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MALVERN, PENNSYLVANIA — April 04, 2012 — Vishay Precision Group, Inc. (NYSE: VPG) today announced that its Vishay Foil Resistors division (VFR) is now offering a wide variety of resistors built on Bulk Metal® Z- and Z1-Foil technology for high reliability and stability in high-temperature applications and harsh environments. Including the new HTHG, winner of the 2011 Best Electronic Design award from Electronic Design magazine, VFR offers a wide variety of resistor styles, configurations, chip packages, and ultra-high-precision specifications for optimized performance.
Z- and Z1-Foil foil resistors are available in a variety of configurations. Devices such as the VCS1625Z, VCS1625P, CSM2512, and CSM3637 offer 4-terminal Kelvin connections for high reliability and accurate current measurement, while the FRSH and VSMP series feature wraparound terminations to ensure safe handling during the manufacturing process, as well as providing stability during repetitive thermal cycling. The flexible terminations of the SMR1DZ and SMR3DZ ensure minimal stress transference from the PCB due to differences in linear CTE (coefficient of thermal expansion), while the hermetically sealed packages of the VHP100 and PRND series eliminate the ingress of moisture and oxygen. For hybrid circuits, the HTHG is connected with gold wire bonding, while the HTHA is suitable for aluminum wire bonding technology.
“Thermally-related effects on the stability of precision resistors have different immediate, short-term, and long-term consequences,” said Yuval Hernik, senior director of application engineering for Vishay Foil Resistors. “The most immediate effect can be seen in the self-heating effect or power coefficient of resistance (power TCR), which registers as a change in resistance as the resistor heats up or cools down due to its power dissipation.
“The second effect is the resistance change due to environmental temperature changes. Both of these changes are functions of the resistor’s inherent temperature coefficient of resistance (TCR) responding to the resistor’s body temperature, and both are independently and incrementally reversible. However, temperature can also cause a permanent change in resistance and even complete resistor failure.”
For high reliability and stability, foil resistors provide high operating temperatures over +175°C, low TCR down to ±0.05 ppm/°C typical, exceptional long-term load-life stability down to ±0.005% at +70°C for 2,000 hours, and power TCR (PCR) of ±5 ppm at rated power.
The TCR of the foil resistor is achieved through a relatively thick cold-rolled foil that maintains the same molecular structure as the raw alloy from which it is formed. This allows the foil to act as a monolithic structure with a fixed and known linear coefficient of thermal expansion over any temperature range the resistor might experience throughout its design life. The device’s materials are engineered for a precise balance of linear coefficients of thermal expansion to achieve the lowest TCR in the industry.
The metal alloy of the resistance grid also has a very low Seebeck coefficient when joined to the termination materials. The Seebeck coefficient multiplied by the difference in temperature between the resistance grid/termination junctions determines the net thermal EMF error across the resistor. Thus, the low Seebeck coefficient combined with the foil’s design for thermal efficiency produce a foil resistor with a very low thermal EMF of only 0.05 µV/⁰C.
The adhesive that holds the foil alloy to the flat ceramic substrate withstands high temperatures and other phenomena such as pulsing power, moisture incursions, shock and vibration, and high-voltage electrostatic discharge (ESD). The flat planar structure of the foil resistor – with the resistance element at the surface (before coating or encapsulation) – lends itself to a unique process for trimming resistors to value while avoiding hot spots and compressed current density where the current’s path changes direction. With these characteristics, the basic technology of foil resistors combines the essential stress compensation that defines the foil technology.
The devices provide wide resistance ranges, with any resistance value within their given range available at any tolerance with no additional cost or lead time effect. Bulk Metal Foil resistors withstand high ESD spikes when compared to thin film and thick film, as demonstrated in a new video on VFR’s website, at http://www.vishaypg.com/foil-resistors/videos/?video=3
Samples and production quantities of the Foil resistors are available now, with lead times of five days for prototype samples and from two days to five weeks for standard orders at the catalog houses, depending on their shelf availability.
About Vishay Foil Resistors
Vishay Foil Resistors is a division of Vishay Precision Group, producing the most precise and stable resistors available. The portfolio comprises products in a variety of resistor and package configurations to meet the needs of a wide range of applications: discrete resistors and resistor networks in surface mount and through-hole (fixed-lead) configurations; customized chip resistor networks; precision trimming potentiometers; and discrete chips for use in hybrid circuits. The foil resistors and current sensors are used in applications requiring a high degree of precision and stability, such as in medical testing equipment, high performance audio equipment, precision measuring instruments, aerospace, and military applications.
About Vishay Precision Group
Vishay Precision Group (VPG) produces sensors based on precision resistive foil technology, and sensor-based systems. It provides vertically integrated products and solutions for multiple growing markets in the areas of stress, force, weight, pressure and current measurements. As a spin-off from Vishay Intertechnology, VPG’s decades-long track record encompasses innovations in precision foil resistors, current sensors, and strain gages, which have served as a foundation for VPG’s more recent expansion into strain gage instrumentation, load cells and transducers, weighing modules and complete systems for process control and on-board weighing. Vishay Precision Group may be found on the Internet at www.vishaypg.com.