CONSTRUCTION OF AN INDUCTOR/ TRANSFORMER USING FLEXIBLE INTERCONNECT

Abstract

This invention is a systematic and repeatable method of building an inductor/transformer with well controlled electrical properties, lower weight and volume, at a reduced cost. It provides a novel way of creating a compact isolating transformer on a flexible substrate, which folds on itself like an accordion. The structure can be extended on either end of the flex substrate to allow the seamless addition of electronic circuits to create subsystem application functions. A highly miniaturized package is produced following these techniques of design layout and interconnection, yielding final products which are all surface mountable with land-grid array (LGA) or other desirable high volume manufacturing formats.

Claims

1. A method of constructing a wire-winding free inductor consisting of: A multilayer flexible base substrate wherein: Several different types of spiraling conductors (hereafter called coils) are printed and etched out in a design specified manner. Buried vias can be used to connect these various coils in series, in parallel, or multi combinations of series and parallel to create an inductor with desired electrical properties.

2. Method to create a galvanic isolation transformer, with specific desired magnetic and electrical properties, through the selective sequencing of coils of claim 1 along with a magnetic core.

3. The electrical properties of the isolating transformer in claim 2 and the inductor of claim 1 can be adjusted to minimize leakage inductance and/or inter-winding capacitance and/or to minimize DC resistance of an effective coil in a very controlled and repeatable manner, for manufacturing, by selecting sets of coils in parallel, in series, adjacent and/or interleaved patterns.

4. Shielding between any winding can be conveniently incorporated in the multi-layer flexible substrate while not affecting any behavior of the primary/secondary parasitics, coupling, or DC resistance of any coil to maintain the electrical properties of the isolating transformer or inductor in claim 3.

5. Creepage distance and Clearance requirements can be easily designed into the transformer or inductor in claim 3.

6. Multi-layer flexible substrate configuration consisting of: Multiple cells containing various layers of coils, and shields and coils per claim 4. A cut-out area for the magnetic core. Interconnecting rings at each end of the flexible substrate with traces for interconnection with a variety of optional electronic circuitry. Flexible strips which bring out connections to selected coils.

7. The flexible substrate of claim 6 is folded like an accordion, having the effect of stacking the various cells within the substrate yielding: Flexible strips which can be folded up or down through the cut-out area, and folded for attachment to the interconnecting ring. Inputs and outputs can be formed with Land-Grid-Array (LGA) pads or other high rate manufacturing pads. Electronic circuits can be installed on the interconnecting ring cells to create any number of desirable subsystem functions.

Description

DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 shows the implementation of a typical spiral conductor trace on a flex base with a center strip. The spiral trace forms an Inductor (points 1-1 and 1-2).

[0013] FIG. 2 shows a two panel version of spiral conductors on a flexible substrate.

[0014] FIG. 3 shows an EQ20 core with post and plate which is a standard configuration used in the manufacture of modern transformers.

[0015] FIG. 4 shows two layers of a flexible base, each with an inductor. The center flex is cut out for the ferrite core (4-5), exposing the tabs to be bent up or down for connection to external circuitry. Connecting points 4-2 and 4-4 with a via allows one leg of a transformer with the two inputs (or outputs) on opposite sides of the strip.

[0016] FIG. 5 shows a typical interconnecting ring used to connect the strips to create a configuration of spirals to provide the desired electrical properties.

[0017] FIG. 6 shows a side view of a typical implementation of an accordion folded flexible substrate that is attached to a substrate and ferrite core post.

[0018] FIG. 7 shows the flexible substrate used to create an entire 48:8:8 turns ratio transformer. In this example the substrate consists of 14 cells and 4 layers. The inner 12 cells contain the various primary, secondary, and interleaved windings and the two outer cells contain the interconnecting rings which provide the inputs and outputs for the device.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The basic building blocks for transformers are a ferrite core and metallic windings or inductors. An example embodiment of an inductor is shown in FIG. 1 where kapton or similar base substrate is used to design conducting traces with regular spiraling circular or polygon forms. The electrical characteristics of an inductor are determined by the number of turns, cross-section, and other geometric and material properties. Through selection of different combinations of winding layers the electrical properties of inductors can be tuned for the circuit application. For example FIG. 2 shows a simple example of two single layer inductors on a flexible substrate. Given the inductor defined by points 2-1 and 2-2, one can connect points 2-1 and 2-3 to result in an inductor defined by points 2-2 and 2-4 with twice the number of turns. Alternatively one can connect points 2-1 and 2-4 and connect points 2-2 and 2-3 to create an inductor defined by points 2-1 and 2-2 with lower ohmic resistance. The connections can be made by folding the flex along the fold line such that the left inductor is on the top side and the right inductor is on the bottom. Then the points can be connected using via's. With multiple layers of conductors on the flex base, complex combinations of inductors, including shielding, can be created to achieve the desired electrical properties.

[0020] All magnetics are built around electromagnetic materials, called core. For simplicity, we will illustrate one embodiment using an EQ shaped ferrite core (FIG. 3) with a plate and a post-more specifically EQ20.

[0021] In this simple example a 2 layer kapton or similar base substrate is used to design conducting traces with regular spiraling polygons or circular form (FIG. 4). FIG. 4 also shows the cut-out areas (4-5) for the ferrite core. One layer is put on the top side of the base and a second layer is put on the bottom of the base. The starting end of the top trace (4-1) is from inside the polygon or circle center. As the spiral goes out towards the edge of the formed base (4-2), a via is used to transfer the conductor continuity to the second layer which happens at the outer edge (4-4). The second spiral is brought back towards the center (4-3) but on the bottom side. The lengths of the traces laying over the post (through the center cut-out) are calculated according to the geometry of the core in use (EQ20) and the mechanism for termination for connection to the external circuitry (4-1 to 4-3).

[0022] To finish the flexible substrate, cover layers of kapton (or similar material) are placed leaving the interconnecting pads exposed. Once the core parts are joined together, with a gap created at the post area or without gap, an elemental magnetics circuit that can be used either as an inductor (gapped) or transformer (gapped or un-gapped) is created. One of the distinguishing aspects of this invention from prior-art of similar approach is the method of producing a strip of adequate width cutout from the post area (4-5) of the base material along with a specific area of similar shape and size as the formed portion with the traces (titled interconnecting ring FIG. 5). The center strip is folded back over on the interconnecting ring. This simple illustration provides the foundation for a more complex magnetic circuit for inductors or transformers.

[0023] In a second embodiment, a long strip of flex-circuit base is cut and formed wherein several such traces, center strips, and vias are created as one piece as in FIG. 7. Most simple designs can be achieved using a single layer of base material, where 2 sides are used for creating desired tracts with desired copper trace widths. More complex designs might require 4 or more layers. The mechanism of center strip cutout and the extra interconnecting area always match up with the designed number of terminations (FIG. 5). During interleaving of the spiral forms, some can be put in series to increase effective number of turns and some can be used in parallel to reduce copper trace resistance. Furthermore, interleaving series and or parallel spirals can be used to reduce leakage inductance and or inter-winding capacitance of the overall windings.

[0024] The usage of a flexible substrate allows a very repeatable and controlled process in manufacturing with a minimum of labor content. The design can incorporate creepage distance and clearance requirements along with control of circuit parasitic effects. Through the usage of a multilayer flex substrate it is convenient to insert shielding between any winding while not affecting any behavior of the primary/secondary parasitics, coupling, or DC resistance of any coil.

[0025] Another unique feature of this invention is that the formed areas can be folded such as in an accordion with center strips oriented according to the orientation of the Interconnecting Rings as shown in FIG. 6. Going back to the example in FIG. 7 the right side of the flex base interconnecting ring is for the primary of the transformer, the left interconnecting ring is for the secondary side of the output. The whole assembly is thus inside the core volume. Thus this invention attains ultimate miniaturization. The input-outputs are formed using Land-Grid-Array (LGA) type pads on one side of the core/wrapped-flex-circuit assembly. The results of this invention yields a highly optimized functional performance of the product, a highly reproducible and manufacturable product, reduced cost to produce, and a design capable of high volume production with lower manual labor.

[0026] It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms include and comprise, as well as derivatives thereof, mean inclusion without limitation. The term or is inclusive, meaning and/or. The phrase associated with, as well as derivatives thereof, means to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The phrase at least one of, when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, at least one of: A, B, and C includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C.

[0027] The description in the present application should not be read as implying that any particular element, step, or function is an essential or critical element that must be included in the claim scope. The scope of patented subject matter is defined only by the allowed claims. Moreover, none of the claims is intended to invoke 35 U.S.C. 112(f) with respect to any of the appended claims or claim elements unless the exact words means for or step for are explicitly used in the particular claim, followed by a participle phrase identifying a function. Use of terms such as (but not limited to) mechanism, module, device, unit, component, element, member, apparatus, machine, or system within a claim is understood and intended to refer to structures known to those skilled in the relevant art, as further modified or enhanced by the features of the claims themselves, and is not intended to invoke 35 U.S.C. 112(f).

[0028] While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the claims.