Review

The ongoing concern of designers as to how best to keep their latest creations from overheating has resulted in development of a steady stream of cooling products. These range from products that provide localized cooling of devices to those that can remove heat from an entire board or chassis filled with several boards. Developments occurred in each cooling product niche over the past 12 months, with several interesting examples described below, starting with heatsinks.

By combining copper and aluminum in a composite strip, Technical Materials (technicalmaterials.com) developed its Solderable Aluminum line of heatsinks to eliminate the need for extensive chemical activation to join aluminum components. The new material is said to provide high thermal conductivity. Cool Innovations's (coolinnovations.com) UltraCool IV pin-fin heatsinks use a special physical structure and highly conductive copper to deliver exceptional cooling capabilities in a small size. The heatsinks have footprints ranging from 0.25" to 0.75" square with overall heights ranging from 0.15" to 0.8". Developed by International Electronic Research (ctscorp.com) for cooling TO-5, TO-8 or TO-18 packages, thermal-link and fan-top heatsinks are said to offer excellent retention to these devices, even under high vibration conditions, due to their 6- to 8-segment fingers, with the multiple fingers providing a smooth press-fit installation without a harmful snap-action effect.

Fan/heatsink combos have become a popular way for removing the heat generated by high-speed micro- processors, with Molex's (molex. com) new 37430 series tailored specifically to work with Pentium 4 processors running at speeds of 3.06 GHz or higher. The units are said to reduce weight and save space compared to existing devices, with the sink portion of the design employing stamped fins linked together and soldered to a base plate. The heatsinks are available in wide range of fin pitches, materials and thicknesses, while multiple fan speeds are available to accommodate boards without variable fan speed technology.

As far as cooling assignments go, fans are the workhorses for chips, PC chassis and set-top boxes, among other equipment. And one thing you want from a fan is low failure rate. As an example, the 2806KL and 2810KL fans boast of a failure rate of less than 60 parts/million. The 70 x 70 x 15-mm 2806KL delivers up to 38 cfm and the 70 x 70 x 25-mm 2810KL up to 31 cfm. Built by NMB Technologies (nmbtc.com), the fans also feature ball bearing motors, with tach output and locked rotor alarm signal capabilities offered as options.

Closed loop cooling systems are typically used to remove heat from electronics-containing cabinets. An example of this type of air conditioner is the K400F, developed by Haewa (haewacorp.com). The unit transfers heat from the cabinet's interior to the outside via a CFC-free, R134a refrigerant—the refrigerant permits below ambient cooling of the cabinet's interior at ambient temperatures ranging from 20°C to 55°C. The cabinet's interior temperature, factory set at 35°C, is field adjustable. The 10.63" x 20.47" x 4.80", 30.5 lb. air conditioners are designed for either external or internal cabinet mounting. Operating voltage is 230V, 50/60 Hz with a nominal current of 1.6A.

Also available for cooling cabinets are brushless blowers like the Windjammer BLDC. Built by Ametek Rotron (ametektmd.com), the blowers support real-time fault monitoring capabilities and programmable parameters. Low speed operation is said to be reliable, with monitoring and protection features including over- and under-voltage protection, surge and short-circuit protection, and fault indication via a LED. Operation is with 120 or 240 Vac.

Cooling is often needed from free-standing units. An example of this type is Melcor's (melcor.com) MRC300 thermoelectric liquid chiller. This compact, free-standing unit provides 300W of cooling power. It measures 353 mm x 203 mm x 338 mm and offers dual, 115/230 Vac operation, a control accuracy of ±0.1°C at a constant ambient temperature and heat load, and settable alarms for high and low temperature limits.

Several advances were made this year in heat transfer materials. The Polarchip CP7500 from W.L. Gore & Associates (gore.com) is a thin (0.010" thick), highly compressible thermal interface material suited for filling air gaps between heat-generating devices and heatsinks, heat spreaders, and metal chassis. The material is said to be useful in applications where there are surface irregularities and where low stress on components is required. A pressure-sensitive adhesive can be laminated to one side of the CP7500 to facilitate attachment.

Bergquist (bergquistcompany. com) has developed a silicone-free, thermally-conductive, electrically-isolating gap filler material for use in applications such as disk drives, open-circuit relays, motors, etc. Gap Pad Sil-Free 1000 material exhibits a thermal conductivity of 1 W/m-K and and is 94V-0 UL rated. The asymmetrical laminate has a low-tack rubber coating on one side of imbedded glass reinforcement and a naturally tacky rubber coating on the other side. Thicknesses range from 0.015" to 0.125".

Sometimes, controllable amounts of heat rather than cooling must be applied to an enclosure, such as encountered in harsh environs. An example of products groomed for this task is a line of element heater assemblies from Minco Products (minco.com). Aluminum, copper and stainless steel plates measuring up to 22" x 72" are available for warming enclosures.

—Joe DelGatto

Outlook

A Cool Future
With more and more circuits and components crammed into ever smaller spaces on pc boards, the efforts to develop smaller, more efficient cooling products is expected to increase. Fans and blowers will grow quieter and have longer life spans. And advances in material science will lead to heatsinks and interfacing materials that can conduct heat more efficiently.

—JDG