1. Tin Whisker Mitigation Systems PERM 33 Virtual meeting
S. Meschter
July 27, 2017

2. Key element of the Defense Acquisition Guidebook (DAG)
Systems Engineering
Key element of the Defense Acquisition Guidebook (DAG)

3. Chapter 3 Systems Engineering
SE planning, as documented in the Systems Engineering Plan (SEP), identifies the most effective and efficient path to deliver a capability, from identifying user needs and concepts through delivery and sustainment. SE event-driven technical reviews and audits assess program maturity and determine the status of the technical risks associated with cost, schedule and performance goals.

4. Chapter 3 Systems Engineering
SE applies critical thinking to the acquisition of a capability. It is a holistic, integrative discipline, whereby the contributions across engineering disciplines, such as structural engineers, electrical engineers, mechanical designers, software engineers, human factors engineers and reliability engineers, are evaluated and balanced to produce a coherent capability -- the system.
The Systems Engineer balances the conflicting design constraints of cost, schedule, and performance while maintaining an acceptable level of risk. SE solves systems acquisition problems using a multi-disciplined approach. The Systems Engineer should possess the skills, instincts and critical thinking ability to identify and focus efforts on the activities needed to enhance the overall system effectiveness, suitability, survivability and sustainability.

5. Chapter 3 Systems Engineering
CH 3–2.7 Systems Engineering Role in Contracting
Within the RFP development team, the Systems Engineer should be responsible for the technical aspects of the RFP and should perform the following actions:
Referencing current required operational documentation and system performance specifications.
Identifying SE process requirements (for example, requirements management, configuration management and risk management; see CH 3–4. Additional Planning Considerations). …
Identifying any design considerations including production; reliability and maintainability (R&M); environment, safety and occupational health (ESOH); human systems integration (HSI); and security.
Identifying for delivery Government-required technical data rights produced by the developer.
Listing and describing technical assessment evidence and events, including technical reviews, audits, and certifications and associated entrance/exit criteria ….
Coordinating with Chief Developmental Tester with regard to the test and evaluation requirements.
Providing a requirements verification traceability database (requirements and test method).
…..
Leading or supporting the technical evaluation during source selection, to include providing inputs to the development of source selection criteria.
Performing schedule risk assessments as part of the source selection evaluation process.
Identifying external or SoS interfaces and ensuring the technical interface requirement and task scope are unambiguous to the offerors.
Providing a clear description of the minimum technical requirements used to determine the technical acceptability of a proposal.
Risk mitigations, including lead-free materials, flow down during sub-contracting

6. Chapter 3 Systems Engineering
CH 3–2.7 Systems Engineering Role in Contracting
Within the RFP development team, the Systems Engineer should be responsible for the technical aspects of the RFP and should perform the following actions:
Referencing current required operational documentation and system performance specifications.
Identifying SE process requirements (for example, requirements management, configuration management and risk management; see CH 3–4. Additional Planning Considerations). …
Identifying any design considerations including production; reliability and maintainability (R&M); environment, safety and occupational health (ESOH); human systems integration (HSI); and security.
Identifying for delivery Government-required technical data rights produced by the developer.
Listing and describing technical assessment evidence and events, including technical reviews, audits, and certifications and associated entrance/exit criteria ….
Coordinating with Chief Developmental Tester with regard to the test and evaluation requirements.
Providing a requirements verification traceability database (requirements and test method).
…..
Leading or supporting the technical evaluation during source selection, to include providing inputs to the development of source selection criteria.
Performing schedule risk assessments as part of the source selection evaluation process.
Identifying external or SoS interfaces and ensuring the technical interface requirement and task scope are unambiguous to the offerors.
Providing a clear description of the minimum technical requirements used to determine the technical acceptability of a proposal.
Key discussion points
Risk mitigations, including lead-free materials, flow down during sub-contracting

7. Chapter 3 Systems Engineering
CH 3–4.1.5 Risk Management Process
Technical community focus

8. Chapter 3 Systems Engineering
CH 3– Risk Management

9. Tin whisker mitigations
Risk Management
CH 3–4.3 Design Considerations
Table 42: Design Considerations
Design Consideration
Section Number
Accessibility (Section 508 Compliance)
4.3.1
Affordability - SE Trade-Off Analysis
4.3.2
Anti-Counterfeiting
4.3.3
Commercial-Off-the-Shelf (COTS)
4.3.4
Corrosion Prevention and Control (CPC)
4.3.5
Critical Safety Item (CSI)
4.3.6
Demilitarization and Disposal
4.3.7
Diminishing Manufacturing Sources and Material Shortages (DMSMS)
4.3.8
Environment, Safety and Occupational Health (ESOH)
4.3.9
Human Systems Integration (HSI)
4.3.10
Insensitive Munitions
4.3.11
Intelligence (Life-cycle Mission Data Plan (LMDP))
4.3.12
Interoperability and Dependency (I&D)
4.3.13
Item Unique Identification (IUID)
4.3.14
Modular Design
4.3.15
Operational Energy
4.3.16
Packaging, Handling, Storage and Transportation (PHS&T)
4.3.17
Reducibility, Quality & Manufacturing (PQM)
4.3.18
Reliability & Maintainability (R&M) Engineering
4.3.19
Spectrum Management
4.3.20
Standardization
4.3.21
Supportability
4.3.22
Survivability (including CBRN) & Susceptibility
4.3.23
System Security Engineering (SSE)
4.3.24
Potential impact areas
Lead-free electronics risks “in-flow”
Many factors flow into the design process

10. GEIA-STD-0005-2 Class 2B whisker mitigations
Uses of Pb-free tin finishes require mitigation. For non-high voltage applications, mitigation requirements shall be fulfilled by any one of the following:
Hard potting or encapsulation
Physical barriers
Circuit design and analysis showing low impact of tin whisker short or FOD
Circuit design and analysis showing that areas sensitive to tin whisker shorts or FOD have at least a 1 cm gap
Parylene conformal coating with validated coverage and gap size, prior to coating, greater than or equal to 150 microns (5.9 mils)
Other, non-parylene, conformal coating with validated coverage and gap size, prior to coating, greater than or equal to than 250 microns (9.8 mils)
Pb-free tin electronic components with gaps greater than 2000 microns (78.7 mils) that have been installed with SnPb and are physically isolated from any Pb-free tin mechanical piece parts
SnPb soldering process with validated complete coverage
Mitigation or combination of mitigations approved by the customer

11. Sn-Pb assembly solder

12. SnPb Assembly solder Solder flow line Original part tin plating SOT3
Older parts may not wet much beyond the J-STD-001 minimum
Tin-lead assembly soldering removes ~20-30% of the tin on the sides

13. SnPb Assembly solder (Cont.)
Original part tin plating
Solder flow line
SOT6
Tin-lead assembly soldering eliminates tin whisker risk
~30% of the sides, 50% of the front

14. Back side of lead fully mitigated even when the front might not be
SnPb Assembly Solder
Back side of lead fully mitigated even when the front might not be
PERM f Self Mitigation

15. SnPb Assembly solder Sometimes the solder might not climb up the lead
PERM f Self Mitigation

16. SnPb hot solder dip variation
Package body
Remaining tin
What if the solder dip didn’t quite make it to the package body?
Solder coating
Dip direction into solder pot
Lead

17. Conformal Coating

18. Critical coating strength required versus coating thickness
Safe region
30 micron coating
118 micron nodule
3 micron coating
52 micron nodule
No nodules under 100 micron coating
7 micron coating
80 micron nodule
S. McKeown SERDP WP2213 SMTA International,
Rosemont, IL, September 27-October 1, 2015
Larger nodule requires greater coating strength or thicker coating
SERDP WP-2213 Project (Strategic Environmental Development Program)

19. Critical coating strength requirement versus coating thickness
Nodule/Whisker
Diameter
Increasing Tin Whisker/Nodule Diameter
No penetration for up to 2 um diameter whiskers
PC18M+20%XP2742
40 MPa yield
10 um
minimum
Larger nodule requires greater coating strength or thicker coating
SERDP WP-2213 Project (Strategic Environmental Development Program)

20. Conformal coating coverage
PC18M+20%X11102PMA
nanoalumina
PC40UMF with 30%XP2742 (6.0 wt% SiO2, 15.54% N3300 isocyanate)
PC18M with 20% XP2742 (6.74 wt% SiO2, 10.36% N3300 isocyanate)
SERDP WP-2213 Project (Strategic Environmental Development Program)

21. Layered coating progressive build-up
QFP44
60x
Dip + 1 (PC18M+20%XP2742) spray
Unfilled PC18M Dip Only
White areas represent coating layers less than 3 microns thick
Coverage improves with added layers
Added spray layers improves coverage and thickness
Dip + 2 (PC18M+20%XP2742) sprays
SERDP WP-2213 Project (Strategic Environmental Development Program)

22. Quantified thickness results

23. WP2213 – Layered coating Dip only Dip + Nanosilica 2 spray Front side
Goal: Demonstrate coating coverage to an 8 micron thick level to ensure whisker mitigation.
Back side
Back
The front side coverage was good. Dip provided a minimum thickness to provide whisker re-penetration. Still some work needed to improve the back-side thickness.

24. WP2213 Layered coating, BU microtome sections: Unfilled dip vs
WP2213 Layered coating, BU microtome sections: Unfilled dip vs. nanoparticle spray thickness
(A)
(D)
Added thickness from the layered spray coating on top of the dip coating is evident, especially in the high shear area of section 2
Nanoparticle spray coating adds substantial thickness to outside, left and right

25. WP2213 Layered coating thickness results: Horizontal cross-section11 12 22 23 33 34 44
Pin numbering
Lead 17
Front
Back
Section plane
Good front and side coverage uniformity around part
Back-side and back-corners need thickness improvement.

26. WP2213 Dip+Spray (2013) vs Dip+Spray+Spray (2015)
Front
2013 Dip + Normal nanosilica spray (PC18M dip with PC18M+20%XP2742 spray)
2015 Dip + Layered 2 nanosilica spray (PC18M dip with PC18M+20%XP2742 spray)
Back
Front side
Back side
Front side with the layered coating had less variation toward expected value. We sought to have a little thinner coating in 2015 than 2013 to prevent pooling above 75 microns. Thicker coating can result in coating cracking over time and lower solder fatigue life in thermal cycling.
Back side coverage with the layered coating was incrementally thicker, exhibited good coverage as seen in the SEM photos. But there remains some work in reducing variation and further increasing back side thickness.
2013
Normal
2015
Layered
2013
Normal
2015
Layered
Layered coating front side more consistent and back side is thicker, but still needs development

27. 5-22arr IPC J-STD-001: Conformal coating and material application industry assessment
Chair: Dave Hillman, Rockwell Collins
Co-chair: Jason Keeping, Celestica
PC18M+20%2742
0.7 mils (17 microns)
0.3 mils (8 microns)
5-22arr Minimum thickness
(= Location T)
~50 micron
The UV cure Urethane is thinner than the solvent based urethane. The same factor that we are observing may be influencing the industry results. The urethane and acrylic thicknesses observed in industry are consistent with the present work. The flat unencumbered surface thickness measurement does not reflect the complex geometry coverage predication on actual leads.
26 sets planned
13 sets complete to date
100’s of cross-sections
Actual minimum thicknesses on leads (solid line) much less than unencumbered flat surface (dashed line) process control measurement

28. The good news

29. The solder might not climb up the lead

30. SnPb hot solder dip might have variation
Package body
Remaining tin
What if the solder dip didn’t quite make it to the package body?
Solder coating
Dip direction into solder pot
Lead

31. 5-22ARR The coating may vary

32. Assembly solder and coating combined
Coating is especially thick at inside corners
Strategic Environmental Research and Development Program (SERDP) Nanoparticle Enhanced Conformal Coating for Whisker Mitigation, S. Meschter, J. Cho, S. Maganty, D. Starkey, M. Gomez, D. Edwards, A. Ekin, K. Elsken, J. Keeping, P. Snugovsky, Eva Kosiba, Zohreh Bagheri and J. Kennedy, SMTA International Conference, Rosemont, IL, Sept. 28 – Oct. 2, 2014
Coating can cover regions that the that solder may not reach
Robust mitigation still obtained in many areas

33. Assembly solder and coating combined (cont.)
Top and front surfaces have good line-of sight to the coating spray nozzle
Photo from
SERDP WP2213
Corners and back side areas  opportunity for improvement
Paint manufacturers have formulated to cover corners for years

34. Questions Coating elongation limited by film defect
Figure 2‑18. a) Bright-field and b) circular- differential interference contrast (C-DIC) image of a defect site in the PU film.
Coating elongation limited by film defect
Cho and Maganty, Binghamton University

35. SERDP/ESTCP projects Active projects Complete projects
Novel Whisker Mitigating Composite Conformal Coat Assessment
SERDP WP-2213 Dr. Stephan Meschter, BAE Systems, May 2012-Present
Enabling Lead-free Interconnects in Weapon Systems
ESTCP WP T2 Dr. S. Meschter
Complete projects
The Role of Trace Elements in Tin Whisker Growth
SERDP WP-1751 Dr. Jean Nielsen, The Boeing Company, Sept. 2013
Microstructurally Adaptive Constitutive Relations and Reliability Assessment Protocols for Lead Free Solder
SERDP WP-1752 Dr. Peter Borgesen, Binghamton University, May 2015
Tin Whisker Testing and Modeling
SERDP WP-1753 Dr. Stephan Meschter, BAE Systems, Dec 2015
Contributions of Stress and Oxidation on the Formation of Whiskers in Lead-Free Solders
SERDP WP-1754 Dr. Elizabeth Hoffman, Savannah River National Laboratory, Jan 2016
Tin Whiskers Inorganic Coatings Evaluation (TWICE)
SERDP WP-2212 Mr. David Hillman, Rockwell Collins, Inc., Jan. 2015