Moisture effects in PEMs intended for space applications. NEPP mid-year review. Alexander Teverovsky, Ph.D QSS/Goddard operations [email protected]

Moisture effects in PEMs intended for space

applications.

NEPP mid-year review.

Alexander Teverovsky, Ph.D

QSS/Goddard operations

[email protected]

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)


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


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?


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


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


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)


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).


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)


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:


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


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.


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


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


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?


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.


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?


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


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


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


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?


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


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


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


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.


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.

Documents

Moisture effects in PEMs intended for space applications. NEPP mid-year review. Alexander Teverovsky, Ph.D QSS/Goddard operations [email protected]