Monday, September 27, 2010

VPG adds ultra-high-precision bulk metal Z-foil resistors

MALVERN, USA: Vishay Precision Group Inc. announced that its Vishay Foil Resistors division has extended the Z Series of ultra-high-precision Bulk Metal Z-Foil resistors with three new devices.

These devices provide very low TCR of 0.05 ppm/deg. C from 0 to 60 deg. C and 0.2ppm/deg. C from -55 to +125 deg. C, +25 deg. C ref., tight tolerances of 0.005 percent (50ppm), and a load life stability of 0.005 percent at 70 deg. C for 2,000 hours or to 0.015 percent at 70 deg. C for 10,000 hours. Qualified in accordance with EEE-INST002 and MIL-PRF 55182, the new Z204, Z205, and Z206 join the previously released Z201 for military/aerospace applications.

The devices are the result of a unique concept in resistor manufacturing, starting with a proprietary bulk metal foil cemented to a special ceramic substrate. A resistive pattern is then photo-etched into the foil by an ultra-fine technique developed by Vishay Foil Resistors and laser-adjusted to any desired value and tolerance.

The Z Series resistors utilize a special trimming method that increases resistance in precise steps, but at positions away from the active grid, so that the etched grid in the active area remains reliable and noise-free.

Since the metals used are not drawn, wound, or mistreated in any way during the manufacturing process, the Bulk Metal Foil resistor maintains all its design, physical, and electrical characteristics of maximum stability and near-zero TCR. These performance characteristics are built into every unit, and do not rely on screening or other artificial means for uniform performance.

The stability of a resistor depends primarily on its history of exposure to temperature. Stability is affected by: changes in the ambient temperature and heat from adjacent components (TCR); destabilizing thermal shock of suddenly-applied power (power TCR); long-term exposure to applied power (load-life stability); and repetitive stresses from being switched on and off.

The Z Series has been developed to successfully deal with these factors. Vishay Foil Resistors' Z-Foil technology provides an order of magnitude reduction in the Bulk Metal Foil element's sensitivity to temperature changes -- both external and internal. This technology provides a low absolute TCR of 0.05ppm/deg. C and a power TCR of 5ppm at rated power.

Over the past few months, there has been considerable growth in the demand for precise, stable, and reliable resistors that can operate in harsh environments, especially at high temperatures. Many analog circuits for industrial, military, aerospace, medical, down-hole, oil well, and automotive applications require passive components such as resistors to have a minimal drift from their initial values when operating above 175 deg. C and in humid environments.

In these applications the most important factor is the end-of-life tolerance and, to a lesser extent, the initial tolerance. The Z Series provides stabilities well under the maximum allowable drift required by customers' specifications through thousands of hours of operation under harsh conditions such as the extreme temperatures and radiation-rich environment of down-hole oil well logging applications; in the frigid arctic; under the sea; or in deep space.

All Z Series resistors receive stabilization processing such as repetitive short-term power overloads to assure reliable service through the unpredictable stresses of extreme operation.

The Z Series offers a resistance range from 10Ω to 600kΩ. Vishay Foil Resistors are not restricted to standard values, and specific "as required" values (e.g. 1.234 kilohms vs. 1 kilohm) can be supplied at no extra cost or delivery time. Total accumulated change in resistance over life (EOL) for the devices is less than 0.05 percent, or better with post manufacturing operations (PMO).

The resistors feature rated power to 1W at +125 deg. C, a rise time of 1ns with effectively no ringing, current noise of less than 40dB, thermal EMF of 0.05 microvolts per deg. C typical, and a voltage coefficient of less than 0.1ppm/V.

Offering the utmost in ESD immunity, the devices withstand electrostatic discharges of at least 25kV for increased reliability, and offer a non-inductive (less than 0.08 microhenries), non-capacitive design. Z Series resistors are available with lead (Pb)-free and tin/lead alloy termination plating.

Samples and production quantities of the Z Series resistors are available now, with lead times of five days for samples and three weeks for standard orders.

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