Influence of Conformal Coatings on the Mechanisms of Nucleation and Growth of Sn Whiskers, and Potential Impact on Mitigation
EMSL Project ID
44757
Abstract
The worldwide acceptance of the European Union's Restriction of Hazardous Substances act (RoHS), meant to reduce Pb contamination in the environment, has resulted in reemergence of the of reliability problems due to formation of Sn whiskers on plating finishes. Several empirical evidences suggest that conformal coating can mitigate Sn-whisker growth. To date, however, the use of conformal coatings to mitigate whisker growth is based on a "trial-and-error" approach, because of a lack of understanding of the underlying mechanisms. In order to introduce predictability into the choice of coating material, coating thickness, and process parameters (including plating surface cleaning and coating application methodology), a fundamental understanding of the mechanisms of whisker-mitigation via conformal coats is imperative. The objective of the proposed research is to obtain a fundamental understanding of the role of conformal coatings on the mechanisms and kinetics of whisker nucleation and growth. The goal will be to characterize the (a) coating properties, (b) adhesion at the interface between plating and coating (interfacial strength or toughness), (c) stresses induced in the plating, and (d) localized breaks / de-cohesions of the coating, and correlate these with the propensity for whisker nucleation and growth. The roles of these parameters on grain boundary diffusion within the plating (which is the principal driving mechanism for whisker growth) will be evaluated by surface-analytical, microscopy, atom-probe tomography, diffraction and creep kinetics studies. This mechanistic study will enable predictable and reproducible optimization of material and process variables for whisker-suppression by conformal coating with maximum efficacy.
The principal innovative aspect of the proposed research is that by producing a validated mechanistic understanding of the role of conformal coating on whisker growth, it will enable a "knowledge-based" (as opposed to "trial-and error") approach to optimizing material-selection and component-design methodologies for maximum resistance to whisker formation. The results of this proposed work will be highly relevant to the long-term reliability of environmentally-friendly Pb-free electronics which are critical to DoD, DoE and space applications. The broader scientific community will benefit from the fundamental mechanistic studies, which will lead to an in-depth understanding of the interaction between Sn-platings and conformal coats, and which will be published in the open, peer-reviewed literature for broad, unrestricted access.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2011-10-01
End Date
2014-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Chang Q, P Rudenko, D Miller, J Wen, D Berman, Y Zhang, BW Arey, Z Zhu, and A Erdemir. 2017. "Operando Formation Of An Ultra-low Friction Boundary Film From Synthetic Magnesium Silicon Hydroxide Additive." Tribology International 110:35-40. doi:10.1016/j.triboint.2017.02.003