Electronic Design

Thick-Film-On-Steel Resistors Prove Worthy In High-Temperature, High-Power Applications

Thick-film-on-steel will enable a new class of power resistors and heating elements that outperforms existing components. A high-temperature technology, it was developed by IRC of Boone, N.C. Resistors produced by thick-film-on-steel are vibration and shock-resistant, and can operate at up to 400°C.

Attributes of thick-film-on-steel materials include greater power-handling and customizable form factors. These features make the components likely replacements for resistors built using thick-film-on-alumina (ceramic) or wire-element methods. Target applications include household appliances, water heaters, and automobiles.

To create a thick-film-on-steel device, a thick ceramic-dielectric glaze is bound to a stainless-steel substrate. The steel can be welded, bent, and shaped into various forms before applying the thick-film material. Resistive elements can therefore be tailored to the dimensions of the application (see the figure). Resistors produced on ceramic substrates generally lack this quality.

Power density also is significantly higher with thick-film-on-steel. It delivers 100 W/cm2. As a result, steel-based resistors will be able to dissipate hundreds or thousands of watts.

According to Harold Warren, director of new business development at IRC, the company is looking to apply thick-film-on-steel to resistor designs in the 1- to 20-in.2 range. Warren also states that the new technology will probably cost about 20% more than thick-film-on-alumina. But for that price premium, designers get a resistor technology that works where alumina devices can't.

Thick-film-on-steel offers advantages over power resistors as well. For instance, the thick-film construction provides a more efficient path for moving heat away from the resistor. This is partially due to the intimate contact that exists between the thick-film material and the steel substrate.

Another benefit of the thick-film part is that it can be shaped and drilled with mounting holes for the attachment of an external heatsink. So, with the thick-film-on-steel device, conduction transfers a high percentage of heat energy out of the resistor. Contrast this with a traditional, hard-to-heatsink power resistor. Such a device may rely on a less-efficient combination of conduction, convection, and radiation to dissipate its heat.

Naturally, efficiency in transferring heat makes thick-film-on-steel useful as a heating element. That type of use also benefits from the flexibility of form offered by the technology. To support such applications, a temperature sensor is included alongside the resistive element in the thick-film material.

For more information, contact the Sales and Marketing Department of IRC Wire and Film Technologies at (828) 264-8861, call the faxback information line at (888) 472-3282, or visit www.irctt.com.

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