Capacitors Blog

Ceramic capacitor is something that a lot of people would need in order to facilitate their life. If you do not think about this before, this is normal indeed. In fact, there are a lot of devices which are using ceramic capacitors nowadays and you normally would not notice about that. When you are using the internet to browse articles, you are actually using the ceramic capacitors already. Yes, it is because there are a lot of devices which would involve the use of ceramic capacitors and the computer could be one.

A lot of organizations would need ceramic capacitors if you think deeper. Yes, they would need this kind of device to continue their innovative processes in the design of the products which involve the high technology. This is also why a lot of people would try to sell this kind of products through various means.

Effect of Frequency: Frequency affects both capacitance and dissipation factor..
The variation of impedance with frequency is an important consideration in the application of multilayer ceramic capacitors. Total impedance of the capacitor is the vector of the capacitive reactance, the inductive reactance, and the ESR. As frequency increases, the capacitive reactance decreases. However, the series inductance (L)  produces inductive reactance, which increases with frequency. At some frequency, the impedance ceases to be capacitive and becomes inductive. This point, at the bottom of the V-shaped impedance versus frequency curves, is the self-resonant frequency. At the self-resonant frequency, the reactance is zero, and the impedance consists of the ESR only.

Of much less concern, yet still important, especially in audio applications, is the micro phonic or piezoelectric effect. Barium titinate which is the base ceramic material for most dielectric systems will exhibit microphonic effects. It is not very difficult to take a Y5V capacitor and put a DC bias with a small signal 1kHz sine wave and get the capacitor to “sing”. Tantalum capacitors exhibit no microphonic effects. The experiment done by AVX involved the opposite phenomena whereby the part was shaken while under bias and the resulting generated voltage was measured. This was done for a series of 1µF devices and the results are shown in Fig below.

Ceramic capacitors are suitable for moderately high-frequency work (into the high hundreds of megahertz range, or, with great care, into the low gigahertz range), as modern ceramic caps are fairly non-inductive compared to the other major classes of capacitors (film and electrolytic). Capacitor technologies with higher self-resonant frequencies tend to be expensive and esoteric (typically, mica or glass capacitors).

Sample self-resonant frequencies for one set of C0G and one set of X7R ceramic capacitors are:

ceramic capacitors consist of electrodes, the interleaved ceramic dielectric and the external terminal connectors. The capacitance is given by the description:

A = Electrode area
n = Number of active layers
d = Distance between electrodes
εr = Dielectric relative
ε0 = Dielectric constant

Whilst the values “A x n” and “d” are respectively determined by the production process the dielectric constant is a function of the ceramic material used.

When sinusiodal or ripple voltage applied to DC Ceramic Disc Capacitors, be sure to maintain the peak-to-peak value or the Peak value of the sum of both AC + DC within the rated voltage.

When start or stop applying the voltage, resonance may generate irregular voltage.

When rectangular or Pulse Wave Voltage is applied to DC Ceramic Disc Capacitors, the self-heating generated by the capacitor is higher than the sinusoidal application with the same frequency. The allowable voltage rating for the rectangular or pulse wave corresponds approximately with the allowable voltage of a sinusoidal wave with the double fundamental frequency.

The allowable voltage varies, depending on the voltage and the waveform.

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Previous blog we have talk the simplest ceramic capacitor consists of a square or circular shaped ceramic with electrodes attached.

Manufacturing starts with finely powdered base ceramic material that are pressed into dies and fired at high temperatures. Individual capacitors may be cut from large sheets of ceramic material. The capacitor electrodes (i.e. the plates) are attached by screen printing a mixture of silver, finely powdered glass, and a binder on both sides of the disk, and firing the ceramic element again. This evaporates the binder, and the melted glass binds the silver to the ceramic surface. Next, hairpin wires are clipped onto the capacitor and it is dipped in solder. Once cooled the capacitor is dipped into paint, marked, and the lower ends of the hairpin cut off. Clearly the whole process lends itself to automation, and dipped ceramic capacitors are very inexpensive. Capacitor characteristics depend on the type of ceramic used.

Dipped ceramic capacitor construction. (a) Capacitor after electrode and hairpin attachment. (b) Capacitor after dipping and marking.

Dipped Ceramic Capacitors. The simplest ceramic capacitor consists of a square or circular shaped ceramic with electrodes attached (see figure). The capacitance is given by

where A is the area of the two plates, is the dielectric permittivity of vacuum, Kd is the dielectric's dielectric constant and d is the distance between the two plates.

MLC capacitors are marvels of modern material science. Manufacturing MLC capacitors is considerably more complicated than manufacturing dipped ceramic capacitors. First, the base ceramic material is mixed with a binder and fashioned into thin sheets. Electrodes are painted onto one side of the sheets using a paint that consists of a liquid binder with fine metal particles in suspension. The metals that are used include gold, palladium, platinum, and silver alloys. The reason for using these metals is that when the base ceramic is fired, oxygen is required for the ceramic proper to form. If one uses a metal such as iron, for example, it would oxidize completely during the firing process.Precious metals do not have this problem, but is a major cost component of monolithic ceramic capacitors. However, recently some manufacturers have reported using nickel and copper for the electrodes. This promises to reduce the cost of the raw materials, but at the expense of more elaborate manufacturing processes.

Once the ink is dry, the sheets are stacked on top of each other. The painted electrodes are arranged so that alternate electrodes exit from opposite ends. The top and bottom most layers do not have painted electrodes. The laminated layers are then compressed and fired, which sinters them into one monolithic structure.

Next, the ends are terminated, often using silver. For leaded capacitors, wires are attached, and finally the capacitor is encapsulated in plastic and marked. In the case of chip capacitors, the silver end terminations are covered with tin to aid soldering. The whole capacitor may be covered with lacquer.