Aluminum Electrolytic Capacitors - Engineering Center€¦ · This structure of an aluminum...
Transcript of Aluminum Electrolytic Capacitors - Engineering Center€¦ · This structure of an aluminum...
Aluminum Electrolytic Capacitors
Design and Characteristics
1V
10V
1 pF 100 pF 10 nF 1 uF 100 uF 10 mF 1 F
100V
1KV
10KV
VO
LT
AG
E
Ceramic
Film
C A P A C I T A N C E
EDLC
Tantalum
Ta Polymer
Technology
AluminumElectrolytic
© 2019 KEMET Corporation
Aluminum Element
13
Al
ALUMINUM
26.9815923
Aluminum: Chemical Symbol: Al Atomic Number: 13Atomic Mass: 26.9815923Discovered in 1825
© 2019 KEMET Corporation
AluminumProperties
• Most abundant element to be found in earth’s crust
(8.1%, after O & Si)
• Reasonable corrosion resistance due to the
formation of air-formed Aluminum oxide in nature
• Thicker Aluminum oxide using electrochemical
method (anodizing)
• Aluminum oxide is a good dielectric substance
Useful properties of Al:
Light weight;
Good electrical conductivity
Good thermal conductivity
Non-toxic
Non-magnetic
No reaction with alcohol & other organic solvent
High reflectivity of light
Environmentally friendly
© 2018 KEMET Corporation
Aluminum ElectrolyticManufacturing Process
Testing
Standard MeasurementsAgingSealingImpregnation
Deck WeldingWindingSlitting
© 2019 KEMET Corporation
Aluminum Electrolytic CanConstruction
Cathode
Foil
Anode
Foil
Separator
Paper
Foil
Tabs
Safety
Vent
© 2019 KEMET Corporation
Anode Foil Etching
Super pure plain aluminum foil (70 – 125 µm thick) undergoes
electrochemical reactions to dissolve the metal substrate of the
foil in the form of a dense network of microscopic channels, in
order to increase the overall surface area providing a maximum
capacitance for a given electrode surface size.
• Electrochemical tunnel “Etching” of 99.99% aluminum
• Tunnel initiation strongly influenced by impurities
• Tunnel diameter 1um - 2um across
• Tunnel length 15um - 50um long
• Density 10 - 25 million tunnels per cm2
• Foil gains 50 to 100 (actual area / plain surface area)The disadvantage of Surface “Etching” is the
reduction of the capacitors ability to
withstand HIGH DC currents.
© 2019 KEMET Corporation
Anode FoilFormed Cross-Section
Surface of foil
Dark area in the
middle is solid core (Al)
3500 times
magnification
© 2019 KEMET Corporation
Foil Technology Evolution
Foil Capacitance Evolution (550 VF)
YearHistoric (µF/cm2)
Current & Prediction (µF/cm2)
1993 0.57
1994 0.63
2001 0.65
2003 0.68
2008 0.71
2011 0.74
2015 0.77
2018 0.79
2019 0.83
Al Anode Foil Capacitance Evolution
~ Foil for 400V Capacitor ~
© 2019 KEMET Corporation
• By etching the anode foil, we increase the capacitance by increasing the surface area
• Thicker dielectric reduces maximum capacitance potential
• Dielectric thickness determines voltage rating
Aluminum ElectrolyticBasic Model
0
Electrolyte
Aluminum Foil
Cathode Plate
Aluminium Oxide Dielectric
Aluminum Foil
Anode Plate
Aluminium Oxide
Dielectric
Separator
© 2019 KEMET Corporation
Electrolyte Composition
• High conductivity, neutral pH
– Acid + Base -> Salt
• Wide operational temperature range
– Stay conductive across range
• Provides ability to reform oxide
– Controlled level of water
• Compatibility with paper and deck material
– Hydrogen gas absorber
• Low flammability, low toxicity
© 2019 KEMET Corporation
Aluminum
Anode
Plate
Forward bias is same as formation bias.
If dielectric gets thin enough, the forward bias voltage will form new dielectric
Thinner than original because VFormation > VRating > Vapplication
Wet
Electrolyte
Reformed dielectric region
Die
lectr
ic
Red
ucti
on
O-2
O-2
Reform
Traditional Aluminum ElectrolyticThe Electrolyte Allows for the Dielectric to Reform (or “Heal”)
© 2019 KEMET Corporation
Separator Papers
• Materials (pulp)
– Kraft, manila, esparto, hemp
– Combinations of pulp are often used
• Properties
– Thickness 12µm to 90µm
– Density 0.3 to 0.8 g/cm3, uniform density, minimum pinholes
– Simplex – single type of paper
– Triplex – three papers joined together
• Usage
– 1 to 3 papers used between anode and cathode
– Up to 5-6 actual layers when triplex paper used
© 2019 KEMET Corporation
Construction
• Can– Diameter and Length
– Vent
– Mounting
• Common Termination styles– Screw Terminals
– 2-5 pin Solder Pin, Pin Tag, Snap-In
– Axial, Radial
– SMD
– Press-Fit
• Sleeve– PVC
– PET; UL recognized
– Polyolefin
© 2019 KEMET Corporation
New Press-Fit Termination
Capacitor is pressed into the PCB, not soldered
Specific poke yoke terminations
Eliminates the problems of soldering on thick PCB copper tracks
Eliminates fractured solder joints
Quick exchange of components
Press-Fit Pin Material
Material:
Copper Nickel Silicon Alloy CuNiSi R580 (C19010)
Plating:
• Ni 1.5-3μ all over
• Sn 100% mat 0.4-1.1μ on press-fit area
• Sn 100% mat 3-6μ on the remaining area
16© 2019 KEMET Corporation
Press-FitSolution for Multiple Issues
Soldering Problems
• Heavy copper tracking on the PCB acts as a heat sink which makes soldering difficult
• This can cause cold spots, voids, splatter, cracks etc
Washing Issues
• More aggressive washing of pcb after reflow soldering can force water
under insulating sleeves of electrolytics
• Avoiding reflow / washing means expensive and additional processes
such as hand soldering, automated selective soldering, or hand washing
of components
Field work
• Preventive maintenance of soldered components often means replacing the entire
(and costly) PCB
1
2
3
© 2019 KEMET Corporation
Characteristics
© 2019 KEMET Corporation
Electrolytic Parameters
• Capacitance
• Equivalent Series Resistance, ESR
• DC Leakage
• Shelf Life & Reforming
• Operational Lifetime
• End of Life
© 2019 KEMET Corporation
Terms and Definitions
© 2019 KEMET Corporation
Basics
The basic principle of the capacitor is to store electrical charge
(Q in coulombs). The potential charge it can hold is determined
by the capacitance (C in Farads) and voltage (V in volts)
An electric equivalent schema of an electrolytic capacitor can be
described as an equivalent series resistance (ESR), equivalent
series inductance (ESL), the capacitance (C) and a parallel
resistance for the leakage current (Rleak).
Rleak depends on the quality of the dielectric.𝑸 = 𝑪 × 𝑽
ESL
Rleak
ESR
C
© 2019 KEMET Corporation
Electrolytic ParametersCapacitance (RC-Ladder)
The RC-Ladder is an effect of the tunnel
created to increase the area of the foil.
The capacitive elements are distributed
along the walls to the bottom of the tunnel,
connected to a cathode extension created
by the electrolyte
As frequency increases more capacitive
elements will ‘drop out’, eventually getting
to point where only those elements near the
surface of the foil
The electrolyte (or cathode) contact has a
resistance that is extremely dependent on
temperature.
As the temperature decreases, the mobility
of the ions in the electrolyte slow down.
Because of this the capacitance drop occurs
at lower frequencies for lower temperatures.
© 2019 KEMET Corporation
Effective capacitance reduces as temperature decreases
(Capacitance change with temperature is greater for lower rated voltages)
Effect of Frequency Change:
Effective capacitance reduces as frequency increases
𝐶 =1
(2𝜋𝑓𝑍)
d
AC r 0=
( )
=
TfOAlr
132
( )
132 OAlAcontacted
=
Tf
1
Electrolytic Parameters Capacitance Change - Frequency and Temperature
Effect of Temperature Change:
© 2019 KEMET Corporation
Capacitance and Capacitance VariationTotal Capacitance of the Capacitor
By design, a non-solid aluminum electrolytic capacitor has a second aluminum foil, the so-called
cathode foil, for contacting the electrolyte. This structure of an aluminum electrolytic capacitor results
in a characteristic result because the second aluminum (cathode) foil is also covered with an insulatin
oxide layer naturally formed by air. Therefore, the construction of the electrolytic capacitor consists of
two single series-connected capacitors with capacitance CA of the anode and capacitance CK of the
cathode. The total capacitance of the capacitor Ce-cap is thus obtained from the formula of the series
connection of two capacitors:
CK is much higher than CA
𝑪𝒆 − 𝒄𝒂𝒑 =𝑪𝑨 ×
𝑪𝑲𝑪𝑨+ 𝑪𝑲
𝟏
𝑪𝒕𝒐𝒕𝒂𝒍=
𝟏
𝑪𝒂𝒏𝒐𝒅𝒆+
𝟏
𝑪𝒄𝒂𝒕𝒉𝒐𝒅𝒆
© 2019 KEMET Corporation
Capacitance and Capacitance VariationTemperature Dependencies
The temperature has a considerable
effect on the capacitance. With
decreasing temperature, the viscosity
of the electrolyte increases, thus
reducing its conductivity.
The resulting typical behavior is
shown in the figure.
© 2019 KEMET Corporation
Capacitance and Capacitance VariationFrequency Dependencies
Frequency Dependence of the Capacitance
The AC capacitance depends not only on the temperature but also on the measuring frequency. The
figure below shows the typical behavior. Typical values of the effective capacitance can be derived
from the impedance curve, as long as the impedance is still in the range where the capacitive
component is dominant.
C - Capacitance [F]
𝒇 - Frequency [Hz]
Z - Impedance [Ω]
Standardized measuring conditions for electrolytic capacitors are an AC
measurement with 0.5V at a typically frequency of 100Hz or 120Hz and
a temperature of 20°C.
𝑪 =𝟏
𝟐𝝅𝒇𝒁
© 2019 KEMET Corporation
Electrolytic ParametersCapacitance Change - Frequency
Freq 20C 50C 85C
20.00 4278.11 4378.17 4504.13
25.00 4271.29 4370.10 4492.97
35.00 4261.24 4356.87 4477.68
50.00 4250.85 4343.88 4461.13
60.00 4245.75 4337.37 4452.97
70.00 4241.73 4331.77 4445.95
80.00 4238.24 4327.49 4440.40
100.00 4232.13 4319.64 4429.39
200.00 4215.23 4296.63 4400.46
400.00 4199.96 4278.80 4375.35
1000.00 4100.00 4125.00 4200.00
2000.00 3650.00 3725.00 3800.00
4000.00 3000.00 3070.00 3400.00
10000.00 1500.00 1750.00 2500.00
20000.00 800.00 1050.00 1700.00
40000.00 400.00 550.00 1000.00
100000.00 150.00 225.00 400.00
1000000.00 10.00 18.00 40.00
1
10
100
1,000
10,000
10 100 1,000 10,000 100,000 1,000,000
Cap
acit
ance
[u
F]
Frequency [Hz]
4700uF/400V, 85°C Screw Terminal
20C
85C
50C
Characteristics of Wet
Technology
© 2019 KEMET Corporation
Electrolytic Parameters Capacitance over time
CAP
Time
Cause of Cap Change: Solution:
Chemical changes within the
electrolyte and drying
• More stable electrolytes
• Lower gassing & diffusion rates
Accelerated with
leakage current
• Improved quality anode foil
giving a lower leakage current
• Consistent quality anode foil
Ripple current and ESR causes
power loss giving higher
temperature
• Lower ESR designs
• Improved thermal conductivity
© 2019 KEMET Corporation
ESR – Equivalent Series Resistance
The equivalent series resistance is the resistive component of the equivalent series circuit. The ESR value
depends on frequency and temperature and is related to the dissipation factor by the following equation:
Lower ESR, Higher Current
Higher ESR, Lower Ripple Current
𝑬𝑺𝑹 =tan δ
ω × 𝑪𝑺
ESR: Equivalent Series Resistance Ω
tan δ: Dissipation Factor
ω: Angular Frequency rad/s
CS: Series Capacitance F
© 2019 KEMET Corporation
ESR – Equivalent Series ResistanceMain Contributors
• Oxide Resistance‒ Determined by oxide thickness, oxide characteristics
and surface area
‒ Frequency dependent
• Electrolyte + Paper Resistance‒ Determined by electrolyte and paper characteristics
and surface area
‒ Temperature dependent
• Foil Resistance‒ Determined by foil type and length
‒ Temperature & frequency independent
• Tabbing & Connection Resistance‒ Determined by number of tabs & construction method
‒ Temperature & frequency independent
© 2019 KEMET Corporation
• The equivalent series resistance (ESR) is a single resistance representing all of the ohmic losses of the
capacitor and connected in series with the capacitance.
• Standardized measuring conditions for electrolytic capacitors are AC measurement with maximum 1 V at
a typical frequency of 100 Hz or 120Hz and a temperature of 20 °C.
ESR – Equivalent Series ResistanceMain Contributors and Dependencies
© 2019 KEMET Corporation
ESR – Equivalent Series ResistanceDependencies
ESR decreases with temperature rising which causes the:
• Electrolyte conductivity to increase.
• Electrolyte viscosity to decrease.
ESR decreases with frequency increment which has a:
• Direct influence of the oxide resistance at low
frequencies.
© 2019 KEMET Corporation
Electrolytic ParametersESR Change (Frequency & Temperature)
ESR Contributors:
• Electrolyte
• Oxide
• Tabbing
• Tissue Density
• Thickness
20°C 50°C 85°C
20.00 34.76 28.84 30.22
25.00 31.28 24.21 24.84
35.00 27.13 19.51 19.15
50.00 23.88 15.76 14.78
60.00 22.64 14.30 13.00
70.00 21.74 13.28 11.88
80.00 21.07 12.53 10.97
100.00 20.11 11.43 9.71
200.00 18.37 9.33 7.23
400.00 17.50 8.31 6.02
1000.00 16.94 7.70 5.32
2000.00 16.72 7.55 5.10
4000.00 16.51 7.47 5.03
10000.00 16.39 7.42 5.04
20000.00 16.41 7.55 5.15
40000.00 16.60 7.88 5.49
100000.00 17.26 8.98 6.49
0
5
10
15
20
25
30
35
40
10 100 1,000 10,000 100,000
ESR
[m
Oh
m]
Frequency [Hz]
4700uF/400V, 85°C Screw Terminal
20C
50C
85C
© 2019 KEMET Corporation
• Distorted polarization of dielectric (Aluminum oxide layer)
• Resolution and formation of dielectric
• Moisture absorption by dielectric
• Breakdown of dielectric due to the existence of chlorine or iron particles
Electrolytic Parameters Leakage Current – Main Causes in Electrolytic Capacitors
Leakage Current
Temperature
Voltage
Ripple Current
Time under Voltage
Storage Time (0V)
The DC leakage current is a small current that flows through a capacitor when voltage is
applied, between the two conductive plates.
Leakage current is primarily caused by imperfections in the oxide layer. This current varies
mainly depending on the applied voltage, time, and capacitor temperature.
The leakage current of an Aluminum electrolytic capacitor increases when the component is
stored for a long period of time.
The specified leakage current value is measured after the rated voltage of the capacitor is
applied at room temperature for a specified time period.
0
0.5
1
1.5
2
2.5
3
3.5
124
47
70
93
116
139
162
185
208
231
254
277
300
323
346
369Le
akag
e C
urr
en
t (m
A)
Hours of Discharge
© 2019 KEMET Corporation
DCL – DC LeakageDependencies
1. DCL increases with temperature rising and the internal temperature TCore must be considered.
2. DCL decreases with time and reaches a stable value which remains quite constant for a long period of time.
3. The leakage current is an increasing function of the applied voltage Vop, and rises quite strongly when Vop exceeds the
rated value VR.
1 2 3
© 2019 KEMET Corporation
Electrical Characteristics Summary
Temperature Increases
Frequency Increases
Voltage Increases
Time under Voltage
Capacitance ~ ~
ESR ~ ~
Leakage Current ~
© 2019 KEMET Corporation
End of Life Criteria
• Catastrophic Failure:
− Open or short circuit
• Mechanical Failure:
− Operation of safety vent often seen as split sleeve
• Parametric Failure*:
− Capacitance change 25-100V – ±20%; +100V 15%
− ESR >3x limit or
− Impedance >3x limit or
− Leakage current > specified limit
Comparisons between
capacitor manufacturers
should be made using
the same criteria.
From catalog *
© 2019 KEMET Corporation
Expected LifeParameters
• Ta → Ambient Temperature
• Tc → Core Temperature
• Vop → Operational Voltage
• Ripple Currents at Frequencies
Airflow significantly
increases the life of
the capacitor.
© 2019 KEMET Corporation
Expected LifeTemperature
If we use the derivative of Arrhenius Law, we can predict the impact of change in
temperature on the expected life of the capacitor.
𝐿𝑜𝑝 = 𝐿𝑜𝑝𝑟 × 2 ×(𝑇𝑚𝑎𝑥 −𝑇𝑎𝑚𝑏)
10
• Since we understand that temperature plays such a large factor, we should also factor in the losses (self-heating)
of the capacitor.
• Ripple current is the main contributor to power loss and self-heating.
• The temperature in the hottest area inside the capacitor, “the hot-spot” has most impact on operational life.
• The “hot-spot” temperature is dependent upon several factors:
‒ Power loss caused by ripple current
‒ Thermal resistance between the hot-spot and the ambient
‒ Ambient temperature and capacitor cooling condition
© 2019 KEMET Corporation
Life Time CalculationHot-Spot Temperature
Calculation of Hot-Spot Temperature
From previous slide we see:
𝑃𝐿𝑜𝑠𝑠 = 𝑅 × 𝐼𝑎𝑐2
• Since ESR is dependent on frequency 𝑓, our 𝑃𝐿𝑜𝑠𝑠 should also consider the
complex current waveform.
• With complex current waveform it is therefore necessary to calculate the
contribution from each harmonic frequency to the power loss.
• Once we have our PLoss value we can calculate the Thot-spot temperature.
Thot-spot = Tamb + 𝑃𝐿𝑜𝑠𝑠 x Rth
𝑃𝐿𝑜𝑠𝑠 = 𝐸𝑆𝑅 𝑓1 × 𝐼𝑎𝑐2 𝑓1 + 𝐸𝑆𝑅 𝑓2 × 𝐼𝑎𝑐2 𝑓2 +⋯(𝑊)
© 2019 KEMET Corporation
Life Time CalculationThermal Model
The thermal resistance Rth, (°C/W) is defined from the power loss (P) and
temperature difference.
ΔT, between the hot-spot and the ambient temperature
ΔT = P x Rth
ΔT = Th–Ta
Power (P) is assumed to be generated in the hot-spot.
Rth (total thermal resistance) can be divided in two parts:
• Rthhc → thermal resistance between the hot-spot and the case
dependent on the capacitor design
• Rthca → thermal resistance between the case and the ambient
dependent on cooling conditions
© 2019 KEMET Corporation
Life Time CalculationHot-Spot Temperature
0
5
10
15
20
25
30
60 65 70 75 80 85 90
Life
Tim
e [y
]
T hot-spot [°C]
4700uF/350V, 85°C Screw Terminal
© 2019 KEMET Corporation
Thermocouples:
We recommend to measure the temperature in the middle
of the cap and also the ambient near the parts.
Snap-In
Screw Screw
Operational Life Time and Hot Spot CalculationHow to Measure the Core Temperature
© 2019 KEMET Corporation
Foil tabs
Tissues
Cathode foil
Anode foil
Extended cathode
Laser welded tabs to deck
• Can spigot for supporting wind
• Ribs for thermal connection of extended cathode
• Anode formation type (oxide layer)
• Number of tab foil connections
• Reduce ESR
Operational Life Time and Hot Spot CalculationHow to Improve Life
Life Time CalculationVoltage vs. Temperature
Voltage Derating
• If Electrolytic capacitors are operated at a voltage below their rated value then the component will be under less operating stress.
• Reduced stress and lower leakage current provides an improvement in the life expectancy.
• Since leakage current increases with temperature, the benefit of a reduced operating voltage is more pronounced at higher temperatures.
Le(Vop) - Life expectancy at operating voltage
Le(VR) - Life expectancy at rated voltage
Kv - Voltage derating factor
Le(Vop) = Le(VR) x Kv
© 2018 KEMET Corporation
Life Time CalculationVoltage vs. Temperature
Voltage derating factor (Kv) for products with a rated temperature of 85°C and core temperatures (Tc ) of 45°C, 65°C and 85°C
Voltage Derating
Rated: 400V, 105⁰C, 7,000h
Operational voltage de-rated for 15% → 340V
At 105⁰C, the Kv: 1.4 (provided by KEMET)
Le(Vop) - Life expectancy at operating voltage
Le(VR) - Life expectancy at rated voltage
Kv - Voltage derating factor
Le(Vop) = Le(VR) x Kv
Recommended derating %
7,000 X 1.4
10,000 h
ECAD
Electrolytic Innovation Center
© 2019 KEMET Corporation
ECAD – Electrolytic Innovation Center
• In-house developed integrated design system
• Product design, specification & costing
• Design history, issue & control
• Bills of material & routings
• Integrated with Oracle manufacturing
• Manufacturing batch cards
48© 2019 KEMET Corporation
ECAD: Screw Terminal, Snap-In & Press-Fit
Theoretical Simulation:
Thermal conditions (ambient, core temperature)
Ripple currents/frequencies
ESR, impedance
Operational life
Airflow
Samples for testing with thermocouples
Measuring the core temperature of the capacitor
Performance in a real application environment
Test data for evaluation
1
2
3
Samples:
© 2019 KEMET Corporation
Electrolytic Capacitor Life Calculatorengineeringcenter.com
Market & Applications Features & Benefits
Applications
• UPS Systems
• Power Supplies
• Data Storage
• Smart Meters
• Wind & Solar
• Drives
• Transportation
• Welding
Features & Benefits
• Long Life Expectancy
• High Transient Voltage Performance
• High Ripple Current
• Wide Range of Mounting & Assembly Options
• Full Design Flexibility / Customized Solutions
• Leading the Design In – Fast Approach
Market Segments
• Automotive
• Industrial
• Alternative Energy
• Medical
• Consumer
• Computer
© 2019 KEMET Corporation
Electrolytic Product Portfolio
Axial/Radial Screw Terminal Snap-In
Radial / Single Ended SMD
Press-Fit
Conductive Polymer
Single EndedConductive Polymer
SMD
Varistors
Relays
© 2019 KEMET Corporation
Thank You!