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SURFACES, INTERFACES AND MICROELECTRONIC PACKAGING
Guna Selvaduray, August 4, 2016
Guna Selvaduray Professor
San Jose State University IEEE Santa Clara Valley
Reliability Chapter
Guna Selvaduray, SJSU
Presentation Overview
Brief Intro to SJSU Surfaces and Interfaces in Packaging Characterization of Surfaces Surface Interactions Solder Interactions
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Acknowledgements, Request
Acknowledgements Many students Many industry colleagues Syed Hussain for invitation
Request Please feel free to ask questions Please feel free to point out any mistakes or
misconceptions
3
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SJSU – Urban Campus 4
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Tower Hall 5
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SJSU Overview
Oldest of 23 campuses of the California State University system
Oldest public institution of higher learning in California – since 1857
32,773 students (in Fall 2015) Undergraduates: 26,822 Graduate students: 5,951
198 degree programs B.S. and M.S. programs
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College of Engineering - 1 7
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College of Engineering - 2
13 Engineering Degree Programs Aerospace Chemical Civil Computer Electrical Industrial and Systems Materials Mechanical Biomedical Software General Aviation Technology
7,348 Students Undergraduates 4,675 Graduate Students 2,673
Located in the heart of Silicon Valley
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College of Engineering - 3
Features Focus: hands-on practical education Approx 95% of graduates work as engineers Close ties with Si Valley industries ABET accredited programs Applied/Translational Research
Provides more engineers to Si Valley than any other university
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What is “Packaging”? 10
http://www.papermart.com/shipping-supplies
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Analogy – the automobile 11
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Analogy – packaged Si die 12
(Engine)
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Why Surfaces?
Surface Roughness Surface Tension/Surface Energy Hydrophobicity & Hydrophilicity Surface Cleanliness Surface Chemistry Surface Analytical Techniques Surface Microstructure in Multiphase Alloys Sterility
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Surface Roughness - NiTi 14
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Surface Chemistry 15
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Surface Stress States (316L SS) 16
15
20
25
30
35
40
45
50
0 5 10 15 20 25 30 35
NTPAEPEPP
Zone of Biocompatibility
Cri
tical
Sur
face
Ten
sion
(mJ/
m2 )
% Surface Plastic Strain (tensile)
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Dual Inline Package (DIP) 17
Surface Interactions
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Flip Chip 18
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Materials Used
Si Interconnects – Cu, Au, Al Encapsulation – Epoxy resin composites
Printed wiring board – FR4 Substrates – FR4, BT, Al2O3, AlN Conformal coatings – polyurethanes, others
Surface finishes – several Solders - Pb-Sn, several Pb-free formulations Die attach – polymer composites with fillers
Several other materials, including special formulations
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Surfaces & Interfaces
Bare surfaces Cu
Interfaces Metal-metal (soldering) Metal-polymer
Several other combinations
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Moisture Intrusion Pathways
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Die
Silicon Die
Mold Compound
Gold Wire
Solder Resist
Solder Resist
Copper Trace
Substrate Core (BT Resin)
Copper Trace
Solder Balls
Die Attach
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Popcorn Cracks 22
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Popcorn Cracks 23
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Delamination 24
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Scanning Acoustic Microscopy 25
Delamination under Si die
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Surface Roughness & Solder Wicking
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(a) horizontal grooves (b) vertical grooves. Roughness: 600 grit, 240 grit, 120 grit, 60 grit
a
b
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Wetting Force 29
Immersion Wetting time (TW)
F 0
F 0
θ
Maximum Wetting Force (FMAX) F 0
θ
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63Sn-37Pb, Cu Substrate Aqueous Flux, T = Tm+62oC
30
-6
-4
-2
0
2
4
6
0 1 2 3 4 5
Time (s)
TW
FMAX
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FMAX of Solders (Bare Cu, T = TM + 62oC) 31
Alloy Tm FMAX (AVG) StDev TW (AVG) StDev(C) (mN) (s)
Sn-37Pb 183 4.792 0.069 0.385 0.038Sn-3.5Ag 221 4.822 0.137 0.400 0.041Sn-58Bi 139 3.518 0.119 0.608 0.079Sn-9Zn 199 1.772 0.287 0.625 0.458
Alloy Tm FMAX (AVG) StDev TW (AVG) StDev(C) (mN) (s)
Sn-37Pb 183 3.486 0.802 1.570 1.139Sn-3.5Ag 221 4.013 0.517 0.785 0.380Sn-58Bi 139 2.410 0.358 4.092 2.223Sn-9Zn 199 -4.300 0.802 x x
Aque
ous-
Cle
an
Flux
No-
Cle
an F
lux
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Fmax vs cold work; T=245°C 32
Flux Solder % Cold Work 0 10 20 30 40 50
Maximum Wetting Force (mN) Aqueous Sn-3.5Ag 3.01 3.05 3.46 3.63 4.11 4.30
Sn-37Pb 3.72 3.85 4.06 4.29 4.58 4.84 Sn-9Zn 0.46 0.78 0.97 0.93 1.48 1.83 Sn-0.7Cu 2.85 3.09 2.90 3.40 3.31 3.51
No-Clean
Sn-3.5Ag -4.89 -3.33 -1.58 -0.88 2.40 1.32 Sn-37Pb 3.41 3.51 3.87 3.65 4.22 3.99 Sn-9Zn -5.72 -3.55 -2.68 -2.15 -1.50 -1.20 Sn-0.7Cu -4.84 -4.95 -1.95 -2.55 -2.41 -4.18
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Soldering & Wetting 33
PCB
Solder Joint + Fillet
Lead Frame
Cu Pad
Package (Body)
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Lap Joint Shear Strength Tests
Cu substrates
Solders: Sn-37Pb, Sn-4.0Ag-0.5Cu, Sn-0.7Cu, Sn-3.5Ag
ASTM D-1002 Reflowed
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35
Lap Shear Specimen
Type of solders used:
1 in
4 in
0.064 in
•Sn-37Pb
•Sn-3.5Ag
•Sn-0.7Cu
•Sn-4Ag-0.5Cu
Overlap area: 0.5 in Copper 99.99% purity
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Joint Shear Strength (psi) 36
Solder Thickness
3mils 4mils
Solder Alloy Average StdDev Average StdDev
SnPb 3246 144 3329 81
Sn-Ag-Cu 2089 208 1655 182
Sn-Ag 2352 162 2388 172
Sn-Cu 1537 51 1736 63
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Voids in Pb-free Solders
X-ray images of Sn-0.7Cu solder joints
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Solder Alloy vs Solder Joint
Wetting Force data consistent with Shear Test data Solder alloy material properties and joint
properties not the same Interfacial interactions crucial in determining solder
joint properties
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Intermetallic Compound Formation
Following slides represent a part of a larger investigation
Intermetallic compound formation as a function of aging
SAC 305 Solder Balls mounted and reflowed on ENIG coated Cu pads
Aged at 150oC, for 0, 10, 20, 30 days Cross-section analyzed metallographically – optical
and SEM
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Cross section after reflow 40
Cross sections from two different solder balls
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5-day aging at 150oC 41
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10-day aging at 150oC 42
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20-day aging at 150oC 43
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30-day aging at 150oC 44
45
Cu-Sn Phase Diagram
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Cu-Ni Phase Diagram
47
Ni-Sn Phase Diagram
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IMC Layer Thickness 48
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Interfaces in FR4 PWB 49
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Thank you
Questions ? Comments?
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