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Thermal Management for Hot Products
December 31, 1969 |Estimated reading time: 5 minutes
By Jody Mahaffey, JDM Resources
Everyone wants to know what will be the next "hot" semiconductor product. On February 16, 2005, MEPTEC, the Microelectronics Packaging and Test Engineering Council, will hold The Heat Is On: Thermal Management Issues in Semiconductor Packaging, in San Jose, Calif., to discuss how to manage the heat generated by high-watt devices.
The semiconductor industry understands that the hot products are here already, and they keep getting hotter. High-end microprocessors and graphic chipsets play a part in electronics. As these devices continue to increase in functionality and performance, speed and circuit density also must increase, which can create some seriously "hot" issues for systems designers and others in the supply chain. In preparation for the conference, MEPTEC polled some industry experts for some insight into the world of thermal management. Participants agree that the entire supply chain must be involved in developing products that meet the thermal management requirements for high-speed, high-performance products. "With increases in power density and compaction at the system level, a holistic view is necessary," says Chandrakant Patel, distinguished technologist for Internet Systems and Storage Laboratory at HP Labs, and presenter of the Systems Level Challenges and Solutions Session.
"Everyone must be involved; however, in the end, the system designer is the one who controls the final design and places the requirements for the system," comments Dr. Gerald (Skip) Fehr, industry consultant and session chair for the Modeling, Characterization and Measurement Session. "In this way, he can influence chip design, package design and system cooling. He then will work with the chip designer and have worked backwards from the board design. The package designer must build a package that meets the system electrical and cooling requirements. The system designer must get everyone on the same page. This often is a back-and-forth process. For large systems, there are a lot of compromises." If any member of the supply chain overlooks the thermal issues, the job of meeting the thermal management goals will be passed along to another portion of the supply chain, adds Dr. Roger Emigh, director, WW Package Characterization at STATSChipPAC and a speaker at the Modeling, Characterization and Measurement Session.
CPUs and GPUs are most commonly thought of as requiring special thermal management; however, there are other areas where thermal management is crucial to end-product performance. Devices such as drivers, power converters and mass storage will require more thermal management as they scale with CPUs, adds Patel.
"Years ago, power supply provided adequate airflow to cool everything. Fansinks were used to increase local airflow, but not the system total. Dedicated fans and fully ducted heatsinks were required," says David Copeland, Packaging Technology Research at Fujitsu Laboratories of America and presenter at the Device Level Challenges and Solutions Session. "Now chipsets and memory have airflow requirements, and some are getting dedicated fans and/or ducting."
"Stacked die packaging also can present challenges, not only when stacking memory onto a logic chip, but when the stack contains die that generates more than a trivial amount of heat," adds Emigh. Unfortunately, one solution may not meet all thermal requirements for all types of devices. With respect to maximum junction temperature, "A device with a limit of 105°C will present a different challenge as opposed to one that can see 125°C," states Emigh.
Furthermore, device performance and lithography density are driving differentiation in thermal management requirements, as not all products require state-of-the-art speed and density. "Low-density and low-speed, even high-density, low-speed devices, will not create the same thermal concern as when both are maximized," says Joel Camarda, industry consultant and session chair for the Systems Level Challenges and Solutions Session. "The requirement is device type (product) driven. However, I believe there is a lot of commonality in the solution."
There are many approaches to managing high-watt devices and associated problems. Issues should be addressed and solved for high-watt devices to work reliably. This includes electrical (usually current capability and noise issues) and other restraints for device designs, claims Fehr. The most difficult problem changes depending on the device and system design. There are many thermal management issues, but are these issues holding back potential developments in the semiconductor market? Most experts feel that thermal management issues are at least limiting development in many markets. "Power management techniques seem to be motivated by thermal management issues and battery life—so one might conclude that thermal management issues are starting to affect the market," claims Patel. "It is not clear that potential developments in semiconductor devices are being slowed down, though that might be the case in the long term." Other experts agree.
Thermal management issues will continue to play a part in the future cost and capability of semiconductor devices. "Increases in power density at the chip level will necessitate active heat removal, particularly to maximize the ability of silicon devices and processes," says Patel. "The cost of the heat-removal mechanism and energy used to remove the heat will become central. Computer equipment commoditization will result in equipment costs becoming secondary to system power usage," adds Patel.
"Packaging costs have become as large as die costs, in many cases," agrees Fehr. "The ability to handle cooling requirements cost effectively is critical for system costs. Presently, there are times when two devices are used in place of one when electrical and cooling requirements are too difficult to solve within the system requirements," he adds. It also is believed that thermal management will impact not only the cost of packaging, but also system cost. Finding solutions to thermal management issues may open new markets in the semiconductor industry—or at least prevent new markets from being limited. But not all experts fully agree. Thermal solutions may not necessarily open new markets, claims Emigh. However, better thermal control will allow designers to build more functionality into smaller systems.
To find thermal management solutions, thermal modeling and simulation are becoming more critical. For example, software enhancements have allowed faster and more accurate simulation of full packaging systems, instead of a small symmetrical section. Wider acceptance of CFD tools also has improved thermal solution recommendations earlier in the design. Experts agree that those recommendations help reduce learning cycle time, and ultimately cost.
Throughout the supply chain, thermal management issues continue to heat up. Discussions and conferences such as The Heat Is On: Thermal Management Issues in Semiconductor Packaging help the industry continue to make strides in the production of faster and more economical products. For more information on the conference, or to register, visit www.meptec.org.