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Tin- Carbon Nanotube Composites as Tin Based Solder Replacements
Keywords: Solder Composite, Stress mitigation, Thermal management
Purely tin solders suffer from stress induced failures in the field, and as a result lead-free solder thermal interface materials are commonly Sn eutectics that have significantly reduced thermal conductivities when compared to the pure material. In this presentation we will discuss the development of Sn-carbon nanotube (CNT) composites that overcome the mechanical limitations of pure Sn while delivering thermal conductivities on par with the base material. As a first step, well dispersed CNTs were added to a metal melt, significantly improving the physical properties of the base metal. Adding 1% CNTs by volume to a metal melt increased the base metals modulus by 76% and hardness by 9%. Furthermore, the electrical conductivity of the base metal was improved by 10% with the addition of CNTs into the melt. These improvements in the physical properties of a tin based composite can mitigate undesired stress-induced whiskering effects commonly observed in tin solders. The Sn-CNT composites are made with vertically aligned carbon nanotube arrays grown directly on copper substrates. The arrays are filled with tin using either pressure infiltration, melt casting or electroplating. Successful infiltration is highly dependent on achieving surface energy compatibility between the CNTs and the molten Sn. Electroplating tin onto the CNT arrays grown on copper substrates proved to be the best means of overcoming the surface energy mismatch between the Sn and the CNT matrix. Bond strength is dependent on the ability of the Sn to wet both the surface of the material being soldered to and the substrate the CNTs are grown on. After reflow, CNTS grown on copper successfully maintained their adhesion to the substrate, indicating great promise for their use as a solder replacement for die attach applications.
Daron Spence,
Georgia Institute of Technology
Atlanta, Georgia
United States

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