MULTILAYER CERAMIC CAPACITORS/AXIAL & …

1 KEMET Electronics Corporation, Box 5928, Greenville, 29606, (864) 963-63004 MULTILAYER CERAMIC CAPACITORS/AXIAL & RADIAL LEADEDM ultilayer CERAMIC capacitors are available in avariety of physical sizes and configurations, includingleaded devices and surface mounted chips. Leadedstyles include molded and conformally coated partswith axial and radial leads. However, the basiccapacitor element is similar for all styles. It is called achip and consists of formulated dielectric materialswhich have been cast into thin layers, interspersedwith metal electrodes alternately exposed on oppositeedges of the laminated entire structure isfired at high temperature to produce a monolithicblock which provides high capacitance values in asmall physical volume. After firing, conductiveterminations are applied to opposite ends of the chip tomake contact with the exposed materials and methods vary depending onthe intended CHARACTERISTICSC eramic dielectric materials can be formulated witha wide range of characteristics.

2 The EIA standard forceramic dielectric capacitors (RS-198) divides ceramicdielectrics into the following classes:Class I:Temperature compensating capacitors ,suitable for resonant circuit application or other appli-cations where high Q and stability of capacitance char-acteristics are required. Class I capacitors havepredictable temperature coefficients and are notaffected by voltage, frequency or time. They are madefrom materials which are not ferro-electric, yieldingsuperior stability but low volumetric efficiency. Class Icapacitors are the most stable type available, but havethe lowest volumetric II:Stable capacitors , suitable for bypassor coupling applications or frequency discriminatingcircuits where Q and stability of capacitance char-acteristics arenot of major importance. Class IIcapacitors have temperature characteristics of 15%or less. They aremade from materials which areferro-electric, yielding higher volumetric efficiency butless stability.

3 Class II capacitors are affected bytemperature, voltage, frequency and III:General purpose capacitors , suitablefor by-pass coupling or other applications in whichdielectric losses, high insulation resistance andstability of capacitance characteristics are of little orno importance. Class III capacitors are similar to ClassII capacitors except for temperature characteristics,which are greater than 15%. Class III capacitorshave the highest volumetric efficiency and pooreststability of any leaded CERAMIC capacitors are offered inthe three most popular temperature characteristics:C0G:Class I, with a temperature coefficient of 0 30 ppm per degree C over an operatingtemperature range of - 55 C to + 125 C (Alsoknown as NP0 ).X7R:Class II, with a maximum capacitancechange of 15% over an operating temperaturerange of - 55 Cto + 125 :Class III, with a maximum capacitancechange of + 22% - 56% over an operating tem-perature range of + 10 Cto + 85 electrical limits for these three temperaturecharacteristics are shown in Table ELECTRICAL LIMITST able IC0GX7RZ5 UDissipation Factor: Measured at following 1 kHz and 1 vrms if capacitance >1000pF1 MHz and 1 vrms if capacitance1000 pFX7R 1 kHz and 1 vrms* or if extended cap range vrmsZ5U 1 kHz and ( @ 25V) Stength: times rated DC Resistance (IR): At rated DC voltage,whichever of the two is smaller1,000 MFor 100 G1,000 MFor 100 G1,000 MFor 10 GTemperature Characteristics.

4 Range, CCapacitance Change withoutDC voltage-55 to +1250 30 ppm/ C-55 to +125 15%+ 10 to +85+22%,-56%* MHz and 1 vrms if capacitance100 pF on military CharacteristicsPass Subsequent IR TestELECTRICAL CHARACTERISTICSThe fundamental electrical properties of multilayerceramic capacitors are as follows:Polarity: MULTILAYER CERAMIC capacitors are not polar,and maybe used with DC voltage applied in either Voltage:This term refers to the maximum con-tinuous DC working voltage permissible across the entireoperating temperature range. MULTILAYER CERAMIC capacitorsare not extremely sensitive to voltage, and brief applicationsofvoltage above rated will not result in immediate , reliability will be reduced by exposure to sustainedvoltages above :The standard unit of capacitance is thefarad. For practical capacitors , it is usually expressed inmicrofarads (10-6farad), nanofarads (10-9farad), or picofarads(10-12farad).

5 Standard measurement conditions are asfollows:Class I (up to 1,000 pF):1 MHz and I (over 1,000 pF):1kHz and II:1 kHz and III:1 kHz and all other practical capacitors , MULTILAYER ceramiccapacitors also have resistance and inductance. A simplifiedschematic for the equivalent circuit is shown in Figure significant electrical characteristics resulting fromthese additional properties are as follows:Impedance:Since the parallel resistance (Rp) is nor-mally very high, the total impedance of the capacitor is:Figure 1C =CapacitanceL =InductanceRS= Equivalent Series Resistance (ESR)RP= Insulation Resistance (IR)RPRSCLZ =WhereZ = Total ImpedanceRS = Equivalent Series ResistanceXC= Capacitive Reactance = 2 fCXL= Inductive Reactance = 2 fL1RS+ (XC- XL)22DF =ESRXcXc2 fC1=Figure 2 OXcESRThe variation of a capacitor s impedance with frequencydetermines its effectiveness in many Factor:Dissipation Factor (DF) is a mea-sure of the losses in a capacitor under AC application.

6 It is theratio of the equivalent series resistance to the capacitive reac-tance, and is usually expressed in percent. It is usually mea-sured simultaneously with capacitance, and under the sameconditions. The vector diagram in Figure 2 illustrates the rela-tionship between DF, ESR, and impedance. The reciprocal ofthe dissipation factor is called the Q , or quality factor. Forconvenience, the Q factor is often used for very low valuesof dissipation factor. DF is sometimes called the loss tangent or tangent d , as derived from this Resistance:Insulation Resistance (IR) is theDC resistance measured across the terminals of a capacitor,represented by the parallel resistance (Rp) shown in Figure a given dielectric type, electrode area increases withcapacitance, resulting in a decrease in the insulation resis-tance. Consequently, insulation resistance is usually specifiedas the RC (IR x C) product, in terms of ohm-farads ormegohm-microfarads.

7 The insulation resistance for a specificcapacitance value is determined by dividing this product bythe capacitance. However, as the nominal capacitance valuesbecome small, the insulation resistance calculated from theRC product reaches values which are , IR specifications usually include both a mini-mum RC product and a maximum limit on the IR calculatedfrom that value. For example, a typical IR specification mightread 1,000 megohm-microfarads or 100 gigohms, whicheveris less. Insulation Resistance is the measure of a capacitor toresist the flow of DC leakage current. It is sometimes referredto as leakage resistance. The DC leakage current may becalculated by dividing the applied voltage by the insulationresistance (Ohm s Law).Dielectric Withstanding Voltage:Dielectric withstand-ing voltage (DWV) is the peak voltage which a capacitor isdesigned to withstand for short periods of time without dam-age.

8 All KEMET MULTILAYER CERAMIC capacitors will withstand atest voltage of x the rated voltage for 60 specification limits for these characteristics atstandard measurement conditions are shown in Table 1 onpage 4. Variations in these properties caused by changingconditions of temperature, voltage, frequency, and time arecovered in the following sections. KEMET Electronics Corporation, Box 5928, Greenville, 29606, (864) 963-63005 APPLICATION NOTES FOR MULTILAYERCERAMIC CAPACITORSA pplication NotesAPPLICATION NOTES FOR MULTILAYER CERAMIC capacitors KEMET Electronics Corporation, Box 5928, Greenville, 29606, (864) 963-63006 TABLE 1 EIA TEMPERATURE CHARACTERISTIC CODESFOR CLASS I DIELECTRICSS ignificant FigureMultiplier AppliedTolerance ofof Temperatureto TemperatureTemperatureCoefficientCoeffic ientCoefficient *PPM perLetterMulti-NumberPPM perLetterDegree CSymbolplierSymbolDegree +15 +106 + +10008+100009* These symetrical tolerances apply to a two-point measurement oftemperature coefficient: one at 25 C and one at 85 C.

9 Some deviationis permitted at lower temperatures. For example, the PPM tolerancefor C0G at -55 C is +30 / -72 2 EIA TEMPERATURE CHARACTERISTIC CODESFOR CLASS II & III DIELECTRICSLow TemperatureHigh Temperature Maximum CapacitanceRatingRatingShiftDegreeLetter DegreeNumberLetterCelciusSymbolCelciusSy mbolPercentSymbol+10CZ+45C2 +65C4 +85C5 +105C6 +125C7 +150C8 +200C9 +22 / -33%T+22 / -56%U+22 / -82%V+10 +20 +30 +40 +50 +60 +70 +80 Effect of Temperature:Both capacitance and dissipa-tion factor are affected by variations in temperature. The max-imum capacitance change with temperature is defined by thetemperature characteristic. However, this only defines a box bounded by the upper and lower operating temperatures andthe minimum and maximum capacitance values. Within this box , the variation with temperature depends upon the spe-cific dielectric formulation. Typical curves for KEMET capaci-tors are shown in Figures 3, 4, and 5.

10 These figures alsoinclude the typical change in dissipation factor for resistance decreases with , the insulation resistance at maximum rated temper-ature is 10% of the 25 of Voltage:Class I CERAMIC capacitors are notaffected by variations in applied AC or DC voltages. For ClassII and III CERAMIC capacitors , variations in voltage affect onlythe capacitance and dissipation factor. The application of DCvoltage higher than 5 vdc reduces both the capacitance anddissipation factor. The application of AC voltages up to 10-20 Vac tends to increase both capacitance and dissipation higher AC voltages, both capacitance and dissipation factorbegin to curves showing the effect of applied AC and DCvoltage are shown in Figure 6 for KEMET X7R capacitors andFigure 7 for KEMET Z5U fect of Frequency:Fr equency affects both capaci-tance and dissipation factor. Typical curves for KEMET multi-layer CERAMIC capacitors are shown in Figures 8 and variation of impedance with frequency is an impor-tant consideration in the application of MULTILAYER ceramiccapacitors.