CA2302793A1 - Core carrier - Google Patents
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- CA2302793A1 CA2302793A1 CA002302793A CA2302793A CA2302793A1 CA 2302793 A1 CA2302793 A1 CA 2302793A1 CA 002302793 A CA002302793 A CA 002302793A CA 2302793 A CA2302793 A CA 2302793A CA 2302793 A1 CA2302793 A1 CA 2302793A1
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Abstract
A core carrier has a footing for engaging a printed circuit board and a mounting for carrying a magnetically permeable core in a sideways orientation. This is done to reduce the surface area of the board covered by the inductive core. A
structural member extends away from the footing and has, at its end, a suction surface that permits a vacuum placement machine to lift and place a loaded coil carrier on a printed circuit board.
structural member extends away from the footing and has, at its end, a suction surface that permits a vacuum placement machine to lift and place a loaded coil carrier on a printed circuit board.
Description
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.
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 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 20739427.2 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 20739427.2 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.
20739427.2 -S-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 20739427.2 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 20739427.2 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.
20739427.2 _$_ 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.
20739427.2 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 20739427.2 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.
20739427.2 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' 20739427.2 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 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.
20739427.2 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.
20739427.2 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 20739427.2 - 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
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.
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 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 20739427.2 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 20739427.2 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.
20739427.2 -S-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 20739427.2 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 20739427.2 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.
20739427.2 _$_ 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.
20739427.2 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 20739427.2 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.
20739427.2 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' 20739427.2 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 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.
20739427.2 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.
20739427.2 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 20739427.2 - 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
Claims (43)
1. A core carrier comprising:
a body for mating with a printed circuit board;
said body having 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; and said body has a vacuum placement interface for engagement by a vacuum placement machine.
a body for mating with a printed circuit board;
said body having 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; and said body has a vacuum placement interface for engagement by a vacuum placement machine.
2. The core carrier of claim 1 wherein said 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 the core is the minimum projected area of the core.
3. The core carrier of claim 1 wherein said body has a footing for mating with the printed circuit board, and a structural member extending to support said vacuum placement interface, said structural member leaving at least a portion of the surface of the magnetic core exposed to ambient.
4. A core carrier comprising:
a body for mating with a printed circuit board;
said body having a mount for supporting a magnetic core;
said mount oriented to support the magnetic core in a position in which the central axis of the core is skewed relative to the normal of the printed circuit board; and said body has a vacuum placement interface for engagement by a vacuum placement machine.
a body for mating with a printed circuit board;
said body having a mount for supporting a magnetic core;
said mount oriented to support the magnetic core in a position in which the central axis of the core is skewed relative to the normal of the printed circuit board; and said body has a vacuum placement interface for engagement by a vacuum placement machine.
5. The core carrier of claim 4 wherein said mount is shaped to support a magnetic core with the central axis of the core parallel to the printed circuit board.
6. The core carrier of claim 4 wherein said body has a footing for mating with the printed circuit board, and a structural member extending to support said vacuum placement interface, said structural member leaving at least a portion of the surface of the magnetic core exposed to ambient.
7. A core carrier comprising:
a body having a footing for mating with a printed circuit board;
said body having a mount for supporting a magnetic core in sideways orientation relative to said footing; and said body has a vacuum placement interface for engagement by a vacuum placement machine;
whereby a magnetic core carried on said body can be mounted with said carrier on a printed circuit board by a vacuum placement machine.
a body having a footing for mating with a printed circuit board;
said body having a mount for supporting a magnetic core in sideways orientation relative to said footing; and said body has a vacuum placement interface for engagement by a vacuum placement machine;
whereby a magnetic core carried on said body can be mounted with said carrier on a printed circuit board by a vacuum placement machine.
8. The core carrier of claim 7 wherein:
said mount is cradling;
said vacuum placement interface is a suction surface; and said body includes. a structural member connecting said suction surface to said footing.
said mount is cradling;
said vacuum placement interface is a suction surface; and said body includes. a structural member connecting said suction surface to said footing.
9. The core carrier of claim 8 wherein said footing has a substantially planar orientation and said suction surface extends substantially parallel to said footing.
10. The core carrier of claim 8 wherein said cradling is located to support a magnetic core between said footing .and said suction surface.
11. The core Garner of claim 8 wherein a projection of said suction surface orthogonal to said footing falls upon the centre of gravity of a magnetic core carried in said cradling.
12. The core carrier of claim 8 wherein said suction surface is located so that the polar axis of inertia orthogonal to said footing of a magnetic core carried in said cradling intersects said suction surface.
13. The core carrier of claim 12 wherein said suction surface is located such that the polar axis intersects said suction surface orthogonally.
14. The core carrier of claim 8 wherein said structural member is formed to leave the majority of the exterior of a magnetic core carried in said cradling exposed to the ambient environment.
15. The core carrier of claim 8 wherein said structural member includes a post extending from said footing to said suction surface, said post having a waist narrower than the inner opening of magnetic cores to be carried by said cradling.
16. The core carrier of claim 8 wherein said post has a web and a flange.
17. The core carrier of claim 7 wherein said footing has a surface mount footprint.
18. The core Garner of claim 17 wherein said footing has four foot pads.
19. The core carrier of claim 7 wherein said body is asymmetric about an axis orthogonal to said footing for facilitating orientation relative to a printed circuit board.
20. The core carrier of claim l9 wherein said asymmetry is an irregularity in said footing.
21. A core carrier comprising:
a cradle for receiving a magnetic core in sideways orientation;
a footing supporting said cradle, for mating with a printed circuit board;
a structural member extending from said cradle away from said footing; and a suction surface mounted to said structural member, capable of engagement by a vacuum placement machine.
a cradle for receiving a magnetic core in sideways orientation;
a footing supporting said cradle, for mating with a printed circuit board;
a structural member extending from said cradle away from said footing; and a suction surface mounted to said structural member, capable of engagement by a vacuum placement machine.
22. The core carrier of claim 21 wherein:
said footing has a long axis and a short axis; and said cradle is oriented to support a magnetic core in a position in which the transverse axis of the magnetic core is parallel to said short axis.
said footing has a long axis and a short axis; and said cradle is oriented to support a magnetic core in a position in which the transverse axis of the magnetic core is parallel to said short axis.
23. The core carrier of claim 22 wherein said core carrier has restraints for discouraging movement of a magnetic core mounted therein normal to said footing and said cradle permits entry in a direction chosen from the set of directions consisting of (a) parallel to said short axis; and (b) parallel to said long axis.
24. The core carrier of claim 23 wherein said cradle permits only one sided entry in said direction.
25. The core carrier of claim 22 wherein said structural member includes a post located in alignment with said short axis.
26. The core carrier of claim 25 wherein said post has a waist to permit windings to be fed through the core opening of cores mounted on said cradle.
27. A magnetic core assembly comprising:
a magnetic core carrier, and a magnetic core carried therein;
said magnetic core carrier having a cradle and said magnetic core being mounted in a sideways orientation therein;
said cradling being supported on a footing for mating with a printed circuit board on a planar interface parallel to the transverse axis of the core; and said carrier having; a structural member extending away from said footing, and having a suction surface lying proud of said core for engagement by a vacuum placement machine.
a magnetic core carrier, and a magnetic core carried therein;
said magnetic core carrier having a cradle and said magnetic core being mounted in a sideways orientation therein;
said cradling being supported on a footing for mating with a printed circuit board on a planar interface parallel to the transverse axis of the core; and said carrier having; a structural member extending away from said footing, and having a suction surface lying proud of said core for engagement by a vacuum placement machine.
28. The assembly of claim 27 wherein the majority of the external surface of said core is exposed to ambient conditions.
29. The assembly of claim 27 wherein said core is a toroid; said footing has a long axis and a short axis; the principal axis of the toroid is said transverse axis; and said short axis is parallel to said transverse axis.
30. The assembly of claim 27 wherein the centre of gravity of said core lies between said footing and said suction surface.
31. The assembly of claim 30 wherein a projection of said suction surface orthogonal to the planar interface of said footing passes through said centre of gravity.
32. The assembly of claim 31 wherein said suction surface is substantially parallel to the planar interface of said footing.
33. The assembly of claim 27 wherein the polar axis of rotation of said core orthogonal to the planar interface intersects said suction surface.
34. The assembly of claim 33 wherein said suction surface is substantially parallel to the planar interface of said footing.
35. The assembly of claim 27 wherein:
said core is a toroid having a central opening, the principal axis of said toroid being said transverse axis; and said structural member is formed to permit windings to be passed about said core while mounted on said carrier.
said core is a toroid having a central opening, the principal axis of said toroid being said transverse axis; and said structural member is formed to permit windings to be passed about said core while mounted on said carrier.
36. The assembly of claim 35 wherein:
said structural member includes a post aligned with said transverse axis; and said post has a waist narrower than said central opening of said toroid.
said structural member includes a post aligned with said transverse axis; and said post has a waist narrower than said central opening of said toroid.
37. The assembly of claim 36 wherein said post has a web and a flange.
38. The assembly of claim 27 wherein said footing has surface mount pads.
39. The assembly of claim 38 wherein said footing has four surface mount pads and a pair of windings are wound about said core and each winding is connected to a pair of said pads to form a surface mountable transformer.
40. A core carrier comprising:
a body having a footprint for mating with a printed circuit board;
said body having 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; and said body having a suction surface for engagement by a vacuum placement machine, whereby a magnetic core mounted on said core carrier can be located on a printed circuit board with said core carrier by a vacuum placement machine.
a body having a footprint for mating with a printed circuit board;
said body having 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; and said body having a suction surface for engagement by a vacuum placement machine, whereby a magnetic core mounted on said core carrier can be located on a printed circuit board with said core carrier by a vacuum placement machine.
41. A core carrier as claimed in claim 40 wherein said body includes a structural support member oriented to extend away from the printed circuit board, and said suction surface is mounted on said structural support member to lie at a distance from the printed circuit board that is beyond the magnetic core
42. A core carrier as claimed in claim 40 wherein said body includes a structural support member for supporting said suction surface, and said mount is located to support the magnetic core between said suction surface and the printed circuit board.
43. The magnetic core carrier of claim 42 wherein said structural support member is shaped to leave at least a portion of the surface area of the magnetic core exposed to ambient.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US39710399A | 1999-09-16 | 1999-09-16 | |
| US09/397,103 | 1999-09-16 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2302793A1 true CA2302793A1 (en) | 2001-03-16 |
Family
ID=23569838
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002302793A Abandoned CA2302793A1 (en) | 1999-09-16 | 2000-03-28 | Core carrier |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2302793A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11510351B2 (en) | 2019-01-04 | 2022-11-22 | Engent, Inc. | Systems and methods for precision placement of components |
-
2000
- 2000-03-28 CA CA002302793A patent/CA2302793A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11510351B2 (en) | 2019-01-04 | 2022-11-22 | Engent, Inc. | Systems and methods for precision placement of components |
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| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |