Enhancing Mechanical Properties and Heat Resistance of Iron Powder Cores for Inductors by Epoxy‐Modified Bismaleimide Resin Coating

ABSTRACT To improve the mechanical properties and heat resistance of iron powder cores for inductors, the carbonyl iron powder was insulation‐treated via phosphating and epoxy‐modified bismaleimide resin coating. The addition of epoxy into bismaleimide resin significantly enhanced the magnetic performance, mechanical strength and thermal stability of powder cores. The optimised core exhibited an effective permeability μ e of 25.8 and a quality factor Q of 54.9 at 1 MHz, with a power loss P cv of 510.2 kW·m −3 at 100 kHz/50 mT. The radial crushing strength increased by 102% compared to the core coated with only bismaleimide. After thermal exposure at 155°C for 336 h, the cores coated with epoxy‐modified bismaleimide showed lower reductions in saturation magnetisation and minimal changes in μ e (4.41%), Q (4.96%) and P cv (3.82%), indicating improved heat resistance. Epoxy modification enhanced bismaleimide performance by forming hydroxyl groups through their interaction, creating strong polar bonds with iron powder. The interaction results in a three‐dimensional network structure consisting of rigid and flexible molecular chains. This structure reinforced the mechanical properties and heat resistance of the iron powder core.