle was to burn in the transistor or mosfet or whatever had to be isolated and after a period of time turn on the screws to tighten the contact with the heatsink.
/Hugo :) |
You would be talking about What Laird sell as Thermaphase. It is the as far as I know best solution, as its easy to deal with and gives you the goo effect. Laird offers an very interesting product that Ive been using for a while with great results, Thermaphase on Kapton film, It have all the properties one could ever ask for, as its easy to handle, dosnt flow all over the place, got low thermal resistance (better than any of the other easy solutions) and is cheap.
Magura:) |
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| lumanauw |
| The yellow / orange sheet in car amp is Kapton? Where to buy this kapton, in sheet or roll? |
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| sam9 |
You can buy Kapton tape from Digikey.
If you can find the page in their catalog where the SilPads are, the same company also makes Kapton based pad. The product name is somethinh like "K-10", anyway, it has a "K" in it. They are not cheap comparred to SilPads but since the tape doesn't deform much, the Kapton pads are probablt better far all but the flaest surfaces.
I've use all of these with no problem, but only in Class-B. Class-A people probably need to be more finicky. |
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| wrenchone |
I am careful to deburr the heat sink when using silpads. A good sharp burr will even do a number on mica. I have also used aluminum oxide (alumina) washers in the past, but torque is really critical because they crack so easily. I wouldn't use them in a production environment without a precision torque wrench. I'm refurbishing one of my old homebrews right now, and I replaced all the alumina under the TO-220s with mica because the alumina were all cracked.
A good way to apply grease to an insulator or device is to smear some on a round toothpick (or dip it) and roll it on.A wooden Q-tip handle works well, too. This technique gives you just enough grease for a good thermal interface without having it squish out everywhere when you tighten down the hardware. BTW, I always called the stuff bird dung (insert other expletive as desired). |
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| JacekPlacek |
| quote: | Originally posted by Andypairo
The problem is their availability (and probably cost).
Do you have a reasonably-priced source?
Cheers
Andrea |
In Poland such pads are available without problems.
For example for transistor case TO218/TO247 ( IRFP044 for example) such pad which has 3mm thickness and has price about
0.9$ with tax for one unit if You take only one and 0.85$ with tax for one unit if You take 5 units. I utilized them in my Aleph3 in one transistor output version ( something like mini-Aleph) where IRFP044N issues over 40W.
With mica and silikon I had problems with case temperature of transistors. With mentioned pads none problems.
Regards
Jacek |
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| JacekPlacek |
| quote: | Originally posted by HBarske
I was wondering if nobody here has ever heard of Kapton insulators. This is a sort of plastics often used for voice coil formers on speakers. I just collected some thermal data from the German company "Fischer Elektronik", they manufacture insulators of a lot of materials. Given a TO-247 footprint, these are the thermal resistances I have found:
Mica: 0,4 K/W
Silicone: 0,4 - 0,96 K/W
Aluminum oxide: 0,3 K/W
Kapton: 0,07K/W
I use Kapton insulators for many years now, and I have a lot less problems then before. |
If we compare only thermal resistance there should be almost none differences between alumnium oxide and mica. But difference at least in my circuits is huge !. I think that very important is thermal conductivity. Alumnium oxide has about 24W(m*K) , best material as beryl oxide almost 201W(m*K), kapton and others significanty less.
Regards
Jacek |
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| richie00boy |
| Do you need to use paste with Kapton insulators? I got 50 TO247 insulators with one of the recent group buys from Fischer :) |
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| HBarske |
| The Kapton insulators I use already are coated with some kind of thermal grease. It is "printed" in stripes on the insulator and tends to flow here it belongs when heating up. |
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| JacekPlacek |
| quote: | Originally posted by HBarske
The Kapton insulators I use already are coated with some kind of thermal grease. It is "printed" in stripes on the insulator and tends to flow here it belongs when heating up. |
Is it reversible process ? I mean what if after utilizing it for few days I will decide to remove transistor from heatsink and further I will have to to fix it again to heatsing via utilized previously kapton pad ?
Regards
Jacek |
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| richie00boy |
Mine are just a plain yellowish colour. They feel just like a bit of thin plastic so I guess there is no such paste on them.
I thought that you didn't need paste with them, like silpads? :xeye: |
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| HBarske |
| quote: | | Is it reversible process ? |
No, it is not. Once the material has filled evey hole you won't be able to use it again.
I clean the insulators in this case and put some normal thermal grease on them. |
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| wrenchone |
| Kapton insulators need goop of some kind to fill the voids between insulator and heat sink, as kapton is not all that conformable and will not flow to fill any voids caused by surface roughness. It is not really very thermally conductive, (it's just a plastic after all, albeit a tough one) and its major virtue is that it is physically strong and resistant to puncture and can be used in extremely thin cross section, just like mica. I find it hard to believe the very low fiigure for thermal resistance shown in at a site mentioned in a previous post. Either this is for an extremely thin insulator or is a typo, as it seems better than a greased junction with no insulator, and is also better than alumina. I will look around and see if I can find any other data to support the figure given, but I am skeptical. I would rate kapton to be about the same as mica when greased. |
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| jacco vermeulen |
Has anyone ever seen insulators like these, and/or know their name ?
It looks like a very thin layer of Mica covered on both sides with something chalky, the outside has a plastic feeling.
I stumbled across some obsolete devices again, the insulators came with them in the bag with Japanese labelling.
Before my time ? :clown: |
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| anatech |
Is it possible that "something chalky" may have been grease 15 yrs ago?
-Chris |
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| GRollins |
Heat sink grease isn't supposed to dry out, but it does. I had to do some maintenance on a piece the other day and the heat sink grease came off in flakes. In that case, I suspect age. Heat can do it also. I was recently given two dead Audio Source amps which had cooked their heatsink grease to brittle flakes in about a year. The culprit here was a lethal combination of too-small heatsinks, playing the amps at high volume, and poor ventilation, with a side order of putting one amp on top of the other. Incidentally, it was easy to see which amp had been on top--its entire circuit board had cooked to a toasty brown; the bottom one was only brown around the output devices.
Grey |
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| choky |
bad grease or ,to be more precise, bad solvent in grease ;
in some cases ,it is visible even in original package ,without any particular use. |
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| mzzj |
| quote: | Originally posted by Nelson Pass
Anodizing is a pretty good insulator, but I'd still use goop.
:cool: |
Nothing beats anodized aluminium in performance, but you must specify/check enough thick layer. Once I checked some brick-sized thick-anodized heatsinks that I had laying around: Dielectric strenght more than 2kV dc. Pretty impressive. |
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| anatech |
You still need grease with anodizing, just mentioning the obvious. BTW, my contaners of grease have a shelf life of five years. Printed right on them. So jacco, you just need to clean and regrease them.
-Chris |
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| jacco vermeulen |
It is not grease.
The mica layer inbetween is thinner than i have ever seen, the white stuff seems to protect the mica layer.
It doesn't feel like thermal grease, it is some sort of coating.
The insulators were in a separate plastic bag in the sealed bag of equal number power devices.
(hope you dont mind me not mentioning the device type, everytime i do that i get emails asking if i am willing to sell)
I dropped an opened pound jar of grease once, i do know thermal grease. |
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| Zapped |
back in Nov 2002 I posted this entry about a Thermalloy product that is better than grease. Check this product out. You will never mess with zinc goop again (unless you put it on your nose at the beach to avoid sunburn)
In an effort to avoid that messy grease, I found an Aavid Thermalloy product (Wakefield makes one too) that is much neater; its a waxy stick that comes in a push out applicator (kinda like a small rectangular stick deoderant!) that goes on real easy. Product spec's indicate It is 20% more efficient than grease, with no runout or "bleeding", expands once it hits 160 degree F (undergoes phase change), and cleans up easily. You can use it on any two surfaces that you would use the grease on, I think.
DigiKey carries it on the same page as other Thermalloy stuff. Look for the picture in upper left catalog page [in 2002]. Not sure if it has a number. Only drawback: costs about $17 per stick, good for 1000 sq. inches. I used it to interface some heat sink modules to a big thick aluminum plate, after getting rid of the grease that used to provide the thermal interface.
:cool: |
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| powerbecker |
| quote: | Originally posted by HBarske
I was wondering if nobody here has ever heard of Kapton insulators. This is a sort of plastics often used for voice coil formers on speakers. I just collected some thermal data from the German company "Fischer Elektronik", they manufacture insulators of a lot of materials. Given a TO-247 footprint, these are the thermal resistances I have found:
Mica: 0,4 K/W
Silicone: 0,4 - 0,96 K/W
Aluminum oxide: 0,3 K/W
Kapton: 0,07K/W
I use Kapton insulators for many years now, and I have a lot less problems then before. |
Holger,
there is a lot misinformation on web and also in the eg
"Fischer-Catalog" !
Al2O3 has a thermal conductivity of about 24W/mK
Kapton has a thermal conductivity of 0.12W/mK (Dupont)
that means Kapton is 200 times poorer.
If You calculate a TO247 base at 3.36 cm2 and You like to transfer 40W and You don´t consider the two crossings:
With Al2O3 thickness 1mm You will get a temperature difference of about 5K!
With Kapton thickness 0.05mm You will get a temperature difference of about 49.6K !
BTW in the 70ths I try Kapton with 20um and 10um (I get samples from a capacitor manufacturer) but this was mechanically not strong enough and also a mess together with the "goop" :D
Regards
Heinz! |
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| powerbecker |
| quote: | Originally posted by JacekPlacek
Hi !
Why nobody consider utilizing pads made of alumnium oxide ?
They are the best. Much better than mentioned one mica and silikon. I utilize them
without problems with transistors when one looses over 40W.
Regards
Jacek |
These parts are indeed interesting.
But as already mentioned it is near impossible to get it.
Long years ago I got some samples from a manufacturer from USA (name ?) and I remember they should withstand 500V !
They consist of a 1mm Al panel witch was on both sides covered with a special hard anodic oxidation, which differs much from the normal anodic oxidation!
I found only one company in Germany which can produce this kind of oxidation but it was too expensive!
Does anyone know this kind of isolators and know where to buy nowadays?
Regards
Heinz! |
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| johndiy |
ive also found that mica+heatsink grease have lower thermal
resistance then silicon washers but they wont last as long
as the silicon washers, i dont know why that is, i guess there
is some cheap mica and grease around that contributed to
these findings-inconclusive related to quality
regards
john |
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| JacekPlacek |
| quote: | Originally posted by powerbecker
These parts are indeed interesting.
But as already mentioned it is near impossible to get it.
Long years ago I got some samples from a manufacturer from USA (name ?) and I remember they should withstand 500V !
They consist of a 1mm Al panel witch was on both sides covered with a special hard anodic oxidation, which differs much from the normal anodic oxidation!
I found only one company in Germany which can produce this kind of oxidation but it was too expensive!
Does anyone know this kind of isolators and know where to buy nowadays?
Regards
Heinz! |
Hi ! Do You really need pads based on pure AL ? What about mentioned by me pads based on pure Al2O3 ? If You are interested , go to Polish site www.tme.com.pl ( german and english languages supported as well ). There are few types of Al203 pads in different shapes with cost no more than 1.5 Euro. I checked today and they are on stock. I do not know if TME do exports packages :( but check it.
Regards
Jacek |
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| jacco vermeulen |
www.diyaudio.com/forums/showthread....7532#post777532
Avid Thermalloy AL2O3s, thanks to the help of Mark Gulbrandsen.
Cut to size with a diamond blade.
Much better than Mica, Kapton, Bergquist K-10 samples.
Or any other silicone pad/sheet i've tried in 20 years time, starting with the 0.25mm V6245 silicone sheet i bought at Bürklin for $45.
(700 watts from 24 devices, with <0.1 C/W on an MT200 device) |
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| EUVL |
Thermal conductivity of Aluminium oxide is 18W/m/°C.
Thermal conductivity of Aluminium nitride is 180W/m/°C.
But they usually come in 1mm thickness, 0.5mm perhaps if you are lucky. And because they are rigid, you still need a grease (or arctic silver, or Aavid Ultrastick, or .....) to fill the gaps on both sides of the insulation to transistor / heatsink. Which increases the thermal resistance.
You may therefore consider this :
Keratherm 86/90
www.kerafol.com
http://kerafol.de/jml/pdfdocs/therm...0er_serie_e.pdf
Thermal conductivity 10W/m/°C (no big deal).
Standard thickness 0.1mm (hence factor of 5 better than 1mm Al2O3).
It is flexible (to an extent) like Silpad, so no need for additional thermal compound.
Datasheet too large to attach, unfortunately.
And a bit tricky to use (fragile to handle). Be warned.
Cheers,
Patrick |
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| jacco vermeulen |
Patrick,
interesting stuff.
Any idea of a corporate distributor of Kerafol products in Deutschland ? (can't seem to find any on their website) |
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| lineup |
| quote: | Originally posted by jacco vermeulen
Thermalloy AL2O3s,
......
Much better than Mica, Kapton, Bergquist K-10 samples.
Or any other silicone pad/sheet i've tried in 20 years time, starting with the 0.25mm V6245 silicone sheet i bought at Bürklin for $45.
(700 watts from 24 devices, with <0.1 C/W on an MT200 device) |
jacco is right
Aluminium Oxide has got low thermal resistance!
It is not as easy to use as silicon sheets or pieces.
For AlO You have to use correct amount of thermal grease on both sides.
A compromise would be to use some silicone sheets for lower power applications
and use Aluminium Oxide bricks for High Power major projects
like Class A, where heating is really a factor.
http://www.elfa.se/en/
• Electromechanics/Pneumatics
•• Heatsinks
••• Installation accessories
http://www.elfa.se/elfa-bin/lt.pl?l...1474382&1474386
Thickness is 3 mm and for TO-220 1.5 mm.| quote: | Manufacturer: Austerlitz
Aluminium oxide washers have a significantly lower thermal resistance than both mica, kapton and silicone rubber. The insulation voltage is also lower. Thickness: 3 mm for ALO-3 and ALO-P3-3, and 1.5 mm for ALO- 220.
Thermal resistance: <0.3 °/W
Isolation voltage: 30 kV
Temperature resistance: >400 °C |
lineup
audio knowledge bank |
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| EUVL |
> Any idea of a corporate distributor of Kerafol products in Deutschland ? (can't seem to find any on their website)
Just call or email them direct. They'll tell you who to contact.
Patrick |
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| powerbecker |
| quote: | Originally posted by JacekPlacek
Hi ! Do You really need pads based on pure AL ? What about mentioned by me pads based on pure Al2O3 ? If You are interested , go to Polish site www.tme.com.pl ( german and english languages supported as well ). There are few types of Al203 pads in different shapes with cost no more than 1.5 Euro. I checked today and they are on stock. I do not know if TME do exports packages :( but check it.
Regards
Jacek |
Jacek,
dziekuje bardzo for the link but this is not what I look for, because that´s pure Al2O3!
This I can get in Berlin laser cut with a thickness of 0.635mm.
But anyway thank You for this link, because my 2. home is at Wroclaw I am always interested about polish electronic traders!
Please can You give me a link to polish electronic magazines?
Regards
Heinz! |
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| powerbecker |
| quote: | Originally posted by EUVL
Thermal conductivity of Aluminium oxide is 18W/m/°C.
Thermal conductivity of Aluminium nitride is 180W/m/°C.
But they usually come in 1mm thickness, 0.5mm perhaps if you are lucky. And because they are rigid, you still need a grease (or arctic silver, or Aavid Ultrastick, or .....) to fill the gaps on both sides of the insulation to transistor / heatsink. Which increases the thermal resistance.
You may therefore consider this :
Keratherm 86/90
www.kerafol.com
http://kerafol.de/jml/pdfdocs/therm...0er_serie_e.pdf
Thermal conductivity 10W/m/°C (no big deal).
Standard thickness 0.1mm (hence factor of 5 better than 1mm Al2O3).
It is flexible (to an extent) like Silpad, so no need for additional thermal compound.
Datasheet too large to attach, unfortunately.
And a bit tricky to use (fragile to handle). Be warned.
Cheers,
Patrick |
Patrick,
thank You for this link!
0.1mm near pure Al2O3 is REALLY interesting!
BTW kerafol call for pure Al2O3 also 24W/m/K.
Regards
Heinz! |
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| GeorgeBoles |
Evening All,
1. I was under the impression that Artik Silver was conductive rather than non-conductive. Can anyone verify one way or t'other, please.
2. Is the silicone goop conductive or non-conductive. I have only finished one power amp requiring insulation of output devices so far, and it sent me absolutely spare trying to ensure that there was no grease contacting front and back surfaces of the mica, and yet still have lots of grease to ensure good contact. I was using a silicon grease, I think ... came with a kit!)
Was I wasting my time??
Regards,
George. |
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| KBK |
How expensive are those oxide insulators?
I remember speaking with a designer (we were sharing cool ideas) of $80K+ items. I had found a item for use in their circuitry that would be 1/4 of the price of what he was paying... for 4x the performance. There were literally 100's of these items in this piece of gear. In the end, after he knew that the new part was superior, he refused. He explaind that his pricing was a factor of costs,and he's have to lower his prices..and make less per item.
I think these are likely to be 'de riguer' for high end amps. :p |
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| GD3 |
Here's an idea
On a flat anodized surface, I mounted some TO-220's directly using automotive RTV as an adhesive. This was in a case where I had no pre-drilled holes for screw mount.
I don't have any data or measurements, but the thin layer (pressure applied while it cured) of silicone that remained after most of it oozed out appears to work well. As long as there are no burrs to pierce the anodizing.
Also, here's a cleaning tip: White silicone goop is easily dissolved with WD-40
In a severe pinch, I've even used it to revive dried goop on an old part... |
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| awpagan |
| quote: | Originally posted by GeorgeBoles
Evening All,
1. I was under the impression that Artik Silver was conductive rather than non-conductive. Can anyone verify one way or t'other, please.
2. Is the silicone goop conductive or non-conductive. I have only finished one power amp requiring insulation of output devices so far, and it sent me absolutely spare trying to ensure that there was no grease contacting front and back surfaces of the mica, and yet still have lots of grease to ensure good contact. I was using a silicon grease, I think ... came with a kit!)
Was I wasting my time??
Regards,
George. |
apparently capactive
http://www.arcticsilver.com/as5.htm
I would like to know if anyone has tried it i audio applications.
and of any suggestions
allan |
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| jacco vermeulen |
| read LGreen's posts. |
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| anatech |
Hi GD3,| quote: | | In a severe pinch, I've even used it to revive dried goop on an old part... |
Don't do that.
Don't even recommend it. :nownow:
-Chris |
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| Stocker |
If you have your devices are mounted directly to a smooth anodized surface, that is great, and will be much better than, say, a bead-blasted surface for thermal transfer. But the surfaces will still not be perfectly mated and the junction will be LOUSY. One of our members polished his heatsink to a mirror finish and looked at it under a microscope and it was still full of scratches.
http://www.koolance.com/technical/cooling101/002.html
http://www.coolermaster.com/index.p...etail&serial=56
Even "smooth" parts need a thermal interface material. Goop is easy, silpads are easiest. Phase change material like the stuff by Aavid Thermalloy is both easy and much better than both the materials mentioned above.
If you already have an electrical insulation with your anodized heatsink... I still have lots of powerstrate available, cheap...
But if you don't want that, PLEASE! don't use 'reconstituted' heat sink grease! you'd be way better off going to ebay and spending a few bucks.
My recommendation to everyone: at some point you most certainly WILL wish you had some sort of thermal interface material to go on your project in the middle of the night when the electronics store is closed.... get some. Mica, Aluminum-whatever, silpads, powerstrate, or even a small tube of grease. Get Something! You will *never* regret having it just laying around. ! |
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| anatech |
Hi Stocker,
Yes.
Well said.
-Chris |
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| GD3 |
You guys take things way too seriously. This is an enthusiast forum, not mil-spec/medical applications.
I never meant to imply that "reconstituted" goop is ideal or even recommended. In my case, it got me by in a pinch while I was troubleshooting a piece of gear and didn't have all my supplies handy.
And if your design depends so critically on thermal transfer, I would follow a previously posted suggestion to spread the load over multiple devices. In certain cases, (like bipolars, not sure for FET's) it can result in better gain linearity and lower noise anyway. |
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| JacekPlacek |
| quote: | Originally posted by GD3
You guys take things way too seriously. This is an enthusiast forum, not mil-spec/medical applications.
I never meant to imply that "reconstituted" goop is ideal or even recommended. In my case, it got me by in a pinch while I was troubleshooting a piece of gear and didn't have all my supplies handy.
And if your design depends so critically on thermal transfer, I would follow a previously posted suggestion to spread the load over multiple devices. In certain cases, (like bipolars, not sure for FET's) it can result in better gain linearity and lower noise anyway. |
People do not know when to stop. :) On other forum some guys discussed whether TXCO with 1ppm is enough good to upgrade clock in CD. :))) I think that if they were able to get clock components utilized by GPS systems or cesium oscilator they would still say about improvements in sound quality of upgraded CD player.
Best regards
Jacek |
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| EUVL |
> People do not know when to stop.
Please let us know whether you have done any measurement for a TO3 or TO247 transistor dissipating ca. 30W to a heatsink, how much temperature there is between the transistor case and the heat sink; i.e. how much temperature rise along is due to the mica / goop / silpad / ... or whateverelse in between.
Best regards,
Patrick |
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| JacekPlacek |
| quote: | Originally posted by EUVL
> People do not know when to stop.
Please let us know whether you have done any measurement for a TO3 or TO247 transistor dissipating ca. 30W to a heatsink, how much temperature there is between the transistor case and the heat sink; i.e. how much temperature rise along is due to the mica / goop / silpad / ... or whateverelse in between.
Best regards,
Patrick |
Patrick, I have not done any measurements excluding my hands or rather fingers :)
I utilized Al2O3 after bad experience with mica and silicon pads but my case was "difficult". I build ( works for two years so far without any problems ) amplifier with output pair transistors in TO247 case, which both dissipate 80W power to one heatsink
on "good day" ( class A )
The base is to have proper heatsink designed to disappated power and one should not save the money for not efficient thermal pads. It is really low cost in comparison to whole project.
Best regards
Jacek |
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| EUVL |
You said for yourself that you had bad experience with Silpad and Mica. It does not really matter whether you dissipate 80W and 30W per transistor. The physics is the same. People here at the Pass forum build Class A amps, so they have enough heat to get rid of.
If you look at the entire thermal chain (from transistor substrate to heatsink), then you would realise that there are 3 major contributors to thermal resistance :
1) Substrate to case (in the order of 0.8°C/W/transistor, as supplied, nothing you can do about);
2) Heatsink (assume 0.2°C/W/transistor, and 4 transistor per heatsink, then also 0.8°C/W/transistor, can be improved but costs a lot of money and space);
3) Insulation between case and heatsink.
For point (3), let say we stick to simple solutions. It does not take much effort to calculate that for a typical TO3 ot TO247 package, a single piece of mica plus 10µm of grease on each side, or a standard silpad, the temperature rise for 30W of dissipation per transistor is in the order of 12°, or 0.4°C/W/transistor.
The sum of the entire thermal train would then be something like 2°C/W. And you can easily reduce this by some 20% with minimum attention to just the choice of insulator. This is much much easier and more cost effective than changing to a larger heatsink.
Of course there are more tricks to get it even further down. But that is another story.
So to response to your comment, I, for one, know where to stop - that is when the thermal resistance across the insulator is less than 5% of the total thermal resistance.
Patrick |
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| jacco vermeulen |
Aluminium oxide insulators were already made and sold 20 years ago, but the only place i knew where to get them was Germany.
At Bürklin in Düsseldorf they were called Al2O-2 back then, AOS types.
You had silicone insulators back then as well, 0.25mm and twice the thermal resistance of the 3mm thick aluminium oxydes for a TO3.
Nowadays availability may be better but still difficult to obtain for many.
The Al2O3s i got from the US are much thinner. For big Japanese devices the nominal gain by obtaining even lower thermal resistance insulators may not be spectacular.
Insulator material with a lower thermal resistance rating AND an easier way to cut it to size for Japan devices than AL2O3 is however.
For TO247s i'd say it is definitely worth gaining 5 Cs or more by using SOTA insulator stuff. |
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| anatech |
Hi GD3,| quote: | | In my case, it got me by in a pinch while I was troubleshooting a piece of gear and didn't have all my supplies handy. |
I've had to service plenty of amplifiers where the heatsink and insulator where not cleaned and freshly greased. I've even seen chunks missing from insulators.
Fix it right, or don't fix it at all. If the repair gets the show going, then do it right, after the show. 99% of the guys won't.
Don't kid yourself, if you don't repair an amp properly, it will break down again. "Close enough for rock & roll" is the dumest phase I've ever heard. Rates right up there with "don't worry about it".
-Chris |
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| JacekPlacek |
| quote: | Originally posted by EUVL
You said for yourself that you had bad experience with Silpad and Mica. It does not really matter whether you dissipate 80W and 30W per transistor. The physics is the same. People here at the Pass forum build Class A amps, so they have enough heat to get rid of.
If you look at the entire thermal chain (from transistor substrate to heatsink), then you would realise that there are 3 major contributors to thermal resistance :
1) Substrate to case (in the order of 0.8°C/W/transistor, as supplied, nothing you can do about);
2) Heatsink (assume 0.2°C/W/transistor, and 4 transistor per heatsink, then also 0.8°C/W/transistor, can be improved but costs a lot of money and space);
3) Insulation between case and heatsink.
For point (3), let say we stick to simple solutions. It does not take much effort to calculate that for a typical TO3 ot TO247 package, a single piece of mica plus 10µm of grease on each side, or a standard silpad, the temperature rise for 30W of dissipation per transistor is in the order of 12°, or 0.4°C/W/transistor.
The sum of the entire thermal train would then be something like 2°C/W. And you can easily reduce this by some 20% with minimum attention to just the choice of insulator. This is much much easier and more cost effective than changing to a larger heatsink.
Of course there are more tricks to get it even further down. But that is another story.
So to response to your comment, I, for one, know where to stop - that is when the thermal resistance across the insulator is less than 5% of the total thermal resistance.
Patrick |
Did You experiment with one transistor dissipating about 40W when heatsink became 70-80 degree centigrade warm ? I did.
Silicon pads I had ( not only one sample ) after dismounting looked like slightly burnt. This is my experience maybe other people have better results. What concider Pass clones take into account that original solutions have pair or even more ( up to six ) transistors connected paralely. I have one transistor . These are much more lighter conditions for transistors ( and pads too ) than in my case ( locally transistors do not have to dissipate so much power in time unit than my transistors have to ) and main factor then is not only thermal resistance but thermal conductivity that was discussed earlier by me and other people.
Regards
Jacek |
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| EUVL |
> Did You experiment with one transistor dissipating about 40W when heatsink became 70-80 degree centigrade warm ?
For your reference, my Class A amp has 12x TO247's each dissipating 34W with heatsink temperature at 70°C, as measured and agreed to calculated value to within 2°C. It has been running for about half a year. I have not had any burnt insulators or short circuits, as yet.
And of course I have also tried mica, silpad, Al2O3, Aluminium nitride, kapton, and various types of Kerafol before finalising my thermal concept, before building.
> main factor then is not only thermal resistance but thermal conductivity
Isn't thermal conductivity = 1 / thermal resistance, or you have a different definition ?
Patrick |
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| jacco vermeulen |
| quote: | Originally posted by EUVL
heatsink temperature at 70°C |
Patrick,
just for the record, what is the temperature of the TO247s ? |
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| Stocker |
| quote: | Originally posted by anatech
If the repair gets the show going, then do it right, after the show. 99% of the guys won't.
-Chris |
Nevermind won't, how about oops I forgot. I couldn't tell you the number of times I did a quick-fix and moved on, forgetting it wasn't 100%.
As far as going too far goes, how about this:
**No interface material: 1, maybe 2 degrees C/W
**Powerstrate: 0.008 degrees C/W
To me, that's hardly splitting straws. More like burning the hayfield. The difference between interface materials when everything is way overbuilt beyond worst-case scenarios may not mean much besides slightly shorter semiconductor life. If the design is constructed according to ideal numbers, it may be the difference between an explosion/fire and perfect operation. |
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| anatech |
Hi Stocker,
All thermal calculations are best case with properly applied interface materials. That also means not overtightened. ;)
You're bang on the money though. If you need special interface materials, and it isn't high voltage, your design is defective. Add that extra transistor.
-Chris |
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| EUVL |
> just for the record, what is the temperature of the TO247s
72 degC case temperature, as measured, sir.
(Substrate temperature would be an additional 27 degC on top, i.e. about 100 degC.)
Patrick |
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| meanman1964 |
What about kapton isulators?
look at www.thel.de |
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| EUVL |
Kapton has a thermal conductivity of 0.37W/m/K.
You can compare that with the values in Post #51.
Patrick |
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| EUVL |
There are Kapton & there are Kapton.
Kapton MT, which is a thermally conductive variant, has 0.37W/m/K.
http://www.dupont.com/kapton/products/H-38497-1.html
In any case 30x worse than Kerafol. But of course one can compensate by using 30 times thinner foils, in this case it would be 3 microns ! Just need to make sure heatsink and transistor are also better than 0.1 microns flat, and do not deform under temperature. Minor details, shall we say.....
: )
Patrick |
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| meanman1964 |
| By Thel-Audio they use the kapton isulators for their projects,that's whij I think you can use them.Or am I wrong? |
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| EUVL |
There are people (amateurs as well as professionals) who use mica, silpad, kapton, aluminium oxide, ........ As long as you know how to calculate, and you are happy that the lifetime of the transistor is not compromised, you can use what you want; just like some people use large heatsinks, some use forced convection, some water cooling ..... The choice is all yours.
The world is a wonderful place because of all these varieties. I merely tried to draw your attention to another. The only recommendation I would make is to understand the physics behind (no rocket science), and then choose the solution for yourself, be it large heatsinks, exotic insulations, ......
And if I am not wrong, Thel's power amps are class AB. So he doesn't have too much dissipation to worry about.
Patrick |
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| john_ellis |
Hi all
I've just installed boron-nitride washers on my latest 100 Watter - and so far the transistors (TO-3) run pretty cool.
Previously I've used mica and grease, and silicon never seemed to be quite as good. Mica+grease is typically rated at 0.4 C/W, silicone washers are supposed to be the same but seem to be not quite so good (but I have not actually measured them).
Stated performance of the boron nitride loaded silicones are 0.2 C/W. I'd say that they are performing better than the mica; but as Nelson P said, they can split and only seem to work once.
But they also cost half the price of the transistor!
cheers
John |
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| Stocker |
| quote: | Originally posted by EUVL
Minor details, shall we say.....
Patrick |
haha, minor! 1 micron small, minor! Funny! :D
| quote: | Originally posted by EUVL
There are people (amateurs as well as professionals) who use mica, silpad, kapton, aluminium oxide, ........ As long as you know how to calculate, and you are happy that the lifetime of the transistor is not compromised, you can use what you want; just like some people use large heatsinks, some use forced convection, some water cooling ..... The choice is all yours.
Patrick |
Well said.
If we could all agree that the other fellow's solutions were (maybe almost) as good as our own and at least good enough, there would be much shorter and less interesting threads. ;) |
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| meanman1964 |
| I'am planning to build the Aleph30,so what should I use for isulator? |
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| EUVL |
http://www.diyaudio.com/forums/show...023#post1032023
For those living on the Continent, Keratherm is now available from www.conrad.de.
E.g. Part no. 189058-29 Keratherm 86/82 190x190x0.25mm
Thermal conductivity 6.5W/mK
Patrick
Disclaimer : I have absolutely no business dealing nor financial interest with the company who produces the stuff !! |
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| nonoise |
Another good grease Laird (use to be Thermagon) T-grease 880
3.1W/mK
Another interesting material is graphite T-gon 800
Also a often overlooked parameter is the optimal pressure on the thermal interface |
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| anatech |
Hi All,
Well, all I can say is that mica and thermal compound are consistent performers. The other types are normally used to increase manufacturing efficiency. I am not a fan of alternative insulators. They have "gottchas" it seems. I have seen many fail in service.
Last point. Watch out for conductive grease! Graphite and other electrically conductive compounds should be avoided. Why tempt fate?
-Chris |
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| awpagan |
Good point Chris.
I do use mica and the goop together
Any kind of goop just by itself, i couldn't trust, or trust myself to correctly apply it.
allan |
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| anatech |
Hi Allan,
The best device I have found so far to apply thermal compound is a #2 artists brush, flat about 1/2" wide. Go to the nearest art supply store. I've worn out two so far and cracked one.
-Chris |
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| Nelson Pass |
Around here we call it Beauty Cream :)
I just dip my fingers in the jar and smear it on. I personally
don't find the pre-applied micas to have a generous enough
amount, although it's true that I have to leave my output stages
horizontal for a few days or it drips.
:cool: |
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| anatech |
Hi Nelson,| quote: | | I just dip my fingers in the jar and smear it on. |
LOL!
I won't let my guys do that. You know grease travels and makes a mess. Also, I don't want the stuff contaminated (8 oz jar). The artists brush naturally leans towards a thin coat that just beads around the insulator when it's torqued down. Just right.
So Nelson, what do you use to get it out from under your finger nails?
-Chris |
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| anatech |
Hi Grey,:confused:
-Chris |
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| GRollins |
Every so often I do a search on my own name just to see if I missed a question directed at me. This is one such time. I'm a bit late answering, but better late than never.
Gojo is a creamy waterless hand cleaner that will remove virtually anything from your hands. No, it's not harsh. In fact, I believe it has lanolin in it. It's readily available here in the US, but perhaps not elsewhere in the world.
Grey |
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