Reliability Issues with Polymer and MnO2 Tantalum Capacitors for Space Applications
Alexander TeverovskyJacobs Engineering, Inc.
Work performed for Parts, Packaging, and Assembly Technologies Office,
NASA GSFC, Code [email protected]
NASA Electronic Parts and Packaging (NEPP) Program
List of Acronyms
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 2
AC alternating current FR failure rate
AF accelerating facor HTS high temperature storage
AT anomalous transients LT life test
C capacitance MSL moisture sensitivity level
CCS constant current stress PEDOT:PSSPoly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)
CPTC chip polymer tantalum capacitor S&Q screening and qualification
DC direct current SCT surge current stress
DCL direct current leakage T temperature
DF dissipation factor TS thermal shock
ER established reliability VBR voltage breakdown
ESR Equivalent series resistance VR voltage rating
Abstract
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 3
This presentation gives a comparative analysis ofdegradation processes, failure modes and mechanisms inMnO2 and polymer technology capacitors. Analyzedconditions include effects of vacuum and radiation, soldering(pop-corning), long-term storage, operation at hightemperatures, stability at low and high temperatures, andanomalous transients. Screening and qualificationprocedures to assure space-grade quality of CPTCs aresuggested.
Outline
Effect of moisture. Effect of soldering. Effect of vacuum. Stability at low and high temp. Effect of storage at high temp. Life testing. Anomalous transients. Quality assurance for space
applications. Summary.
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 4
Ta slug
carbon
polymer
silver epoxy
Polymer
Ta slug
MnO2
silver epoxy
carbonMnO2
Capacitors have similar design but MnO2 is replaced with conductive polymer
Advantages and Disadvantages of CPTCs for Space Applications
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 5
Advantages: Better volumetric efficiency (smaller case sizes); Higher operating voltages (up to 125V); Lower ESR (milliohm range); A relatively safe failure mode (no ignition); Radiation hardness is similar to MnO2 parts (up to 5 Mrad Si).
Disadvantages: Variety of materials and processes for cathode formation; Desorption of moisture in vacuum can be a benefit or a hazard; Intrinsic ESR degradation processes at high temperatures; A new phenomena: anomalous transients; S&Q system developed for MnO2 capacitors is not sufficient
due to new failure and degradation mechanisms.
Breakdown failures
poly
mer
MnO2
Effect of Moisture
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 6
CPTCs are more sensitive to moisture compared to MnO2 caps. Capacitance variations can reach 40% and DCL >104 times.
Relaxation of leakage currents
1.E-9
1.E-8
1.E-7
1.E-6
1.E-5
1.E-4
1.E-3
1.E-2
-80 -60 -40 -20 0 20 40 60 80 100 120 140
curre
nt@
1000
s, A
temperature, deg.C
22uF 25V
HUM
virgin
BAKE
Deviation of AC characteristics, 𝑃𝑃𝑤𝑤𝑤𝑤𝑤𝑤−𝑃𝑃𝑑𝑑𝑑𝑑𝑑𝑑
𝑃𝑃𝑎𝑎𝑎𝑎𝑑𝑑× 100 , for 25
lots of MnO2 and 22 lots of CPTCs
Temperature dependence
Failures after Soldering
7To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020
Pop-corning due to the presence of moisture increases delamination, introduces cracks in package and might damage Ta2O5 dielectric.
Cracks in packages facilitate penetration of oxygen that increases the rate of ESR degradation in CPTCs.
Damage to dielectric causes first power-on failures in MnO2 capacitors. The effect has not been observed yet in CPTCs.
Damage caused by soldering is lot-related. Pop-corning issues can be resolved by baking. Requirements for MSL testing should include
measurements of ESR and surge current testing.
Test CWR29, 10uF 35Vas is Bake MoistureAC testing 0/20 0/20 0/20SCT at 15V 2/20 0/20 9/20SCT at 35V 1/18 0/20 8/11
MnO2 first power-on failure (1.5Ω)
Crack in CPTC, MSL test
Effect of Soldering
8To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020
Decrease of C in CPTCs is greater than in MnO2 capacitors. Soldering increases ESR in most types of capacitors, but the
level of variations is lot-related. Soldering results in drying off capacitors by 50 to 93%.
MnO2 G1
PolymG2
PolymG3
PolymGM
PolymA1
PolymA2
PolymAQ
∆Csold/Cinit, % 1.4 10.9 8.4 6.2 13.1 18.8 8.3∆Cmax/Cinit,% 2.3 11.8 9.8 6.9 21.5 26 16.6
∆Csold/∆Cmax, % 63 93 86 89 61 72 50
Variations of capacitance in 35V capacitors during MSL1 testing
Variation of AC characteristics
Effect of Vacuum
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 9
Drying in vacuum has a similar effect as drying in air:oDecreasing of capacitance and DF;oA relatively small changes in ESR;oVariations of C and DF with V;oIncreasing of transient leakage
currents, especially at low T.0
0.51
1.52
2.53
3.54
4.55
0 0.2 0.4 0.6 0.8 1cu
rrent
, Atime, msec
10V and 6.3V caps after 2000hr in vac
polym 220uF 10VMnO2 330uF 6.3VMnO2 220uF 10Vpolym 330uF 6.3V
Variations of C, DF, and ESR after 1000hr at 75C, 1E-6 torr
Relaxation of leakage currents
Surge current test
1.E-5
1.E-4
1.E-3
1.E-2
1.E-1
1.E+0
0.01 0.1 1 10 100
curr
ent,
mA
time, min
T598 and T495 33uF 25V in vacuum
-20C-30C-50C+20C
CPTCMnO2
33uF 25V caps in vac 1E-6 torr
Variations of Characteristics with Time after Vacuum
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 10
Moisture sorption after vacuum testing results in extremal variations of DF.
CPTCs remain dry and can be tested after vacuum for several days at room conditions.
∆𝑚𝑚∆𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚
=∆𝐶𝐶
∆𝐶𝐶𝑚𝑚𝑚𝑚𝑚𝑚 Tantalum pellet can be used as a moisture sensor:
Stability of Characteristics at Low and High Temperatures
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 11
Capacitance in CPTCs increases with T to a greater degree than in MnO2, but ESR is much more stable.Results of stability testing might depend on moisture content.CPTCs might be used for cryogenic applications.DCL in CPTCs might increase above DCLmax at low temeratures.
Variations of C and ESR with temperature Variations of DCL with T
1.E-9
1.E-8
1.E-7
1.E-6
1.E-5
1.E-4
1.E-3
-65 -50 -35 -20 10 25 55 85 125 145 165
curr
ent,
A
temperature, deg.C
47uF 35V capacitors
polym MnO2
Hysteresis of Leakage Currents during Temperature Variations
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 12
Extremal variations of leakage currents in the process of heating. Maximum currents can be reached at temperatures from -65 ºC
to 0 ºC and exceed the specified limit. Hysteresis can exceed 6 orders of magnitude and is one of
manifestations of anomalous transients.
1.E-9
1.E-8
1.E-7
1.E-6
1.E-5
1.E-4
1.E-3
-75 -50 -25 0 25 50 75 100 125 150 175
curre
nt, A
temperature, deg.C
CPTC AB 15uF 25V
SN1SN2SN3
1.E-9
1.E-8
1.E-7
1.E-6
1.E-5
1.E-4
1.E-3
-60 -20 20 60 100 140
curre
nt, A
temperature, deg.C
CPTC AH 33uF 75V
SN1
SN2
SN3
1.E-8
1.E-7
1.E-6
1.E-5
1.E-4
1.E-3
-60 -10 40 90 140
curre
nt, A
T, deg.C
CPTCs 330uF 6.3V (auto)
AQ heatingC8 heatingAQ coolingC8 cooling
Leakage currents were measured in the process of heating and cooling at a rate 3 K/min without voltage interruptions
Effect of HTS
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 13
Contrary to MnO2, CPTCs are degrading with time due to thermo-oxidative processes. The rate of degradation depends on part type. ESR is most sensitive to HTS and increasesexponentially with time after incubation period. In air: Ea = 0.62 eV ±0.17eV, but in vacuum Ea ~2 eV, so successful testing at 125 ºC for 1000hr guarantees long-term stability of ESR in space. Some auto CPTCs were stable for more than 4 khr at 125 ºC.
0.1
1
10
100
0 2000 4000 6000 8000 10000
DF,
%time, hr
100C 125C
150C 175C10
100
1000
10000
100000
0 2000 4000 6000 8000 10000
ESR
, moh
m
time, hr
100C 125C 150C 175C
Degradation of C, DF, and ESR at 100, 125, 150, and 175 ºC for 10uF 25V CPTCs
1.E+0
1.E+1
1.E+2
1.E+3
1.E+4
0 2000 4000 6000 8000 10000 12000
ESR
, moh
m
time, hr
HTS CPTC B2
100C
125C
Life Testing of CPTCs
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 14
No catastrophic failures during life testing and SSLT in 23 lots. CPTCs can operate reliably at high T at steady-state conditions. Increasing of leakage currents with time is similar to MnO2 caps. Post-test DCL measurements might fail the limit. Erratic behavior of currents in some samples/lots.
Monitored 1000 hr life testing at VR: 11 lots at 85C and 125C, 10 to 20 pcs in a group. Monitored step stress life testing at VR: 12 lots consequently at 85, 105, 125, 145, and 165C. 200hr steps, 10 to 20 pcs in a group.
1.E-8
1.E-7
1.E-6
1.E-5
0 200 400 600 800 1000
curre
nt, A
time, hr
CPTC AJ 33uF 35V at 125C 35V
0.E+0
1.E-6
2.E-6
3.E-6
4.E-6
5.E-6
0 20 40 60 80 100 120
curre
nt, A
time, hr
CPTC AB 10uF 35V at 165C 35V
Lot S
Lot M
Spiking of leakage currents
1.E-5
1.E-4
1.E-3
1.E-2 1.E-1 1.E+0 1.E+1 1.E+2
curre
nt, A
time, hr
CPTC C1 330uF 16V at HALT165
Anomalous Transients
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 202015
AT are caused by increased conductivity of Ta2O5 in discharged polymer capacitors.
AT is more significant in dry CPTCs and at low temperatures.
The conductivity gradually (hours) decreases with time under bias.
The phenomena manifests as: Increased 10x DCL limits compared to MnO2
capacitors;Parametric SCT failures; Variations of C and DF with voltage and time
under bias; Increasing leakage currents at low T;Anomalous charging currents (ACC); Failures during power cycling.
Examples of AT
0
5
10
15
20
25
0 5 10 15 20 25 30
volta
ge,
Vtime, sec
220uF 10V after 1 wk at 125C0.5 mA1 mA3 mA5 mA10 mAMnO2 0.5 mA
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1
curre
nt, A
time, msec
CPTC after 2000hr in vacuum
220uF 16V 33uF 25V330uF 6.3V 10uF 35V22uF 35V
Mitigation of AT and Derating Requirements
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 16
Effects related to AT can be mitigated by:Using special S&Q procedures.
- e.g. testing after bake for SCT, DCL at low T, C-V and DF-V, power cycling, etc.
Modification of polymer materials.- might result in increasing of ESR.Analysis of application conditions.
- operations at low T, especially cold start-ups.Voltage derating to 30 - 50% of VR.
Due to thermo-oxidative degradation in CPTCs, Tmax should be limited to 100 ºC.
1.E-6
1.E-5
1.E-4
1.E-3
1.E-2
1.E-1
1.E+0
1.E+1
0.01 0.1 1 10 100
curr
ent,
mA
time, min
10uF 25V after 2000hr in vac B -50CB -35CB -20CB 0CB 20CB 35CB 50C
modified
standard
Effect of polymer modification
Effect of voltage
0.1
1
10
100
0 0.2 0.4 0.6 0.8 1 1.2 1.4
DF,
%
V/VR
CPTCs after 2000hr in vacuum
22uF 35V10uF 35V220uF 16V330uF 6.3V220uF 10V
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
0 0.2 0.4 0.6 0.8 1 1.2 1.4
curre
nt, A
V/VR
CPTC C8 22uF 35V at -65C
wet
dry
Recommendations for S&Q
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 17
GeneralCPTCs should be preconditioned before qualification testing.Life testing, HTS, and TS should be carried out using capacitors
soldered per specified MSL. Testing for FR is not necessary for the following reasons:
o Field failures rarely happen at life test conditions;o Uncertainty in AFs creates orders of magnitude errors in FR;o Due to derating, actual FRs are orders of magnitude below the mission
requirements;o Most microcircuits that has been successfully used for space are
non-ER components. Screening (Gr.A) should include:Surge current testing. The existing MIL-PRF-55365 requirements
limiting maximum current after 1 msec can be used for CPTCs. Burning-in at 105 ºC 1.1VR for 40 hours.
Recommendations for S&Q, Cont’d
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 18
LAT (or gr. B qualification test) should include: Life testing at 105 ºC, 1.1VR for 1000 hr. High temperature storage test, 1000 hr at 125 ºC. Thermal shock, 100 cycles between -55 and +125 ºC. Testing after baking at 125 ºC for 168 hours:
o Surge current test at -55 ºC, 25 ºC, and +85 ºC.o Stability at low and high temperatures (including DCL at low
temperatures). o Power cycling 100 cycles at RT and 0.75VR (5 sec ON/OFF
using a power supply capable of rising voltage in less than 1 msec).
Summary
To be presented by A. Teverovsky at the NEPP Electronics Technology Workshop (ETW), Greenbelt, MD, June 15-18, 2020 19
Specific features of polymer compared to MnO2 capacitors include: Greater sensitivity to the absence of moisture. Intrinsic mechanism of ESR degradation during high T storage or
operation in presence of oxygen. Anomalous transient phenomena. Smaller probability of catastrophic, short circuit failures. Increased probability of noisy behavior.
Space systems would benefit from using CPTCs if: Selected parts pass space-level screening and qualification testing. Operating voltage is derated to 50% VR. Application conditions are analyzed regarding possible effects of AT
especially at low T (special testing is necessary for missions requiring cold start-ups).
Reliability Issues with Polymer and MnO2 Tantalum Capacitors for Space ApplicationsList of AcronymsAbstractOutlineAdvantages and Disadvantages of CPTCs for Space ApplicationsEffect of MoistureFailures after SolderingEffect of SolderingEffect of VacuumVariations of Characteristics with Time after VacuumStability of Characteristics at Low and High TemperaturesHysteresis of Leakage Currents during Temperature VariationsEffect of HTSLife Testing of CPTCsAnomalous TransientsMitigation of AT and Derating RequirementsRecommendations for S&QRecommendations for S&Q, Cont’dSummary
