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Accelerated Stress Testing and Reliability Conference
Thin MLCC (Multi-Layer Ceramic Capacitor) Reliability Evaluation Using an Accelerated Ramp
Voltage Test
John Scarpulla
The Aerospace Corporation
September 28- 30 2016, Pensacola Beach, Florida January-4-17 1
Accelerated Stress Testing and Reliability Conference
Thin* Layer MLCCs
www.ieee-astr.org September 28- 30 2016, Pensacola Beach, Florida
15 μF
22 μF
0.1 μF
Standard MLCC DUT
(end-bell terminations)
*~2-4 µm thick vs >20 µm in heritage devices
Ubiquitous
Construction
Accelerated Stress Testing and Reliability Conference
Sample MLCC Cross-Sections
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• Concerns:
• A: Irregular metal layers
• B: Thin polycrystalline ceramic
• C: Voids & defects
• ?: Oxygen vacancies?
• ?: Other potential failure mechanisms?
A
B
C
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Thinner and Thinner MLCCs
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• Dielectric thickness are steadily decreasing
– 1970: 25 – 50µm
– 1980: 18 – 25 µm
– 1990: 10 – 20 µm
– 2000 8 – 15 µm
– 2010 4 – 8 µm
– 2016 2 – 5 µm
– Future submicron BME = base metal electrode
PME = precious metal electrode
IDC = inter-digitated capacitor
BMEs
PMEs
• Our technique useful for:
MLCCs
end bell capacitors
BMEs
PMEs
IDCs
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Need for Improved Test Methods
• Limited failures in traditional long constant stress tests yield ambiguous reliability results
– 1000’s-hour lifetests often give essentially zero failures
• Our method :
– is faster & provides 100% failures
– can predict “teenage mortality”
• (an elevated failure rate in 1st 10,000hrs)
– can determine screening efficacy
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The effective thickness concept:
Each defect is assigned an “effective thickness” irrespective of its physical nature or observability
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kT
EBEt An
F exp
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Extracting xeff
• Recall the P&V* model
• Electric field
• Solve for xeff
– which states that the effective thickness can be extracted from the failure time (at constant Voltage)
– But …Voltage is not constant in actual usage
– …P&V model parameters are unknown
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kT
EBEt An
F exp
*T. Procopowicz and R. Vaskas, 1968
effxVE
nkT
EB
tVx
An
nF
eff
exp1
1 EA
n
B
coefficients:
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Ramp Voltage Technique
• Generalize the P&V model to non-constant stress
• Assume a ramp voltage with T constant
• Ramped test produce 100% failures
– (We reliability engineers live or die with failures!)
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F Ft t
dttkT
E
x
tV
Bdttf A
n
eff0 0
1exp1
)( Cumulative damage function
RttV
nkT
ERnBVx Annn
Feff exp111 Extract xeff from ramped
breakdown voltages
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Ramped Breakdown Test Results
• Test setup • Ramped breakdowns
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This array is called BV and is referred to as the "long" BV vector
50 100 150 200 250 3000
0.2
0.4
0.6
0.8
1
Failure Voltage (Volts)
Fra
ctio
n F
aile
d
120C
103
77
… +
DUT board in temperature chamber
Agilent 34980ASwitch/Measure
system
computerBallast resistor and switch board
Kepco BHK 300-0.6MGramp voltage generator
32 MLCCs per test “cell”
32 9 cells = 288 failures
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Extract P&V coefficients from Ramp data
• Key assumption:
– VF95’s are at nominal thickness x0
– Allows the P&V coefficients to be extracted
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kTn
Ex
n
nRnB
nV A
F1
ln1
ln1lnln1
1ln 095
bxmxmy 2211transformation and multiple linear regression
95th percentiles of VF from ramped breakdown test
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P&V regression results
• VF95 9-cell multiple regression
regression
coefficients
P&Vmodel
coefficients
units
m1 0.115 n 7.723 dimensionless
m2 0.132 EA 1.154 eV
b 0.679 B 1.7510-3 hr(V/m)n
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0 1 2 3 4 54.6
4.8
5
5.2
5.4
5.6
x1 = ln(R)
y =
ln
(V9
5)
T = 77C
103
120
Now the effective thicknesses can be extracted, but first….
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Seeds model
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• Seeds* model -- yield worsens with defect density and area - basic semiconductor yield model
– (it approximates a Poisson distribution of defects)
• Solve for cumulative defect density D :
– Expressed as a function of the xeff
– Typical units are defects/cm2
DAYPf
1
111
f
feff
P
P
AxD
1
1)(
DATA TRANSFORMATION
VF xeff Pf D
*R. Seeds 1967
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D vs. xeff curve MLCC properties
quantity value units
Capacitance C 0.1 µF
Case size - 0402 -
Rated voltage Vrat 10 V
Rated temperature
Trat 125 °C
Active electrode length
L 0.77 mm
Active electrode width
W 0.27 mm
Number of layers N 73 -
Total active area A 0.152 cm2
Nominal dielectric thickness
x0 3.70 µm
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1 2 3 4 50.01
0.1
1
10
100
1 103
1 104
effective thickness, xeff (um)
def
ect den
sity
, D
(cm
-2)
90% C.I.
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An MLCC Birth to Retirement in 4 phases
phase & duration
V (V)
T (C)
effective thickness
xeff (m)
defect density
Du
(cm-2)
Cum. failure
prob. (%)
Cond. failure
prob. (%)
1
DWV test
1 sec
25 25 0.0586 1.31210-2 0.2 0.2
2
Part screen 168 hrs 10 125 0.566 1.71610-2 0.26018 6.1310-4
3
Board burn-in 320 hrs
8 85 0.567 1.71710-2 0.26026 7.9910-7
4 Mission 15 yrs
8 85 1.14 2.32210-2 0.352 9.1710-2
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xeff for the four MLCC Life Phases
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1
1
111 exp
nkT
E
B
tVx A
n
eff
n
AnAneff
kT
E
B
tV
kT
E
B
tVx
1
2
22
1
112 expexp
n
AnAnAnAneff
kT
E
B
tV
kT
E
B
tV
kT
E
B
tV
kT
E
B
tVx
1
4
44
3
33
2
22
1
114 expexpexpexp
n
AnAnAneff
kT
E
B
tV
kT
E
B
tV
kT
E
B
tVx
1
3
33
2
22
1
113 expexpexp
DWV is part of manufacturing
screening
mission
Accelerated Stress Testing and Reliability Conference
Unconditional D vs. xeff curve
• Usage times at rated conditions (125C, 10V) map to ever increasing xeff
• Curve is unconditioned for the DWV screen test (0.2%)
• From this curve any desired reliability predictions can be made
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1 sec
1 min
1 hr
1 day
1 wk
1 mo
1 yr
DWV screen
5 10 15 20 yrs
0 1 2 3 4 5 0.01
0.1
1
10
100
1 10 3
´
1 10 4
´
effective thickness, xeff (um)
def
ect
den
sity
, D
(cm
-2)
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0.1
1
10
100
0 5 10 15
ave
rage
fai
lure
rat
e (
FITs
)
mission time (years)
Example Reliability Prediction
• Failure rate
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• Effective thicknesses mapped
V= 8 V
T = 85C 0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 5 10 15
effe
ctiv
e t
hic
kne
ss x
eff(
m)
mission time (years)
“Standard” burn-in
7 FITs
@15 yrs
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Example Reliability Prediction (Fluctuating Temperature)
• Failure rate
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• Effective thicknesses mapped
0.1
1
10
100
0 5 10 15
ave
rage
fai
lure
rat
e (
FITs
)
mission time (years)
V= 8 V
T fluctuates yearly
between 85C & 50C 0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 5 10 15
effe
ctiv
e t
hic
kne
ss x
eff(
m)
mission time (years)
“Standard” burn-in
Temperature
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1
10
100
1000
0 5 10 15
ave
rage
fai
lure
rat
e (
FITs
)
mission time (years)
Example Reliability Prediction with reduced burn-in
• Failure rate
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• Effective thicknesses mapped
V= 8 V
T = 85C 0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 5 10 15
effe
ctiv
e t
hic
kne
ss x
eff(
m)
mission time (years)
With burn-in reduced 10X in duration and 25C in temperature
xeff smaller in first year –
Higher failure rate
“teenage” mortality
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Compare to the Traditional Constant Failure Rate
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1E-091E-08
0.00000010.000001
0.000010.0001
0.0010.01
0.11
10100
100010000
0 1 2 3 4 5
def
ect
den
sity
,D(c
m-2
)
effective thickness, xeff (m)
traditional method – inconceivably low defect densities
ramp method
• Assume an exponential distribution with = 7 FITs
• Use same P&V coefficients (not available traditionally)
• RESULT:
– Shows that conventional method is overly optimistic
– Cannot predict “teenage mortality” despite actual P&V coefficients
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Conclusions
• A new method of MLCC testing has been proposed
– Effective thickness concept
– Ramp voltage test technique is fast (2 wks for this example)
– Seeds defect model (from the semiconductor industry)
– Allows more realistic computations of failure rate • under realistic variable usage conditions
– Permits essentially 100% failures (We live or die on failures)
– Extracts P&V model coefficients
– Evaluates screening stratagems
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