Basics of Ceramic Chip Capacitors
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This presentation is a quick overview of ceramic chip capacitors. Subjects covered are: basic structure, manufacturing process, specifications, and basic characteristics.
Ceramic Capacitor Basics
Capacitors are devices that store energy in the form of an electric field. They can also be used to filter signals of different frequencies. The capacitance value is an indicator of how much electrical charge the capacitor can hold.
Multilayer ceramic capacitors consist of alternating layers of ceramic and metal.
The process of making ceramic capacitors involves many steps.
Base Metal vs. Precious Metal Systems
There are two material systems used today to make ceramic capacitors: Precious Metal Electrode and Base Metal Electrode. The precious metal system is the older technology and uses palladium silver electrodes, silver termination, then nickel and tin plating. Today this material system is mostly used on high voltage parts with a rating of 500V and higher. The base metal system is a newer technology and uses nickel electrodes, nickel or copper termination, and nickel and tin plating. This material system is typically used for parts with voltage ratings lower than 500VDC.
The capacitance value of a capacitor is determined by four factors. The number of layers in the part, the dielectric constant and the active area are all directly related to the capacitance value. The dielectric constant is determined by the ceramic material (NP0, X7R, X5R, or Y5V). The active area is just the overlap between two opposing electrodes.
The dielectric thickness is inversely related to the capacitance value, so the thicker the dielectric, the lower the capacitance value. This also determines the voltage rating of the part, with the thicker dielectric having a higher voltage rating that the thinner one. This is why the basic trade off in MLCCs is between voltage and capacitance.
The critical specifications of a capacitor are the dielectric constant, dissipation factor, dielectric withstanding voltage, and insulation resistance.
Dielectric constant: this depends on the ceramic material used. The table shows differentdielectrics and some of their specifications. As you can see NP0 has the lowest dielectricconstant, followed by X7R which has a significantly higher constant, and Y5V which ishigher still. This is why the capacitance values for X7R capacitors are much higher thanNP0 capacitors, and Y5V has higher capacitance than X7R. The capacitance change vstemperature is very small for NP0 parts from -55C to 125C, and gets larger for X7R, theneven larger for Y5V. So, the more capacitance a material provides, the lower the stabilityof capacitance over temperature.
Dissipation Factor: this is the percentage of energy wasted as heat in the capacitor. Asyou can see, NP0 material is very efficient, followed by X7R, then Y5V which is the leastefficient of the three materials.
Dielectric withstanding voltage: this refers to the momentary over voltage the capacitor iscapable of withstanding with no damage.
Insulation resistance: this is the DC resistance of the capacitor, it is closely related to theleakage current.
Characteristics of Ceramic Capacitors
Low impedance, equivalent series resistance (ESR) and equivalent Series Inductance (ESL). As frequencies increase, ceramic has bigger advantage over electrolytics
The final part of this presentation will cover the characteristics of ceramic capacitors.MLCCs have low impedance when compared with tantalum and other electrolyticcapacitors. This includes lower inductance and equivalent series resistance (ESR). Thisallows ceramic capacitors to be used at much higher frequencies than electrolyticcapacitors.
Characteristics of Ceramic Capacitors
Temperature Coefficient: Describes change of capacitance vs.temperature. Ceramic materials are defined by their temperaturecoefficient
Temperature Coefficient of Capacitance: Describes change of capacitance vs.temperature. Ceramic materials are defined by their temperature coefficient. For example,X7R means that the capacitance can change by +/-15% across a temperature range of -55C to 125C. The graph shows the temperature coefficient of NP0, X7R, and Y5Vmaterials.
Voltage Coefficient: Describes change of capacitance vs voltageapplied. Capacitance loss can be as much as 80% at ratedvoltage. This is a property of ceramic materials and applies to allmanufacturers
Voltage Coefficient of Capacitance: describes change of capacitance vs DC voltageapplied. This is a property of ceramic materials and applies to all manufacturers. Thegraph shows typical voltage coefficient curves for 500VDC rated X7R and NP0 capactiors.Note that the capacitance of the NP0 remains stable with applied voltage, while the X7Rmaterial can have a capacitance loss of 80% at rated voltage.
Aging: X7R, X5R, and Y5V experience a decrease in capacitance over timecaused by the relaxation or realignment of the electrical dipoles within thecapacitor.
For X7R and X5R the loss is 2.5% per decade hour and for Y5V it is 7% perdecade hour, NP0 dielectric does not exhibit this phenomenon
De-Aging: aging is reversible by heating the capacitors over the "CuriePoint" (approx 125°C), the crystalline structure of the capacitor is returned toits original state and the capacitance value observed after manufacturing.
Aging: X7R, X5R, and Y5V experience a decrease in capacitance over time caused by the relaxation or realignment of the electricaldipoles within the capacitor. For X7R and X5R the loss is 2.5% per decade hour and for Y5V it is7% per decade hour, NP0 dielectric does not exhibit any aging.
Aging is reversible by heating the capacitors over the "Curie Point" (approx 125°C), thecrystalline structure of the capacitor is returned to its original state and the capacitancevalue observed after manufacturing.
This slide is for reference and shows the Johanson Dielectrics part number breakdown.
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