Two- and three-dimensional arrays of magnetic microspheres

A novel fabrication approach for two- and three-dimensional arrays of magnetic microspheres is presented in this paper. The magnetic microsphere is made from 47 mu m size Al2O3 spheres onto which a 2-3 mu m thick nickel layer is coated through electroless plating. After proper anneal, the outer nickel layer is converted to exhibit a crystalline structure. As an example for utilizing such magnetic microspheres, a two-dimensional, anisotropically conductive matrix is made by transferring the magnetic microsphere array from a template to a transparent adhesive tape using a magnetic attractive force. In addition, a three-dimensional array has also successfully been constructed on a metal plate. The two-dimensional conductor array may be useful for high-density circuit packaging applications in the semiconductor industry, and the three-dimensional array may open up a possibility for constructing three-dimensional photonic crystals.