Design, Fabrication, and Characterization of a Low-Temperature Curable Magnetic Composite for Power Electronics Integration

To simplify the integration process of embedding magnetic components in power electronics converters, we fabricated a magnetic-filled-benzocyclobutene composite that can be cured at temperatures below 250 °C without pressure. The magnetic fillers used in the formulation were a round-shaped particle of permalloy and a flake-shaped particle of Metglas 2705 M. To guide the formulation, we first constructed 3-D finite-element models of the composite consisting of periodic unit cells of magnetic particles and flakes in the polymer matrix and used Ansoft Maxwell to simulate magnetic properties of the composite. Then, flowable pastes of the composite with varying amounts of Metglas in the magnetic fillers up to 12.5 wt% were prepared, and toroid cores were poured and cured at 250 °C. Subsequently, magnetic properties of the cores, i.e., complex permeability and core loss density, were measured. We found that the real part of the composite's relative permeability increased with Metglas addition, reaching a value of 26 at 12.5%. However, the core loss data at 1 and 5 MHz showed that the addition of Metglas flakes also increased the core loss density. The measured properties were consistent with the Maxwell simulation results. Microstructures of the cores were examined by scanning electron microscopy. We found that the magnetic particles were uniformly dispersed and isolated by the polymer, which explained the high electrical resistivities of the composite and relatively low core loss densities due to suppression of inter-particle eddy-current losses.