Physical and Mechanical Characteristics
of Pb-free Solder - Copper Joints
Project funded by OFES (Switzerland)
Within the framework of :Cost Action 531:Within the framework of :Cost Action 531:
J. Janczak-Rusch* , T. Rütti*,
A. Mellal@ and John Botsis@
*EMPA; @EPFL
New generation particle reinforced Pb-free solders: initial tests
• Experimental setup– tensile test specimen dimensions: 20mm x 1mm cross section– solder alloy: Sn-3.5Ag-0.5 Cu– soldering cycle: 6 min ( 30 s) to melt, 1 min ( 10 s) in liquid phase, fast
cooling (solder jig placed into water); peak temperature: 230°C– tensile test conditions: Instron 5848 MicroTester in displacement control
mode at 1µm/s; strain measured with a 50mm clip gauge
• Test matrix– effect of solder gap width: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8 and 1.0mm
– effect of room temperature ageing (TH= 0.6): 1day, days, 1 week, 2 weeks, 1 month, 2 months
– effect of ageing at elevated temperatures: 1 week and 2 weeks at TH =0.75 and TH = 0.9
Thermal cycling
Extensometer's displacement
0
0.005
0.01
0.015
0.02
0.025
0.03
0 50 100 150 200 250 300
Time (s)
Dis
pla
cem
ent
(mm
)
Recorded load
0
100200
300400
500600
700800
900
0 50 100 150 200 250 300
Time (s)
Lo
ad (
N)
h
b
e
t
h = 50 mm
b = 20 mm
e = 1 mm
t = variable
Mechanical testing
Preliminary results• Results
– a notable number of gas pores form in the solder joint under the given soldering conditions
– yield stress, tensile stress, Young’s modulus and strain at fracture are not significantly influence by ageing at room temperature
– ageing at high temperatures reduces yield and tensile strengths and increases strain (ductility)
– decreased solder gap width increases yield and tensile strengths and decreases strain (ductility)
Ageing temperature
solder gap width
Yield strength
Tensile strength
Young’s modulus
Strain at fracture
[mm] [MPa] [MPa] [GPa] [%]
TH = 0.60 0.1 47.8 ± 2.0 50.5 ± 5.7 109.8 ± 3.1 0.051 ± 0.006
TH = 0.60 1.0 29.7 ± 3.1 41.1 ± 2.6 100.8 ± 8.3 0.068 ± 0.009
TH = 0.75 1.0 27.3 ± 0.3 37.5 ± 0.1 104.4 ± 2.9 0.072 ± 0.017
TH = 0.90 1.0 23.7 ± 1.3 33.4 ± 2.0 98.4 ± 2.8 0.081 ± 0.013
Typical microstructures
cross-section (etched)
Sn-4.0Ag-0.5Cu solder joint
typical fracture surface
Purpose
Numerical simulation of solder joints mechanical behavior
Model description: Geometry (h = 50 mm, extensometer’s length) Boundary conditions: same as experiment, T=25°C FE Mesh (Plane stress, 2 axial symmetries) Constitutive law
•Copper: Elastoplastic (E=112 GPa, =0.33, y=69 MPa)
•Solder: elasto-viscoplastic (E=56 GPa, =0.35, y=32.5 MPa)
creep: Garofalo’s type power law
Finite Element Analysis
h
b
x
y
sin expncr Q
A BRT
Lead-free joint1mm gap
0
200
400
600
800
1000
0,000 0,005 0,010 0,015 0,020 0,025 0,030
Displacement (mm)
Fo
rce
(N)
Experiment Simulation
Calibration of constitutive model:
Finite Element Analysis
Lead-free joint0.15mm gap
0
200
400
600
800
1000
1200
0,000 0,005 0,010 0,015 0,020 0,025 0,030
Displacement (mm)
Forc
e (N
)
Experiment Simulation
Simulation of different thickness specimen:
Finite Element Analysis
New generation particle reinforced Pb-free solders
• Next steps– soldering under vacuum/ reduced pressure to
eliminate gas pores– testing of different base solder alloys: Sn-Ag and
Sn-Cu compared to Sn-Ag-Cu– incorporation of strengthening particles into solder
alloy