1 Deformation and damage of lead free materials and joints J. Cugnoni*, A. Mellal*, Th. Rütti @, J....
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Transcript of 1 Deformation and damage of lead free materials and joints J. Cugnoni*, A. Mellal*, Th. Rütti @, J....
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Deformation and damage of lead free Deformation and damage of lead free materials and jointsmaterials and joints
J. Cugnoni*, A. Mellal*, Th. RüttiJ. Cugnoni*, A. Mellal*, Th. Rütti@@, J. Janczak, J. Janczak@@, J. Botsis*, J. Botsis*
* LMAF / EPFL ; * LMAF / EPFL ; @@ EMPA EMPA
SwitzerlandSwitzerland
Project funded by OFES (CH)Project funded by OFES (CH)
Cost 531 Mid-Term Meeting, Lausanne, 25.02.2005Cost 531 Mid-Term Meeting, Lausanne, 25.02.2005
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LMAF / EPFLLMAF / EPFLObjectives and tasksObjectives and tasks
Objectives:Objectives:
ManufacturingS
ize
/ Con
stra
inin
g
Eff
ects
Thermo-
mechanical H
istory
Micro S
tructure
Inte
rfac
e
Nature of Irreversible Deformations
ConstitutiveEquations
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LMAF / EPFLLMAF / EPFL
Validation and Comparison
with SnPb
Compl
ete
Chara
cter
izat
ion
of
SnAgC
u
Inve
stig
atio
ns o
n Siz
e Effe
cts
Effects of Constraints
Objectives and tasksObjectives and tasks
Modelling
Experimental
Finite Element Model
Constitutive LawType
Mixed Num. / Exp.Identification
Micro StructureAnalysis
OpticalStrain
Measurement
Designof
Experiments
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LMAF / EPFLLMAF / EPFLMechanical characterizationMechanical characterization
Elasto-plastic constitutive law :Elasto-plastic constitutive law :
...,,,, LTpvmy
...,,, LTEE cst
Characterization:Characterization: should be carried out on real solder should be carried out on real solder
joints (size and constraining effects)joints (size and constraining effects) temperature, strain rate and joint temperature, strain rate and joint
thickness are independent thickness are independent parameters and must be changedparameters and must be changed
a correlation between thermal a correlation between thermal history, microstructure and history, microstructure and constitutive behaviour must be foundconstitutive behaviour must be found
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LMAF / EPFLLMAF / EPFLLead-free solders specimensLead-free solders specimens
Bulk solder specimen:Bulk solder specimen: Solder bar from manufacturer glued in special fixtures, 25 x 6 mm cylinder Solder bar from manufacturer glued in special fixtures, 25 x 6 mm cylinder
Idealized joint specimen:Idealized joint specimen: Dimension: 120 x 20 x 1 mm, joint thickness from 0.1 to 1 mmDimension: 120 x 20 x 1 mm, joint thickness from 0.1 to 1 mm Solder: ECOREL Sn-4.0Ag-0.5CuSolder: ECOREL Sn-4.0Ag-0.5Cu
Production: Production: joint cast in a special fixture, temperature cycle: heated at 40 K/min up to melting joint cast in a special fixture, temperature cycle: heated at 40 K/min up to melting
point, held 60s in liquid phase, and then rapid cooling of the jig (water).point, held 60s in liquid phase, and then rapid cooling of the jig (water).
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LMAF / EPFLLMAF / EPFL
Mechanical characterization of Mechanical characterization of constrained jointsconstrained joints
ObjectivesObjectives characterize the stress - strain law of lead-characterize the stress - strain law of lead-
free solders in a real joint (constrained)free solders in a real joint (constrained) optical strain measurement technique to optical strain measurement technique to
measure the real strains of the solder only measure the real strains of the solder only (not the average strains of the joint)(not the average strains of the joint)
Optical measurement techniqueOptical measurement technique a grid of fine dots (pitch = 0.2 mm) glued on a grid of fine dots (pitch = 0.2 mm) glued on
the surface or the natural pattern of the the surface or the natural pattern of the material is usedmaterial is used
the deformation of the surface pattern is the deformation of the surface pattern is observed through a microscope (24x) and observed through a microscope (24x) and recorded by a high resolution video camera recorded by a high resolution video camera (1.3 MPixels) at 1 frame per second(1.3 MPixels) at 1 frame per second
custom made video extensometry (Matlab) by custom made video extensometry (Matlab) by motion tracking based on a Normalized Cross motion tracking based on a Normalized Cross Correlation (NCC) or Digital Image Correlation (NCC) or Digital Image Correlation (DIC) algorithm Correlation (DIC) algorithm
Resolution: displacement 0.2 Resolution: displacement 0.2 m, strain m, strain 0.01%0.01%
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LMAF / EPFLLMAF / EPFLBulk solder propertiesBulk solder properties
Preliminary results:Preliminary results: specimens of pure solder produced in several waysspecimens of pure solder produced in several ways important effects of thermal history and processingimportant effects of thermal history and processing properties must be characterized "in-situ" properties must be characterized "in-situ"
Bulk solder stress-strain curves
0.00E+00
1.00E+07
2.00E+07
3.00E+07
4.00E+07
5.00E+07
6.00E+07
0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0% 3.5% 4.0%
Strain
Str
ess (
Pa)
PureSolder SnAg Pure Solder SnAgCu (casted, slow cooling) Pure Solder SnAgCu (bulk)
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LMAF / EPFLLMAF / EPFLMixed num./exp. identificationMixed num./exp. identification
Identify constitutive properties even with very complex stress / strain field Identify constitutive properties even with very complex stress / strain field
=> use a finite element model instead of a simple analytical solution=> use a finite element model instead of a simple analytical solution
Mixed num. / exp. identification of the constitutive parameters
Initial guess x = x0
Numerical Solution Snum(x)
Identified parameters x
Experimental data Sexp
Error norm (Snum,Sexp)
Parameter updating x( minimization of )
> min
< min
N
i
iinum
F
uFuFnormError
1
2
exp
exp )()(
2
1 ],,[ 0 bQParameters y x
DIC measurement(Matlab) :
load - displacement curve
Non linear least squares
optimization (Matlab Optim Toolbox)
Parametric FEM (Matlab - Abaqus)
Bulk solder data
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LMAF / EPFLLMAF / EPFLInitial guess / identified solutionInitial guess / identified solution
Initial guess Identified solution
ParamParam 0 0
(MPa)(MPa)QQinf inf
(MPa)(MPa)b b (-)(-)
InitialInitial 3232 1717 5050
FinalFinal 24.924.9 11.511.5 344344
Execution time ~ 1h, ~ 50 FE solutions
We can determine the real constitutive parameters of the
solder inside a constrained joint
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LMAF / EPFLLMAF / EPFLFuture workFuture work
Characterization of the solderCharacterization of the solder Identify the elasto-visco-plastic constitutive parameters with our mixed Identify the elasto-visco-plastic constitutive parameters with our mixed
numerical-experimental identification procedure and an optical strain numerical-experimental identification procedure and an optical strain measurementmeasurement
at a given strain rate and room temperature, with at a given strain rate and room temperature, with variable joint thicknessvariable joint thickness (size / constraining effects)(size / constraining effects)
at different at different strain ratesstrain rates and and temperaturestemperatures
investigate the constraining and size effectsinvestigate the constraining and size effects Comparison with bulk solder properties at different strain rates / Comparison with bulk solder properties at different strain rates /
temperaturestemperatures
Microstructure evolution Microstructure evolution (in collaboration with EMPA, Switzerland)(in collaboration with EMPA, Switzerland)
Correlate the mechanical properties with the microstructure of the solder Correlate the mechanical properties with the microstructure of the solder Evaluate the evolution of micro structure and mechanical properties in Evaluate the evolution of micro structure and mechanical properties in
function of the thermal historyfunction of the thermal history