Power Electronics

Precision Resistors with Operating Temperature Over +175°C

Vishay Precision Group, Inc. 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 four-terminal Kelvin connections for high reliability and accurate current measurement, and the FRSH and VSMP series feature wraparound terminations to ensure safe handling during the manufacturing process, as well as to provide 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.

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/°C.

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.

Samples and production quantities of the Z- and Z1-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.

Vishay Precision Group, Inc.
Part Number: HTHG

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