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Embedded Magnetics Opens Door to New Approach to Circuit Design

Sat, 10/15/2011 - 7:35am
Steven R. Kubes, TE Connectivity, www.te.com
Impedance matching and filtering of wide bandwidth data lines has long been the domain of hand-wound toroidal chokes and transformers. A new planar magnetic technology is paving the way to the manufacture of these devices utilizing established printed circuit fabrication and IC testing techniques.

Advanced magnetic technology leverages the latest 3-D printed circuit board (PCB) processes to manufacture wideband planar transformers and common-mode chokes embedded in a substrate. Well-established PCB techniques are used to more efficiently manufacture reliable, consistent structures. While the approach was known for many years, recent advances in design methodology have reduced the variations that plagued earlier attempts to commercialize planar magnetics for precise data communications requirements.

Theembedded magnetics Figure 1 Manufacturing Process

The process starts by drilling a series of controlled depth holes in FR4 PCB material. (See figure 1.) Next, ferrite cores are inserted and an epoxy polymer is used to fill the cavities and to surround and protect the ferrite cores. After the epoxy polymer is cured, a planarization process ensures a very flat structure. Following this procedure, the FR4 material with the embedded ferrite cores is clad with copper on top and bottom. Standard PC board manufacturing techniques are then employed to drill and plate vias and etch the circuit traces that form the windings around the embedded ferrite cores. After laser marking, a thin tape layer is applied to one side and the opposite side is sawn and singulated into individual components similar to a semiconductor process. Then testing is performed on each device similar to the 100% testing techniques used for semiconductors to verify conformance to critical parameters and the consistency of the manufacturing process.

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. The automated processing that leverages well-established PCB technology helps improve performance, quality, and reliability and helps provide previously unattainable supply stability. Highly automated testing on each completed assembly leverages experience for verifying the conformance of semiconductor devices. In addition to resistance, inductance, opens and shorts and high-pot (high potential) testing, in some instances digital testing is performed for high speed parametrics. When compared to hand wound coils, planar magnetics have substantially greater benefits from automation due to their inherently predictable characteristics.
embedded magnetics Fig 2
Application to Connectors

Figure 3 demonstrates how embedded magnetic components can be used to create a remarkably compact RJ-45 connector with filtering and impedance matching magnetics integrated into the package. This product, the Mag45 connector from TE Connectivity, provides demonstrated improvements over coil-wound designs. Figure 4 shows the performance of the TE PlanarMag product compared to a coil-wound product.

Because of the controllability in the manufacturing of the embedded planar magnetics, it is possible to characterize the design by applying filter theory as opposed to transmission theory. Today, with wound coils, impedance matching is an art with iterations performed until matching is achieved. Any variations create impedance mismatches that can cause spikes and anomalies associated with parasitics that are related to electromagnetic interference or compliance and specification performance issues.

embedded magnetics Figure 3Since the embedded magnetic PlanarMag product structure performs as a tightly controlled narrow pass filter with a high degree of consistency and repeatability, the Bob Smith termination typically used for impedance matching can be eliminated or the components reduced in many applications. Testing for IEEE 802.3 as well as electromagnetic interference (EMI) and surge testing have demonstrated this capability. This tight control and consistency has allowed designers to reduce the components on their designs while delivering products that truly match the system requirements. In addition, PlanarMag product technology helps facilitate consistent product lead times and supply chain for main-stream, high-volume applications.

For wound coils, what works for one application frequently does not work for another. As a result, customization is a common requirement for wound coils. With the higher performance and highly repeatable embedded magnetics product technology, standard products can be used in many applications. The ability to use standard products can eliminate the custom design costs and time-to-market lag from both the design and qualification delays as well as potential unavailability of product in production.

embedded magnetics figure 4The Potential of Planar Technology

The data commumications industry has demanded more automation, greater predictability, improved quality, better performance and, of course, lower cost for wound coils. With planer magnetic product technology, all of these previously illusive goals can be achieved. The attributes of PlanarMag products helps deliver significant advantages for data communications applications. The substrate-based technology provides substantially greater control over the impedances and other design attributes compared to wound-coil devices. 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 a highly reliable supply chain. The end results are performance for today’s high-volume data communications applications and a path to the future.
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