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Surface-mount power resistor delivers greater thermal cycling performance

Posted: 20 May 2005 ?? ?Print Version ?Bookmark and Share

Keywords:power resistor? thermal cycling? thermal isolation?

Designed to resolve thermal cycling issues with power components in high-temperature environments, IRC has developed a "capped" version of its cylindrical power resistor that is said to deliver superior thermal compliance and thermal isolation.

Based on IRC's family of cylindrical Metal Glaze power resistors, the rugged SMC series devices feature a MetalGlaze thick-film element fired at 1,000?C to a solid ceramic substrate and a high temperature dielectric coating that is impervious to degradation in high-moisture environments. Featuring compliant metal caps, the cylindrical design provides excellent heat dissipation and much higher surge/pulse capability than comparably rated flat chips, said the company, with a significantly lower profile than traditional surface mount wirewound devices. These new resistors can be a potential cost saving replacement for bulky surface-mount wirewound devices in certain applications, according to the company.

The SMC series resistors were designed to solve the problem of thermal mismatch between FR4 PC-boards and ceramic components, according to David Winkler, product manager for IRC's Wirewound and Film Technologies Division.

"Adding a compliant metal cap to the ends of our surface-mount cylindrical power resistors gives them the compliance needed to address thermal management issues that our customers were experiencing with ceramic chip resistors," Winkler said, in a statement. "The capped ends of the SMC series resistors not only provide a closer thermal match to the PC board, but they also raise the device up slightly to provide better airflow and result in lower overall board temperature."

Available in ratings up to 2 watts, the SMC1 series resistors are rated for 1 W at 70?C, with resistance values from 0.1Ω to 1 MΩ, in standard tolerances of ?1%, ?2% and ?5%, with temperature coefficient of resistance (TCR) ratings as low as ?25 ppm/?C. The SMC2 series resistors are rated for 2 W at 25?C, with resistance values from 0.2Ω to 2.2 MΩ, in standard tolerances of ?1%, ?2% and ?5%, with TCRs as low as ?25ppm/?C. The standard operating temperature range is -55?C to 150?C. Custom specs are available. All devices are RoHS compliant and suitable for high temperature soldering processes.

Applications include high power-density applications, such as under-the-hood automotive control units, GFI control circuits, as well as any high-thermal stress application.

Typical pricing for the SMC resistors is $0.15 each in quantities of 5,000. Delivery is from stock to six weeks.

- Gina Roos

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