Rapid and Positioned Fabrication of Pure Gold Microsphere Arrays with Stable Deep-pressing Anisotropic Conductivity for Next-generation Advanced Packaging.

Abstract A simple and rapid technique is developed to fabricate pure gold microsphere arrays through a positioned transient-emulsion self-assembly and laser-irradiated ripening strategy. It enables the assembly of uniform gold colloidosomes in a pre-designed microhole array, transforming them into uniform microspheres within 10 seconds based on a layer-by-layer mechanism of laser-heating, melting fusion and merging growth. Theoretical simulations attribute this layer-by-layer mechanism to the finite skin depth of laser, creating a localized photo-thermal effect on the colloidosome surface. The key advantage for this technique is the final size of gold microsphere determined by the templating microholes, simplifying control through lithography techniques and making it applicable to various nanostructures using as gold source. Importantly, these pure gold microspheres demonstrate stable conductivity under deep compression, making them promising for reliable connections in soldering micro-sized chips onto integrated circuits.