What you should know about electrolytic aluminum capacitors ?

Discover the basic information about electrolytic aluminum capacitors, to improve your choice


1. Basic construction

Structure of an electrolytic aluminum capacitor is shown hereunder:

  1. Anode: aluminum foil
  2. Dielectric: aluminum oxide
  3. Papers spacers impregnated with electrolyte
  4. Ionic conduction assumed by electrolyte
  5. Cathode: aluminum foil

 

The positive plate is an etched aluminum foil covered with alumina which is the dielectric of the capacitor.


The negative plate is constituted by a second aluminum foil which serves as a current supply, and by electrolyte-impregnated papers layers.


The metal used for anode is a ≥ 99,98 % grade aluminum.


The dielectric has a thickness of 13 Å / V.


The aluminum used for the cathode is a ≥ 98 % grade aluminum covered with a dielectric layer with a thickness of about 40 Å.

 

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2. Diagram of the equivalent circuit

CA = Capacitance of the anode
CK = Capacitance of the cathode
Rp = Parallel resistance due to the aluminum oxide f Ilms.
RL = Series resistance of connections, plates and impregnated spacer.
Ls = Inductance of winding and connections.

 

A standard simplified diagram is :

 

Cs is the series capacitance of both anode and cathode capacitances.
Electrolytic aluminum capacitors are naturally polarized because of the insulating f Ilm on the anode.

Given the very thin aluminum oxide layer, a reversed voltage should not exceed 1.5 V when there is energy supply.
Short duration reverse voltages can be absorbed by special construction, second anode replacing the former cathode.

3. Electrical characteristics

✪ Rated capacitance Cr

The rated capacitance is defined at 100 Hz and at ambient temperature.

 

✪ Rated voltage Ur

Ur is the maximum DC voltage which may be applied in continuous operation.
When applying a superimposed alternating voltage, the peak value of the resulting waveform should not exceed the rated voltage.

 

✪ Peak voltage Up


Up is the maximum repetitive voltage which can be applied within short periods.
Defined in CECC 30 300 and IEC 60 384-4: 
1000 cycles of 30 s charge followed by a no load period of 5 min. 30 s with upper category temperature.

Up ≤ 1,15 UR (UR ≤ 315 V)
Up ≤ 1,10 UR (UR > 315 V)

 

✪ Dissipation factor Tan

The dissipation or loss factor is defined by its tangent Tand

 

✪ Equivalent series resistance ESR

The relation between ESR and dissipation factor Tand.

 

✪ Impedance Z - Inductance L


The impedance is given by: 
Z =g R2 + (Lv –1 )2
                        Cv
L inductance. Generally L = 5 to 20 nH

 

Z and ESR as function of frequency typically follows the chart: 

 

✪ Permissible ripple current (I r.m.s.)

The current is defined at the maximum climatic category and at 100 Hz.

It is the root mean square value r.m.s. The value I0 is the rated value for calculations of expected life up to3 I0.

 

✪ Leakage current Il

Il is measured at 20°C after a 5 min. polarization under rated voltage.


For CR in μF and UR in V: 
 Il ≤ 0,01 CR UR or 1 μA*
when CR UR ≤ 1000 μC
 Il ≤ 0,006 CR UR + 4 μA
when CR UR > 1000 μC
For UR > 350 VDC it can be specified: 
with K = 4, 6 or 8
or
 Il ≤ 0,3 (CR UR)0,7 + 4 μA (CECC 30 300)


* Whichever is the greater

 

✪ Characteristics

Versus temperature (typical values).

 

- Capacitance drift
Versus temperature

- ESR and Z drifts at 100 Hz
Versus temperature


- Leakage current drift

Versus temperature

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4. Specification to apply

Electrolytic aluminum capacitors are defined in: 

  • NF and UTE French national standard
  • CECC European specifications
  • IEC international specifications

Quality insurance procedures are described in these specifications.

5. Endurance tests / life time


✪ Standard endurance test

at max category temperature: 

Standard endurance tests do not exceed 2000 hours at 125°C. However, present EXXELIA technologies concerning liquid electrolytes have led to endurance tests up to 5000 hours at 125°C (PRORELSIC 125 - FELSIC 125 RS) and even 20000 hours at 125°C (PRORELSIC 145 - ALSIC 145).

 

✪ Performance requirements on standard endurance tests


Permissible capacitance drift ∆C/C (%)
Permissible increase factors on Tand, ESR, Z and Il initial values
 

(1) Tand or ESR: for initial value, take standard value.
(2) Z: for initial value, take specified value (see data sheet ).

Specific requirements can be taken into consideration with regards to initial values of dissipation factor or equivalent series resistance and impedance.

 

✪ Failure criteria for electrolytic capacitors

Failure criteria are defined in CECC 30 301

  • Non measurable defaults leading to complete failure.
  • Measurable defaults leading to adjustment losses of the load circuit (failure due to variations).

 

- Non measurable defaults
They might be summed up as: 

  • Open circuit
  • Short circuit
  • Operation of pressure relief device
  • Severely damaged insulation
  • Unusable terminations

 

- Measurable defaults
Variations exceeding the values given below characterize a default.

  • Capacitance drift ∆C/C (%): 3 times the limit for standard endurance testing or 50 % (whichever is the smallest).
  • Tand or ESR: 3 times standard max initial values.
  • Z: 3 times standard max initial values.
  • Il: initial limit (under load conditions).

Specific requirements can be taken into consideration with regards to lower drifts.

 

Influence of main parameter on operational life.

- Temperature

The capacitors operational life is highly dependent upon its internal temperature Ui and therefore upon the ambient temperature and the ripple current.
Knowing ESR and dissipated power values one can figure out, the internal temperature rise and then determine the capacitors expected life.
With present high boiling point electrolytes
Ui max = 125 to 185°C depending on styles.


- Ripple current
The ripple current flowing through the capacitor increase the internal temperature through power dissipation.
Standards define the permissible current at 100 Hz and generally consider a temperature rise of 5 to 10°C of max category temperature.
Current waveforms and frequencies make it difficult to clearly determine the capacitors internal temperature rise, which defines the operationally life.
Experiments confirm following relationship: 


Ui = Ua + (Uc - Ua) K


Where: 

  • Ui = Internal hot spot temperature
  • Ua = Ambient temperature
  • Uc = Case temperature
  • K = Parameter depending upon case diameter and cooling

Ø ≥ 51 k = 2 ± 0,5
Ø < 51 k = 1,5 ± 0,5    (air cooling - 0,2 m/s)

 

r.m.s. value according to current waveform.

 

- Dissipated power versus case dimension
For calculations of ripple currents, considering an internal temperature rise of 10°C

 

P = ESR.I ²
P = Dissipated power (mW)
(Ui - Ua = 10°C)
ESR: Equivalent series resistance (100 Hz 20°C)
I: Ripple current (r.m.s. value at 100 Hz)
For different frequencies from 100 Hz, I must be multiplied by the factor F, according to above chart.

 

- Thermal resistance Rth and air cooling
Rth is static thermal resistance (without cooling) between capacitor central hot spot and ambient temperature measured at a distance of one capacitor diameter


 

Forced or not cooling air can lead to a significant decrease of these values.
Consequently, r.m.s. ripple current can be increased as a function of air cooling speed: 

This parameter shall be applied to one capacitor alone.
For capacitors in bank, ambient temperature must be strictly equal around all capacitors.


- Quality guaranty
We guarantee products manufactured during 2 years from the data of shipment against defaults of material and assembly.
This guaranty can be involved by the buyer only if our products are used within normal conditions, always according to the state of the art and taking in account storage conditions.
The equipment design should take into consideration possible failures of our capacitors and related effects in order to avoid them.
Guaranty is not applicable for damages occurred by surge voltage, irregular use, polarity inversion or maintenance default.
Guaranty is exclusively limited to the replacement of individual defective capacitors within the terms of delivery. This rule applied to all cases and particularly to any further consequence of failures.


- Reliability
Failure rate: 
FR = Number of components tested x test duration / Number of failures


Failure rate is measured in FIT (failure in time = 10–9 / hour).
The failure rate is set up during the life time of the capacitor (phase II)


I. Early failure phase (generally excluded during ageing process).
II. Operational life time of the capacitors
III. End of life

 

Mean time between failures MTBF = 1/FR mesured in years

Multiplying factor of FR with voltage and temperature

 

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6. Information on application

✪ Cleaning solvents

Use aliphatic alcohols, such as denatured ethyl alcohol, isopropanol, or butylacetate, or else alkaline d Iluted solutions. Avoid incompatible solvents (halogenous for example).

 

✪ Shelf life

There is no electrical characteristics variation for long periods of storage except leakage current which can increase.
It is caused by chemical reactions between the dielectric alumina and the electrolyte. These reactions are reversible when switched on. Capacitors can generally be stored at temperature between –5° and +50°C without reforming for the following periods of time: 

  • For UR ≤ 100 V, storage time:     5 years
  • (up to 10 years under specific conditions)
  • For 100 V < UR ≤ 360 V storage time:     3 years
  • For 360 V < UR < 500 V storage time:     1 year
  • For UR ≤ 500 V, storage time:     6 months

Generally when these periods are overstepped, one hour at rated voltage causes the decrease of leakage current under the specified limits. An other way to avoid this leakage current increase problem is to always limit ava Ilable power through capacitor during first seconds or minutes after storage or transport, according to the following chart: 
 

✪ Low pressure resistance

EXXELIA capacitors can be used with ambient low pressure decreasing up to 10 mbar (altitude 28000 m – 92000 feet).
 

✪ Mounting screw terminals capacitors (FELSIC)

Capacitors may be used vertically (terminals on top) or horizontally. When used horizontally, the following position in relation to the safety vent, is recommended: 
Mounting capacitors in series may be used for operating voltage exceeding Ur. See FELSIC in bank.

 

✪ Mounting solder type capacitors

They may be used in any position. During mounting, avoid applying excessive force to capacitor pins or wires. There is a risk of damaging internal connections.
After soldering and for the same reasons, do not try to move the capacitor's body.


✪ Electrolytes: safety rules

Electrolytes used in EXXELIA capacitors are manufactured by EXXELIA. Main solvents are generally g butyrolactone and ethylene glycol, very stable high boiling point solvents. Ionic conductive salts in electrolyte induce a very weak acidity (pH 5 to 7).

 

✪ Environment

In aluminium capacitors with liquid electrolyte there is no component showing a pollution risk, in small amounts, of air or water. EXXELIA is always involved in this security field particularly in using chemicals for electrolyte, without well-known risks.

  • Dimethylformamide (DMF) dangerous solvent forbidden in several uses is completely excluded by EXXELIA,since 1990.
  • There is no halogen compound such as chlorofluorocarbon (CFC or FCKW in german) or polychlorobiphenyl (PCBPyralene) or pentabromodiphenylether or octabromodiphenylether.

There is neither benzene, toluene or phenyl compound nor explosive such as picric acid, nor asbestos in plastic covers. All the capacitors made by EXXELIA since 1991, can be scrapped or used in raw materials recycling processes without special care in compliance with Community rules.


EXXELIA aluminium capacitors with non-solid electrolyte are particularly suitable for different kinds of environment taking in account severity increasing laws.
European directives 2003/11/EC, 2002/96/EC (WEEE) and 2002/95/EC (RoHS) applies to all EXXELIA capacitors including every solder type, manufactured with pure tin coated pins or wires, since at least January 2006.

 

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Published on 12 Dec 2021 by Stephane PERES

What you should know about Ceramic Capacitors ?

▲ What you should know about Ceramic Capacitors ?   1. Materials expert For 50 years and as a market leader, EXXELIA’s comprehensive knowledge of the materials properties and performances have enabled us to design capacitors in Porcelain, NPO, BX, 2C1, BP, X7R and –2200ppm/°C ceramics. > See our capacitors in catalog   2. Custom Designs Our catalog products don’t meet your application?  Based on the valuable experience accumulated over the design of 2,000+ specific ceramic capacitors, you can trust EXXELIA to define a qualitative custom solution in a time effective manner.   3. No Obsolescence Choosing a standard or custom EXXELIA product means you won’t have to worry about obsolescence.   4. Typical Applications Aerospace & Defense: cockpit panels, flight control, radio systems, missile  guidance systems… Space: military and commercial satellites, launcher… Medical: MRI, external defibrillators, implantable devices… Telecommunications: base stations… Oil and gas: drilling tools, MWD, LWD, wellheads…   5. ISO 9001 And AS9100C Quality is at the core of Exxelia’s corporate culture. Each sites has its own certifications.    6. Certifications Capacitors manufactured by EXXELIA comply with American and European standards and meet the requirements of many international standards. For Space qualified parts (ESA QPL), please refer to our catalog «Ceramic capacitors for Space applications».   7. Quality & Reliability EXXELIA is committed to design and manufacture high quality and reliability products. The test cycles reproducing the most adverse operating conditions over extended periods (up to 10 000 hours) have logged to date well over 5.109 hours/°Component. Failure rate data can be provided upon request. 8. Conflict minerals EXXELIA is committed to an approach based on «Conflict Minerals Compliance». This US SEC rule demands complete traceability and a control mechanism for the mineral procurement chain, encouraging importers to buy only «certified» ore. We have discontinued relations with suppliers that procure from the Democratic Republic of the Congo or an adjoining country.   9. Environment EXXELIA is committed to applying a robust environmental policy, from product design through to shipment. To control its environmental footprint and reconcile this with the company’ functional imperatives, our environmental policy provides for the reduction or elimination of hazardous substances. We also focus on compliance with European Union directives and regulations, notably REACH and RoHS. 10. RoHS Compliancy SMD CAPACITORS The capacitor terminations are generally protected by a nickel barrier formed by electrolytic deposit. This barrier gives chip capacitors leaching performance far exceeding the requirements of all applicable standards. The nickel barrier guarantees a minimum resistance to soldering heat for a period of 1 minute at  260°C in a tin-lead (60/40) or tin-lead-silver (62/36/2) bath without noticeable alteration to the solderability. It also allows repeated soldering-unsoldering and the longer soldering times required by reflow techniques. However nickel barrier amplifies thermal shock and is not recommended for chip sizes equal or greater than CNC Y (30 30) - (C 282 to C 288 - CNC 80 to CNC 94). LEADED COMPONENTS As well as for SMD products, leaded capacitors ranges can also be RoHS. These products, which are characterized by the suffix «W» added to the commercial type, are naturally compatible with the soldering alloys used in RoHS mounting technology. The connections coating is generally an alloy SnAg (with a maximum of 4% Ag). However, on a few products that EXXELIA will precise on request, the coating is pure silver.   11. MLCC Structure   12. Equivalent circuit Capacitor is a complex component combining resistive, inductive and capacitive phenomena. A simplified schematic for the equivalent circuit is:   13. Dielectric characteristics  Insulation Resistance (IR) is the resistance measured under DC voltage across the terminals of the capacitor and consists principally of the parallel resistance shown in the equivalent circuit. As capacitance values and hence the area of dielectric increases, the IR decreases and hence the product (C x IR) is often specified in Ω.F or MΩ.µF. The Equivalent Series Resistance (ESR) is the sum of the resistive terms which generate heating when capacitor is used under AC voltage at a given frequency (f). Dissipation factor (DF) is the ration of the apparent power input will turn to heat in the capacitor: DF = 2π f C ESR When a capacitor works under AC voltage, heat power loss (P), expressed in Watt, is equal to: P = 2π f C Vrms2 DF   The series inductance (Ls) is due to the currents running through the electrodes. It can distort the operation of the capacitor at high frequency where the impedance (Z) is given as: Z = Rs + j (Ls.q - 1⁄(C.q)) with q = 2πf When frequency rises, the capacitive component of capacitors is gradually canceled up to the resonance frequency, where : Z = Rs and LsC.q2 = 1 Above this frequency the capacitor behaves like an inductor.   Manufacturing steps > See our capacitors in catalog SMD environmental tests Ceramic chip capacitors for SMD are designed to meet test requirements of CECC 32100 and NF C 93133 standards as specified below in compliance with NF C 20700 and IEC 68 standards: Solderability: NF C 20758, 260°C, bath 62/36/2. Adherence: 5N force. Vibration fatigue test: NF C 20706, 20 g, 10 Hz to 2,000 Hz, 12 cycles of 20 minutes each. Rapid temperature change: NF C 20714, –55°C to + 125°C, 5 cycles. Combined climatic test: IEC 68-2-38. Damp heat: NF C 20703, 93 %, H.R., 40°C. Endurance test: 1,000 hours, 1.5 URC, 125°C. > See our capacitors in catalog   STORAGE OF CHIP CAPACITORS TINNED OR NON TINNED CHIP CAPACITORS Storage must be in a dry environment at a temperature of 20°C with a relative humidity below 50 %, or preferably in a packaging enclosing a desiccant.  STORAGE IN INDUSTRIAL ENVIRONMENT: 2 years for tin dipped chip capacitors, 18 months for tin electroplated chip capacitors, 2 years for non tinned chip capacitors, 3 years for gold plated chip capacitors. STORAGE IN CONTROLLED NEUTRAL NITROGEN ENVIRONMENT: 4 years for tin dipped or electroplated chip capacitors, 4 years for non tinned chip capacitors, 5 years for gold plated chip capacitors. Storage duration should be considered from delivery date and not from batch manufacture date. The tests carried out at final acceptance stage (solderability, susceptibility to solder heat) enable to assess the compatibility to surface mounting of the chips.   LEAD STYLES   SOLDERING ADVICES FOR REFLOW SOLDERING   Large chips above size 2225 are not recommended to be mounted on epoxy board due to thermal expansion coefficient mismatch between ceramic capacitor and epoxy. Where larger sizes are required, it is recommended to use components with ribbon or other adapted leads so as to absorb thermo-mechanical strains. RECOMMENDED FOOTPRINT FOR SMD CAPACITORS  Ceramic is by nature a material which is sensitive both thermally and mechanically. Stresses caused by the physical and thermal properties of the capacitors, substrates and solders are attenuated by the leads. Wave soldering is unsuitable for sizes larger than 2220 and for the higher ends of capacitance ranges due to possible thermal shock (capacitance values given upon request). Infrared and vapor phase reflow, are preferred for high reliability applications as inherent thermo-mechanical strains are lower than those inherent to wave soldering.    SOLDERING ADVICES FOR IRON SOLDERING Attachment with a soldering iron is discouraged due to ceramic brittleness and the process control limitations. In the event that a soldering iron must be used, the following precautions should be observed: Use a substrate with chip footprints big enough to allow putting side by side one end of the capacitor and the iron tip without any contact between this tip and the component, place the capacitor on this footprint, heat the substrate until the capacitor’s temperature reaches 150°C minimum (preheating step, maximum 1°C per second), place the hot iron tip (a flat tip is preferred) on the footprint without, touching the capacitor. Use a regulated iron with a 30 watts maximum, power. The recommended temperature of the iron is 270 ±10°C. The temperature gap between the capacitor and the iron tip must not exceed 120°C, leave the tip on the footprint for a few seconds in order to increase locally the footprint’s temperature, use a cored wire solder and put it down on the iron tip. In a preferred way use Sn/Pb/Ag 62/36/2 alloy, wait until the solder fillet is formed on the capacitor’s termination, take away iron and wire solder, wait a few minutes so that the substrate and capacitor come back down to the preheating temperature, solder the second termination using the same procedure as the first, let the soldered component cool down slowly to avoid any thermal shock.   14. Packaging TAPE AND REEL The films used on the reels correspond to standard IEC 60286-3. Films are delivered on reels in compliance with document IEC 286-3 dated 1991. Minimum quantity is 250 chips. Maximum quantities per reel are as follows: Super 8 reel - Ø 180: 2,500 chips. Super 8 reel - Ø 330: 10,000 chips. Super 12 reel - Ø 180: 1,000 chips. Reel marking complies with CECC 32100 standard: Model. Rated capacitance. Capacitance tolerance. Rated voltage. Batch number.   15. Dimensional characteristics of chips tray packages   16. High Q Capacitors Tape and Reel Packaging Specifications   17. EIA standard capacitance values Following EIA standard, the values and multiples that are indicated in the chart below can be ordered. E48, E96 series and intermediary values are available upon request.   18. EIA capacitance code The capacitance is expressed in three digit codes and in units of pico Farads (pF). The first and second digits are significant figures of the capacitance value and the third digit identifies the multiplier. For capacitance value < 10pF, R designates a decimal point.  See examples below:   19. Part marking voltage codes Use the following voltage code chart for part markings: 20. Part marking Tolerance codes Use the following tolerance code chart for part markings:   21. Reliability levels Exxelia proposes different reliability levels for the ceramic capacitors for both NPO and X7R ceramics.   As the world’s leading manufacturer of specific passive components, we stand apart through our ability to quickly evaluate the application specific engineering challenges and provide a cost-effective and efficient solutions. For requirements that cannot be met by catalog products, we offer leading edge solutions in custom configuration: custom geometries, packaging, characteristics, all is possible thanks to our extensive experience and robust development process, while maintaining the highest level of reliability. Where necessary, special testing is done to verify requirements, such as low dielectric absorption, ultra-high insulation resistance, low dissipation factor, stability under temperature cycling or under specified environmental conditions, etc. > See our capacitors in catalog