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106 DESIGN007 MAGAZINE I SEPTEMBER 2020 plus a power supply. The system weighed some 60,000 pounds, was 100' x 10' x 3', and contained roughly 19,000 vacuum tubes; 1,500 relays; hun- dreds of thousands of resistors, capacitors, and inductors; and required 500,000 hand-soldered interconnections. Its power consumption was about 200 kilowatts. The smartphones we carry in our pockets are several orders of magnitude both smaller and more powerful than the ENIAC, but use a fraction of the energy. Transistors are much more efficient; however, the energy den- sity of the processor chip in watts per square millimeter is still arguably many times greater. It's all a matter of perspective. Both computers require cooling to perform efficiently. The ENIAC employed a forced- air cooling system to deal with the mas- sive amount of heat generated by the tubes. Those who remember cathode ray televisions will likely remember just how warm the area around the TV was. When it comes to managing heat, there are only three fundamental ways: conduction, convection, and radiation, as well as a number of ways to augment them. Of these, conduc- tion is arguably the easiest, fastest, and most efficient, but conduction needs a thermal sink to further remove heat from the conduction source to keep it cool, and that is convection— the means by which the heat is transferred to air. Radiation is the least efficient (it's also the way the Earth attempts to rid itself of excess heat at night as the Earth rotates and at least part of the reason global warming is a prob- lem), but for electronics, all three methods can be and often are combined to keep things cool. To help deal with the heat, thermal engineers have developed many clever solutions over the years to protect electronics from overheating. This often happens in concert with system designers. One such solution is what has been called a "stepped phased system protection" protocol. The first level of thermal protection is passive thermal protection. These include heat sinks, heat spreaders, heat pipes, and the like to remove heat directly through conduction aided by convection from the device (normally a CPU). If things get too hot for the passive and semi-passive solutions, a fan is often engaged to assist heat removal at the first thermal thresh- old. Additional sophistication and the use of software is the next solution, where the CPU/ system clock speed is reduced to reduce energy generation when a threshold is reached. This is followed by an overheat condition warning to the user. If that fails, to get a response, the system will automatically shut down. There have been many solutions to the ther- mal problem as watt densities increase. It is recommended that the designers familiarize themselves with both the solutions and to not ignore the importance of thermal interface materials (TIM), which are vital to assuring that the first thermal pathway is a good one. Thermal challenges are unlikely to go away so long as electronics persist. Photonics have been suggested as one prospective solution. There have also been suggestions that biologic computers using neural networks assembled by DNA are in the future by some futurists, but— come to think of it—isn't that what humans are? Stay cool—and give all those thermal management engineers some well-deserved respect. FLEX007 Joe Fjelstad is founder and CEO of Verdant Electronics and an interna- tional authority and innovator in the field of electronic interconnection and packaging technologies with more than 185 patents issued or pending. To read past columns or contact Fjelstad, click here. Download your free copy of Fjelstad's book Flexible Circuit Technology, 4 th Edition, and watch the micro webinar series on flexible circuit technology. The smartphones we carry in our pockets are several orders of magnitude both smaller and more powerful than the ENIAC, but use a fraction of the energy.

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