Abstract
Alkali silicate glass (ASG) coatings were investigated as a possible method for inhibiting tin whisker initiation and growth. The aqueous-based ASG formulations used in this study were deposited with equipment and conditions that are typical of those used to apply conventional conformal coatings. Processes for controlling ASG coating properties were developed, and a number of ASG-based coating combinations were applied to test components with pure tin surfaces. Coatings were applied both in a laboratory environment at Rockwell Collins and in a manufacturing environment at Plasma Ruggedized Solutions. Testing in elevated humidity/temperature environments and subsequent inspection of the test articles identified coating combinations that inhibited tin whisker growth as well as other material combinations that actually accelerated tin whisker growth. None of the coatings evaluated in this study, including conventional acrylic and Parylene conformal coatings, completely prevented the formation of tin whiskers. Two of the coatings were particularly effective at reducing the risks of whisker growth, albeit through different mechanisms. Parylene conformal coating almost, but not completely, eliminated whisker formation, and only a few tin whiskers were found on these surfaces during the study. A composite of ASG and alumina nanoparticles inhibited whisker formation to a lesser degree than Parylene, but did disrupt whisker growth mechanisms so as to inhibit the formation of long, and more dangerous, tin whiskers. Additional testing also demonstrated that the conformal coatings had relatively little effect on the dielectric loss of a stripline test structure operating at frequencies over 30 GHz.
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Abbreviations
- 85/85THC:
-
85°C temperature/85% relative humidity conditioning
- Al2O3 :
-
Aluminum oxide
- ANOVA:
-
Analysis of variance
- ASG:
-
Alkali silicate glass
- CTE:
-
Coefficient of thermal expansion
- DoD:
-
Department of Defense
- DOE:
-
Design of experiments
- MVA:
-
Metal vapor arc
- PLCC:
-
Plastic leaded chip carrier
- PRS:
-
Plasma Ruggedized Solutions
- RC:
-
Rockwell Collins
- SEM:
-
Scanning electron microscopy
- SMT:
-
Surface mount technology
- SOIC:
-
Small outline integrated circuit
- SERDP:
-
Strategic Environmental Research and Development Program
- TWICE:
-
Tin whisker inorganic coating evaluation
- ZnO:
-
Zinc oxide
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Acknowledgements
The TWICE program was part of a multi-project investigation supported by the Strategic Environmental Research and Development Program (SERDP), within the Weapons Systems and Platforms (WP) Program Area, as SERDP Project Number WP-2212. The authors would like to thank multiple individuals from Rockwell Collins, including Ken Blazek, the Rockwell Collins Component and Material Evaluation Laboratory and Dave Westergren, as well as Mike Forney of PRS, for project support.
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Hillman, D., Wilcoxon, R., Lower, N. et al. Alkali Silicate Glass Coatings for Mitigating the Risks of Tin Whiskers. J. Electron. Mater. 44, 4864–4883 (2015). https://doi.org/10.1007/s11664-015-4057-1
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DOI: https://doi.org/10.1007/s11664-015-4057-1