With more electronic functions embedded into systems, power dissipation increases and makes thermal design more critical. To ensure system reliability, it's imperative to keep all components operating within safe temperature limits. Among the available thermal management products for cooling electronic systems are coolers, heatsinks, heat spreaders, thermal gap fillers, fans, temperature measurement devices, and CAD/CAE software that verifies the system's thermal design.

Heatsinks are among the most widely used thermal management products. A new series of heatsinks, Therma-Vent^™ by Thermacore, uses enhanced fin technology to increase the heatsink surface area and create turbulent airflow to disperse heat more efficiently. Using a new rolled and slit fin technology to maximize surface area, the flow of heat from the chip into the local ambient air increases (Photo 1). They reduce mass, have less system volume, and cost less, compared with traditional extrusions and folded fin products. Brazed attachment of the fins to base ensures mechanical and thermal joint integrity and minimizes the chance of cracks forming, as can happen with an epoxy bond.

The company is initially launching a standard active Therma-Vent^™ heatsink solution for the Pentium^® 4 processor (Socket 478). Derivative devices for desktop and notebook computers, embedded applications, communications equipment, and other electronics cooling applications can be rapidly customized for quick time to market.

Cool Innovations employs different technology with its UltraCool IV pin fin heatsinks that employ forged, highly conductive, oxygen-free copper (Photo 2, on page 48) intended to cool devices dissipating high heat loads. They are omni-directional, allowing efficient cooling because of their pin fin structure and use of highly conductive copper. The pin fin structure provides a large surface area that's effective with slow and moderate airflows (100 LFM to 400 LFM). The use of oxygen-free copper provides a thermal conductivity premium of 20% over pure aluminum and a 40% premium over other aluminum extrusion alloys.

These heatsinks' footprint range is 0.25 in. × 0.25 in. to 1.5 in. × 1.5 in. and from an overall height of 0.15 in. to 0.8 in. Pin diameter ranges from 0.06 in. to 0.125 in. The heatsinks are offered with a mechanical spring-clip suitable for various package types.

R-Theta's Fabfin series of aluminum heatsinks now has embedded heat pipes. This allows an engineered solution to common heat spreading issues created by higher power electronic devices. This process embeds heat pipes in the heatsink's baseplate, resulting in a cost-effective solution that doesn't significantly increase weight. With the added advantage of a patented swaging process for high-performance, high-ratio solutions, this represents an efficient heatsink when used with forced air for many thermal cooling applications. The fabrication process is identical for any aluminum FabFin heatsink and is offered on MF and AF fin spacing (3.43 mm and 5.49 mm), respectively.

Another variation for R-Theta's Fabfin heatsinks is an added copper inlay. This new technique improves heat spreading in high power electronic devices. The technique allows standard aluminum baseplates with embedded copper material in selected areas to accommodate specific heat spreading needs. The design allows selection of copper thickness according to dissipation requirements. Previously, engineers had to use expensive and heavy full-copper-based solutions to solve heat-spreading problems. These inlay solutions have the added advantage of a patented swaging process, for high-performance, high-ratio capability. This is an efficient FabFin heatsink when used with forced air cooling.

Coolers

Enertron offers a Compact Cooler for power electronics applications with limited space. It dissipates as much as 150W in a 155 mm × 45 mm × 25 mm space (Photo 3). Due to the space constraint, the heat is carried from the heat source to the heatsink using heat pipes. The heatsink consists of highly efficient, thin, copper fins through which the heat pipes pass. Two 40 mm × 40 mm axial fans provide the required airflow. The total thermal resistance of this cooler is 0.60°C/W.

The heat collector and heatsink are mechanically joined with the aluminum housing, preventing stress on the heat pipes. The two fans are fastened to the housing to create a single thermal solution ready to be installed into the system. Use of heat pipes provides design flexibility. You can adjust heat pipe length and orientation to suit other applications, such as all-in-one desktop computers, enclosure cooling, telecom laser cooling, etc.

JMC's new SkyJet 60 CPU cooler features a patented Dual-Pass Airflow architecture from Agilent (Photo 4, on page 50). Designed specifically for future Intel^® Pentium^® 4 desktop and server processors, it can handle up to 75W. It's a radial fin heatsink that utilizes dual-pass airflow by taking air in from the top and all sides of the heatsink, creating a vacuum and expelling added airflow through the bottom of the heatsink. The cooler exhibits 0.32°C/W of thermal resistance with thermal interface material. It contains a top-mounted, high-speed 60 mm × 25 mm, 5000 rpm dc fan that supplies 25 cfm. The heatsink mounts to standard microprocessor sockets, including Socket 478 and Socket 603. The assembly is 57 mm (H) × 69 mm (D) and weighs 290 g, providing a compact design with efficient airflow and minimum noise levels.

Thermal Interface Material

The interface between the heated device and the heatsink are critical to thermal management solutions. This interface must provide optimized thermal conductivity while providing electrical isolation between the two mating surfaces. In addition, the material used in the interface must be able to accommodate surfaces that are not perfectly flat. Silicone grease has been used for this purpose, but new substances are easier and cleaner to handle while providing competitive thermal resistance.

Thermoset, Lord Chemical Products has developed a new thermal interface material: MT-315. This low stress adhesive has a bulk thermal conductivity of 7.3W/mK and can achieve bondline thicknesses of 1.5 mils to 2 mils. MT-315 exhibits very low thermal resistance, low contact resistance and highly effective conductivity when tested in package. The result is a lower contribution of the adhesive to the overall thermal budget.

MT-315 was specifically developed for high-power devices to bridge the gap between commercially available thermal interface materials and solder. It exhibits excellent adhesion to a variety of substrates including gold, silicon, ceramic, and nickel. Its minimal shrinkage and superior adhesion result in excellent resistance to delamination and degradation in the thermal pathway during reliability testing. This adhesive is engineered for lid attach on Flip Chip assemblies, to be used as the die to heat spreader thermal interface, as well as perimeter adhesive. Its excellent electrical conductivity makes MT-315 well suited for grounding and RF shielding on a high-speed, high-power semiconductor. MT-315 is engineered to provide a high-performance interface solution where a mechanical attach isn't possible or desired. At 25°C, it has a viscosity of 85,000 cps at 2 rpm and is suited for syringe dispense or printing operations.

Fujipoly of America Corp. supplies the SARCON^® XR-e and XR-j thermal gap filler pads that feature excellent thermal conductivity, thermal resistance, consistency, and elasticity. These silicone gel sheets are well suited for filling air gaps and uneven surfaces in a variety of electronic designs, including the computer, consumer, communications, automotive and industrial applications.

These thermal gap filler pads have thermal conductivity of 11W/m-K and 14W/m-K, respectively. The thermal conductivity produces thermal resistance of 0.11 in.²/W to 0.14 in.²/W for the SARCON XR-e and 0.09 in.²/W to 0.12 in.²/W for the SARCON XR-j. Both Thermal Gap Filler Pads have flame retardancy that satisfies UL94 V-0 class.

Made from silicone compound, the pads are flexible enough to conform to a variety of design considerations, such as tolerance backups and multiple component heights. They can easily adhere to components in a wide variety of shapes and sizes, including protrusions and recessed areas and are also available in custom die-cut pieces. When mounted on substrates or at heatsink junctions, they can virtually eliminate thermal impedance, yielding higher temperature transfer gradients.