Tin Whiskers Inorganic Coatings Evaluation (TWICE)
WP-2212
Objective
The transition to lead-free electronics has changed some of the ground rules for designing reliable electronics for use in harsh environments. One of the most significant changes has been the need to address the phenomenon of tin whiskers, which can grow from the pure tin surfaces commonly used on lead-free devices. One of the more practical measures for inhibiting tin whiskers is to coat pure tin surfaces with a conformal coating that protects them from moisture and other factors that could corrode tin oxide surfaces, captures and contains any tin whiskers that do form, and can be cost-effectively applied such that it uniformly covers all tin-whisker-susceptible surfaces in an electronics assembly.
The objective of this project is to investigate the use of alkali silicate glass (ASG) materials as a conformal coating for tin whisker mitigation and compare the performance of this material to conventional conformal coatings such as parylene and acrylic coatings. The properties of ASG are such that the material can be much harder and impermeable than conventional coatings.
Technical Approach
The project will be conducted in two phases over a two year period. Phase 1 focuses on developing materials and the necessary processing steps to generate coatings that provide a range of conditions on tin surfaces. These results will lead to two parallel activities: 1) a Design of Experiments study will characterize the impact of the combinations of coating properties on test samples that have known tin whisker growth properties; 2) samples of that same test vehicle will be coated with a variety of conformal coatings, including both conventional materials (parylene and acrylic) and ASG materials. All samples coated in these two activities will be subjected to elevated temperature and humidity for a total of 4000 hours to induce tin whisker growth, which will be monitored and documented. In addition, test samples used for assessing the risk of metal vapor arcing (MVA) will be coated with both ASG formulations as well as conventional coatings for MVA testing. Test samples will also be subjected to thermal cycle testing to assess ASG coating durability.
Benefits
The expected ability to provide extremely high control over surface conditions and the superior hardness and permeability characteristics of ASG materials provide a means for establishing a broad range of controlled conditions on pure tin surfaces. Observing the impact that these conditions have on resulting tin whisker growth will lead to a better scientific understanding in the mechanisms by which tin whiskers form and how they can be controlled with conformal coatings. The ultimate benefit of this work will be achieved by characterizing how conformal coatings can mitigate the effects of tin whiskers, both by limiting and preventing their growth and initiation and by minimizing failures induced by tin whiskers through processes such as metal vapor arcing. This will require coatings that are not only robust, but also can be applied so as to have uniform consistent coverage over all surfaces that could be susceptible to tin whiskers. Because conformal coatings can be applied on an as-needed basis, they offer especially significant benefit to manufacturers of harsh environment electronics by allowing them to ruggedize commercial electronics rather than produce customized rugged components. (Anticipated Project Completion - 2014)
Points of Contact
Principal Investigator
Mr. David Hillman
Rockwell Collins, Inc.
Phone: 319-295-1615
Document Types
- Fact Sheet - Brief project summary with links to related documents and points of contact.
- Final Report - Comprehensive report for every completed SERDP and ESTCP project that contains all technical results.
- Cost & Performance Report - Overview of ESTCP demonstration activities, results, and conclusions, standardized to facilitate implementation decisions.
- Technical Report - Additional interim reports, laboratory reports, demonstration reports, and technology survey reports.
- Guidance - Instructional information on technical topics such as protocols and user’s guides.
- Workshop Report - Summary of workshop discussion and findings.
- Multimedia - On demand videos, animations, and webcasts highlighting featured initiatives or technologies.
- Model/Software - Computer programs and applications available for download.
- Database - Digitally organized collection of data available to search and access.