The following steps are taken in the manufacturing of a resistor:
(1) PREPARATION OF SUBSTRATE: Substrate should hold the resistive element. It should be a good insulator. The overall characteristics of resistors are highly dependent upon that of substrate. Ceramic such as steatite, porcelain, mullet, forsterite, and alumina are used as substrates. Advantages of using ceramics as substrate are that they can be shaped into desired dimensions and coefficients of linear expansion can be matched with the resistive element on top of it. It has good mechanical strength and can withstand high temperatures.
(2) PREPAREATIONS OF RESISTIVE ELEMENT: Generally used resistive materials are metal alloys, carbon and graphite with binders. The resistance wire used has lower temperature coefficient. Nickel-copper, nickel-chromium and nickel-aluminium are the materials frequently used. Resistive materials may be in the form of film or slug.
(3) END CONNECTIONS OR TERMINAL FITTING: Terminals are used to make electrical connections of the resistive element to the circuit. This is done by using wire leads and metallic lugs. Terminals can be fitted either axially or radically by press fitting, welding or soldering.
(4) PROTECTIVE COATING: The protective coating is applied on resistance element to provide protection against mechanical and environmental forces. By choosing proper coating material, the resistor can withstand higher temperatures. Cement mixed with binds, virtuous, enamel or silicon and generally used as protective coating material.
(5) COLOR COADING OF BAND: Resistors use a pattern of collared strips to point out resistance value, tolerance and other ratings. Then they are finally packed.