Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For transformer
Reexamination Certificate
2000-12-11
2003-09-30
Cuneo, Kamand (Department: 2827)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For transformer
C361S298400, C361S299200, C336S200000
Reexamination Certificate
active
06628531
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to miniature printed circuit boards (PCB) for microelectrical applications. More particularly, the invention relates to multi-layer, user configurable and stackable miniature printed circuit boards for static electromagnetic components such as transformers.
DESCRIPTION OF THE RELATED TECHNOLOGY
Transformers are widely known electromagnetic components used in electrical devices and power supply units. In general, static magnetic components such as transformers have traditionally been constructed using windings of ordinary conducting wire having a circular cross section. The conventional transformer comprises an insulator gap between a primary coil and a secondary coil, and the voltage generated in the secondary coil is determined by the voltage applied to the primary coil multiplied by the winding ratio between the primary coil and the secondary coil. Manufacture of these traditional structures involves winding the wire around a core or bobbin structure, a process that often involves considerable amounts of expensive hand labor. Furthermore, high power applications often require a magnetic component having a bulky core and large wire sizes for the windings. Even though the transformer is often an essential component of an electrical apparatus, it has been historically the most difficult to miniaturize.
New operational requirements with respect to circuit size and power density and the increasing necessity to reduce circuit manufacturing costs have made the traditional static magnetic component very unattractive as a circuit component. Newly designed circuits, for example, need low profiles to accommodate the decreasing space permitted to power circuits. Attaining these objectives has required the redesign of magnetic components to achieve a low profile and a low cost component assembly.
Planar magnetic components fabricated with flexible circuit and multi-layer printed circuit board (PCB) technologies offer an alternative to address the new operational and cost requirements. With planar technology, transformers have been formed from single or multi-layered printed circuit boards.
FIG. 1A
illustrates an example of a typical planar transformer constructed from printed circuit boards. Specifically,
FIG. 1A
depicts a side view of such a component
100
attached to the main board
110
of an electrical device. The component
100
includes a PCB
130
with multiple internal layers. Windings of the PCB
130
are connected to the main board by connecting pins
140
.
FIG. 1B
illustrates the manner in which the component
100
is assembled and
FIG. 2
schematically depicts the individual layers of the PCB
130
.
The basic construction of the component
100
comprises a spiral conductor on each layer of the PCB
130
forming one or more inductor “turns.” As shown in
FIG. 1B
, the core
120
can comprise two separate and identical E-shaped sections
122
and
124
. Each E-shaped section
122
,
124
includes a middle leg
126
and two outer legs
128
. A hole
132
is drilled in the center of the PCB
130
. The middle leg
126
of the E-shaped section
122
,
124
can be supported within the hole
132
to form part of the core
120
. The middle leg
126
has a circular cross-section and each of the outer legs
128
has a circular or rectangular cross-section. The remaining section of the E-shaped sections
122
,
124
is formed by a ferrite bar, which is bonded to the legs
126
,
128
. The E-shaped sections
122
,
124
are assembled so that the legs
126
,
128
of each E-shaped section are bonded together. Primary and secondary pins connecting the primary and secondary windings, respectively, can penetrate the PCB via terminal holes
134
drilled near the outer edges of the PCB as will be explained below.
The width of the spiral conductor depends on the current carrying requirement. That is, the greater the current carrying requirement, the greater the width of the conductor. Typically, a predetermined area is reserved for the inductor and the one or more turns are printed on each layer according to well known printed circuit board technology. (See, for example, U.S. Pat. No. 5,521,573.) After each layer is so printed, the layers are bonded together into a multi-layer PCB by glass epoxy. Through-hole “vias” or blind “vias” are used to interconnect the turns of the different layers.
A through-hole via is formed by drilling a hole through the layers at a position to intersect ends of two of the spiral conductors and then “seeding” the inner surface of the holes with a water soluble adhesive. Next, copper is electrolessly plated on the adhesive to interconnect the conductors. Next, additional copper is electrically plated over the electroless copper plate to the desired thickness. Finally, the holes are filled with solder to protect the copper plate. A separate via is required for each pair of spiral conductors on adjacent layers to connect all of the turns in series. Each such through-hole via is positioned not to intersect the other conductors.
Drilling holes in selected layers before the layers are bonded together forms a “blind” via. Then, the layers are successively bonded together and, while exposed, the inner surface of the holes is seeded with nickel, electrolessly plated with copper and then filled with solder. The resultant vias extend between the two layers sought to be electrically connected. Thus, the hole does not pass through other layers, and no area is required on these other layers to clear the via. However, the blind via fabrication process is much more expensive than the through-hole fabrication process. As shown in
FIG. 1A
, primary pins
140
connecting the primary windings and secondary pins
150
connecting the secondary windings are then positioned to penetrate the multi-layer PCB
130
.
FIG. 2
illustrates a process for manufacturing a printed coil with conventional planar technology in a PCB. In the layers of the PCB of
FIG. 2
, a primary winding and secondary winding can be formed by connecting multiple coil traces from five layers
200
,
220
,
240
,
260
, and
280
. The primary winding, for example, can have an outside terminal
202
connected to a coil trace
204
on layer
200
. The inside terminal of the coil trace
204
can be connected to an inside terminal of a connection trace
242
on layer
240
by an inner peripheral terminal
208
through a via. The outside terminal of the connection trace
242
is connected by a primary terminal
210
through a via to an outside terminal
282
of a coil trace
284
on layer
280
. The inner terminal of the coil trace
284
is connected to the inner terminal of connection trace
244
on layer
240
by a peripheral terminal
286
through a via. Connection trace
244
is connected to outside terminal
246
, thereby forming a primary winding between outside terminals
202
and
246
from coil traces
204
and
284
on layers
200
and
280
, respectively.
A secondary winding can be formed by connecting a coil trace
224
on layer
220
and a coil trace
264
on layer
260
in a similar fashion. An outside terminal
262
of coil trace
264
can be connected through a via to a corresponding outside terminal
222
of coil trace
224
by a primary terminal
266
. The inside terminal of coil trace
224
is connected to the inside terminal of coil trace
284
through a via by peripheral terminal
226
. Because the inside terminal of each coil trace
224
and
264
is connected and the outside terminals of each coil trace
224
and
264
is connected, the coil trace
224
and the coil trace
264
are connected in parallel.
FIG. 3
illustrates a typical twelve-layer layout where each individual layer is shown separately. These layers can be connected in a fashion similar to that described above with reference to
FIG. 2
to form a PCB having a primary winding and a secondary winding. In this conventional layout, a twelve layer PCB includes traces of both the primary and secondary windings as similarly described with reference to FIG.
2
. However, as a result,
Cuneo Kamand
Dinh Tuan
Knobbe Martens Olson & Bear LLP
Pulse Engineering Inc.
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