Overview of Reliability Models and Data Needs

Overview of Reliability Models and Data Needs Ahmer Syed Amkor Technology Workshop on Modeling and Data Needs for Lead-Free Solders Sponsored by NEM...
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Overview of Reliability Models and Data Needs

Ahmer Syed Amkor Technology

Workshop on Modeling and Data Needs for Lead-Free Solders Sponsored by NEMI, NIST, NSF, and TMS

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

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

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Failure Modes & Mechanisms Related to Solder Joint  Failure Modes – Failure in Bulk Solder 1 – Failure at Intermetallic Layer – Trace Failures 3 – PCB Failures 4

Component 2

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

1

2

Solder Mask Trace Laminate

4 3

Board

Component

1

© 2001 Amkor Technology, Inc.

2

Ahmer Syed/ TMS 2001

Causes of Failures  Thermal/Power Cycling – CTE Mismatch, ∆T, dT/dt, Tmax, Tmin, Time @ Tmax and Tmin  Failure in Bulk Solder - Creep-Fatigue  Failure at Intermetallic - Overstress

 PCB Bend, Cyclic Bend, Vibration – Relative Displacement Between Package & Board  Failure in Bulk Solder - Fatigue, Creep Rupture  Failure at Intermetallic Layers - Overstress  Trace & PCB Failures - Solder Alloy/Intermetallic Strength

 Shock & Drop – High Gs, Large Displacements  Failure at Intermetallic Layers - Overstress  Trace & PCB Failure - Solder Alloy/Intermetallic Strength

 Ball Shear – Intermetallic or Bulk Solder

How Well Can We Predict? © 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Life Prediction Model Requirements/Steps Load Profile

Component Description

Fatigue Test

Analysis - Analytical - FEA

Failure Definition & Failure Data

Material Behavior

Stress,Strain, Energy Density

Model Validation

Life Prediction Model

Predictions for New Designs and Conditions

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Sn/Pb Solder Fatigue Life Prediction Models  Early Attempts (mid to late 80s) – Traditional Coffin-Manson Eqn ∆ε p = C N f − k

– Isothermal Mechanical Fatigue – Plastic Strain Range Controlled Tests  Temperature Modification  Frequency Modification – Very Little Data on Real Solder Joints

Wen & Ross, ASME EEP-9 Investigator Coomb Wild Shine Kitano Enke Gua/Cutionco Solomon Guo/Conrad Kluizenaer Aldrich

© 2001 Amkor Technology, Inc.

C 0.52 1.18 0.16 0.6 0.565 0.19 0.1538 0.24 0.26 0.34 1.32 3.00 0.39 1.3 4.72 10.12

k 0.68 0.46 0.30 0.39 0.30 0.53 0.415 0.41 0.52 0.49 0.52 0.70 0.51 0.637 0.653 0.643

Remarks Torsion Lap Shear Tensile Joint 1/15 CPM Shear Joint 5 CPM Shear Joint 1 Hz, Tensile 0.5Hz

Tensile Tensile strain rate 0.1/sec 4 x 10-4/sec 1 x 10-5/sec

Ahmer Syed/ TMS 2001

Sn/Pb Solder Fatigue Life Prediction Models  Models Incorporating Time & Temperature Dependent Behavior of Solder (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 Data  Calculated Creep Strain

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

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Sn/Pb Solder Fatigue Life Prediction Models

o

γ (T/G) exp(Q/kT)

(K/sec/psi)

 Energy Density Based (Darveaux et al, Ball Grid Array Technology, Ed. J. Lau) – Crack Initiation & Growth – Inelastic Constitutive Eqn – Finite Element Analysis 10 6 10 5 10 4 3 10 10 2 10 1 10 0 10 -1 -2 10 10 -3 10 -4 10 -5 10 -5

99C 129C 133C 27C 100C 68C MASTER

10 -4

τ /G

10 -3

10 -2

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Sn/Pb Solder Fatigue Life Prediction Models

 two mechanisms

– Finite Element Analysis 1.E+00

-50 C Steady State Creep Strain Rate (1/s)

1.E-02

0C 25 C

1.E-04

75 C 125 C

1.E-06

1.E-08

1.E-10

1.E-12

1.E-14 1.E-06

1.E-05

1.E-04 Normalized Stress ( σ/E)

1.E-03

Nf =

(0.02 xΕGBS

+ 0.063 xΕ MC )−1

100000

Cycles to Mean Failure (Predictions)

 Partitioned Creep Strain Based (Syed, 1996 SEM) – Wong et al Constitutive Eqn (CHMT, 1989)

PBGAs LCCCs QFPs Flip Chips *

10000

PBGAs - Motorola TSOPs * Master 2X Above 2X Below 25% Above

1000

25% Below

Open Symbols : Model Development Closed Symbols : Model Validation

100

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

1.E-02

10 10

100

1000

10000

100000

Cycles to Mean Failure (Test)

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Material Property Characterization  Stress-Strain ( Shi et al, JEP, 1999)

Stress-Strain

Modulus

Strength

Ductility © 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Material Property Characterization  Creep Behavior

Steady State Strain Rate (1/sec)

– 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 0 10 10 -1 10 -2 10 -3 -4 10 10 -5 10 -6 10 -7 10 -8 10 -9 10 -10

27C 67C 100C 132C 10 1

Bulk Solder (Wong et al Model)

10 2 10 3 Shear Stress (psi)

10 4

Real Joints (Darveaux) © 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

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

Stainless Steel Grips Steel Rods Solder Joint Array

Ceramic Substrates

Adhesive

LVDT Double Lap Shear Fixture

© 2001 Amkor Technology, Inc.

Tensile Fixture

Ahmer Syed/ TMS 2001

Stress Analysis  Analytical Models – CTE Mismatch – Pure Shear MC : 14 ppm/oC Silicon : 2.6 ppm/oC BT/Cu Composite ~ 16 ppm/oC PCB : 15 - 18 ppm/oC

 Finite Element

25 to -40oC

25 to 125oC © 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Finite Element Modeling  3-Dimensional Models

 Inelastic Constitutive Models  Accurate Loading Conditions  Multiple Responses – Stress, Strain, Energy Density © 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Failure Data  Failure Definition - Electrical Open  Thermal Cycle Fatigue Test Data – Different Cycling Conditions – Test Board Variables – Component Design Variables 99.00

99.00

Weibull Sn-Pb_TC1 W2 RRX - SRM MED

F=12 / S=3 Sn-Pb_TC3

50.00

W2 RRX - SRM MED

F=14 / S=1 10.00 5.00

1.00 1000.00

90.00

W2 RRX - SRM MED

Cumulative Failures (%)

Cumulative % Failed

90.00

F=11 / S=23 TC1_62 mils Brd 50.00

W2 RRX - SRM MED

F=38 / S=1

10.00 5.00

1.00

10000.00

1000.00

Cycles to Failure β1=10.40, η1=3164.00, ρ=0.98 β2=12.95, η2=6194.94, ρ=0.97

Weibull TC1_20 mils Brd

10000.00

Cycles to Failure β1=12.80, η1=3161.34, ρ=0.96 β2=7.30, η2=1968.64, ρ=0.97

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Solder Joint Reliability Temperature Cycle Test Data

 45% and 60% Reduction in Life with Wafer Thickness of 0.5 and 0.625 mm

– Ball Size  Mounted Height < 1mm for 0.33mm Balls  30% Improvement in Fatigue Life with 0.45mm Solder Balls

54 Lead wsCSP, 20 mils Boards, TC2 Condition 99.0

Cummulative % Failed

 wsCSP – 54 Lead Center Pad, 9x11 mm – Wafer Thickness

0.33ball/0.35wafer P=2, A=RRX-S F=9 | S=29 0.33ball/0.50wafer P=2, A=RRX-S F=30 | S=0

50.0

0.33ball/0.625wafer P=2, A=RRX-S F=45 | S=0

10.0

0.45ball/0.50wafer P=2, A=RRX-S F=43 | S=1

5.0

1.0 500.0

Cycles to Failure 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

© 2001 Amkor Technology, Inc.

5000.0

Ahmer Syed/ TMS 2001

Life Prediction Model Correlation

Cycles to Mean Failure

for wsCSP

7000 6000

Test Predictions

5000 4000 3000 2000 1000

Ball Size (mm) Wafer Thk. (mm) PCB Thickness (mm) Temp Cycle

0 0.33 1 0.35 0.50 TC2

0.33 2 0.50 0.50 TC2

0.45 3 0.50 0.50 TC2

0.33 4 0.625 0.50 TC2

5

0.33 6 0.35 1.60 TC2

0.33 7 0.50 1.60 TC2

0.45 8 0.50 1.60 TC2

0.33 9 0.625 1.60 TC2

0.33 10 0.50 0.50 TC1

 Predictions within 25% Except for 2 Cases  Same Trend Predicted as Observed from Tests

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Solder Joint Reliability Prediction Prediction Vs. Measured

Failure Free Life (Cycles)

3000 2 7 3 8

2500 2000

1000

Measured First Failure

1 7 5 0

1 7 2 1

1500

Estimated, 75% of Predicted CMF

7 7 6 5 8 0

500

9 8 3 5 5 0

9 1 3

1 1 5 4 7 2 8 0

1 5 6 8 6 6 6 3 4 0

7 3 4

m 14 m 4, Di 7. e 4x 8. Fl 3 ex m BG m A Di 14 e 4, Fl 9. 6 ex m BG m A Di 16 e 0, Fl 7. 2 ex m BG m A Di 16 e 0, Fl 8. ex 9 BG m m A Di 18 e 0, Fl 4. 45 ex BG m m A Di 18 e 0, 9. 25 m m Di e

Di e

Fl ex BG A

14 4, 3. 65

m m Fl ex BG A

13 2, 9. 5

Fl ex BG A

Fl ex BG A

13 2, 6. 4

m m

Di e

0

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Solder Joint Reliability Prediction Field Conditions

Application : Cell Phone Assumed Worst Case Field Conditions Sales Person; May - October : Arizona, November - April : Alaska Arizona Cycling : +20 to +55 C, 6 Cycles/Day, 1000 Cycles in 6 Months Alaska Cycling : -20 to +20 C, 6 Cycles/Day, 1000 Cycles in 6 Months

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

0 to 100 C -25 to 100 C -40 to 100 C -40 to 125 C -40 to +85 C -40 to 100 C -40 to 125 C -55 to 125 C

Realistic Reliability Requirements Chamber 1 Year Life 5 Years Life Zones Single 180 900 Single 125 625 Single 120 600 Single 90 450 Dual 130 650 Dual 90 450 Dual 70 350 Dual 60 300

Realistic

Specified Reliability Requirements

Realistic - Excessive © 2001 Amkor Technology, Inc.

1500 Cycles 700 Cycles 800 Cycles 500 Cycles 300 - 500 Cycles 800 Cycles 500 Cycles 300 Cycles

Excessive Ahmer Syed/ TMS 2001

Solder Joint Reliability Prediction Temperature Cycle Condition

Test Condition Comparison

1450

TC7

-40 to 85, Dual Zone, 30 minutes Cycle

TC6

-40 to 100, Dual Zone, 1 Hr Cycle

TC5

-40 to 100, 15 minutes Ramps and Dwells, 1 Hr Cycle

TC4

1000

800

1300

-40 to 125, Dual Zone, 30 minutes Cycle

TC3

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

TC2

-25 to 100, 15 minutes Ramps and Dwells, 1 Hr Cycle

TC1

1000 0

500

2000

1400 -40 to 125, 15 minutes Ramps and Dwells, 1 Hr Cycle

1000

1500

2000

2500

Relative Cycles to Failure

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

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Cyclic 3-Point Bending

PCB Strain Level ( µε )

 PCB Strain vs. Life – 12mm-132 lead fleXBGAs – 0.85mm thick Board (h) – Measured Strain Level 1600

1200

800

400 1,000

10,000

100,000

Cycles to Failure

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

3-Point Bend Cycle Simulation  Bend Cycle Fatigue Stress (MPa)

80 60 40

Darveaux’ Data

20 0 0

0.1

0.2

0.3

Strain 1

Strain (Simulations)

0.03

EPPLEQV Total EPEQ

0.025

Strain

0.02 0.015 0.01 0.005

EPPLEQV (Range) Total EPEQ (Accumulated)

0.1

0.01

Thin Brd 3mm 2mm

Thk Brd. 2mm

0.001 f

Nf = 42.66(EPEQ)-1.09 0.0001

0

1000

0

0.2

0.4

0.6

0.8

1

1.2

Time (second)

© 2001 Amkor Technology, Inc.

10000

100000

Cycles to Mean Failure (Test)

Ahmer Syed/ TMS 2001

What is Needed for Pb Free Solder Load Profile

Component Description

Fatigue Test

Analysis - Analytical - FEA

Failure Definition & Failure Data

Material Behavior

Stress,Strain, Energy Density

Model Validation

Life Prediction Model

Predictions for New Designs and Conditions

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Material Behavior

What is Needed for Pb Free Solder  Material Charaterization – Stress-Strain Behavior

0.6

Sn/Ag/Cu

0.7

Sn/Bi

0.8 Sn/Cu

 Creep & Stress Relaxation  Stress to Rupture

0.9

Sn/Ag

– Ductility & Strength – Temperature Dependent Modulus – Temperature Dependent Inelastic Behavior

1

Sn/Pb

 strain rates dependent, and  temperature dependent

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

0.5 0.4 0

0.5

1

1.5

2

2.5

-40 to 125oC Cycle Range © 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

What is Needed for Pb Free Solder

Material Behavior

 Of all Pb free Alloys, Sn/Ag has been Characterized the most 10 -1

 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 dependent material behavior is of most Importance.

Steady State Strain Rate (1/sec)

– Not as much as Sn/Pb

10

-2

10 -3 10 -4 10

-5

27C

10 -6 10 -7 10

80C

-8

10 -9 10

132C

-10

10 2

10 3 Shear Stress (psi)

10 4

Steady State Creep Data on Sn/Ag by Darveaux et al (Ball Grid Array Technology, Ed. J. Lau)

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Material Behavior

What is Needed for Pb Free Solder  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

Steady State Strain Rate (1/sec)

0

10 10 -1 10 -2 10 -3 -4 10 10 -5 10 -6 10 -7 10 -8 10 -9 10 2

Stainless Steel Grips

Joint

Bulk

10 3 10 4 Tensile Stress (psi)

Steel Rods

Darveaux - 60Sn40Pb Darveaux - 62Sn36Pb2Ag Darveaux - 60Sn40Pb S->T Darveaux - 62Sn36Pb2Ag S->T Subrahmanyan - 60Sn40Pb S->T Skipor - 63Sn37Pb Kashyap - 62Sn38Pb 28.4um Kashyap - 62Sn38Pb 9.7um Schmidt - 62Sn38Pb

10 5

© 2001 Amkor Technology, Inc.

Ceramic Substrates

Solder Joint Array

ture

Adhesive

Tensile Fixture

Ahmer Syed/ TMS 2001

What is Needed for Pb Free Solder Analysis - Analytical - FEA  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

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

What is Needed for Pb Free Solder

Failure Data

 Sn/Pb vs. Sn/Ag/Cu (fleXBGA Package) -55 to 125 C Cycle 99.00

Weibull Sn-3.4Ag-0.7Cu

90.00

F=25 / S=5 Sn-4.0Ag-0.5Cu

50.00

F=10 / S=20 Sn-Pb

10.00 5.00

F=30 / S=0

1.00 1000.00

Cycles to Failure

Cumulative % Failed

Cumulative % Failed

99.00

0 to 100 C Cycle

90.00

Weibull Sn-3.4Ag-0.7Cu

50.00

F=11 / S=4 Sn-4.0Ag-0.5Cu F=9 / S=6 Sn-Pb

10.00 F=14 / S=1 5.00

1.00 2000.00

Cycles to Failure 20000.00 β1=13.95, η1=9983.61, ρ=0.99 β2=15.70, η2=10368.55, ρ=0.84 β3=12.95, η3=6194.94, ρ=0.97

10000.00

β1=16.07, η1=2886.19, ρ=0.98 β2=19.28, η2=2809.33, ρ=0.91 β3=15.16, η3=2409.32, ρ=0.99

 No Difference in two Sn/Ag/Cu Compositions – Sn/Ag/Cu Better than Sn/Pb  25% for -55 to 125oC Cycle  80% for 0 to 100oC Cycle

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Failure Data

What is Needed for Pb Free Solder Effect 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  -55125oC, 70 minute Cycle – 2X Reduction in Life for A14!

Mean Life (Cycles)

8000 Sn/Pb

6000

Sn/4.0Ag/0.5Cu 4000 2000 0 PBGA

fleXBGA

LCCC

Package Type

 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 Creep Resistant at High Stresses!  Will a Ceramic Component Soldered with Sn/Ag/Cu Perform worse than Sn/Pb in Actual Field Conditions? © 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001

Failure Data

What is Needed for Pb Free Solder Effect of Test Conditions

 Field Conditions Much More Benign than Accelerated Test Conditions  A Package-Alloy Combination Performing Worse in Accelerated Test Condition May Actual Perform Same or Better in Field Conditions  Performance Comparison from Only One Accelerated Test Maybe Misleading – At Least two test conditions should be used © 2001 Amkor Technology, Inc.

10000

TC1 TC3

8000 6000 4000 2000 0

Sn/Pb

Sn/Ag/Cu (A14) Alloy

Acceleration Factors from TC3 to TC1

6 Acceleration Factor

– Different for each Alloy – -40125C Î0100 C  Sn/Pb: 2X Higher Life  Sn/Ag/Cu: 3.5X Higher Life

12000 Mean Life (Cycles)

 Acceleration Factors Depend on Accelerated Test Condition & Alloy

5 4 3 2 1 0 A1

A11 A14 A21 A66 B63 Alloy

Ahmer Syed/ TMS 2001

Life Prediction for Pb Free Solder  Materials need to be characterized for time and temperature dependent 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-strain behavior

© 2001 Amkor Technology, Inc.

Ahmer Syed/ TMS 2001