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Hybrid Conformal Coatings Used for Mitigating Whisker Growth
Hybrid Conformal Coatings Used for Mitigating Whisker Growth
In this work, we have synthesized a conformal polyurethane coating consisting of hard (hexamethylene di-isocyanate) and soft (polyol) segments.
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Authored By:
Junghyun Cho, Suraj Maganty1
Binghamton University (SUNY)
Binghamton, NY, USA

Stephan J. Meschter
BAE Systems
Endicott, NY, USA

Dale Starkey, Mario Gomez, David G. Edwards
Henkel Electronic Materials LLC
Irvine, CA, USA

Abdullah Ekin, Kevin Elsken
Bayer MaterialScience LLC
Pittsburgh, PA, USA

Jason Keeping, Polina Snugovsky, Jeff Kennedy
Celestica Inc.
Toronto, ON, Canada

Summary
A conformal coating of polyurethane (PU) consisting of hard and soft segments is being studied in an effort to prevent tin whisker penetration. For this, the coating needs to possess optimum mechanical properties by providing sufficient strength, modulus, and hardness while maintaining good ductility and toughness. Typical monolithic PU films, however, do not possess all these required properties, so silica nanoparticles are incorporated into a PU film to improve its whisker mitigation effectiveness.

In the present work, nanoparticles were functionalized to bind them to the polymer structure while avoiding the agglomeration among the particles. Selection of the ideal concentration of nanoparticles is determined by establishing microstructure-property relations. Structural features at different length scales are characterized by various instruments including atomic force microscope (AFM) and scanning electron microscope (SEM) while mechanical properties are evaluated via macroscopic tensile testing as well as nanoindentation.

In particular, the nanoindentation testing emulates the whisker penetration behavior by producing local deformation of PU around an indenter tip.

Conclusions
Functionalized nanosilica particles approximately 20 nm in diameter were added to a PU coating in an attempt to attain its optimum mechanical properties for mitigating tin whisker growth. It was shown that mechanical properties do not continuously increase with the nanosilica concentration. This was due to non-uniform distribution of nanosilica and polymer structure change with added nanoparticles.

Phase separation also seemed to be affected by the presence of nanosilica. In particular, microdefects created during film processing are responsible for film brittleness and limited ductility. Establishment of the structure - property relationship is essential to identify optimal microstructures of the nanoparticle-filled PU, which can be of importance in tin whisker mitigation.

Initially Published in the SMTA Proceedings

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