Bulk Metal Foil Surface-Mount Resistors for Military, Avionics, and Space Applications

Several factors need to be considered when choosing a resistor for space and military applications, including TCR (ambient temperature), PCR (self heating), load-life stability, end-of-life tolerance, thermal EMF, and ESD. Some precision resistor technologies offer designers tight initial tolerances as low as 0.05% at the expense of poor load life stability, high end-of-life tolerance, long thermal stabilization, and ESD sensitivity. Other resistor technologies provide low TCR at the expense of poor rise time and uncontrolled drifts during operational life.

Vishay's Bulk Metal Foil resistors offer designers the complete set of top performance characteristics to simplify circuitry and lower overall system costs by reducing the number of required parts, while assuring a better end product. Vishay's devices feature long-term load-life stability within a maximum of 0.05% for 2000 hours under full rated power at +70°C. In addition to their low TCR, the devices offer PCR (ΔR due to self heating) to ±5 ppm at rated power; tight tolerances from 0.01%; and thermal EMF of < 0.1 µV/°C.

Current design practice has been to overspecify resistors to allow for expected tolerance degradation in service. Vishay offers a new approach with lower prices to bring foil resistors within the reach of designers whose end-of-life tolerance target is 0.05% or less.

The resistors feature a non-inductive (< 0.08 µH), non-capacitive design and are available with 4-Kelvin connections for low values, wraparound terminations, and flexible terminations (SMRXD series) to ensure minimal stress transference from the PCB due to a difference in thermal coefficient of expansion (TCE).

While other resistor technologies can take several seconds or even minutes to achieve a steady state thermal stabilization, Vishay foil resistors feature an almost instantaneous thermal stabilization time, and a nearly immeasurable 1.0-ns rise time with effectively no ringing. The devices offer a variety of screening options that are suitable for military and space applications according to EEE-INST-002, DSCC, EPPL, and MIL-PRF 55342/55182/49465, and are built to handle unconventional environmental conditions with minimal drift.

Offering the utmost in ESD immunity, Bulk Metal resistors withstand electrostatic discharges to 25 kV, for increased reliability. Within a resistance range from 2 mΩ, Vishay foil resistors are manufactured with any resistance value (e.g., 1 kΩ or 1.1234 kΩ) at no additional cost or lead time effect. The devices are radiation tested, and include short-time overload testing as part of the standard production process.

Typical applications for the resistors include dc-to-dc converters, feedback circuits, and precision amplifiers in test and measurement instrumentation, medical systems, satellites and aerospace systems, commercial and military avionics, weapons systems, audio systems, and high-temperature systems including down-hole drilling.