Everything You Know Is Wrong August 2002

Answers to those Doggone Thermal Design Questions

By Tony Kordyban

Copyright by Tony Kordyban 2002

Dear Thermal Wizard,

I have been in the electronic packaging game for about 5 years.  In college they taught me calculus and strength of materials and dynamics, so naturally my first job was drawing cable harnesses.  Now that I am pretty good at that, my boss wants me to start doing thermal analysis.  My company doesn’t have a “thermal guru”,  so there is nobody here to learn it from.  Luckily I have six weeks to figure this thermal stuff out before I begin my new assignment.  Is there a “Cooling Electronics for Dummies” book or seminar that could help me?

D. Gale from Kansas


Dear Dorothy,

Six weeks to become a certified Electronics Cooling Dummy?

I admire your ambition, and I welcome you to the field of Electronics Cooling.  As a beginner in it, you are not alone.  Many of the fine men and women in this field were thrown into it with no preparation whatsoever, and some of them against their will.  They were working on an electronics project, were confronted with a thermal problem, and there was no one else to solve it, so they did the best they could.  That’s what engineering is like, I guess.

I don’t have much patience or admiration for your boss, and the myriad like him, who think they can create an instant thermal expert by sending you to a short course or giving you a book to read.  Electronics Cooling is not for “dummies.”  There is no “cookbook” for it, either, because of the very nature of a cookbook.

What is in a real cookbook?  Recipes for pork chops and salads and cakes.  They work because you are doing something that has been done before, thousands of times.  If you follow the steps, you will get the same pork chop the chef/author did.  It instructs you how to do the same thing over and over to get the same result.  It doesn’t teach you how to create new dishes.  In the electronics business, you don’t develop the same products over and over.  Each new product is supposed to be different — even better, maybe — than the last one.  Or at least better than the competitor’s product.  The products are always changing, and presenting new thermal challenges.  You can’t solve them by following a recipe.

There is a draft of a thermal cookbook in my files.  I don’t look at it much, because it gives advice such as how to solder a thermocouple to the lead of a 16-pin DIP.  Some engineer had written down the steps he had done on his last couple of projects, assuming they might be useful in the future.  But his attempt quickly become outdated.  What that cookbook lacked were any general principles of heat transfer that might be useful for a long time.  That’s why you’ll have a hard time finding a “Thermal for Dummies” book.

Having said that, there are several textbooks available that deal specifically with electronics cooling.  (I listed some of them last year in my column.)  My favorite is still Gordon Ellison’s Thermal Computations for Electronic Equipment.  Unfortunately, it is out of print.  Maybe you can find it on ebay or at a good university library.

You should buy one or two of those texts.  They will come in handy later.  They are good as references, but I seriously doubt that you could sit down and just read them yourself and come away with a good enough understanding to start working in the field.  Not that the books are not poorly written.  But before you can start to use the good information that is in them, you have a large barrier to overcome.

First you have to un-learn all the wrong things you already know about heat and temperature.  And just as with any other mental affliction, admitting you have a problem is the first step to recovery.  You have found my columns, read some of them, and even written for advice.  That qualifies you to receive the following certificate.

You remember the diploma that the Wizard of Oz gave to Scarecrow.  Scarecrow was looking for some brains, but what he really lacked was the confidence to use the smarts that he already had.  The Wizard’s diploma gave Scarecrow that confidence.

This certificate is not like that.  What you have found at the end of this yellow-brick web page is the exact opposite.  I want to destroy the confidence that you have in your own knowledge of how to cool electronics, because it will mislead you.

Print out your certificate, and spend the first of your six weeks looking at it and thinking of all the things you know about heat and electronics.  How aluminum sucks up heat like a sponge, or that you can find the junction temperature of a component using Theta j-a, and how that is WRONG!  Only after you have thoroughly convinced yourself that not only do you know nothing about heat and temperature, but that everything you did know about it was wrong, should you sign your certificate and hang it on your office wall for all to see.

Then you will be ready to begin your education.

In an ideal world (not this one), you would go back to college for a couple of years and study heat transfer and fluid mechanics at the graduate level.  Then you would work for a prosperous electronics company as an apprentice to a thermal expert for a couple of years, learning to apply your theoretical knowledge to real products in an atmosphere of deadlines and design compromises.

But you only have five weeks left.  Order your textbooks, or find them in a library.  You won’t be able to read them in less than five weeks, but you can at least read the Tables of Contents and look at the pictures to see what they cover.

Then find and attend short courses on electronics cooling.  Oh, I suppose you need me to find and list them for you, and tell you which ones are the best.  Unfortunately, I haven’t attended any short courses intended for beginners for more than 10 years, so I can’t give any personal recommendations (unless you can find Bob Moffat’s course on thermal measurement techniques).  But a quick search on google.com has yielded the following (admittedly incomplete) list of short courses:

Advanced Thermal Solutions
2-day short courses
Thermal Management of Electronic and Telecommunications Systems by MJM Engineering
TustinTechnical Institute

Maybe you can do better by googling for training yourself.  Sometimes you can find FREE training, which employers seem to favor.

It is very common for short courses to be offered when there is a conference on electronics cooling, such as SemiTherm or ITherm.  You can find a list of future conferences at www.ieee.org or www.asme.org.

Will attending these short courses and reading books make you a thermal design expert?  Are you nuts?  Of course not!  The most you should expect to get out of a two-day course is an introduction to the topic. You will learn some terminology, and maybe how to apply a few basic equations.  That will help you get started.  Then you will just have to jump in and learn by doing, just like you did when you learned how to lay out cable harnesses.

Personally, I think the “Everything You Know About Cooling Electronics Is Wrong” certificate will be more valuable to you than the ones you earn at short courses.  But only if you truly take it to heart.


Isn’t Everything He Knows Wrong, Too?

The straight dope on Tony Kordyban

Tony Kordyban has been an engineer in the field of electronics cooling for different telecom and power supply companies (who can keep track when they change names so frequently?) for the last twenty years.  Maybe that doesn’t make him an expert in heat transfer theory, but it has certainly gained him a lot of experience in the ways NOT to cool electronics.  He does have some book-learnin’, with a BS in Mechanical Engineering from the University of Detroit (motto:Detroit— no place for wimps) and a Masters in Mechanical Engineering from Stanford (motto: shouldn’t Nobels count more than Rose Bowls?)

In those twenty years Tony has come to the conclusion that a lot of the common practices of electronics cooling are full of baloney.  He has run into so much nonsense in the field that he has found it easier to just assume “everything you know is wrong” (from the comedy album by Firesign Theatre), and to question everything against the basic principles of heat transfer theory.

Tony has been collecting case studies of the wrong way to cool electronics, using them to educate the cooling masses, applying humor as the sugar to help the medicine go down.  These have been published recently by the ASME Press in a book called, “Hot Air Rises and Heat Sinks:  Everything You Know About Cooling Electronics Is Wrong.”  It is available direct from ASME Press at 1-800-843-2763 or at their web site at http://www.asme.org/pubs/asmepress,  Order Number 800741.