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. The mechanisms of inanition and growth of tin whiskers and the Probability of occurrence of Induced Short are investigated. 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 as a root cause. The effects tin whiskers may have on the ability of conformal coatings to protect Circuit Boards from corrosion is also studied.

1. INVESTIGATION INTO THE
MECHANISMS OF INITIATION AND
GROWTH OF TIN WHISKERS AND
THE PROBABILITY OF
OCCURRENCE OF INDUCED
SHORTS
Dr. H. Aglan, Tuskegee University
David Burdick, The Boeing Co.

2. Tuskegee University:
Collaborative Research with the
Boeing Company
• Heshmat Aglan, Dean
• College of Engineering
• David Burdick, ATF Senior Engineer
• The Boeing Company

3. • TUSKEGEE
• UNIVERSITY
• 1881
Overview of the College of Engineering
Tuskegee University

4. Tuskegee University
The University
 Independent - State-related and Land Grant 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
Overview

5.  The university is the largest producer of African-Americans with baccalaureate degrees in math,
science and engineering in Alabama.
 Tuskegee’s Materials Science and Engineering Program graduates the largest number of black
PhD students in the U.S.
 Tuskegee University is the No. 1 producer of African-American aerospace engineers in the
nation.
 Tuskegee University is the only HBCU with a fully accredited College of Veterinary Medicine
that produces over 75 percent of the African-American Veterinarians.
 Tuskegee is the only college or university campus in the nation to be designated a National
Historic Site by the U.S. Congress.
 More U.S. presidents have visited Tuskegee University than any other HBCU.
 The Tuskegee Airmen, who trained at the Tuskegee Air Field in July 1941, were the first
African-American fighter pilots in the U.S. Army Air Corps.
 The ROTC program at Tuskegee has produced more African-American general officers in the
military than any other institution, including the service academies.
 Tuskegee University is the leading producer in the country of African-American engineering
graduates in chemical, electrical and mechanical engineering.
 Tuskegee University is the only HBCU in the nation designated as the location for National
Center for Bioethics in Research and Health Care.
Points of Distinction
Tuskegee University

6. 6
Center for Biomedical
Research
(NIH-RCMI)
Directors : Dr. Clayton Yates &
Dr. Temesgen Samuel
National Center for
Bioethics in Research and
Healthcare
(NIH)
Director : Dr. Rueben Warren
Center for Advanced
Materials (T-CAM)
Director : Dr. Shaik Jeelani
Alabama Center for
Nanobio Science and
Sensors
(NSF-EPSCoR)
Director : Mahesh Hosur
Carver Integrative
Sustainability Center
Director : Dr. Raymon Shange
Tuskegee
University’s
Centers of Excellence
George Washington Carver
Agricultural Experiment
Station (Land Grant-USDA)
Director : Dr. Walter Hill
Center of Information
Assurance Education
(DHS)
Director : Dr. Hira Narang
Tuskegee Center for
Academic Excellence &
Innovative Learning
(T-CAEL)
Director : Ms. Sherry King
NUCOR Education and
Research Center (NERC)
Director : Dr. Heshmat Aglan
Center for Research
Excellence in Science and
Technology
(NSF-CREST)
Director : Mahesh Hosur
Centers of Excellence
Tuskegee University

7.  Four ABET accredited engineering
programs: Aerospace, Chemical, Electrical,
and Mechanical
 #1 producer of African American Ph.D. in
Materials Sciences and Engineering (MSE) –
30 to date
 #1 producer of African American women in
U.S. academics (top ten in engineering talent
production)
 Top ten producer of African American
engineers in the nation
 Historic producer of flag rank officers for US
Military: AROTC; NROTC; AFROTC.
 Graduates: ~ 100/ year; ~ 15% enter
graduate school
College of Engineering
7
Highlights

8. Aerospace: experimental aerodynamics, vortex-dominated flows, flight simulation,
configuration aerodynamics, human interface.
Chemical: microfluidics, corrosion, carbon capture, bio-fuels, adsorption, water &
wastewater treatment, smart manufacturing, bio-chemical engineering, chemical
process modeling.
Electrical: electronic warfare and technology; systems engineering; control systems,
wireless sensors and data gathering networks, information assurance; integrated
circuits; cyber; power/energy.
Mechanical: fracture and fatigue evaluation, additive manufacturing, proton and ion
conductive membranes, corrosion and coatings, environmental aging of materials,
dislocation dynamics in materials, fuel cells.
Materials Science & Engineering: synthesis and chemical analysis of materials,
processing of bio materials, performance and nondestructive evaluation, and modeling.
8
Core Strengths and Capabilities
 Number of students: ~600 undergraduate and ~40 graduate
 Number of Faculty and Staff: 36 and 10
 Number of graduates ~ 100/ year
 Annual Research Awards and Contracts: ~ $ 10 M
 Refereed Publications in ~ 50/ year
College of Engineering

9. Education, Outreach, and Student Success
Middle school students
hands-on activities
Teacher training activities
Dr. Kristy Crews (2016
graduate)with mentor Dr. Curry
REU student Demetrius
Findley
Summer FASTREC student
activities
International Collaborations
College of Engineering

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
pearlitic
bainitic
Microstructure of rail steel dictates its
overloading behavior.

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

12. Detection and Assessment of Low Cycle Fatigue Damage

13. 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
Fatigue Crack Propagation Kinetics of Bainitic and Pearlitic Rail
Steels

14. Rail Steel Repairs

15. Slot weld Continuous Weld
Rail Steel after Welding

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

17. Nanostructured Polymeric and Cementitious Materials
Dispersion of Nanoparticles
Well dispersed Acid treated MWCNTs

18. 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.

19. The European Union’s Reduction of
Hazardous Substances
The European Union’s RoHS legislation banned the use
of four hazardous materials one of these materials was
Lead. Lead is used in solder alloys and is the connecting
medium in electronic circuits

20. Aerospace, Defense & High Performance
Electronics are affected by this legislation

21. Aerospace, Defense and High Performance
Electronics are affected at the component level
Since the RoHS
legislation
Commercial
Component
terminations are
now plated with
Tin

22. Tin plating material has a long history of
growing Tin whiskers

23. What are Tin Whiskers?
Tin Whiskers are
electrically
conductive single
crystalline tin
structures that
grow from pure
tin-plated surfaces

24. Tin Whiskers are very small
Picture courtesy of NASA Goddard Space Flight Center

25. Components are getting smaller and the
gap between terminations is narrowing
Gap spacing is
decreasing

26. Tin Whiskers closing the gap

27. What are Conformal Coatings and can they
help?
Below is a conformal coated
circuit board
Above is a circuit board prior to
conformal coating

28. Tin Whiskers versus Conformal Coatings
Tin Whiskers
will grow
through
conformal
coatings, so
how can
conformal
coatings
help?

29. Growing out is easy growing in is more
difficult
Once out it is
a long trip to
the other
termination.

30. Because of Tin Whiskers Bad things have
happened
Galaxy IV Satellite
Galaxy VII Satellite
Solidaridad 1 Satellite
Galaxy IIIR Satellite
Toyota Accelerator
Heart Pacemaker
Recall
Dominion Millstone
Duane Arnold
Dresden
South Texas Project
Nuclear Reactors
Phoenix Missile
Patriot Missile
Aircraft Relay
Aircraft Radar

31. If Conformal coatings can protect circuits
from shorts can they prevent corrosion on
Naval Vessels?
Tin plated brass
coupons coated
with Epoxy,
Acrylic, Urethane
and silicon
conformal
coatings are
submerged in a
salt solution
waiting for the
growth of Tin
Whiskers

32. The search for Tin Whiskers
The Olympus G5000 Optical Microscope
However to
study Tin
Whiskers you
we must be able
to find them.
Students at
Tuskegee start
their search
with an Optical
Microscope

33. The students start their search for whiskers
using the Microscope and a grid
The Test Coupon The Grid
A B C D
1234567

34. The they take the Coupon and examine the locations
under a Scanning Electron Microscope
Dr. Aglan and graduate students
examining a Tin Whisker
The Hitachi S3400N
Scanning Electron
Microscope

35. Tuskegee Students use a Scanning Electron
Microscope and XRD to confirm it is a Tin Whisker
SEM micrograph showing salt
crystals on acrylic coating from
scratched flat coupon after 9500
hour exposure to corrosive
environment (aqueous NaCl);
magnification is 400X (a); XRD is
shown on right (b). The
percentages of tin and oxygen are
4.38% and 11.08%, respectively.
SEM micrograph showing
conjoined whiskers from
scratched flat coupon after 7000
hours of exposure to corrosive
environment (aqueous NaCl);
magnification is 4000X. The
percentages of tin and oxygen are
56.34% and 34.61% respectively.

36. With patience and a lot of searching students at
Tuskegee are growing and finding Tin Whiskers

37. Conformal Coated Coupons in a Thermal
Chamber
Coupons going through a Thermal
Cycling process to accelerate the
growth of Tin Whiskers.
A coupon half covered with a
conformal coating and the other
half exposed.

38. Conformal Coated Coupons in a Thermal
Chamber
A coupon half covered with a conformal coating and the other
half exposed. Determining the effectiveness of the various
conformal coatings to inhibit the growth of Tin Whiskers

39. Probability of a Tin Whisker Shorting
between two Adjacent Leads

40. David Burdick and graduate students
reviewing the progress and the next steps

41. The Next Steps
 The study to determine if one conformal coating is better at
mitigating the effects of corrosion is still on going.
 The study to calculate the probability of a Tin Whisker causing a short
is on going.
 The study to determine if one conformal coating it better at
mitigating the risk of a Tin Whisker short is on going.
 A new effort is being considered to improve the effectiveness of
preventing penetration of conformal coatings by Tin Whiskers by
using nanoparticles.
 A new project is being considered to studying the reliability of various
Pb-free solder alloys.

42. Questions?