Overview of Reliability Models and Data...

© 2001 Amkor Technology, Inc. Ahmer Syed/ TMS 2001

Overview of Reliability Models andData Needs

Ahmer SyedAmkor Technology

Workshop on Modeling and Data Needs for Lead-Free Solders

Sponsored by NEMI, NIST, NSF, and TMS


Outline

Failure Mechanisms Related to Solder Joint

Life Prediction Model Requirements

Lessons Learned from Sn/Pb– Life Prediction Models– Material Behavior– Stress Analysis Approach– Test Data

Data Needs for Pb Free Solder


Failure Modes & MechanismsRelated to Solder Joint

Failure Modes– Failure in Bulk Solder– Failure at Intermetallic Layer– Trace Failures– PCB Failures

Failure Mechanisms– Temperature Related: T, dT/dt, ∆T– Displacement Related: ∆D– Acceleration: G, Grms

1

3

2

4

Component

Board

Laminate

Solder MaskTrace

1 2

Component

1

2

3

4


Causes of Failures

Thermal/Power Cycling– CTE Mismatch, ∆T, dT/dt, Tmax, Tmin, Time @ Tmax and Tmin

Failure in Bulk Solder - Creep-FatigueFailure at Intermetallic - Overstress

PCB Bend, Cyclic Bend, Vibration– Relative Displacement Between Package & Board

Failure in Bulk Solder - Fatigue, Creep RuptureFailure at Intermetallic Layers - OverstressTrace & PCB Failures - Solder Alloy/Intermetallic Strength

Shock & Drop– High Gs, Large Displacements

Failure at Intermetallic Layers - OverstressTrace & PCB Failure - Solder Alloy/Intermetallic Strength

Ball Shear– Intermetallic or Bulk Solder

How Well Can We Predict?


Life Prediction Model Requirements/Steps

LoadProfile

MaterialBehavior

Analysis- Analytical- FEA

Stress,Strain,Energy Density

Fatigue Test

ComponentDescription

Failure Definition&

Failure Data

Life Prediction Model

Model Validation

Predictions for NewDesigns and Conditions


Sn/Pb Solder Fatigue Life Prediction Models

Early Attempts (mid to late 80s)– Traditional Coffin-Manson Eqn

– Isothermal Mechanical Fatigue– Plastic Strain Range Controlled

TestsTemperature ModificationFrequency Modification

– Very Little Data on Real SolderJoints

Wen & Ross, ASME EEP-9Investigator C k Remarks

0.52 0.68 Torsion1.18 0.46 Lap Shear0.16 0.30 Tensile Joint0.6 0.39 1/15 CPM Shear Joint

0.565 0.30 5 CPM Shear JointShine 0.19 0.53 1 Hz, Tensile

0.1538 0.415 0.5Hz0.24 0.41

Enke 0.26 0.52Gua/Cutionco 0.34 0.49Solomon 1.32 0.52Guo/Conrad 3.00 0.70 TensileKluizenaer 0.39 0.51 Tensile

1.3 0.637 strain rate 0.1/sec4.72 0.653 4 x 10-4/sec

10.12 0.643 1 x 10-5/sec

Coomb

Wild

Kitano

Aldrich

kfp NC −=∆ε



Models Incorporating Time & Temperature Dependent Behavior ofSolder (Mostly Analytical Treatment)– Damage Integral Method (Subrahmanyan et al, CHMT 1989)

Stress Based

– Energy Partitioning Approach (Dasgupta et al, ASME, EEP, 1993)Elastic + Plastic + Creep

– Fracture Mechanics Based (Pao, CHMT 1992)

– Matrix Creep Model (Shine & Fox, ASTM STP 942)Isothermal Test DataCalculated Creep Strain

– CSMR Model ( Clech et al, 43rd ECTC)Analytical ModelInelastic Strain Energy



Energy Density Based (Darveaux et al, Ball Grid Array Technology, Ed. J. Lau)

– Crack Initiation & Growth– Inelastic Constitutive Eqn– Finite Element Analysis

10 -210 -310 -410 -510 -510 -410 -310 -210 -110 010 110 210 310 410 510 6

99C129C133C27C100C68CMASTER

τ

γ

/G

(T/G

) ex

p(Q

/kT

) (

K/s

ec/p

si)

o



Partitioned Creep StrainBased (Syed, 1996 SEM)– Wong et al Constitutive

Eqn (CHMT, 1989)

two mechanisms

– Finite Element Analysis

10

100

1000

10000

100000

10 100 1000 10000 100000

Cycles to Mean Failure (Test)

Cyc

les

to M

ean

Fai

lure

(P

red

icti

on

s)

PBGAs

LCCCs

QFPs

Flip Chips *

PBGAs - Motorola

TSOPs *

Master

2X Above

2X Below

25% Above

25% Below

* Unpublished Test DataTest Data & Predictions Scaled by the Same Factor

Open Symbols : Model DevelopmentClosed Symbols : Model Validation

( ) 1063.002.0 −Ε+Ε= MCGBSf xxN

1.E-14

1.E-12

1.E-10

1.E-08

1.E-06

1.E-04

1.E-02

1.E+00

1.E-06 1.E-05 1.E-04 1.E-03 1.E-02

Normalized Stress (σ/E)

Ste

ady

Sta

te C

reep

Str

ain

Rat

e (1

/s)

-50 C

0 C

25 C

75 C

125 C


Material Property Characterization

Stress-Strain ( Shi et al, JEP, 1999)

Stress-Strain

Ductility

Modulus

Strength



Creep Behavior– Aldrich & Avery, Kashyap & Murty, Grivas, Mohamed & Langdon, Lam et

al, Arrowood and Mukherjee, and others– Hall, Solomon, Wilcox, Wong, Shine & Fox, Darveaux, Busso, Hong, and

others

10 410 310 210 110 -10

10 -910 -8

10 -710 -6

10 -5

10 -410 -3

10 -210 -1

10 0

Shear Stress (psi)

Stea

dy S

tate

Str

ain

Rat

e (1

/sec

)

27C

67C

100C132C

Bulk Solder (Wong et al Model)Real Joints (Darveaux)



Mechanical Test Fixture for Creep Test of Real Joints– (Darveaux et al, Ball Grid Array Technology, Ed. J. Lau)

Double Lap Shear Fixture

Steel Rods CeramicSubstrates

SolderJointArray

Adhesive

Tensile Fixture

LVDT

StainlessSteelGrips


Stress Analysis

MC : 14 ppm/oC

Silicon : 2.6 ppm/oCBT/Cu Composite ~ 16 ppm/oC

PCB : 15 - 18 ppm/oC

25 to -40oC

Analytical Models– CTE Mismatch– Pure Shear

Finite Element

25 to 125oC


Finite Element Modeling

3-Dimensional Models

Inelastic Constitutive Models

Accurate Loading Conditions

Multiple Responses– Stress, Strain, Energy Density


Failure Data

Failure Definition - Electrical Open

Thermal Cycle Fatigue Test Data– Different Cycling Conditions– Test Board Variables– Component Design Variables

1000.00 10000.001.00

5.00

10.00

50.00

90.00

99.00

Cycles to Failure

Cum

ulat

ive

Fai

lure

s (%

)

WeibullTC1_20 mils Brd

W2 RRX - SRM MED

F=11 / S=23

β1=12.80, η1=3161.34, ρ=0.96

TC1_62 mils Brd

W2 RRX - SRM MED

F=38 / S=1

β2=7.30, η2=1968.64, ρ=0.97

1000.00 10000.001.00

5.00

10.00

50.00

90.00

99.00

Cycles to Failure

Cum

ulat

ive

% F

aile

d

WeibullSn-Pb_TC1W2 RRX - SRM MED

F=12 / S=3

β1=10.40, η1=3164.00, ρ=0.98

Sn-Pb_TC3W2 RRX - SRM MED

F=14 / S=1

β2=12.95, η2=6194.94, ρ=0.97


Solder Joint ReliabilityTemperature Cycle Test Data

wsCSP– 54 Lead Center Pad,

9x11 mm– Wafer Thickness

45% and 60%Reduction in Life withWafer Thickness of0.5 and 0.625 mm

– Ball SizeMounted Height <1mm for 0.33mm Balls30% Improvement inFatigue Life with0.45mm Solder Balls 1.0

5.0

10.0

50.0

99.0

500.0 5000.0

54 Lead wsCSP, 20 mils Boards, TC2 Condition

Cycles to Failure

Cum

mul

ativ

e %

Fai

led

0.33ball/0.35waferP=2, A=RRX-S F=9 | S=29

β1=14.5, η1=3279.6, ρ=0.8


β2=7.8, η2=2505.9, ρ=1.0


β3=7.7, η3=1508.9, ρ=1.0


β4=11.0, η4=2910.2, ρ=1.0


Life Prediction Model Correlationfor wsCSP

Predictions within 25% Except for 2 Cases

Same Trend Predicted as Observed from Tests

0

1000

2000

3000

4000

5000

6000

7000

1 2 3 4 5 6 7 8 9 10

Cyc

les

to M

ean

Fai

lure

TestPredictions

Ball Size (mm) 0.33 0.33 0.45 0.33 0.33 0.33 0.45 0.33 0.33Wafer Thk. (mm) 0.35 0.50 0.50 0.625 0.35 0.50 0.50 0.625 0.50PCB Thickness (mm) 0.50 0.50 0.50 0.50 1.60 1.60 1.60 1.60 0.50Temp Cycle TC2 TC2 TC2 TC2 TC2 TC2 TC2 TC2 TC1


1721

768

2738

983

913

1420

664

1568

734

1750

750

550

1578

630

0

500

1000

1500

2000

2500

3000

FlexB

GA 132,

6.4 m

m Die

FlexB

GA 132,

9.5 m

m Die

FlexB

GA 144,

3.65 m

m Die

FlexB

GA 144,

7.4x8

.3 mm D

ie

FlexB

GA 144,

9.6 m

m Die

FlexB

GA 160,

7.2 m

m Die

FlexB

GA 160,

8.9 m

m Die

FlexB

GA 180,

4.45 m

m Die

FlexB

GA 180,

9.25 m

m Die

Fai

lure

Fre

e L

ife

(Cyc

les) Estimated, 75% of Predicted CMF

Measured First Failure

Solder Joint Reliability PredictionPrediction Vs. Measured


Realistic Realistic - Excessive Excessive

Condition Specified Reliability RequirementsChamber

Zones1 Year Life 5 Years Life

0 to 100 C Single 180 900 1500 Cycles -25 to 100 C Single 125 625 700 Cycles -40 to 100 C Single 120 600 800 Cycles -40 to 125 C Single 90 450 500 Cycles -40 to +85 C Dual 130 650 300 - 500 Cycles -40 to 100 C Dual 90 450 800 Cycles -40 to 125 C Dual 70 350 500 Cycles -55 to 125 C Dual 60 300 300 Cycles

Realistic Reliability Requirements

Solder Joint Reliability PredictionField Conditions

Application : Cell PhoneAssumed Worst Case Field Conditions

Sales Person; May - October : Arizona, November - April : AlaskaArizona Cycling : +20 to +55 C, 6 Cycles/Day, 1000 Cycles in 6 MonthsAlaska Cycling : -20 to +20 C, 6 Cycles/Day, 1000 Cycles in 6 Months

Required Life/Year : 2000 + 20% = 2400 Cycles


1000

1400

2000

800

1300

1000

1450

0 500 1000 1500 2000 2500

TC1

TC2

TC3

TC4

TC5

TC6

TC7

Tem

per

atu

re C

ycle

Co

nd

itio

n

Relative Cycles to Failure

-40 to 125, 15 minutes Ramps and Dwells, 1 Hr Cycle

-40 to 100, Dual Zone, 1 Hr Cycle


-40 to 125, Dual Zone, 30 minutes Cycle

0 to 100 C, 10 minutes Ramps 5 Minutes Dwells, 30 minutes Cycle


-40 to 85, Dual Zone, 30 minutes Cycle

Single Zone : Slow RampsDual Zone : Fast Ramps (2-3 Sec Transfer), Steady State at Board Level within 2-3 minutes

Solder Joint Reliability PredictionTest Condition Comparison


Cyclic 3-Point BendingPCB Strain vs. Life– 12mm-132 lead fleXBGAs– 0.85mm thick Board (h)– Measured Strain Level

400

800

1200

1600

1,000 10,000 100,000

Cycles to Failure

PC

B S

trai

n L

evel

(µε

)


3-Point Bend Cycle Simulation

Bend Cycle Fatigue

0

20

40

60

80

0 0.1 0.2 0.3

Strain

Str

ess

(MP

a)

Darveaux’ Data

0

0.005

0.01

0.015

0.02

0.025

0.03

0 0.2 0.4 0.6 0.8 1 1.2Time (second)

Str

ain

EPPLEQVTotalEPEQ

0.0001

0.001

0.01

0.1

1

1000 10000 100000

Cycles to Mean Failure (Test)

Str

ain

(S

imu

lati

on

s)

EPPLEQV (Range)Total

EPEQ (Accumulated)

fNf = 42.66(EPEQ)-1.09

Thin Brd3mm 2mm

ThkBrd.2mm


What is Needed for Pb Free Solder

LoadProfile

MaterialBehavior


Stress,Strain,Energy Density

Fatigue Test

ComponentDescription

Failure Definition&

Failure Data

Life Prediction Model

Model Validation

Predictions for NewDesigns and Conditions



Material Charaterization– Stress-Strain Behavior

strain rates dependent, andtemperature dependent

– Ductility & Strength– Temperature Dependent

Modulus– Temperature Dependent

Inelastic BehaviorCreep & Stress RelaxationStress to Rupture

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5S

n/P

b

Sn

/Ag

Sn

/Cu

Sn

/Ag

/Cu S

n/B

i

-40 to 125oC Cycle Range

Pb Free Alloys In ConsiderationHave Homologous Temperature of ~ 0.5 at -40oC

MaterialBehavior



Of all Pb free Alloys, Sn/Ag hasbeen Characterized the most– Not as much as Sn/Pb

Very Little data on other alloys– Recent data on Strength and

Ductility on Sn/Ag, Sn/Cu,Sn/Ag/Bi,Sn/Ag/Cu by Xiao et al (J.of Electronic Materials, 2000)

– Time &Temperature dependentmaterial behavior is of mostImportance.

10 410 310 210 -10

10 -9

10 -8

10 -7

10 -6

10 -5

10 -4

10 -3

10 -2

10 -1

Shear Stress (psi)

Stea

dy S

tate

Str

ain

Rat

e (1

/sec

)

132C

80C

27C

Steady State Creep Data on Sn/Ag by Darveaux et al

(Ball Grid Array Technology, Ed. J. Lau)

MaterialBehavior



Bulk versus Joint Behavior– Data from bulk solder samples might not be directly applicable to solder joints

Constraining effect of the solder / substrate interfaces,

Precipitation strengthening from dispersed intermetallics, and

Difference in grain structure, grain size, or grain / specimen size ratio.

– Data from Real Solder Joint Samples is Preferred

10 510 410 310 210 -9

10 -8

10 -7

10 -6

10 -5

10 -4

10 -3

10 -2

10 -1

10 0

Darveaux - 60Sn40PbDarveaux - 62Sn36Pb2AgDarveaux - 60Sn40Pb S->TDarveaux - 62Sn36Pb2Ag S->TSubrahmanyan - 60Sn40Pb S->TSkipor - 63Sn37PbKashyap - 62Sn38Pb 28.4umKashyap - 62Sn38Pb 9.7umSchmidt - 62Sn38Pb

Tensile Stress (psi)

Stea

dy S

tate

Str

ain

Rat

e (1

/sec

)

Joint

Bulk

ture

Steel Rods CeramicSubstrates

SolderJointArray

Adhesive

Tensile Fixture

StainlessSteelGrips

MaterialBehavior



Analysis Tools and Methodologies are in Place

Constitutive Equations Need to be developed– Consideration must be given on how to implement a particular

constitutive Equation in FEA Software packages.Provide guidelines or User subroutines




Sn/Pb vs. Sn/Ag/Cu (fleXBGA Package)

No Difference in two Sn/Ag/Cu Compositions– Sn/Ag/Cu Better than Sn/Pb

25% for -55 to 125oC Cycle80% for 0 to 100oC Cycle

1000.00 10000.001.00

5.00

10.00

50.00

90.00

99.00

Cycles to Failure

Cum

ulat

ive

% F

aile

d

WeibullSn-3.4Ag-0.7Cu

F=25 / S=5

β1=16.07, η1=2886.19, ρ=0.98

Sn-4.0Ag-0.5Cu

F=10 / S=20

β2=19.28, η2=2809.33, ρ=0.91

Sn-Pb

F=30 / S=0

β3=15.16, η3=2409.32, ρ=0.99

2000.00 20000.001.00

5.00

10.00

50.00

90.00

99.00

Cycles to Failure

Cum

ulat

ive

% F

aile

d

WeibullSn-3.4Ag-0.7Cu

F=11 / S=4

β1=13.95, η1=9983.61, ρ=0.99

Sn-4.0Ag-0.5Cu

F=9 / S=6

β2=15.70, η2=10368.55, ρ=0.84

Sn-Pb

F=14 / S=1

β3=12.95, η3=6194.94, ρ=0.97

-55 to 125 C Cycle 0 to 100 C Cycle

FailureData


What is Needed for Pb Free SolderEffect of Package Type

PBGA– 2X Higher Life for Sn/4.0Ag/0.5Cu (A14) Compared to Sn/Pb

fleXBGAs– 25% Higher Life for A14

20 Lead LCCCs– NCMS TMF Test

-55<>125oC, 70 minute Cycle– 2X Reduction in Life for A14!

Performance is Highly Dependent on Package Type– Solder Deformation Behavior is a Strong Function of Stress, Strain

Rate, and Temperature

Sn/Ag/Cu More Creep Resistant at Low Stresses, Less CreepResistant at High Stresses!

Will a Ceramic Component Soldered with Sn/Ag/Cu Performworse than Sn/Pb in Actual Field Conditions?

0

2000

4000

6000

8000

PBGA fleXBGA LCCC

Package Type

Mea

n L

ife

(Cyc

les) Sn/Pb

Sn/4.0Ag/0.5Cu

FailureData


What is Needed for Pb Free SolderEffect of Test Conditions

Acceleration Factors Depend onAccelerated Test Condition & Alloy

– Different for each Alloy– -40<>125C 0<>100 C

Sn/Pb: 2X Higher LifeSn/Ag/Cu: 3.5X Higher Life

Field Conditions Much More Benignthan Accelerated Test Conditions

A Package-Alloy CombinationPerforming Worse in Accelerated TestCondition May Actual Perform Same orBetter in Field Conditions

Performance Comparison from OnlyOne Accelerated Test MaybeMisleading– At Least two test conditions should be

used

0

2000

4000

6000

8000

10000

12000

Sn/Pb Sn/Ag/Cu (A14)Alloy

Mea

n L

ife

(Cyc

les) TC1

TC3

Acceleration Factors from TC3 to TC1

0

1

2

3

4

5

6

A1 A11 A14 A21 A66 B63Alloy

Acc

eler

atio

n F

acto

r

FailureData


Life Prediction for Pb Free SolderMaterials need to be characterized for time and temperaturedependent behavior– Creep deformation will still play a dominant role for temperature cycle

failures– Time independent plasticity more relevant for vibration and other high cycle

fatigue simulation– Data from realistic joint samples is more useful

Temperature cycle data on real components is needed– Isothermal fatigue data is not useful for life prediction model development– Publish as much as you can, don’t normalize– Use multiple cycling conditions & components

Modeling Techniques Exist– Easy implementation of Constitutive Equation in FEA software is the key

Guidelines or user subroutines should be provided for complex stress-strainbehavior

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