IEEE Power Electronics Magazine - December 2015 - 31

This article uses definitions for "3-D packaging," "component embedding," and "substrate" identical to those
used in the technology report, "Current Developments
in 3-D Packaging with Focus on Embedded Substrate
Technologies," on which this article is based and which
was funded and published by Power Sources Manufacturers Association [1]. There are two classes of embedded
components, as illustrated in Figure 1. First, there is a
discrete device, termed the inserted component. In this
case, the surface-mount passive devices, R, L, or C, manufactured prior to embedding into the printed circuit board
(PCB) are referred to as an inserted component. These
are mounted in laser-machined cavities within the PCB
or embedded using the layup and press process. Second,
there is a formed component, manufactured as element(s)
within the PCB.

Embedded Passive Components
Magnetic Components

technology to achieve this performance is the embedding of active and passive components in stacked 3-D
structures.
The efforts required to scale previous embedded milliwatt approaches to power electronic applications with
a power spectrum from tens of watts to kilowatts are
formidable, encompassing the handling of high current
and requiring new benchmark efficiency, much improved
thermal transfer, and high-volume, high-throughput manufacturing, while improving performance and reliability
beyond what is attainable with presently available power
electronic technology.

Major past efforts have been to develop embedded inductors for radio-frequency and microwave and other lowenergy applications that include magnetic sensors embedded in PCBs and other substrates. However, power converters require magnetic passive components that are
primarily energy-storage elements, such as inductors (both
standard and coupled) and transformers that are significantly larger. Therefore, initial embedded magnetic implementations have been for low-wattage power converters,
such as point-of-load (POL) nonisolated dc-dc converters,
granular POLs, and larger power converter gate drivers.
Low-profile inserted inductors are available from a
number of suppliers worldwide. Companies such as TDK,
Taiyo Yuden, Coilcraft, and KAO Speer, to name a few,
have developed thin-film inductors with a thickness of
0.5-2 mm. The inductors are thin enough to embed in substrates. The inductance is in a dc-dc converter sweet spot
of 0.74-2.2 nH. The major limitation is allowable dc current, which is usually below 1 A. Figure 2 illustrates a conventional inductor design and a thin-film power inductor
with a magnetic metal core with a 1-mm package height.
A remarkably small 10-A, 4-MHz POL footprint of
150 mm 2 and 0.8-mm height was reported using a coupled
low-temperature cofired ceramic (LTCC) inductor design
[2]. The design used GaN devices, and it was operated at
4 MHz. The converter exhibited greater than 1 kW/in3;
however, the cost of LTCC inductors is generally viewed
as prohibitive.
NEC-Tokin developed Senfoliage, an alloy flake magnetic material that is very promising for embedding. The
Center for Power Electronic Systems has successfully developed a dc-dc converter utilizing this material [3]. The
advantage of the alloy flake material stems from its 2-D
characteristic as opposed to one-dimensional (1-D) fiber
materials, as shown in Figure 3. Note that a fiber has a very
small width, so it is considered to have a single dimension.
December 2015

 IEEE POWER ELECTRONICS MAGAZINE

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Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - December 2015