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Proper group for heatsink question?

To be fair, I indicated that the OP should post more detailed info ( which certainly needn't have encroached on an NDA ) or 'shut up'.

It seems that you too have come to the same conclusion that the enclosure in which this IC is to be installed is the limiting factor.

I despair sometimes at the poor level of practical skills in engineering exhibited today - and especially by 'academics'. A basic understanding of heat flow would have fixed this.

Something this simple should have been considered at the beginning. Leaving ' thermal manageent ' to the end is begging for failure. And sadly it looks like failure is the conclusion here.

Graham

Reply to
Pooh Bear
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On a related question, what's your opinion of thermal paste vs. silicone pads vs. mica vs. aluminum nitride or any other conductive ceramic, with or without paste?

I'm interested in putting a half bridge of 600Vceo IGBTs on the same heatsink (which will be copper, if I can cast and machine a slab suitably :).

Tim

-- Deep Fryer: a very philosophical monk. Website:

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Reply to
Tim Williams

Just a note of caution: You may run across BeO (beryllium oxide) touted as a good heat sink material. No doubt, but be aware that the stuff is incredibly toxic if you get it into a cut, breathe dust, etc. The manufactured ceramic pieces are probably not a serious danger (compared to the raw metal or powdered oxide), but not something to mess around with as a prototype. No filing, grinding, etc, and handle it with care. Personally, I'd avoid it if at all possible.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Home of DaqGen, the FREEWARE signal generator

Reply to
Bob Masta

AlN is almost as good as BeO. Both should be used with filled silicone paste. The problem with any insulator is its thickness... thermal resistance is proportional to thickness, and it's hard to beat the 100 micro-inches of just silicone grease.

I like to mount an electrically hot semoconductor directly to a copper heat spreader, and insulate *that* from the main heatsink. You can increase the effective thermal footprint of the part many-fold.

Lateral heat spreading on a heatsink is a much-ignored issue, and a spreader helps here, too.

John

Reply to
John Larkin

Ah yes, good point! But where do you get insulators for the nonstandard footprint? Machinable AlN? Somehow I doubt that. :(

Tim

-- Deep Fryer: a very philosophical monk. Website:

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Reply to
Tim Williams

One way is to hard-anodize the main heatsink, and the spreader as well if it's aluminum. Then just use grease or epoxy. 0.001" of hard anodize, chemically Sapphire, is a reliable insulator up to, say, 200 volts, and has a low thermal resistance.

You can buy AlN in slabs, cut to order, if you have modest quantities. I haven't tried to machine it myself, but I'd bet you could work a thin slab with a Dremel.

Or, bond the spreader to the main sink with thermal epoxy, using tiny bits of mylar or monofilament as spacing shims, or load the epoxy with just a dash of Cataphote glass beads to enforce spacing before it cures.

Even better, don't insulate the semiconductor, insulate the entire heatsink!

John

Reply to
John Larkin

Does "attaching" mean you need an adhesive, as well as thermally conductive compound?

Look at:

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--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
                                             (Stephen Leacock)
Reply to
Fred Abse

Of course, the simplest approach for standard items like IGBTs is to buy parts that are already electrically insulated, then just use silicone grease. I haven't checked out if the insulated parts have higher thermal resistance than their hot counterparts, but they sure are a snap to use!

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

formatting link
Home of DaqGen, the FREEWARE signal generator

Reply to
Bob Masta

I would love to have a 600V, 100A, high speed, half bridge IGBT module, but a quad of 600V, 50A, TO-247's was cheaper ($44 from Allied, saved 10% vs. Digikey!).

Tim

-- Deep Fryer: a very philosophical monk. Website:

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Reply to
Tim Williams

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