Developed 2D CAD model of flip chip package using Hypermesh Fatigue analysis using ABAQUS CAE was done, predicting the life of solder balls in completely-filled clean and non-clean flip-chip packages Assessed and identified the fatigue life of a completely clean model is higher than that of incomplete non-clean model

1. PRATIK SAXENA GD8959
Reliability of Flip-Chip
Packages
INDIVIDUAL PROJECT
ME 7680 MANUFACTURING PROCESSING
MECHANICS
PRATIK SAXENA | GD8959 | April 30, 2017

2. PRATIK SAXENA GD8959
Problem Statement
Individual Project Code: - P9N2
Dimensions of Flip-Chip Package
Flip-Chip Model with dimension

3. PRATIK SAXENA GD8959
Thermal loading cycle:
Cyclic thermal load from -40ᵒ C (233K) to 125ᵒ C (398K)
Properties of Flip-Chip Components
Component MATERIAL PROPERTIES
SILICON CHIP Silicon Isotropic, Elastic with temperature dependent
Coefficient thermal Expansion (CTE).
SUBSTRATE FR-4 Orthotropic, Elastic with constant Coefficient
Thermal Expansion (CTE) in terms of
temperature.
SOLDER Eutectic
Isotropic, Elastic-Plastic (strain rate
BALL
Solder dependent) with temperature dependent
Coefficient Thermal Expansion (CTE).
Alloy
UNDER FILL Epoxy Isotropic, Elastic-Plastic (strain rate
dependent) with temperature dependent
Coefficient Thermal Expansion (CTE).

4. PRATIK SAXENA GD8959
Modelling and Pre-Processing
The Flip-Chipmodel wasmodelledwithappropriate dimensionsinmm, andas the critical regionsare Solder
ball and Underfill,theywere finelymeshedcomparedtootherregions.Also,care wastakenwhile meshing,
such that onlyquadelementswere created.
The elementtype used for modellingwas CPE8 which is Continuum 2nd
order Plain Strain 8 nodded
element.

5. PRATIK SAXENA GD8959
Following is the Procedure involved: -
1. The geometryforbothmodelscompletelyfilledandunfilledwere createdwithappropriate dimensionsin
mm.
2. The ‘mat_milli.inp’file wasimportedandthe propertiesandmaterialswere assignedtoChip,solderballs,
underfillandsubstrate.
3. Meshing- Asmentionedabove 2-DquadmeshwascreatedwithCPE8 elementtype,concentratedmesh
was createdincritical areasand coarse meshin non-concernareasandfor continuitybetweencoarse mesh
and fine meshbiasingandadjustingmeshdensitywasdone.
4. The componentswere nodal equivalence.Andthe elementnormal were adjustedin‘+ve’Z-direction
5. Boundaryconditions- Constraintthe leftvertical side withDOF-1,bottomhorizontal side withDOF-2
6. Appropriate thermal loadcollectorswere createdforapplyingthe thermal loadsof Initialconditionat
230C (296K), and temperature variationfrom - 40oC (233K) tempand 125oC (398k) temp.
7. The loadstepsfordifferentloadingconditionswerecreatedandLoadingwasassignedusingloadstepsto
assignvariationof temperature andcyclicloading.
Step1: Anincrementof 10 overthe periodof 600 secs at temperature of 233 K
Step2: Anincrementof 10 overthe periodof 900 secs at temperature of 398 K
Step3: we againgive the incrementof 10 overthe periodof 900 secsat temperature of 233 K.
8. When we applythese conditionandloadstepswe getthe cyclicthermal loadingforthe flipchipasgiven
inthe problem.
9. The ‘.inp’file wasexportedfromhypermeshandthenimportedtothe Abaqusforanalysis.
10. The same model isrepeatedfornon-cleanmodel.
 Cleaned Situation mode
 Non-cleaned situation model with gaps in underfill near solder ball.

6. PRATIK SAXENA GD8959
Post-Processing
Complete Cleaned Situation Model
STEP 1 - PEEQ Valuesfor solder balls.
STEP 2 - PEEQ Valuesfor solder balls.
STEP 3 - PEEQ Valuesfor solder balls.

7. PRATIK SAXENA GD8959
Thus, the values of PEEQ obtained at the end of each step is shown below
Step 1 Solder Ball 1 Solder Ball 2
A 0.00976957 0.00981717
B 0.00655985 0.00975423
C 0.00863323 0.00787514
D 0.00865754 0.00820041
Step 2 Solder Ball 1 Solder Ball 2
A 0.0153944 0.015042
B 0.0097726 0.014954
C 0.0135969 0.012753
D 0.0146645 0.013256
Step 3 Solder Ball 1 Solder Ball 2
A 0.029848 0.0296366
B 0.019861 0.0296587
C 0.027302 0.0283539
D 0.032486 0.0287295
Non-Cleaned Situation Model
STEP 1 - PEEQ Valuesfor solder balls with gap.
STEP 2 - PEEQ Valuesfor solder balls with gap.

8. PRATIK SAXENA GD8959
STEP 3 - PEEQ Valuesfor solder balls with gap.
Thus, the values of PEEQ obtained at the end of each step is shown below
Step 1 Solder Ball 1 Solder Ball 2
A 0.00130356 0.00306766
B 0.00298461 0.00271752
C 0.00310662 0.00236528
D 0.00220359 0.00268751
Step 2 Solder Ball 1 Solder Ball 2
A 0.0017144 0.0040108
B 0.0039505 0.0035083
C 0.0042498 0.0032076
D 0.0030076 0.0036964
Step 3 Solder Ball 1 Solder Ball 2
A 0.0022040 0.00554792
B 0.0055195 0.00434429
C 0.0061759 0.00423043
D 0.0041816 0.00524395
Fatigue Life Analysis
The PEEQ value for complete and incomplete model at three different step condition were calculated at
four corners of the solderball i.e.H, G, E & F to calculate the fatigue life and resultswere tabulated based
on Coffin Manson’s equation.
Solder ball (ABCD) Nomenclature
A B
D C

9. PRATIK SAXENA GD8959
The fatigue life of a flipchip package is given by Coffin- Manson's equation
(N f) 
 
= C 
Where,
β= Fatigue ductility exponent(β= 0.51) Nf= Fatigue life
ΔγP
= Appliedplastic/inelastic strain range CP
= Fatigue ductilitycoefficient. (CP
= 1.14)
Applied plastic / inelastic strain range, Δγp
= (value of step 2) – (value at step 1) & (value of step 3) –
(value at step 2) of each of the four corners of the solder ball (H, G, E, F respectively).
Thus, the tabulated values are given below,calculations are done in excel
For Solder Ball 1
FATIGUE LIFE: STEP 2 – STEP 1:
A B C D
Cleaned 33352.43 14161.68 42619.75 29319.48
Non-Cleaned 56409.41 105543.30 75850.34 15124.88
FATIGUE LIFE: STEP 3 – STEP 2:
A B C D
Cleaned 5241.64 10608.54 5817.67 3476.15
Non-Cleaned 4000.38 4077.34 2727.40 7199.17
For Solder Ball 2
FATIGUE LIFE: STEP 2 – STEP 1:
A B C D
Cleaned 38543.01 38908.08 44102.28 41113.60
Non-Cleaned 11059.04 15623.86 13804.57 9691.54
FATIGUE LIFE: STEP 3 – STEP 2:
A B C D
Cleaned 5142.81 5067.58 4512.54 4585.68
Non-Cleaned 4244.97 1401.22 9434.79 4188.68

10. PRATIK SAXENA GD8959
Conclusion:
a) From the above table, it can be inferred that, the fatigue life of completely clean model is
higher than that of incomplete non-clean model. This proves that the non-cleaning model
decreases the mechanical stability and, shortens the life time of flip-chip package
b) The fatigue life is decreased due to the gaps present in the incomplete non-clean model.
Thus, manufacturing defects such as gaps, voids create more plastic/ inelastic strains i.e.
reduces the mechanical stability of the flip chip and reduces the fatigue life of the structure.
c) Since all the four components are having differentmaterials, which have differentcoefficient
of thermal expansion, and as flip chip is subjected to temperature variation it results into
different thermal stresses
d) From the above analysis, it can be inferred that perfect under-fill layers will have good
reliability of flip-packages
e) Though in real world situation it is almost impossible to achieve the ideal completely
filledflipchip package so reducing the manufacturing defects we can increase the
fatigue life of the package.
Reference:
1. Jianjun Wang, Daqing Zou, Zhengfang Qian, Wei Ren and Sheng Liu, Effect of
Manufacturing Induced Defects on The Reliabilityof Flip-ChipPackages,” ASME 1998,
pp.35-42.
2. Class Notes for flip-chip packaging.