Reliability Issues with New Technology Wet Tantalum … 2013 WTC...Presented by Alexander Teverovsky...

Alexander TeverovskyDell Services Federal Government, Inc.

work performed for NASA Goddard Space Flight Center, Parts, Packaging, and Assembly Technologies Office, Code 562

[email protected]

NASA Electronic Parts and Packaging Program

1Presented by Alexander Teverovsky at the Components for Military & Space Electronics Conference & Exhibition (CMSE 2013), February 19-22, 2013, Los Angeles, CA, and published on nepp.nasa.gov.

Specifics of wet tantalum capacitors (WTC). New designs. Reverse bias operation. Random vibration testing. Failure modes and

mechanisms. Conclusion and

recommendations. Guidelines for selection,

S&Q.


If Ta2O5 is damaged, anodic oxidation continues under normal, forward bias conditions resulting in oxide growth thus effectively eliminating the defect.

Self-healing contributes substantially to the reliability of WTC – is it a panacea?


0

1

2

3

4

5

6

7

0 25 50 75 100 125

VBR

/VR

rated voltage, V

Wet Tantalum Capacitors

M39006

advanced wet

0

1

2

3

4

5

6

7

0 25 50 75 100 125

VBR

/VR

rated voltage, V

Wet Tantalum Capacitors

M39006

advanced wet

Better performance of advanced WTC is achieved by reducing the thickness of the cathode layer, increasing the size of the slug, and using powder with a higher CV.

Different manufacturers are using different cathode materials, e.g.: activated C/NbO; Pd/Cu; RuO2.

Better performance does not come free. Reliability effect: reverse bias and mechanical stresses.


M39006 DWG93026

Robustness to RB is needed to get additional margin for testing and unforeseen events.

First tantalum capacitors in silver case had failures under low RB due to silver electrodepositing and dendrite growth.

The use of a tantalum case and oxidized sintered Ta powder allowed to improve substantially the robustness against RB.

New design WTC do not have protection against RB. 93026: RB < 1.5V and Q < 0.05C (?); 04005: no RB requirements.

Ta/Ta2O2 cathode


Electrodeposition of cathode metals

In most cases the transfer charge is below the specified value of 0.05C.

Time to failure varies from part-to part substantially.

Failures might happen even at voltages as low as ~0.1V

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

0.001 0.01 0.1 1 10 100

curr

ent,

A

time, hr

93026 470uF 50V RBS 0.5V

SN6 8E-3SN7 1E-2SN8SN9 2.1E-2

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

0.001 0.01 0.1 1 10 100

curr

ent,

A

time, hr

93026 470uF 50V RBS 0.5V

SN6 8E-3SN7 1E-2SN8SN9 2.1E-2

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

0.01 0.1 1 10 100

curr

ent,

A

time, hr

93026 220uF 50V RBS 0.5V

SN30 1.8E-3

SN31 5.7E-4

SN32 1.8E-3

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

0.01 0.1 1 10 100

curr

ent,

A

time, hr

93026 220uF 50V RBS 0.5V

SN30 1.8E-3

SN31 5.7E-4

SN32 1.8E-3

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

0.01 0.1 1 10 100

curr

ent,

A

time, hr

93026 110uF 75V RBS 0.5V

SN10 1.6E-3

SN11 5.9E-2

SN12 8.1E-3

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

0.01 0.1 1 10 100

curr

ent,

A

time, hr

93026 110uF 75V RBS 0.5V

SN10 1.6E-3

SN11 5.9E-2

SN12 8.1E-3


Pd deposition on the surface of Ta2O5 reduces the barrier height and increases forward leakage currents.

Electrodeposition at defects prevents self-healing.Degradation is reversible only partially.

DWG#93026, 220uF 50V

Pd/Cu cathode coating


RBS causes gradual degradation of RBand Forward Bias (FB) leakage currents.

Capacitance decreases under RBS and then stabilizes.

The loss of capacitance might be due to electropolishing or detachment of the cathode layer.

0

100

200

300

400

500

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

C, u

F

frequency, Hz

Mfr.A 93026 AVX 470uF 75V

init-1.5-2-2.5-3-3.5

0

100

200

300

400

500

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

C, u

F

frequency, Hz

Mfr.A 93026 AVX 470uF 75V

init-1.5-2-2.5-3-3.51.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1 10 100 1000

curr

ent,

A

time, sec

Mfr.A 93026 470uF 75V 5 m RBS

75V init -1.5V 5m75V, 1.5V RBS -2V75V, 2V RBS -2.5V75V, 2.5V RBS -3V75V, 3V RBS

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1 10 100 1000

curr

ent,

A

time, sec

Mfr.A 93026 470uF 75V 5 m RBS

75V init -1.5V 5m75V, 1.5V RBS -2V75V, 2V RBS -2.5V75V, 2.5V RBS -3V75V, 3V RBS


Temperature and deformation of the case were measured using flexible sensors.

Strain increases linearly with time due to the pressure building up.Strain ~0.07% corresponds to a pressure of dozens of

atmospheres.

H2 generation at cathode:2e- + 2H2O(L) => H2(g) + 2OH-(aq)

y = 0.0027x

y = 0.0022x + 0.02

0

0.02

0.04

0.06

0.08

0.E+00 5.E+00 1.E+01 2.E+01 2.E+01

stra

in, %

time, hr

DWG93026 470uF 75V RBS 1mA

RBS 1mA 1

RBS 1mA 2

RBS 1mA 3

calc at V=10mm3y = 0.0027x

y = 0.0022x + 0.02

0

0.02

0.04

0.06

0.08

0.E+00 5.E+00 1.E+01 2.E+01 2.E+01

stra

in, %

time, hr

DWG93026 470uF 75V RBS 1mA

RBS 1mA 1

RBS 1mA 2

RBS 1mA 3

calc at V=10mm3

FztIn

VRTnP

hErP


SN19 failed after 100hr 2V RBS due to lead fell-off caused by electrolyte leak.

Pressure deforms the case, forces electrolyte above the Teflon bushing, and causes corrosion of the weld.


700

750

800

850

900

C_12

0Hz,

uF

DWG04005 980uF 60V 100hr RBS

700

750

800

850

900

C_12

0Hz,

uF

DWG04005 980uF 60V 100hr RBS

DWG04005 capacitors feature a sharp decrease in RB current and open circuit failure mode.

0

50

100

150

200

250

init 0.5V 0.75V 1V 1.25V 1.5V 2V

capa

cita

nce,

uF

04005 210uF125V 100hr RBS

SN650

SN638

SN535

SN657

0

50

100

150

200

250

init 0.5V 0.75V 1V 1.25V 1.5V 2V

capa

cita

nce,

uF

04005 210uF125V 100hr RBS

SN650

SN638

SN535

SN657

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0.01 0.1 1 10 100

curre

nt, A

time, hr

04005 210uF 125V RBS 2V

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0.01 0.1 1 10 100

curre

nt, A

time, hr

04005 210uF 125V RBS 2V

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0.01 0.1 1 10 100

curre

nt, A

time, hr

DWG04005 870uF 60V RBS at 2V

A5A6A7A8

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0.01 0.1 1 10 100

curre

nt, A

time, hr

DWG04005 870uF 60V RBS at 2V

A5A6A7A8


Pressure starts building up after a few sec at 1V.

Pressure remains in the case when parts are unbiased and can cause electrolyte leak and corrosion.

DCL did not degrade after 100hr of 2V RBS; whereas C and ESR fail.

Strain ~3% => pressure up to 50 atm.1.E-02

1.E-01

1.E+00

1.E+01

1 10 100 1000 10000 100000

stra

in, %

time, sec

04005 I sens 870uF 60V

RBS 1V RBS 1.5VRBS 1.5V r RBS 2V

RBS 2V r

1.E-02

1.E-01

1.E+00

1.E+01

1 10 100 1000 10000 100000

stra

in, %

time, sec

04005 I sens 870uF 60V

RBS 1V RBS 1.5VRBS 1.5V r RBS 2V

RBS 2V r

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1 10 100 1000 10000

curr

ent@

50V,

A

time, sec

DWG04005 sens.I 870uF 60V

17.5hr 1V RBS

3hr 1.5V RBS

40hr 1.5V RBS

3hr 2V RBS

72hr 2V RBS

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1 10 100 1000 10000

curr

ent@

50V,

A

time, sec

DWG04005 sens.I 870uF 60V

17.5hr 1V RBS

3hr 1.5V RBS

40hr 1.5V RBS

3hr 2V RBS

72hr 2V RBS


0

200

400

600

800

1000

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

capa

cita

nce,

uF

f requency, Hz

04005 sens III 980uF 60V

init100hr 0.3mA24hr 1mA72hr 1mA6hr 3mA15hr 3mA24hr 5mA10ma 24hr

0

200

400

600

800

1000

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

capa

cita

nce,

uF

f requency, Hz

04005 sens III 980uF 60V

init100hr 0.3mA24hr 1mA72hr 1mA6hr 3mA15hr 3mA24hr 5mA10ma 24hr

0

0.3

0.6

0.9

1.2

1.5

1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06

stra

in, %

time, sec

04005 sens III 980uF 60V RBS

0.3mA0.7mA1mA3mA3mA5mA10mA

0

0.3

0.6

0.9

1.2

1.5

1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06

stra

in, %

time, sec

04005 sens III 980uF 60V RBS

0.3mA0.7mA1mA3mA3mA5mA10mA

Strain accumulates with each cycle.Stabilization of pressure with time is

likely due to voltage drop below the threshold level.

FB currents do not degrade substantially.

Decrease of roll-off frequency with RBS

Failures in an open circuit mode.


Internal pressure causes bulging.

Bulging strains the wire that fractures eventually. (max wire deformation ~ 0.25 mm; deformation of a clamped 20 mil membrane at 50 atm~0.23 mm)

The absence of a Teflon gasket facilitates electrolyte leakage.

Wire fracture and electrolyte leakage cause open circuit failures.


Capacitors per DWG#93026 and #04005 are qualified to 20 g sin high frequency vibration only.

Sample size is not set (in some cases 2 samples only are tested).

Test conditions are not specific. Random vibration testing is not

required and is performed only if specified by the purchase order.

Random vibration test is more appropriate for space applications than HF sinusoidal vibration, and MARs for most projects require box-level random vibration testing at 14.1 Grms.


1.E-08

1.E-07

1.E-06

1.E-05

1.E-04in

itz

20g

xy 2

0gz

34g

xy 3

4gz

54g

xy 5

4gz

65g

xy 6

5gz

65g

15m

xy 6

5g 1

5mz

65g

15m

rxy

65g

15m

r

curr

ent,

A

Mfr.B 470uF 50V DC0524

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04in

itz

20g

xy 2

0gz

34g

xy 3

4gz

54g

xy 5

4gz

65g

xy 6

5gz

65g

15m

xy 6

5g 1

5mz

65g

15m

rxy

65g

15m

r

curr

ent,

A


1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

init

xy 2

0gxy

34g

xy 5

4gz

65g

15m

z 65

g 15

m r

z 65

g 15

m 3

z 65

g 15

m 4

z 65

g 15

m 5

z 65

g 15

m 6

z 65

g 15

m 7

z 65

g 15

m 8

z 65

g 15

m 9

x y 6

5g 1

5m 1

0

curr

ent,

A


1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

init

xy 2

0gxy

34g

xy 5

4gz

65g

15m

z 65

g 15

m r

z 65

g 15

m 3

z 65

g 15

m 4

z 65

g 15

m 5

z 65

g 15

m 6

z 65

g 15

m 7

z 65

g 15

m 8

z 65

g 15

m 9

x y 6

5g 1

5m 1

0

curr

ent,

A

Mfr.B 110uF 75V DC08101.E-08

1.E-07

1.E-06

1.E-05

1.E-04

init z 20g xy 20g

z 34g xy 34g

z 54g xy 54g

curr

ent,

A

DWG93026 Mfr.A 470uF 75V

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

init z 20g xy 20g

z 34g xy 34g

z 54g xy 54g

curr

ent,

A

DWG93026 Mfr.A 470uF 75V

Different part types have failures from 20 to >65 Grms.

1.E-08

1.E-07

1.E-06

1.E-05

init z 20g

xy 20g

z 34g

xy 34g

z 54g

xy 54g

z 65g

xy 65g

curr

ent,

A


1.E-08

1.E-07

1.E-06

1.E-05

init z 20g

xy 20g

z 34g

xy 34g

z 54g

xy 54g

z 65g

xy 65g

curr

ent,

A



05

101520253035404550

0 250 500 750 1000

volta

ge, V

time, sec

DWG93026 470uF 75V at 10.7 rms g

SN6 SN7SN8 SN9SN10

05

101520253035404550

0 250 500 750 1000

volta

ge, V

time, sec

DWG93026 470uF 75V at 10.7 rms g

SN6 SN7SN8 SN9SN10

1.E‐07

1.E‐06

1.E‐05

1.E‐04

1.E‐03

1.E+1 1.E+2 1.E+3

curr

ent,

Atime, sec

DVG93026 470uF 75V after 10.7 rms g

SN6SN7SN8SN9SN10

1.E‐07

1.E‐06

1.E‐05

1.E‐04

1.E‐03

1.E+1 1.E+2 1.E+3

curr

ent,

Atime, sec

DVG93026 470uF 75V after 10.7 rms g

SN6SN7SN8SN9SN10

Some DWG#93026 parts can fail at vibration levels that are below MAR requirements.


Several anomalies have been observed during thermal vacuum testing. However, at the end of the testing the unit operated normally.

Post-testing internal examinations revealed damaged sleeve, discoloration and charring of conformal coating around one of the WTCs.

The cracks were due to stresses caused by the building-up of gas pressure in the case and hydrogen embrittlement of tantalum at cold work areas.


Failures during vibration are likely caused by NbO and carbon particles penetrating inside the slug.

Under mechanical stresses these particles might create local stresses sufficient to cause damage to the dielectric and increase leakage current.


DWG#93026 and 04005 parts might fail at low-voltage (0.5V and less) RB conditions and random vibration as low as 10.7 Grms.

The probability of failure does not depend on rated voltage.RB and vibration can result in increased leakage currents, internal

gas pressure, case fractures, electrolyte leak, and corrosion.Parts with Pd-based cathode appeared to be more sensitive to RB,

whereas parts with Nb-based cathode are more sensitive to vibration.Manufacturers are working on new designs to improve reliability.Advance WTCs can self-heal, are resilient to environmental

stresses, but not to the degree of M39006 capacitors. To operate reliably, the robustness against mechanical stress (random vibration at 20 Grms) and RB (to 1.5V at 85C) should be verified.Guidelines for selection, S&Q and DPA of the WTC are suggested.



I. Scope

II. Background

III. Failure rate

IV. Construction analysis/DPA

V. Lot acceptance testing

VI. Qualification testing

VII. Freshness policy

VIII. Derating

http://nepp.nasa.gov

Reliability Issues with New Technology Wet Tantalum … 2013 WTC...Presented by Alexander Teverovsky...

Documents

Transcript of Reliability Issues with New Technology Wet Tantalum … 2013 WTC...Presented by Alexander Teverovsky...