Testing the Effects of Seacoast Atmosphere on Tantalum Capacitors

Abstract

The goal of this research was to test the effects of seacoast atmosphere on tantalum capacitors. Four tests were chosen for this purpose: the 85/85 test was chosen for testing the effects of the combination of high humidity and high temperature, salt spray testing was done for examining the effects of high humidity and salt, temperature cycling test was applied for testing the effects of temperature changes, and a 100% RH humidity test was developed for examining the effects of very high humidity. The results show that combination of high humidity and high temperature did not possess a significant risk for these capacitors during their normal use.Very high humidity and radical temperature changes both affected the breakdown voltages of tantalum capacitors. Salt fog caused corrosion of these components and had a small effect on breakdown voltage but did not have an effect on capacitance or ESR.

Full text

Hindawi Publishing Corporation
Active andPassive Electronic Components
Volume 2011, Article ID 108423, 9pages
doi:10.1155/2011/108423
Research Article
Testing the Effects of Seacoast Atmosphere on
Tantalu m C a p a c i t o rs
Johanna Virkki1and Pasi Raumonen2
1Department of Electronics, Tampere University of Technology, P.O. Box 692, 33101 Tampere, Finland
2Department of Mathematics, Tampere University of Technology, P.O. Box 553, 33101 Tampere, Finland
Correspondence should be addressed to Johanna Virkki, johanna.virkki@tut.fi
Received 14 January 2011; Accepted 23 March 2011
Academic Editor: Jiun Wei Horng
Copyright © 2011 J. Virkki and P. Raumonen. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
The goal of this research was to test the effects of seacoast atmosphere on tantalum capacitors. Four tests were chosen for this
purpose: the 85/85 test was chosen for testing the effects of the combination of high humidity and high temperature, salt spray
testing was done for examining the effects of high humidity and salt, temperature cycling test was applied for testing the effects
of temperature changes, and a 100% RH humidity test was developed for examining the effects of very high humidity. The results
show that combination of high humidity and high temperature did not possess a significant risk for these capacitors during their
normal use. Very hig h humidity and radical temperature changes both affected the breakdown voltages of tantalum capacitors. Salt
fog caused corrosion of these components and had a small effect on breakdown voltage but did not have an effect on capacitance
or ESR.
1. Introduction
Electronic devices are exposed to varying and harsh envi-
ronments, and thus common reasons for failures in elec-
tronics are environmental contaminants and conditions such
as temperature and humidity with other failures deriving,
for example, from vibration, ripple voltage, overvoltage, and
corrosion. These all affect the reliability of electronic compo-
nents [1].
Seacoast atmosphere is very stressing environment for
electronics. Humidity is very high, temperature can change
between extremes, and salt is one of the most corrosive
constituents in the atmosphere. Exposure to humidity and
salt poses a common risk of corrosion for electronic devices
[2–4]. A definition of corrosion is given as the chemical or
electrochemical reaction between a material (usually metallic
material) and its environment [5,6].
Reliability tests seek to simulate the component’s use
environment in order to find the effects of environmental
stresses. Because such testing is very time consuming, ac-
celerated testing becomes necessary. Accelerated testing
means acceleration of failures with the single purpose of
quantification of the characteristics of the product at
normal use conditions [7].Thus,inacceleratedtesting,test
conditions are intensified to cut down the time required
to obtain a weakening effect similar to one resulting from
normal service conditions.
Tantalum capacitors are used in various applications
because of their size and achievable levels of capacitance.
However, a lot of electronic component failures are found
in seacoast-like conditions [8–10]. The starting point for
this research was as the following: tantalum capacitors were
used in LED matrix display units in seacoast conditions, and
breakdown voltages were found to be very low compared to
normal use conditions.
Two kinds of tantalum capacitors were used in this
paper. Both capacitors were surface mount capacitors that
differ only in capacitance and maximum voltage. Tantalum
capacitors of a maximum voltage of 50 V, a capacitance
of 10 μF (referred to as “50/10-capacitor”), and tantalum
capacitors of a maximum voltage of 10V and a capacitance
of 33 μF (“10/33-capacitor”) were used. Both capacitors have
operating temperature from −55◦C to +125◦C.

2Active and Passive Electronic Components
Pellet structure
Silver coating
Carbon coating
Manganese dioxide
Tantalum pentoxide
Negative termination
Molded case
Tantalum wire
Pellet
Positive termination
Figure 1: Structure of a tantalum capacitor.
The goal of this research was to test the effects of seacoast
atmosphere on tantalum capacitors. Four tests (three stan-
dard tests and one new test) were chosen for this purpose.
(1) The steady-state temperature humidity bias life test
according to standard JESD22-A101C [11]wascho-
sen for testing the effects of combination of high
humidity and high temperature during normal use.
We tested 36 50/10-capacitors in test conditions and
36 50/10-capacitors in room conditions.
(2) The salt spray test according to standard SFS-ISO
9227 [12] was chosen for testing the effects of
combination of high humidity and salt. We tested 10
10/33-capacitors for each chosen testing time.
(3) The temperature cycling test, according to the stan-
dard JESD22-A104D [13] was chosen for testing the
effects of temperature changes. We tested 18 50/10-
capacitors.
(4) A 100% relative humidity (RH) test was developed
for examining the effects of very high humidity. We
tested 18 50/10-capacitors for each chosen testing
time.
2. Tantalum Capacitors
In this section, the structure and substantial failures of these
capacitors are reviewed.
2.1. Structure of Tantalum Capacitors. A tantalum capacitor
consists of three main elements: an anode, a cathode,
and a dielectric layer of tantalum pentoxide that separates
them. The capacitor contains an embedded tantalum pellet
(anode), surrounded by a tantalum pentoxide, amorphous
dielectric layer. The cathode is a semiconductor, manganese
dioxide. This pellet is coated with carbon and then with
silver to provide the final connecting layer to the cathode
terminal. The tantalum wire passes through these layers
and connects the positive termination to the tantalum. The
negative termination of the capacitor is attached with a
silver adhesive to the silver paint layer. Tantalum capacitor
structure is shown in Figure 1 [14,15].
2.2. Failures of Tantalum Capacitors. The reliability of tan-
talum capacitors is greatly affected by environmental con-
ditions. In addition, strong ripple currents and mechanical
stresses can cause failures [16,17]. This section is a review of
conditions that usually have the biggest effect on tantalum
capacitor reliability and the failure mechanisms they may
cause.
2.2.1. Effects of Humidity. The reliability of a tantalum capac-
itor is heavily influenced by humidity with various effects
inside the capacitor. Moisture can penetrate the polymer
encapsulating material and degrade the characteristics of the
capacitor. These effects can later cause the capacitor to fail
[18].
Numerous humidity-related failure mechanisms have
been reported [18–20], but the reason behind the failure
mechanisms of tantalum capacitors in humid environments
has not been clearly explained.
Tantalum capacitors are manufactured by sintering high-
ly dispersed micrometer-size tantalum powder to form
sponge-like porous pellets. After a tantalum pellet is ano-
dized and a tantalum pentoxide dielectric is formed, a cath-
ode electrode is applied. The following pyrolysis transforms
manganese nitrate into a conductive manganese dioxide
cathode layer. The high porosity of the pellet makes it diffi-
cult for the whole area of the dielectric to be covered with
manganese oxide, and some areas may remain uncovered.

Active and Passive Electronic Components 3
Besides, during the pyrolyses, the substance shrinks, creating
microscopic voids and gaps between the manganese dioxide
and the nearby surface of tantalum pentoxide [18,21]. Due
to the high dielectric permittivity of tantalum pentoxide,
few nanometer gaps can already significantly reduce the
capacitance of a surface element compared to a situation
without gaps. This indicates the presence of capillary-like
passive cells without a cathode contact. The size of the passive
cells is most likely in the range from tens of nanometers to
micrometers [18].
Variations in capacitance in dry and humid environ-
ments have been explained by the passive cells remaining
inactive until activated by absorbed moisture. In humid envi-
ronments, moisture diffuses into the passive cells and creates
an extremely thin conductive layer on the surface of the
dielectric material. This water layer then works as a cathode
electrode, connecting the passive area with the surrounding
manganese dioxide and increasing the capacitance of the part
[18,22]. To activate a sleeping cell, the resistance of the
moisture layer should be low enough to provide necessary
electrical conductivity over the passive area. The sleeping
cells are most likely not empty, clean tantalum pentoxide
cylinders, as assumed above, but have some contamination
remaining after the manufacturing processes. In humid
environments, sleeping cells may become active in various
ways. These processes include formation of a moisture-
adsorbed layer, capillary condensation, and moisturizing of
the hygroscopic remnants in the cell [18,19].
Self-healing has also been investigated to explain the
humidity-generated failures. The current in a small defect
within the dielectric is concentrated into a small, finite
volume of the cathode plate in contact with the fault site.
This concentrated current causes the temperature within this
very small region to rise significantly. As the manganese
dioxide heats up past 380◦C, it begins to release oxygen,
changing the material structure from manganese dioxide to a
reduced state. Because this reduced material has much higher
resistivity than the original, the current going through this
fault is pinched off.Thiseffect is called self-healing, because
it eliminates the fault site from the active electrification
of the capacitor, though it has not healed the fault site
[23]. Storing of the capacitors in humid environments may
result in oxidation of the low oxide forms of the manganese
oxide layer, thus increasing its conductivity. Oxidation of the
reduced manganese oxide at the self-healed defects would
reactivate these defects, causing breakdown in the part [21].
Moisture-induced failures may also be related to a
moisture-generated silver dendrite growing on cathode con-
tacts. After shorting, these dendrites are “arcing,” igniting the
manganese oxide and creating a powerful chemical reaction,
thus causing catastrophic failure of the part [20]. Moisture
intrusion in tantalum capacitors is mostly limited by the
molding compound. However, absorbed humidity obviously
has harmful effects inside the capacitor.
2.2.2. Effects of Temperature. Temperature varies the rates of
physical and chemical reactions that cause failure mecha-
nisms. Thus, temperature is often used in reliability testing
as an accelerating parameter. However, at high temperatures,
new failure mechanisms previously dormant because of their
high activation energy may become activated. Thus, if a
test is run at too high temperatures, failure may occur
because of a mechanism unlikely during normal operating
conditions [24]. Heat, whether generated externally or inter-
nally, degrades the performance and reliability of tantalum
capacitors [25]. The use of tantalum capacitors at high
temperatures has been studied, and such use is found to be
challenging [26].
Temperature has also a specific effect inside a tantalum
capacitor, known as crystal growth [27,28]. The tantalum
pentoxide dielectric is considered an amorphous material
and inherently thermodynamically sensitive. An amorphous
state tends to order and crystallize to reduce its internal
energy. Once the dielectric crystallizes, conductivity and
leakage current increase. The conductivity of the crystallized
structure has been reported tobe higher than that of a dielec-
tric in an amorphous state [28]. However, the latest findings
suggest that the crystals themselves are good insulators with
very limited conductivity [27]. The exact conductivity mech-
anism related to the crystal phase is not yet fully understood.
The increase in leakage current may still be caused by other
mechanisms accelerated by the crystal growth. However,
studies show that field crystallization may have only a limited
impact on the end use of tantalum capacitors [27].
2.2.3. Effects of Temperature Changes. Mechanical stresses
related to the soldering of surface mount tantalum capacitors
affect their performance and reliability and account for
their turn-on breakdowns. In addition, thermomechanical
stresses can generate new fault sites in the components. A
tantalum capacitor package passing through radical temper-
ature changes may undergo material expansions at different
rates depending on each material’s thermal expansion and
suffer from tensile forces on the pellet structure. During
heating, shear forces are exerted on the anode wire. The
moldedcasepushesontheleadframeinonedirectionand
the pellet in another, generating forces that pull the wire
away from the anode structure. Once the device has passed
though high temperatures and its elements are shrinking
while cooling, they may not fit together as they did before
the expansion. Compressive forces may appear on the pellet
structure and produce fractures. A crack in the dielectric at
a corner or edge, when exposed to high stress, may lead to
catastrophic failure [29–31]. Besides, during soldering, such
a phenomenon may also occur during radical temperature
cycling in the field.
3. Tests for Seacoast Atmosphere
3.1. High Humidity/High Temperature Test. The steady-state
temperature humidity bias life test (known as the 85/85 test,
in which temperature is held at a constant 85◦Candata
RH of 85%) “is performed for the purpose of evaluating the
reliability of non-hermetic packaged solid-state devices in
humid environments. It employs conditions of temperature,
humidity, and bias which accelerate the penetration of

4Active and Passive Electronic Components
moisture through the external protective material or along
the interface between the external protective material and
the metallic conductors which pass through it” [11]. During
continued bias testing, heat from power dissipation tends
to prevent moisture-related failure mechanisms. In contrast,
cycled bias allows moisture to collect during offperiods when
the device produces no heat. According to the standard, “the
die temperature should be quoted with the results whenever
it exceeds the chamber ambient by 5◦C or more, and cycled
bias should be chosen if the temperature exceeds the chamber
ambient by 10◦C or more.” In this test, the temperature of
these passive components did not significantly rise when the
voltage was on, so continued bias was chosen.
Such a standard test is often used to identify possible
failure types caused by high moisture and high temperature
and was used in this research for 36 50/10-capacitors. There
were also 36 50/10-capacitors in room conditions. To test the
capacitors, we monitored them in real time with continuing
DC voltage of 15 V. Capacitor failures were registered as
a rise in the leakage current. The current circuit of the
measuring instrument measured the leakage current, and the
series resistor changed the passing current into a comparable
voltage, which was measured in real time. The failure limit
was set to measured voltage of 3 V.
3.2. Accelerated Corrosion Test. Accelerated corrosion tests
simulate the effects of severe seacoast atmosphere on all
exposed surfaces. Basically, the salt spray test procedure
involves the spraying of a salt solution onto the samples being
tested. This is done inside a temperature-controlled chamber.
These are severe conditions. We wanted to find a standard
test for testing the effects of salt fog.
Salt atmosphere test according to standard JESD22-
A107B [32] was the first alternative. “This salt atmosphere
test is conducted to determine the resistance of solid state
devices to corrosion. During the test, the chamber shall be
held at a temperature of 35◦C. The deposit in the test area
shall be 30 ±10 g per square meter per 24 h. The pH of
the salt solution shall be maintained between 6.0 and 7.5
when measured at 35◦C minimum. The minimum duration
of exposure of the salt atmosphere test is 24 h, 48 h, 96 h, or
240 h.”
Another suitable standard for salt spray testing is SFS-
ISO 9227 standard [9]. According to the standard, the
temperature in the test chamber must be kept in 35◦C
during the test. Recommended testing periods are 2 h, 6 h,
24 h, 48 h, 96 h, 168 h, 240 h, 480 h, 720 h, or 1000 h. The
standard also states that the duration must be suitable for
the tested component. Concentration of sodium chloride
(NaCl) in solution must be 50 g/L ±5g/L, equivalent to5%
concentration of NaCl in deionized water. The value of pH of
the solution must be between 6.5 and 7.2 [12].
These two standard tests are very similar, and we
designed the test based on SFS-ISO 9227 standard and chose
the testing times to be 24 h, 96 h, and 240 h, since they are
common to both tests. We tested 10 10/33-capacitors for each
chosen testing time: we measured capacitance, equivalent
series resistance (ESR), and breakdown voltage before testing
and after each testing time. For breakdown voltage, the
capacitors were tested after each testing time for voltage that
was slowly increased (rate of voltage increase: 1 volt per
second) from 0V to 93 V provided no failure occurred. The
voltage range was chosen because of equipment limitations.
The accuracy of measurement was 1 V.
3.3. Temperature Cycling Test. We wanted to fin d a s t a n d a rd
test for testing the effects of temperature changes. The
temperature cycling test, according to the standard JESD22-
A104D [13] “is conducted to determine the ability of com-
ponents and solder interconnects to withstand mechanical
stresses induced by alternating high- and low-temperature
extremes. Permanent changes in electrical and/or physical
characteristics can result from these mechanical stresses.”
This standard includes numerous temperature cycling condi-
tions and cycle times. The test usually lasts 500 or 1000 cycles.
We chose nonradical temperature extremes because we
wanted to simulate the actual environment and accelerate
the effects just a little. In our test, the temperature changed
between −40◦Cand85
◦C, and one cycle lasted for 0.5 h.
The test lasted for 500 cycles and had 18 50/10-capacitors
tested. We measured breakdown voltages (again between 0
and 93 V) before and after temperature cycling.
3.4. 100%Humidity Test. Our last test is not a standard
test. It was developed for measuring the moisture absorption
and to study the effects of absorbed moisture. The 100%
RH test will examine the effects of moisture absorption in
a very high humidity conditions on 50/10-capacitors. Before
moisture absorption was measured, capacitors were baked
for dry out for 24 h at 125◦C to remove all moisture from the
components, a procedure required by the standard JESD22-
A113F [33]. 18 50/10-capacitors were first tested for their
breakdown voltage, without humidity, to find out if they
failed with voltage as the only stress factor. Other capacitors
were weighed after each submission—1 h, 21 h, 144 h, and
336 h—to 100% RH. 18 capacitors were weighed after each
submission, and their average weights were calculated. After
weighting, we measured their breakdown voltages (again
between 0 and 93 V).
4. Results and Discussion
4.1. Effects of the High Humidity/High Temperature Test. The
capacitors were tested for 2500 h. None of the tested 36 + 36
tantalum capacitors failed during 2500 h. Obviously, 85◦C,
85% RH, and 15 VDC combined did not represent a stress
high enough for the tantalum capacitors to fail.
4.2. Effects of the Accelerated Corrosion Test. Capacitors after
24 h, 96 h, and 240 h in salt spray are seen in Figures 2,3,
and 4, respectively. The material of capacitor terminations
is copper that is plated with 100% matte tin (Sn), which
provides sacrificial protection for copper. Lead frames com-
prising copper with high electrical conductivity are typically
utilized as a main lead frame material in electronic products
using surface mount technology for assembly. Matte tin

Active and Passive Electronic Components 5
Figure 2: Capacitor after 24 h in salt spray (left) and a nontested
capacitor (right).
Figure 3: Capacitor after 96 h in salt spray (left) and a nontested
capacitor (right).
Figure 4: Capacitor after 240 h in salt spray (left) and a nontested
capacitor (right).
(in contrast to bright tin) is characterized by low whiskers
growing, and therefore it is used in electronics.
In pure water, tin has an excellent corrosion resistance.
Except for chlorine, the usual atmospheric pollutants have no
significant effects on tin. Tin can resist corrosion by forming
a passive film on its surface. A thin protective film rapidly
10987654321
Capacitor number
Capacitances
30
31
32
33
34
35
36
37
38
39
40
Capacitance (μF)
0h
48 h
96 h
240 h
Figure 5: Capacitance measurements for 10/33-capacitors in salt
spray (accuracy ±1μF).
10987654321
Capacitor number
Equivalent series resistances
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Resistance (Ohm)
0h
48 h
96 h
240 h
Figure 6: ESR measurements for 10/33-capacitors in salt spray
(accuracy ±0.1 Ω).
covers the surface and increases with moisture [34]. Under
most atmospheric exposure conditions, the corrosion of tin
depends on the formation and stability of the oxide film
[35]. Corrosion can be expected at discontinuities in the tin
coating, due to galvanic couples formed between the tin and
the underlying copper through these discontinuities. In this
case, corrosion caused by salt spray decreases the tin plating.
Porosity increases as the coating thickness decreases in salt
spray.
After 24 h, there is no observable difference between a
tested capacitor and a new capacitor. The corroded area is
easily observed in the optical micrograph after 96 h, and it
grows with time to 240 h.
Capacitances and ESRs of these 10/33-capacitors after
0h,24h,96h,and240hinsaltspraycanbeseeninFigures5
and 6, respectively. Salt spray testing has no significant effect
on ESRs or capacitances of these capacitors. Capacitances
increased very slightly, which is probably because of moisture
that diffused into the passive cells.

6Active and Passive Electronic Components
10987654321
10 capacitors/each time in test
Breakdown voltages
0
5
10
15
20
25
30
35
40
45
Volt a g e ( V )
0h
48 h
96 h
240 h
Figure 7: Breakdown voltages for 10/33-capacitors in salt spray test
(accuracy ±1V).
Figure 8: An example of a failed capacitor.
Breakdown voltages after salt spray testing can be seen
in Figure 7. Maximum voltage given for these capacitors was
10 V. All capacitors failed because of too high voltage, but
none of them failed at voltages under 10 V. An example of
a failed capacitor can be seen in Figure 8.
To estimate the mean breakdown voltage of these capac-
itors, from this sample of ten capacitors, a distribution was
fitted to the data. The Weibull distribution [36,37]was
used for data analysis, because of its good fit. The Weibull
distribution can be fitted to many kinds of data [7,38].
Once a distribution is specified with its parameters,
one needs to fit the model (Weibull distribution) to data
(breakdown voltages). Parameter estimation was done with
Reliasoft’s Weibull++ [39], and the least squares method [40]
was used. This method is a good choice when the data sets
contain only complete data, with no suspensions, such as this
data.
Mean voltages to failure with 90% confidence were
calculated for capacitors. The results, including the shape
parameters (β)andthescaleparameters(η), are shown in
Tabl e 1 . Weibull distributions with β>1haveafailure
Tab le 1: Calculated mean voltages to failure (90% Confidence),
shape parameters, and scale parameters for 10/33-capacitors in salt
spray test.
0 h 48 h 96 h 240h
Upper (90%) 39 V 37 V 38 V 37 V
Mean 36 V 34 V 33 V 30 V
Lower (90%) 32 V 31 V 28 V 24 V
β5.7 7.7 3.8 2.6
η38 36 36 33
Figure 9: A cross-section of a failed capacitor.
rate that increases with time, which was the case in all
tests. Mean breakdown voltages for capacitors after 0 h, 48 h,
96 h, and 240 h were 36 V, 34 V, 33 V, and 30 V, respectively.
This means that salt spray testing decreases breakdown
voltage.Thescaleparameterisequaltothecharacteristic
life; 63.2% of all values fell below it. The characteristic
life for capacitors after 0 h, 48 h, 96 h, and 240 h were
38 V, 36V, 36 V, and 33 V, respectively, which also shows
that lifetime (breakdown voltage) decreased in salt spray.
However, changes in breakdown voltage were not radical and
thus may not possess a high risk during field use. Tests with
a larger amount of components should be done for statistical
reliability.
4.3. Results of the Temperature Cycling Test. There were
no failures in a group of nontemperature-cycled capacitors
between 0 and 93 V. Temperature cycling test caused 5
failures out of 18 tested capacitors. Failure voltages were
50 V, 79 V, 81 V, 84 V, and 91 V. This means that temperature
changes do have an effect on these tantalum capacitors and
their breakdown voltages. This should be taken into account
in their use. However, none of the failures occurred under
50 V that is the maximum voltage given by the manufacturer.
Failed components were further examined. They
were cross-sectioned and analyzed for failure by optical
microscopy (shown in Figure 9). Cross-sectioning of all the
failed tantalum capacitors showed redness in corners where
overheating had burned the capacitors’ internal materials
and molding.

Active and Passive Electronic Components 7
4003002001000
Time (h)
0.4975
0.498
0.4985
0.499
0.4995
0.5
0.5005
0.501
0.5015
0.502
0.5025
Weight (g)
Figure 10: Moisture absorption in 100% RH.
Mechanical stresses related to temperature changes have
affected their performance and account for their break-
downs. Compressive forces have probably appeared on the
pellet structure and produced fractures. Faults have probably
occurred in the oxide. During radical temperature changes, it
may have crackedwith a slight shear. Evenif the pellet has not
fractured, there may have been enough compressive pressure
for a fault site in the dielectric to grow that can develop into
a breakdown spot at these lower voltages.
4.4. Effects of the 100%Humidity Test. Results (Figure 10)
show how much tantalum capacitors absorbed moisture
when subjected to 100% RH.
The given maximum voltage for these capacitors was
50 V, but capacitors not submitted to humidity did not fail
at voltages below 93 V. Later failures (listed in Table 2 )in
this test seemed to result from the absorbed moisture and
soon after added voltage. After 1h at 100% RH, there were 8
failures out of the 18 tested capacitors. However, the moisture
absorption between 1 h and 144h did not significantly affect
the failure voltage, and after 144 h, there were 9 failures out
of the 18 tested capacitors. After 336h at 100% RH, the
failure rate was higher than after 144 hours, and there were
14 failures.
Mean voltages to failure with 90% confidence were
calculated for capacitors (Ta b l e 3 ). Weibull was again used as
distribution. Parameter estimation was done with maximum
likelihood estimation (MLE) [36]. MLE is versatile and
applicable to most models and different types of data and can
be used with a data set with only few exact breakdown voltage
points, such as this data that contains a lot of suspensions
[37,38].
The scale parameter (characteristic life; 63.2% of all
values fell below it) decreased in 100% RH. The characteristic
life for capacitors after 1 h, 144 h, and 336 h was 128 V, 120 V,
and 63 V, respectively, which means that breakdown voltage
decreased as a function of time in 100% RH. There is no
significant difference between 1 h and 144 h, but after 336 h,
the breakdown voltage is much lower. The same thing can
be seen with calculated mean voltages to failure that for 1 h,
144 h, and 336 h, are 116 V, 113 V, and 60 V, respectively.
These results mean that moisture will quickly (after
1 h) be absorbed inside capacitor through the moulded
compound, but it takes considerable time for moisture to
Tab le 2: Breakdown voltages for 50/10-capacitors after each time in
100% RH (accuracy ±1V).
0 h 1 h 144 h 336 h
>93 V 31 V 23 V 15 V
>93 V 34 V 24 V 16 V
>93 V 35 V 24 V 16 V
>93 V 36 V 23 V 17 V
>93 V 36 V 30 V 20 V
>93 V 39 V 31 V 23 V
>93 V 45 V 31 V 26 V
>93 V 67 V 70 V 26 V
>93 V >93 V 80 V 28 V
>93 V >93 V >93 V 29 V
>93 V >93 V >93 V 30 V
>93 V >93 V >93 V 31 V
>93 V >93 V >93 V 31 V
>93 V >93 V >93 V 80 V
>93 V >93 V >93 V >93 V
>93 V >93 V >93 V >93 V
>93 V >93 V >93 V >93 V
>93 V >93 V >93 V >93 V
Tab le 3: Calculated mean voltages to failure (90% Confidence),
shape parameters, and scale parameters for 50/10-capacitors in
100% RH test.
0 h 1 h 144 h 336 h
Upper (90%) ×183 V 185 V 91 V
Mean ×116 V 113 V 60 V
Lower (90%) ×74 V 69 V 40 V
β×1.4 1.2 1.1
η×128 120 63
affect the deeper interior of the capacitor. Moisture inside a
capacitor has a lowering effect on the breakdown voltage.
Failed components were removed from the board for
further examination. They were cross-sectioned and ana-
lyzed for failures by optical microscopy (Figure 11). Obvi-
ously, moisture had seeped through their epoxy covers
and degraded the characteristics of the capacitor, lowering
the breakdown voltage and causing a voltage breakdown.
This may be because of moisture-generated silver dendrite
growing on cathode contacts or because of activation of the
sleeping cells. The cross-sections looked red where excessive
heat had burned the internal materials and the molding of
the capacitor. All capacitors failed in the same way.
5. Conclusions
In this paper, 4 tests were done in order to examine the effects
of seacoast atmosphere on two kinds of surface mount tanta-
lum capacitors: tantalum capacitors of a maximum voltage
of 50 V a capacitance of 10 μF and tantalum capacitors of

8Active and Passive Electronic Components
Figure 11: An example of a failed component in 100% humidity
test.
a maximum voltage of 10 V and a capacitance of 33 μFwere
used.
The results show that combination of high humidity
and high temperature did not possess a significant risk for
50 V/10 μF capacitors during their normal use. Very high
humidity and radical temperature changes both affect the
breakdown voltages of these capacitors and can cause turn-
on breakdowns. Salt fog caused corrosion of 10V/33 μF
capacitors but did not have an effect on capacitance or ESR.
It did have a lowering effect on breakdown voltage, but the
decline was not radical. These effects should be taken into
account when using these tantalum capacitors at seacoast
atmosphere.
Acknowledgment
J.VirkkiwouldliketothanktheVilho,Yrj¨
o, and Kalle V¨
ais¨
al¨
a
Foundation.
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