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January 1999

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Tue, 5 Jan 1999 13:44:04 -0600
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Love the way you think. Some don't bother at all.

Look at it this way: Heat pipes are neat because they self generate air movement. That is, when a
"pipe" is free to conduct or convect heat, it does it more efficiently, right? Once air is heated,
it wants to move, no matter the direction. It's like the "Servel" principle but a little different.
With Freon, heating it causes it to compress, move, condense, and do its thing. It's the same with
air but, of course, heated air likes to move up. No matter, it wants to move.

There are some products out there that are said to enhance thermal transfer and motion. Some of
them we use, or overuse, to bond or more closely couple heat sinks to components. Often, we use to
much of the stuff and reverse the process making the adhesive an insulator.

In the good old days, we used open heat pipes (plated holes) connected directly to internal cores
as constraining and thermally conductive. I still use the same principle. Attached is a pretty/ugly
picture of a 10 oz copper plane sandwiched inside an 8 layer board with heat pipes doing what they
do best. Unfortunately, the board fabricator for this PCB didn't understand or manage the
lamination process well. I did much better, of course.

Let me know how it goes as you begin measuring the thermal transfer capabilities of your designs
and boards.

Earl Moon

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