View
218
Download
3
Category
Preview:
Citation preview
Corrosion and Accelerated Testing
Rob Sorensen 505-844-5558 nrsoren@sandia.gov Sandia National Laboratories
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
What is corrosion?
Aqueous (general & localized attack) • electrochemical • oxidation / reduction
Atmospheric • gas-metal reaction (slow) • condensed phase
electrochemical • pollutant gasses (ppt levels of H2S, NO2, Cl2 …)
Environmental degradation of materials
Processing
Use
Corrosion normally occurs due to defects or unexpected environments
Cruise missile fuel line
A plastic encapsulated IC failed after 5 years in dormant storage.
Defects:
Damaged passivation
Au (galvanic couple)
0
500
1000
1500
2000
2500
3000
3500
4000
0 5000 10000 15000 20000Energy (eV)
Cou
nts
W
Au
W
AlAu
Several non-traditional corrosion mechanisms exist in microelectronics that involve electrical bias
Electrolytic dissolution
Cathodic corrosion (alkalization)
Electrolytic migration
Conditions required for electrolytic migration
Applied voltage • powered system
Susceptible alloy • Ag used in ground plane • Solder • Copper
Conductive surface • flux residue (activator)
Electrolyte • High humidity Temperature cycling
• Seacoast environment (NaCl)
Corrosive environments can contact metallization features
Breach in hermetic packaging in CHP Use of encapsulants in PEMs with
high water permeability
Specific unintended exposures (e.g., military) high T, RH, [Cl-] possible
Materials Degradation Affects Reliability
8
Probability of failure-free performance, item's useful life, or a specified timeframe specified environmental duty-cycle conditions.
Cost Reliability
Lab and Field Data Accelerated Tests
Accelerated testing plays a key role in determining reliability Must be applicable to failure
modes Reproduce field failures
Acceleration factor Range of stresses Long term tests
The inverter is a significant contributor to reliability issues
9
Sun Edison – Owner/Operator (A. Golnas, “PV System Reliability: An Operator’s Perspective,” in 38th Photovoltaic Specialists Conference, Austin, TX, Jun. 2012, pp. 1–32.)
EVENTS
2003
2003
2003
2003 20
03
2003 2003
2003
2004
2004
2004
2004
2004
2004 20
04
2004
2005
2005
2005
2005
2005
2005
2005 2005
2006
2006
2006
2006
2006
2006 2006
2006
2007
2007
2007
2007
2007
2007 2007
2007
0
10
20
30
40
50
60
Inve
rter
Ligh
tnin
g
Row
Box
AC d
isco
nnec
t
PV M
odul
e
208V
/480
V Tr
ansf
orm
er
480V
/34.
5kV
Tran
sfor
mer
Mar
shal
ling
Box
Coded Category By Year
Num
ber o
f Eve
nts
20032004200520062007
Tucson Electric Springerville Plant. Sandia Study
What? Component life tests High stresses
• Single or combined • Activate “appropriate” failure modes • Measureable
Time compression (cyclic stresses) Failure analysis Why? Time Full system is expensive and complicated
What is ALT & why?
Failure Modes for Crystalline Silicon (John Wolgemuth – BP Solar)
Broken interconnects Broken Cells Corrosion Delamination and/or loss of elastic properties Encapsulant discoloration Solder bond failures Broken glass Hot Spots Ground faults Junction box and module connection failures Structural failures
Would you expect a single test to capture all of the expected failure modes?
It is important to understand the degradation mechanism and select appropriate stress level
12
Tem
pera
ture
Reaction Coordinate
25°C, 45 days
40°C, 30 days
100°C, 12 min
500°C, 5 min
13
High T data are extrapolated to “use” conditions (room temperature)
14
How you extrapolate can influence lifetime predictions.
~50% in ~ 1000 years
~50% in ~ 100 years
~50% in ~ 20 years
Two approaches to accelerated testing are used throughout industry
Qualitative Accelerated Tests • HALT tests • HAST tests • HASS tests
Quantitative Accelerated Life Tests
• Controlled application of accelerated stress
• Produces acceleration factors (AF) Usage rate acceleration
(Time compression) Overstress acceleration
Small sample size Severe level of stress
Increase reliability (product improvement) Qualify new designs Design quantitative ALT
Reliability under normal use conditions
Used to determine TTF Determine reliability
Long Time Need degradation / failure mechanisms
The Goal of an ALT program is to produce acceleration factors
Often empirical correlations
Limited root-cause analyses
++
−=
obVabVa
n
oRHRH
T1
oT1
kaE
expAF
=
testMTTFMTTFAF field
Time-to-Fail40
1
510
25
50
75
9095
99
50 80 100Cu
mul
ativ
eFa
ilure
Perc
entil
e
MTTF
ALT must capture valid degradation / failure mechanisms
17
10080604020
exp [B(T + RH)](RH) exp (E /kT)a
n
exp [E /kT + B(RH) ]a2
exp [E /kT + B/(RH)]a
exp [A/kT + B(RH)/kT + C(RH)]
RH (%)
AF
0
1
102
104
106
Calibration data collected here
Atmospheric Corrosion of Micrelectronics
Example:
• Five recognized models for corrosion in micro-electronics
• All agree at 85%RH
• Disagreement at 10%-30% prevent uniform application of either model
Acceleration factors depend on the stress characteristics
Thermal (Arrhenius) • Activation energy • Verify no mechanism change • Bin damage by time at temperature
∆T • Linear (time compressions), • Increased temperature range • Frequency analysis (rainflow counting)
Voltage • Linear (must understand relationship)
Humidity • Tends to be complex (adsorbed water)
8/1/2
011
7/26
/2011
7/21
/2011
7/16
/2011
7/11
/2011
7/6/2
011
80
70
60
50
40
30
20
10
Date and Time (MST)-July
Tem
pera
ture
(C)
Capacitor (°C)-JulyHeat Sink (°C)-JulyTorroid (°C)-JulyEnclosure (°C)-July
Variable
107550250-25
240
180
120
60
0
q
Torroid (°C)-Feb
Humidity
Rat
e
Issues with ALT
Unknown failure mechanisms Unknown / variable use environment Changing mechanisms as function
of environmental stress Difficult to control and
characterize defects Long duration experiments Evolving / improving technology
What are the likely stresses that lead to Inverter Failure?
Voltage Temperature Thermal cycling Thermal Shock Vibration Mechanical Shock Humidity Contamination Mechanical Stress ??? ???
Heat
Light Moisture
Other
How do we apply ALT to predicting end-of-life (wear out)?
Determine Failure Mechanisms (field exposures)
Understands stresses that activate the failure mechanisms
Devise ALT conditions that accelerate degradation / failure
Perform ALT (range of stressses)
Determine acceleration factors
Qualify Product
Improve Product Reliability
Validate New Designs
Estimate or Predict Reliabilty
Analysis of metal foil tape degradation
))(028.0(10 α+= tR
Generate ALT data
Develop “acceleration factors”
Module
Load RIE ×=
RIVIP ×=×= 2
Mean +2σ
-2σ
Determine performance effect
Apply acceleration factors to field
0
10
20
30
40
50
60
70
0 500 1000 1500 2000 2500
Resi
stan
ce (o
hm)
Time (Hrs)
Slide 13 Thermal Cycle
Circuit 1
Circuit 2
Circuit 3
Circuit 4
Circuit 5
Circuit 6
Circuit 7
020406080
100120140160180
0 3000 6000 9000 12000
Resis
tanc
e (o
hm)
Thermal Cycles
Ch 1
Ch 2
Ch 3
Ch 4
Ch 5
Ch 6
Use the ALT data to predict long-term performance degradation (wear-out???)
23
Summary
Accurate prediction of reliability is complex Requires understanding of degradation processes Data Driven
• Field data • Accelerated testing
Effect on performance (what is failure?) Includes uncertainty
Extra Slides
Example: Al bondpad corrosion: corrosion requires moisture and contamination & is accelerated by temperature.
26
0
500
1000
1500
2000
2500
3000
0 1000 2000 3000
Res
ista
nce
(m-o
hm)
Exposure Time (hrs)
1ug/cm2, 30C, 80% RHPEM 402
d1-w 1
d1-w 3
d1-w 4
d1-w 11
d1-w 12
d1-w 14
d1-w 15
d1-w 22
Three environmental variables (T, RH, [Cl])
No Failures!
Increasing contaminant level causes failure.
27
0
500
1000
1500
2000
2500
3000
0 50 100 150 200
Res
ista
nce
(m-o
hm)
Exposure Time (hrs)
20 ug/cm2, 30C, 80% RHPEM 414
d1-w 1
d1-w 3
d1-w 4
d1-w 11
d1-w 12
d1-w 14
d1-w 15
d1-w 22
0
500
1000
1500
2000
2500
3000
0 1 2 3
Res
ista
nce
(m-o
hm)
Exposure Time (hrs)
43 ug/cm3, 30C, 80% RHPEM 416
d1-w 1
d1-w 3
d1-w 4
d1-w 11
d1-w 12
d1-w 14
d1-w 15
d1-w 22
20X chloride
40X chloride
Distribution of failure times Not all failed Clear effect of [Cl]
Statistical treatment (life-data analysis) provides a means of analyzing the bondpad data
28
ReliaSoft Weibull++ 7 - www.ReliaSoft.comReliability vs Time Plot
β=0.2360, η=943.6290, ρ=0.8798
Time, (t)
Relia
bility
, R(t)
=1-F(
t)
0.000 1000.000200.000 400.000 600.000 800.0000.000
1.000
0.200
0.400
0.600
0.800
x 4
x 3
x 2
x 3
Reliability
Data 1Weibull-2PRRX SRM MED FMF=16/S=15
Data PointsReliability Line
Rob SorensenSandia National Labs5/28/201010:46:25 AM
10 ug/cm2, 30C, 30% RH
ReliaSoft Weibull++ 7 - www.ReliaSoft.comReliability vs Time Plot
β=0.7073, η=5.2052, ρ=0.9889
Time, (t)
Relia
bility
, R(t)
=1-F(
t)
0.000 90.00018.000 36.000 54.000 72.0000.000
1.000
0.200
0.400
0.600
0.800
x 2
Reliability
Data 1Weibull-2PRRX SRM MED FMF=14/S=0
Data PointsReliability Line
Rob SorensenSandia National Labs5/28/201010:50:59 AM
20 ug/cm2, 30C, 80% RH
ReliaSoft Weibull++ 7 - www.ReliaSoft.comReliability vs Time Plot
β=2.0355, η=0.6531, γ=0.3818, ρ=0.9576
Time, (t)
Relia
bility
, R(t)
=1-F(
t)
0.000 3.0000.600 1.200 1.800 2.4000.000
1.000
0.200
0.400
0.600
0.800
x 2
x 2
x 3
x 2
Reliability
Data 1Weibull-3PRRX SRM MED FMF=13/S=0
Data PointsReliability Line
Rob SorensenSandia National Labs5/28/201010:57:34 AM
40 ug/cm2, 30C, 80%RH
• Provides distributions • Includes suspension results • Basis for models {Pfail = f(T, RH, [Cl])}
=
testMTTFMTTFAF field
Bondpad corrosion is modeled as an additional series resistor
Voltage Comparator Circuit Prediction of the effect of corrosion on reliability
as f(storage location)
The distributed wirebond property (probability of failure) is input into an electrical system model & other component outcomes (reliability, performance threshold) can be determined
y p
0.97
0.975
0.98
0.985
0.99
0.995
1
0 20 40 60 80 100Time (years)
Desert
Gulf Coast
Arctic
Accelerated aging induced capacitor degradation.
30
500505510515520525530535540545550
0 500
Cap
acita
nce
(µF)
Time (hr)
C = 98% Co
561 661 761 861Time (hr)
Capacitance vs. Time
900V 80oC
C = 98% Co ~
~
Inverter Temperature Profile
8/1/20117/26/20117/21/20117/16/20117/11/20117/6/20117/1/2011
100
75
50
25
0
Date and Time
Tem
pera
ture
(C)
Ambient TemperatureTransformer CoreCapacitorInverter BackplateAmbient
Variable
Solectria Inverter - July
Pre failure signature
Capacitor failed in accelerated testing
Accelerated aging stresses included voltage and temperature
Accelerated Aging • Voltage & Temperature • Capacitor failure • Failure pre-cursor (decreased
capacitance)
Laboratory testing provides vital information for PV system reliability
Field Data (O&M, Failures, …)
Accelerated Testing / Lab Tests
System performance model must include wear out (end of life) information
Accelerated Aging of Tape Joint – Thermal
Cycling
ALT
Acceleration Factors
Lin k to Performance
Field failure data from very large plants indicate correlation between temperature and failure
32
Predictor Variables AC_Power Cabinet_Temp Coolant_Temp DC_AC DC_Current DC_Power DC_Voltage Inv_Amb
28 30 32 34 36 38 400.93
0.94
0.95
0.96
0.97
0.98
0.99
Cabinet Temp
AC
/DC
Failures concentrated here
50 52 54 56 58 60 62 64 66 680.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
Temperature (C)
CD
F
Surviving Units
Failed Units
Data from large plant
Cabinet Temp
<35.4 >35.4
1 Failed Inverter 222 Operational Inverters
AC/DC
<.95 >.95
10 Failed Inverters 55 Operational Inverters
0 Failed Inverters 20 Operational Inverters
N=308
N=85
Accelerated Aging for Inverter Development • No PV specific industry standard exists • HALT testing is spotty; independently applied • Separate needs identified for residential and commercial scale inverters • Failure modes identified but not in a uniform program applicable across the
industry • System predictive models will require inputs for inverters
Atmospheric Corrosion
Ceramic flat pack
Au/Al wirebond
Diode
Examples of electrolytic migration
LF amplifier - Puerto Rico • high humidity • seacoast environment (NaCl) • powered system • Ag used in ground plane
Printed wiring boards • cyclic humidity • flux residue (activator) • powered electronics • Sn/Pb solder
Recommended