SURFACES, INTERFACES AND MICROELECTRONIC PACKAGING · 2018. 2. 14. · SURFACES, INTERFACES AND...

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

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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

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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

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-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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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

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Cu-Sn Phase Diagram

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Cu-Ni Phase Diagram

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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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