PLANAR LITZ WIRE COIL AND METHOD OF MAKING SAME

• US 20140085031A1
• Filed: 09/27/2012
• Published: 03/27/2014
• Est. Priority Date: 09/27/2012
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho (Toyota Motor Corporation)
• Original Assignee: Toyota Motor Engineering & Manufacturing North America Incorporated (Toyota Motor Corporation)
• Inventors: NOMURA, Tsuyoshi, TOSHIYUKI, Ken, Guo, Yuanbo
• Granted Patent: US 8,973,252 B2
• Time in Patent Office: Days
• US Class Current: 336/200
• CPC Class Codes: H01F 41/00 Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
• CPC Class Codes: H01F 5/02 wound on non-magnetic supports, e.g. formers
• CPC Class Codes: H05K 1/0242 Structural details of individual signal conductors, e.g. related to the skin effect
• CPC Class Codes: H05K 1/028 Bending or folding regions of flexible printed circuits H05K1/0283 takes precedence
• CPC Class Codes: H05K 1/165 incorporating printed inductors
• CPC Class Codes: H05K 2201/055 Folded back on itself
• CPC Class Codes: Y10T 29/4902 Electromagnet, transformer or inductor
• CPC Class Codes: Y10T 29/49073 by assembling coil and core
• CPC Class Codes: Y10T 29/49155 Manufacturing circuit on or in base

Abstract

Several embodiments of a circuit device using principles of planar Litz wire construction are disclosed using flexible printed circuit boards on which a given set of conductors is located on one surface only. The FPCBs are folded at strategic locations to effectively cause conductors in adjacent parallel planes to effectively cross one another to realize the advantages of braided Litz wire conductors, but without the use of vias or circuit interconnections between opposite sides of any given FPCB or between different sections of a continuous FPCB wherein each section defines its own coil or coil set.

Claims

1. A printed circuit characterized by low AC impedance and an absence of through-hole connections comprising:

a flexible printed circuit board (FPCB) defining a series of straight sections alternatingly interspersed by contiguous turn sections, the straight sections having longitudinal fold lines;

at least two non-crossing planar conductor strands applied to a surface of the unfolded FPCB and extending without interruption through the straight and turn sections;

at least some of the conductor strands being arranged to cross the fold lines;

whereby fully folding the FPCB along the fold lines results in conductor strands parallel planes effectively crossing one another.

2. The circuit defined in claim 1 wherein each turn section is contiguous with an integral straight section and includes fold lines.

3. A multi-turn, two-sided coil which, in the developed state, comprises:

a flexible printed circuit board (FPCB) exhibiting a regular repeating pattern of parallel sections joined by integral connector sections of alternatingly opposite direction;

a continuous pattern of multiple, non-crossing conductors located on one side of the FPCB and extending through said offset parallel sections and connector sections to create a substantially sinusoidal pattern between an input and an output;

wherein each of the parallel sections can be longitudinally folded onto itself to cause said conductors, in the folded state, to effectively cross one another, albeit in different planes.

4. The coil defined in claim 3 further wherein each of the connector sections can be fully folded onto itself to form one or more coils in stacked relationship.

5. The method of constructing a multi-layer printed circuit characterized by low AC resistance and an absence of through-hole connections comprising the steps of:

fabricating a flexible printed circuit board (FPCB) so as to define a series of straight sections joined by turns wherein the turns prior to folding the board are alternatingly in opposite directions and wherein the straight sections have longitudinal fold lines;

locating multiple non-crossing planar conductors on one side only of the FPCB in such a way that said conductors extend without interruption through the straight sections and turns and at least some of said conductors extend over said fold lines; and

folding the FPCB along the fold lines to produce a double-sided FPCB coil wherein the conductors in opposite parallel sides of each folded straight section effectively cross one another one or more times.

6. The method defined in claim 5 wherein the turns are 90°

.

7. The method defined in claim 5 wherein the turns are 180°

.

8. A method of forming a multi-layer flexible printed circuit board (FPCB) comprising the steps of:

forming a flexible printed circuit board (FPCB) into a plurality of alternatingly interconnected, parallel lengths, each having an equal number of parallel lateral straight sections joined by alternatingly opposite turn sections;

placing a plurality of continuous, non-crossing conductors on one side of the FPCB so as to extend in a sinusoidal pattern through each section and onto the next section; and

folding each of the sections into multiple overlying layers along parallel fold lines extending through the conductors sets to effectively cause the conductor sets on opposite sides of the folded FPCB to cross one another while flipping adjacent folded sections on top of one another to create a stack of interconnected turns through which the conductors run without interruption.

9. A method as defined in claim 8 wherein the circuit board forms an inductor.