Between December 2000 and August 2010 these articles, packed with advice on cooling electronics, appeared in the monthly on-line magazine of CoolingZone.com.\u00a0 In response to popular demand, they have been re-formatted and collected into this convenient one-stop library.\u00a0 It begins with the opening article from December 2000, on why heat sinks never seem to work as well as you think they should, and will eventually contain every wise and wise-cracking article in the series.\u00a0 Additional articles will be added approximately every week, so if you haven\u2019t found your favorite Cooling Q&A yet, keep coming back.<\/p>\n
December 2000<\/strong><\/a> — Heat sinks are the most popular method of reducing component temperature.\u00a0 Here are four reasons why they don\u2019t work.<\/p>\n January 2001<\/strong><\/a> — Does it take any special training to enter the field of cooling electronics?\u00a0 Can the circuit board which is already there act as a heat sink?<\/p>\n February 2001<\/strong><\/a> — Does heat have \u201cinertia\u201d?\u00a0 Why does component temperature seem to overshoot when the electrical power and fan are turned off at the same time?<\/p>\n March 2001<\/strong><\/a> — Converting watts to BTUs, and is it possible (and ethical) for an IR camera to see through clothes?<\/p>\n April 2001<\/strong><\/a> — Vias in printed circuit boards conduct heat, but how much?\u00a0 What books besides his own does Tony recommend?<\/p>\n May 2001<\/a><\/strong> — As chips shrink and logic voltage goes down, isn’t cooling digital electronics actually getting easier with time? \u00a0And did Electronics Cooling save Star Trek?<\/p>\n June 2001<\/a><\/strong>\u00a0— Fan noise is getting pretty annoying. \u00a0Aren’t there any laws that can help reduce the noise? \u00a0Of course. \u00a0They’re called the Fan Laws.<\/p>\n July 2001<\/a><\/strong>\u00a0— Sometimes Something I Know Is Wrong. \u00a0The June 2001 article gave an incorrect Fan Law. \u00a0Here is another stab at it. \u00a0Plus, Do-It-Yourself Thermocouples.<\/p>\n August\u00a02001<\/a><\/strong>\u00a0— An apology to PEs. \u00a0And a tribute to the garage-and-basement pioneers of electronics cooling — The Overclockers!<\/p>\n September\u00a02001<\/a><\/strong>\u00a0— How accurately can a CFD tool like ANSYS or FloTherm predict component temperatures? \u00a0To get a handle on that you have to realize that CFD tools can’t predict temperature at all.<\/p>\n October\u00a02001<\/a><\/strong>\u00a0— How much do thermal engineers add to the company’s bottom line? \u00a0Nobody buys a laptop because it has a great new heat pipe, right?<\/p>\n November\u00a02001<\/strong><\/a>\u00a0— It’s not the heat, it’s the humidity (at least at the family reunion picnic in July in Michigan.) \u00a0Do changes in humidity have any effect on electronic component temperatures?<\/p>\n December\u00a02001<\/strong><\/a>\u00a0— There’s a thin piece of tape between your temperature probe and a hot component. \u00a0Could that tape make the temperature reading wrong by as much as 100\u00b0C?<\/p>\n January 2002<\/a><\/strong>\u00a0— Finally! \u00a0The absolute ultimate answers to the three most nagging questions in cooling electronics:<\/p>\n February 2002<\/a><\/strong>\u00a0— How come when you attach a heat sink incorrectly, it makes the component hotter, but when you attach a thermocouple incorrectly, it makes the component cooler?<\/p>\n March\u00a02002<\/a><\/strong>\u00a0— Which CFD software is the best? \u00a0And why Type J thermocouples are always the most appropriate (for me, at least.)<\/p>\n April\u00a02002<\/a><\/strong>\u00a0— How come you can’t just look up the formula for ? J-A<\/strong> in a heat transfer textbook?\u00a0 And finally the answer to the long-standing dispute: \u00a0which temperature scale is better — Celsius or Fahrenheit?<\/p>\n May\u00a02002<\/a><\/strong>\u00a0— If you know power dissipation, you can calculate temperature. \u00a0If you know a component’s temperature, does that mean you can find its power? \u00a0You’ve heard of “thermal resistance”, and maybe “thermal impedance.” \u00a0What about “thermal intransigence?”<\/p>\n June\u00a02002<\/a><\/strong>\u00a0— Legend has it that Ludwig Prandtl was fond of saying, “The longest thermal analysis begins with a single hand calculation.” \u00a0How will you begin that next electronics cooling assignment if you can’t start with hand calculations? \u00a0Here are some tricks to get you started.<\/p>\n July 2002<\/a><\/strong>\u00a0— Fans are coolers, but they can also be heaters. \u00a0Heat from the electric motor raises the temperature of the air stream. \u00a0How much of the fan’s electric power turns into heat?<\/p>\n August\u00a02002<\/a><\/strong>\u00a0— How to become a thermal guru in six short weeks (maybe less), the Wizard of Oz way.<\/p>\n September\u00a02002<\/a><\/strong>\u00a0— Are suppliers of Thermal Interface Materials exaggerating their thermal performance?<\/p>\n October\u00a02002<\/a><\/strong>\u00a0— You can use a chimney to cool your electronics, even if you are no longer using coal to power your boiler.<\/p>\n November 2002<\/a><\/strong>\u00a0— Theta j-c — the thermal resistance between junction and case. \u00a0You don’t need to know exactly what its value is to know it is not a safe way of calculating junction temperature.<\/p>\n December 2002<\/a><\/strong>\u00a0— Theta j-c is no good, so how do we figure out junction temperature?<\/p>\n January 2003<\/a><\/strong>\u00a0— Everybody has heard of the speed of light. \u00a0But what about the speed of heat? \u00a0You can actually figure it out for yourself without having to pretend to understand the Theory of Relativity.<\/p>\n February 2003<\/a><\/strong>\u00a0— Thermally-conductive epoxy: \u00a0better than non-thermal epoxy, but still a pretty good insulator.<\/p>\n March\u00a02003<\/a><\/strong>\u00a0— Heat sinks always seem to be anodized. \u00a0Doesn’t that add an insulating coating that defeats the purpose of the heat sink?.<\/p>\n April\u00a02003<\/a><\/strong>\u00a0— How much can thermal grease reduce the temperature of a microprocessor (without the heat sink?) \u00a0Can a laptop computer produce burns on the user’s “lap”, or is this another urban legend?.<\/p>\n May\u00a02003<\/a><\/strong>\u00a0— My components are cooled only by conduction into the board. \u00a0I need Theta J-B to do thermal analysis, but the component datasheets never have it. \u00a0Can I safely substitute Theta J-C for Theta J-B?<\/p>\n June 2003<\/a><\/strong>\u00a0— My product is exposed to the sun. \u00a0The sun makes it run hotter. \u00a0Can I test it by just running the thermal chamber a little hotter to simulate the sun? \u00a0How many degrees hotter? \u00a0Also, what is the spreading angle for heat conducting from a small component into a big heat sink? \u00a0My text book says 45 degrees. \u00a0Doesn’t it depend on the material?<\/p>\n July 2003<\/a><\/strong>\u00a0— How to explain the difference between heat and temperature to your mother-in-law. \u00a0And, are the laws of physics stacked against the electronics cooling engineer?<\/p>\n August 2003<\/strong><\/a>\u00a0— Is there a Thermal Interface Material (TMI) that changes thermal conductivity with temperature? \u00a0With luck, the conductivity would increase<\/em> with temperature.) \u00a0And, is it possible to define the “still air environment” so that a method of testing electronics in it could be invented?<\/p>\n September\u00a02003<\/strong><\/a>\u00a0— Is there a textbook equation to predict the average convection coefficient for a pin fin heat sink? \u00a0Does a push-pull fan alternate between pushing and pulling?<\/p>\n October\u00a02003<\/strong><\/a>\u00a0— It was a joke, but now it’s real: \u00a0Purdue University really did develop an air mover based on the traditional Japanese hand fan. \u00a0Plus, did updates in the JEDEC standards make Theta J-C any safer to use?<\/p>\n November\u00a02003<\/strong><\/a>\u00a0— Which cell phone is better at giving off heat to the surrounding air: \u00a0the one with a uniform skin temperature or one with a local hot spot? (Assuming both have the same average skin temperature.)<\/p>\n December\u00a02003<\/strong><\/a>\u00a0— Air in motion is a coolant. A trapped layer of air an insulator. Can we predict whether a particular pocket of air will be one or the other?<\/p>\n January 2004<\/strong><\/a>\u00a0— What is the temperature of the sky? You might want to know, if your electronics are used outside, and can radiate heat to the sky. And can thermal problems be solved remotely? (Such as over the phone?) The answer might surprise you, considering this column is giving advice over the Internet.<\/p>\n February\u00a02004<\/strong><\/a>\u00a0— A more complicated method of determining component power by measuring its temperature, except it is not quite complicated enough. And, do fans make air cooler? It sure feels cooler when I stick my hand in front of the fan!<\/p>\n March 2004<\/strong><\/a>\u00a0— It’s not the heat, it’s the Relative Humidity. Most of the time cooling electronics is not affected by humidity. But if you are cooling below ambient, watch out for the Dew Point Wall.<\/p>\n April\u00a02004<\/strong><\/a>\u00a0— Burn-In Testing: does it weed out infant mortality in electronics, or does it just burn up time in the manufacturing cycle?<\/p>\n May\u00a02004<\/strong><\/a>\u00a0— Now that gigabytes and disk space are practically free, why do we need to be careful about how we mesh our CFD models? Shouldn’t we just mesh the heck out of them to get the most accurate results every time? Why take a chance of losing accuracy just to save a few grid cells?<\/p>\n June\u00a02004<\/strong><\/a>\u00a0— A disk drive has a maximum operating temperature of 35\u00b0C in “still air”? If you blow air across it with a fan, can it operate at 40\u00b0C? There’s a difference between being the feasibility and advisability of such an action.<\/p>\n\n