INVESTIGATION INTO THE MECHANISMS OF INITIATION AND GROWTH OF TIN WHISKERS AND THE PROBABILITY OF OCCURRENCE OF INDUCED SHORTS

Dr. H. Aglan, Tuskegee UniversityDavid Burdick, The Boeing Co.

Tuskegee University: Collaborative Research with the

Boeing Company

• Heshmat Aglan, Dean• College of Engineering

• David Burdick, ATF Senior Engineer• The Boeing Company

• TUSKEGEE• UNIVERSITY

• 1881

Overview of the College of EngineeringTuskegee University

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

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

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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 ShangeTuskegee

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

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

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.

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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

Education, Outreach, and Student Success

Middle school students hands-on activities

Teacher training activitiesDr. Kristy Crews (2016

graduate)with mentor Dr. Curry

REU student Demetrius Findley

Summer FASTREC student activities

International Collaborations

College of Engineering

Microstructural Analysis of Bainitic and Pearlitic Rail steels

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Stre

ss

MPa

Strain %

Pearlitic steel

Bainitic steel

pearlitic

bainitic

Microstructure of rail steel dictates its overloading behavior.

Microstructural Gradient of Old and New Railheads

New Railhead

O ld Railhe ad

Top Layer

M iddle Layer

Bottom Layer

Fine grains due to head hardening.

More ductile features

Elongated grains due to service shear and compressiveloading.

Brittle-like features

Old railheadNew railhead

Detection and Assessment of Low Cycle Fatigue Damage

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

0 10 20 30 40 50 60 70Energy Release rate, J* (kJ/m2)

Cra

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Bainitic Pearlitic

Fatigue crack propagation kinetics correlationwith fracture surface morphology. (fast crack region)

bainitic

pearlitic

Fatigue Crack Propagation Kinetics of Bainitic and Pearlitic Rail Steels

Rail Steel Repairs

Slot weld Continuous Weld

Rail Steel after Welding

Hypervelocity Impact Analysis of Aerospace Materials

Aluminum Alloy Phenolic Resin Silicon Carbide

Plasma Drag Hypervelocity Particle Accelerator

Nanostructured Polymeric and Cementitious Materials

Dispersion of Nanoparticles

Well dispersed Acid treated MWCNTs

Mechanical Performance of Nanostructured MWCNT Tetrafunctional Epoxy Systems

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0 0.2 0.4 0.6 0.8 1 1.2Deflection, mm

Flex

ural

Stre

ss, M

Pa

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MWCNT dispersed in epoxy matrix

A considerable enhancement in the flexural strength has been achieved with MWCNT

reinforcement.

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

Sn/Pb Solder Electronic Components

Lead

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

Aerospace, Defense and High Performance Electronics are affected at the component level

Since the RoHS legislation Commercial Component terminations are now plated with Tin

Tin plating material has a long history of growing Tin whiskers

What are Tin Whiskers?

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

Tin Whiskers are very small

Picture courtesy of NASA Goddard Space Flight Center

Components are getting smaller and the gap between terminations is narrowing

Gap spacing is decreasing

Tin Whiskers closing the gap

What are Conformal Coatings and can they help?

Below is a conformal coated circuit board

Above is a circuit board prior to conformal coating

Tin Whiskers versus Conformal Coatings

Tin Whiskers will grow through conformal coatings, so how can conformal coatings help?

Growing out is easy growing in is more difficult

Once out it is a long trip to the other termination.

Because of Tin Whiskers Bad things have happened

Galaxy IV SatelliteGalaxy VII Satellite

Solidaridad 1 SatelliteGalaxy IIIR Satellite

Toyota Accelerator

Heart Pacemaker Recall

Dominion MillstoneDuane Arnold

DresdenSouth Texas Project

Nuclear Reactors

Phoenix Missile

Patriot Missile

Aircraft Relay

Aircraft Radar

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

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

The students start their search for whiskers using the Microscope and a grid

The Test Coupon The Grid

A B C D

1

2

3

4

5

6

7

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

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.

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

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.

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

Probability of a Tin Whisker Shorting between two Adjacent Leads

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

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.

Questions?