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Capacitors are electronic charge-storing and signal-filtering devices that block direct current but allow the passage of alternating current within design parameters. Each capacitor includes two conductors with an insulating, polarizable dielectric layer sandwiched between them. A chip capacitor generally is a rectangular device that is the capacitor of choice for high-frequency electronic circuitry. Its size typically is less than a quarter of an inch (6.35 mm), and it operates at a power of a fraction of one watt. A chip capacitor is not often sold individually, but in reels, often by the thousands and can cost less than $1 US Dollar per 100 capacitors.
A chip capacitor is made up of multiple layers, which is why it is often called a multi-layer ceramic chip capacitor (MLCC). The ceramic powder needs to be formed into sheets of specific thickness. This means that the powder must be combined with carefully controlled quantities of binding agents and solvents. After it has been blended, the slurry is poured, then baked on conveyor belts. The ceramic sheets are not yet cut to size; the conductor application and layering must take place first.
Conductive metal ink is made from powdered metal, ceramic and solvents, using a crushing, blending and finishing device called a three-roll mill. The ink or paste is then screened on through specially patterned “silk screens” and hot air dried. At this point, the structure can be likened to green pottery. Sheets are then layered in the correct manner and number. After pressure is applied to unite these layers into a single structure, it is cut into individual pieces.
Next, the pieces must be fired. The heart of this process is a kiln with a very slow-moving conveyor belt that carries the pieces through a tunnel with a very carefully profiled heating cycle, and, if need be, a controlled atmosphere. This step plays a large role in the characteristics of the finished devices. At this point, terminals must be applied at both ends of the devices, using powdered metal and glass, with solvent. These are sufficiently fired.
Electroplating is the final process that proceeds testing. The plating takes place in layers, the first of which is a barrier layer of nickel, to protect the underlying device. Afterward, a layer of tinplate keeps the nickel from corroding and, during end-use, improves the soldering compatibility, if the devices are to be soldered. After all of these steps have been accomplished, the devices are tested. Quality-control values and tolerances are established and carefully recorded, then the capacitors are packaged and sold.
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