3-D Modeling is Key to Substrate-Embedded Magnetics for Next-Gen Connectors
By Steve Kubes, TE Connectivity

According to an IDC Insights Forecast (January 2010), foreseeable growth of Ethernet ports will remain steadily constant for switch ports but increase for desktop and portable PCs and servers (Figure 1). Consequently, as the performance demands of communications systems continues to rapidly increase, growth of the RJ-45 connector used for terminating the Ethernet twisted pair will continue to increase in applications ranging from enterprise switches and routers to power over Ethernet (PoE) and IP phones.

As an essential element of high-speed data communications interfaces, magnetics components have proven particularly challenging in terms of achieving the tighter tolerances and reduced product variations required by higher data-rate channel performance. In response to market forces, the data communications industry is demanding more automation, greater predictability, improved quality, better performance, and, of course, lower-cost wound coils.

At its current stage of development, planar magnetics product technology is now viewed as a viable means for achieving these previously illusive design goals. In turn, the technology driver for planar magnetics in data communication applications is the need for automaton for peak demand cycles, combined with more consistent manufacturability in terms of repeatable, predictable performance behavior. 

Beyond economics and scalability, however, is the achievable performance advantage for high-speed communication circuits. Advanced manufacturing and test methods are now being used to achieve these goals. For example, the latest 3D printed circuit board (PCB) processes are being employed to manufacture wideband planar transformers and common-mode chokes embedded in substrate, using proven techniques to more efficiently manufacture reliable, consistent structures. While this approach has been attempted before, recent advances in manufacturing and design methodology have reduced the variations that plagued earlier attempts to commercialize planar magnetics for precise data communications requirements.

The planar magnetics fabrication process utilizes 14x16 or 18x20-inch FR4 panels into which magnetic components are embedded. The panels are then processed to create devices that are pin-compatible with discrete coil-based components. Slightly larger than the base of a comparable wound coil, the pads align so that the planar magnetics can directly replace the wound coil magnetics. From the standpoint of performance and manufacturability, the planar magnetics advantage provides complete control over leakage inductance, capacitance, and the shapes of the petals or wrappings. The consistency of the manufacturing process is based on design rules for controlling the depth, width and size of the component.   

With embedded magnetics technology, automated processing and proprietary materials are used to embed highly sensitive magnetic ferrites into standard PCBs. As shown in Figure 2, PCB-based technology using precision photolithography allows the manufacturing of boards containing hundreds and even thousands of planar magnetic devices.

This technology is in the early phases of being applied to Ethernet products, including integrated connectors, discrete magnetics, and media filtering. Based on this technology, TE’s own PlanarMag Technology products use a 3D-electromagnetic simulator with unique design techniques to create patented proprietary winding structures. Shown in Figure 3, this design capability allows subtle nuances to be addressed quickly for a variety of standard as well as custom applications.
 

The next step to enhancing the simulation process is full integration, where the complete mechanical design is modeled including integrated circuits and the parasitic traces on the host board, through the pin of the connector, and finally to the RJ-45 plug. Based on test bench measurements with empirical data and correlation to the simulations in an iterative process, the simulation environment has been refined and correlates extremely well with the actual empirical measurements for the planar magnetic designs. The result is that the integral details can be resolved much more quickly and design-to-manufacturing implementation occurs much faster.

At this juncture, substrate-based planar magnetics technology provides substantially greater control over the impedances and other design attributes compared to other device types. In addition, more-tightly controlled impedances can eliminate the matching termination and reduce system costs. Finally, high-volume, scalable manufacturing with consistency and quality allows highly predictable processing to provide customers with a very reliable supply chain. The end results are performance for today’s high-volume data communications applications and a path to the future.