Home made heat sink pads

Cut a piece off a mylar potato chip bag. Mylar doesn't melt easy. You're only using 12 volts, so super-thin chip bag mylar is perfect. Assuming it really is mylar. A commonly used dielectric. I have some mylar sheet I use for insulators, but it's thicker than chip bags. I can tell you, that stuff doesn't melt easy.

On Thu, 28 Dec 2006 09:20:19 +1100, "Phil Allison" Gave us:

Wrong. The creepage distance for 3 to 6kV is too far for the leads and package bodies of most of the devices they cover. Regardless of what it may take to pierce the pad, the application won't work without arcing at those potentials. They list their breakdown Voltage at 3500 to 4500 volts for their original product. The problem is that no unencapsulated circuit could operate at those voltages unless the pad were several millimeters larger than the device footprint.

The word for today is "CREEPAGE".

The electrical kind.

You're just a CREEP of the net kind.

The regular Dow Corning thermal grease must have some very small fill particles. With just modest pressure, I've measured its added spacing at below 100 microinches (0.1 mils), which is the limit of the micrometer I had at hand. It flows out of the gap. Right, it's not a very good thermal conductor, but it does squish out very thin... a sil-pad may be 50-100 times as thick!

Grease over flat, 0.5 mil hard anodize is about as good as it gets.

The sil-pad looking phase-change films I've tried are terrible because they don't squeeze out thin. The wax/crayon things might, but I'd be worried about air pockets. Silicone grease is messy but it sure works.

Eeyore is technically sound, ignoring politics.

John

On Wed, 27 Dec 2006 19:10:36 -0800, John Fields Gave us:

Trying to show your mettle, eh?

(Let me re-phrase that)

Trying to show your metal, eh?

Trying to show your meddle, eh?!

Heheheh :-]

On Wed, 27 Dec 2006 17:50:56 -0800, John Larkin Gave us:

Yep. Shame that we can't get a good high dielectric strength yet highly thermally conductive thin film of something to bond with copper. It conducts heat better than Al, IIRC (not gonna bother to google it, I'm sure I'll get chastised if I err).

Oh, yeah, that silver filled stuff the CPU tweak hounds use is awesome stuff too, and they HAVE done lots of recent research and testing!

Try "Tom's Hardware" for reports about thermal compounds.

"JoeBlow It Out His Arse F*****AD "

- YOU ASININE CUNT HEAD

........ Phil

Have you looked at aluminum nitride? It's almost as good as BeO but it's not toxic. For high-voltage and high thermal density, I'd go for a non-insulated copper heat spreader over an AlN insulator, all greased... if you can stand the capacitance!

I think BeO has the best ratio of thermal conductivity to dielectric constant, except for diamond. Or flowing distilled water.

John

John Larkin *is* an expert. I'm sorry if that is painful for you, but you would do well to listen carefully to what he has to say.

Ed

You really don't know how to use newsgroups, do you? You just wade in, insulting people randomly just because they don't agree with something you read on a webpage somewhere (and remember, despite being pretty flame-proof, John et.al. are *real* people - would you talk like that face to face?).

If you had bothered to do your homework, you'd have read some threads here for a while, so you know who you are talking to - John really is an expert at this stuff (as is Eeyore, and others in this thread), and I'd count his opinion above a random webpage any time. It's lucky for you that he and others find the problem interesting, and are therefore discussing it despite your attitude.

On Wed, 27 Dec 2006 18:13:08 -0800, John Larkin Gave us:

I'll bet the winner is still plain old mica.

For liquid try fluorinert. Much safer.

After reading your posts in this thread, I conclude that toilet paper would serve your purpose.

No, you're being a dork, and people are noticing, and starting to ignore you.

Like I said before, you might eventually find someone who will tell you what you want to hear, but probably not as long as you're being such an insufferable, petulant, whining brat.

Good Luck! Rich

I've still got a tube of DC-340 (or maybe 320 - I don't remember exactly) that I lifted when I was in the USAF in the 1970's; I'll swear by the stuff. Whenever I replace a MB/CPU/heatsink I wipe off the goo that comes with the heatsink and use my good ol' trusty Dow Corning, that's how much I trust it.

I wonder if it would make good sunblock? ;-)

Cheers! Rich

As long as there isn't a metal burr to puncture the paper and the device isn't tightened to the point where it can make a compression cut it should work.

Some old mica windows from kerosene heaters can be cut to make insulating pads - mica conducts heat well (still need silicone grease because it isn't perfectly flat).

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I just dissected a Lays Classic 250gm potato chip bag. It measured 2 mil thick and was composed of several layers.

The two outside layers appeared to be mylar, approximately 500 microinches thick. There was a thin layer of paint, a super-thin layer of metallization, and the rest was a layer of soft polyethylene that appeared to be 1 mil thick. This corresponds to a description of barrier layers in food packaging needed to keep out oxygen:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Barrier Films - An Overview

Single layer films are generally quite permeable to most gases.

Barrier films are usually multi-layer films that have been designed to be impervious to gas migration. Some common examples of barrier films will be found in any grocery store. Bags used for packaging potato chips and meat products are gas barrier bags, garbage, freezer, and sandwich bags are not. To understand the difference in practical terms, compare the longevity of a helium-filled balloon made of rubber to a balloon made of foil barrier - the rubber balloon will shrink within hours, but the barrier film balloon will continue to wish you a "happy birthday", or "get well soon" in mid-air for weeks.

Construction

Almost all gas barrier films are made of multiple layers. The outer/top layer will be a strong (usually transparent) plastic with a relatively high melting point, often made of polyester (Mylar) or polypropylene. The inner/middle layer will be the gas barrier material (see next). The inside/bottom layer is almost always low density polyethylene, which softens at relatively low temperatures.

Barrier layer materials

Most of the cross section of a barrier film is occupied by its inner (polyethylene) sealing layer. The outer support layer is often surprisingly thin, and the middle (barrier) layer can sometimes be of microscopic thickness. (Note that it is the compostion of the barrier material, and not its thickness that is most important in determining its permeability).

Metal foil (usually aluminum) is generally the most effective gas barrier material, closely followed closely by transparent ceramic barriers (Escal). Sputtered Aluminum, EVOH, barrier nylon, and saran are transparent plastic barrier layers often used in the food industry. The barrier layer of Aclar film is similar in composition to Teflon. Each specific barrier material and formulation has it's own unique barrier properties.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The polyethylene layer may mean food wrapping is a poor choice for a heat sink insulator since it melts at such a low temperature. However, Christmas wrapping may be more robust. I'm on my way to WalMart to see if they still have any on sale:)

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:

Hey John, these guys

(*) Wrongly-oriented graphite, though, is terrible.

The dielectric constant of water's pretty high though, right?

I also wonder about: a) electroplaning/polishing, for ultra-ultra-flat, smooth surfaces and b) microplasmic or other anodic coating (denser than ordinary anodize)

Cheers, James Arthur