rating and derating for low-voltage multilayer ceramic ... · low-voltage multilayer ceramic...

Rating and Derating for Low-Voltage Multilayer Ceramic

Capacitors (MLCCs)Alexander Teverovsky

Dell Services Federal Government, Inc.work performed for Code 562, GSFC

[email protected]

NASA Electronic Parts and Packaging (NEPP) Program

1To be published on nepp.nasa.gov.

List of Acronyms

2To be published on nepp.nasa.gov.

MLCC Multilayer ceramic capacitorBME Base metal electrodePME Precious metal electrodeDWV Dielectric withstanding voltage IR Insulation resistanceEMR Electromechanical resonance VBR Breakdown voltageCCS Constant current stressSTD Standard deviationHAST Highly accelerated stress testingHALT Highly accelerated life testingVR Rated voltage

Rated Voltages and Derating for MLCCs

3

Scope: Class II MLCCs rated to voltages ≤ 100V.

Outline: Breakdown voltages in BME and PME. Effect of voltage on capacitance. How performance of MLCCs is affected by voltage?

Dielectric withstanding voltage (DWV) Insulation resistance (IR) Electromechanical resonance (EMR) Voltage conditioning and life test.

How the parts are rated? Derating requirements. Where derating does not work? Conclusion

To be published on nepp.nasa.gov.

1

10

100

0 25 50 75 100 125

VBR

/VR

rated voltage, V

Ceramic and Tantalum Capacitors

Ta wet

1

10

100

0 25 50 75 100 125

VBR

/VR

rated voltage, V

Ceramic and Tantalum Capacitors

Ta wet

MLCC

Breakdown Voltage in Capacitors

4

VBR seems to be the most natural limit to VR:VR = VBR - margin

How much margin is necessary?

VBR does not limit VR for low-voltage MLCCs. Margin decreases as VR increases. There appears no difference in VBR for PME and BME.

0

20

40

60

80

100

120

140

160

0 10 20 30 40 50 60

E_B

R, V

/um

thickness, um

X7R MLCCs

PME

BME


Constant Current Stress Testing

5

CCS is a useful tool to test for VBR and quasi-static capacitance:

Non-linearity of V-t characteristics is due to C(V) and I(V) variations.

At V > VR capacitance drops substantially.

0

100

200

300

0 10 20 30 40

volta

ge, V

time, sec

1uF 50V at 5uA

Mfr.M 0805 SN3Mfr.A 1812 SN2Mfr.M 2220 SN1Mfr.C 1210 SN1Mfr.A 2220 SN1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 25 50 75 100 125 150

capa

cita

nce,

uF

voltage, V

1uF 50V at 5uA

Mfr.M 0805 SN3Mfr.A 1812 SN2Mfr.M 2220 SN1Mfr.C 1210 SN1Mfr.A 2220 SN1

( ) ( )[ ] dttIIC

tVt

Lch∫ ×−×=0

1dtdVIVC ch=)(

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25

volta

ge, V

time, sec

1uF 50V Mfr.M 0805

3 uA10 uA30 uA


Effect of Voltage on Capacitance

6

0.45

0.6

0.75

0.9

1.05

0 10 20 30 40

C(V

)/C(0

)

voltage, VPME Mfr.V 1825 0.47uF 50V PME Mfr.C 1825 0.47uF 50VBME Mfr.C 1825 0.47uF 50V BME Mfr.A 1825 0.47uF 50VBMEMfr.T 1210 10uF 25V PME Mfr.P 1825 1uF 50VBME 1206 22uF 6.3V

0.6

0.75

0.9

1.05

0 10 20 30 40

C(V

)/C(0

)

voltage, V

Mfr.T 1210 0.1uF 50VMfr.A 0805 0.1uF 25VMfr.M 1206 10uF 16VMfr.C 0402 0.01uF 6.3V

Decrease of C with voltage is greater for high volumetric efficiency parts.

Do we need limiting the voltage effect on C similar to MIL-PRF-55681 or leave the decision to the designer?

0

4

8

12

16

20

24

1.E+02 1.E+03 1.E+04 1.E+05

capa

cita

nce,

uF

freqiency, Hz

1206 Mfr.M 22uF 6.3V

0V 2V 4V 6V 9V 12V 20V 30V

Standard measurements of capacitance at 1 kHz.


Effectiveness of DWV Test

7

Gr.6 2225 Mfr.C 1uF 50V

breakdown voltage, V

cum

ulativ

e pr

obab

ility,

%

60 2000100 10001

5

10

50

90

99

virgin

TS

X-sect

MF

DWV test requires 2.5VR.Only ~20% of parts with gross

defects failed DWV test.19 out of 30 (63%) lots of parts

damaged by X-sect and TS had the probability of DWV test failure of less than 1%.

Some Mfr. testing parts at 5VR, JAXA - 30VR?

VBR is sensitive to the presence of defects and reflects quality of the lot.

The effectiveness of the existing DWV testing is low. Guidelines: - (5% level)/2 Average VBR and STD should be provided by manufacturers.

( )σ×−×= 25.0 avrcr VBRVBR


Effect of Voltage on IR

8

1uF 50V MLCCs Mfr.M

current, A

cum

ulativ

e pr

obab

ility,

%

1.E-10 1.E-71.E-9 1.E-81

5

10

50

99

22201206

0805

1000 sec60 sec

n = 0.76n = 0.71

n = 0.61

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E+0 1.E+1 1.E+2 1.E+3 1.E+4

curr

ent,

A

time, sec

Mfr.A 0.12uF 50VMfr.C 1uF 6.3VMfr.N 0.12uF 16VMfr.C CDR31 0.018uF 50V

IR requirements for BMEs are relaxed vs.MIL parts. Does it mean they are worse?

Does voltage affect IR?According to spec, IR does not depend

H and V, but depends on the value of C:

However, ρ is not constant, and due to Schottky conduction IR should decrease exponentially with V/H.

HSC 0εε

=SHIR ρ

=C

IR 0ρεε=

ntItI −×= 0)(

Currents in MLCCs follow Curie von Schweidler law:

Will an increase in voltage reduce IR?What currents are measured during

first 120 sec of electrification?To be published on nepp.nasa.gov.

Leakage Currents in MLCCs

9

R = 5.6E8

R = 1.5E10

R = 3.7E8R = 2.4E8

0.0E+00

5.0E-08

1.0E-07

1.5E-07

0 20 40 60 80

curre

nt at

120

sec

, A

voltage, V

4.7uF 25V0.47uF 25V10uF 16V22uF 6.3V

n = 0.7

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E+0 1.E+1 1.E+2 1.E+3 1.E+4

curre

nt, A

time, sec

virgin

crack

),,(),(),(),(),,( RHVTIVTIVtIVtIVTtI dlilabsch +++=

Absorption currents prevail up to several hours of electrification.

Iabs increases linearly with voltage, hence IR does not depend on how accurately VR is determined.

IR in high-C MLCCs is not sensitive to the presence of defects.

n = 0.83

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06

curre

nt, A

time, s

Ct=1, rt=1e8Ct=2, rt=1e9Ct=3, rt=1e10Ct=4, rt=1e11sum

n = 2.02

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06

curre

nt, A

time, s

Ct=1, rt=1e8Ct=0.33, rt=1e9Ct=0.1, rt=1e10Ct=0.033, rt=1e11sum

Capacitor with absorption

∑

−++=

i iiild

tr

VRV

RVtI τexp)( 000


Effect of Voltage on EMR

10

y = 4.09E+06x

0.E+00

1.E+06

2.E+06

3.E+06

4.E+06

5.E+06

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

frequ

ency

, Hz

1/2W, 1/mm

Resonance frequencies in X7R MLCCs with different size

Inverse piezoelectric effect results in acoustic waives in polarized capacitors.

Several resonance frequencies. The amplitude increases with V (=>VR).EMR results in excessive noise and might

cause mechanical damage and failure.History case: a stacked capacitor failed in

PS systems. The major fres depends on the width,

W, of the capacitor: fres = v/(2W), v is the sound velocity.

For X7R materials v ~4.1×103 m/sec. Guidelines: warning about EMR effect

and impedance spectroscopy if necessary.

0.001

0.01

0.1

1

1.E+05 1.E+06 1.E+07

ES

R, O

hm

frequency, Hz

1uF 50V MLCC

Gr.5 0V

0.001

0.01

0.1

1

1.E+05 1.E+06 1.E+07

ES

R, O

hm

frequency, Hz

Mfr.C 1812 1uF 50V

Gr.5 0VGr.5 40V


Effect of Voltage on Life Test

11

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

2 4 6 8 10

time,

yea

rs

voltage acceleration constant, n

Time at 50C and 0.5VR that is equivalent to 96 hr of testing at 125C 2VR

0.7eV 0.9eV1.1eV 1.3eV1.5eV 1.7eV1.9eV

−×

==

211

2

222

111 11exp),(),(

TTkE

VV

TVTVAF a

n

ττ

Large VBR allows for extremely high voltage acceleration.

IR degradation and failures due to VO++

are observed mostly during HAST.

Voltage conditioning at 125C, 2VR for 100 hr corresponds to thousands of years of operation at 50C and 0.5VR.

Shiota (Murata, CARTS’13): - acceleration at HV might result in errors of extrapolation to operating conditions;- a stress by T acceleration instead of V.

Derating is an effective means for reducing risk of failures caused by VO

++.To be published on nepp.nasa.gov.

Early HALT Failures

12

1.E-06

1.E-05

1.E-04

1.E-03

0.001 0.01 0.1 1 10 100

curre

nt, A

time, hr

BME 1uF 50V at 182C 200V

Mfr.A 2220 SN1 Mfr.A 2220 SN2Mfr.A 2220 SN3 Mfr.C 2225 SN1Mfr.C 2225 SN2 Mfr.C 2225 SN3

1.E-07

1.E-06

1.E-05

1.E-04

0.001 0.01 0.1 1 10 100

curre

nt, A

time, hr

1825 BME fract. Mfr.A 1uF 50V at 125C 100V

fr. SN1 fr. SN2fr. SN3 fr. SN4contr

Cracks might appear as IR degradation

Cracks might cause early HALT failures

1.E-05

1.E-04

1.E-03

0 100 200 300 400 500 600

curr

ent,

A

time, hr

Mfr.M 1210 10uF 25V 125C at 50V

Are parts from Mfr.A better than from C? At E=1 eV, n=3 “failures” at 30hr 182C

200V correspond to >47,000 years at 25V and 55C.

Early failures might be more important than wear-out failures.

Early HALT failures and IR degradation might be due to cracks.To be published on nepp.nasa.gov.

How Voltage for Capacitors is Rated?

13

In ferroelectric materials the dielectric constant decreases with electric field.

For BaTiO3 type materials ε(E)function depends on the composition, structure of the dielectric, and is sensitive to the process conditions, and probably H => proprietary information.

Based on the acceptable level of the ε(E) variations, Emax can be selected.

For a given thickness of the dielectric, H, the rated voltage is VR = H × Emax – margin (?)

VR in low-voltage MLCCs is controlled by polarization processes in the dielectric, and is not related to breakdown voltages.

VR is a technical parameter chosen so that voltage dependent characteristics and reliability remain within the specified limits.


14

Guidelines for Derating Requirements

Part TypeVoltage

derating factor 1/

Maximum operating

temperature

Ripple current derating factor

2/

MIL 0.6 110 °C NA

BME 0.5 100 °C 0.75Notes:1/ The derating factor applies to the sum of peak AC ripple and DC polarizing voltage.2/ Ripple currents in power applications shall be derated to 75% of the manufacturers’ recommendations. The frequency of ripple current should be outside the electromechanical resonance frequency for the part.

Derating = stress reduction => increase of reliability and mitigation of unforeseen events (e.g. EMR).

Derating is based on history of applications and consensus. Danger of over-derating: larger parts weight more and might

be more susceptible to fracturing.To be published on nepp.nasa.gov.

15

Where Derating Does not Work?

Failures due to VO++ are observed mostly during HAST and can

be mitigated by derating. Failures due to the presence of cracks observed during box-

level testing and operation at low voltages. Bad news: derating does not help for low-voltage failures. Good news: BMEs are less susceptible to low-voltage failures.

BME, WLT at 0.8V, 23 min


16

Conclusion

Rating of capacitors is a prerogative of manufacturers. Manufacturers should assure and demonstrate reliability of

their product at rated conditions. (For Hi-Rel parts the requirements and test conditions are set by users.)

Manufacturers should also provide acceleration factors and methods used for their calculation. (Standardization of HAST?)

Derating is an efficient means for users to reduce risks of IR degradation and failures caused by Vo

++ ; it might also work for cracking related failures.

A 50% voltage derating seems reasonable. An open issue: should we limit a decrease of

capacitance at rated voltages. (Derating might be sufficient to take care of the problem if manufacturers specify C at VR.)


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