moisture effects in pems intended for space applications. nepp mid-year review. alexander...
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Moisture effects in PEMs intended for space
applications.
NEPP mid-year review.
Alexander Teverovsky, Ph.D
QSS/Goddard operations
4/09/02 NEPP meeting 2
No moisture in space. Do we have any problems?
Mechanism Degradation conditions
Ground phase In space
Corrosion RH > 70%, bias -
Popcorning Assembly, m>0.1% -
Leakage current RH > 70 % -
Charge instability RH > 50 % ? T?
Swelling RH > 50 % Shrinkage
Avoid high humidity
Ensure reliability for Gnd phase
Avoid high humidity
Ensure reliability for Gnd phaseD(T)D(T)
4/09/02 NEPP meeting 3
Purpose of work (two subtasks):I. Analyze moisture evolution in PEMs to develop
risk mitigation measures and techniques.II. Evaluate moisture swelling effects in linear devices.Purpose of presentation:• To discuss the problem and our approach.• To report major achievements.• To suggest future plans.Outline:I. Moisture diffusion characteristics. How to measure
and how to use?II. Moisture swelling/shrinkage in MC.III. Environmental hysteresis in MC & linear devices
4/09/02 NEPP meeting 4
Conventional D(T) measurements: time domain
IDT QFP144, DC 9832 at 85C/85%RH
0
5
10
15
20
25
0 50 100 150 200 250 300 350 400 450
time, hr
dM, m
g
pac_1
pac_2
pac_3
MC_1
MC_2
MC_3
Diffusion coefficient calculations
00.2
0.40.6
0.81
1.21.4
1.61.8
2
0 20 40 60 80 100 120 140 160
t^0.5/L
dM/M
sat
D = 3.3*10-8 sm2/s
T = Ti
D(T) = Do exp(-U/kT)
Di
D(T) in literature: Kitano’88?
D(T) in literature: Kitano’88?
4/09/02 NEPP meeting 5
New D(T) technique:temperature domainIDT QFP144 molding compound, 121C/100%/24hr
0
2
4
6
8
0 50 100 150 200
temperature, deg.C
dM(t)
, mg
IDT QFP144
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
2 2.25 2.5 2.75 3 3.25 3.5
1000/T, 1/K
D, c
m^2
/s
MC 121C/100%/24h
package 121C/100%/192hr
MC after 85/85/186
dt
dT
dT
TdMTdM
dM
hTD
)()(
2)( 2
2dt
dT
dT
TdMTdM
dM
hTD
)()(
2)( 2
2
Equipment:TGA orT-chamber
Equipment:TGA orT-chamber
4/09/02 NEPP meeting 6
D(T) measurement results.Saturation at 85C/100%RH/168hr
Mfr.: Actel V3Semi AMD XILINX
Package: QFP144 QFP160 PLCC32 QFP240
DC: 9505 9652 9550 9608
dM, % 0.52 0.44 0.49 0.43
U, eV 0.5 0.45 0.31 0.41
D20, sm2/s 3E-9 2.4E-9 3.2E-8 4.5E-9
D85, sm2/s 1.2E-7 6.9E-8 3.2E-7 9.4E-8
D130, sm2/s 7.8E-7 3.7E-7 1E-6 4.3E-7
4/09/02 NEPP meeting 7
In-situ D(T) technique.Areas of application.
• Lot characterization of molding compound.(ROBOCOTS: need rapid assessment methods)
• Evaluation of moisture leaks along the leads of a plastic package. (CSAM: gaps of > 0.1 m)
• Virtual qualification of moisture content evolution during pre-launch period.
• HAST alternative. (application-tailored testing).
• Calculation of characteristic times of moisture diffusion: (T) = 0.85h2/D(T)
4/09/02 NEPP meeting 8
Bake-out conditions.
Package thickness 40 oC 125 oC 150 oC
DIP-24 3.8 mm 1929(1608-1632)
57(48)
26.5
DIP-8 3.2 mm 1368(1608-1632)
40.5(48)
18.8
PQFP-44 2 mm 534(504-1632)
16(18-48)
7.3
PLCC-32 3 mm 1202(1608-1632)
36(48)
16.5
TSOP-32 1 mm 134(120-456)
4(4-14)
1.8
Calculated (hrs) and JEDEC recommendations (x-x).
4/09/02 NEPP meeting 9
Do we need HAST?
Stewart Peck [86]:
kTERHAt an
f exp)(
HAST:1. biased and unbiased ($$$ and $)
2. JEDEC – 96 hrs, NAVSEA SD18 –150 hrs, projects – 250 hrs
3. 130oC > oper.T
4. Power parts?
HAST:1. biased and unbiased ($$$ and $)
2. JEDEC – 96 hrs, NAVSEA SD18 –150 hrs, projects – 250 hrs
3. 130oC > oper.T
4. Power parts?
Equivalent life time at 25 oC/ 60% ambient
conditions (HAST 130oC/85% 100 hrs)
0
100
200
300
400
500
600
700
10 20 30 40 50 60 70
device temperature, oC
life
time,
yea
rs
0
10
20
30
40
50
60
70
80
90
effe
ctiv
e R
H, %
RH = Pa/Ps(T)
4/09/02 NEPP meeting 10
Do we need HAST alternative?
Alternative: Unbiased HAST => (ionic activation) + HTB stress
Alternative: Unbiased HAST => (ionic activation) + HTB stress
AMAM
f
nf
AM
AMK
1
][][ 02
kT
UKK exp0
The equilibrium constant:
0UU In a medium with low :
kT
UAn
2exp 0
Ionic dissociation in polymer:
4/09/02 NEPP meeting 11
Bias HAST alternative: Unbiased HAST + HTB
Moisture distribution after diffusion during 0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1X/h
C/C
o
0 0.001
0.003 0.010
0.030 0.100
0.300 0.600
0.800 1.000
1.500 2.000
D(T) data Pckg type
C(t,x) calculations
Test conditions:T/RH/t HAST, T/t HTB
)(
)()( 0
TC
tCtRH eff
Acceleration factor
4/09/02 NEPP meeting 12
Part II. Moisture swelling.
• Is it important?
AE[(MC - LF)T + m],
- hygroscopic expansion coefficient (rare to find in literature).At =0.1-0.4 and m~0.5%, the strain is equivalent to deformation at T~30-120 oC.
• How to measure ? Conventional techniques:
Instrumental microscope (poor accuracy on PEMs); Moire interferometry (CALCE – special equipm., grating corrosion); Strain gage (corrosion);
• Suggestion: Hygroscopic weighting – simple, accurate, fast, in-situ.
4/09/02 NEPP meeting 13
Hygroscopic weighting technique
Necessary equipment:
• Balance ±0.1 mg;
• Beaker;
• Piece of wire;
Liquid.(low molecular weight perfluoropolyether fluid, 1.77 g/cc, Tb = 175oC)
Archimedes of SyracuseBorn: 287 BC in Syracuse, Sicily
liquid
imPPV
init
init
initmoist
initmoist
V
M
MM
VV
3
1
4/09/02 NEPP meeting 14
Hygroscopic weighting technique
Standard deviation: 3 to 5 %
In-situ: MC (0.8-0.9)pac MC
LF
MC
LF
MC
LF
pacMC
V
VV
V
1
1
4/09/02 NEPP meeting 15
High T exposure shrinks packages?
IDT QFP144 Effect of Bake Temperature
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
dM
, (d
V),
%
dVdm
205 oC 2hr
165 oC 24hr
125 oC 96hr
No popcorning.Is SMT a reliability risk?
Qualification?
No popcorning.Is SMT a reliability risk?
Qualification?
4/09/02 NEPP meeting 16
Part III. Environmental hysteresis in PEMs
• Assumption:Linear devices are most sensitive to swelling/shrinkage
effects and are known HAST failures.
• Parts:Several types of Vref, Opamp, DAC, ADC in different
plastic and ceramic packages used in NASA projects have been purchased.
• Measurements:ATE A540. Capabilities restored. Programming is
ongoing.A set-up for high precision measurements.
4/09/02 NEPP meeting 17
Set-up block-diagram
PC-based System
for linear devices:• I => pA range• V=>µV range (ppm)• T=> -120 to +200 °C• Automatic switching,
measurements and recording
Reliability precursors?
Cherry picking?
Reliability precursors?
Cherry picking?
4/09/02 NEPP meeting 18
Temperature hysteresis
AD780 average deviation
-200
0
200
400
600
-50 -25 0 25 50 75 100
temperature, deg.C
dV
, pp
m
AR
BR
Mfr. data?
20 ppm/1000 hr
Mfr. data?
20 ppm/1000 hr
4/09/02 NEPP meeting 19
Vref errors in ADC, DAC
Resolution, bit 1LSB, ppm8 390610 97712 24414 6116 15
Temperature effect: ~ 50 – 200 ppm
LT hysteresis: ~ 150 – 300 ppm
Radiation effects [AD2710, JPL’97]:
Co60, 100 krad(Si): ~ 150 ppm
protons, 200 MeV, 45 krad(Si): ~ 500 ppm
LT hysteresis causes significant errorLT hysteresis causes significant error
4/09/02 NEPP meeting 20
Effect of external mechanical stress
LT1461 Stress effect
-1800
-1500
-1200
-900
-600
-300
0
300
-50 -25 0 25 50 75 100
temperature, deg.C
dV
, p
pm
free
attached
AD780 Stress effect
-800-600
-400-200
0
200400
-50 -25 0 25 50 75 100
temperature, deg.C
dV, p
pm
BR
BR-at_bake
Strain Gage in pot epoxy (Struers)
-0.8
-0.6
-0.4
-0.2
0
0.2
-50 -30 -10 10 30 50 70 90
temperature, deg.C
defo
rm
ati
on
, %
CTE = 73 ppm/oC
epoxy
to set-upT - chamber
External stress: no additional LT hysteresis
External stress: no additional LT hysteresis
4/09/02 NEPP meeting 21
Relaxation at RT after LT exposure
AD789. Relaxation at RT after exposure to -65 deg.C 15 min
0
50
100
150
200
250
300
0 100 200 300 400 500 600 700 800time, hr
dV
, p
pm
AR
BR
LT1461. Relaxation at RT after exposure to 165 deg.C 15 min
y = -0.0017x + 175.47
0
50
100
150
200
250
300
0 200 400 600 800
time, hr
dV
, pp
m
Relaxation: • RT: >1200 hrs; • 85 oC: minutes; • 75 oC & 55 oC ?
Questions: • Multiple TC? • T & duration of exposure? • Mechanical integrity? • Relaxation or switching?
Questions: • Multiple TC? • T & duration of exposure? • Mechanical integrity? • Relaxation or switching?
4/09/02 NEPP meeting 22
Moisture hysteresis
2h = 1.5 mmD85=4e-8 cm2/s
= 0.85h2/D 35 hr
AD780 ageing at 85. Different preconditioning
-200
-150
-100
-50
0
50
100
150
200
250
0.1 1 10 100 1000
time, hr
dV5,
ppm
AR 85/85
AR
BR 85/85
BR
Moist. Hysteresis:85/85 => 150-250ppm
Moist. Hysteresis:85/85 => 150-250ppm
4/09/02 NEPP meeting 23
Vacuum hysteresis
AD780 Vacuum test
-50
-40
-30
-20
-10
0
0 50 100 150 200
time, hrd
V5
, pp
m
AR
BR
LT1461 vacuum test
-140-120-100-80-60-40-20
020
0 50 100 150 200
time, hr
dV
, p
pm Vacuum hysteresis:
dV > 50-100 ppm; t > 1500 hrs
Vacuum hysteresis: dV > 50-100 ppm; t > 1500 hrs
2h = 1.5 mmD20 = 3E-9 cm2/s
= 0.85h2/D 1500 hr
4/09/02 NEPP meeting 24
Effect of preconditioning on LT hysteresis
AD780. Environmental hysteresis.
-300
-200
-100
0
100
200
300
400
500
600
700
init
afte
r -6
5
bake
150
/15
afte
r -6
5
85/8
5/16
8
afte
r -6
5
bake
150
/15
afte
r -6
5
85/1
00%
/187
afte
r -6
5
150/
24 b
ake
afte
r -6
5
121C
/100
/121
afte
r -6
5
bake
150
/24
afte
r -6
5
dV
, pp
m
AR
BR
LT hysteresis: - Humid cond. ~ 170 ppm
- Dry cond.: ~ 265 ppm
synergistic effectof T & vacuum?
synergistic effectof T & vacuum?
Possible cause of HAST/PCT failures
4/09/02 NEPP meeting 25
Expected results in 2002:
• Two in-situ methods for moisture characterization of molding compounds in PEMs.
• Analysis of moisture diffusion in different PEMs and recommendations for moisture-prevention measures.
• Analysis of environmental hysteresis effects caused by LT, moisture, and vacuum conditions in Vref PEMs.
• Deliverables: papers, presentations, recommendations.
4/09/02 NEPP meeting 26
Suggestions for 2003
• Analysis of environmental hysteresis (T, RH, vacuum) in MC and advanced linear PEMs (opamps, AD, DA converters).
• Experimental and theoretical analysis of effectiveness of HAST for space applications. Development of adequate accelerated testing technique.
• Virtual qualification of moisture evolution in PEMs to mitigate risks with flight parts.