chapter 8 - mechanical characterization

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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12

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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13

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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14

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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15

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)





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,323 ! Temperature = 323TBDATA,1,34,(39-34)/(0.45-0.025) ! Stresses at temperature = 323 (50)


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




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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31

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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33

:...

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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36

(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 )


37/43

37 Three Point Bendinghree Point B ending


38/43

38

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
http://www.doitpoms.ac.uk/tlplib/BD1/secondmoment.phphttp://www.doitpoms.ac.uk/tlplib/BD1/secondmoment.php


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39

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


40/43

40 F our Point B endingour Point Bending


41/43

41 F our Point Bending I nst rumentour Point B ending I nst rument


42/43

42 4-Point B ending A ppl icat ionoint Bending A ppl icat ion


43/43

43

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.

chapter 8 - mechanical characterization

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