Metal Foil Resistors

Metal Foil Resistors

Preface.

Bulk Metal Foil technology outperforms all other resistor technologies available today for applications that require precision and stability. Bulk sheet metal products are offered in a variety of strength configurations and package types to meet the needs of a wide range of applications. Manufactured bulk sheet metal products offer an absolute temperature coefficient of resistance (TCR) of ±0.2 ppm/°C (–55°C to +125°C, +25°C ref), an order magnitude better than previous foil technologies.

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The lower the absolute TCR, the better a resistor can maintain its precise value despite ambient temperature variations and self-heating when power is applied. A specific foil alloy with known and controllable properties (Ni/Cr with additives) is cemented to a special ceramic substrate, resulting in a thermomechanical balance of forces. A resistive pattern is then photographed on the sheet. This process uniquely combines the important features of low TCR, long-term stability, non-inductance, ESD insensitivity, low capacitance, fast thermal stabilization, and low noise in a single resistor technology. To acquire a precision resistance value, the Bulk Metal Foil chip is trimmed by selectively removing the built-in «shorting bars». To increase resistance in known increments, selected areas are cut, resulting in progressively smaller resistance increases. In the flat sheet, the parallel pattern element design reduces inductance, the maximum total inductance of the resistor is 0.08 μH. The capacitance is 0.5 pF maximum. A 1 kΩ resistor has a rise time of less than 1 ns up to 100 MHz. The rise time depends on the value of the resistor, but the higher and lower values ​​are only slightly slower than the mid-range values. . The absence of ringing is especially important in high-speed switching, such as signal conversion. The DC resistance of a 1 kΩ bulk metal foil resistor compared to its AC resistance at 100 MHz can be expressed as: AC resistance / DC resistance = 1.001. Foil techniques produce a combination of highly desirable and previously unattainable strength specifications. By taking advantage of the overall stability and reliability of VFR resistors, designers can significantly reduce circuit errors and greatly improve overall circuit performance.

Despite all the benefits mentioned above, it is an expensive component that requires extreme care during installation in systems and especially in those where repair is impossible, such as an aerospace system.