I am planning an amp build using a pair of TO-264 devices on the output of each channel, but am having trouble finding a matching thermal pad which is not electrically conductive. Datasheets for Bergquist suggest there should be Sil-Pads of appropriate size, but I cannot seem to find them in-stock at my usual suppliers (Arrow, Mouser). It looks like the DIY Audio Store's Keratherm pads will work, but the price is rather steep.
Does anyone know of thermal pads of sufficient size and affordable price? Is it possible to make these work with careful orientation?
Does anyone know of thermal pads of sufficient size and affordable price? Is it possible to make these work with careful orientation?
Yes, those should work with the right positioning, and are made for a TO-247, which is fairly similar to TO-264.
SP900S-0.009-00-104 Bergquist | Fans, Thermal Management | DigiKey
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The 900S has 1.6C/W, while the K10 has 1.3C/W. Either should be ok,
but if there is high dissipation, use the K10. The 900S is thicker also.
You can get Bergquist Sil-pad material by the sheet. About a foot square in the $55 range. That will make a lot of TO264s. The largest TO247s are almost big enough, but not quite if you're concerned about creepage distances. They would be ok on 40 or 50 volt rails, but when you push 200+, it would be iffy.
I'll use less than 30V rails, so am not too concerned about electrical leakage. The thicker 900S may be a good idea, though, if the pads don't entirely cover the metal backing. That would give a little extra buffer space.
I have considered buying a full sheet, and may end up doing that before its over...
I have considered buying a full sheet, and may end up doing that before its over...
Better use Ceramic, Alumina Al2O3
Excellent heat transfer, indestructible and much less prone to failure then softer insulators that could be cut by the sharp edges of transistors.
See this post.
Here's a seller with TO-264
Excellent heat transfer, indestructible and much less prone to failure then softer insulators that could be cut by the sharp edges of transistors.
See this post.
Here's a seller with TO-264
Al2O3 isn't actually the best Al-based ceramic for this though, AlN is a lot better (expensive still I believe), and ceramic pads have to be much thicker to avoid breaking up into pieces, defeating a lot of the advantage of the better thermal conductivity over flexible pads.
Soft pads filled with ceramic powder are probably the way to go, conforms to contours and fills any surface texture with intimate contact, is thin and has good but modest conductivity. If you can lap the surfaces super-flat and apply even pressure then solid ceramic would be the best, but that's not really practical in most contexts. Sanding off rough edges to avoid cut-through is much more practical.
Having said that it is tempting to experiment with some of the super conductive materials (diamond pads are available for instance, way better than copper even).
Well tempting till you see the price and realize you'll need to laser-drill a mounting hole!
- But Al2O3 is much more obtainable.
AlN is the best of cause but most situation usual and popular Al2O3 suites as good.
You may possibly need AlN only for the most demanding designs.
Folks:
I know this will likely be a dumb question, but would an AI203 insulator and a thin smear of grease achieve a more ideal result? I'm running low on thermal pads and am considering my options -- Keratherm Red from the Store has been my standard, but I'm open to superior (and perhaps less expensive) solutions.
Regards,
Scott
I know this will likely be a dumb question, but would an AI203 insulator and a thin smear of grease achieve a more ideal result? I'm running low on thermal pads and am considering my options -- Keratherm Red from the Store has been my standard, but I'm open to superior (and perhaps less expensive) solutions.
Regards,
Scott
I usually use Wakefield-Vette’s CD-02-05-264 (1.05” x 0.85”, TO264, single mounting hole).
Mouser #: 567-CD-02-05-264
Always use thermal compound with alumina/ceramic pads.
With a 1mm thickness they're almost indestructible and still excellent in heat transfer, see page 25 in EUVL's article for a comparison.
I don't like the softer pads, especially with transistors that have the bolt closer to one side,
then most of the pressure is on that side and can cut through the pad, I experienced this.
I think the softer pads are more for automated installation when there's no time to mess with thermal grease.
With a 1mm thickness they're almost indestructible and still excellent in heat transfer, see page 25 in EUVL's article for a comparison.
I don't like the softer pads, especially with transistors that have the bolt closer to one side,
then most of the pressure is on that side and can cut through the pad, I experienced this.
I think the softer pads are more for automated installation when there's no time to mess with thermal grease.
No idea, I've bought the 1mm version.
I never broke one, I suppose the 0.635 will also be fine,
even if they break between the transistor and heatsink because of an uneven surface,
the transistor will still be at 0.635/1mm distance from the heatsink.
I use them in my Alpha20 amp, each transistor/TO-264 transfers 50W of heat without problems.
I never broke one, I suppose the 0.635 will also be fine,
even if they break between the transistor and heatsink because of an uneven surface,
the transistor will still be at 0.635/1mm distance from the heatsink.
I use them in my Alpha20 amp, each transistor/TO-264 transfers 50W of heat without problems.
danny_66 & Co.:
Okay, one more dumb and possibly off-topic question: I've been looking at thermal pastes and the ones that appear to have good thermal conductivity qualities (e.g., Arctic MX-4 and Arctic Silver 5, both of which seem marketed to CPU hot-rodders) apparently require periodic replacement. I was hoping for a use-it-and-never-touch-it-again solution. Am I over-thinking things?
Regards,
Scott
Okay, one more dumb and possibly off-topic question: I've been looking at thermal pastes and the ones that appear to have good thermal conductivity qualities (e.g., Arctic MX-4 and Arctic Silver 5, both of which seem marketed to CPU hot-rodders) apparently require periodic replacement. I was hoping for a use-it-and-never-touch-it-again solution. Am I over-thinking things?
Regards,
Scott
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