The document discusses the development and technical challenges of high-temperature solid tantalum capacitors, highlighting key construction elements and known failure mechanisms. It outlines advancements in operating temperatures from 125°C to a targeted 230°C, along with performance testing methods and material enhancements used to improve reliability. Various factors affecting the capacitors' performance under high temperatures, such as leakage current and dielectrics, are also examined.

1. © 2015 KEMET Electronics
Solid Electrolytic Capacitors Designed
for High Temperature Applications
Kristin Tempel and Randy Hahn
High Temperature Electronics Network
July 7, 2015
http://go.kemet.com/wp1015

2. © 2015 KEMET Electronics
Outline
• Basic construction of Solid Tantalum Capacitor
• High temperature timeline
• Known temperature related failure mechanisms
• Technical challenges at high temperature
• Performance testing and path forward
• Questions
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3. © 2015 KEMET Electronics
Basic Construction of Solid Ta Capacitor
Fundamental Materials:
• Ta anode
• Ta2O5 Dielectric
• MnO2 Cathode
Secondary Materials:
• Carbon
• Metallized Layer
• Adhesive
• Leadframe
• Mold Epoxy
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4. © 2015 KEMET Electronics
What Makes Tantalum Special?
• Surface area per unit of weight creates high CV/g
– Volumetric efficiency
• Valve metal capable of growing thin dielectric
– High dielectric breakdown voltage: 470V/µm
Vr
Ta2O5
Thickness (nm)
2 16
4 32
6 48
16 128
35 280
50 400
𝑪 ∝
𝒌𝑨
𝒅
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5. © 2015 KEMET Electronics
Surface Mount Tantalum Timeline
• 125°C maximum temperature for decades
• 2003 first 150°C release
• Capability increases by 25°C approximately every 4 years
• Multiple manufacturers poised to release 230°C platforms
125°C 150°C 175°C 200°C 230°C
2003 2007 2011 2015
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6. © 2015 KEMET Electronics
Temperature Related Failure
Mechanisms

7. © 2015 KEMET Electronics
Temperature Related Failure Mechanisms
Known Failure Mechanism Method to Mitigate
Crystallization: defects in Ta-Ta2O5
interface creates leakage site
• Low charge Ta powders
• High Vf:Vr
• F-TECH technology increases
chemical purity and eliminates hidden
dielectric defects
Oxygen Migration into Ta metal from
Ta2O5 leave oxygen vacancies creating
conductivity across dielectric. Causes
cap change with bias, temperature,
frequency.
• Higher Vf:Vr
• Heat treatment
Ta
Ta2O5
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8. © 2015 KEMET Electronics
Technical Challenges at High
Temperatures

9. © 2015 KEMET Electronics
All of the external cathode layers were modified, and in some
cases replaced, in order to provide a robust design capable of
withstanding up to 1000 hours at 230°C.
Cathode Layers
Silver
MnO2
Carbon
Ta
Mold epoxy
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10. © 2015 KEMET Electronics
MnO2 Solid Electrolyte
• Stable to temperatures in excess of 500°C
• Deposition process modified to ensure adequate buildup to
protect the anode
-8
-6
-4
-2
0
2
4
6
8
-10
-8
-6
-4
-2
0
0 200 400 600 800
HeatFlow
WeightLoss(%)
TGA for MnO2
Weight Loss (%) Heat Flow
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11. © 2015 KEMET Electronics
Carbon Layer
• Binder in conventional Carbon 1
degrades at temperatures in excess
of 200°C
• In-house Carbon 2 formulated to
withstand continuous operation at
230°C
• Weight loss observed between 230-
400°C due to oxidation to CO2 of
oxygen containing surface functional
groups of carbon black
-10
0
10
20
30
40
-50
-40
-30
-20
-10
0
0 200 400 600 800
HeatFlow
WeightLoss(%)
TGA for Carbon 1
Weight Loss (%) Heat Flow
-5
0
5
10
15
20
25
30
-40
-30
-20
-10
0
0 200 400 600 800
HeatFlow
WeightLoss(%)
TGA for Carbon 2
Weight Loss (%) Heat Flow
-20
-15
-10
-5
0
0 100 200 300 400 500 600
WeightLoss(%)
TGA for Components of Carbon 2
Carbon Black Graphite Binder11

12. © 2015 KEMET Electronics
Metallized Layer
• Binder in the silver paint improved
the capability to withstand
temperature: Conventional Silver 1
vs Modified Silver 2
• Silver migration at elevated
temperatures is known issue
• Experiments confirmed leakage
shifts occurred only after the
application of the silver paint
-10
0
10
20
30
40
50
-20
-15
-10
-5
0
0 200 400 600 800
HeatFlow
WeightLoss(%)
TGA for Silver 1
Weight Loss (%) Heat Flow
-10
0
10
20
30
40
50
-14
-12
-10
-8
-6
-4
-2
0
0 200 400 600 800
HeatFlow
WeightLoss(%)
TGA for Silver 2
Weight Loss (%) Heat Flow
10001001010.1
99
95
90
80
70
60
50
40
30
20
10
5
1
0.1
Leakage (uA)
Percent
Initial
1000 hr
Leakage Shift During 220°C Shelf Strorage
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13. © 2015 KEMET Electronics
Silver migration at elevated
temperature  unstable leakage
Nickel plating  stable leakage
Metallized Layer
100101
99
95
90
80
70
60
50
40
30
20
10
5
1
LC
Percent
16
1,555 0,5361 53 6,532 <0,005
1,438 0,3551 53 3,229 <0,005
1,403 0,3593 53 2,790 <0,005
1,477 0,3797 53 3,121 <0,005
1,400 0,3582 53 3,139 <0,005
Loc Scale N AD P
0h
250h
500h
750h
1000h
200C
Time @
Lognormal - 95% CI
Probability Plot of LC
DC Leakage (mA)
DC Leakage
10001001010,1
99
95
90
80
70
60
50
40
30
20
10
5
1
LC
Percent
16
0,6831 0,2943 30 1,591 <0,005
1,484 1,096 30 4,843 <0,005
3,032 1,308 30 0,962 0,013
3,802 0,9251 30 2,574 <0,005
Loc Scale N AD P
1xC/-/Ag 0h
1xC/-/Ag 250h
1xC/-/Ag 500h
1xC/-/Ag 750h
VAR 200ºC
TIME @
Probability Plot of LC
Lognormal - 95% CIDC Leakage
DC Leakage (mA)
KEMET has developed proprietary and patented materials and processes to successfully
plate metals on the carbon layer in Tantalum capacitors
Solid Electrolytic Capacitors with Improved Reliability, Chacko, Antony; US Patent 8,310,816 & 8,896,985 &
8,503,165
Solid Electrolytic Capacitors with High Temperature Leakage Stability, Chacko et al, USP Pending, US
2014/0055913
Several additional patents are pending13

14. © 2015 KEMET Electronics
Adhesive
• Replacing standard silver adhesive with Transient Liquid
Phase Sintering (TLPS) adhesive improves peel strength at
elevated temperatures when used with Ni plated metallized
layer
METHOD OF IMPROVING ELECTROMECHANICAL INTEGRITY OF CATHODE COATING TO
CATHODE TERMINATION INTERFACES IN SOLID ELECTROLYTIC CAPACITORS, Chacko,
Antony; US 8,896,986
0
0.05
0.1
0.15
0.2
0.25
0.3
Ag/Ag adhesive Ag/TLPS Ni/Ag adhesive Ni/TLPS (Trial 1) Ni/TLPS (Trial 2)
PeelStrength(kg)
Plating Layer/Adhesive
Peel Strength Comparison
Room Temp 165°C
Peel Test
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15. © 2015 KEMET Electronics
Encapsulant Material
• Severe layer separation occurred at high temperature with
conventional mold epoxies
• High temperature epoxy greatly enhanced ESR stability
Conventional Epoxy High Temperature Epoxy
Anode AnodeCathodeCathode
Epoxy Epoxy

16. © 2015 KEMET Electronics
• Breakdown voltage (BDV) is the ultimate test of dielectric strength
• BDV correlates with long term reliability
• SBDS is a non-destructive testing technique that simulates BDV
• Does not damage dielectric
• Screening performed on 100% of product
Screening of Electrolytic Capacitors, Freeman, Yuri; US Patent 7,671,603
Apparatus and Method for Screening Electrolytic Capacitors, Paulsen, Jonathan, et al. US 8,441,265
Simulated Voltage Break Down Screening
(SBDS): Concept
LKG Before vs. After Screening
495X107K016
0
2
4
6
8
10
12
14
16
18
0 2 4 6 8 10 12 14 16 18
DCL BEFORE uA
DCLAFTERuA
I(V) in KO D16-25
0
5
10
15
20
25
30
35
40
0 20 40 60
Voltage, V
Current,uA
#9
#12
1.2 MOhm
7.1 MOhm
9 MOhm
BDV
AVER
RV
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17. © 2015 KEMET Electronics
Simulated Voltage Break Down Screening
(SBDS): Results
Final Voltage, V
Percent
50403020100
99.9
99
95
90
80
70
60
50
40
30
20
10
5
1
0.1
Mean 37.26
StDev 4.604
N 290
AD 66.448
P-Value <0.005
SCREENING
495X107K016 0646H128
BDV mean = 43 V. TEST V = 58.5. Rs = .47 Mohm. tmax = 90 s
Excellent
Weak
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18. © 2015 KEMET Electronics
Performance Testing

19. © 2015 KEMET Electronics
Mounting Reflow Profile
• High Melting Point (HMP) Solder used to attach parts to
specially designed high temp boards for all testing
• Liquidus temperature 302°C
• Soldering iron and convection reflow oven used
• Zero post mount failures
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20. © 2015 KEMET Electronics
Capacitance Change with Temperature
6.50
7.00
7.50
8.00
8.50
0 50 100 150 200 250
Capacitance(mF)
Temperature (°C)
Capacitance vs. Temperature
T502D685-035
Capacitance change with temperature follows typical curve for solid Ta capacitor
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21. © 2015 KEMET Electronics
DC Leakage vs Temperature
0.0001
0.01
1
100
2.00 2.25 2.50 2.75 3.00 3.25 3.50
y=11*exp((0.55/8.62)*(2.0-x)*100)
Median DCL
25ºC65ºC105ºC155ºC200ºC
230ºC 175ºC 125ºC 85ºC 45ºC 0ºC
Vtest = 7V
Rs = 82k
Median DCL Calculated from a sample of 20pcs.
Inverse Absolute Temperature 1/T (10
-3
, K
-1
)
MedianDCL(mA)
Inverse Absolute Temperature vs. Median DCL. T502D685K035
Test Procedure:
• Parts subjected to temperatures ranging from 230°C to
0°C with 0.2Vr bias applied.
• Measurements were plotted on a lognormal graph
• Median leakage values from each temperature were
plotted vs inverse absolute temperature.
• The following Arrhenius equation was used to form a fit
line:
𝑀𝑒𝑑𝑖𝑎𝑛 𝐷𝐶𝐿 = 𝐷𝐶𝐿 𝑀𝑎𝑥 𝑇𝑒𝑚𝑝 × 𝑒
𝐸 𝑎
ℎ
×
1
𝑀𝑎𝑥 𝑇𝑒𝑚𝑝
−
1
𝑇𝑒𝑚𝑝
Where:
𝐸 𝑎= Activation Energy (eV)
ℎ=Boltzmann’s constant (8.62x10-5 eV K-1)
Temperatures in Kelvin
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22. © 2015 KEMET Electronics
230°C Life Test Summary
• Qualification test – 500 hours at 0.2Vr
– Leakage generally increases 4x
– No leakage failures observed
– Initial shift in ESR observed, but stabilizes through 500 hours
• Additional testing to 1,000 hours
– Leakage shifts 2x from 500hr readings, but none above post test limit
– ESR continues to shift
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23. © 2015 KEMET Electronics
Thank You!
Kristin Tempel
New Product Development Engineer
Tantalum Innovation Center
http://go.kemet.com/wp1015