Controllable Fabrication of Nanoporous Gold Microspheres from Low-Gold-Content Cu–Au Alloys for Stable, Deep-Pressing Electronic Packaging

Porous gold materials, with advantages such as low relative density and high chemical stability, are widely used in biosensing, chemical energy storage, etc. Currently, traditional methods still face challenges in the preparation of ultrafine nanoporous gold microspheres, which limit their application in advanced electronic packaging. In this study, we propose a strategy for the controlled preparation of nanoporous gold microspheres using low-gold-content alloy microspheres, which includes wet chemical reduction, crystal diffusion and growth, liquid-solid interfacial nonwetting effect, and chemical-free corrosion dealloying. Nanoindentation results show that, compared to the brittle crushing under deep pressing of polymer microspheres, the newly prepared nanoporous gold microspheres exhibit significantly low-pressure-stable deep-press anisotropic conductive properties. Specifically, the nanoporous gold microspheres achieve up to 80% compression deformation under a load of approximately 5 mN, primarily due to their unique nanoporous structure, reducing hardness. In terms of piezoresistive performance, the nanoporous gold microspheres maintain stable low-resistance conductive properties during both loading and unloading processes, which is mainly attributed to the large compression deformation enhancing the connection reliability between substrates. When applied to anisotropic conductive film preparation and device encapsulation testing, the results demonstrate that with a powder loading of 5 wt %, the nanoporous gold microsphere-based anisotropic conductive film exhibits a significantly wide pressure encapsulation range (0.1-0.5 MPa), which is directly related to the large compression deformation ability of the nanoporous gold microspheres. This ability can not only reduce the requirement for uniform particle size distribution and save sorting costs but also effectively improve the conductivity of interconnected devices.