Ceramic Capacitor - Application Classes For Ceramic Capacitors - Classes, Disambiguation

Classes, Disambiguation

Several standards define and specify so-called “application classes” or short “classes” for the different characteristics of ceramic capacitors. These characteristics are based on the different materials used for the capacitors. Very stable and linear behavior of capacitance values within a specified temperature range and low losses at high frequencies are the result of using mixtures of paraelectric substances based on titanium dioxide. But these mixtures have a relatively low permittivity so that the capacitance values of these capacitors are relatively small.

Higher capacitance values for ceramic capacitors can be attained by using mixtures of ferroelectric materials like barium titanate together with specific oxides. These dielectric materials have much higher permittivities, but at the same time their capacitance value are more or less nonlinear over the temperature range, and losses at high frequencies are much higher.

These different materials are the reason for the division of ceramic capacitors into different classes. Regarding international standardization, the IEC (including the European standards EN) specify two application classes:

• Class 1 ceramic capacitors with high stability and low losses for resonant circuit application
• Class 2 ceramic capacitors with high volumetric efficiency for decoupling, smoothing, by-pass and coupling applications

In addition to these two classes, the IEC standard had specified in the 1960/1970s a third class:

• Class 3 barrier layer capacitors or semiconductive ceramic capacitors. These capacitors have a very high permittivity but much lower stability of the capacitance value than class 2 capacitors. Because it is not possible to build multilayer capacitors with this doped ferroelectric ceramic material, the production of this capacitor today (2012) is only run in very small quantities for leaded single layer types. The “class 3” ceramic capacitor is no longer defined in the IEC standard.

In the past, ceramic capacitors were not limited to specification by an IEC standard. Manufacturers, especially in the US, preferred EIA standards. In many parts very similar to the IEC standard, the EIA RS-198 defines four application classes for ceramic capacitors.

• Class I or also written class 1 ceramic capacitors with high stability and low losses for resonant circuit application
• Class II or class 2 ceramic capacitors with high volumetric efficiency for buffer, by-pass and coupling applications
• Class III or class 3 ceramic capacitors with higher volumetric efficiency than class II and typical change of capacitance by -22% to +56% over a temperature range of 10 °C to 55 °C. They are comparable with class 2- Y5T/Y5U/Y5V capacitors of IEC definition
• Class IV or class 4 are barrier layer capacitors

The different class numbers within both standards are the reason for a lot of misunderstandings interpreting the class descriptions in the datasheets of many manufacturers. The EIA ceased operations on February 11, 2011, but the former sectors continue to serve international standardization organizations. In the following, the definitions of the IEC standard will be preferred and in important cases compared with the definitions of the EIA standard.