Note: Descriptions are shown in the official language in which they were submitted.
CA 02302793 2000-03-28
Ref:
No. 57326/21
APPLICATION FOR CANADIAN LETTERS PATENT
CORE CARRIER
TO ALL WHOM IT MAY CONCERN:
BE IT KNOWN THAT
John G. Davis, of 124 Ridge Road, Vestal, New York, 13850 U.S.A.; and
William A. Shumir~, of 1504 Seymour Road, Vestal, New York, 13850 U.S.A.
have invented a CORE CARRIER of which the following is a specification.
Applicant: Celesti~ca International Inc.
CA 02302793 2000-03-28
CORE CARRIER
Field of Invention
This invention relates generally to devices for mounting magnetically
permeable
cores to printed circuit boards. More specifically, it pertains to core
earners, and core
carrying assemblies that permit inductive devices having magnetically
permeable cores to
be placed on printed circuit boards by automated equipment.
Background of the Invention
As the computing power of integrated circuit devices has increased, there has
been an enduring desire to increase the number, and capability, of electronic
devices
mounted to printed circuit boards, whether by through-hole pin technology or
by surface
mount technology. However, each increase in device density has tended to cause
an
increase in the amount of heat to be removed, and, particularly, the amount of
heat to be
removed per unit of printed circuit board surface area.
As the number of dlevices per circuit card increases, there is a premium on
the use
1 S of devices that have a small footprint, since the smaller the footprint of
the device, the
less surface area it occupies on the board. The challenges of manufacturing
printed
circuit board assemblies include the; need rapidly, and reliably, to mount
large numbers of
different items on each card, with relatively high levels of precision. A
vacuum
placement machine can, generally, place many different kinds of devices,
including
particularly small devices, on printed circuit boards faster, and with greater
consistency
than individuals placing the devices by hand. The manufacturing process is
thus made
more efficient by reducing the number of elements that require manual
placement.
One type of element that has posed a challenge for designers is the
magnetically
permeable toroidal core. These devices may be provided with a single multi-
turn
winding to act as an inductor, or may be provided with two windings, of the
same or
different numbers of turns, to act as a transformer. Magnetic cores tend to be
relatively
large, and relatively heavy. They can also become quite hot in use. It is
therefore
desirable not only to mount these devices in a manner requiring as little
surface area on
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the printed circuit board ass possible, but in a way that permits them to be
cooled. In
terms of manufacturing processes, toroidal cores, by their geometric nature,
tend to be
difficult for vacuum placement machines to secure upon. In one direction, the
central
hole of the dough-nut shaped toroid makes it difficult for the vacuum head of
the
placement machine to obtain a satisfactory suction engagement. In the other,
or sideways
direction, the rounded core shape tends not to be flat enough to yield a good
suction
surface, given the weight of the core relative to its size.
Two older forms of mounting system have been tried. In some instances the
magnetic cores have been placed within flat walled drums, or canisters. While
these
enclosures can be picked up by vacuum placement machines, they pose a
significant
thermal disadvantage, since they i mpede heat transfer from the core.
Similarly, in an
example of an older type of sealed device, as shown in U.S. Patent 3,590,480
of Johnson
Jr., et al., issued July 6, 1971, the transversely mounted toroidal core is
encapsulated in a
potting compound. In U.S~. Patent 2,823,362 of Geroulo et al., issued February
11, 1958
a pulse transformer is shaven in an hermetically sealed enclosure. Notably,
neither of
these devices were developed in the context of the problems of surface mount
technology, and, in particular, in the context of vacuum placement machines.
Another device, the transmission line transformer of U. S. Patent 5,140,706 to
Maeda et al., issued August 18, 1992, shows a relatively exposed toroidal
core, and
windings, but the footprint of the resultant device on the wiring board is
significantly
greater than the area of the core and windings by themselves, let alone a core
placed on
edge sideways.
It would be desirable to turn the magnetically permeable core on its side such
that
the central axis through the toroid opening is parallel to the planar surface
of the wiring
board. In this way, the determinant of the size of the footprint of the core
relative to the
wiring board is not the cir<;ular area of the core in plan view, but rather
the sideways area
of the core taken in profile view.
It would also be desirable to provide a surface to which a vacuum placement
machine can secure, the surface preferably standing proud of the core, that
leaves most of
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the surface area of the magnetic core exposed to the ambient conditions inside
the
computer or other device in which the core is to be used. In this way heat
transfer away
from the core by convection and radiation is not as severely impeded as when
such
devices are enclosed in casings or potted. To that end, it would be desirable
to use a core
carrier having a structural member, whether in the form of a relatively
Spartan
framework, some more elaborate latticework, trellis work, a spider, a cage or
merely one
or more posts or cantilevered arms. It is also desirable to use a core Garner
that has an
indexing feature of some kind, typically a mechanical asymmetry such as a lug,
a nub, an
indent, or similar feature so that the placement machine can readily
distinguish the
orientation of the device and align it in a unique manner with the mating
footprint of the
wiring board.
Summary of the Invention
In an aspect of the invention, a core carrier comprises a body for mating with
a
printed circuit board. The body has a mount for supporting a magnetic core in
an
orientation relative to the printed circuit board in which the area of the
projected image of
the core orthogonal to the printed circuit board is less than the maximum
projected area
of the core. The body has a vacuum placement interface for engagement by a
vacuum
placement machine.
In an additional feature of that aspect of the invention the mount is oriented
to
support the magnetic core in an orientation relative to the printed circuit
board in which
the area of the projected image of t:he core is the minimum projected area of
the core. In a
further additional feature of that aspect of the invention, the body has a
footing for mating
with the printed circuit board. A structural member extends to support the
vacuum
placement interface. The structural member leaves at least a portion of the
surface of the
magnetic core exposed to ambient.
In another aspect of the invention, a core carrier comprises a body for mating
with
a printed circuit board. 'The body has a mount for supporting a magnetic core.
The
mount is oriented to support the magnetic core in a position in which the
central axis of
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the core is skewed relative to the normal of the printed circuit board. The
body has a
vacuum placement interface for engagement by a vacuum placement machine.
In an additional feature of that aspect of the invention, the mount is shaped
to
support a magnetic core with the central axis of the core parallel to the
printed circuit
board. In another additional feature of that aspect of the invention, the body
has a footing
for mating with the printed circuit board. A structural member extends to
support said
vacuum placement interface. The structural member leaves at least a portion of
the
surface of the magnetic core exposed to ambient.
In another aspect of the invention there is a core carrier. It has a body
having a
footing for mating with a printed circuit board. The body has a mount for
supporting a
magnetic core in sideways orientation relative to the footing. The body has a
vacuum
placement interface for engagement by a vacuum placement machine, whereby a
magnetic core carried on the body can be mounted, with the carrier, on a
printed circuit
boaxd by a vacuum placement machine.
1 S In an additional feature of that aspect of the invention, the mount of the
core
carrier is cradling, the vacuum placement interface is a suction surface, and
the body
includes a structural member connecting the suction surface to the footing. In
another
additional feature of that aspect of the invention, the footing of the core
carrier has a
substantially planar orientation and the suction surface extends substantially
parallel to
the footing. In a further additional feature of that aspect of the invention,
the cradling of
the core earner is located to support a magnetic core between the footing and
the suction
surface. In a still further additional feature of that aspect of the
invention, a projection of
the suction surface orthogonal to the footing falls upon the centre of gravity
of a magnetic
core earned in the cradling. In yet a further additional feature of that
aspect of the
invention, the suction surface is located so that the polar axis of inertia
orthogonal to the
footing of a magnetic core carried in the cradling intersects the suction
surface. In yet
still a further additional feature of that aspect of the invention, the
suction surface is
located such that the polar axis intersects the suction surface orthogonally.
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In another additional feature of that aspect of the invention, the structural
member
is formed to leave the majority of the exterior of a magnetic core carried in
the cradling
exposed to the ambient environment.
In yet another additional feature of that aspect of the invention, the
structural
member includes a post extending from the footing to the suction surface, the
post having
a medial portion narrower than the inner opening of magnetic cores to be
carried by the
cradling. In yet still another additional feature of that aspect of the
invention, the post has
a web and a flange.
In a further additional feature of that aspect of the invention, the footing
has a
surface mount footprint. In yet a further additional feature of that aspect of
the invention,
the footing has four foot p<~ds.
In still yet a further additional feature of that aspect of the invention, the
body is
asymmetric about an axis orthogonal to the footing, for facilitating
orientation relative to
a printed circuit board. In another additional feature of that aspect of the
invention, the
asymmetry is an irregularity in the footing.
In another aspect of the invention there is a core carrier. It has a cradle
for
receiving a magnetic core :in sideways orientation, and a footing supporting
the cradle, for
mating with a printed circuit board. A structural member extends from the
cradle away
from the footing, and a suction surface mounted to the structural member,
capable of
engagement by a vacuum placement machine.
In an additional feature of that aspect of the invention, the footing has a
long axis
and a short axis, and the. cradle is oriented to permit a magnetic core to be
loaded
thereinto in a position in which the transverse axis of the magnetic core is
parallel to the
short axis.
In another additional feature of that aspect of the invention, the core
carrier has
restraints for discouraging movement of a magnetic core mounted therein normal
to the
footing and the cradle permits entry in a direction chosen from the set of
directions
consisting of parallel to i:he short: axis and parallel to the long axis. In
yet another
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additional feature of that aspect of the invention, the cradle permits only
one sided entry
in the chosen direction.
In still yet another additional feature of that aspect of the invention, the
structural
member includes a post located in alignment with the short axis. In an
additional feature
of that aspect of the invention, the post has a waist to permit windings to be
fed through
the core opening of cores rnounted on the cradle.
In another aspect o:f the invention, there is a magnetic core carrier, and a
magnetic
core carried therein. The magnetic core carrier has a cradle and the magnetic
core is
mounted in a sideways orientation therein. The cradle is supported on a
footing for
mating with a printed circuit board on a planar interface parallel to the
transverse axis of
the magnetic core. The carrier has a structural member extending away from the
footing
which a suction surface is mounted in a position proud of the core, for
engagement by a
vacuum placement machine.
In an additional feature of that aspect of the invention the majority of the
external
1 S surface of the core is exposed to arr~bient conditions.
In a further additional feature of that aspect of the invention, the core is a
toroid,
the footing has a long axis and a short axis, the principal axis of the toroid
is the
transverse axis, and the short axis is parallel to the transverse axis.
In yet a further additional feature of that aspect of the invention, the
centre of
gravity of the core lies between the; footing and the suction surface. In
still yet a further
additional feature of that aspect of the invention, a projection of the
suction surface
orthogonal to the planar interface of the footing passes through the centre of
gravity. In
another additional feature of that aspect of the invention, the suction
surface is
substantially parallel to the planar interface of the footing. In yet another
additional
feature of that aspect of the invention, the polar axis of rotation of the
core orthogonal to
the planar interface intersects the suction surface.
In a further additional feature of that aspect of the invention, the core is a
toroid
having a central opening. The principal axis of the toroid is the transverse
axis. The
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structural member is formed to permit windings to be passed about the core
while
mounted on the carrier. In yet a further additional feature of that aspect of
the invention,
the structural member includes a post aligned with the transverse axis. The
post has a
waist narrower than the central opening of the toroid. In still a further
additional feature
of that aspect of the invention, the post has a web and a flange.
In still yet a further additional feature of that aspect of the invention, the
footing
has surface mount pads. In yet another additional feature of that aspect of
the invention,
the footing has four surface mount pads. A pair of windings are wound about
the core
and each winding is connected to a pair of the pads to form a surface
mountable
transformer.
In a still further aspect of the invention, a core carrier comprises a body
having a
footprint for mating with a~ printed circuit board. The body has a mount for
supporting a
toroidal magnetic core in an orientation in which the central axis of the
toroid is
substantially parallel to the printed circuit board. The body has a suction
surface for
1 S engagement by a vacuum placement machine, whereby the magnetic core, when
mounted
on the core carrier, can be placed onto the printed circuit board with said
core carrier by a
vacuum placement machine.
In an additional future of that aspect of the invention, the body includes a
structural support member oriented to extend away from the printed circuit
board. The
suction surface is mounted on the structural support member to lie at a
distance from the
printed circuit board that is beyond the magnetic core. In an alternative
additional feature
of that aspect of the invention, the body includes a structural support member
for
supporting the suction surface. 'The mount is located to support the magnetic
core
between the suction surface and the printed circuit board. In a further
additional feature
of that aspect of the invention, the structural support member is shaped to
leave at least a
portion of the surface area of the magnetic core exposed to ambient.
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_$_
Brief Description of Drawings
The principles of the invention are explained below with the aid of the
following
illustrative Figures:
Figure 1 is a general arrangement, isometric view of an example of a core
carrier
S according to the principles of the present invention.
Figure 2 shows the core carrier of Figure 1 with a core installed.
Figure 3a is a front view of the core Garner of Figure 1.
Figure 3b is an sid<; view of the core carrier of Figure 1.
Figure 3c is a top view of the core carrier of Figure 1.
Figure 3d is a bottom view of the core carrier of Figure 1.
Figure 3e is an alternative bottom view to the bottom view of Figure 3d.
Figure 4a is a front view of the core carrier and core of Figure 2.
Figure 4b is an sidf; view of the core carrier and core of Figure 4a.
Figure 5 shows an alternative embodiment to that of Figure 1 having a bunk in
which a core can be supported.
Figure 6 shows an alternative embodiment to the core carrier of Figure 1 with
an
arcuate bunlk.
Figure 7 shows an alternative embodiment to the core carrier of Figure 1 with
a
hangar bracket.
Figure 8 shows an alternative embodiment to the core Garner of Figure 1 with a
structural member having a sideways basket handle.
Figure 9 shows an alternative embodiment to the core carrier of Figure 1 with
a
structural member h<~ving a lengthwise arch.
Figure 10 shows an alternative embodiment to the core carrier of Figure 1 with
a
structural member in the form of a spider.
Figure 11 shows an alternative embodiment to the core carrier of Figure 1 with
an
eccentric suction surface.
Figure 12 shows an alternative embodiment to the core carrier of Figure 1 with
a
footprint falling within the projected area of a core.
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Detailed Description of the Invention
The description v~hich follows, and the embodiments described therein, are
provided by way of illustration of an example, or examples of particular
embodiments of
the principles of the present invention. These examples are provided for the
purposes of
S explanation, and not of limitation, of those principles and of the
invention. In the
description which follows, like parts are marked throughout the specification
and the
drawings with the same respective reference numerals. The drawings are not
necessarily
to scale and in some instances proportions may have been exaggerated in order
more
clearly to depict certain features of the invention.
By way of a general overview, in Figure 1 an example of a core carrier
according
to the principles of the present invention is indicated generally as 20. It
has a body 22
having a footing 24 for mating with a printed circuit board (not shown). Body
22 also
has a mount, in the nature: of cradling 42, for supporting a magnetically
permeable core
60 in a sideways orientation (that is, tipped up on its side 61, rather than
lying flat on its
disc face 63) relative to footing 24. Body 22 has a structural member 92 that
extends
away from footing 24 and terminates at a vacuum placement interface, in the
nature of a
suction surface 100 for engagement by a vacuum placement machine (not shown).
In
use, magnetically permeable core 60 can be mounted on core earner 20 and fixed
in
place. Windings 88 and 90, shown in Figure 2, can be made about the core as
desired for
a particular application. 'When ready, a vacuum placement machine can lift the
entire
assembly by engaging the vacuum placement interface, suction surface 100. It
can then
locate the assembly on a printed circuit board.
By way of a more detailed description, core carriers, such as core carrier 20,
are
sometimes referred to as "boats", since the lower part of body 22 is
monolithic, and can
have an appearance like a bathtub or boat. Monolithic body 22, is molded from
an
electrically insulating material. It has footing 24 for placement next to a
printed circuit
board. Footing 24 has a footprint 26 that has a substantially planar interface
for mating
with a corresponding contact pattern of the printed circuit board. That is,
footing 24 seats
substantially parallel to the surface of the printed circuit board, and may in
some cases
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seat flush against the board. In the embodiment shown in Figure 3d, footprint
26 is a
leadless footprint having pads 28, 30 32 and 34 for surface mounting to the
board.
In an optional alternative embodiment shown in Figure 3e, and otherwise
similar
to the embodiment illustrated in Figure 3a, 3b and 3d, a stand-off and a keyed
asymmetric stub array 36 protruding from footing 24 could be used for the
purposes of
permitting only a unique orientation of carrier 20 relative to a printed
circuit board. In
such a case, the printed circuit board must have mating features impressed
upon it to
engage keyed asymmetric stub array 36.
Body 22 also includes mounting 40 for a magnetically permeable toroid core,
the
mounting being in the nature of a seat, or cradling 42 upon which the core can
rest, as
noted above. Cradling 42 has a long axis 44, and a corresponding pair of left
and right
hand long sides 46 and 48. It also has a short axis 50 and a pair of front and
rear short
sides 52 and 54. Long side 46 is open to permit magnetic core 60 to be
introduced as
shown in Figure 2. Long side 48 and short sides 52 and 54 have raised
gunwales, or
1 S sidewalls, against which nuagnetic core 60 can abut. In addition, cradling
42 has support
such as a floor 62 upon which core 60 may rest. The effect is to yield a seat
for magnetic
core 60. Each of the short side end walls 64 and ~56 has a central cleavage 68
or 70 to
provide a clear separation such that each of the four corners of footing 24
may have its
electrical contact footpad 2;8, 30, 32 or 34 segregated from all others,
thereby permitting a
four terminal device to be used, such as, for example, a transformer.
Vertical and horizontal channels 72 and 74 are shown in the outside and
underside
faces of body 22 adjacent each of its corners, with the intersection of the
respective
vertical and horizontal channels being smoothly radiused as at 76, shown in
dashed lines
in Figure 3b. The L-shaped rebates of semi-circular cross-section thus formed
accommodate the lead wires 80, 82, 84, as shown, or a fourth lead wire,
diagonal to lead
wire 82, not visible in Figure 2, of inductive windings 88 or 90 wound about
magnetic
core 60 in the manner of inductors or transformer coils. The smooth radius at
76 serves to
discourage overly sharp bc,nds of the lead wires, such as might otherwise
cause them to
snap or cleave.
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structural member 92, in the nature of a single post 94, is formed integrally
with
footing 24 and cradling 42. It extends perpendicularly away from footing 24,
to
terminate at a distal end 96 surmounted by a cantilevered member in the nature
of a
platform 98 whose outer surface is imperforate suction surface 100. Suction
surface 100
is of a size capable of bc;ing engaged by a vacuum placement machine (not
shown).
Platform 98 terminates at its most distant end in a notched tang 102 which
permits a
vacuum placement machine to sense the orientation of carrier 20, and thereby
to place it
in the proper, unique orientation desired relative to an underlying footprint
on a printed
circuit board. Post 94 has both a web 104 and a flange 106 oriented at right
angles to
each other to form a T-shaped section, with the flange extending parallel to
the long sides
of cradling 42, and the lei; of the ''T' extending inward from the flange
toward cradling
42, to terminate flush with raised sidewall 108 of long side 48.
As shown in the front view of Figure 3a post 94 of structural member 92 has an
inwardly tapered root, 110; a slim waist, or medial section 112; and an
outwardly tapered
distal portion 114. As shown in Figure 4a medial section 112 is narrower than
the
internal diameter of magnetic core 60, thus facilitating the introduction of
wires through
the central opening 116 of core 60, by which means windings, 88 and 90 can be
formed
once core 60 is in place in cradling 42.
A magnetic core, such as core 60, seated in cradling 42, is restrained in both
directions normal to the printed circuit board, (that is, by floor 62 and by
the underside of
cantilevered platform 94 in the other), in both directions along long axis 44
(by raised
sidewalls 64 and 66) and in one direction along short axis 50 (by raised
sidewall 108).
Core 60 is fixed in this restrained position by the use of a hardening resin,
glue, or epoxy,
or other suitable adhesive or fastening means. In the preferred embodiment
epoxy is used.
In the preferred err~bodiment of Figure 1, the location of the central, or
principal,
axis of the toroidal core is indicated in Figures 4a and 4b as transverse axis
120. That is,
transverse axis 120 is, in this embodiment, the axis about which the toroidal
body of
revolution has been formed and is parallel to short side axis 50. Similarly,
an axis
orthogonal to the planar interface of footing 24 that intersects the center of
gravity, 'CG'
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of the installed core is indicated as axis 122. As illustrated, axis 122 is
also the polar axis
of rotational inertia of core: 60 relative to the planar interface.
In the preferred embodiment shown in Figure 1 the center of gravity of a core
60
carried on cradling 42 lies between footing 24 and suction surface 100. It
does so in such
a manner that a projection of suction surface 100 orthogonal to the planar
interface of
footing 24 passes through the center of gravity 124 of toroidal core 60.
Further, in the
preferred embodiment of Figure 1, polar axis 122 of toroidal core 60 passes
generally
centrally, and orthogonally, through the planar interface of footing 24 and
generally
centrally and orthogonally through suction surface 100. This means that first
a vacuum
placement machine (not shown) can grasp the embodiment of Figure 1 with little
or no
bending moment to resolve; at the suction head; and, second, can spin the
assembly to the
desired orientation with little or no polar inertial eccentricity to manage.
Although this is
not essential, it is preferablle for ease of operation of the vacuum placement
machine. As
shown, the use of a structural member rather than a sealed box or potting,
permits
relatively large portions of the surface of core 60 to remain exposed to
ambient.
A number of alternative types of cradling are possible. For example, as shown
in
the alternative embodiment of Figure 5, a carrier 140 has a pair of opposed,
spaced apart
parallel bunks, or rungs 1.42, 144 could be used, with the core fixed to them,
as noted
previously, with a resin, glue, or epoxy of suitable properties. Similarly, as
shown in
Figure 6, a carrier 150 having a single bunk 152 in the form of a partial arc
corresponding
to the radius of the outer dliameter of the magnetic core could be used.
Alternatively, as
shown in Figure 7 a carrier 160 has cradling in the form of a hanger bracket,
or horizontal
spindle 164, that can be iintroduced through the central aperture of the
toroidal core,
whether held in an interference fit or otherwise.
In the embodiment shown in Figure 1, cradling 42 opens to the side. That is,
one
long side and both short sides, have abutments to restrain core 60, such that
it can only be
introduced, or removed, by the open side, indicated as side 46. It would, for
example, be
possible in an alternative Embodiment to use one of the other sides, such as
one of the
short sides for this purpose.
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In the embodiment shown in Figure 1, structural member 92 is formed by a
single,
monolithic flanged post. Although this embodiment is preferred, and permits a
relatively
simple mould to be used, .a number of other alternative embodiments could be
used. In
one non-exhaustive example, in the embodiment of Figure 8 a core carrier 170
has an
entry 172 to cradling 174 by the short side 176. structural member 178 has the
form of a
basket handle, having twin posts 180 and 182 and a lintel 184. In the
embodiment of
Figure 9, a core carrier 1!~0 has cradling 192 that again opens on a long side
194. A
structural member 196 has the form of an arched structure 198 extending upward
from
the short sides 200 and 20:L, that is., away from footing 204, and having a
suction surface
206 mounted atop arched structure 198. In Figure 10 a core carrier 210 has a
structural
member 212 formed with four corner posts 214, 216, 218 and 220 that meet, as a
spider
222, with a suction surface 224 mounted to spider 222 centrally above the core
holding
space 226.
The asymmetry provided by notched tang 102 can be formed in other ways on
other parts of the assembly. For example, in the embodiment of Figure 9
footing 204 has
an indexing notch 208 located uniquely along one of the long sides. A nub,
key, boss, or
other similar feature could be used to similar effect, as in Figure 3e, noted
above.
In the embodiment shown in Figure 1, suction surface 100 is parallel to, and
centrally placed relative to, footing 24. That is, an orthogonal projection of
suction
surface 100 would fall on t:he center of footing 24. This need not necessarily
be the case.
It may be that an angled surface may be desired in some circumstances. That
is, the
suction surface may not be for location parallel to the printed circuit board,
but rather
inclined to the printed circuit board. It may also be that an eccentric
surface may suit
geometric requirements in other circumstances. In Figure 11, a core carrier
230 has a
structural member 232 upon which a platform 234 having a suction surface 236
is
asymmetrically mounted relative to footing 238. That is, the center of area of
suction
surface 236 does not lie dlirectly above the center of area of footing 238, or
above the
center of gravity 'CG' of core 60, but is significantly offset from them.
Suction surface
100 need not necessarily be perfectly flat or level, provided the surface has
a locus upon
which a suction head can act.
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In Figure 12 a core carrier 250 has a base 252 that has a width 'W' that falls
within the projected profile of core 60 perpendicular to the PCB (that is, in
effect,
perpendicular to the footprint of base 252 for mounting to a PCB). Another way
of saying
this is that, in the embodiment of Figure 12, the long dimension, width W, is
equal to the
diameter of core 60, before windings 254 and 256 are added. Base 252 also has
a
thickness 'T' over its cleft short end faces 258 that is less than the
thickness of core 60,
before windings 254 and :L56 are added. Carrier 250 has a running board face
260 on
each of its longitudinal sides. A structural member in the nature of upright
post 262 is
formed to extend upwardly (relative to a horizontally oriented PCB) from one
running
board face 260. Post 262 terminates at a distal end from which a substantially
horizontal
plate 264 is cantilevered inwardly over the body of core 60. Horizontal plate
264 has a
suction surface 266 suitable for engagement by a vacuum placement machine, as
noted
above. Carrier 250 has an arcuate cradle 270 shaped to receive core 60, which
can be
retained therein by a bonding agent or adhesive. Other, mechanical, retainers
such as
threaded fastened, detents, and the like could be used as well. Dimension 'W'
could be
somewhat less than the diameter of core 60, and dimension 'T' could be
somewhat less
than the thickness of core 60, subject to the need for the resultant footprint
to be able to
support core 60 in a stablf: position relative to the underlying PCB. A
nominal profile
(except for post 262) that lies within the projected profile of core 60
permits a desirably
economical use of PCB surface area.
Furthermore, in thc: assembled form in which a magnetically permeable core is
mated with the electrically insulating core carrier, the core need not be a
circular toroid.
For example, it is known that magnetic cores can be square, rectangular, oval,
elliptical,
or arbitrarily shaped.
In the preferred embodiment illustrated in Figures 1 and 2, the core carrier
has a
mounting for a magnetic care that holds the core in an orientation in which
the projected
image of the core orthogonal to the printed circuit board is a rectangle
defined by the
diameter of the core on its long side and the thickness of the core on its
short side. The
area of this projected image is less than the area of the projected image of
the toroid taken
parallel to the central axis of revolution of the toroid. In this example, the
projected
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CA 02302793 2000-03-28
- IS -
image of the side view of the toroid is also the minimum projected area of the
toroid - no
projection taken from any other angle will yield a smaller projected area.
It is preferred to use the orientation having the smallest projected area,
since this
correlates with a small footprint on the printed circuit board. However it is
possible to
choose a larger projected area that is, nonetheless, less than the maximum
projected area
of the core. This condition will be satisfied when the central axis of the
toroid is not
parallel to a normal drawn from the printed circuit board. That is, it will be
satisfied
when the central axis of nhe core, such as axis 120 is skewed relative to a
line drawn
orthogonal to the printed circuit board, such as, by definition, its normal.
For example,
IO the core could be tilted on an angle other than a right angle.
A preferred embodiment has been described in detail and a number of
alternatives
have been considered. As changes in or additions to the above described
embodiments
may be made without departing from the nature, spirit or scope of the
invention, the
invention is not to be limited by or to those details, but only by the
appended claims.
20739427.2
