- The resistor which uses metal film to limit the flow of electric current to a certain level is called a metal film resistor.
- Metal film resistors are resistors in which special metals or alloys are used as resistor materials, and the resistor film layer is formed on ceramic or glass by vacuum evaporation or sputtering.
- Metal film resistors have better performance than carbon or wire wound resistors. They are also more dependable than other types of electronic parts. For these reasons, metal film resistor is often used as replacements for other types of electronic components.
- The alloy material is evaporated on the surface of the ceramic rod skeleton by vacuum evaporation. Metal film resistors have higher accuracy, better stability, and noise and temperature coefficient calibration than carbon film resistors, and are widely used in instrumentation and communication equipment.
Construction of Metal Film Resistor
- The construction of metal film resistors is done by vacuum depositing a metal layer onto a high-purity ceramic cylindrical rod. The thicker the metal film deposited, the more stable the resistor value. Typically, the film thicknesses between 50 and 250nm are used as material thicknesses in most regions because it provides a greater long-term stability level. Different techniques can be used for the construction of metal film resistors but the most common method is Sputtering. Metal normally deposited is nickel Chromium, NiCr, other metals including gold with platinum, or tantalum nitride may be used for specialized applications.
- As soon as the film is deposited a metal end cap is pressed over the deposited metal. This makes contact with the resistive film and has the leads incorporated. The next stage in the process is trimming the value of the resistance to the required figure. This can be achieved by using lasers to cut a helix into the metal film. With this, the length of the metal element is extended and also reduces the width of the current-carrying track whilst keeping the deposited material thickness within the optimum range for long stability.
Applications of Metal Film Resistor
- Due to the good advantages of metal film resistors, they are used in almost all electronic circuits. They give superior performance in many respects to metal oxide film resistors and they stand the position of standard resistors commonly used. They are used when a high tolerance or more accurate value is needed in a circuit. They are also used for bridge circuits, filter circuits, and low-noise analog signal circuits. Metal film resistors are not suitable for applications that expose them to surge transients. This is due to their size and construction, unlike, carbon composition resistors that can tolerate transients way better.
Advantages of Metal Film Resistor
- The metal film resistors are normally applied to the axial leaded components, although thin film surface mount chip resistors use the same technology to create the resistors.
- One advantage of metal film resistors over carbon composition resistors is that they don’t change their value with age and their tolerance is better than the carbon resistor.
Other benefits include
- Better performance
- Lower cost
- Universally adopted
- High tolerance
- Good temperature coefficient of resistance
- Use less space in the circuit
- Long-term stability
Disadvantages of Metal Film Resistor
Despite the good advantages of metal film resistors, some limitations still occur. Below are the disadvantages of metal film resistors in their various applications
- They are slightly inductive
- Not suitable for high-frequency applications
- Installation may be difficult
- Professional is required for their work