Lessons Learned from Screening and Qualification of COTS

Capacitors

Alexander TeverovskyJacobs Engineering, Inc.

Work performed for EEE Parts, Photonics and Assembly Branch, NASA GSFC, Code 562

Alexander.A.Teverovsky@nasa.gov

NASA Electronic Parts and Packaging (NEPP) Program

List of Acronyms

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AEC Automotive Electronics Council MSL moisture sensitivity level

BI burn-in PST power surge test

DCL direct current leakage PWB printed wiring board

DLA Defense Logistics Agency RB reverse bias

EM electrical measurements RVT random vibration test

ER established reliability S&Q screening and qualification

ESA European Space Agency SS sample size

ESR equivalent series resistance TC temperature cycling

FR failure rate TS thermal shock

IDC inter-digitated capacitor TTF time to failure

LAT lot acceptance test VR voltage rating

LT life test

Abstract

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A traditional approach to screening and qualification of hi-relCOTS capacitors and its limitations are analyzed. Results oftesting of four types of COTS capacitors for L2 projects aresummarized. The types include DLA drawing tantalum MnO2capacitors, high-voltage hermetically sealed polymer tantalumcapacitors, multianode COTS+ capacitors, and feedthrough BMEceramic capacitors. Lessons learned from this experience mightaccelerate processes and reduce risks of inclusion of COTScomponents in space projects.

Outline

Traditional approach to screening and qualification of hi-rel COTS capacitors and its limitations

Case 1: DLA drawing MnO2 capacitor Case 2: High-voltage hermetically sealed polymer

tantalum capacitors Case 3: Multianode COTS+ tantalum capacitors Case 4: Feedthrough ceramic capacitors Lessons learned

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COTS vs. MIL-Grade Capacitors

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Capacitors for different level space projects are selected based on reliability/FR grading.

Risk of using a COTS capacitor: Pm × (consequences of failure).

𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅 → λ𝑚𝑚 = λ/𝐴𝐴𝐴𝐴

The major benefit of using ER MIL-grade parts is that they are assumed to be acceptable for most space projects if operating conditions are within the MIL range of temperatures and voltages.

Lack of confidence in consistency of quality in different lots of COTS capacitors → difficulties in reliability assessments for a given part type.

Contrary to MIL applications, space projects are often interested in a single lot of capacitors that are to be used at a relatively benign conditions → the need to assess reliability of a particular batch for a specific application.

Existing guidelines for S&Q of COTS parts typically follow MIL-spec requirements developed for relatively old technologies.

𝑃𝑃𝑚𝑚 = 1 − exp −λ𝑚𝑚𝑡𝑡𝑚𝑚 ,

1.E-5

1.E-4

1.E-3

1.E-2

1.E-1

1.E+0

1%/1000hr 0.1%/1000hr 0.01%/1000hr 0.001%/1000hr

prob

abili

ty o

f mis

sion

failu

re

failure rate

1 year3year10year20year

Life Testing of COTS Capacitors

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Increasing risks of WO failures for new technology capacitors can be managed.

If a COTS part can pass the relevant MIL spec requirements is it as good as a MIL part? Due to a small SS during LT and low confidence/trust

in quality consistency for COTS it is impossible to get acceptable FR without significant acceleration. Test results cannot be generalized for a given part

type → each lot should be tested. Existing LT for COTS capacitors is a quality compliance, but not a reliability test. LT conditions in the existing guidelines might be not applicable for advanced COTS.

If COTS capacitors fail MIL requirements for life testing, can it still be used? If not, but you wish to use the part very much, then should we:

A. Relax the requirements in the MIL spec (IDC, hybrids)?B. Assess acceleration factors and prove reliability for the mission?

IM failures WO failures

spec

failu

re ra

te

time

useful life

new technology

The beauty of WO failures: PoF approach and modeling

DLA #13008

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Benefits of frameless design: Better polarity indication Elimination of wire welding Extended range The part has a good self-healing

capability (10% of damage after scintillation breakdown)

T97 max rating 22uF, 250 mΩ, 63V

Sn/Pb

Silver epoxy

Ni

Examples of cracking at the anode and cathode in CWR06 capacitors

Potential problems: Integrity after soldering Insufficient screening (85C/40hr/VR)

Life test is optional (85C/2000hr/VR)

CWR06max rating

4.7uF, 1.5Ω, 50V

DLA #13008 10uF 63V S&Q

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Application conditions for a project: 28V, survival T range from -25ºC to 65ºC; possible transients during power-up 2-5 ms. Screening verification included monitored BI at 85C 63V for 160hr.One out of 85 samples failed after 50 hours. The appearance of the failure site suggested scintillation breakdown. Qualification tests using 45 samples reflow soldered onto test PWB: monitored cycling (30 TC -35 to +85C), power surge, and life test (2000hr, 85C).

-60

-40

-20

0

20

40

60

80

100

0.0E+0

2.0E-6

4.0E-6

6.0E-6

8.0E-6

1.0E-5

1.2E-5

1.4E-5

0 5 10 15 20 25 30

tem

pera

ture

, deg

.C

curre

nt, A

time, hr

0.0E+0

5.0E-6

1.0E-5

1.5E-5

2.0E-5

2.5E-5

3.0E-5

0 500 1000 1500 2000

curre

nt, A

time, hr

85C 63V

The frameless technology improves performance and quality of the parts. DLA drawing parts might require BI verification. Life test at 85C 63V for 2khr corresponds to >1000yr during the mission.

Monitored TC life test

1/85 sample failed screening

TCH Capacitors

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A project selected 22uF 100V Ta caps to be used in 35V power lines with possible transient spikes up to 43V. Turn ON/OF cycles are relatively slow, ~300 µsec. Operational T~ 25 ºC and possible variations -20 to +30 ºC. Ripple currents below 20 mA, which is ~10 times below the specified limit.

TCH series are hermetically sealed polymer Ta caps developed for space applications per ESA requirements.

C-shape terminals were selected to reduce stresses from PWB. Screening of 420 samples included:

5 TC (-55C to +125C), power surge, hermeticity, and monitored BI (85C/100V/168hr).

LAT was carried out for 3 groups after reflow soldering onto test PWB or soldering simulation. Gr.I (20pcs): 100TC -55 to +125C -> EM -> humidity (85C/85% RH/2wk)

-> EM -> power surge cycling. Gr.II (20pcs): reflow soldering -> EM ->

stability at HT and LT -> RVT. Gr.III (60pcs): reflow soldering ->EM ->

monitored life test (85C/100V/2000hr)

Potential problems:• Dehermetization or excessive leak• Reverse bias pulses• Reliability at operating conditions

Effect of Dehermetization

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Small holes were drilled in several engineering samples of the part. AC characteristics were measured after dehermetization, exposure

to moisture, 100 TS, and HTS125 up to 3000 hours.

Significant capacitance variations in non-hermetic parts indicate moisture presence. Epoxy foam inside the package does not substantially delay moisture penetration. The level of moisture corresponding to RC does not degrade the parts. Hermetically sealed parts can withstand > 3000hr of HTS125, whereas non-hermetic

parts can fail even after 1000hr due to thermo-oxidative degradation of PEDOT/PSS.

Effect of Reverse Bias Pulses

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During PST, the parts were stressed by 60V 0.5 sec pulses with a ramp time < 0.3msec. Similar pulses in reverse polarity were applied at increasing voltages. The currents were also monitored at 60V RB.

0

10

20

30

40

50

60

70

0.01

0.1

1

10

0 1 2 3 4 5

volta

ge, V

curre

nt, A

time, msec

TCH 22uF 100V at FB

I_FB_60FB 60V

0

10

20

30

40

50

60

70

0.01

0.1

1

10

0 1 2 3 4 5

volta

ge, V

curre

nt, A

time, msec

TCH 22uF 100V at RBI_10 I_20I_30 I_40I_50 I_6010V 20V30V 40V50V 60V

0

10

20

30

40

50

60

70

0.001

0.01

0.1

1

10

0 5 10 15

volta

ge, V

curre

nt, A

time, sec

TCH 22uF 100V at 60V RB

I4V4

Reverse bias during PST does not damage the part. At 60V, failures at reverse bias can be observed after 10 sec. RB failures result in charring of polymer around the whole surface of the slug.

RB failure at 60V

Results of Life Testing (Gr. III, 60 pcs)

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SN100

0.0E+0

5.0E-7

1.0E-6

1.5E-6

2.0E-6

0 500 1000 1500 2000

curre

nt, A

time, hr

life test at 85C 100V

Screening: 4.3% of 420 pcs failed DCL before BI and 0.7% failed during BI.

Life test: No failures or significant

anomalies during monitored life testing.

No parametric degradation or failures after life testing.

Limit 220uA

Variations of AC characteristics through the testing

Conservative estimations show that 2khr life test at 85C, 100V corresponds to more than 1000 years during the mission.

Evaluation of Multianode TBM Capacitors

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Multianode capacitors allow for a substantial reduction of ESR that can be reduced to 35-70 mohms for MnO2 capacitors.

Available with Weibull Grade “B” reliability (0.1%/1000hr). Potential reliability problems: Greater risk of popcorning due to increased number of edges. Greater risk of breakdown due to a larger surface.

Soldering of 6 types of TBM capacitors (720 pcs) shows that with proper baking the parts can be safely soldered onto PWBs.

MSL1Preliminary tests showed that multianodecapacitors preconditioned per MSL1 have

cracks after reflow soldering

LAT of Multianode Capacitors

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No failures in 5 lots of capacitors. In one lot, 2 out of 120 samples failed life test.

Additional screening (BI) might be necessary in one of 6 tested lots. Using a 45(1) criterion per the guidelines, would have 83% chance of passing life test. Parts that passed the life test 120(0) at 1.1VR will have the probability of failure during a

20 year mission < 0.01%.

Test flow Qualification tests Life Test for a Failed Lot

SN18SN33

1.E-7

1.E-6

1.E-5

1.E-4

0 200 400 600 800 1000

curr

ent,

A

time, hr

22uF 35V at 85C 1.1VR

Multianode 22uF 35V capacitors

TTF, hr

cumu

lative

prob

abilit

y, %

1.E-1 1.E+1110 1000 100000 1.E+7 1.E+91.E-1

5.E-1

1

5

10

50

90

100

1.E-1

85C u=1.1

85C u=0.5

788 years

b=3.5

b=0.33

75C u=0.14use cond.

life test simul based on AF, use cond

simul. u=1.1, 85Csimul. u=0.5, 85Csimul. u=0.14, 75C

simul based on AF, 85C u=0.5

IM

WO

Feedthrough BME Capacitors

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AEC Q-200 feedthrough BME 0805, X7R, 10nF, 50V for use in 5V lines at 65 ºC max.

300 samples passed monitored BI at 125 ºC/100V/160hr with zero failures.

Monitored LT of 60 soldered samples at 125 ºC/100V/2000hr resulted in 2 failures.

For some AEC-Q200 parts BI is not necessary. Conservative estimations showed that at the mission conditions TTF > 10,000 years. Parts failing MIL life test requirements can be used for a space mission at

substantially derated conditions.

Life Test

time-to-failure, hr

cumu

lative

prob

abilit

y, %

1.E+2 1.E+121.E+3 1.E+4 1.E+5 1.E+6 1.E+7 1.E+8 1.E+9 1.E+10 1.E+111.E-1

5.E-1

1

5

10

50

90

100

1.E-1 x 58

125C, 100V

65C, 5V atAF=1.42E6

60% CB

Lessons Learned

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Instead of qualifying a COTS capacitor “for space”, we need to ensure that a given batch of parts has an acceptable probability of failure at specific application conditions for the required mission time.

Paradigm shift: reliability for the mission instead of compliance with MIL-spec (relaxed?) requirements.

Development of S&Q plans for COTS capacitors should include: Analysis of potential reliability concerns specific to the design. Qualification testing using sufficiently large SS of soldered capacitors. Analysis of application conditions. Assessments of reliability acceleration factors.

COTS+ capacitors require BI, unless opposite is proven statistically.