IEEE Power Electronics Magazine - September 2016 - 32

on the inductor. Embedding magnetics and capacitors in the printed circuit
board (PCB) has been demonstrated
L
Q1
but requires a complex fabrication
process. Moreover, the thermal perc
Q2
Gate Drive
R
formance of the embedded magnetic
C
dc +
-
material is reduced because of the
Constant On-Time
Control
surrounding circuit board (usually
FR4 or another similar substrate). Lowtemperature cofired ceramic technology has become very popular and can
achieve a very high power density but
FIG 1 A schematic of a buck converter with constant on-time control.
tends to be expensive [4]-[6]. Microinductors based on thin-film technology
have
been
used
experimentally
for power modules. The dismodules. However, its drawback is that the switching freadvantage of this technology is that it has higher direct-curquency varies and cannot be synchronized. Some control
rent resistance (DCR), which results in a much greater loss
chips offer an option between the two control modes.) The
compared with conventional inductors [7]-[9].
power MOSFETs are often combined with the gate drive and
This article discusses a patented new packaging techcontrol into a single semiconductor component. The internology called Power Supply in Inductor (PSI2), which can
nal input and output capacitors are quite small and usually
supplemented by external capacitors outside the module.
simultaneously achieve high efficiency, high power density,
The inductor is the largest component and a dominant facand low cost. A customized magnetic component acts as
tor in the overall module physical design and assembly.
both the buck inductor and the case of the whole power
The ultimate objectives for a commercial power module
module [1]-[3].
are high efficiency, small size (high power density), and low
cost in volume production. As is well known, it is relatively
A New Approach
easy to achieve any two of these objectives but to achieve
There are two common packaging approaches for making
all three simultaneously can be very difficult. Some of the
high-density power modules. The first is based on a PCB
approaches that are often considered include the following:
substrate. The power-controller IC, inductor, and other parts
1) increase the switching frequency (this approach can
are soldered or wire bonded onto the substrate, and the
reduce the inductor size but lowers the efficiency and
whole substrate is packaged using plastic injection molding.
raises the cost)
The second approach is based on a lead frame, to which all
2) use MOSFETs with a lower on-resistance (this can
components are connected through wire bonding, and the
improve the efficiency but raises the cost)
whole module is then packaged with injection molding. No
3) increase the size of the inductor (a larger inductor can
matter which approach is used to package the module, the
improve the efficiency but increases the size)
inductor is generally the largest component and must be
4) use a topology other than buck (this may reduce the
accommodated within the package. To leave some space for
inductor size but increases the complexity and cost and
plastic material, the inductor must be smaller than the mold,
requires a custom controller).
and it generally takes up only about one-third of the whole
These options consider the circuit and components themvolume of the module.
selves, but the overall packaging is equally important. Recent
Figure 2 shows the structure of a traditional power
experimental work has focused on improving the packaging
module using plastic packaging. It has one or more active
of high-density power modules with a particular emphasis
devices, an inductor, and some auxiliary components
mounted on the substrate, and the whole substrate is then
packaged with plastic material by injection molding.
Figure 3 shows the structure of a power module using
the new PSI 2 packaging. The substrate is similar to
the one used in the plastic packaging, but the inductor
Plastic
Inductor
becomes the package for the whole module and can be
PCB
much larger.
The magnetic core has a cavity in one part and an
embedded coil in the other part (Figure 3). The buck regulator and the auxiliary components are mounted underneath
(a)
(b)
the cavity. The magnetic core and the embedded coil function as both a power module package and a buck inductor in
FIG 2 A conventional substrate with plastic packaging: (a) the
the converter. Thermally conductive glue is used to attach
power module and (b) the structure.

IEEE PowEr ElEctronIcs MagazInE

z September 2016

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - September 2016