Vishay Expands Bulk Metal Foil Resistor Offering for Hi-Rel Applications With Improved Devices Featuring TCR From ±0.2 ppm/°C, Load-Life Stability to 0.005 % (50 ppm), End-of-Life Less Than 0.05%, and ESD Immunity of 25 kV or Better

These new-generation precision resistors are virtually insensitive to destabilizing factors. Their resistive elements are made of a solid alloy that displays the desirable bulk properties of its parent material; thus it is inherently stable, noise-free, and immune to ESD to 25 kV and beyond. The resistive element and matched substrate form a single entity with balanced temperature characteristics for an unusually low and predictable TCR over a wide temperature range from -55°C to more than +200°C. Resistance patterns are photo-etched to permit trimming of resistance values to very tight tolerances.

Several factors need to be considered when choosing a resistor for space and military applications, including TCR (ambient temperature), power TCR (self heating), load-life stability, end-of-life tolerance, thermal EMF, thermal stabilization, and ESD. These Bulk Metal Foil resistors, based on a new generation technology and improved production methods starting in December 2010, 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 foil resistors feature a long-term load-life stability within 0.005% after 2,000 hours and 0.015% after 10,000 hours under full rated power at +70°C. In addition to their low absolute TCR, the devices offer power TCR (ΔR due to self heating) to ±5 ppm at rated power, tight tolerances from 0.01% — or even 0.001% (10 ppm) in hermetically sealed packages — and thermal EMF of 0.05 µV/°C.

Often designers over-specify resistors to allow for an expected tolerance degradation during service. Vishay foil resistors allow designers whose end of life tolerance is 0.05% or less to avoid this approach with cost-effective commercial-off-the-shelf (COTS) devices that provide all the long-term reliability and stability they need for the most demanding applications.

The resistors feature a non-inductive (<0.08 μH), non-capacitive (<0.5 pF) design and are available with a 4-Kelvin connection for increased accuracy. Devices with wraparound terminations and flexible terminations (SMR1DZ and SMR3DZ series) are available to ensure minimal stress transference from the PCB due to differentials in the coefficient of thermal expansion (CTE).

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 ns rise time, effectively with no ringing. The devices are offered with a variety of high-reliability options that are suitable for military avionics and space applications according to EEE-INST-002, DSCC, EPPL, QPL, and MIL-PRF 55342/55182/49465, and are built to handle unconventional environmental conditions with minimal drift.

Offering high ESD immunity, Bulk Metal Foil resistors withstand electrostatic discharges to at least 25 kV for increased reliability. With resistance ratings as low as 1 mΩ, Vishay foil resistors are manufactured with any required resistance value (e.g. 1 kΩ or 1.1234 kΩ) at no additional cost or lead time. The devices have been radiation tested, and include short-time overload and thermal cycling testing as part of the standard production process.

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