Resistor Technologies and Key Parameters

By Sanjay Chawla On Jun 09, 2010 Site: Electronics Design Engineering Lounge (Public) Type: Blog - Tags: Electronics - # of views: 1395

Chip resistors are in high demand now-days and are among the basic building blocks of various circuits. They are more space efficient than the discrete encapsulated resistors.

Key parameters of chip resistors are electrostatic discharge (ESD) protection, thermal electromotive force (EMF), temperature co-efficient of resistors (TCR) and self-heating properties, long-term stability, power coefficient and noise.

Wire wound resistors are mostly used in the precision circuits and are not available in true chip form so are not useful in the applications where size and weight limitations demand precision in the chip resistor format.

In the discrete-resistor industry, advances have been made in wire-wound, thick film, thin film, and foil resistor technologies, with each offering various tradeoffs in performance per unit cost.

Precision wire-wound resistors have better ESD stability and lower noise than thin or thick film resistors. Wire-wounds also have a lower TCR and better stability.

Thin films can produce a higher resistance per given area than wirewound or Bulk Metal® Foil resistors, and are cheaper as well. This makes them quite economical and more space-efficient where high resistances are needed with intermediate levels of precision.

Thick film resistors are much more universally used because of their much greater resistance density (high resistance/small size) and much lower cost. They have faster frequency response, similar to thin films and foil, but are the noisiest of all currently used resistor technologies.

A specific foil alloy with known and controllable properties (Ni/Cr with additives) is applied to a special ceramic substrate, resulting in a thermo-mechanic balance of forces. A resistive pattern is then photo-etched in the foil. This process uniquely combines the important characteristics of low TCR, long-term stability, non-inductance, ESD insensitivity, low capacitance, fast thermal stabilization, and low noise in one single resistor technology.

These capabilities bring high stability and reliability to system performance without any compromise between accuracy, stability, and speed. To acquire a precision resistance value, the Bulk Metal Foil chip is trimmed by selectively removing built-in "shorting bars."