Use of Embedded Ferrites for Routing Under Inductors in Compact Printed Circuit Boards

Routing signals on a Printed Circuit Board (PCB) under inductors and other electromagnetic interference (EMI)-emitting components, such as switching field-effect transistors (FET), can be challenging since they induce noise to other signals. For example, using current methods, many high-speed signals cannot be routed under an inductor on any layer of the PCB stack up. By implementing embedded ferrite material in the PCB as described here, the routing constraints can be relaxed, which can enable signal routing under these devices.In this solution, ferrite is laminated as part of the PCB stack-up structure to either replace copper or dielectric insulation or both. Ferrite placement within the PCB is defined during the PCB layout design phase, so it can be placed exactly where the application requires it. This ferrite layer, or layers, may be local or may consist of the whole PCB area within the applicable layer(s) depending on application needs.Simulations of embedded ferrite placed under the typical power delivery inductor, with ferrite on dielectric layers between layers 1, 2, and 3 and traces on layer 4 of the PCB, showed up to 25-55% reduction in common mode noise when compared to a design without the embedded ferrite.By laminating ferromagnetic material as part of PCB structure to act as magnetic shield within the PCB, we can enable high speed signal routing under inductors, or free up this space to decrease the board size, increase customer product’s battery size and capacity, and reduce the overall costs. All these create compelling new products and product categories for customer systems with longer battery life.