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Weibull Grading and Surge Current Testing for Tantalum

Capacitors

Weibull Grading and Surge Current Testing for Tantalum

Capacitors

Alexander TeverovskyDell Services Federal Government, Inc.

Work performed for GSFC Code 562, Parts, Packaging, and Assembly Technologies Office,

[email protected]

NASA Electronic Parts and Packaging (NEPP) Program

1Presented by Alexander Teverovsky at an iNEMI (International Electronics Manufacturing Initiative) WebEx, June 2013 and deliverable to NASA Electronic Parts and Packaging (NEPP) Program to be published on nepp.nasa.gov.

OutlineOutline

2

Scintillation breakdown and self-healing in tantalum capacitors

Failures as Time Dependent Dielectric Breakdown (TDDB)

Weibull Grading Test (WGT) Surge Current Test (SCT).

Presented by Alexander Teverovsky at an iNEMI (International Electronics Manufacturing Initiative) WebEx, June 2013 and deliverable to NASA Electronic Parts and Packaging (NEPP) Program to be published on nepp.nasa.gov.

Failures in Ta capacitors occur typically either under steady-state operating conditions, or at the first power turn-on.

To reduce the probability of the first type of failures, capacitors are screened/qualified by WGT.

SCT is used to mitigate the risk of the second type of failures.

What are these tests, how effective they are, and what can be done to improve the efficiency?

Failures in Ta capacitors occur typically either under steady-state operating conditions, or at the first power turn-on.

To reduce the probability of the first type of failures, capacitors are screened/qualified by WGT.

SCT is used to mitigate the risk of the second type of failures.

What are these tests, how effective they are, and what can be done to improve the efficiency?

Scintillation Breakdown and Self-Healing (SH) in Tantalum

Capacitors

Scintillation Breakdown and Self-Healing (SH) in Tantalum

Capacitors


Self-Healing in Wet Ta CapacitorsSelf-Healing in Wet Ta Capacitors

4

Scintillations are local momentary breakdowns terminated by self-healing.

SH occurs almost instantaneously and is due to additional electrochemical oxidations of Ta in the electrolyte (sulfuric acid).


Breakdown margin reduces substantially with rated voltage, VR.

SH is important to assure reliability of the parts, but it is not a panacea because of the pressure build-up due to H2 generation.

Breakdown margin reduces substantially with rated voltage, VR.

SH is important to assure reliability of the parts, but it is not a panacea because of the pressure build-up due to H2 generation.

0

1

2

3

4

5

6

7

0 25 50 75 100 125

VBR

/VR

rated voltage, V

Wet Tantalum Capacitors

standard, M39006high volumetric efficiency

0

1

2

3

4

5

6

7

0 25 50 75 100 125

VBR

/VR

rated voltage, V

Wet Tantalum Capacitors

standard, M39006high volumetric efficiency

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20

volta

ge, V

time, sec

04005 wet Ta capacitors

210uF 125V, 2.5mA

870uF 60V, 10mA

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20

volta

ge, V

time, sec

04005 wet Ta capacitors

210uF 125V, 2.5mA

870uF 60V, 10mA

Self-Healing in MnO2 Ta CapacitorsSelf-Healing in MnO2 Ta Capacitors

5

SH is due to local overheating of MnO2 and its transformation to a high-resistive Mn2O3, thus isolating the defective area of Ta2O5.

Tantalum can oxidize by oxygen released from MnO2.


Although the breakdown margin decreases with VR, it remains above ~2. Scintillations were damaging in ~30% cases. The larger the nominal capacitance and the lower the equivalent series

resistance, ESR, the greater the probability of damage. SH is a benefit of MnO2 parts, but scintillations should be considered as

failures during screening and qualification.

Although the breakdown margin decreases with VR, it remains above ~2. Scintillations were damaging in ~30% cases. The larger the nominal capacitance and the lower the equivalent series

resistance, ESR, the greater the probability of damage. SH is a benefit of MnO2 parts, but scintillations should be considered as

failures during screening and qualification.

1

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70

VBR

/VR

rated voltage, V

Ceramic and Tantalum Capacitors

MIL Ta chip

COM Ta chip

1

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70

VBR

/VR

rated voltage, V

Ceramic and Tantalum Capacitors

MIL Ta chip

COM Ta chip

051015202530354045

0 20 40 60 80 100 120

volta

ge, V

time, sec

MnO2 Ta 100uF 16V at 100uA CCS

SN6SN7SN8

051015202530354045

0 20 40 60 80 100 120

volta

ge, V

time, sec


SN6SN7SN8

0

10

20

30

40

50

60

0 20 40 60 80 100 120 140

volta

ge, V

time, sec


SN1SN2SN9

0

10

20

30

40

50

60

0 20 40 60 80 100 120 140

volta

ge, V

time, sec


SN1SN2SN9

Self-Healing in Polymer Ta Capacitors?Self-Healing in Polymer Ta Capacitors?

6

Contrary to MnO2 capacitors, where ignition is possible due to the exothermic reaction of oxygen that is emitted by MnO2 with Ta, polymer capacitors do not ignite.

For this reason, manufacturers “suggest” derating to 0.8VR compared to 0.5VR that is “recommended” for MnO2 capacitors.


Preliminary results show that all polymer capacitors failed in a short circuit mode – no self-healing.

There are other concerns that need to be addressed before using polymer capacitors in high-rel applications (e.g. effect of humidity).

Preliminary results show that all polymer capacitors failed in a short circuit mode – no self-healing.

There are other concerns that need to be addressed before using polymer capacitors in high-rel applications (e.g. effect of humidity).

0

5

10

15

20

25

30

0 5 10 15 20

volta

ge, V

time, sec

Polymer Ta 10uF 10V at 30uA CCS

SN11SN12SN13SN14SN16

0

5

10

15

20

25

30

0 5 10 15 20

volta

ge, V

time, sec



0

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30 35

volta

ge, V

time, sec



0

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30 35

volta

ge, V

time, sec



Life Test Failures as TDDBLife Test Failures as TDDB


Scintillations during life testing should be considered as failures. Life test results can be simulated using the TDDB model, but

parameters should be adjusted.

Scintillations during life testing should be considered as failures. Life test results can be simulated using the TDDB model, but

parameters should be adjusted.

100uF 16V 144hr at RT 32V

1.E-07

1.E-06

1.E-05

1.E-04

0.01 0.1 1 10 100 1000

time, hr

curre

nt, A

100uF 16V 144hr at RT 32V

1.E-07

1.E-06

1.E-05

1.E-04

0.01 0.1 1 10 100 1000

time, hr

curre

nt, A

1

1ln pVBR

BRo

BRo V

VkTHt

VV

kTH

kTHtTTF 1expexpexp

100uF 16V at 125C 24V

time, hr

cum

ulat

ive

prob

abili

ty, %

1.E-2 10001.E-1 1 10 1001

5

10

50

90

100

Thermochemical model (TCM) of TDDB:

Time-to-failure, TTF, can be calculated based on distribution of VBR:

kTHEtTF o exp

H -energy for ions displacement, - field acceleration parameter, to - time constant.

simulation

experiment

Simulation at=40.2V, =5.8H=1 eV, t0=10-3 hr

Presented by Alexander Teverovsky at an iNEMI (International Electronics Manufacturing Initiative) WebEx, June 2013 and deliverable to NASA Electronic Parts and Packaging (NEPP) Program to be published on nepp.nasa.gov. 8

Infant Mortality FailuresInfant Mortality Failures

35V capacitors with characteristic VBR=95V

breakdown voltage, V

cum

ulat

ive

prob

abili

ty, %

20 2001001.E-1

5.E-1

1

5

10

50

90

100

1.E-1

b=3

b=5b=10

b=20

b=40

Life Test Simulation 35V capacitors at 85C 52.5V

time, hrcu

mul

ativ

e pr

obab

ility

, %1.E-1 1.E+91 1.E+1 1.E+2 1.E+3 1.E+4 1.E+5 1.E+6 1.E+7 1.E+8

1.E-1

5.E-1

1

5

10

50

90

100

1.E-1

1.1 (40)

0.52 (20)

0.25 (10)

0.11 (5)

0.05 (3)

Experimental distributions of TTF for chip Ta capacitors in most cases can be described as 2-parameter Weibull function with < 1

Majority of failures can be considered as infant mortality (IM) failures. Monte-Carlo simulation of VBR

distributions at different Times to failure calculated based

on TDDB model

At the level of VBR that is typically observed for tantalum capacitors (5 to 20), simulations show that all failures, up to the end of life, are defect related IM failures.

At the level of VBR that is typically observed for tantalum capacitors (5 to 20), simulations show that all failures, up to the end of life, are defect related IM failures.

Weibull Grading TestWeibull Grading Test



Weibull Grading TestWeibull Grading Test WGT is a combination of two tests: burn-in (screening to remove IM

failures) and reliability qualification (to assess the failure rate, FR). If < 1 and can be monitored during testing, then the test can be

stopped when the necessary is achieved.

F(t)

t

63%

WGTnormalcond.

_WGT _norm

Original notion [Didinger’64]: “to pay for only as much grading as needed, without the risk of getting too little or overpaying for too much reliability”.

1

)(

tt

ttF exp1)(

WGTnorm AF

WGTnormWGTWGT tAFAFt )(WGTnorm

If all failures are due to IM, then any lot can be screened out to as high FR level as necessary.

If all failures are due to IM, then any lot can be screened out to as high FR level as necessary.


WGT ConditionWGT Condition WGT condition per MIL-PRF-55365:

oAt 85 oC for 40 hr and voltage from 1.1VR to 1.53VR.oA failure is defined as a blown 1A or 2A fuse.oFailures calculated at 2 hr and 40hr of testing.oFR is calculated using an empirical equation obtained ~ 40 years ego:

Considering that at V = VR accelerating factor, AF, is equal to 1:

B is the voltage acceleration constant (B = 18.77249321???)

Life test at 85 oC can confirm ~1%/1000hrs which is more than 100 times greater than is required for T-grade capacitors.

)exp( uBAF 1VRVu

RVVAF 77249321.18exp1003412025.7)(Factor on Accelerati 9

Long-term reliability is determined by a 40-hr accelerated testing! Long-term reliability is determined by a 40-hr accelerated testing!


WGT ProblemsWGT Problems Two groups of problems for FR assessment

using WGT: testing and calculations. Problems with test conditions:

o Verification of contacts in fixtures.o Only 300 samples are used for calculations.o Test results with different fuses might be different.o Short current spikes below ~10A (scintillations) will remain unnoticed.o Only two points to draw the F(t) line and calculate and . Problems with calculations:

o Early failures (before 15 min) are neglected.o Calculations do not account for the uncertainty in times to failure.o Due to insufficient sample size, small changes in the number of failures

might result in significant variations of FR.o If no failures observed, wear-out degradation (e.g. due to field-induced

crystallization or Vo++ migration) can be missed.

The most significant errors, up to 3 orders of magnitude, are due to incorrect voltage acceleration factors.

The most significant errors, up to 3 orders of magnitude, are due to incorrect voltage acceleration factors.

F(t)

t

63%

WGT

normalcond.

_WGT _norm


Historical Data on Voltage Acceleration Factor (AF)

Historical Data on Voltage Acceleration Factor (AF)

Experimental data from Navy Crane report, 1982, for various hermetic solid tantalum capacitors and data reported by KEMET in 1972 and 2006

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1 1.1 1.2 1.3 1.4 1.5

acce

lera

tion

fact

or

V/VR

MIL-C-39003 capacitors

MIL-spec, B=18.77NC min, B=10.3NC max, B=24.4KEMET-1972, B=14.7Paulsen'06, B=8

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1 1.1 1.2 1.3 1.4 1.5

acce

lera

tion

fact

or

V/VR

MIL-C-39003 capacitors

MIL-spec, B=18.77NC min, B=10.3NC max, B=24.4KEMET-1972, B=14.7Paulsen'06, B=8

The data confirm an increase of AF errors with V and wide range of variations of B, from 8 to 24.4.Note: Paulsen’s data for chip capacitors were recalculated from power [AF=(V/VR)n] to exponential [AF=exp(Bu) ] dependence on voltage.

The range of B is close to predictions of the TDDB model. The range of B is close to predictions of the TDDB model.


Manufacturers’ Reliability AFManufacturers’ Reliability AF

0.0001

0.001

0.01

0.1

1

10

100

1000

0 0.2 0.4 0.6 0.8 1 1.2 1.4

acce

lera

tion

fact

or

V/VR

MIL-PRF, B=18.77AVX, B=8.1KEMET, B=14.7NEC/TOKIN, B~7.2Hitach, B~6.8Vishay*, B=18.3Panasonic, B=3.4

0.0001

0.001

0.01

0.1

1

10

100

1000

0 0.2 0.4 0.6 0.8 1 1.2 1.4

acce

lera

tion

fact

or

V/VR

MIL-PRF, B=18.77AVX, B=8.1KEMET, B=14.7NEC/TOKIN, B~7.2Hitach, B~6.8Vishay*, B=18.3Panasonic, B=3.4

AF calculated at 85 oC using vendors’ and MIL-spec data

Manufacturer Ea, eVAVX 0.63

KEMET 1.17MIL-PRF-55365 2.1

HITACHI 0.62NEC/TOKIN 0.66

Vishay*/MIL-HDBK-217F 0.15Panasonic 0.16

Activation energy, Ea, calculated based on vendors’ and MIL-spec data

Manufacturers’ data on voltage and temperature acceleration factors vary substantially.

Inconsistency in the data require more analysis.

Manufacturers’ data on voltage and temperature acceleration factors vary substantially.

Inconsistency in the data require more analysis.


Highly Accelerated Life Testing (HALT) at Different Test Conditions

Highly Accelerated Life Testing (HALT) at Different Test Conditions

22uF 50V capacitors at different BI conditions

time, hr

cum

ulat

ive

prob

abili

ty, %

1.E-3 10001.E-2 1.E-1 1 10 1001

5

10

50

90

99

125C 80V

130C 60V

22C 100V

22C 87.5V

Ro nV

VkTH 1expModel prediction for characteristic life:

4.7uF 50V capacitors at different BI conditions

time, hr

cum

ulat

ive

prob

abili

ty, %

1.E-2 10001.E-1 1 10 1001

5

10

50

90

99

112.5V 22C 75V 125C87.5V 85C

100V 22C

87.5V 22C

75V 22C

Results of HALT for 22 F, 50 V and 4.7 F, 50 V capacitors at different voltages and temperatures


Statistical Model of FailuresStatistical Model of Failures

22110exp XX

00 ln kH

1 TX 1

1 RVnk

H

2

TVX 2

The characteristic life can be presented as a general log-linear relationship

PART F S 0 1 2 t0, hr H, eV n B_85C

4.7uF 50V 90 117 0.24 -15.06 12761.6 -68.61 2.9E-07 1.1 3.7 9.6

22uF 50V 40 41 0.40 -28.13 21026.1 -124.49 6.1E-13 1.8 3.4 17.4

22uF 63V 59 43 0.24 -28.45 25072.2 -145.03 4.4E-13 2.1 3.5 20.6

Based on TDDB model, the following conversion was used:

Results for 7 part types showed that the acceleration constant B varies from 10 to 20.

Results for 7 part types showed that the acceleration constant B varies from 10 to 20.

WGT SummaryWGT Summary


Errors in FR calculations related to the testing conditions sum up to an order of magnitude.

Errors related to incorrect AFs can change FR up to 103 times.Reliance on MIL-PRF-55365 method for reliability rating might

be misleading.TDDB model predicts an exponential dependence of AF on

voltage with the voltage acceleration constant B depending on temperature.

Temperature dependence of AF can be presented in the Arrhenius-like form with Ea varying with voltage.

AF can be obtained using HALT and approximation of test results with a general log-linear relationship at two levels of stress factors.

Surge Current TestingSurge Current Testing


Mechanisms of Surge Current FailuresMechanisms of Surge Current Failures

19

Sustained scintillation breakdown.If current is not limited, self-healing does not have time to develop.

Electrical oscillations in circuits with high inductance.

Local overheating of the cathode. Mechanical damage to tantalum

pentoxide dielectric caused by the impact of MnO2 crystals.

Stress-induced-generation of electron traps caused by electromagnetic forces developed by high currents.

In all models the rate of voltage increase is critical. In all models the rate of voltage increase is critical.

TaMnO2

Ignition due to exothermic reaction in tantalum capacitors. Prymak 2006.


Effect of dV/dt on Breakdown VoltageEffect of dV/dt on Breakdown Voltage

20

Scintillation breakdown voltage, VBRscint (dV/dt ~ 1 to 5 V/sec) is always greater than the surge current breakdown voltage, VBRsurge(dV/dt ~ 105 to 106 V/sec)

The rate of voltage increase changescharges and electrical field at the interface.

Accumulation of electrons on traps at the MnO2-Ta2O5 interface with time increases the barrier, the level of electron injection, and the probability of avalanching.

The rate of voltage increase is critical for breakdown. A resistor in series with a capacitor reduces dV/dt and failures. The rate of voltage increase is critical for breakdown. A resistor in series with a capacitor reduces dV/dt and failures.

Fast voltage rise Slow voltage riseFast voltage rise Slow voltage rise

TaMnO2


40

60

80

100

120

140

160

40 60 80 100 120 140 160

VBR

_3SC

T, V

VBR_scint, V

Effect of dV/dt on VBR for 50V capacitors

40

60

80

100

120

140

160

40 60 80 100 120 140 160

VBR

_3SC

T, V

VBR_scint, V

Effect of dV/dt on VBR for 50V capacitors

Surge Current Derating RequirementsSurge Current Derating Requirements

21

History of requirements for circuit resistance (Rac): In the 1960s: 3 Ω per each volt of operating voltage. By the 1980s: 1 Ω per each volt. From the 1990s: 0.1 Ω per volt or 1 ohm, whichever is greater. Manufacturers consider surge current failures as the major

reason for voltage derating. Do we need derating of currents in addition to voltage? The limit for acceptable surge currents is set by the SCT

conditions: the current during applications should not exceed the current during testing: Iappl.< Itest

Improvements in reliability and the need to increase the efficiency of power supply systems resulted in reduction of Rac.

At what conditions we can allow circuit designs without Rac? Need a closer look at how the Itest is specified.

Improvements in reliability and the need to increase the efficiency of power supply systems resulted in reduction of Rac.

At what conditions we can allow circuit designs without Rac? Need a closer look at how the Itest is specified.

“use as tested”“use as tested”


MIL-PRF 55365 SCT RequirementsMIL-PRF 55365 SCT Requirements

22

SCT per MIL-PRF-55365H: Number of cycles: Nc = 4 surge cycles. Energy storage capacitor: CB = 20×CDUT Test voltage: VR Charge time, tch, and discharge time, tdisch, ≥ 1sec. Total DC resistance of the test circuit, Rtc, including the wiring, fixturing, and

output impedance of the power supply should not exceed 1 Ω. Measurements after SCT: DCL, C, DF (still no requirements for ESR) The minimum surge peak current shall be: Itest ≥ VR/(Rtc + ESRspec), Rtc = 1 Ω. Failure condition: current = 1A after 1ms for C ≤ 330uF; 10ms for C ≤ 3.3mF,

and 100ms for C > 3.3mF. Before 12/1/2012: Nc = 10. tdisch = tch = 4 sec. Rc ≤ 1.2 Ohms. CB ≥ 50 mF. No Itest requirements.

New specifications recognize the role of ESR as a limiting factor for surge currents. However, no specifics for Itest verification.M55365 does not guarantee reliable

operation at VR: Vtest = VC_MAX = 0.95×VR, => the need for voltage derating.

New specifications recognize the role of ESR as a limiting factor for surge currents. However, no specifics for Itest verification.M55365 does not guarantee reliable

operation at VR: Vtest = VC_MAX = 0.95×VR, => the need for voltage derating.


Application vs. Testing ConditionsApplication vs. Testing Conditions

23

Typical application conditions: No limiting resistors, minimal inductance. Minimal contact resistance.

Resistance of the circuit, Rac, is minimal and the current is limited mostly by ESR.

Surge Current Test conditions: Unspecified contact resistance of fixtures. Limiting resistor can be up to 1 Ω. Relatively long wires and inductance. No clear requirements for Itest verification (when, how?).

Parts with poor contacts in the fixture can pass the testing.

Application conditions might be more severe than test conditions.There is a need in tightening test requirements.Application conditions might be more severe than test conditions.There is a need in tightening test requirements.

Example:• A 15F 10V CWR06 capacitor with specified ESR=2.5Ω and real ESR = 0.5Ω is used in a 5V line.• During application the part can experience a spike:

Iappl = 5/0.5 = 10 A.• During the testing it will be verified to the current:

Itest ≥ VR/(Rtc + ESRspec)Itest =10/(1+2.5) = 2.8 A

Example:• A 15F 10V CWR06 capacitor with specified ESR=2.5Ω and real ESR = 0.5Ω is used in a 5V line.• During application the part can experience a spike:

Iappl = 5/0.5 = 10 A.• During the testing it will be verified to the current:

Itest ≥ VR/(Rtc + ESRspec)Itest =10/(1+2.5) = 2.8 A


Specifics of Surge Current TestingSpecifics of Surge Current Testing

24

Theory and experiments show that the rate of the voltage increase is critical for SCT.

High current spike is a byproduct of the fast voltage rise, rather than the major cause of failure.

Even minor variations (~0.1 Ω) of Rc affect results of SCT.

Measurements of voltage level across the capacitor during testing that are used to assure that the part passed SCT are not informative without indication of timing.

The amplitude of the current spike is the most adequate characteristic to verify SCT conditions.The amplitude of the current spike is the most adequate

characteristic to verify SCT conditions.

0

0.2

0.4

0.6

0.8

1

0

1

2

3

4

5

0 100 200 300 400

V/Vo

I/Vo,

A/V

time, uS

I_0.1 OhmI_0.4 OhmI_0.7 OhmV_0.1 OhmV_0.4 OhmV_0.7 Ohm

0

0.2

0.4

0.6

0.8

1

0

1

2

3

4

5

0 100 200 300 400

V/Vo

I/Vo,

A/V

time, uS

I_0.1 OhmI_0.4 OhmI_0.7 OhmV_0.1 OhmV_0.4 OhmV_0.7 Ohm

Calculations for 220uF capacitor at Lc= 400 nH, ESR=0.1Ω Rc-var


Factors Affecting SCT ResultsFactors Affecting SCT Results

25

Rac includes resistance of wires and contacts.

The length of wires affects inductance. Type of switch. The rate of voltage increase in

case of using field effect transistor (FET).

To simulate worst case conditions Isp should be maximized. To simulate worst case conditions Isp should be maximized.

-30

0

30

60

90

120

150

0 10 20 30 40 50

curr

ent,

A

time, us

4" wires

12" wires

24" wires

-30

0

30

60

90

120

150

0 10 20 30 40 50

curr

ent,

A

time, us

4" wires

12" wires

24" wires

-30

0

30

60

90

120

150

0 10 20 30 40 50

curr

ent,

A

time, us

110 nH

400 nH

900 nH

-30

0

30

60

90

120

150

0 10 20 30 40 50

curr

ent,

A

time, us

110 nH

400 nH

900 nH

47uF R=0.25Ohm L-var. Simulation.

‐30

0

30

60

90

120

150

0 10 20 30 40 50

curr

ent,

A

time, us

0 kOhm

0.8 kOhm

1.6 kOhm

‐30

0

30

60

90

120

150

0 10 20 30 40 50

curr

ent,

A

time, us

0 kOhm

0.8 kOhm

1.6 kOhm

0

2

4

6

8

10

12

-15 0 15 30 45 60 75 90

gate

vol

tage

, V

time, us

0 kOhm1.6K Ohm.8 k ohm

0

2

4

6

8

10

12

-15 0 15 30 45 60 75 90

gate

vol

tage

, V

time, us

0 kOhm1.6K Ohm.8 k ohm

47uF 20Vexperiment

Effect of resistors at FET gate on Vg and Isp for 47uF 20V capacitors


Effective Resistance of the CircuitEffective Resistance of the Circuit

26

Isp increases linearly with voltage allowing for calculations of the effective resistance of the circuit, Reff,.

Reff corresponds to the impedance of the circuit and includes Rac, ESR, resistance of contacts, and circuit inductance, Lc.

Isp increases linearly with voltage allowing for calculations of the effective resistance of the circuit, Reff,.

Reff corresponds to the impedance of the circuit and includes Rac, ESR, resistance of contacts, and circuit inductance, Lc.

47uF 10V

10uF 16V

220uF 6V

0

40

80

120

160

200

0 20 40 60 80

curr

ent s

pike

, A

voltage, V

47uF 10V

10uF 16V

220uF 6V

0

40

80

120

160

200

0 20 40 60 80

curr

ent s

pike

, A

voltage, V

0

40

80

120

160

200

0 15 30 45 60 75 90

curr

ent,

A

time, us

6V 8V10V 12V14V 16V18V 20V

220uF 6V

0

40

80

120

160

200

0 15 30 45 60 75 90

curr

ent,

A

time, us

6V 8V10V 12V14V 16V18V 20V

220uF 6V

‐40

0

40

80

120

160

200

240

‐10 0 10 20 30 40 50 60 70

curr

ent,

A

time, us

20V 24V28V 32V36V

47u 20V

‐40

0

40

80

120

160

200

240

‐10 0 10 20 30 40 50 60 70

curr

ent,

A

time, us

20V 24V28V 32V36V

47u 20V Test anomalies, e.g. poor contacts, can be revealed by Isp(V) curves

good contacts

poor contacts0

50

100

150

200

250

300

0 5 10 15 20 25 30 35

curr

ent s

pike

, A

voltage, V

3SCT 220uF 6V

good contacts

poor contacts0

50

100

150

200

250

300

0 5 10 15 20 25 30 35

curr

ent s

pike

, A

voltage, V

3SCT 220uF 6V

after adjustment


Effect of Reff on Breakdown VoltageEffect of Reff on Breakdown Voltage

27

Different lot date codes of 22 F 35V capacitors.

Effect of temperature Parts with larger ESR (Reff) had greater VBR.

Temperature decreases ESR resulting in lower VBR.

An increase in Reff by ~0.1Ωresults in increase of VBR ~10%.

Parts with larger ESR (Reff) had greater VBR.

Temperature decreases ESR resulting in lower VBR.

An increase in Reff by ~0.1Ωresults in increase of VBR ~10%.

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

0.2 0.22 0.24 0.26 0.28 0.3 0.32 0.34

ESR

, Ohm

Reff, Ohm

TBJD226K035LRLB0024

DC0513 DC0516

DC0824 DC0836

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

0.2 0.22 0.24 0.26 0.28 0.3 0.32 0.34

ESR

, Ohm

Reff, Ohm

TBJD226K035LRLB0024

DC0513 DC0516

DC0824 DC0836

30

40

50

60

70

80

90

0.2 0.22 0.24 0.26 0.28 0.3 0.32 0.34

VBR

_SC

T, V

Reff, Ohm

TBJD226K035LRLB0024

DC0513 DC0516

DC0824 DC0836

30

40

50

60

70

80

90

0.2 0.22 0.24 0.26 0.28 0.3 0.32 0.34

VBR

_SC

T, V

Reff, Ohm

TBJD226K035LRLB0024

DC0513 DC0516

DC0824 DC0836

0

0.1

0.2

0.3

0.4

0

20

40

60

80

-60 -40 -20 0 20 40 60 80 100

Reff,

Ohm

VBR_

SCT,

V

temperature, deg.C

47uF 20V VBR220uF 6V VBR47uF 20V Reff220uF 6V Reff

0

0.1

0.2

0.3

0.4

0

20

40

60

80

-60 -40 -20 0 20 40 60 80 100

Reff,

Ohm

VBR_

SCT,

V

temperature, deg.C

47uF 20V VBR220uF 6V VBR47uF 20V Reff220uF 6V Reff


Correlation between ESR and ReffCorrelation between ESR and Reff

28

In an optimized set-up the difference between Reff and ESR is 0.1 - 0.2 Ω.

In an optimized set-up the difference between Reff and ESR is 0.1 - 0.2 Ω.

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Ref

f, O

hm

ESR, Ohm

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Ref

f, O

hm

ESR, Ohm

Effective resistancde during SCT and ESR

R, Ohmcu

mul

ativ

e pr

obab

ility

, %0.10 0.800.24 0.38 0.52 0.661

5

10

50

99ESR\TM8A106K016CBZNormal-2PRRX SRM MED FMF=16/S=0

Data PointsProbability Line

ESR\TM8T476K010CBZNormal-2PRRX SRM MED FMF=16/S=0


Reff\TM8A106K016CBZNormal-2PRRX SRM MED FMF=16/S=0


Reff\TM8T476K010CBZNormal-2PRRX SRM MED FMF=15/S=0


20 lots of HV capacitors microchips

y = 0.6118x + 0.1963

0.3

0.35

0.4

0.45

0.2 0.25 0.3 0.35 0.4

Ref

f, O

hm

ESR, Ohm

47uF 10V uchips

y = 0.6118x + 0.1963

0.3

0.35

0.4

0.45

0.2 0.25 0.3 0.35 0.4

Ref

f, O

hm

ESR, Ohm

47uF 10V uchips

ESRRIVRR ac

speff


SCT SummarySCT Summary

29

Results of SCT depend on the rate of voltage increase. To assure proper SCT conditions, current spike

amplitudes, Isp, should be measured for each part, and conditions VR/Isp = Reff < 0.5 + ESR should be verified.

Tantalum capacitors manufactured per M55365 might fail at first power turn-on due to non-adequate SCT conditions.

Additional testing and analysis (to compare levels of current spikes during testing and application) are necessary to use tantalum capacitors without limiting resistors.


weibull grading and surge current testing for tantalum ... and sct 2013_n235.pdf · weibull grading...

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