multilayer ceramic capacitors (mlccs)

1

Multilayer Ceramic Capacitors (MLCCs)

Design and Characteristics

© 2019 KEMET Corporation

CapacitorWhat is it?

DielectricElectrode

Distance

𝐶 =𝜖𝑜𝐾𝐴

𝑑

𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑎𝑛𝑐𝑒 (𝐹) =𝑄 = 𝐶ℎ𝑎𝑟𝑔𝑒 (𝐶)

𝑉 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉)

+ -

Farads


Ideal CapacitorsBucket of Water Analogy

D𝑒𝑝𝑡ℎ 𝑜𝑓 𝑊𝑎𝑡𝑒𝑟 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒

𝐴𝑟𝑒𝑎 = 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑎𝑛𝑐𝑒 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑊𝑎𝑡𝑒𝑟 = 𝐶ℎ𝑎𝑟𝑔𝑒, 𝑄

Much less water (charge) stored

for the same voltage

X7RC0G

𝑟


Form Factor


Design


MLCCs

C = Design Capacitance

K = Dielectric Constant

A = Overlap Area

d = Ceramic Thickness

n = Number of Electrodes

C = e0KA(n-1)

d

Detailed Cross Section

Inner Electrode

End Termination

Barrier Layer

Termination Finish

Dielectric Material

+

-

Capacitances in parallel are additive

CT=C1+C2+C3+….Cn


Typical Construction

Ceramic Dielectric

Internal Electrode (Ni for

BME, Ag/Pd for PME)

Termination (External

Electrode, Cu for BME, Ag

for PME)

Plated Sn finish

for Solderability

Barrier Layer

(Plated Ni)


Dielectric Technology

C0G

PME & BME

200oC

U2J

BME

X8R

BME

X8L

BME

X7R

PME & BME

175oC

X5R

BME

Y5V

BME

Z5U

BME

BP

PME

C0G @ Rated V

BX

PME

X7R +15/25% @

Rated V

BR

PME

X7R & +15/-40% @ Rated V

Commercial & Automotive Grade Dielectric Materials

Military & Hi-Rel Dielectric Materials

Class 1 Class 2 Class 3

Class 1 Class 2


Characteristics


Relative Capacitance vs. Temperature (TCC)

Temperature

‘K’

Ma

gn

itu

de

X7R

C0G (NP0)

X5R

Z5U

Y5V

‘Room’Ambient

U2J

Class 3

Class 2

Class 1


Dielectric ClassificationClass 1 (Per EIA – 198)

Alpha

Symbol

Significant

Figure of

Temp

Coefficient

ppm/ºC

Numerical

Symbol

Multiplier to

significant

figure

Alpha

Symbol

Tolerance of

Temp

Coefficient

± ppm/ºC

C 0 0 -1 G 30

B 0.3 1 -10 H 60

L 0.8 2 -100 J 120

A 0.9 3 -1000 K 250

M 1.0 4 -10000 L 500

P 1.5 5 +1 M 1000

R 2.2 6 +10 N 2500

S 3.3 7 +100

T 4.7 8 +1000

U 7.5 9 +10000

Class I Dielectrics

C0G Example

U2J Example

Operating Temperature -55oC to +125oC


Dielectric ClassificationClass 2 and 3 (per EIA-198)

Alpha

Symbol

Low

Temperature

(ºC)

Numerical

Symbol

High

Temperature

(ºC)

Alpha

Symbol

Max cap

change over

temp. range

(%)

Z +10 2 +45 A ±1.0

Y -30 4 +65 B ±1.5

X -55 5 +85 C ±2.2

6 +105 D ±3.3

7 +125 E ±4.7

8 +150 F ±7.5

9 +200 P ±10

R ±15

S ±22

* L +15 to - 40

T +22 to - 33

U +22 to - 56

V +22 to - 82

CL

AS

S 3

CL

AS

S 2

* Industry Classification (Non EIA-198)


-90%

-80%

-70%

-60%

-50%

-40%

-30%

-20%

-10%

0%

10%

0 4 8 12 16 20

Cap

acit

ance

Ch

ange

DC Voltage (V)

Capacitance versus DC VoltageX7R 1206 10uF 16V

Capacitance StabilityVersus DC Voltage – Class 2 and Class 3


Capacitance StabilityVersus DC Voltage – Class 2 and Class 3

-60%

-50%

-40%

-30%

-20%

-10%

0%

10%

0 1 2 3 4 5 6

Cap

acit

ance

Ch

ange

DC Voltage (V)

Capacitance Change vs. DC Bias1210 vs 0805, X7R, 10uF, 6.3V

1210

0805


Voltage Coefficient (Class 2 and 3)DC Bias

BaTiO3 above Curie point

• Cubic

• No Dipole

BaTiO3 below Curie point

• Tetragonal

• Creates Dipole

Face Centered Cubic

Crystal Structure

+

-


-70%-60%-50%-40%-30%-20%-10%0%10%

0 4 8 12 16 20Cap

acit

ance

Ch

ange

DC Voltage (V)

Capacitance versus DC VoltageX7R 1206 10uF 16V

Voltage Coefficient (Class 2 and 3)DC Bias

+V

-VDomains

10V DC

VDC

-


Class 2 BaTiO3

Ferroelectric

VAC

Ferroelectric dipoles in domains align with

the AC Field

Domain wall heating &

Signal distortion

Class 1 CaZrO3

Paraelectric

Paraelectric dipoles align with AC field

No domains, so

No Domain wall heating &

Reduced signal distortion

VAC

AC Coupling and Signal Distortion X7R vs. C0G


-10.0%

-5.0%

0.0%

5.0%

10.0%

0 0.5 1 1.5 2 2.5 3

Cap

acit

ance

Ch

ange

AC Voltage (Vrms)

Capacitance versus AC VoltageX7R 1206 10uF 16V

Voltage Coefficient (Class 2 and 3)AC Bias

Measurement Conditions

Capacitance Frequency Voltage (AC)

≤10uF 1kHz 1Vrms

>10uF 120Hz 0.5Vrms

VAC


Capacitance Measurements of Class 2 Capacitance out of Spec???? VAC

✓ Instrument Calibrated

✓ AC Voltage 1Vrms

✓ Frequency 1kHz

Example: 1210 10uF 10% Tolerance

Capacitance out of Specification!!!!


Capacitance Measurements of Class 2 VAC

Danger Zone: >1uF

Measurement frequency switches

from 1kHz to 120Hz

VSZS

Instrument

ZCap

VCap


Capacitance Measurements of Class 2 ALC Function (Auto Leveling Control)

VAC

Example: 1210 10uF 10% Tolerance

Within

Specification!!!!


Capacitance Measurements of Class 2 Lower Source Impedance Meters

VAC

No ALC NeededKeysight E4981A Capacitance Meter


Class 1 MLCCsUltra Stable versus Voltage VAC

-20%

-10%

0%

10%

20%

0 4 8 12 16 20

Cap

ch

ange

(%

)

DC Voltage (V)

Capacitance Change vs DC VoltageC0G 1210 220nF 25V

-10.0%

-5.0%

0.0%

5.0%

10.0%

0 0.5 1 1.5 2 2.5 3

Cap

ch

ange

(%

)

AC Voltage (Vrms)

Capacitance Change vs AC BiasC0G 1210 220nF 25V

No change with DC voltage No change with AC voltage

DC Voltage AC Voltage


-20%

-15%

-10%

-5%

0%

5%

10%

15%

20%

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

Pe

rce

nta

ge

No

min

al

Time Post Heat (Hours)

Capacitance StabilityVersus Time (Aging) Class 2

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

Re

fere

nc

e

Solder Process

8,7

77 H

r=

1Y

r

87,7

70

Hr

= 1

0 Y

r

Nominal Capacitance Tolerance


-15%

-10%

-5%

0%

5%

10%

15%

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

Pe

rce

nta

ge

No

min

al

Time Post Heat (Hours)

Capacitance StabilityVersus Time (Aging) Class 1

No change with Time


Piezoelectricity and Electrostriction

- -

- - - -

+ + + +

+ +

Mechanical Distortion

+

-

+

-


Audible Noise

AC Voltage

Piezoelectricity and Electrostriction

Z

X

Y

Electrical Noise

PiezoelectricityElectrical Noise Electrostriction

Audible Noise


Common Failure Modes


Ceramic Materials are Inherently Brittle

Ceramic Properties• High chemical bond strength

• High Elastic Modulus

• Low Ductility

• Very Hard


Typical Crack Signatures

The major sources of MLCC cracks are:

• Mechanical damage (impact)

‒ Aggressive pick and place

‒ Physical mishandling

• Thermal shock (parallel plate crack)

‒ Extreme temperature cycling

‒ Hand soldering

• Do not touch electrodes while hand soldering!

• Flex or Bend stress

‒ Occurs after mounted to board

‒ Common for larger chips (>0805)

Mechanical

Damage

Flex Crack

Thermal Shock Crack

Failure is not always immediate!


External Forces on Ceramic Material

Force

Compression

Strong under compression

Force Force

Tension

Weak under tension

Force


Flex CrackingExcessive Bending

High Stress Region

MLCC Under Tension

Finite Element Analysis


Flex CrackingExcessive Bending

Flex crack signature

MLCC Active Area

Starts here


Capacitor Mitigation SolutionsLevel 1 Protection – Basic Level of Crack Protection

MLCC Active AreaFloating Electrode Open Mode

Pros• Serial design

• Fails open

Cons• Reduced capacitance in the same volume

Pros• Crack doesn’t go through active area

• Fails open



Capacitor Mitigation SolutionsLevel 2 Protection – Intermediate Level of Crack Protection

Pros• Increased flex capability

• High volumetric efficiency

Cons• Fail short

Flexible Termination (FT-CAP)

End Termination/

External

Electrode (Cu)

Flexible

Termination

Epoxy Layer (Ag)

Barrier Layer (Ni)

Termination Finish

(100% Matte

Sn/SnPb–5% Pb min)

Conductive-Epoxy

Conductive-Epoxy

Crack


Capacitor Mitigation SolutionsLevel 3 Protection – High Level of Crack Protection (Hybrid Technology)

Pros• Increased flex capability

• Floating Electrode design

• Fail Open


Flexible Termination (FT-CAP) +

Floating ElectrodeFlexible Termination (FT-CAP) +

Open Mode


Thermal ShockWhy is it an issue?

Circuit BoardInner Electrode

End Termination

Barrier LayerTermination Finish

Dielectric Material

CTE – Coefficient of Thermal Expansion

Thermal Shock Cracks → CTE Mismatch


Thermal ShockCauses – Hand Soldering

Internal Temperature GradientsUneven Expansion and Contraction

COLD HOTHand Solder Tips• Don’t touch capacitor termination

• Pre-heat assembly

• Larger case sizes are more sensitive


Thermal ShockCauses – Solder Wave

Solder Wave

Molten Solder

PCB Travel


Thank You

multilayer ceramic capacitors (mlccs)

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