Ageing and Life Prediction Conference 2008 Palmen

8/12/2019 Ageing and Life Prediction Conference 2008 Palmen

1/42

Copyright VTT

Ageing and life prediction

Helge Palmn, 25.9.2008CEEES, Helsinki


2/42

2

Ageing and ageing effects

Life prediction Accelerated life-tests

Test planning

Acceleration factors

Case example Problems in life prediction and

reliability testing

Corrosion on PCB

Contents


3/42

3

Ageing and ageing effects

Stresses that cause ageing:

Temperature Temperature variation

Humidity

Mechanical stresses

vibration and shocks handling

Voltage and current

Electrical overstress and electrostatic discharges

Other considerations include factors such as Number of starts/power-ups (on off cycling)

Biological effects

Etc.


4/42

4

Failure modes:

Component failures exhibit themselves as:

opens

shorts or changes in

leakage currents

breakdown voltages

operational parameters

functional operation


5/42

5

Ageing / failure mechanisms

The effect of stresses is cumulative damage or degradation is

progressive

Integrated circuits, semiconductor devices:

Gate oxide breakdown

Ionic contamination

Electromigration

Hot electrons

Corrosion

Intermetallic reactions, contact migration Breakdown of oxide or pn-junctions due to EOS/ESD

Etc.


6/42

6

Passive components: Drying of electrolytic capacitors

Mechanical damage to chip components or solder joints due to

Stresses due to vibration or mechanical shocks

Temperature (high/low, variation due to TCE diferences)

Bending, handling

Corrosion metal parts, component pins, PCB tracks etc.

Metallic parts:

Corrosion

Whisker growth

Mechanical damage (stresses due to vibration, shocks, bending,etc.)


7/42

7

Connectors

Contact corrosion (humidity, pollutants), oxidation and / orcontamination

Fretting corrosion

Mechanical damage to solder joints

Cables

Insulation / shield material (polymer) degradation mechanisms- due to moisture, heat or radiation

Loss of plasticizer leading to cracking

Mechanical ageing or damage Chemical attack

Electromechanical components:

Contact corrosion, oxidation and / or contamination

Coil burn-out or insulation material degradation Spacer degradation (plastic material, loss of plasticizer)


8/42

8

Life predictionReliability data can be found based on

Operational experience field data collection

Usually tells only about random failures before any wear-out has taken place

Reliability tests / Life tests

Knowledge about use conditions - stresses

What are the relevant failure mechanisms technology,materials

Acceleration models are also needed

Prediction models (such as MIL-STD-217F, Notice 2 etc.)

Unfortunately these dont include models for wear-out


9/42

9

Accelerated life tests Simulation of the products

life cycle, including:

transport

storage

assembly and installation use/operation

maintenance

Purpose to find

, MTTF failure mechanisms

Life tests especially aim at:

useful life failure rate,lifetime

Stress screening in turnaims at eliminating the earlyfailures


10/42

10

Accelerated life tests, cont.

Goals

to study occurrence of failures during the life cycle

transport, storage, installation and operation simulated

find distribution of failures in time

find out failure mechanisms

How

accelerated conditions or increased frequency of stresses are used

stresses:

temperature and temperature change

mechanical stresses (bump, shock, vibration)

Humidity

etc.


11/42

11

Accelerated life tests, cont.

Step stress test, principle:

This test is useful in quickly finding the limits and weak points in the design

The test is continued until: enough margin has been reached

all fail

irrelevant failures appear

Stress

level

Time

Functional limit

Technological limit

Figure 2. Principle of step-stress testing


12/42

12

Test planning

Steps:

1. Definition of requirements (reliability, life time)

2. Environmental conditions

3. Determination of duty cycles4. Extreme conditions (temperature, humidity, mechanical,

electrical., EMI/EOS/ESD etc.)

5. Planning of life test

tests describing transport, storage, installation tests describing operation


13/42

13

Step stress test example, testing of electromagnetic

relays

Figure 1. Step stress test results for one relay

Step stress, relay no 32

0,0

20,0

40,0

60,0

80,0

100,0

120,0

140,0

160,0

180,0

200,0

0 h 55 C 168 h 70 C 168 h 100 C 242 h 115 C 160 h 130 C 183 h 140 C 169 h

Temperature and test time at step

Delays[ms],conctactresistance[m]

Delay 1

1

Delay 2

2

R


14/42

14

Acceleration factors

Acceleration factors are needed for:

Temperature

Change of temperature

Humidity Mechanical stress

Other considerations


15/42

15

Acceleration factors, continued

Temperature

Arrhenius:

A = tref/ttest = e[EA/k * (1/Tref - 1/Ttest)]

Activation energies, problems:

depend on failure mechanism

not always known

multiple failure mechanisms exist


16/42

16

Activation energies for different failure mechanisms

Failure mechanism (semiconductor devices) Activation energy, EA [eV]

Ionic contamination 1,0

Dielectric breakdown (TDDB) 0,2 - 0,35 (0,3)

Hot carrier trapping in oxide -0,06

Electromigration 0,5

Contact electromigration 0,9

(Al at sidewall) 0,8 - 1,4

Contact metal migration through barrier layer 1,8

Au-Al intermetallic growth 1,0

Corrosion, electrolytic 0,79 - 0,9

And what about failure mechanisms for other components, parts, materials etc.


17/42

17

Effect of activation energy on acceleration factor

1

10

100

1000

10000

100000

25 35 45 55 65 75 85 95 105 115

Test temperature [C]

Accelera

tionfactor

1,2 eV

1,0 eV

0,9 eV0,8

0,7 eV

0,5 eV

0,3 eV


18/42

18


Change of temperature

A =

n

use

test

use

test

ttx

daycyclesdaycycles

/

/

The acceleration factor is made of two factors - duty cycleand temperature difference, (n 1):


19/42

19


Humidity

Model presented by Peck (1987) for plastic encapsulated

integrated circuits (Al conductor electrolytic corrosion)

Note: Other models exist (and are used) for plastic devices (e.g.Lawsons model for thick film and semiconductor devicedegradation)

A = tref/ttest= (RHtest/RHref)3*e

[EA/K * (1/Tref- 1/Ttest)]

where the activation energy for corrosion is 0,9 eV.


20/42

20


Mechanical stress

MIL-STD810E, gives for sinusoidal and random vibration respectively:

W (ref) / W (test) = [ T (test) / T (ref) ]n-1/b

where W is the sinusoidal level of vibration (peak

acceleration), and

W (ref) / W (test) = [ T (test) / T (ref) ]n/b

where W is the random vibration level (acceleration

power spectral density)

The MIL standard gives n/b = 1/6 and (n-1)/b = 1/4


21/42

21


Other considerations:

time compression - ON/OFF cycles (length/frequency) EMI, EOS, ESD


22/42

22

Case: Electronic energy meter

A three phase household energy meter

Operating conditions:

T = 23 C, RH

Test conditionsT = 100 C, test length 12 000 h

Acceleration factor was calculated using Siemens Norm 29500


23/42

23

Case: Energy meter, continued

refarefa

aa

zEzE

zEzE

TeAeA

eAeA

+

+= 21

21

)1(

)1(

with2,0

11(1TTk

zrefamb

= )

and1,0

11(

1

TTkz refamb =) in (eV)-1


24/42

24


Table 3. Failure rates at 23 C and 100 C (FIT, failures in 109h)

[FIT]N 23 C % 100 C % Acceleration factorIntegrated circuits 2 7 4 156 5 24

Transistors 7 6 4 136 4 24

Diodes 22 5 4 140 5 26

Capacitors 37 20 13 1922 63 98

Resistors 76 58 56 345 16 6

Inductive 3 7 5 38 1 6

Crystals 1 6 4 163 5 26

Electromechanical 1 15 10 15 1 1

Optocouplers 1 2 2 127 4 57

Total 126 100 3042 100 24


25/42

25


Life test results

no failures

stability - conformed to IEC 61036 standard 82 FIT

1998-1999 observed field failure rate 73 Siemens Norm: 125 FIT

T2

)22(2 %60 += i s th e d e g r e e o f f r e e d o m , i s t h e n u m b e r o f f a i l e d o n e s a n d T i s t h e c u m u l a t i v e t o t a l t e s t

t i m e c o n v e r t e d t o o p e r a t i n g c o n d i t i o n s


26/42

26

Problems in life prediction and reliability testing

No or limited field experience time or failure mechanisms

The true life cycle stresses are not always known

Limitations of the models extrapolation from test conditions to useconditions is difficult (especially for humidity, corrosive gasses)

Too high stress levels in testing: non-typical failure mechanisms are

introduced

Too low stress levels: no failures no knowledge of failure mechanisms Too few samples low statistical significance of results

Multiple failure mechanisms: for example at high temperatures those

mechanisms with high activation energy may dominate (and mask more

relevant mechanisms) Failure analysis after test may not always be successful


27/42

27

Silver dendrites


28/42

28

Zinc whiskers, relay


29/42

29

Origin of zinc whisker


30/42

30

Zinc whiskers on cabinet structures, air conditioning strucutres


31/42

31

Relay spacer degradation


32/42

32

Cracked smart card IC


33/42

33

Corroded pins of an IC (sulphur in factory athmosphere)


34/42

34

MOS-transistor (ESD tai EOS)


35/42

35

Corrosion on IC metallization


36/42

36

???contamination on PCB contact


37/42

37

Oxidized metaalized capacitor film (moisture in fabrication process)


38/42

38

Corroded IC pins


39/42

39

An example of decapsulated ICs (by applying hot fuming nitric and sulphur acid)


40/42

40

Contact contamination -> intermittent contact


41/42

41

Human problems are also possible


42/42

42

Thank you for your attention!

Ageing and Life Prediction Conference 2008 Palmen

Documents

Transcript of Ageing and Life Prediction Conference 2008 Palmen