As the name suggests, the metal film resistor is manufactured by keeping a slim layer of metal onto a ceramic former. Here the metallic film behaves in the same manner as the resistance wire. You can even control its thickness, length, and width such that it can be produced to a high tolerance.
The metal film resistor can be pre-aged. Not only this, but the metal protected to ensure it does not see any deterioration in its quality with time. Thus, the stability for the long term is good.
In the present time, these metal film resistors are a well-known choice for leaded axial resistors and because of this, they are utilized in large quantities.
Construction of Metal Film Resistor
The metal film resistor is made by vacuum which deposits a layer of metal on a highly purified ceramic cylinder rod. Often, the more the thickness of the metal film deposited, the more is the stability in the value of the resistor. Generally, the thickness of the film lies in the range of 50 to 250nm as the stability levels are directly proportional to the thickness of the material. A variety of techniques can be utilized for this, but the most popular one is sputtering. The metal that is used for depositing are generally Chromium, Nickel, NiCr, but other metals like platinum with gold, or tantalum nitride may also be taken into consideration for some highly specialized applications.
As soon as the film gets deposited, a metal end cap is pressed over it. This reaches the resistive film and has the leads joined.
The next phase in the manufacture is to bring the value of resistance to the desired figure. This is achieved generally with the help of lasers to trim a helix into the metal film. This decreases the width of the current-carrying track while keeping the thickness of the deposited material within an optimum range for providing stability for long term.
Laser trimming’s accuracy level means that the resistor can be made to an extremely close tolerance level. A tolerance of 0.5%, 0.25%, 0.1%, as we all 2% and 1% are present. The tolerance of 1 and 2 percent are available on a wide scale. This makes the electrical circuits to keep up decent repeatability starting with one unit then onto the next.
It is also to be noted that the metal film resistor also keeps an optimum temperature co-efficient which lies in the range of 50 and 100ppm /K.
The final step in the manufacturing process of the metal film resistor is to add up the markings and the protective coating. Generally, this protective coating comprises a resin that is included in many layers that are separately heated on. And at the end, the marking rings are added to demonstrate the estimation of metal film resistor and the other applicable attributes.
This was all we have regarding metal film resistors. Hope you liked going through the article. Brands that manufacture them are Vishay, Yageo, and KOA Speer. Make sure to check them out using the links as provided.
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