Aluminium Electrolytic Capacitors – Failure Modes

Selection (and precautions for use) of
Aluminum Electrolytic Capacitors
in LED Lighting Applications
Page 1 of 25
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Electrolytic Capacitor in LED Driver App
5 Watt LED Driver Circuit
Junction Temperature
~+95 C
Diffusion Temperature
~+70 C
PCB Ambient Temperature +50 C ~+65 C
100uF / 25VDC x 2
220uF / 25VDC x 1
INPUT CAPACITANCE
The total capacitance
should be at least 200µF
With 20VD (of higher
VDC rating)
Electrolytic Capacitor
with a 220µF/25VDC
rating for low cost
Page 3 of 25
Capacitor Requirements
Establish life time (hours) goal for application
Example: 80,000 hours
(9+ years @ 24/7 application)
Establish ambient operating temperature
Example: Multiple end-use applications
•
PCB operation over range of +50 C ~ +65 C
Capacitance value needed?
Example: 220uF
Voltage rating needed?
Example: 25VDC (minimum)
Selection of capacitor
Capacitor Requirement
CV: 220uF @ 25VDC
Life: 80,000 Hrs @ +65 C
Page 4 of 25
Component Specification Review
Load Life Rated at
maximum rated
temperature (i.e. +105°C)
and WVDC
Load Life Rating by Component
Diameter
( Ø mm )
Based upon endurance test results
performed by component manufacturer
Load Life Test Limits
NOTE: Possible variation in test
limits between component
manufacturers
Example: ±30% instead of ±20% limit
for Δ Capacitance
Page 5 of 25
Aluminium Electrolytic Capacitor Construction
X-Ray
Image
Aluminum
Can
End Seal
Safety Vent
Capacitor
Element
Mechanical
Seal
Lead Wire
Electrolyte dissipation follows the Arrhenius Rate
Page 6 of 25
Capacitor Life Time vs. Temperature
Aluminum electrolytic capacitor life time is reduced at higher
operating temperatures
Temperature
Period
24 / 7
8 Hours/Day
+105°C
5000 hours
0.6 years
1.7 years
+85°C
20,000 hours
2.3 years
6.8 years
+65°C
80,000 hours
9.1 years
27.4 years
Page 7 of 25
Aluminium Electrolytic Capacitor Life Time
1200uF @ 10VDC, 10x20mm Size: 4000 Hour Load Life Rating @ +105 C @ WVDC
Performance Characteristic Change over Time @ Rated Temperature
10,000 hours @ +105 C @ 10VDC
Capacitance
Change (%)
Test Time (1000 hours)
Capacitance = 1200uF
1056uF
948uF
Dissipation of the liquid electrolyte from the capacitor reduces the cathode connection,
resulting in Capacitance decrease & Dissipation Factor (ESR) increase
The rate of dissipation follows the Arrhenius equation for chemical reactions
Reaction rate will double for each 10 C increase in temperature
Î Capacitor life time expectation doubles for 10 C decrease in operating temperature
Page 8 of 25
Aluminium Electrolytic Capacitor Life Time
1200uF @ 10VDC, 10x20mm Size: 4000 Hour Load Life Rating @ +105 C @ WVDC
Performance Characteristic Change over Time @ Rated Temperature
10,000 hours @ +105 C @ 10VDC
DF
Loss
Tangent
(%)
Test Time (1000 hours)
Tan δ = 0.19
0.38
120Hz ESR = 0.26 ohm
0.66 ohm
Increasing resistive losses over time
Capacitor becomes less efficient over time of operation
ESR (series resistance) increases over time
Page 9 of 25
Aluminium Electrolytic Capacitor Life Time
Î Capacitor Life time Expectation doubles for 10°C decrease in operating temperature Í
+45°C
+55°C
+65°C
+75°C
+85°C
+95°C
+105°C
64,000
32,000
16,000
8,000
4,000
2,000
1,000
128,000
64,000
32,000
16,000
8,000
4,000
2,000
>15 Yrs
96,000
48,000
24,000
12,000
6,000
3,000
>15 Yrs
128,000
64,000
32,000
16,000
8,000
4,000
>15 Yrs
>15 Yrs
80,000
40,000
20,000
10,000
5,000
Capacitor Requirement
CV: 220uF @ 25VDC
5000 Hrs
@ +105°C
Life: 80,000 Hrs @ +65°C
Page 10 of 25
Component Selection
Capacitor Requirement
CV: 220uF @ 25VDC
Life: 80,000 Hrs @ +65 C
Rating of 5000 Hrs @ +105 C
SMT V-Chip Type:
5000 hours @ +105°C
220uF
25VDC (or greater)
»
»
Radial Leaded Type:
5000 hours @ +105 C
» 220uF
» 25VDC (or greater)
PN: NAZT221M25V8X10.5
220 µF, 25VDC, 8X10.5mm
-40C ~ +105 C
5000 hrs @ +105 C
20,000 hrs @ +85 C
80,000 hrs @ +65 C
2 Times Reflow
80 Sec >+200 C
40 Sec >+230 C
Peak = + 260 C
PN: NREHL221M25V8x11.5
220 µF 25VDC, 8x11.5mm 3.5mm LS
-40C ~ +105C
7000 hrs @ +105 C
28,000 hrs @ +85 C
112,000 hrs @ +65 C
Page 11 of 25
Component Selection
DOUBLE
LIFETIME
»
»
Capacitor Requirement
CV: 220uF @ 25VDC
Life: 80,000 Hrs @ +75°C
Rating of 10,000 Hrs @ +105°C
SMT V-Chip Type:
10,000 hours @ +105°C
» 220uF
» 25VDC (or greater)
»
»
Radial Leaded Type:
10,000 hours @ +105°C
» 220uF
» 25VDC (or greater)
2 Times Reflow
60 Sec >+200°C
20 Sec >+230°C
Peak = + 250°C
PN: NAZV NAZV221M25V8X10.5LBF
220 µF, 35VDC, 10X10.5mm
-40C ~ +105C
10,000 hrs @ +105°C
40,000 hrs @ +85°C
80,000 hrs @ +75°C
> 15 years @ +65°C
PN: NRSH221M50V10x16F
220 µF, 50VDC, 10x16mm 5mm LS
-40C ~ +105C
10,000 hrs @ +105°C
40,000 hrs @ +85°C
80,000 hrs @ +75°C
> 15 years @ +65°C
Page 12 of 25
Component Selection
Capacitor Requirement
CV: 220uF @ 25VDC
Life: >80,000 Hrs @ +75°C
FURTHER
EXTENDED
LIFETIME
»
SMT V-Chip Type:
PN: NSPE-T271M25V10X10.8NBYF
270uF, 25VDC in 10X10.8mm
2 Times Reflow
80 Sec >+217°C
40 Sec >+230°C
Peak = + 260°C
12,000Hrs @ 105°C
48,000Hrs @ +85°C
96,000Hrs @ +75°C (11 Yrs )
PN: NSPE-Y271M25V10X10.8NBYF
270uF, 25VDC in 10X10.8mm
2000Hrs @ 135°C
16,000Hrs @ 105°C
64,000Hrs @ +85°C (7.3 Yrs )
128,000Hrs @ +75°C (14.6 Yrs )
Page 13 of 25
Component Selection
Capacitor Requirement
CV: 200uF @ 25VDC
Life: 80,000 Hrs @ +75°C
Rating of 10,000 Hrs @ +105°C
» Radial Leaded Type:
» 10,000 hours @ +105°C
» 2 X 100uF
» 25VDC
PN: NRGB101M25V6.3X11F
100 µF, 25VDC, 6.3x11mm 2.5mm LS
-40C ~+105C
10,000 hrs @ +105°C
40,000 hrs @ +85°C
80,000 hrs @ +75°C
160,000 hrs @ +65°C
Low Cost &
Smallest Size
Solution
Page 14 of 25
Component Selection
For higher voltage requirements (>16VDC) look to aluminium electrolytic
capacitors
Lowest cost solution
• Aluminium E-cap :
– 100uF @ 25VDC ≈ $0.08 each
– 220uF @ 25VDC ≈ $0.12 each
• Tantalum E-cap:
– 100uF @ 25VDC = >$0.80 each
Wide range of offerings CVs – sizes: SMT & LDD
Voltages to 450VDC
Transient resistant:
– Ability to handle transient events
– Excellent inrush current characteristics
– Reverse bias tolerant
Stable characteristic under voltage bias
Open mode wear-out (safe)
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Solid Aluminium Electrolytic Capacitors
10,000 hours @ +105°C @ 6.3VDC
Capacitance
Change
Stable Over Time
(%)
Test Time (hours)
Î Solid Aluminum (polymer electrolyte) has stable characteristics (no wear-out)
Î Solid aluminum construction limited to ≤16VDC maximum rating
Page 16 of 25
Aluminium Electrolytic Capacitors – Failure Modes
Product Type:
Aluminum Electrolytic Capacitors – Liquid Electrolyte Construction
Failure Modes:
Parametric Change
Open
Intermittent
Short
Causes:
Wear-out
Electrical
Thermal
Mechanical
Corrosion
Altitude
Page 17 of 25
Aluminium Electrolytic Capacitors – Failure Modes
Product Type:
Aluminum Electrolytic Capacitors – Liquid Electrolyte Construction
Potential Failure Mode - Causes:
»
Electrical Over-stress failures ... rapid failure >> case opening - case rupture >>
or accelerated wear-out, joule heating, decreased cap, increased DF & ESR >>
open circuit (Short circuit, Arcing; under extreme overstress conditions)
Causes:
Reverse Bias
Over-voltage or Over-current
Rapid charge - discharge
Remedies - Fixes:
+ Anode
- Cathode
Assure polarity
Use within specification limits
Use alternate types:
Low ESR & High RCR, Strobe–Photoflash or Solid technology
Page 18 of 25
Aluminium Electrolytic Capacitors – Failure Modes
Product Type:
Aluminum Electrolytic Capacitors – Liquid Electrolyte Construction
Potential Failure Mode - Causes:
»
Thermal Stress failures ... end-seal compromised >> accelerated wear-out
>> open circuit
Causes:
Can Bulge - Deform
Excessive soldering (reflow) heat
Remedies - Fixes:
Use higher reflow rated component
Revise reflow conditions
Revert to radial LDD & wave soldering
Terminal Lift, Base-plate Warp
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Aluminium Electrolytic Capacitors – Failure Modes
Thermal Stress
Page 20 of 25
Aluminium Electrolytic Capacitors – Failure Modes
Product Type:
Aluminum Electrolytic Capacitors – Liquid Electrolyte Construction
Potential Failure Mode - Causes:
»
Corrosion failures ... Parametric changes, increased leakage current >> joule
heating >> leading to short or disconnection; open circuit
Causes:
Halogenated fluxes and cleaning solvents
Harsh end use environments
Remedies - Fixes:
Eliminate use of halogenated fluxes & solvents
Sealer – coatings to protect components
Page 21 of 25
Aluminium Electrolytic Capacitors – Failure Modes
Product Type:
Aluminum Electrolytic Capacitors – Liquid Electrolyte Construction
Potential Failure Mode - Causes:
»
Mechanical stress failures ... stress to leads >> end-seal
compromised >> accelerated wear-out >> open circuit
Causes:
Lead wire trimming
Stress to component after mounting to PCB
Lifting PCB by component case
Remedies - Fixes:
Review lead trimming
Review PCB handling practices
Page 22 of 25
Aluminium Electrolytic Capacitors – Failure Modes
Product Type:
Aluminum Electrolytic Capacitors – Liquid Electrolyte Construction
Potential Failure Mode - Causes:
»
Mechanical stress failures ... stress to case >> dielectric compromised >>
increased leakage current or short circuit
Causes:
Mishandling
Stacking PCBs
Improper Bulk Storage
Remedies - Fixes:
Review handling & storage practices
Page 23 of 25
Aluminium Electrolytic Capacitors – Failure Modes
Product Type:
Aluminum Electrolytic Capacitors – Liquid Electrolyte Construction
Potential Failure Mode - Causes:
»
Altitude (reduced pressure) failures ... accelerated wear-out decreased cap,
increased DF & ESR>> open circuit
Causes:
Differential between internal pressure to outside pressure
Exposure to high altitude or aviation
Altitude (m)
Air Pressure (hPa)
0
1013.3
2,000
795.0
4,000
616.4
Minimal Impact
6,000
471.8
Will Impact Lifetime
8,000
356.0
10,000
264.4
20,000
54.7
Remedies - Fixes:
Use of alternate construction (solid)
Page 24 of 25
Aluminium Electrolytic Capacitors – Failure Modes
Wear-Out Accelerators
Electrical Overstress
Over-voltage
Rapid charge–discharge
Reverse operation
Mechanical & Thermal Stress
Corrosive Agents
Cleaning solvents & fluxes
Environment
Reduced Pressure
High altitude [ >20,000 Feet = >6100 Meters ]
Page 25 of 25