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Cooling off hot laptop models
By Tom Staudter
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To satisfy the ever-increasing demand for faster and more powerful laptop models, the capacity and strength of computer processing units (CPUs) have increased dramatically in recent years. But these super-efficient laptops have a downside: They let off more heat. Though the electronic components of these machines could work at much higher temperatures, the heat can be an uncomfortable annoyance for the average commuter pecking away at the latest sales report. Consider how long you can hold a 40-watt light bulb, for instance.
Coming to the rescue of certain IBM ThinkPad laptop models is an innovative heat dissipation system featuring a device known as a thermal hinge. Developed by IBM Research staff member Dr. Lawrence Mok, the system actually works like an old-fashioned radiator. Small pipes transport some of the heat generated by the computer's processing hardware and other components through a hinge that connects the keyboard to the display panel.
There's nothing old-fashioned about the thermal hinge, though. It's a patented, one-of-a-kind innovation that keeps ThinkPad computers literally cooler than the competition.
Turning up the heat
Many typical laptops are comprised of CPUs that use nearly 20 watts of power, and in the near future chips in portable computers will work on more than double the present wattage levels, "making them real lap warmers," jokes Dr. George Chiu, senior manager of Advanced Server Hardware Systems at IBM Research.
Most laptop models already utilize other methods of heat dissipation. The heat from CPUs of up to about three watts can be vented passively without mechanical assistance through the keyboard or the sides of the laptop units, and for the last few years a small fan at the back of the keyboard has pushed more heat out from the computer as well.
Even still, laptop computers can be warm to the touch—and they're getting hotter. Larger fans have been used to tackle rising heat generation in the laptops, with some fans taking up more than eight square inches of precious space inside the units. Concerns about space, battery drain and ambient noise from the fans were enough for IBM executives to declare a solution to the problem of heat dissipation in laptops a "critical need." In early 1996 they asked IBM Research for help.
Hot on the case
Not surprisingly, staff members at IBM Research had already begun looking at the problem of heat dissipation for portable computers. "We realized that the limit of passive cooling of CPUs in laptops would be about three watts, and beyond that other measures would be necessary," says Chiu.
Mok, in particular, had devoted significant attention to the problem of heat dissipation in laptops. Most of the 16-year IBM veteran's research focused on heat transfer models for electronic packages, and while dealing with laptops he'd already amassed more than a dozen patents for features like slideable keyboards, thermal storage and heat sinks.
"We considered a lot of different ideas, but more often than not they compromised the overall size and weight of the ThinkPads," says Mok. "Fins that emanated from the case of the computer were even suggested, and though they certainly would have aided the natural convection of heat away from the components, the laptop would have looked like a porcupine." Moving the CPU closer to the keyboard resulted in additional passive cooling, and it also inspired Mok to search for other solutions.
The "thermal hinge" (removed from laptop) |
On a flight to Japan to meet with ThinkPad development teams, Mok sketched out his idea for the thermal hinge. Based on a simple principle of heat transfer, a small, hollow, copper pipe, filled with liquid (such as water since it boils at room temperature in a near vacuum sealed pipe), and sealed to create a vacuum, is attached to a metal alloy block near the CPU. When the CPU heats up, the liquid in the pipe begins to boil and heads toward the pipe's cooler end. In this case, the pipe terminates in the metal hinge, which is placed at the boundary connecting the keyboard half of the ThinkPad to the display half.
Inside the hinge is the end of another pipe. As the metal hinge heats up, it transfers the heat to the second pipe that then carries the heat behind the display to a flat metallic pad that is glued to the inner surface of the ThinkPad's plastic cover, allowing the heat to dissipate uniformly over its outer surface. The circulation of cooled liquid back to the hot end of the two pipes allows the process to repeat itself endlessly, just like a radiator.
Putting it all together
Built with the assistance of senior engineer Thomas Cipolla, who has worked with Mok for the past 10 years on other projects, the thermal hinge seemed an ideal answer to the laptops' heat dissipation problems, and its efficacy in tandem with the work of the small fan was impressive: a good portion of heat from the CPU exited the unit from the back, thanks to the fan, while the cooling pipes moved the rest to the display area. Getting management's approval to introduce the device into ThinkPads was the next step, and Mok and Cipolla made many presentations before they received a green light.
"Product managers, by nature, exhibit a great deal of healthy skepticism toward new ideas," says Chiu. "They want to thoroughly check each design modification, test the product over and over, and see if it affects the appearance any. Once everything is okayed, though, you can't ramp up your innovation fast enough."
"It's very hard for Research to get something into a product that's already on the market," concurs Cipolla, "and when you do come up with a new idea most managers will challenge you for every tenth of a millimeter.
"Ideally, they want you to be able to introduce your idea into the product without taking up any space or adding any weight and for no extra cost, which can be next to impossible. Convince management that you can do all that and they'll help you in whatever way they can."
IBM Fellow Arimasa Naito, the development manager of ThinkPad in Japan, monitored the work on the thermal hinge closely, says Mok, "and gave us a lot of encouragement." With the thermal hinge in place, a ThinkPad A20 prototype was put through a rigorous open/close life cycle test without any degradation of performance in the computer. After all, the hinge still had to perform its chief function—enabling the two parts of the laptop to fold and close together.
It took two years from the time Mok and Cipolla, with the help from the product design team, began to design the thermal hinge until it was a bona fide part of the product. When it was launched in 1999, the ThinkPad A20 was the only portable computer on the market to have a thermal hinge and a small fan in place, making it one of the lightest and quietest—and coolest—machines around.
The wattage of CPUs has continued to rise since then, though. For the past year Mok and Cipolla have been developing a second generation of the thermal hinge, which will transfer heat through the machine in a more efficient manner and can be more easily assembled on the production line.
"The general idea of moving the heat from the CPU to the display side in a laptop wasn't really new," says Mok. "In fact, we discovered that in 1986 a Japanese company had even patented something along the lines of transferring the heat to the back of the LCD (liquid crystal display). Our contribution to the design was to make the thermal hinge reliable and small enough to fit into a ThinkPad while still dissipating sizable heat at the lowest cost possible. As it stands, IBM was the first company to put a thermal hinge in a real product."
Thomas Hildner, a mobile technology strategist in the Personal Computer Division, adds, "In large companies it is natural to have a mentality that if it isn't their invention or the way things are normally accomplished, then they want no part of it. With ThinkPad we've proven in the past that the things that have made this brand successful are innovation and quality. We always keep our eyes open to new ideas and work as a team to evaluate and integrate them."
