What are MLCC or Multi-Layer Ceramic Capacitors?

Multilayer ceramic capacitors (MLCC) are a type of capacitor that have multiple layers of ceramic material that act as a dielectric. They can also be thought of as consisting of many single-layer capacitors stacked together into a single package. MLCCs have alternating layers of metallic electrodes along with layers of dielectric ceramic. These capacitors work as a 'dam' that temporarily charges and discharges electricity. They regulate the current flow in a circuit and prevent electromagnetic interference between components.

The thickness of a single dielectric and the number of stacked layers are directly proportional to the capacitance of the MLCC. Various technologies are used for thinning each layer in order to stack more layers to develop ultra-small high-capacity capacitors. The multi-layered construction allows them to achieve high capacitance values while still maintaining a small physical size, making them ideal for applications where space is limited.

MLCCs are composed of multiple layers of ceramic material, with conductive material placed between each layer to form the capacitor plates. The ceramic material used in MLCCs is typically a mixture of finely ground granules of paraelectric or ferroelectric raw materials like metal oxides, such as titanium dioxide, with a high dielectric constant. The conductive material used for the plates is typically a metal, such as nickel, silver, or palladium.

Manufacturing Process

A thin ceramic foil is cast from a suspension of the powder with a suitable binder. Rolls of foil are cut into equal-sized sheets, which are screen printed with a metal paste layer, which will become the electrodes. In an automated process, these sheets are stacked in the required number of layers and solidified by pressure. The electrodes are stacked in an alternating arrangement slightly offset from the adjoining layers so that they each can later be connected on the offset side, one left, one right. The layered stack is pressed and then cut into individual components. High mechanical precision is required, for example, to produce a 500 or more layer stack. The number of layers in an MLCC can range from a few to several hundred, depending on the desired capacitance and voltage rating. 

After cutting, the binder is burnt out of the stack. This is followed by sintering at temperatures between 1,200 and 1,450 °C producing the final, mainly crystalline, structure. This burning process creates the desired dielectric properties. Burning is followed by cleaning and then metallization of both end surfaces. The layers get stacked together and compressed. Through the metallization, the ends and the inner electrodes are connected in parallel and the capacitor gets its terminals.

MLCCs don't have leads, and as a result, they are usually smaller than their counterparts with leads. They don't require through-hole access in a PCB to mount and are designed to be handled by machines rather than by humans. As a result, surface-mount components like MLCCs are typically cheaper.

MLCCs have capacitance values ranging from 100 pF to 100 µF. The capacitance formula (C) of an MLCC capacitor is based on the formula for a plate capacitor enhanced with the number of layers:

where ε stands for dielectric permittivity; A for electrode surface area; n for the number of layers; and d for the distance between the electrodes.

MLCC Case Sizes

MLCCs are manufactured in standardized shapes and sizes for comparable handling. Because the early standardization was dominated by American EIA standards the dimensions of the MLCC chips were standardized by EIA in units of inches. A rectangular chip with the dimensions of length 0.06 inch and width 0.03 inch is coded as "0603". This code is international and in common use. JEDEC (IEC/EN), devised a second, metric code with units in mm. The same before-mentioned example of 0603 (EIA) coded capacitor is 1608 in IEC/EN metric code with dimensions of length 1.6 mm and 0.8 mm width.

Advantages of MLCC

One of the main advantages of MLCCs is their high capacitance density. Due to their multi-layered construction, MLCCs can achieve much higher capacitance values than other types of capacitors, while still maintaining a small physical size. This makes them ideal for applications where space is limited, such as mobile devices.

Another important property of MLCCs is their low equivalent series resistance (ESR). ESR is a measure of the internal resistance of a capacitor, and a lower ESR indicates that the capacitor can discharge more quickly and efficiently. This is particularly important in high-frequency applications, where rapid discharge times are required.

Applications of MLCC

MLCCs are used in a wide range of applications due to their high capacitance and low cost. They are commonly used in power supplies and voltage regulators, where they are used to filter out unwanted noise and ripple. They are also used in decoupling circuits, where they are used to isolate one circuit from another to prevent interference.

In addition, MLCCs are used in timing circuits, where they are used to stabilize the frequency of oscillators and provide accurate timing signals. They are also used in RF filters, where they are used to tune circuits to specific frequencies and reject unwanted signals.

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