May 9, 2016 1

Reliability Prediction based on Multiple Accelerated Life Tests

Prof. Joseph B. Bernstein

Faculty of Engineering Ariel University

Josephbe@ariel.ac.il

May 9, 2016 2

Handbooks look to find MTBF

Suppliers need to report FIT; (l)

MTBF = 109/FIT

FIT = 109/MTBF

May 9, 2016 3

Constant Rate Model Works !!!

If it ain’t broke, don’t fix it.

May 9, 2016 4

Field Data Results Example

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

0

2

4

6

8

10

12

14

16

18

20

Feb

-03

Dec

-03

Oct

-04

Au

g-0

5

Jun

-06

Ap

r-07

Feb

-08

Dec

-08

Cu

mu

lati

ve

Wo

rkin

g M

on

ths

Mo

nth

ly F

ail

ed IC

s

Cumulative Working Months

Monthly Failed ICs

0.00%

0.02%

0.04%

0.06%

0.08%

0.10%

0.12%

0.14%

Feb

-03

Dec

-03

Oct

-04

Au

g-0

5

Jun

-06

Ap

r-0

7

Feb

-08

Dec

-08

Fai

lure

Rat

e [%

]

Monthly Failure Rate Cumulative Failure Rate

LOOK !?! Constant Rate

MTBF model works !

6-Sigma monitored failure

return for electronic system.

This is typical for most

observed electronic devices.

May 9, 2016 5

MILITARY HANDBOOK 217

PREDICTION (part-count)

λp =λb πT πC πV πSR πQ πE Where;

lp = part failure rate,

lb = base failure rate,

πT = temperature factor,

πC = capacitance factor,

πV = voltage stress factor,

πSR = series resistance factor,

πQ = quality factor,

πE = environment factor.

Values are assigned to the base failure rate and each stress

factor from tables in MIL-HDBK 217

One failure rate per part, but do factors multiply ?

May 9, 2016 6

A B C D Success =

RT(ABCD)

Success = Probability of Zero Failures

Reliability of each component is modeled as a

constant rate Poisson Process, l:

Ri = e-lit

So each factor adds to lT

RT = e-lA t ·e-lB t ·e-lC t ·e-lD t = e- lT t

Where: lT = lA + lB + lC + lD

May 9, 2016 7

JEDEC Publication JEP 122G Rev. Oct. 2011

I Bet You didn’t know JEDEC says this: 2 Terms and definitions (cont’d)

quoted failure rate: The predicted failure rate for typical

operating conditions. (This is the FIT)

NOTE: The quoted failure rate is calculated from the observed failure rate under accelerated stress conditions multiplied by an

accelerated factor; e.g…..

“ When multiple failure mechanisms and thus

multiple acceleration factors are involved, then

a proper summation technique, e.g., sum-of-

the-failure rates method, is required.”

May 9, 2016 8

Proper Failure Rate Estimation

Serial System Reliability

Model

FM1 FM2 FM3

Nth Component

Each component is comprised of

several sub-components in

proportion to their function and

relative reliability stress.

 

lO = lO '·PO = (B1-OlHCI +B2-OlTDDB +B3-OlEM +B4-OlNBTI )·PO

 

lD = lD '·PD = (B1-DlHCI +B2-DlTDDB +B3-DlEM +B4-DlNBTI )·PD

 

lS = lS '·PS = (B1-SlHCI +B2-SlTDDB +B3-SlEM +B4-SlNBTI )·PS

 

lJ = lJ '·PJ = (B1-JlHCI +B2-JlTDDB +B3-JlEM +B4-JlNBTI )·PJ

Base Failure rate can be determined at

various accelerated conditions in order

to normalize the matrix and make

physics based reliability assessment

from test data combined with knowledge

of the application

May 9, 2016 9

3.00E+08

4.00E+08

5.00E+08

6.00E+08

7.00E+08

8.00E+08

9.00E+08

1 1.5 2 2.5 3

Performance vs. Reliability

I could double the speed for free If I KNOW the reliability, maybe I CAN improve performance !?!?

Why not operate here? Here is Nominal

Freq.

(Hz)

(45 nm FPGA)

May 9, 2016 10

“In G-d we trust; all others

must bring data.”

May 9, 2016 11

Multiple Mechanisms Don’t Add Up !!!

Single Mechanism Model (traditional thinking):

–AFsystem = AFThermal* AFElectrical

–So, 1/MTTFuse = 1/(MTTFtest *AFMM)

Multiple Mechanism Model: –1/MTTFuse = P1/(MTTFtest *AFmech1) + P2/(MTTFtest *AFmech2)

–Therefore, the effective AF for multiple mechanisms is:

AFMM = 1

P1 P2

AFmech1 AFmech2

•The True acceleration factor is the SMALLER one, not the one which exposes a failure at accelerated test.

+

May 9, 2016 12

To Accelerate is Human,

But, To extrapolate

DIVINE

May 9, 2016 13

Separation of Mechanisms - MTOL

Failure Mechanisms can be separated by

properly selecting test conditions.

This is in contrast to HTOL at One condition.

Multi-Temperature Overstress Lifetest

•High T, High F and Low Voltage tests EM

•High T, Low F and High Voltage tests NBTI

•Low T, High F and High Voltage tests HCI

May 9, 2016 14

FPGA Ring-Oscillator Verification

•FPGA is built from

the basic CMOS

Cells in the listed

technology node

•Entire device is filled

with oscillators

•Continuous

measurements

eliminates recover !

•45nm and 28nm

2n + 1 stages

•150 oscillators of 3 stages

•50 oscillators of 5 stages

•20 oscillators of 33 stages

•3 oscillators of 333 stages

•1 oscillator of 1001 stages

•Incorporates Averaging

with number of stages

May 9, 2016 15

y = 7.159E+08e-1.173E-03x

706000000

708000000

710000000

712000000

714000000

716000000

718000000

0 2 4 6 8 10 12

Ring Frequency versus square-root of time

Degradation Slope Considering

Physics

Slope(a) = DF/F0/Dsqrt(t)

TTF = 10%/Slope

FIT = 109/TTF

FIT = 109 x (10a)2

Square-root of time (hrs)

Frequency (Hz)

a

May 9, 2016 16

28nm Ring Oscillator Frequency

Distribution

0.00E+00

2.00E-02

4.00E-02

6.00E-02

8.00E-02

1.00E-01

1.20E-01

1.40E-01

1.60E-01

1.80E-01

2.00E-01

5000000 50000000 500000000

Weibull Plot of

High Frequency

rings

b = 7.8

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

8.2 8.4 8.6 8.8

Weibull

Weibull Plot shows

Poisson distribution of

degradation within

the chip after less

than 100 hours of

degradation

Log (Freq)

b=1.4 -6

-5

-4

-3

-2

-1

0

1

2

0.001 0.01 0.1 1

Weibull

May 9, 2016 17

Model Parameter Extraction

0.01

0.1

1

10

100

30 35 40 45 50 55

EA = 0.52 eV

-61

-60

-59

-58

-57

-56

-55

-54

-53

35 40 45 50 55

EA = -0.38 eV

FIT = V 23

0.000001

0.000100

0.010000

1.000000

100.000000

10000.000000

1 1.5 2 2.5 3 3.5

HCI Arrhenius

BTI Arrhenius

HCI Voltage factor

Through separation of

mechanisms, Activation

energies and voltage/current

acceleration factors are

determined at the chip level

May 9, 2016 18

Simple to use Excel File G(HCI)= 22.7 Ea(HCI)= -0.375

G(BTI)= 3.8 Ea(BTI)= 0.52

G(EM)= 3.8 Ea(EM)= 1.24

V(oper)= 1

T(oper)= 318

Kboltz= 0.00008617

Conditions

KT T°C V F(GHz) HCI BTI EM Measured Ratio Calculated FIT Experimental

0.01818187 -62 1.2 1 56847640831 3.62741E-11 4.80938E-30 30 95% 2.86E+01 0.03429566 125 1.2 1 3516678.425 2.48596E-05 3.96698E-16 997.4 99% 9.88E+02

0.03670842 153 1.2 1 1713998.047 6.73446E-05 4.27115E-15 3672 100% 3.67E+03

0.02050846 -35 2.5 0.5 4.71349E+16 1.30044E-07 8.96311E-26 23750000 100% 2.38E+07

0.03679459 154 1.2 0 0 6.96163E-05 0 2420 100% 2.42E+03

0.04291266 225 2.8 1 8.82364E+13 0.228176427 1.41211E-11 11535700 107% 1.24E+07

0.03558821 140 2.2 0 0 0.001927405 0 66200 101% 6.70E+04

0.02162867 -22 2.8 1 4.78991E+17 1.51187E-06 6.31726E-24 240000000 101% 2.41E+08 0.02438611 10 3 1 3.22896E+17 4.90037E-05 5.36768E-21 156000000 104% 1.63E+08

INVERSE MATRIX P-values -4.45217E-28 2.12157E-17 -3.96313E-20 5.03873E-10

0 0 14364.46052 34761994.46

2.34129E+14 -8513.801753 -2.26489E+14 3.11618E+17

Spreadsheet

shows 7-orders

of magnitude

agreement ±

5%

Constants

extrapolated from

experiments

May 9, 2016 19

1

10

100

1000

10000

100000

1000000

10000000

-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

FIT

Temp °C

1.4V at 2 GHz

1.2V at 1 GHz

1.2V at 10 MHz

FIT vs. Temperature for 45nm FPGA

Reliability Prediction !!!

3 Dominant Mechanisms throughout the useful range of

operating conditions

HCI

EM BTI

May 9, 2016 20

0.0001

0.001

0.01

0.1

1

10

100

1000

10000

100000

-50 -30 -10 10 30 50 70 90 110 130 150

Prediction for 28nm

BTI

FIT

(1.0 V nominal)

1 V

0.8 V

1.2 V

May 9, 2016 21

Observations

•What reliability prediction tool can

give you these results?

•No handbook can calculate the effects of

multiple mechanisms simultaneously.

•Reliability must fit the engineering goals !

• Physics Based Reliability

Qualification is Required