Tin Whisker Testing and Modeling
WP-1753
Objective
Recent reduction of hazardous substances (RoHS) legislation from the European Union and associated supply chain trends have resulted in the elimination of lead from many electronic assemblies. As a result, a large amount of lead-free tin-rich finishes and solders are replacing heritage tin-lead alloys. This may increase the risk to Department of Defense (DoD) systems due to tin whisker electrical short circuits. The new lead-free tin alloys have an increased susceptibility to spontaneous growth of filament-like structures (tin whiskers) that are a result of a poorly understood metallurgical phenomenon that creates fine metallic growths by solid state diffusive transport mechanisms in the presence of a compressive stress or corrosion. Historically, the addition of lead into the tin alloy is thought to have a multifaceted role in the inhibition of whisker growth. It has the potential of reducing internal compressive tin stress because it has low yield strength. In addition, lead alters the grain structure, the surface oxides, and the intermetallic morphology. Unfortunately, the elimination of lead in military and aerospace systems that are exposed to many diverse environments makes whisker risk management an increasingly important element of critical electronic systems design.
The objective of this project is to perform systematic tin whisker testing that will assess the key part, manufacturing, and environmental variable combinations hypothesized to contribute to whisker growth. In addition, two types of conformal coating will be evaluated against non-coated assemblies for whisker growth inhibition and short circuit prevention for parts typical of functional assemblies.
Technical Approach
One of the challenges accompanying real electronic systems is understanding the details associated with the components, product design, manufacturing process, and service environments that contribute directly or conspire with one another to exacerbate whisker growth. This project provides testing of relevant materials in conjunction with metallurgical analysis to better understand the factors contributing to whisker growth. In addition, depending upon the whisker growth data fidelity, the system risk assessment framework developed will enable the designer or systems engineer to either make a relative or quantitative whisker risk assessment of a circuit function or assembly.
Benefits
This study of the interactions associated with part selection, manufacturing assembly process materials, and environmental test protocols will provide insights to whisker growth and potential mitigation actions. In particular, the project will develop an understanding of the long-term whisker growth and long-term conformal coating mitigation performance. By providing a tin whisker short circuit risk assessment framework for circuit functions and assemblies, the designer will be able to select appropriate combinations of parts, solders, manufacturing processes, and conformal coatings to manage the risk of lead-free tin use and ensure continued reliability of DoD systems. (Anticipated Project Completion - 2015)
Interim Results
The experimental tin whisker tests are staged. The short-duration tests are staggered from 2010 to 2013 and include an assessment of power cycling, high humidity, and thermal cycling. In parallel, a long-term test at lower humidity will start in 2010 and proceed until 2014. The probabilistic tin whisker risk assessment framework will be updated periodically throughout the project as experimental data and metallurgical examination results become available.
Points of Contact
Principal Investigator
Dr. Stephan Meschter
BAE Systems
Phone: 607-429-8828
Fax: 607-755-6615
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.