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8/2/2019 Chapter 8 - Mechanical Characterization
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Chapt er 7hapt er 7M echanical Charact erizat ion of t heechanical Charact erizat ion of t heE lect ronic Packageslectronic Packages
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Thermal M ismat chhermal M ismat chSi (CTE=2~3 ppm/C)
Substrate (CTE=15~20 ppm/C)
EU solder (CTE=25 ppm/C)Underfill (CTE=7 ppm/C)
Thermal mismatch in elect ronic package is due to t he diff erent
coeff icient s of t herm al expansion (CTE) in dissim ilar m aterials(Si/ solder, Si/ underfi l l , Si/ subst rate) or t he temperaturegradient
Thermal st ress and t he associated therm al st rains w ill ar ise in
t he connect ion joint or all interconnect ions.
Thermal fatigue failures result from the therm al m ismatchduring t herm al cycle (uniform temperature environment ) orpower cycle (pow er on/ off, program running)
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Thermal F at iguehermal F at igue
Low cycle fat igue ( LCF) : below 106 cycles, plast icity encount ered w it hobvious plast ic deform ation.
High cycle fat igue(HCF) : above 106 cycles, st rains are elastic andw it hout obvious plast ic deformation.
Thermal fat igue is a classic case of low cycle fat igue (LCF)
For solder, the st rain encount ered in t hermal cycle can be a few t imes
as large as t he yield strain
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F at igue L i f e Predict ion Procedureat igue L i f e Predict ion ProcedureF
F
M
M
Shear Stress
Shear Strain
1. Det ermine syst em forces and deformations
2. Det erm ine local stresses and str ains in solder
3. Est imate fat igue life
Estimation
Local st resses/ st rains are cri t ical t o the suscept ible element inpackages (solder j oint )
Local shear st rains in solder j oint dominate t he failure mode and areused fro t he predict ion of t he thermal fat igue l i fe
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Thermal St ress/ St rainhermal Stress/StrainChip "1"
Joint "C"
Substrate "2"
=T
=L
=C
h
=
Temperaturerise
Beam length
Joint height
CTE
Shear St ress Shear St rain
( )
cc
cc
c
c
IE
Ah
G
h
TL
12
3
21
+
=
( )
ch
TL
=21
1. E1, E2, I 1, I 2 are very large values
2. Shape of solder is righ t circular cylinder
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Coffinoff in-M anson Relat ionshipanson Relat ionshipL
ch
Formation
Large t emperat ure excursions cause diff erentdamage mechanism w hich depends onoverstress and st rong variat ion of t heproper t ies of solder
Solder j oint qualit y w hich may cause fracturein solder t hat fails t his model
High frequency/ low temperat ure make solderbehavior like an elast ic material, t hus plast icst rain is not close to t he local st rain
C
f
fN
1
'22
1
=
442.0
325.0'
=
=
C
f
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Examplexample5 mm
100 um
dia.hc
1
2
C
Temperatur e range: 35C t o 85C
Solder height effect on fat igue life:
6100
110
5020
100
3874
90
Nf (cycle)
Height ( um)
442.0;325.0;50)3585(
/4.4/)6.27(
' ====
==
cCT
CppmCppm
f
502065.0
011.0
2
1 442.01
=
=
fN011.0
100
504.45000=
=
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Pref erred Solut ionreferred Solution Thermal st ress:
By decreasing:
By increasing:
Thermal st rain:
By decreasing:
By increasing:
ccEGLT ,,,,
LT,,
c
c
c I
A
h ,
ch
The height of solder j oint is suggested the higher t he bet t er
can be low ered by selected a proper substrate
Smaller suggested using soft er solder material
DNP(L): t he dist ance betw een a solder j oint and the neut ral point of t hechip ( chip cent er)
ccGE ,
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Quick E st imat ion of Solder H eightuick E st imat ion of Solder H eight The solder volume of a spherical solder j oint :
Height of a furst rum of a crone:
Vert ical loading per j oint :
( )[ ]222 36
css
s rrHH
V ++=
[ ] [ ] 31
3231
32 BAABAAHs
++++=
VA 3= 22
scrrB +=
( )223
sscc
crrrr
VH++
=
( )sc
sn
HHHHFf
=
( ) ( ) ( ){ }
++
++
= 21
22
21
222
2
222
2 244
csccssscs
s
css
s
sc
rrHrrHHrrH
rrHr
HHF
sH
cH
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D if f erent Solder V olumeif f erent Solder V olume I nput Data
Final Height & Deposit ion Height + / - Variat ion:
cmdyne
gfdynef
umcmr
umcmr
n
s
c
/325
005.09.4
50005.0
50005.0
===
==
==
70
110
78
X 502 X 110
CASE 3
64
90
69
X 502 X 90
CASE 2
67
100
73
X 502 X 100
CASE 1
)( 3umV
)(umHs
)(umHc
)(umH
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Examplexample400um
600um
TRADE-OFF BETWEEN FATIGUE, THERMAL AND PROCESSING
PROCESSING VARATIONStandard joint height: 15um ; deposition thickness: 15.2 um
Standard deviation 10% of specified thickness (within 3-sigma deviation)
Max. joint height = 19.3um Min. joint height = 10.6um
FATIGUE AND THERMAL RESISTANCE VARIATION
51
23000
Min.
54
51000
Mean
56
93000
Max.
Thermal resistance (C/ W)
Fat igue life (cycles, delt a T = 60C)
Joint height
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M icrost ruct ure of 63Sn/ 37Pb E ut ect ic Soldericrost ruct ure of 63Sn/ 37Pb E ut ect ic Solder
The coarsened region is inherent ly w eaker and t hrough w hich crackspropagate to fi nal solder f ailure
The heterogeneous coarsened band is approx imately parallel t o t heimposed shear strain
Quant it ative modeling of t he microst ructure change is not possible
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A u/ N i M et al li zat ion on a Cu Padu/ N i M et al l izat ion on a Cu PadSolder Ball
Die
Solder MaskCu Pad/Trace
Solder Ball
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F ini t e E lement A nalysis of Solder F at igue L i f eini t e E lement A nalysis of Solder F at igue L i f e
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A nalysis A lgori t hm f or Solder F at iguenalysis A lgori t hm f or Solder F at igue
ANSYS Modeling
Fatigue Life
* Material Properties Analysis Procedure
Data Output Prediction Model
Solder ball profile Solder Material Specific Temp. cycle
Solution MethodologyGeometry consideration Bump+Underfill
composite properties
Converge criteriaBoundary conditionsComponent properties
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F E A M odel ing SchemesE A M odel ing SchemesReferred from: Finite Element Modeling of BGA Packages for Life Prediction
2000 Electronic Components and Technology Conference, pp.1059-1063
Modeling Method Modeling Desciption Advantage/Disadvantage Remark
Nonlinear slice model
1.Octant symmetry, untilizes inly a diagonal slice of the package
2.The model imposes symmetric boundary conditions on the slice plane coinciding
with the true symmetry plane
Reduce computation time Most Conservative
Nonlinear global model withlinear super model
1.Package and board are modeled as two super element and all of the solder ballsas three-dimensional finite elements
2.Except for the critical joints, the solder balls are modeled with a coarse mesh
Avoid the assumptions associated withthe boundary conditions of the slice
model
Not acceptable
Linear global model with
nonlinear submodel
1.Linear model of substrate and board and all of the solder balls using three-
dimensional f inite elements
2.The global model includes only linear material properties, whereas the submodel
includes nonlinear material behavior
3.The linear global model is s
Permit the simulation of any thermal
cycle using only one set of global model
results
Most f idelity
Nonlinear global model with
nonlinear submodel
1.Nonlinear global model with a very coarse mesh for the substrate and board and
for the solder balls
2.Providing the critical solder joint for the subsequent nonlinear submodeling
Displacements become the coundary
conditions for the nonlinear submodel of
the critical joint in accordance with the
thermal cycling
Nonlinear global model
1.Global model employs a relatively coarse mesh for all of the components of a
package except for the critical joints
2.It is not feasibile to model all of solder joints if the package consists of a large
number of solder joints
Time consuming
Selected Modeling Methodologies:
Nonlinear slice model: single chip package
Linear global model with nonlinear sub-model: SiP or MCM packages
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Approaching Architecturespproaching A rchi t ect uresViscoplasticity
Plasticity
Elasto-plastic + Creep
- curves (SOLID185)
Creep Model (SOLID185)
Anands Model (VISCO107)
Darveaux (plastic work)
Coffin-Manson (Equivalent plastic strain)
2
10
K
aveWKN =dN
da
aN += 0
m
f
p CN=
Finite Element Solution DomainExperimental+Analytical Solution Domain
ANSYS Environment
43 KaveWK
dN
da
= 2=ffN
Approaching Method Property Implement Advantages Disadvantagess
1. popular for life prediction of eutectic solder 1. limitation of material informations (LF)
2. has been proven and widely used 2. only plastic work can be read out
3. nonlinear plasticity & creep involved 3. life prediction variables are dif ficult obtained1. stress-strain curves can be experimented (LF) 1. only plasticity behavior without creep effect
2. Cof fin-Manson variables can be determined
3. both two kinds of life prediction methods can be used
1. can be used for low frequency fatigue analysis 1. difficult converge and time consuming
2. both two kinds of life prediction methods can be used 2. not real plasticity behavior involved
3. creep functions can be determined by experiments
Viscoplasticity
Plasticity
Temp. dependent elastic
modulus and creep functionElasto-plastic + Creep
Temp. dependent
stress-strain curves
Anand's model
Plasticity (high-cycle fatigue) +Creep (low-cycle fatigue) = Viscoplasticity (in-elastic fatigue)
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F at igue A nalysis using A N SYS Codeat igue A nalysis using A N SYS Codecr
eq
pl
eq
in
eq +=
( ) ( ) ( )i
in
eqi
in
eq
in
eq = +1
( ) ( ) ( )saturated
in
eqn
in
eqn
in
eq === + L1
( )Csaturated
in
eqf BN =
FEM: Plasticity & Elasto-plastic +Creep
After nth cycles
Modified Coffin-Manson Law
Plasticity: equivalent plastic strain grows in the ramp duration and stays in the hold-time (dwell)
Elasto-plastic + Creep: creep strain accumulates more in the hold-time duration (dwell)
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Tw ow o-st age A nalysis M et hodt age A nalysis M et hodC*** SOLDER !MATERIAL PROPERTIES OF SOLDER BALL
MP,EX,1,30E3MP,NUXY,1,0.4
MP,ALPX,1,24.7E-6
TB,BKIN,1,3
TBTEMP,273 ! Temperature = 273
TBDATA,1,46,(55-46)/(0.45-0.025) ! Stresses at temperature = 273 (0)
TBTEMP,323 ! Temperature = 323
TBDATA,1,34,(39-34)/(0.45-0.025) ! Stresses at temperature = 323 (50)
TBTEMP,373 ! Temperature = 393
TBDATA,1,18,(20-18)/(0.45-0.025) ! Stresses at temperature = 393 (100)
EquivalentEquivalent Plastic StrainPlastic Strain
C*** SOLDER !MATERIAL PROPERTIES OF SOLDER BALL
MP,EX,1,30E3
MP,NUXY,1,0.4
MP,ALPX,1,24.7E-6
TB,BISO,1,3
TBTEMP,273 ! Temperature = 273
TBDATA,1,46,(55-46)/(0.45-0.025) ! Stresses at temperature = 273 (0)
TBTEMP,323 ! Temperature = 323TBDATA,1,34,(39-34)/(0.45-0.025) ! Stresses at temperature = 323 (50)
TBTEMP,373 ! Temperature = 393
TBDATA,1,18,(20-18)/(0.45-0.025) ! Stresses at temperature = 393
(100)
TB,CREEP,1,,,8 !CREEP MODEL
TBDATA,1,12423.2,0.125938,1.88882,61417
Stage 1: Plasticity analysis
-Temp. dependent stress-strain curves
-Nonlinear kinematic strain hardening
EquivalentEquivalent Creep StrainCreep Strain
Stage 1: Plasticity + Creep analysis
-Temp. dependent stress-strain curves
-Isotropic strain hardening
-Creep function
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Temperature Cycle Prof i leemperature Cycle Prof i le
0
100
25
1st cycle 2nd cycle 3rd cycle
Dwell period of 5 mins Ramp rate = 10/min
(L)
(A) (B)
(C) (D)
(E) (F)
(G) (H)
(I) (J)
(K)
Time
Temp
183
Remark:
Board Level TC: 0~100C; 5 mins dwell and ramp rate with 10C/min
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Stresstress-st rain Curves of Solder Jointt rain Curves of Solder JointKinematic Hardening
Stress-Strain Curves of Eutectic Solder (63Sn/37Pb)
Remark: To used bi-linear stress-strain model instead of multi-linear
model can make a balance between computation accuracy and
time consuming
Kinematic hardening effect must be considered into the FEA
analysis
C
D
Yield Surface
Bauschinger Effect
F
0
3
2
O
S
0.0 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.5
Strain
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
Stress(MPa)
Temp. = 0 C
Temp. = 50 C
Temp. = 100 C
B
A
O
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M at erial Propert iesat erial Propert iesMaterial Type Temp. (K) Yield Strength (MPa)
22000 x,y 0.28 xz,yz 19 x,y
10000 z 0.11 xy 70 zSolder Mask 298 3448 0.35 elastic 30
Copper Pad 298 68900 0.34 69 16.7
26000 x,y 0.39 xz,yz 15 x,y
11000 z 0.11 xy 52 z
< 70 7 32
> 70 0.04 110
Silicon Chip 298 162000 0.28 elastic 2.3< -120
> -120 0.35 232
< 49 39
> 49 162
Heat Spreader 298 71 0.0334 elastic 18
0.38 elastic
Temp.-dependent
nonlinear0.3Adhesive
TIM
7/273,4/298,0.7/323,0.09/348,0.
075/373,0.075/423
BT Laminate 298 elastic
Underfill 0.33 elastic
Elastic Modulus (MPa) Poisson's Ratio CTE (ppm/K)
FR-4 Board 298 elastic
Solder creep function: for 63Sn/37Pb solder( )[ ] Tcreep e88882.1
125938.0sinh2.12423= 61417
&
U S U S U Eeq, Geq, veq, eq
j+1
j+1
j
j j
j
j+1
j+1Solder bump + Underfill
V
uVsV
VVn uu /=
VVn ss /=Total volume:
Bump volume:Underfill volume:
ssuueq nEnEE += ssuueq nn +=
Equivalent material properties
Composite Algorithm
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F ini t e E lement M odel & BCinit e E lement M odel & B Cs
Remark:
Diagonal slice modeling for single-chip module
Solder ball profile is determined by program prediction
Coupling constraints make structure behave plane strain condition
Coupling UY
UX=0
UY=0
Coupling UX
Fix
Single-chip Module Modeling
Symmetric BCs
Symm
etricBCs
Slice Model
Substrate opening: 0.5 mm
PCB opening: 0.4 mm
Standoff height: 0.4 mm
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A ccumulated Plast ic and Creep St rainccumulated Plast ic and Creep St rainAccumulated equivalent
plastic strain (1st cycle)
Accumulated equivalent
plastic strain (2nd cycle)
Accumulated equivalent
plastic strain (3rd cycle)
Accumulated equivalentcreep strain (2nd cycle) Accumulated equivalentcreep strain (3rd cycle)Accumulated equivalentcreep strain (1st cycle)
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E xample of Case St udyingxample of Case Studying(a) 4112 cycles
(b) 1897 cycles
(c) 1151120 cycles
(d) 18036 cycles
(a) (c)
Ni PEEQ CEEQ IEEQ IEEQ Ni PEEQ CEEQ IEEQ IEEQ
Cycle 1 0.012766 1.332E-15 1.277E-02 0.0127660 Cycle 1 0.001228 5.995E-15 1.228E-03 0.0012280Cycle 2 0.028515 1.998E-15 2.852E-02 0.0157490 Cycle 2 0.002155 1.044E-14 2.155E-03 0.0009270
Cycle 3 0.044276 2.665E-15 4.428E-02 0.0157610 Cycle 3 0.003071 1.488E-14 3.071E-03 0.0009160
(b) (d)
Ni PEEQ CEEQ IEEQ IEEQ Ni PEEQ CEEQ IEEQ IEEQ
Cycle 1 0.025338 1.332E-15 2.534E-02 0.0253380 Cycle 1 0.009468 1.776E-15 9.468E-03 0.0094675
Cycle 2 0.049560 2.665E-15 4.956E-02 0.0242220 Cycle 2 0.017186 3.109E-15 1.719E-02 0.0077185
Cycle 3 0.073809 3.997E-15 7.381E-02 0.0242490 Cycle 3 0.024829 4.441E-15 2.483E-02 0.0076430
Substrate Edge / Substrate Side
Substrate Edge / PCB Side
Chip Edge / Substrate Side
Chip Edge / PCB Side
Fatigue life at substrate edge / substrate side: 4412 cycles
Fatigue life at substrate edge / PCB side:1897 cycles (ASE:2000 cycles )
Fatigue life at chip edge / substrate side:1151120 cycles
Fatigue life at chip edge / PCB side:18036 cycles
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Predict ion of Solder B al l Prof i leredict ion of Solder B al l Prof i le
-1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.000.00
0.10
0.20
0.30
0.40
PBC pad open: 0.380 mm
PBC pad open: 0.400 mm
PBC pad open: 0.475 mm
PBC pad open: 0.500 mm
Substrate pad open PCB pad open Standoff height
Case1 0.525 mm 0.380 mm 0.404 mm
Case2 0.525 mm 0.400 mm 0.399 mm
Case3 0.525 mm 0.475 mm 0.381 mm
Case4 0.525 mm 0.500 mm 0.374 mm
Programming by CY @ CCU (2000)
Original data are followed by KC
Pitch: 1 mm
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PCB Pad Opening E f f ectCB Pad Opening E f f ectTime (min) Pad=0.38 mm Pad=0.4 mm Pad=0.475 mm Pad=0.5 mm
0 0.000E+00 0.000E+00 0.000E+00 0.000E+00
600 1.572E-03 1.509E-03 1.409E-03 1.368E-03
900 1.572E-03 1.509E-03 1.409E-03 1.368E-031500 2.495E-02 2.467E-02 2.060E-02 1.983E-02
1800 2.790E-02 2.753E-02 2.285E-02 2.201E-02
2400 3.442E-02 3.397E-02 2.852E-02 2.754E-02
2700 3.442E-02 3.397E-02 2.852E-02 2.754E-02
3300 5.238E-02 5.099E-02 4.181E-02 3.972E-02
3600 5.527E-02 5.376E-02 4.405E-02 4.187E-02
4200 6.232E-02 6.054E-02 5.023E-02 4.789E-02
4500 6.232E-02 6.054E-02 5.023E-02 4.789E-02
5100 8.018E-02 7.733E-02 6.298E-02 5.960E-025400 8.310E-02 8.012E-02 6.523E-02 6.176E-02
cycle1 2.790E-02 2.753E-02 2.285E-02 2.201E-02
cycle2 2.738E-02 2.623E-02 2.120E-02 1.987E-02
cycle3 2.783E-02 2.636E-02 2.118E-02 1.989E-02
PEEQ 2.760E-02 2.630E-02 2.119E-02 1.988E-02
Time (min) Pad=0.38 mm Pad=0.4 mm Pad=0.475 mm Pad=0.5 mm
0 0 0 0 0
600 0.000E+00 0.000E+00 0.000E+00 0.000E+00
900 8.882E-16 8.882E-16 8.882E-16 8.882E-161500 1.332E-15 1.332E-15 1.332E-15 1.332E-15
1800 1.332E-15 1.332E-15 1.332E-15 1.332E-15
2400 1.332E-15 1.332E-15 1.332E-15 1.332E-15
2700 2.220E-15 2.220E-15 2.220E-15 2.220E-15
3300 2.665E-15 2.665E-15 2.665E-15 2.665E-15
3600 2.665E-15 2.665E-15 2.665E-15 2.665E-15
4200 2.665E-15 2.665E-15 2.665E-15 2.665E-15
4500 3.553E-15 3.553E-15 3.553E-15 3.553E-15
5100 3.997E-15 3.997E-15 3.997E-15 3.997E-155400 3.997E-15 3.997E-15 3.997E-15 3.997E-15
cycle1 1.332E-15 1.332E-15 1.332E-15 1.332E-15
cycle2 1.332E-15 1.332E-15 1.332E-15 1.332E-15
cycle3 1.332E-15 1.332E-15 1.332E-15 1.332E-15
CEEQ 1.332E-15 1.332E-15 1.332E-15 1.332E-15
1000
1500
2000
2500
3000
3500
Pad=0.38 mm Pad=0.4 mm Pad=0.475 mm Pad=0.5 mm
Predictition ASE
Pad Open 0.38 mm 0.40 mm 0.475 mm 0.50 mm
Prediction 1470 1617 2469 2797
ASE Data 1710 2056 2780 3388
Difference 16.3% 27.2% 12.6% 21.1%
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M oire I nt erf eromet ryoire I nt erf eromet ry M et hodethod
oire I nt erf eromet ry ethod
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M oire I nt erf eromet ry M et hod
M oire I nt erf eromet ryoire I nt erf eromet ry M et hodethod
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32 Shadowhadow M oireoire M et hodethod
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:...
Shadowhadow M oireoire M et hodethod
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34 Shadowhadow M oireoire M et hodethod
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35 E lect rical Speckle Pat t ern I nt erf eromet er (E SPI )lect rical Speckle Pat t ern I nt erf eromet er (E SPI )
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(ESPI)
:(NDE) ...
E lect rical Speckle Pat t ern I nt erf eromet er (E SPI )lect rical Speckle Pat t ern I nt erf eromet er (E SPI )
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37 Three Point Bendinghree Point B ending
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Stiffness is a measure of how easily an object will bend when put under. It isoften necessary to have stiff components, and this is achieved through the
combination of design, ie the geometry, and material selection. The main material
property that affects the stiffness is the Young's modulus, which has a large range
of values for different materials.
A strip of balsa undergoing a 3-point
bending test
The three-point bend can also
allow us to find the Young'sModulus (E) of the material once
the second moment of area (I) isknown.
This is done by relating the
vertical displacement , to theload W (= Mg) using the formula:
= WL3/48EIwhere L = distance between thesupports.
D erivat ion of equat ion under 3erivat ion of equat ion under 3-point Bendingoint B ending
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Starting with
take moments about left hand end:
and integrate:
At x = L/2, dy/dx = 0, hence C1 = WL2/16
Integrate again:
At x = 0, y = 0, hence C2 = 0.
y is at a maximum at x = L/2, so
and
3-Point B ending f or F ract ure I nt ensi t yoint Bending f or F ract ure I nt ensi t y
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40 F our Point B endingour Point Bending
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41 F our Point Bending I nst rumentour Point B ending I nst rument
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42 4-Point B ending A ppl icat ionoint Bending A ppl icat ion
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Four point bending test
With four point bending fixture a constant bending moment is achieved betweenthe two indenters. In three point bending the moment increases linearly from
support to the indenter.
The strain (and stress) in four point bending varies linearly across the test
specimen. e = M y / EI, where y is distance from the center of test sample Because
the bending moment is constant between the indenters also the strain is.
When the reliability of solder joints is tested 4 point bending test is good because
all joints between the indenters are under equal loading.