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Over-Molded Inductor (OMI) - Feasibility Demonstration in a DC-DC Converter

3-D models of discrete inductor on a PCB
Fig. 1. Realizations of the inductor in a dc-dc converter: (a) Discrete inductor; (b) Over-molded inductor.
Switched-mode dc-dc converters serve a variety of products, such as point-of-load power modules, gate drivers, and mobile devices. An inductor is usually needed to attenuate the switching noise for the load. The inductor can be implemented as a discrete component, a substrate, or a package enclosure. A discrete inductor is shown soldered to a printed circuit board (or substrate) carrying the remainder of the converter in Fig.1(a). Non-magnetic encapsulant may be added to protect the assembly against environmental stresses. Any additional shielding or isolation for protecting the magnetic device from encapsulant may increase the volume.

This paper presents an alternative to inductor fabrication called "over-molding." As depicted in Fig. 1(b), the winding is first attached to the substrate. Magnetic paste is then injected into the unused space that is normally occupied by encapsulant and is cured under atmospheric pressure below 250 °C to realize the core. The prototype of the OMI is shown in Fig. 2(a).

The impact of the OMI on the converter's efficiency (Fig. 2(b)), operating temperature, and switching noise was demonstrated to be similar to that of the commercial inductor. Also demonstrated was the feasibility of storing magnetic energy in the volume normally filled by encapsulant. The next goal would be to improve the power density, which is tied directly to permeability. The materials and fabrication process will be examined to improve the homogeneity of over-molded magnetic mixtures using a low curing temperature under atmospheric pressure.

Fabricated discrete inductor and DC-DC Converter and converter efficiency to output current graph
Fig. 2. (a) Winding on PCB and prototype of converter with OMI. (b) Comparison of efficiencies for dc-dc converter with discrete inductor and OMI.
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