Reliability Assessment of Magnetic Cores and 3-D-Printed Constant-Flux Inductors

Constant-flux inductors (CFIs) are designed to have more uniform flux distribution in the core for efficient use of magnetic material and higher inductance density. However, they require elaborate winding structures, which pose challenges to fabrication by conventional fabrication techniques. Recently, we applied a paste-extrusion 3-D printer to fabricate spiral windings with different turn-to-turn widths for a pot-core CFI. The printed windings were sintered at 850 °C and then potted in a low-temperature curable magnetic composite to form inductors measured at 5 mm × 5 mm × 2 mm. In this article, reliability of the CFIs and the corresponding magnetic cores was evaluated by temperature cycling between -40 °C and 125 °C and storage testing at 125 °C. After 1000 temperature cycles and 1000 h at the storage temperature, the dc winding resistances of the pot-core CFIs had no significant change, while the inductances dropped by only 4.8% and 2%, respectively. The drop in inductance was found to correlate with the drop in magnetic permeability of the core, which was caused by degradation of the magnetic material under thermomechanical stresses.