Magnetic Properties of Iron-Based Alloy Powder Coils Prepared with Screen Printing Using High-Solid-Content Magnetic Pastes

A molding coil is prepared by filling and dry pressing granulated alloy magnetic powders directly onto enameled wire. As the molding coil is developed toward miniaturization, the granules consisting of magnetic powder and organic binder cannot uniformly fill the small space in the coil center column during molding. This leads to a porous microstructure or cracks. The uneven packing problem in the coil center column was effectively solved in this study by applying a screen printing process using high-solid-content magnetic pastes. Bisphenol A epoxy resin has the benefits of excellent mechanical, bonding, electrical, corrosion resistance, low shrinkage and low cost properties. However, the viscosity is too high for use as a binder for high-solid-content magnetic paste. The magnetic paste viscosity can be reduced by substituting some low viscosity reactive diluent (butyl glycidyl ether) for Bisphenol A epoxy resin. It was observed that the relative density and magnetic properties (such as initial permeability, saturation magnetization, and core loss) can be effectively improved by increasing the monomer addition because the monomer acts as a lubricant that helps the magnetic particles rearrange during compaction. However, as monomer addition becomes greater than half the epoxy resin weight percent, the sample bending strength decreases.