Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Creep Properties of Lead-free Solder Joints
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
UCLA Workshop on Pb-Free Solder September 4-5, 2002
Department of Materials Science and Engineering, University of California, Berkeley and Materials Science Division, Lawrence Berkeley National Laboratory
Intel Corporation, Santa Clara, California
1
2
J.W. Morris, Jr1, H.G. Song1 and F. Hua2
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Motivation
• High homologous temperature during thermal fatigue means that creep is a major deformation mode.
• Creep behavior of Lead(Pb)-free solder joints in shear must be known to use them reliably in microelectronic applications.
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Pb-Free Solders of Interest in This Work
Solder System M.P.(?C) Constituent phases T/Tmat R.T.
Sn-0.7Cu 227 β-Sn, Cu6Sn5 0.596
Sn-3.5Ag 221 β-Sn, Ag3Sn 0.603
Sn-10In-3.1Ag 204 β-Sn, Ag2In, γ-InSn 0.625
Sn-3Ag-0.5Cu 218 β-Sn, Ag3Sn, Cu6Sn5 0.607
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Experimental Procedure
• Solder alloy manufacturing– Alloyed by vacuum arc melting – Rolled to make foil after homoginization– Punched to get the constant volume of solder
• Test specimen manufacturing– Manufactured solder masked Cu coupons with 9 pads – Assembled to single-shear specimens with bare Cu and electroless
Ni/immersion Au plated coupons – Reflow and annealing
• Creep tests– Performed at 60, 95, 130?C under constant load conditions
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Reflow Profile (at N2 atmosphere)
Reflow peak temperature of 235oC for SnAg, SnInAg, SnAgCu and 245oC for SnCu
5 10 15 20 25Time(min)
0
Tem
pera
ture
(?C
)
50
250
200
150
100
300
Cooling (2.7oC/sec)
Flux Activation
Reflow
Preheat
245oC
235oC
Followed by aging at 160oC for 4 hours.
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Geometry of Single-Shear Specimen
Cu or Ni/Au metallization
Alignment hole
Oxygen-free Cu plate
66m
m
2.23mm
1.21mm
3.18mm
Solder Resist Coating
13mm
t
F
F
(160µm)
One coupon has Cu pads
One coupon haselectroless Ni / immersion Au pads.
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Creep Test Apparatus
LVDTLVDT
micrometermicrometer
specimenspecimen
gripgrip
specimenspecimen
oil bathoil bath
loadload
heating coilheating coil
micrometermicrometerLVDTLVDT
thermocouplthermocouplee
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Typical Creep Curves of Solder Joints
0.0 2.0x104 4.0x104 6.0x104 8.0x104
0
20
40
60
80
100
Shea
r stra
in(%
)
Time(sec)
0 5 10 15 20 Time(hrs)
Sn-0.7Cu at 130oC
3.63MPa4.53MPa5.44MPa
2.72MPa1.81MPa
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
1 2 3 4 5 6 7 8 910 20 30 4010-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
1(all)n-value
St
rain
rate
Shear Stress(MPa)
n=3.5
n=4.0
n=4.1
95?C130?C
60?C
n=7.0 n=7.7
n=9.4
SnCu: Shear Stress vs. Shear Strain rate
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
1 2 3 4 5 6 7 8 910 20 30 4010-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
2(all)n-value
St
rain
rate
Shear Stress(MPa)
95?C130?C
60?C
n=4.7
n=5.1
n=3.9
n=6.8n=7.6
n=11.5
SnAg: Shear Stress vs. Shear Strain rate
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
SnInAg: Shear Stress vs. Shear Strain rate
1 2 3 4 5 6 7 8 910 20 30 4010-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
3(all)n-value
St
rain
rate
Shear Stress(MPa)
n=6.4
n=8.9
n=10.1
n=3.4
n=7.6
n=2.7
95?C130?C
60?C
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
SnAgCu: Shear Stress vs. Shear Strain rate
1 2 3 4 5 6 7 8 910 20 30 4010-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
4(all)n-value
Stra
in ra
te
Shear Stress(MPa)
95?C130?C
60?C
n=5.0
n=6.0n=4.4
n=9.2
n=9.9
n=11.2
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Sn Joints vs. Sn-0.7Cu Joints
1 2 3 4 5 6 7 8 910 20 30 4010-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
5(all)n-value
St
rain
rate
Shear Stress(MPa)
Sn (95?C)Sn(130?C)
Sn-0.7Cu (95?C)Sn-0.7Cu (60?C)
Sn (60?C)
Sn-0.7Cu (130?C)
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Stress vs. Strain rate at 60°C
1 2 3 4 5 6 7 8 910 20 30 4010-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
all data at 60oC
St
rain
rate
Shear Stress(MPa)
Sn-0.7CuSn-3.5AgSn-10In-3.1Ag
Sn
Sn-3Ag-0.5Cu
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Stress vs. Strain rate at 95°C
1 2 3 4 5 6 7 8 910 20 30 4010-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
all data at 95oC
Stra
in ra
te
Shear Stress(MPa)
Sn-0.7CuSn-3.5AgSn-10In-3.1Ag
Sn
Sn-3Ag-0.5Cu
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Stress vs. Strain rate at 130°C
1 2 3 4 5 6 7 8 910 20 30 4010-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
all data at 130oC
St
rain
rate
Shear Stress(MPa)
Sn-0.7CuSn-3.5AgSn-10In-3.1Ag
Sn
Sn-3Ag-0.5Cu
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Sn: Data normalized separately for high and low stress
* G=16302-40.5T(oC) *ignore abnormal three data points in the middle of 60oC data
10-4 10-3103
105
107
109
1011
1013
Q=65kJ/moln=7.7
Linear Fit for highbestQ65_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 30.59578912 1.66987798B 7.65551495 0.5125511------------------------------------------------------------
R SD N P------------------------------------------------------------0.99115368 0.13191349 6 0.00011704------------------------------------------------------------
Linear Fit for lowbestq85_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 27.05320746 0.70435624B 5.83229439 0.19952462------------------------------------------------------------
R SD N P------------------------------------------------------------0.99824909 0.02774625 5 <0.0001------------------------------------------------------------
Sn
Q=85kJ/moln=5.8
5(all)normalized
(dγ/d
t)(T/
G)e
xp(Q
/kT)
τ/G
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
SnCu: Data normalized separately for high and low stress
10-4 10-3103
105
107
109
1011
1013
Q=85kJ/moln=8.9
Linear Fit for highbestQ85_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 37.6043741 1.94970366B 8.93998794 0.59572225------------------------------------------------------------
R SD N P------------------------------------------------------------0.98481205 0.17253109 9 <0.0001
Linear Fit for lowbestQ90_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 19.51329522 1.48199311B 3.48933532 0.41021243------------------------------------------------------------
R SD N P------------------------------------------------------------0.96095021 0.1098452 8 0.00014454------------------------------------------------------------
Sn-Cu
Q=90kJ/moln=3.5
1(all)normalized
(dγ/d
t)(T/
G)e
xp(Q
/kT)
τ/G* G=16302-40.5T(oC)
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
SnAgCu: Data normalized separately for high and low stress
* G=16302-40.5T(oC)
10-4 10-3103
105
107
109
1011
1013
Q=75kJ/moln=10.7
Linear Fit for highbestQ75_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 38.85671556 3.42953034B 10.71607452 1.12409539------------------------------------------------------------
R SD N P------------------------------------------------------------0.96853874 0.16823437 8 <0.0001------------------------------------------------------------
Linear Fit for lowbestq95_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 28.94647642 1.09756496B 6.59206594 0.33401804------------------------------------------------------------
R SD N P------------------------------------------------------------0.99113337 0.10584323 9 <0.0001------------------------------------------------------------
Sn-Ag-Cu
Q=95kJ/moln=6.6
4(all)normalized
(dγ/d
t)(T/
G)e
xp(Q
/kT)
τ/G
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
SnAg: Data normalized separately for high and low stress
* G=16302-40.5T(oC)
10-4 10-3103
105
107
109
1011
1013
Q=75kJ/moln=10.6
Linear Fit for highbestQ75_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 38.66983847 4.26777359B 10.64805911 1.41418521------------------------------------------------------------
R SD N P------------------------------------------------------------0.95094443 0.24799469 8 0.00028437------------------------------------------------------------
Linear Fit for lowbestQ80_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 20.48530855 0.77686578B 4.54995587 0.23534619------------------------------------------------------------
R SD N P------------------------------------------------------------0.99206895 0.07182148 8 <0.0001------------------------------------------------------------
Sn-Ag
Q=80kJ/moln=4.5
2(all)normalized
(dγ/d
t)(T/
G)e
xp(Q
/kT)
τ/G
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Q-n Values from Normalized data
n Q(KJ/mole)Solders
low high low highτ/G at transition
Sn-Cu 3.5 8.9 90 85 3~4 x 10-4
Sn-Ag 4.5 10.6 80 75 7~8 x 10-4
Sn-In-Ag 5.4 9.5 100 115 6~7 x 10-4
Sn-Ag-Cu 6.6 10.7 95 75 7~8 x 10-4
Sn 5.8 7.7 85 65 3~4 x 10-4
* Based on Shear Modulus for Pure Sn, G=16302-40.5T(oC)
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Sn: Normalized data(when Q=80KJ/mole)
* G=16302-40.5T(oC) *ignore abnormal three data points in the middle of 60oC data
10-4 10-3102
104
106
108
1010
1012
Linear Fit for Q80oneline_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 37.28741683 2.41900461B 9.05265081 0.74248747------------------------------------------------------------
R SD N P------------------------------------------------------------0.98681141 0.19109141 6 0.00025976------------------------------------------------------------
Linear Fit for Q80oneline_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 26.70960208 2.00197406B 5.93326631 0.56710381------------------------------------------------------------
R SD N P------------------------------------------------------------0.98657198 0.07886247 5 0.00186413------------------------------------------------------------
Sn
Q=80kJ/mol
5(all)normalized
(dγ/d
t)(T/
G)e
xp(Q
/kT)
τ/G
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
SnAgCu: Normalized data(Q=85KJ/mole)
* G=16302-40.5T(oC)
10-4 10-3103
105
107
109
1011
1013
Linear Fit for Q85oneline_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 40.69250029 4.23097289B 10.84431281 1.3867838------------------------------------------------------------
R SD N P------------------------------------------------------------0.95427771 0.20754884 8 0.00023084------------------------------------------------------------
Linear Fit for Q85oneline_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 26.15301591 1.50970796B 6.16712045 0.45944405------------------------------------------------------------
R SD N P------------------------------------------------------------0.98112296 0.14558807 9 <0.0001------------------------------------------------------------
Sn-Ag-Cu
Q=85kJ/mol
4(all)normalized
(dγ/d
t)(T/
G)e
xp(Q
/kT)
τ/G
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
SnAg: Normalized data( when Q=75KJ/mole)
* G=16302-40.5T(oC)
10-4 10-3103
105
107
109
1011
1013
Linear Fit for Q75oneline_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 38.66983847 4.26777359B 10.64805911 1.41418521------------------------------------------------------------
R SD N P------------------------------------------------------------0.95094443 0.24799469 8 0.00028437------------------------------------------------------------
Linear Fit for Q75oneline_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 19.8536637 1.09701095B 4.57227197 0.33233199------------------------------------------------------------
R SD N P------------------------------------------------------------0.98451812 0.101419 8 <0.0001------------------------------------------------------------
Sn-Ag
Q=75kJ/mol
2(all)normalized
(dγ/d
t)(T/
G)e
xp(Q
/kT)
τ/G
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
SnCu: Normalized data( when Q=85KJ/mole)
* G=16302-40.5T(oC)
10-4 10-3104
106
108
1010
1012
1014
Linear Fit for Q85oneline_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 37.6043741 1.94970366B 8.93998794 0.59572225------------------------------------------------------------
R SD N P------------------------------------------------------------0.98481205 0.17253109 9 <0.0001------------------------------------------------------------
Linear Fit for Q85oneline_B on linearized scales.yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 19.19073465 1.74943932B 3.59317129 0.48424095------------------------------------------------------------
R SD N P------------------------------------------------------------0.94959744 0.12966829 8 0.00030813------------------------------------------------------------
Sn-Cu
Q=85kJ/mol
1(all)normalized
(dγ/d
t)(T/
G)e
xp(Q
/kT)
τ/G
Materials Science DivisionLawrence Berkeley National Laboratory
Department of Materials Science and EngineeringUniversity of California at Berkeley
Conclusion
• Sn-rich solders show two regimes of steady-state creep behavior– nL ~ 3.5-6.5 at low stress– nH ~ 8-11 at high stress– Break at τ/G ~ 4x10-4 (Sn,SnCu), 7x10-4 (SnAgX)
• The high-stress exponent (nH) increases dramatically near room temperature– due to dominant Sn constituent
• Nonetheless, overall creep behavior is reasonably well fit by two-stage curve with Q ~ 80 KJ/mole
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