Post on 13-Apr-2018
Crack Initiation at Underfill/Passivation Interfaces
Raymond A. Pearson
Center for Polymer Science and EngineeringDepartment of Materials Science and Engineering
Lehigh University, Bethlehem, PA 18015rp02@lehigh.edu
October 2002
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Problem Statement• Underfill protects interconnects from thermal
expansion stresses in flip-chip• Underfill adhesion important to flip chip reliability
Solder Interconnects
UnderfillPassivation
Substrate
Silicon Die
Thermal cycling can result in debonding at UF/PI interface
Baseline 100TC 200TC
300TC 500TC 1500TC
3
• Bulk toughness testing of commercial underfills:
• Dexter underfill resin exhibits higher toughness.
K IC (MPa-m 1/2 ) G IC (J/m 2 )
Dexter FP-4511 2.15 431.4
Zymet X6-82-5 1.47 201.7
UnderfillSEN-3PB Test Method
Background
R. A. Pearson and P. Komnopad, Proc. IMAPS Material, 344 (1999)
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Interface Tested Failure Mode Gc (dry) J/m2
UF/PI 2525:DEXTER FP 4527ZYMET X6-82-5
Interfacial UF/PICohesive near PI
14.9 ± 1.5 81.4 ± 3.9
• Adhesive strength of commercial underfill resins:
Background
R. A. Pearson and P. Komnopad, Proc. IMAPS Material, 344 (1999)
• Differences in adhesion attribute to chemical interactions.
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3-LIQUID PROBE METHOD
L
S
V
γsv
γLV
γs L
θ
WA = WLW + WAB = γ1 + γ2 - γ12
WLW = 2 (γ1 γ2 ) 1/2
WAB = 2 (γ1 γ2 ) 1/2 + 2 (γ1 γ2 )1/2
LW LW
+ +- -
SAMPLE BED
VALVE
TWIN SYRINGE PUMPS
Solve nt plusad so rb at e
Solve nt
MICROCALORIMETER
DETECTOR
FLOW MICROCALORIMETRY
-∆HAB = CACB + EAEBBoth methods use probe liquids to characterize interactions between solid surfaces.
Background
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Surface CA EA CB EB γLW γ+ γ -
“Dexter”
“ Zymet”
PI-2525
BCB
1.70
0.05
0.73
0.40
1.10
0.00
0.61
1.40
1.49
4.60
* * *
4.60
0.22
0.00
* * *
0.44
41.9
46.6
46.8
40.1
0.60
0.11
0.24
0.45
1.25
4.64
5.70
1.63
* * * - no appreciable exotherm detected.Bases: acetone, acetonitrile, ethylacetate, pyridine, triethylamine.Acids:chloroform, iodine, phenol.
Drago-type characterization predicts strong bond between Zymet underfill resin polyimide.
-∆HAB = CACB + EAEB
Background
R. A. Pearson and P. Komnopad, Proc. IMAPS Material, 344 (1999)
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Interface Tested Failure Mode Gc (dry) J/m2
UF/PI 2525 (control):DEXTER FP 4527
UF/PI 2525 (HPS):DEXTER FP 4527
UF/PI 2525 (UV/ Ozone):DEXTER FP 4527
UF/PI 2525 (Plasma/02):DEXTER FP 4527
Interfacial UF/PI
Interfacial UF/PI
Slightly cohesive
Moderately cohesive
14.9 ± 1.5
18.1 ± 1.0
105.2 ± 7.0
130.9 ± 10.0
Background
R. A. Pearson and P. Komnopad, Proc. IMAPS Material, 344 (1999)
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A. J. Kinloch, G. K. A Kodokian & J. F. Watts, J. Mater. Sci. Lett., 10 (1991) 815.
Background
9
Underfill side
O2/PlasmaUntreated UV/ Ozone
PI sideBackground - FP 4527 on PI
R. A. Pearson and P. Komnopad, Proc. IMAPS Material, 344 (1999)
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O
C
O
O
OC
O
C
O
O
C O CH2
CH CH2
O
OCH2
HCH2C
O H
H N
N
H
C2H5
CH3
C
CH3
CH3
O CH2
CH CH2
O
OCH2
HCH2C
OHN N CH2CH2NH2
B. J. McAdams and R. A. Pearson, Proc. Adhesion Soc. Conf. Williamburg, VA, Feb. (2001)
Background - Three Model Underfills
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Type of Failure Gc (Dry) J/m2Cycloaliphatic/ Anhydride (Unfilled)
Adhesive at UF/PI Interface 24.2 ± 2.5
Cycloaliphatic/ Anhydride (Filled)
Adhesive at UF/PI Interface 13.4 ± 5.3
Bisphenol F/ 2,4-EMI (Unfilled)
Adhesive at UF/PI Interface 27.9 ± 2.8
Bisphenol F/ 2,4-EMI (Filled)
Adhesive at UF/PI Interface 35.2 ± 2.9
Bisphenol A/ AEP (Unfilled)
Adhesive at PI/Al Interface 147.1 ± 10.0
Bisphenol A/ AEP (Filled) Cohesive in PI >200
Adhesion to PI-2555 (Untreated)Underfill
Background
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Background - Epoxy/PI Strength
C.K. Gurumurthy,” Ph-D Dissertation”, Cornell University (2000)
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Background
Equilibrium interpenetration zone or width of polymer interface(W)
W = 2b/(6W = 2b/(6χχ))0.50.5
χχ = V/RT(= V/RT(δδaa--δδbb))22
b: statistical segment length
χ: Flory-Huggins intermolecular interaction
V: molar volume
R: gas constant
T: temperature(°K)
δ: solubility parameter
R.P. Wool, Polymer Interfaces-Structure and Strength, Hanser , NY 1995,34
W
W= width of interphase region
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Background
Polymers can adsorb onto surfaces via dispersive and site specific interactions.
P.G. de Gennes, Soft Interfaces: the 1994 Dirac memorial lecture, Cambridge University Press, 1997
Molecular Interactions
Gc = WA(1 +φ)
Gc ~ 1/χ
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• To investigate the role of polyimide chemical structure on the strength epoxy-polyimide interfaces.
• To determine the strength of epoxy-polyimide interfaces using a fracture “mechanics-like” approach.
Objectives
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Materials - Model Polyimides
N N
O
O
O
O
O
n
Poly(pyromellitic dianhydride-oxydianiline)
PMDAPMDA--ODAODA
N
O
O
N
O
O
n
O
5(6)-Amino-1-(4-amino-1-(4-aminophenyl)-1,3,3-trimethylindanbenzophenonetetracarboxylic) dianhydride copolymer
BTDABTDA--DAPIDAPI
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N
O
O
N
O
O
CF3F3C
O
n
6FDA6FDA--ODAODA
Poly(hexafluoroisopropylidenediphthalic anhydride-oxydianiline)
Materials - Model Polyimides
N
O
O
N
O
On
Poly(3,3’,4,4’-biphenyltetracarboxylic dianhydride-phenylene diamine)
BPDABPDA--PDAPDA
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Materials - Model Underfill System
H
CH
O OH2C CH2
O O
N
NCH2CH3
H
H3C
Bisphenol F Resin-unfilled
Imidazole Curing Agent(2,4-EMI)
Curing:
60°C- 4 hours
150°C-2 hours
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Approach - Sample Preparation
SurfacePolishing/Cleaning
SurfacePolishing/Cleaning
SpinCoating/
Sputtering
SpinCoating/
Sputtering
ADCBSample
Assembly
ADCBSample
Assembly
Underfill Flow
And Cure
Underfill Flow
And Cure
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P
P
a
Approach - ADCB Testing
PC δ=
=
dadC
wPGc 2
2max
C: complianceδ: displacementP: loadw: specimen widtha: crack length
D. Reedy and T. Guess, Sandia National Laboratories
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P
P
δ
Approach ~ ADCB Testing
2'4/1''1
33'
1
2
])()(1)[1()(6a
hBYhE
PaGc−++= ληρη
Testing ParametersLoading:
Monotonic, UniaxialCrosshead Rate:
1.27 mm/min
0
20
40
60
80
100
120
140
160
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
Displacement (mm)
Load
(N)
aP
C →=δ
Bao et al, Int. J. Solids Struct, 29 (1992)
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3-LIQUID PROBE METHOD
L
S
V
γsv
γLV
γs L
θ
WA = WLW + WAB = γ1 + γ2 - γ12
WLW = 2 (γ1 γ2 ) 1/2
WAB = 2 (γ1 γ2 ) 1/2 + 2 (γ1 γ2 )1/2
LW LW
+ +- -
SAMPLE BED
VALVE
TWIN SYRINGE PUMPS
Solve nt plusad so rb at e
Solve nt
MICROCALORIMETER
DETECTOR
FLOW MICROCALORIMETRY
-∆HAB = CACB + EAEB
Approach -Three Liquid Probe Method
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Approach - Butt Tensile Joint
• Pull BTJ specimen in screw-driven Instron at 0.2mm/s • Record maximum nominal applied tensile stress• Calculate stress intensity factor associated with the
singular stress field surrounding the interface corner
2hθ
KF =σ h1−λ Ap (ν )
E.D. Reedy and T. Guess, Sandia Nat. Lab.
Fixture LockingHole
Instron GrippingHole
KFC =σ*h1−λ Ap (ν)
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• Tensile plugs are precision machined to guarantee ends are flat and perpendicular to cylinder axis, and the edges are left sharp.
• Surfaces are polished carefully without breaking corners.
• Surfaces are cleaned, and coated with the appropriate coating, if necessary.
• Samples are locked in a collar fixture, using a removable shim to get the appropriate bond line thickness.
• The edges of the gap are sealed, with small holes in the front and back of the specimen; tubes are pressed up against the holes to form a tight seal.
• The sample is brought to flow temperature, underfill is forced into the gap and cured.
• The sample is removed during cooling and the seal removed.
Approach - Sample Preparation
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Type of Failure G c (Dry) J/m 2
PMDA-ODA Adhesive at UF/PI Interface 37.16
BTDA-DAPI Adhesive at UF/PI Interface 178.87
6FDA-ODA Adhesive at UF/PI Interface 78.70
BPDA-PDA Adhesive at UF/PI Interface 20.69
Adhesion to UnderfillPolyimides
Results - Interfacial Strength
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Results - Epoxy on PI contact angles
Wa = γl(1+cosθ)
γBis F/EMI = 45.2 mJ/m2
Polyimide Type θAdv Wa Gc
Bis F/EMI-24 (mJ/m2) (J/m2)
PMDA-ODA 47.9 75.53 37.2
BTDA-DAPI 18.9 87.98 179
6FDA-ODA 30 84.37 78.7BPDA-PDA 19.1 87.94 20.7
Contact Angle Epoxy -> Work of Adhesion
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Van Oss, Good and Chaudhury
R.J. Good, Journal Adhesion Science and Technology,(6) 12, 1992, 1269-1302
Wa = γl(1+cosθ) = 2(γlLW γs
LW)½ + 2(γl+ γs
-)½ + 2(γl- γs
+)½
Polyimide Type θAdv θAdv θAdv γs LW γs
+ γs - Gc
water Ethylene glycol Diiodomethane (J/m2)
PMDA-ODA 76.6 59.6 49.2 34.7 0.004 12.18 37.16
BTDA-DAPI 71.5 58.7 28.2 44.9 1.44 35.4 178.87
6FDA-ODA 81.4 62.1 39.1 40.1 0.168 8.065 78.7BPDA-PDA 79.2 57.1 19.8 47.84 0.34 7.55 20.69
Results - Probe Molecules on PI
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• Adsorption of bis F epoxy on PI surface is mostly reversible (~83%)
• Adsorption of EMI is about 25% reversible!
Results - Epoxy and EMI Molecules on PI Surface SA Mass Solvent Probe Conc. Ads Peak Disp kJ/mole
(m^2/g) (g) (mM) (mJ) (uM)
PI 2611 17.4 0.0246 Xylene Bisphenol F 10.4 178.758 1.841 226.98PI 2611 17.4 0.0246 Xylene Bisphenol F 10.4 180.671 1.831 230.54
PI 2611 17.4 0.0246 Xylene Bisphenol F 10.4 149.873 1.868 187.457PI 2611 17.4 0.0246 Xylene Bisphenol F 10.4 149.184 1.84 189.435PI 2611 17.4 0.0246 Xylene Bisphenol F 10.4 149.399 1.842 189.502
PI 2611 17.4 0.025 Xylene EMI 2,4 10.75 84.296 0.813 238.356PI 2611 17.4 0.0245 Xylene EMI 2,4 10.75 80.452 0.802 235.479
PI 2611 17.4 0.025 Xylene EMI 2,4 10.75 28.66 0.59 111.669PI 2611 17.4 0.025 Xylene EMI 2,4 10.75 19.346 0.736 60.426PI 2611 17.4 0.025 Xylene EMI 2,4 10.75 16.597 0.697 54.74
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ADCB vs. BTJ Results
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Fracture Surfaces
Completely Cohesive Fracture Predominantly Adhesive
Significant Cohesive Fracture Some Cohesive
Cycloaliphatic/Anhydride
System
Bisphenol F/2,4-EMISystem
6061-T6 Aluminum Surface PI-2555 Polyimide Surface
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Future Work
AB
C
D
E
FA
B
CA
TOP VIEW
SIDE VIEW
STRESSSINGULARIES
A B C
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Summary/Conclusions• PI-Epoxy adhesion is sensitive to the structure of the
polyimide.
• Contact angle generated Acid-Base parameters qualitatively predicts the best and the worst adhesion.
• Microflowcalorimetry experiments indicate that EMI adsorption plays an important role in adhesion.
• Crack initiation tests agree well with conventional fracture mechanics tests. More tests are underway!
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Acknowledgements• HD Microsystems for providing polyimide resins.
• Arch Chemicals for providing polyimide precursors and monomers.
• Zymet Corporation for providing underfill materials.
• Loctite/Dexter Corporation for providing underfill materials.
• SRC and PITA for their financial support.