1

They’re JUST capacitors?

James LewisMarketing Directorjameslewis@kemet.com

@baldengineer

2 Different materials make different capacitors

Electrode Plates Dielectric

Basic Capacitor

C = ε0KA(n−1)d

3

Topic List

• Ceramics– Why they lose capacitance

• Aluminum– Why they don’t last forever

• Tantalum– Why are they are safe to use

• Supercapacitors– Why they are called super

We need a context…

4

Capacitors should be voltage derated 50%

True Or False

It Depends…

5

Ceramics

6

Multilayer Ceramic Capacitor (MLCC)Typical Construction

Ceramic Dielectric

Electrode (Ni for BME, Ag/Pd for PME)

Termination (Cu for BME, Ag for PME)

Finish(Plated Sn)

Barrier Layer (Plated Ni)

+-

Capacitances in parallel are additive

CT=C1+C2+C3+….Cn

C = ε0KA(n−1)d

Max Capacitance is limited by “larger” layers

7

Relative Capacitance vs. TemperatureTemperature Coefficients

C0G (NP0)

Temperature

‘K’

Mag

nitu

de

X7R

X5R

Z5U

Y5V

‘Room’Ambient

U2J

8

Voltage Coefficient (Class II and III)1210 vs 0805, X7R, 10uF, 6.3V

-60%-50%-40%-30%-20%-10%

0%10%

0 1 2 3 4 5 6

Cap

acita

nce

Cha

nge

Applied DC Bias (VDC)

Capacitance Change vs. DC BiasRated 6.3V

How much capacitance do you really get?

1206

0805

9K-SIM: ESR, Z, SPICE Model, VCC, and S-Parameters

ksim.kemet.com

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X7R Aging Rate1.5% per Decade Hour (Limit)

-14-12-10

-8-6-4-202468

101214

1 10 100 1,000 10,000 100,000

Time Post Heat

Perc

enta

ge N

omin

al

Ref

eren

ce

8,77

7 H

r=1

Yr

87,7

70 H

r =1

0 Y

r

https://ec.kemet.com/aging-calculator-for-ceramics

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Aluminum Electrolytic

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Aluminum ElectrolyticForm Factors

Axial/Radial Screw Terminal Snap-In

Single Ended SMD Motor Start

Same construction different form factors

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CathodePlate

Electrolyte

Aluminum Untreated Surface Area

AnodePlate

C1 C2 If C2 >> C1,then Ct ~ C1

dAC r 0εε=

0ε

( ) 932 =OAlrε

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dAC r 0εε=

Electrolyte

AnodePlate

Aluminum Acid-Etched Surface Area

C1 C2

C2 must remain >> C1

CathodePlate0ε

15

Anode FoilEtched Surface

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AluminumAnode

VFormation > VRating > Vapplication

WetElectrolyte

Reformed dielectric regionD

iele

ctric

Dep

letio

n

O-2O-2

Reform

Reforming / Self-Healing Wet Aluminum

Electrolyte“Cathode”

Dielectric

Voltage contributes to operational lifetime

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Tantalum

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All Tantalums explode… or do they?

MnO2 MnO2 MnO2 MnO2 MnO2

Poly Poly Poly Poly Poly

2x Rated Voltage, applied with reverse polarity and

>20 amps of current.

18Every capacitor on this board failed as “short”

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• Stable C (No Temp or Bias Effects), DCL (t)• Reliable (Decreasing FR) • Long Life (Exceeds Expected Life of All Hardware) • Most Volumetrically Efficient (CV/cc, E/cc)

MilitarySpaceMedicalAutomotiveComputersTelecom

Ta

Ta2O5

SEM of a Sintered Ta Anode

Ta

Why use Tantalum?

Ta Oxide Dielectric

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Polymer Electrolytic:A “new” kind of capacitor

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Difference in Self-Healing

“Traditional”MnO2

NewPolymer

Current through fault generates enough heat and oxygen for ignition.

Conductive polymer consumes oxygen preventing ignition.

Tantalum Crack

Impurity

Ta Polymer

Polymer oxidized

Ta2O5

Crack

Impurity

Ta MnO2

Mn2O3Ta2O5

If a polymer fails, it fails safely.

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Tantalum Voltage DeratingDepend on cathode material

• Typical derating guidelines:• Tantalum MnO2: 50%• Tantalum Polymer: 20%(>10V), 10% (≤10V)• Aluminum Polymer: 0%!

35

12

4

0

126%

Ta-Poly KOVR>10VDC

6,310@100% VRated

FR(PPM)

1,700@90% VRated

FR(PPM)

458@80% VRated

FR(PPM)

9@50% VRated

FR(PPM)

0

0

0

0

235%

8

2

1

0

197%68%100 PPM FR

% VRated

Alum-Poly AOTa-Poly KOVR≤10VDC

Ta-MnO2

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Supercapacitors

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What Is A “Super” Capacitor?

APowerCap

BestCap

BoostCap

CAP-XX

DLCAP

EneCapTen

EVerCAP

DynaCap

Faradcap

GreenCap

Goldcap

HY-CAP

Super capacitor

SuperCap

AS Capacitor

PowerStor

PseudoCap

Ultracapacitor

Electrostatic Double-Layer Capacitor (EDLC)

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(Electrical) Double Layers

1. IHP Inner Helmholtz Layer2. OHP Outer Helmholtz Layer3. Diffuse layer4. Solvated ions5. Specifically adsorptive ions6. Solvent molecule

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Traditional and EDLCComparison

Aluminium Reference

+++++++

-------

AlAl2O3Dielectric

Al

+++++++

-------

C = QV

-------

+++++++

BatteryElectrode

SolventMolecule

(~0.3 to 2 nm)

C

Symmetric“Supercapacitor”

+++++++

-------

C

Separator

+++++++

-------

Asymmetric“Hybrid Capacitor”

C

Separator

C = ε0KAd

Surface area of carbon

Inner Helmholtz Layer

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Electrolytes

Acetonitrile

– CH3CN– Common for SC– Dielectric constant:

37– Burns to HCN– BP: ~80°C

Propylene Carbonate (PC)– C4H6O3

– Dielectric constant: 64

– Destructive effect on graphite

– BP: ~240°C

Sulfuric Acid

– H2SO4

– Used in lead-acid batteries

– Dielectric constant: ~100

– BP: 337°C

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Tools

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Mobile Catalog Apps

Access to over 350 catalogs and 4.8MM data sheets

www.kemet.com/mobileapps

31

ksim.kemet.com

32www.engineeringcenter.com

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james@baldengineer.comemail | www | twitter

www.baldengineer.com & www.addohms.com

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Capacitors should be voltage derated 50%

True Or False

It Depends…

35

Summary

• Ceramic– More capacitance

• Aluminum Electrolytic– Longer operational life

• Tantalum– Power-On Reliability

• Supercapacitors– Operational Life

Why do you voltage de-rate a capacitor?

Slides: www.baldengineer.com/hddg11

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Thank You!