Impact of RoHS Legislation on the High Performance Industry In 2006 the European Union issued a Directive on the Restriction of Hazardous Substances (RoHS) which among other materials banned the use of lead in electronics. The Aerospace and Defense (A&D) industry in the US designs and manufactures products that carry more than three billion passengers worldwide on any given day as well as systems which are vital to our national security. In order to transition to lead-free electronics the A&D industry demands careful analysis and research into the performance, reliability and safety of these materials in order to maintain public safety and assure our war-fighters’ mission success is not compromised or risked. In this effort the College of Engineering at Tuskegee University and the Boeing Company has teamed to fill some of the many knowledge gaps that surround this new technology. Researchers at Tuskegee are undertaking an effort to understand the growth mechanism associated with the formation of tin whiskers and how to mitigate these risks. Since the formation of binary compounds are suspected of causing fractures in these new Pb-free solder alloys, Tuskegee is studying the migration of binary compounds in a root cause investigation. Also Tuskegee is studying the effects tin whiskers may have on the ability of conformal coatings to protect Circuit Boards from corrosion.

1. Tuskegee University:
Collaborative Research with the Boeing Company
Legand Burge, Dean
Heshmat Aglan, Associate Dean
College of Engineering
David Burdick
The Boeing Company
Presented at BEYA 2015, Washington DC

2. The College of Engineering
Enabling Education and Leadership; Exploration and
Discovery; Engagement and Service; Technology and
Application
by Legand L. Burge, Jr., Dean
TM

3. Tuskegee University Overview
Independent and state-related institution of higher
education
The academic programs are organized into five
colleges and two schools
The curricula for these colleges and schools currently
offer over 50 degrees including 39 Bachelor's, 13
Master's, 3 Doctor's of Philosophy: Materials Science
and Engineering, Integrative Bio-Sciences,
Interdisciplinary Pathobiology and the Doctor of
Veterinary Medicine.
Tuskegee enrolls more than 3,000 students and
employs approximately 900 faculty and support
personnel.
Physical facilities include more than 5,000 acres of
forestry and a campus on which sits more than 100
major buildings and structures.

4. College of Engineering (CE)
CE
AEROSPACE
SCIENCE
ENGINEERING
MECHANICAL
ENGINEERING
ELECTRICAL
ENGINEERING
CHEMICAL
ENGINEERING
WITH
ENVIRONMENTAL
OPTION
MATERIALS
SCIENCE &
ENGINEERING

5.  Tuskegee University partner with prime Jacobs Engineering on
ESSSA – Prime with NASA
 NASA Mentor-Protégé Program Jacobs Engineering (ETSA)
 Current Kr for Products, Services, Consultancy – Dynetics;
Aerojet; Teledyne Brown; Boeing; Lockheed Martin; Raytheon
 Proposals with URS, L-3 Comm, SAIC
 $12.5M – Government Grants/Contracts (NSF, DoD, NSA,
CIA, DoEd, DoEnergy, USDA, FAA, DOT(FRA), NRC,
 Pending Proposals - $8M
 Career Fair, Fall 2015: Internships/Cooperative Ed
 Talent Acquisition – Fortune 500 Companies
 Benchmark Industries – Procter & Gamble; Ford Motor; 3M;
Boeing Co., Nucor Steel Co., Chevron; ExxonMobil; Boeing;
Lockheed Martin; John Deere; Jacobs; Kellogg; Southern
Company; Microsoft; Nucor
Overview - College of Engineering – Past Performance

6.  Utilize current infrastructure for insert Veterans into
undergraduate and graduate courses
 Tuskegee University current partnership with consortium
institution easy to add to ongoing courses and internship
experiences particularly with prime from NASA, e.g., Jacobs
Engineering in Huntsville, AL, Steins, MS, Orlando, FL, etc.
 Undergrad programs provide ease to move into STEM areas
 Graduate programs focus on Systems Engineering (Navy)
 Utilize HBCU Engineering Deans (14) to utilize nation-wide
approach for Veterans, particularly for southeastern states
 Utilize Fortune 500 collaborations
 Utilize nation-wide Career Fair, online and for
Internships/Cooperative Ed for Vets
 GI Bill funding easy for Online/On-campus courses/programs
 Talent Acquisition – Fortune 500 Companies
Proposal Overview - College of Engineering

7. Selective Research Capabilities
Nucor Education and Research Center (NERC) :
Focuses on industry based research in the latest trends in steel
technologies including dual phase microstructure, HSLAS, weathering
and corrosion resistance and high impact resistant steels, etc.
Nanomaterials Lab:
Focuses on fabrication, chemical, thermal , and mechanical
characterizations of high performance materials that include thin films
for the next generation solar concentrators, nanostructured conformable
coatings, proton and anion conducting membranes, etc.
Building Materials Lab:
Development; testing and evaluation of energy efficient building
materials including Composite Structural Insulate Panels (CSIPs),
thermally resistive cement binders, nanostructured cementitious surface
compounds and remediation of oil polluted building components, etc.

8. NUCOR –Education and Research Center
(NERC)
• The Center is comprised of three main components:
• Educational
• Research
• Outreach
• The NERC pursues a balance between these
components to provide engineering graduates with
basic and applied knowledge of steels and their
related technologies.

9. NERC Research
• Microstructure- properties relationship of structure steels
• Processing- properties relationships of structure steels
• Analysis of surface defects in hot and cold rolled steels
• Accelerated corrosion studies on enameled and galvanized
steels
• Microstructure – properties relationships of low carbon steels
• Improvement of wear, strength and corrosion resistance of
carbon steels using nanocoatings.

10. Microstructural Analysis of Bainitic and
Pearlitic Rail steels
0
200
400
600
800
1000
1200
1400
1600
0 2 4 6 8 10 12 14
StressMPa
Strain %
Pearlitic steel
Bainitic steel
Microstructure of rail steel dictates its
overloading behavior. pearlitic
bainitic

11. Microstructural Gradient of Old and New
Railheads
Fine grains due to
head hardening.
More ductile
features
Elongated grains
due to service
shear and
compressive
loading.
Brittle-like
features
New railhead Old railhead

12. Detection and Assessment of Low Cycle
Fatigue Damage

13. Fatigue Crack Propagation Kinetics of
Bainitic and Pearlitic Rail Steels
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
0 10 20 30 40 50 60 70
Energy Release rate, J* (kJ/m2)
CrackGrowthrate,da/dN
(m/cycle)
Bainitic Pearlitic
Fatigue crack propagation kinetics correlation
with fracture surface morphology. (fast crack
region)
bainitic
pearlitic

14. Rail Steel Repairs

15. Rail Steel after Welding
Slot weld Continuous weld

16. Hypervelocity Impact Analysis of Aerospace
Materials
Phenolic ResinAluminum Alloy Silicon Carbide
Plasma Drag Hypervelocity
Particle Accelerator

17. Fracture and Fatigue Studies of
Vanadium Alloys
Processing Orientation Fracture
Toughness Relationship of Vanadium
Alloys

18. Nanostructured Polymeric and
Cementitious Materials

19. Well dispersed Acid treated MWCNTs
Dispersion of Nanoparticles

20. Mechanical Performance of Nanostructured MWCNT
Tetrafunctional Epoxy Systems
0
20
40
60
80
100
120
140
160
180
200
0 0.2 0.4 0.6 0.8 1 1.2
Deflection, mm
FlexuralStress,MPa
nano
neat
MWCNT dispersed in epoxy matrix
A considerable enhancement in the flexural
strength has been achieved with MWCNT
reinforcement.

21. Thermal Conductivity of Aligned MWCNT
Number of
Stack Layers
Thermal
Resistance
( m2K/W)
Overall Stack
Assembly
Thickness (mm)
MWCNT/
Epoxy
Thickness (mm)
Thermal
Conductivity
(W/mK)
3 6.79E-3 8.59 2 178
2 6.29E-3 8.0 1.4 178
1 5.96E-3 7.1 0.4 178
.
Summary of thermal resistances and corresponding thicknesses of stacks

22. Fabrication of Thin Films
Neat Polyimide Film 0.5%MWCNT Polyimide Film

23. Fabrication
Woven Carbon/Phenolic Composites

24. Pulse Laser Degradation of Nanostructured
Composites
0
5
10
15
20
25
30
35
40
45
0 0.5 1 1.5 2 2.5
Stress,MPa
Strain, %
Neat Epoxy - 2 min
0.15% MWCNT/Epoxy - 2 min
2% NC/Epoxy - 2 min
Top view of the laser damaged area of the (a) neat epoxy, (b) 2%
nanosilicate/epoxy and (c) 0.15% MWCNT/epoxy.
a b c

25. UV Aging of Polymers
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2
Stress,MPa
Strain, %
1 month 2 months 3 months 4 months
Neat Epoxy
0
1
2
3
4
5
6
7
0 10 20 30 40 50 60 70 80 90 100
Strain(%)
Stress(MPa)
Before aging
1 Month UV
2 Months UV
3 Months UV
4 Months UV
5 Months UV
Before Aging 1 Month
2 Months
3 Months
4 Months
5 Months
Neat Polyurethane

26. 0
5000
10000
15000
20000
25000
30000
35000
-20000 0 20000 40000 60000 80000 100000 120000 140000
Imaginaryaxis,-Z(Ω)
real axis, Z (Ω)
18%MPI 21% MPI 25% MPI 30% MPI
1.5
MHz
10 Hz
10 Hz
10 Hz
Proton Conductivity
Nanoparticle Proton Conductivity, (S/cm)
Membrane
Nanostructured
Membrane
Increase, %
Activated Silica 1.28×10-5 1.44×10-5 12.5
Fumed Silica 5.14×10-5 1.44×10-4 180
Liquid Silica 2.6×10-3 1.4×10-2 400

27. Sand-Jet Edge Erosion of Coated Graphite
Epoxy Composites
Uncoated Coated
Typical values of mass loading vary from 0.0001 g/cm2
(extremely light) to 1.0 g/cm2 (extremely heavy).

28. Nanoreinforced Coatings
Before
immersion
Neat VYHH
20 days
immersion
Nano VYHH
20 days
immersion
• Corrosion and blistering started on the neat VYHH coated sample (middle)
• Nanocoatings have shown no corrosion for the same immersion period
Neat VYHH
Nano VYHH

29. Effect of Nanosilicate Loading on the Mechanical
performance of Cementitious Compounds
0
2
4
6
8
0 2 4 6 8 10
IndirectTensileStrength,MPa
NS Replacement Ratio, %
Unactivated nanosilicate
Activated nano silicate
AFM morphology of un-activated material AFM morphology of activated material

30. Expandable Thermoplastic Microspheres (ETM) Study
Hollow microspheres filled with hydrocarbons
gaseous
Expand upon heating (150~200 C)
Loading in cement ranges was up to 1%wt.
Un-expanded
Expanded
Cement binder
Cement binder
with 1% wt.ETM

31. Lab and Field Testing of Energy-Efficient Flood-Damage-
Resistant Residential Envelope Systems
Flooding for 3 days
Flooding for 21 days
Mold growth upon re-entry after flooding
Samples taken for mold identifications

32. A research effort to understand the growth
mechanism of Tin Whiskers and methods of risk
mitigation
By
David Burdick, The Boeing Co.
Heshmat Aglan, Tuskegee University

33. The Banned Substance
 The European Union’s RoHS (Reduction of Hazardous
Substances) legislation banned the use of four hazardous
materials one of these materials was Lead. Lead is used in
solder alloys

34. The Change
 Lead is also used as a plating material for high
performance electronic components
Component
terminations are
plated with Tin/Lead
solder

35. The Problem
 The replacement plating material is Tin and to our
disadvantage Tin grows whiskers.

36. What are Tin Whiskers
 Tin Whiskers are electrically
conductive single crystalline tin
structures that grow from pure tin-
plated surfaces
 They can and have caused short
circuits in electronic circuits
 They can break from the surface and
interfere with the operation of
mechanical or optical assemblies
 They are a threat to the aerospace and
defense industry
Tin whiskers
(Courtesy of NASA)

37. What are Tin Whiskers
Tin Whiskers Up Close
(Courtesy of DUART Productions)

38. Tin whisker growing from tin
surfaces near electrical components
Tin whisker growing from the
surface of tin connector guides.
(Acquired from nepp.nasa.gov)
How do they Cause Shorts

39. (Acquired from nepp.nasa.gov)
Shorts Cause Equipment Failures
On-Orbit commercial (non-NASA) Satellite failures:
 GALAXY VII (PanAmSat) Both primary and redundant SCP failed
 SOLIDARIDAD 1 (SatMex) Both primary and redundant SCP failed
 GALAXY IIIR (PanAmSat) Both primary and redundant SCP failed
Medical Equipment Failures:
 Heart Pacemaker Recall
 Apnea Monitor Failures
Industrial Power Failures
 Dresden Nuclear Reactor - Tripped Channel B
 Duane Arnold Nuclear Reactor - Reactor Scram
 Duane Arnold Nuclear Reactor - Reactor Scram/Controlled Shutdown
 Dresden Nuclear Reactor - Reactor Scram
 Dominion Millstone - Reactor Trip
Military System Failures
Patriot Missile
 Phoenix Missile
 F-15 Radar

40. Tuskegee’s Research Project
 Many scientists agree that compressive stress in the tin
film is the fundamental driving force behind tin whisker
growth.
 Other factors proposed are oxidation, re-crystallization,
thermal mismatch between metallic surfaces, corrosion,
impurities, inter-metallic compound growth and
migration.
 The students at Tuskegee University are attempting to
determine the root cause of Tin Whisker growth and to
find a way to mitigate the risks they cause to electronic
circuits.

41. Observation of Tin Whisker Growth under Hygro-Thermal
Exposure and 5% NaCl Water Immersion
funded by Boeing Co.
Whiskers protrusion seen at magnification 5KX
Thermotron Test Chamber (a) (b)
Coupons arrangement – (a) Thermotron and (b) Corrosion chambers
(a) (b)

42. The First Step in the Process
Tin plated brass coupons immersed in 5% NaCl
solution.
Tuskegee is Growing Whiskers

43. Coupons Used in the Research at Tuskegee
Coupons removed from the NaCl Solution show signs of
corrosion that may induce stresses. The next step is to check for
Tin Whiskers
(c)
(d) (e)

44. How do we find a Whisker
Optical Microscope (Olympus G5000)
Scanning Electron Microscope (Hitachi S3400 N)
Optical Microscope Scanning Electron Microscope

45. Forensic Science
 Why do we need microscopes?
Image provided by NASA

46. How do we know we have found one?
 After optical observations of something that looks like a
protrusion growing out of the surface, we confirmed our
suspicion by elemental analysis using X-ray diffraction (XRD)
 In this test tin whisker growth was evident by the elemental tin
peak (100% tin shown)
SEM Micrographs showing (a) whisker growth and (b) XRD analysis showing
100% tin peak

47. Whiskers Growing at Tuskegee
Whiskers were found Growing from a Sample coupon
(a) (b)
Figure 23: SEM micrograph showing long and bent whisker from scratched flat coupon after 5700
hour exposure to corrosive environment (aqueous NaCl); magnifications are 5000X (a) and 3000X (b)
(a) (b)
Figure 24: SEM micrograph showing conjoined whiskers from scratched flat coupon after 7000 hours of
exposure to corrosive environment (aqueous NaCl); magnification is 4000X.

48. Tin Whisker Growth - Factors
Intermetallic
Tin
Copper Substrate
Courtesy of: A History of Tin Whisker Theory
George T. Galyon
IBM eSG Group

49. Tin Whisker Growth - Factors
Whisker Nodule
Intermetallic Cu6Sn5
Tin (Sn)
Cu194
Courtesy of: A History of Tin Whisker Theory
George T. Galyon
IBM eSG Group

50. Next Steps
Sectioning at the root
Whisker root analysis
Study the migration of binary
compounds
Follow the trail