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KEMET SMD film capacitors for high temperature applications



Trends of several applications like down-hole drilling, commercial aviation (e.g. jet engines), heavy industrial and automotive are challenging the capabilities of capacitors and other electronic components. The growing harsh-environment conditions for these applications are: high temperature, high voltage and high current. At the capacitor component level, required features are: very high reliability under mechanical shock, rapid changes in temperature, low leakage current (high insulation resistance), small dimensions, good stability with time and humidity, and high peak withstanding voltage. Capacitors for power-conversion circuitry must maintain a low AC loss and DC leakage at high temperatures. KEMET has recently designed film capacitor series using PEN to address the needs of the above mentioned circuits, in particular regarding the working temperature, voltage and current. This paper will cover technological advances in film capacitor technology to address harsh environment conditions needs, providing test results on temperature, voltage and thermal shock acceleration factor.
KEMET SMD Film Capacitors for High Temperature Applications
Luca Caliari, Paola Bettacchi, Evangelista Boni, Davide Montanari, Arrigo Gamberini, Luigi Barbieri,
Francesco Bergamaschi
KEMET Electronics Italy, via San Lorenzo 19, 40037 Sasso Marconi (Bologna), Italy
Tel: +39 51 939 910, Fax: +39 51 939 324, e-mail:
Trends of several applications like down-hole
drilling, commercial aviation (e.g. jet engines),
heavy industrial and automotive are challenging
the capabilities of capacitors and other electronic
The growing harsh-environment conditions for
these applications are: high temperature, high
voltage and high current. At the capacitor
component level, required features are: very high
reliability under mechanical shock, rapid changes
in temperature, low leakage current (high
insulation resistance), small dimensions, good
stability with time and humidity, and high peak
withstanding voltage. Capacitors for power-
conversion circuitry must maintain a low AC loss
and DC leakage at high temperatures.
KEMET has recently designed film capacitor
series using PEN to address the needs of the above
mentioned circuits, in particular regarding the
working temperature, voltage and current.
This paper will cover technological advances in
film capacitor technology to address harsh
environment conditions needs, providing test
results on temperature, voltage and thermal shock
acceleration factor.
Key words: drilling, temperature, capacitor,
current, voltage, automotive
1 – Introduction
Film capacitors are especially renowned for
their reliability, their high current and voltage
withstanding capability and their resistance to
intense mechanical shocks, due to their intrinsic
physical elasticity. R&D activities focused on
automotive and other markets’ needs have made it
possible to increase the working temperature film
capacitors up to 170 °C. Thanks to the last fifteen
years reliability data, 170 °C is a temperature at
which film capacitors can be considered to perform
exteremely well and be safe a component[1].
Temperature is clearly the most challenging
parameter when looking at the design of film
capacitors for drilling and aviation applications,
where the maximum temperature exceeds 200 °C,
and reaches up to 220 °C. Furthermore, in
automotive and industrial applications the
temperature is steadily growing and is forecasted to
reach these very same levels in the upcoming years.
Even though the melting temperatures of many
plastic film raw materials is well above 240 °C, it is
clear that the film material must be properly treated
(not only chemically during the extrusion of the
raw material production process, but also
physically and thermally during the production
process of the film components) so that a long life
can be expected and all the special electrical and
mechanical properties of film capacitors are
preserved when exposed to these working
temperature ranges.
At a mounting technology level, in applications
where capacitance needs to be very stable over a
wide temperature range with good reliability and
long life expectancy, through-hole (radial) film
capacitors are an optimum choice with a very good
performance/cost ratio. Anyway, the need of a new
generation of equipment, very miniaturized and
manufactured on fully-automated assembly lines,
has requested several improvements in film
capacitors technology to create SMD components
able to withstand lead free (LF) reflow process,
maintaining excellent electrical behavior, very high
reliability and long life expectancy at higher and
higher working temperatures.
The aim of this paper is to show designers that
film capacitors can be a choice for extremely harsh
environment applications like down-hole drilling,
jet engines, industrial and automotive applications,
even though their typical working temperature
range reaches (or will soon reach) temperatures
around 220 °C.
At the same time, it is clear that future
developments of these applications will represent a
challenge for film components, should working
temperatures increase even further, so a roadmap of
R&D activities will be described, on which
KEMET is focusing already so that film capacitors
can keep being considered a choice for these high-
temperature applications also in the future. A full
characterization of film components as of today
will therefore be the key information content of this
work and will be summarized in the last section.
2 – Experimental Methods
Here is the description of the instruments, tools
and methods used during the performed
measurements. For each of them, the specific
measured parameters have been specified.
Agilent E4980, HP4284A Precision LCR meter and
HP4192A Impedance Analyzer (1 kHz and 1
Vrms): Capacitance (C), dissipation factor (tg
delta), Equivalent Series Resistance (ESR).
Radio Meter IM6 megaohmeter (1 999 V):
Insulation Resistance.
Heraeus Mod. UT6060 Oven: Operational life DC
and High Temperature Exposure.
Tenney JR Environmental Test Chamber: Shock
test performed manually by using oven @ 220°C
and Environmental Test Chamber @ -55°C.
Bertan 225 High Voltage Power Supply:
Operational life DC.
Kikusui TOS9201: First Break Down Voltage -
FBDV - test equipment. The test is carried out
applying the following voltage ramp (Figure 1-1)
on the capacitor.
DSC (Differential Scanning Calorimeter) test
equipment (Figure 1-2): This test allows the study
of polymers’ behavior when they are heated up at a
specific heat rate (°C/s) and it is commonly used to
observe and study polymers’ thermal transitions
(i.e. the melting point of an amorphous/semi-
crystalline polymer or the glass transition).
Figure 1-1: Voltage Ramp-up Used in the FBDV
Figure 1-2: Differential Scanning Calorimeter
Test Equipment.
Shock test system Lansmont Model 23: This
system has a magnesium table that rides on a set of
vertical linear guides. The sample is mounted to a
fixture/table, that is lifted on the guides, and then
released downward where it will be accelerated by
gravity. It is programmed to control the
acceleration and duration the impact of the table in
order to generate the desired 500G, 2 msec shock
pulse. An accelerometer is mounted on the fixture
to record the observed acceleration level for each
shock pulse. The accelerometer data is logged with
a Lansmont TP-USB data logging system.
3 – Film Capacitors Overview
Film capacitors are made of several plastic
layers put on top one another, assuring by
construction an excellent elasticity. The
capacitance is created through the deposition of a
thin aluminum layer on top of each plastic film
layer. In the following figure, two among the most
widespread film capacitors’ technologies are
shown: a standard one, in which the capacitor is
made of single-sided metallized films, and one that
withstands higher peak-currents named “double
metallized”, in which the capacitor is made of a
sequence of plain films layers (with no
metallization) and double
metallized layers:
Figure 2: Single and Double Metalized Technologies
Plastic film dielectrics used nowadays for
capacitors are
[2] [3]
PP: polypropylene;
PET: polyethylene terephthalate;
PEN: polyethylene naphthalate;
PPS: polyphenylene sulphide.
Table 1: Characteristics Comparison Between Plastic Film Dielectrics
Dielectric Constant (@1 KHz) 2,2 3,3 3,0 3,0
Min Commercial Thickness (µm) 2,4 0,9 1,4 1,2
DF (% @ 1 KHz) 0,02 0,5 0,4 0,05
TCC (DC/C), -55 °C to +125 °C ± 2,5 % ± 5,0 % ± 5,0 % ± 1,5 %
Min Temperature (
C) -55 -55 -55 -55
Max Temperature Typical (
C) 105 125 125 125
Max Temperature Extended (
C) 125 150 170 170
Dielectric Breakdown (V/µm) 400 280 300 220
Melting Temperature (°C) 178 254 266 283
Reflow & Multiple Reflows Tmax (°C) for SMD NO 245 245 - 255 260
Self-healing good medium medium-low low
The self-healing property of film dielectrics
(film’s ability to self-regenerate an internal drop of
insulation resistance) ensures a safe failure mode
(open circuit). Looking at table 1, PP film is the
best in terms of self-healing while it is the worst in
terms of melting temperature. This “rule” applies in
general for all plastic films: PET has a higher
melting temperature than PP, but has lower self-
healing capabilities. PEN and PPS are the most
suitable films for SMD applications (in particular
to withstand the LF reflow process), but they have
not the right properties for applications where
voltage peaks, higher than the capacitor’s rated
voltage, are combined to the 50-60 Hz network
To compare the self-healing properties of
different materials, their chemical composition
must be considered. The lower the ratio between
the number of Carbon (C) and Hydrogen + Oxygen
(H+O) atoms, the lower the possibility to have
conductive Carbon residues as an undesirable
outcome of the self-healing process (see figure 3
here below):
Figure 3: C/(H+O) Number of Atoms Ratio in Different Plastic Film Dielectrics
There are also many other parameters to be
considered in the study of self-healing phenomenon
and, in particular, the higher the clearing energy
content during the process, the higher the efficiency
of the healing, taking place in the insulation
between two adjacent metal layers
[4], [5], [6]
At a mounting level, SMD capacitors must
withstand higher temperatures during the soldering
process (reflow) than radial capacitors. Naked
SMD film capacitors are today capable of
withstanding the high temperatures of the LF
reflow process (up to 245 °C as per Jedec 020D1
capacitor volume > 350 mm
, H
> 2,5 mm).
Among the film dielectric listed, PET cannot be
the right dielectric since, due to several laboratory
tests, its physical characteristics deteriorate heavily
on working temperatures over 150 °C, PP’s melting
temperature is 178 °C and PPS has an extremely
high cost and low self-healing properties. On the
contrary, PEN shows good characteristics under all
these perspectives, therefore it will be the dielectric
under analysis.
In the following figure, a DSC (Differential
Scanning Calorimeter) graph is shown, in which it
is evident that the PEN melting process starts at
Figure 4: DSC thermograph of PEN
4 – High Current, Voltage and Temperature Applications: Description and Challenges
4 – 1 Down-hole drilling
New oil reserves are being found further and
further down in the ground, which is causing
temperature requirements of drilling, exploration
equipment, valve control and safety equipment to
be extended. Typically, a 10 °C increase every 3
years is the norm. One of the most widespread
applications in down-hole drilling is the Cockcroft
Walton Generator, whose schematic (in full wave
form) is hereafter shown:
Figure 5: Cockcroft Walton Generator (full wave)
In this application, capacitors are combined with
diodes to generate the very high voltages needed to
create the pulse needed in the reverse Magnetic
Resonance Imaging (MRI), used to explore into
rock formations in looking for oil. The main
requirement, from a mechanical point of view, is
the dimension (a few inches is often the diameter
they need to fit in). Other down-hole drilling circuit
applications include decoupling, energy storage,
filtering of inductive spikes (originated because of
the very long power cables used in the drilling
equipment), signal measurement, and feedback
circuits. Typical voltages, capacitance and sizes
used in all these applications are 560 pF to 1,000
pF 1,500 VDC rated (real maximum voltage
applied reaches 1,300 VDC).
Due to the extreme mechanical shocks
equipment are subject to in down-hole drilling
applications, most manufacturers elect to use
through-hole (radial) parts, due to the fear that
surface-mount products might "fall-off" during
operation. Other manufacturers who use surface-
mount tend to use products with gold extended
terminations, to assure a greater resistance to
mechanical shocks. High temperature, reaching a
peak of 220 °C peak in these applications, is not the
only issue for plastic film, though: humidity is also
to be considered, as when equipment are removed
from high-temperature environments and are
withdrawn through a cooler, condensation forms on
the circuits (designers need, therefore, to consider
this issue). Furthermore, equipment left "top-side"
may be exposed to salty and humid conditions
(depending on application). The resistance and
reliability combination of these three factors
(temperature, humidity and salty environment),
should then drive the design choice at a component
level in terms of box or naked components mainly.
4 – 2 Aviation
In the proximity of jet engines, many electronic
applications at extremely high temperatures take
place: pressure and temperature sensors and thrust
regulators just to name a few. These applications
are typically low voltage, and include
coupling/decoupling, filtering, operational
amplifiers and instrumentation-amplifier feedback
circuits, line filters, wave forms shaping. Hereafter,
some general schematic showing their principles of
Figure 6: Filters Schematics
Figure 7: Filters Schematics
5 – Tests and Performances
A photograph showing naked SMD film
capacitors in different sizes is shown here below:
Figure 8: Naked SMD PEN Capacitors
In order to evaluate the usage of PEN film at
high temperatures, PEN film has been
characterized up to 240 °C regarding the shrinkage
level and up to 220 °C regarding capacitance, tg
delta (dissipation factor) at different frequencies
and insulation resistance (IR).
Figure 9: PEN MD (Machinery Direction) Figure 10: PEN TD (Transversal Direction)
Shrinkage Shrinkage
In figure 9, an exponential increase with
temperature of the machinery direction (MD)
shrinkage is shown, for film that has not been
subject to a thermal treatment (the “core” phase of
the film components manufacturing). With
“machinery direction” it is intended that the
shrinkage is tested into the same direction of the
film extrusion. The thin metallization layer onto the
film does not change significantly the shrinkage
level (see “plain film” vs. “metallized film”). These
shrinkages have to be considered during the
process design of the film capacitors. On the
contrary it’s possible to see in figure 9 that the
specific thermal treatment, performed on the SMD
capacitors during their manufacturing, strongly
reduces the shrinkage (that is however not zero).
Similar considerations can be made regarding
the transversal direction (TD) shrinkage. With
“transversal direction” it is intended that the
shrinkage is tested in a perpendicular direction with
respect to the extrusion.
Figure 11: PEN % Capacitance vs. Temperature Figure 12: PEN % Capacitance Change Interval
In the above figures (11 and 12) it is possible to
see the average PEN increase of the capacitance
value and its interval plot up to 220 °C. The
increase is contained within +12% with a negligible
change between 200 °C and 220 °C:
T [°C]
DC/C% [1kHz]
Interval Plot of DC/C% [1kHz]
95% CI for the Mean
T [°C]
Tg [1kHz]
Interval Plot of Tg [1kHz]
95% CI for the Mean
Figure 13: PEN Dissipation Factor vs. Figure 14: PEN Dissipation Factor Change
Temperature @ 1 kHz Interval Plot @ 1 kHz
Figure 15: PEN Dissipation Factor vs. Figure 16: PEN Dissipation Factor vs.
Temperature @ 10 kHz Temperature @ 100 kHz
In the above figures (13, 14, 15 and 16) PEN tg
delta (dissipation factor) behavior vs. temperature
at 1, 10 and 100 kHz is shown. These graphs show
an extremely positive result: the dissipation factor
starts decreasing above 160 °C, reaching extremely
low levels at 220 °C, strongly reducing, therefore, a
potential further temperature increase due to the
self-heating of the capacitors in application. This is
also considered important since, in each
application, equilibrium is to be reached between
the thermal power generated inside the component
and the dissipated one. Equilibriums reached at
temperature above 160 °C are considered stable:
higher temperatures show a lower dissipation
factor, therefore lower internal power generated.
In order to consider the usage of PEN film
capacitors at such high temperatures as technically
safe, an evaluation of the physical-chemical
structure of the film with timing has been carried
on and, to do this, it was decided to monitor the
weight change with time of capacitors exposed
continuously to 220 °C. At the end of the test, a
comparison using a DSC (Differential Scanning
Calorimeter) test has been made on a film sample.
Figure 17: PEN % Weight Change vs. Time (@ 220 °C)
The above trend provides very important
information: the weight change is negligible. This
result shows the absence of chemical reactions that
could deteriorate the film, generating gas and,
therefore, reducing the film weight.
87 051 036 522 0300
20 00
15 00
10 00
50 0
Life at 22 0°C [h]
FB DV a ft er re flo w
HNS 50 .40 - 70 nF 1 000V dc - Co mpo nen ts pl aced at 220° C fo r dif fere nt tim e
Figure 18-1: DSC Analysis on Film Sample Figure 18-2: DSC Analysis on Film Sample
Without Treatment at 220 °C Treated at 220 °C
The 2 DSC tests above (figure 18-1 and 18-2)
show that, after 1,000 h at 220 °C, the film
cristallinity grade has increased (Delta H goes from
49.6 J/g to 78.9 J/g, with Delta H intended as the
enthalpy needed to melt the crystalline portion of
material subject to test) but without showing
anomalies: this result conjugated with the weight
test result bring to the conclusion that, from a
theoretical point of view, PEN film capacitors can
work up to 220 °C. However, the increase in
cristallinity grade indicates that a voltage de-rating
will probably be needed when working at these
temperature ranges.
In order to evaluate the aging of the film with
temperature and time, several first break down
voltage (FBDV) tests have been carried out at
different time frames, in order to monitor the break
down voltage decrease with time at 220 °C. These
tests have been performed on 1,000 VDC and 400
VDC rated PEN SMD film capacitors.
Figure 19: PEN First Breakdown Voltage Level vs. Time (@ 220 °C)
In figure 19 it is clear that the original high
voltage break down level decreases (as it was
expected) reaching, after 1,000 h, a value 75 to
80% lower than the starting value. This result
indicated that a PEN capacitor should be 75-80%
de-rated to work at 220 °C. A confirmation of this
result was found on PEN 400 VDC rated capacitors
(400 VDC capacitors can work up to 100 VDC at
220 °C). Here below a simple table summarizing
the findings on PEN de-rating (reference is the 25
°C voltage level):
Table 2: PEN de-rating vs. temperature
DC Voltage level (V)
25°C 1,000 400 250
105°C 1,000 400 250
220°C 200 100 50
In down-hole drilling, in several circuits 50
VDC and 100 VDC capacitors are typically used.
As per the above table, for a usage at 50 VDC at
220 °C a 250 VDC rated product should be chosen,
and for a usage at 100 VDC / 220 °C a 400 VDC
rated product should be selected. In order to
confirm again the above data, several life tests have
been carried on at 170 °C and at 220 °C on 1,000
VDC PEN SMD film capacitors:
time [h]
95% CI for the Mean
Interval Plot of DC% - Operational Life DC - 450V 170°C
Figure 20: PEN % Capacitance Change vs. Time
Figure 21: PEN % Capacitance Change (@ 450
(@ 450 VDC / 170 °C) VDC / 170 °C) Interval Plot
time [h]
DC %
95% CI for the Mean
Interval Plot of DC% - Operational Life DC - 250V 22C
Figure 22: PEN % Capacitance Change vs. Time Figure 23: PEN % Capacitance Change (@ 250
(@ 250 VDC / 220 °C) VDC / 220 °C) Interval Plot
time [h]
95% CI for the Mean
Interval Plot of DC% - High Temperature Exposure 220°C
Figure 24: PEN % Capacitance Change vs. Time Figure 25: PEN % Capacitance Change (@ 220
(@ 220 °C) °C) Interval Plot
The above graphs show the capacitance
deviation with time, up to 1,000 h, in different
environmental/electrical conditions. The graphs
confirm that no critical effects are underlined up to
220 °C (the capacitance drop clearly shows a
decreasing % reduction as time passes by, bringing
to an equilibrium).
A summary of the results is shown in the below
Figure 26: PEN % Capacitance Change at Different Life Test Conditions
The above graph leads to several conclusions
about the effects on the capacitors caused by two
stresses applied separately or simultaneously:
voltage and temperature. At 450 VDC/170 °C an
average capacitance deviation of -1,4% is recorded
after 1,000 h. With only temperature applied (220
°C), an average capacitance drop of -3,2% after
1,000 h is shown.
Applying both voltage and temperature
determines a positive synergism of the two stresses,
bringing the average capacitance drop to -8,3%
with a minimum value recorded of -12,2%.
However, the capacitance drop is limited within -
15% and, therefore, these tests are considered as a
very positive result: the usage of PEN film at such
temperature levels is safe.
Another stress cause to be considered in these
applications is represented by intense mechanical
shocks. A specific test at 500 g has been carried
on, as per figure 27-2. Shock testing was performed
on PCB board units installed onto special fixtures
designed especially for shock test equipment.
The boards were subject to 500 g / 2 msec half-
sine shock testing, in 6 directions (Z+, Z-, X+, X-,
Y+, and Y-), see figure 27-1. Test samples were
visually inspected after each test orientation
without observing any physical changes on any of
the test samples.
Figure 27-1: 500 g Shock Test Waveform
Figure 27-2: Boards Used for the 500 g Shock Test
In the here below figures it is possible to see the
change of capacitance and tgδ value after the shock
beforeafter shock
Cap %
Boxplot of Cap% - Before/after Shock Test 500G
beforeafter shock
D.F. @1kHz
Boxplot of D.F. @1kHz - Before/after Shock Test 500G
Figure 28-1: PEN % Capacitance Change vs. Figure 28-2: PEN Dissipation Factor Change vs.
500 g Shocks Interval Plot 500 g Shocks Interval Plot
The two above graphs show a negligible
capacitance and tg delta (dissipation factor)
deviation. This confirms the great performances of
film capacitors vs. mechanical shocks. Capacitors
have been measured also in terms of insulation
resistance (IR) and dielectric strength (DS) voltage
withstanding. Any anomaly has not been seen nor
recorded on insulation resistance and dielectric
strength performances and from a microscopic
analysis point of view either. Applications that
foresee high temperature levels, usually stress the
electronic board and its components also due to
rapid changes of temperature. In order to verify the
robustness of film capacitors vs. this important
aspect, 1,000 cycles from -55 to +220 °C have been
carried on (on parts soldered on a PCB).
SMD components have been selected because
their thermal stress during the mounting on the
PCB is considered to be a worst case (reflow). In
fact, if components with leads and resin are used
(box radial components), the stress is absorbed not
only from the plastic film of the component but
from the leads, too. Any anomaly either from
aesthetical point of view or from electrical point of
view has not been observed. Comparing figure 29-1
with figure 24, it is clear that what influences the
capacitance change is not the thermal cycle itself
but the exposure to the high temperature level
10 0 06 0 03 0 01 0 00
cy c le s
95 % C I fo r th e M ean
In ter va l P lot of DC % - Ra pi d C han ge of T em pe rat ure -5 5° C / 2 20 °C
Figure 29-1: PEN % Capacitance Change vs. Figure 29-2: PEN % Capacitance Change vs.
Thermal Shocks Thermal Shocks Interval Plot
6 – Summary, Future Trends and Challenges
Film capacitors are historically used for their
excellent reliability characteristics, but they have
never been used with working temperatures above
170 °C, as there are no data about their suitability
for these high temperatures, either from the film
supplier nor from the film capacitors producers. In
this paper, PEN film capacitors have been tested
from physical, chemical, electrical and
environmental point of view, in order to highlight
any anomaly to working temperatures up to 220 °C.
Each data and test has not confirmed any critical
aspect on working at such temperatures, for a time
frame up to 1,000 h. The film is physically stable,
the capacitance deviations reach equilibrium levels,
the tg delta (dissipation factor) decreases after 160
°C, reducing further temperature increase (self-
heating), which might determine avalanche
The only aspect that has to be considered is the
right voltage de-rating to apply, which depends on
the final temperature reached by the capacitors,
considering also the potential self-heating
effect.PEN film capacitors, either in SMD or radial
technology, can therefore be a choice for working
temperatures up to 220 °C.For future developments
on film capacitors on these applications, based on
the good results found, a general guide is:
1) Up to 200 °C, standard tin capacitor
terminations can be used, while above this
temperature modifications of the
terminations design (e.g. gold material)
should be evaluated. Moreover, for SMD
components, standard SAC solder paste
can be used up to 200 °C.
2) HMP (High Melting Point) solder cannot
be used due to their very high melting
temperature (301 °C) and a standard
reflow peak of 380 °C. At such reflow
temperatures, common plastic film raw
materials are not suitable: other mounting
technologies have to be evaluated.
3) The good result on tg delta values over
160 °C might strongly influence the ripple
current withstanding capabilities from that
temperature and above.
7 –
[1] Evangelista Boni et al., “SMD Naked Film Capacitor Technologies for Severe Environments and Circuit
Functions” 2011 CARTS Proceedings, March 2011, Jacksonville, FL, USA
[2] Paola Bettacchi, et al., “Power Film Capacitors for Industrial Applications” 2010 CARTS Proceeding,
November 2010, Munich, Germany
[3] Davide Montanari, et al., “Film Capacitors for Automotive and Industrial Applications”, 2009 CARTS
Proceedings, April 2009, Jacksonville, FL, USA
[4] X. Dai, et al., “Influence Factors for the Self-healing of Metallized Polypropylene Capacitors” 2000
Conference on Electrical Insulation and Dielectric Phenomena
[5] J.-H. Tortai et al., “Diagnostic of the Self-healing of Metallized Polypropylene Film by Modeling of the
Broadening Emission Lines of Aluminum Emitted by Plasma Discharge” J. of Applied Physics 97, 053304,
[6] J. Kammermaier, et al., “Modeling of Plasma-induced Self-healing in Organic Dielectrics” Siemens AG,
Corporate Research and Development, 8520 Erlangen, 7 April 1989
[7] JEDEC 020D1 Publication: “Moisture/Reflow Sensitivity Classification for Nonhermetic Solid State
Surface Mount Devices” Joint Industry Standard March 2008
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Conference Paper
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The demand for energy savings and for alternative energy sources has called for an accelerated introduction of products such as Hybrid Electric Vehicles, Solar Converters, and Wind Generators. A DC to AC inverter is a key system for the operation of these devices. The inverters require Filter and DC-Link Capacitors with higher operating voltages and ripple currents in order to support the need of increasing power. Other important parameters are low inductance to limit the switching transient voltages, high frequency capability , large range of working temperature, long expected life time, low dissipation factor and low ESR, high stability vs. time of the Capacitance value, withstanding of high peak voltage, mechanical strength, low weight, maximum flexibility of adaptation to the shape of the available space, customized termination technology (through hole wires, tabs, bus-bars, lead frames, and SMD), and low total cost. The Film capacitor is the type of capacitor that comes closest to satisfying these requirements. Several choices of film capacitor manufacturing technologies are available: Wound, Soft-Winding, and Stacked. There have been recent advances in these technologies. The Wound and Soft-Winding capacitors have seen significant advances in capacitance, voltage and current capabilities, and expected life time (100kh continuous use). The Soft-winding capacitors have benefited from very thin and high temperature Polypropylene film in combination with a new process of winding and thermal treatment. The Stacked capacitors can now use two base plastic films (Polypropylene and Polyester) and new techniques of metallization and insulation during the cutting process. This paper will discuss the technical basis for advances in each of these technologies and give some guidance on the optimum areas (capacitance, size, voltage and current) for the application of each technology.
Metallized-film capacitors have the property, even under high continuous voltage, to self-heal i.e., to clear a defect in the dielectric. The self-healing process is a consequence of a transient arc discharge. It has been previously shown that during the discharge, due to Joule effect, the metal is vaporized until the arc extinguishes. The discharge duration has been found to be inversely proportional to the mechanical pressure applied on the layers of metallized films making up a capacitor. The aim of this study is to understand the physical processes involved in this spontaneous extinction of the arc discharge. Emission spectroscopy has been used to provide information about the physical properties (temperatures, electronic and neutral particles densities, etc.) of the plasma induces by a self-healing. An analysis, based on the broadenings and shifts of Al atomic lines, of the experimental light spectra obtained has shown that the self-healing process leads to the generation, from the vaporized metal, of a high-density and relatively weakly ionized aluminum plasma. The plasma density increases with the pressure applied on the film layers and, consequently, the density power needed to extend the plasma zone increases as well and the arc discharge goes out faster as experimentally observed.
Conference Paper
After the local breakdown of the metallized film, the self-healing of the capacitor is influenced by several factors, including the capacitance of metallized capacitor, pressure, as well as the applied voltage. In this paper, they are investigated fundamentally in reference to their influence towards the insulation recovery of the metallized polypropylene. Single metallized polypropylene film and metallized film capacitors are used as experimental samples to study the effect of these factors after local breakdown of the film under the conditions of impregnation and nonimpregnation. The results show that, these factors impose their influences via the infusion energy passing the breakdown path. It is also found that excess the infusion energy will be adverse to the self-healing of metallized polypropylene capacitors
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  • Paola Bettacchi
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Modeling of Plasma-induced Self-healing in Organic Dielectrics" Siemens AG, Corporate Research and Development
  • J Kammermaier
J. Kammermaier, et al., "Modeling of Plasma-induced Self-healing in Organic Dielectrics" Siemens AG, Corporate Research and Development, 8520 Erlangen, 7 April 1989