Presented March 05, 2015- Presentation Slides
Microstructurally Adaptive Constitutive Relations and Reliability Assessment Protocols for Lead Free Solder by Dr. Peter Borgesen
The long term reliability of a microelectronics assembly is commonly limited by failure of the solder joints. The quantitative prediction of that is much more critical for DoD applications than for most commercial and industrial products. The objective of this project was to provide practitioners with the tools and understanding required to interpret accelerated test results in terms of the life of lead free solder under the relatively unique long term service conditions characteristic of such applications. This is becoming increasingly important as a growing part of the DoD sector transitions to lead free technologies.
The prediction of long term reliability requires extrapolations that cannot be validated in time; i.e., these must rely on a mechanistic understanding. Fatigue of a ductile metal like solder is notoriously difficult to understand at a sufficiently fundamental level. However, it was shown that quantitative predictions are possible based on a quantitative understanding of the rather complex evolution of the solder microstructure in cycling and aging. The constitutive relations required to model and predict life at the design stage, as well as for product development and qualification, were developed.
Whisker Mitigating Composite Conformal Coat Assessment by Dr. Stephan Meschter
Many DoD weapon systems are heavily dependent upon sophisticated software running on economical commercial-off-the-shelf (COTS) electronics adapted to a particular platform. This project supports SERDP’s efforts to utilize lead-free COTS materials while maintaining high reliability during long term storage and service. Unfortunately, lead-free COTS assemblies and parts often use pure tin, tin rich alloys and/or zinc metals, which are prone to long term whisker growth under certain conditions. Whiskers are high aspect ratio electrically conductive metallic filaments that have caused electrical short circuits thereby severely impacting some DoD programs. In a recent commercial case, a 1.9 mm long tin whisker created a 248 ohm short on a 2003 accelerator pedal position sensor rendering the vehicle essentially un-drivable in 2009. Some equipment manufacturers mitigate whisker risk by using conformal coatings to either keep whiskers contained or prevent contact from adjacent surface whisker growth. The objective of the current project is to develop a composite polymer spray coating material with improved strength and film thickness uniformity. The project utilizes functionalized nanoparticles covalently bonded to the coating resin matrix to provide improved mechanical properties while minimizing impact to the spray characteristics. This presentation described the mechanical testing, coverage evaluation and whisker penetration resistance testing.
Dr. Peter Borgesen has been a professor of Systems Science and Industrial Engineering at Binghamton University (SUNY) since 2009. For the past decade, Peter has focused a major part of his research on the reliability of microelectronics assembled with lead free solder joints. Peter earned a Ph.D. in Physics from University of Aarhus, Denmark, in 1982. He worked at the Riso National Laboratory in Denmark and at the Max Plack Institute for Plasmaphysics in Germany, spent 8 years in the Materials Science Department at Cornell University, and 15 years in industry running a multi-million dollar consortium sponsored research program on electronics manufacturing.
Dr. Stephan Meschter has over 30 years of experience in advanced packaging, failure analysis and reliability testing of electronic assemblies at BAE Systems Electronic Systems in Endicott, NY. He has designed and evaluated electronic assemblies for power, flight and jet engine control systems used in spacecraft, aircraft and ground vehicles. Starting in 2004, Stephan began evaluating the commercial lead-free materials transition impact to high-reliability, high-performance aerospace and defense electronic systems. He was a member of the 2009 U.S. DoD Lead-free Electronics Manhattan Project team that published a set of best practices to mitigate the risks associated with lead-free electronics usage in high performance DoD systems. Since 2010, Stephan has been working with SERDP on lead-free tin whisker formation research and short circuit risk mitigation using enhanced polymer conformal coatings. He earned a bachelor’s in mechanical engineering from the University of Hartford in Hartford CT in 1984, and he holds both a master’s degree (1987) and a doctoral degree (2001) in Mechanical Engineering from the State University of New York in Binghamton, NY. Stephan currently participates in the IPC Lead(Pb)-free Electronics Risk Management (IPC-PERM) Council and is currently supporting revision of several SAE Lead-free Aerospace and Defense risk management standards.