Here are some of our Frequently Asked Questions. Have an additional question not listed below? Feel free to reach out to one of our Engineers using the “Ask a Question” button.

KEMET’s medical, automotive, industrial as well as commercial grade ceramic capacitors are qualified such that the testing criteria covers “Pollution Level 2” (non-conductive dust and pollution environments).  Our test labs for electrical and reliability testing are not in “clean room” environments.  Also, we also test for 1,000 hours at rated voltages under 85°C/85% relative humidity in the same lab environment.  Thus, it is safe to say that our finished components will function as specified and are safe to use in Level-2 dust and pollution environments.  We do, however, recommend that the customer follows storage and use conditions described in our catalogs.

Each series of Flex Suppressors have a different response curve. In general, Flex Suppressor is useful for noise above 1MHz. The EFG series is capable of suppression up to 10GHz.

Note that µ’ is defined as inductance and µ’’ is defined as magnetic impedance (loss). A high µ’ material has a strong magnetic field, absorbs more EMI, and is better at absorbing and reshaping magnetic fields. µ’’ is a critical parameter to look at when trying to attenuate EMI/RFI. Higher µ’’ values are better at suppressing unwanted noise.

The KEMET Flex Suppressor Datasheet contains more information.

Manganese dioxide (MnO2) and Conductive Polymer are two types of cathode materials used in Tantalum capacitors.

Electrolytic Capacitor Construction

The basic capacitor construction consists of two dielectric plates separated by a dielectric. In the case of electrolytic capacitors, one plate consists of a positively charged anode while the other consists a negatively charged anode. The anode of a tantalum capacitor is a porous pellet of sintered Ta metal. This porosity creates a large surface area within the pellet structure, which results in the tantalum capacitor’s high capacitance characteristic. The dielectric is tantalum pentoxide (Ta2O5). The cathode is a semiconductor material, either MnO2 or a conductive polymer.

About Polymer

Conductive organic polymeric materials were discovered by Alan Heeger, Alan MacDiarmid and Hideki Shirakawa. They were awarded the 2000 Nobel Prize in Chemistry for the discovery and development of conductive polymers. One of the first industrial applications of new polymer organic material was to replace manganese dioxide (MnO2) in tantalum capacitors.

Polymer Advantages

  • When used as the cathode material, polymer offers electrolytic capacitors several advantages.
  • ESR is available in the 1, 10, and 100 mOhm range
  • Turn-on reliability is significantly higher compared to MnO2
  • In the event of failure, polymers fail benign — they do not ignite.
  • KEMET Polymer Electrolytic capacitors can be identified in their datasheet where the name KO-CAP® is shown.

Surface mount tantalum capacitors typically have derating guidelines associated with them, regardless of capacitor manufacturer. The derating guideline is different based on the cathode material used in the construction.

Guidelines to Derate Polymer Capacitors

This information applies to Polymer Electrolytic capacitors with a Ta2O5 dielectric and PEDOT cathode system. These capacitors are also known as KO-CAP.

For polymer electrolytic capacitors, the typical voltage derating for the capacitor depends on its rated voltage. If the rated voltage is ≤10V, the recommended derating is 10%. However, if the rated voltage of the capacitor is >10V, then the recommended derating is 20%. These derating guidelines are typically specified to 105°C. Additional derating may be necessary up to 125°C.

Figure 1 – T525 Derate Polymer Capacitors Chart Example

Look for a derating or “recommended application voltage” section of a data sheet for more information. As an example, Figure 1 is the derating curve for a KEMET T525 KO-CAP Polymer Electrolytic capacitor.

Surface mount tantalum capacitors typically have derating guidelines associated with them, regardless of capacitor manufacturer. The Derating guideline is different based on the cathode material used in the construction.

Derating Tantalum MnO2 Capacitors

This information applies to Tantalum Capacitors with MnO2 cathodes. For Polymer Tantalum type capacitors, see this question on Polymers.

For MnO2 based tantalum capacitors, the typical voltage derating for an application is 50% of rated voltage, for temperatures up to 85°C. For temperatures greater than 85°C, additional derating is applied.

Figure 1 -Derate Tantalum Curve Example

Look for a derating or “recommended application voltage” section of a data sheet for more information. As an example, Figure 1 is the derating curve for a KEMET T491 Tantalum MnO2 capacitor.

Sometimes when looking on a datasheet for Ceramic Capacitors you might see references to the terms “PME” and “BME”?  What do these mean and why should you pay attention?  These acronyms are describing the metals used for the electrode plates.

Definitions

BME stands for “Base Metal Electrode” while PME stands for “Precious Metal Electrode.”  This means PME typically uses metals like Palladium-Silver (PdAg).  BME, on the other hand, will use less expensive metals like Nickel or Copper.  Nickel is the most common while Copper may be used in specialized capacitors like KEMET’s CBR Series which are RF Ceramic Capacitors.  Copper has similar conductivity to Silver-Palladium without the extra cost.

RoHS

Cost isn’t the only reason to give consideration to PME or BME.  Another reason refers to RoHS Compliance.  In order to manufacture a PME ceramic with Palladium-Silver, the dielectric material will have Lead(Pb) added to it.  BME ceramics, on the other hand, do not.  All PME capacitors, that I know of, are inherently not RoHS compliant.  While all BME, at least from KEMET, are RoHS compliant.

For example, KEMET’s line of Commercial C0GX7RX5RY5V, and Z5U ceramic capacitors are all BME and RoHS compliant.

Expected lifetime and failure rates are based on the component’s rated voltage. The rated voltage is usually lower than the “breakdown voltage”, which depends on the capacitor’s dielectric-typed and rated voltage.

Breakdown Voltage

Typically for MLCCs up to 200 V, the breakdown voltage is 4x rated. While parts rated for 200 V up to 1,000 V the breakdown voltage may be up to 1.2X rated. Parts over 1,000 V may have a breakdown such as 1.15X rated. (Please see a capacitor’s datasheet for specified values.)  These breakdown multipliers will decrease with increasing temperature.

Self-Heating

The breakdown voltage does not change over frequency. However, the impedance of a capacitor is lower with higher frequencies. This change in impedance may see a rise in ripple current. The current increase creates a self-heating, dependent on the component’s ESR.

Calculating Power Loss

The power loss (PLoss) of the MLCC requires a reduction in voltage to keep the current below a limit the power limit of the capacitor.

Figure 1 – KEMET K-SIM Example

Equation 1

For power calculation use the RMS (root mean square) values.

The VRMS = Vr/ √2 is only valid for sinusoidal waveforms. For other waveform shapes, use the integral shown in Equation 2.

Equation 2

Yes, KEMET has gone through great length to ensure that its Tantalum is conflict-free. Please see: http://www.kemet.com/conflictfree for more information.

A: Information regarding a film capacitor’s ESR can be found in the series datasheet. For some of KEMET’s surface mount film capacitors, K-SIM can be used. K-SIM will provide the impedance and ESR of a capacitor for an application’s voltage, temperature, and frequency.

Film Capacitor’s ESR Example

This K-SIM’s ESR plot is from the LDB Series Surface Mount Film Capacitors.

Film Capacitor Markings can vary by series. Please check the “Marking” section of the series datasheet for detailed information. You can also use the Contact Us form to ask detailed questions of an application engineer.

R74 Film Capacitor Markings Example

Yes, most datasheets will provide film capacitor temperature derating, for that series.

Film Capacitor Temperature Derating Example

The R74 Capacitor for AC Applications is rated at 85°C, but can operate up to 105°C. In the Performance Characteristics section of the datasheet, a voltage de-rating above 85°C is provided. In this example, the derating is 1.25%/°C.

If the information is not in the datasheet, please use the Contact Us Form to ask a KEMET Field Application Engineer (FAE).

KEMET has been a successful supplier of ceramic military product for over 30 years.

Recent customer applications demand the voltage and capacitance capability of commercial surface mount capacitors, but with a reduced or known reliability risk. For these applications, KEMET offers “COTS Grade” Ceramic Capacitors.

COTS Ceramic Capacitors are produced with the same material sets and manufacturing processes as our commercial and automotive grade capacitors. Additional screening, sometimes called “up-screening”, based on MIL-SPEC drawings is available.

Examples of available test levels are shown in Figure 1.

Figure 1 – Up-screening for COTS Ceramic Capacitors

Additional information can be found in the COTS-X7R and COTS-C0G datasheets.

The primary difference between standard (100% Matte-Tin) and Tin/Lead (Pb) terminations is the final plating. Both termination options utilize a copper or silver frit system that is barrier plated with Nickel. The final termination layer is then plated over the nickel barrier layer.

Details about the layers used in a ceramic capacitor’s construction can be found in the series datasheet. For example, an image like this is found in the commercial X7R surface mount ceramic capacitor datasheet.

Diagram showing construction with standard termination.

Ceramic temperature coefficients specify how much a MLCC’s capacitance will change with applied temperature. Sometimes this coefficient is called the “dielectric type.”

Each letter of the designation has a meaning, as shown these charts.

Class 1 Ceramic Temperature Coefficient

Coefficient ppm/°C Multiplier                 Tolerance of Temp Coefficient (ppm)
C = 0 0 = -1 G = 30
B = 0.3 1 = -10 H = 60
U = 0.8  2 = -100  J = 120
 A = 0.9  3 = -1000  K = 250

For example, C0G can vary 30ppm / °C

Class 2 and 3 Ceramic Temperature Coefficients

Low Temp Range High Temp Range Cap Shift from 25°C
X = -55°C 5 = +85°C R = ±15%
 Z = +10°C  7 = +125°C  S = ±22%
 Y = -30°C  8 = +150°C  U = +22 / -56%
 V = +22 / -82%

For example, X7R can vary ±15% from -55°C to +125°C

Additional Information

EIA-198 from ECIA provides more information.

The most common failure mode we see with ceramic capacitors is called “flex cracks.” A flex crack develops after the capacitor has been soldered to the board. When the PCB is flexed, the strain on the capacitor’s terminals causes a mechanical cracking.

When flex failures occur, we typically see them near a board edge, next to a screw hole, or next to a connector.

Flex cracks are not always immediate failures. It may take some time for each moisture to penetrate the crack and cause a failure. The capacitor may appear as either a short or partial open and is not deterministic.

AO-CAPs, or Aluminum Organic Capacitors, use a solid conductive polymer as their counter electrode. There is no electrolyte in the finished capacitor. Unlike traditional “wet” style aluminum electrolytic capacitors, the rated lifetime is significantly longer.

Please note that many times customers mistake the “Endurance” or “Lifetime Test” for AO-CAP as equivalent to the estimated life-time of a wet Aluminum Electrolytic. In the case of AO-CAP, these qualification tests. These test conditions are similar to other dielectric’s test conditions.

The Surge Voltage for Aluminum Electrolytics is a factor of magnitude, duration, and frequency of the surge. Datasheets may provide some general information and guidelines.

The image provided is a from the KEMET ALC10 datasheet.

For application specific information, please contact your local KEMET FAE.

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