U.S. patent application number 09/971790 was filed with the patent office on 2002-07-11 for method and apparatus for forming a magnetic component on a printed circuit board.
Invention is credited to Jitaru, Ionel.
Application Number | 20020089405 09/971790 |
Document ID | / |
Family ID | 24683085 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020089405 |
Kind Code |
A1 |
Jitaru, Ionel |
July 11, 2002 |
Method and apparatus for forming a magnetic component on a printed
circuit board
Abstract
A method and apparatus for forming a magnetic component on a
printed circuit board. The printed circuit board has at least one
layer including a trace that forms a winding of the magnetic
component. Another winding of the magnetic component is formed by a
length of wire that is disposed externally to the printed circuit
board.
Inventors: |
Jitaru, Ionel; (Tucson,
AZ) |
Correspondence
Address: |
BIRDWELL, JANKE & DURANDO, PLC
Suite 1925
900 SW Fifth Avenue
Portland
OR
97204
US
|
Family ID: |
24683085 |
Appl. No.: |
09/971790 |
Filed: |
October 4, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09971790 |
Oct 4, 2001 |
|
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09668620 |
Sep 22, 2000 |
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Current U.S.
Class: |
336/200 |
Current CPC
Class: |
H05K 1/165 20130101;
H01F 27/2866 20130101; H01F 27/2804 20130101; Y10T 29/4902
20150115; Y10T 29/49071 20150115 |
Class at
Publication: |
336/200 |
International
Class: |
H01F 005/00 |
Claims
1. A method for forming a magnetic component on a printed circuit
board, comprising providing the circuit board with at least one
layer having a trace that forms a winding for the magnetic
component, forming a first length of wire into a loop that forms
another winding for the magnetic component, and disposing said
first length of wire externally to the printed circuit board.
2. The method of claim 1, wherein said step of disposing said first
length of wire includes placing said first length of wire on a
first external surface of the printed circuit board.
3. The method of claim 2, further comprising tacking said first
length of wire to said external surface with an adhesive.
4. The method of claim 2, further comprising forming a second
length of wire into a loop that forms yet another winding for the
magnetic component, and disposing said second length of wire on a
second, opposite external surface of the printed circuit board.
5. The method of claim 1, further comprising interconnecting
electrical components to the magnetic component by soldering a lead
of the electrical components directly to an end of said first
length of wire.
6. An apparatus for forming a magnetic component, comprising a
printed circuit board having at least one layer having a trace that
forms a winding for the magnetic component, and a first length of
wire that is formed in a loop that forms another winding for the
magnetic component, said first length of wire being disposed
externally to said printed circuit board.
7. The apparatus of claim 6, wherein said first length of wire is
disposed on a first external surface of said printed circuit
board.
8. The apparatus of claim 7, further comprising a second length of
wire that is formed as a loop that forms yet another winding for
the magnetic component, said second length of wire being disposed
on a second, opposite external surface of said printed circuit
board.
9. The apparatus of claim 6, further comprising an electrical
shield element disposed over said length of wire.
10. The apparatus of claim 6, wherein the magnetic component
includes a ferrite core element, and wherein said printed circuit
board includes cut-out areas to permit at least a portion of said
ferrite core element to extend through said printed circuit board.
Description
[0001] This is a continuation-in-part of the inventor's previous
application Ser. No. 09/668,620, now pending, incorporated by
reference herein in its entirety. The present invention relates to
a method and apparatus for forming a magnetic component on a
printed circuit board, such as a transformer or inductor.
BACKGROUND OF THE INVENTION
[0002] The inventor's U.S. Pat. No. 5,973,923, incorporated by
reference herein in its entirety, describes a packaging technology
for power converters and power magnetics, wherein the windings of a
magnetic element or component are incorporated as traces on layers
of a multiple layer printed circuit board. This concept has
provided many advantages, including reducing the printed circuit
board surface area that must be devoted to magnetic circuit
components, and reducing the reactance associated with the leads of
the magnetic component. As just one example, a particularly
advantageous application of the concept is described in the
inventor's U.S. Pat. No. 5,990,776, also incorporated by reference
herein in its entirety. Notwithstanding the concept's many
advantages, however, there are some practical limitations.
[0003] One limitation is that, especially where the traces are
long, there may need to be many layers in the printed circuit board
to carry the traces. However, the cost to fabricate the printed
circuit board generally increases dramatically with the number of
layers, so that it is usually desirable to minimize this
number.
[0004] Another limitation is that the traces, when etched, have a
reduced cross-sectional area, so that a given desired conductance
of the traces requires additional circuit board area.
[0005] Yet another limitation is that the resistance of the traces
may not be sufficiently well controlled in the standard printed
circuit board fabrication process for a given application of the
magnetic component. Precise control of the dimensions of the traces
is typically not critical in printed circuit board fabrication;
however it may become critical where the traces are employed as
part of the magnetic component, especially where the windings of
the component are long and their combined resistance becomes
appreciable.
[0006] Accordingly, there is a need for a method and apparatus for
forming a magnetic component on a printed circuit board that
provides for reducing the cost of fabricating the circuit board as
well as the completed assembly, and that provides for increased
control over the electrical resistance of the magnetic
components.
SUMMARY OF THE INVENTION
[0007] The method and apparatus for forming a magnetic component on
a printed circuit board of the present invention solves the
aforementioned problems and meets the aforementioned needs by
providing a printed circuit board having at least one layer having
a trace that forms a winding of the magnetic component. At least
one other winding of the magnetic component is provided by a
supplemental length of wire formed in a loop that is disposed
externally to the printed circuit board. Each type of winding
provides advantages, and the proportion of each may be selected to
optimize cost and circuit parameters.
[0008] Therefore, it is a principal object of the present invention
to provide a novel and improved method and apparatus for forming a
magnetic component on a printed circuit board.
[0009] It is another object of the present invention to provide a
method and apparatus for forming a magnetic component on a printed
circuit board that provides for decreasing the manufacturing cost
of the printed circuit board as well as the completed assembly.
[0010] It is still another object of the present invention to
provide a method and apparatus for forming a magnetic component on
a printed circuit board that provides for increasing control of
critical component parameters, such as the resistance of the
magnetic component.
[0011] It is yet another object of the present invention to provide
such a method and apparatus that provides for decreasing parasitic
electrical effects.
[0012] The foregoing and other objects, features and advantages of
the present invention will be more readily understood upon
consideration of the following detailed description of the
invention, taken in conjunction with the following drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a side elevation of an apparatus for forming a
magnetic component on a printed circuit board, according to the
present invention.
[0014] FIG. 2 is a plan view of the apparatus of FIG. 1.
[0015] FIG. 3 is a plan view of the apparatus of FIG. 1 showing a
shield according to the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0016] Referring particularly to FIG. 1, an apparatus 10 for
forming a magnetic component 12 on a printed circuit board 14
according to the present invention is shown. The magnetic component
is shown as a transformer; however, the invention may be used for
forming any magnetic component, the characteristic feature of which
is a conductive pathway for carrying an electric current for
generating a magnetic field of a controlled value for use in an
electrical circuit. Typically, such magnetic components include a
ferrite core element 16 to enhance the strength of the field by
confining it locally and the field is produced for the purpose of
storing energy in the circuit, as in an inductor, or to couple
energy between two parts of the circuit, as in a transformer.
[0017] The printed circuit board (hereinafter "PCB") 14 has two
external sides 11 and 13, and one or more conductive traces 22. The
conductive traces may lie on top of one of the external sides as
shown in FIG. 1, or may lie on one or more inner layers of a
multilayer PCB.
[0018] The traces 22 are formed in the usual manner, e.g., by
forming a pattern of photo resist on copper that has been plated or
deposited on a given layer, and etching the copper where it is not
protected by a covering of the photo resist.
[0019] The traces 22 are formed as loops which may be spirals as
discussed in U.S. Pat. No. 5,990,776. Each trace may be connected
to another trace or to the external surfaces of the PCB through
conductive vias, which are plated holes that extend between
selected layers of the PCB. The traces are provided and coupled to
one another through the vias so that a desired number of "turns"
result in the magnetic component, the magnetic field resulting
generally being proportional to this number.
[0020] Where all of the turns necessary in the magnetic component
can be provided by traces 22 without unduly compromising the cost
of the circuit board or the performance of the magnetic component
in its intended application, this is usually most desirable.
[0021] However, as mentioned above, the etching process generally
creates a trapezoid shaped cross-section for the trace as the
etchant undercuts the photo resist, and results in reduced
cross-sectional area for conduction. Since the spacing between the
traces must be no less than a predetermined minimum, the decreased
conductance of the traces results in more board space being
consumed. Moreover, the etching process may not be sufficiently
well controlled to fix the cross-sectional area of a given trace
along its length to provide for use of the trace as part of a
magnetic circuit component. These considerations may represent
serious disadvantages to employing the traces 22 as the windings of
the magnetic component.
[0022] Therefore, it may be that either or both the cost of the PCB
14 and the performance of the magnetic component are unsatisfactory
when all of the turns are provided by the traces 22. In that case,
according to the present invention, not all of the turns that are
desired for the magnetic component need be provided by traces on or
in the PCB 14. Instead, some turns may be provided by the traces
such that, e.g., the tolerance in the combined resistance of the
traces, or the acceptable cost of the circuit board, is not
exceeded. Remaining turns required to complete the windings of the
magnetic component are provided by supplemental wiring 30 external
to the PCB.
[0023] The supplemental wiring 30 is preferably a length of
insulated wire 31 that is disposed on the surface 11 or 13 in the
form of a spiral as shown in FIG. 2. The wire provides a uniform
and controlled resistance for the turns which it forms, and may do
so at relatively low cost where, in the alternative, additional
inner layers would otherwise be required in the PCB 14. The
proportion of the windings of the magnetic component 12 that are
provided on inner layers of the PCB with respect to windings
provided on external surfaces of the PCB may be selected to provide
any desired balance of the advantages provided by each type.
[0024] The wire 31 may be tacked to the PCB 14 with an adhesive 7,
or it may be fixed with respect to the PCB with any appropriate
fastening means, such as clamps or ties. Preferably, the wire 31 is
held against the sides of the PCB 14 by a thin, rigid material 17
as shown in FIG. 3. The material 17 may be attached to the PCB with
an adhesive or other appropriate fastening means, such as threaded
or snap fasteners.
[0025] Where the magnetic component 12 is a transformer, the traces
may be formed on inner layers of the PCB 14 and the supplemental
wiring 30 may be employed as one or the other of the primary and
secondary windings. This is not essential to practice the
invention, however. It is also advantageous to solder electrical
components associated with the magnetic component 12, such as the
diode "D" shown in FIG. 3, directly to the end 33 of the wire 31,
to minimize parasitic effects.
[0026] Referring to either FIGS. 2 or 3, the PCB 14 includes
cut-out areas 24 for receiving portions of the core element 16.
Typically the core element 16 is provided in two halves, one of
which is adapted to be installed from one of the external sides of
the PCB, e.g., side 11 and protrude through the circuit board,
through the cut-out areas 24, while the other half is adapted to
mate therewith, being installed from the other external side of the
PCB, here side 13, to form a closed pathway for the magnetic field.
The two halves of the core element may be attached to one another
with, e.g., screws or a clamp 3 shown.
[0027] Referring to FIG. 4, a shorting ring 32 of a conductive
material such as a copper foil is provided around the core element
16 to short the leakage field emanating therefrom and thereby
prevent it from affecting the operation of electrical or magnetic
components disposed outside the ring. As is shown, the ring is
spaced from the core element to prevent a direct electrical short.
Preferably, the ring is provided on both sides of the PCB 14, and
may be affixed to the PCB or directly to the insulated wire 31, or
to the rigid material 17, with any known fastening means, such as
any of the fastening means mentioned above.
[0028] It is to be recognized that, while a particular method and
apparatus for forming a magnetic component on a printed circuit
board has been shown and described as preferred, other
configurations and methods could be utilized, in addition to those
already mentioned, without departing from the principles of the
invention. For example, traces on the external surfaces of the PCB
14 could be employed instead of the wire 31 where it is desired to
minimize the number of inner layers, and the wire 31 may be
disposed partially or completely above the external surfaces where
it is desired to minimize the footprint of the magnetic component
on the PCB. For example, the wire 31 may be coiled axially instead
of or in addition to being coiled radially as in the spiral
configuration.
[0029] The terms and expressions which have been employed in the
foregoing specification are used therein as terms of description
and not of limitation, and there is no intention of the use of such
terms and expressions of excluding equivalents of the features
shown and described or portions thereof, it being recognized that
the scope of the invention is defined and limited only by the
claims which follow.
* * * * *