EP0602838A1

EP0602838A1 - Planar magnetic components

Info

Publication number: EP0602838A1
Application number: EP93309635A
Authority: EP
Inventors: Lennart Daniel Pitzele; Matthew Anthony Wilkowski
Original assignee: AT&T Corp
Current assignee: AT&T Corp
Priority date: 1992-12-17
Filing date: 1993-12-02
Publication date: 1994-06-22
Also published as: JPH06224044A

Abstract

Disclosed is a planar magnetic component which utilizes a discrete, foldable, flexible circuit (10) to form each conductor winding. Interconnection of rings (14-19) within a winding is provided by conductors (20, 21) which are outside the periphery and displaced from the center axis (22) of the rings in order to improve the fill factor of the flex circuit on a given volume.

Description

Background of the Invention

This invention relates to magnetic components, such as inductors and transformers.
Traditionally, planar magnetic components comprise individual conductor rings which are connected in series or parallel to form windings. Usually, each ring is formed on an individual dielectric layer and the rings are stacked in a magnetic shell core. Lead outs are coupled to each ring and are soldered to copper posts located outside the ring perimeter protruding from a terminal header. The resistances of the lead outs can give rise to considerable losses.
One way of eliminating the lead outs and solder posts is to form a plurality of conductive rings on a flexible circuit and then fold the circuit in order to form a primary winding (see, e.g., U.S. Pat. No. 5,017,902). A single flexible circuit can also include one or more secondary windings (see, e.g., U.S. Pat. No. 4,959,630).
A problem still exists with such flexible circuit designs in that the folds of the circuit tend to pile up within one space in the magnetic core window resulting in a less than optimum fill factor in a given volume.

Summary of the Invention

The invention is a magnetic component comprising a plurality of conductive rings formed on a surface for a flexible dielectric layer. The rings are formed adjacent to one another in a row having a central axis. A conductive path is formed between adjacent rings to provide electrical connection between said adjacent rings. The path is formed outside the periphery of the adjacent rings and displaced from the central axis. The dielectric is folded so that the adjacent rings are stacked vertically.

Brief Description of the Drawing

These and other features of the invention are delineated in detail in the following description. In the drawing:

FIG. 1 is a plan view of an unfolded flexible circuit in accordance with an embodiment of the invention;
FIG. 2 is a plan view of the opposite surface of the unfolded flexible circuit;
FIG. 3 is an exploded view of the flexible circuit and a magnetic shell core in accordance with an embodiment of the invention;
FIG. 4 is a plan view of the flexible circuit and magnetic shell core of FIG. 1; and
FIG. 5 is a plan view of an unfolded flexible circuit in accordance with a further embodiment of the invention.

Detailed Description

FIGS. 1-4 illustrate a magnetic component in accordance with one embodiment of the invention. It will be understood that "magnetic component" is intended to include inductors, transformers and other components which include a conductive winding.
FIGS. 1 and 2 show conductive layers on opposite major surfaces of a flexible circuit 10. The circuit includes a dielectric layer 11, which is typically polyimide film. The dielectric layer usually has a thickness of 0.05 mm to 0.08 mm. The conductive layer on what is termed the "top" of the circuit in FIG. 1 is designated 12 while the conductive layer on the "bottom" in FIG. 2 is designated 13. It will be appreciated that FIG. 2 is a view of the bottom conductive layer from the same side as FIG. 1 but with the top conductor layer 12 removed in order to more clearly illustrate the super-position of the two conductive layers.
Each conductive layer, 12 and 13, forms a series of three conductive rings, 14-16 and 17-19, respectively. Each ring is electrically connected to at least one adjacent ring either on the same surface or on the opposite surface of the circuit. Interconnection between adjacent rings on the same surface (i.e., rings 15, 16 and 17, 18) is provided by conductive bars 20 and 21, respectively. t will be noted that the conductive bars 20 and 21 are displaced from, and essentially parallel to, the longitudinal central axis, 22, of the row of rings 14-19. The advantage of this displacement will be discussed below. Interconnection between adjacent rings on opposite surfaces (e.g., 14, 17) is provided by conductive via holes (e.g., 23) formed through the dielectric layer between the rings.
Two sets of tabs (e.g., 24, 25 and 26, 27) are also formed in the dielectric layer adjacent to each ring on different sides of the central axis 22. Each tab includes a hole (e.g., 28 and 29) formed through the dielectric layer and including conductive material on the side walls thereof. In two of these holes (28 and 30), the conductive material is coupled to a corresponding ring (14 and 19, respectively) in order to form electrical terminations. The remaining holes in the tabs are not electrically coupled to any ring in the unfolded state shown in FIGS. 1 and 2. However, as will be made clearer, the holes on the left-hand side of FIGS. 1 and 2 will be electrically coupled to one or the other of the termination holes 28 and 30 when the circuit is folded. The holes on the opposite side of the axis (e.g., 31 and 32) will serve as anchors when the circuit is folded.
The conductive layers, via holes, tabs, and tab holes are formed by standard processing. The dielectric layer including the tabs is formed by stamping. Via holes and tab holes are then formed by drilling. Both surfaces of the dielectric are then plated with copper to a thickness of approximately 0.10 mm to 0.20 mm, and the copper is patterned in accordance with standard photolithographic procedures. After conductor layer formation, each conductive layer, 12 and 13, is covered with a further layer of dielectric material (not shown for the sake of clarity) to avoid shorting of adjacent rings when the circuit is folded. These layers can be the same material as the dielectric base layer (11) and typically have a thickness of approximately 0.05 mm to 0.08 mm. The additional dielectric layers may also be formed by stamping and deposited by a standard lamination process.
The resulting circuit can then be folded along the horizontal dashed lines shown in FIGS. 1 and 2 in order to form a conductive winding as illustrated in FIGS. 3 and 4. The folded circuit is placed within a magnetic shell core 40 which comprises a magnetic material such as MgZn ferrite formed in two halves. Each half includes a base portion 44, a center core 41, and a pair of side walls, 42 and 43, spaced from the core. The base, core and side walls define a core "window" which houses at least a portion of the conductive rings 14-19 of the flexible circuit, with the cores of the two halves passing through the ring holes. Although not shown in FIG. 3, it will be appreciated that a secondary winding can also be included in the structure by interleaving a plurality of rings on dielectric layers with the rings of the flexible circuit 10.
The stackup resulting from the folding and placing of circuit 10 within the core 40 can best be understood by looking at FIG. 4. It will be noted, for example, that the interconnecting bars 20 and 21 fall outside the core window and, further, are disposed in opposite folds. Thus, the interconnections of the rings do not stack up within the window or in a single position outside the window, thereby improving the fill factor of the flexible circuit in a given volume.
It will also be noted that all the tab holes on the left side of the circuit of FIGS. 1 and 2 will line up with either tab hole 28 or 29 in the stack up of FIG. 4, and, similarly, all the tab holes on the right side will line up with either tab hole 31 or 32. Electrical connection is provided to the holes aligned with holes 28 and 29 by soldering the holes to a lead frame (not shown). This will establish a conductive path through the winding which starts at the tab including hole 30 and ends at the tab including hole 28 (see FIGS. 1 and 2). The holes aligned with holes 31 and 32 will serve as anchors to keep the winding together. This is accomplished by also soldering the tabs including these holes to the lead frame so that the winding is secured in four positions on the frame.
Of course, it will be appreciated that the invention is not limited to the particular ring configuration previously shown and described. For example, additional rings can be produced by making use of a spiral-type pattern illustrated in the plan view of FIG. 5. Here, the conductor pattern on the top surface of the dielectric is illustrated by the solid lines and the conductor pattern on the bottom surface is illustrated by dashed lines. Connection between top and bottom conductors is, again, established by via holes. Each spiral pattern, 50-52, has three turns and, therefore, comprises three rings. Thus, a total of 9 rings is formed, 6 on the top surface and 3 on the bottom surface.
Again, interconnection between at least two adjacent rings in the winding is provided by interconnection bars 53 and 54 which are displaced from the longitudinal center axis 55 of the rings to improve the stackup as previously described. Tabs are provided adjacent each spiral pattern for electrical connection and anchoring as before. The dielectric would be folded along the horizontal dotted lines 56 and 57 to form the winding and placed in a core such as that shown in FIGS. 3 and 4.

Claims

1. A magnetic component comprising:

a flexible dielectric layer (11) having major surfaces;

a plurality of conductive rings (14-19) formed on at least one major surface of the dielectric layer in a row having a central axis (22),

said dielectric being folded so that the adjacent rings are stacked vertically,

CHARACTERIZED IN THAT

a conductive path (20, 21) is formed between at least two adjacent rings (15, 16 and 17, 18) to provide electrical connection between said rings, said path being formed outside the periphery of the rings and displaced from the central axis.

2. The component according to claim 1 further comprising

a shell (40) having a central magnetic core (41) and side walls (42, 43) defining a window, the core extending through holes within the rings while the conductive path falls outside the window.

3. The component according to claim 1 wherein the conductive path comprises at least two conductive bars (20, 21) each coupling two adjacent rings, said bars being formed on two different folds of the dielectric.

4. The component according to claim 1 wherein the dielectric further comprises tabs (24, 25, 26, 27) extending adjacent to each ring, each tab including a hole (28, 29, 31, 32) formed therethrough aligned with other holes in adjacent tabs in the folded dielectric.

5. The component according to claim 1 wherein rings are formed on both major surfaces of the dielectric and the rings are electrically connected through via holes (23) formed in the dielectric layer.

6. The component according to claim 1 whenever a plurality of rings is formed about a central hole by means of a spiral conductor pattern (FIG. 5).