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