Wideband planar transformer

• US 20090002111A1
• Filed: 01/04/2008
• Published: 01/01/2009
• Est. Priority Date: 01/11/2007
• Status: Active Grant

• Current Assignee: PlanarMag, Inc. (TE Connectivity Ltd. (United Kingdom))
• Original Assignee: PlanarMag, Inc. (TE Connectivity Ltd. (United Kingdom))
• Inventors: Harrison, William Lee, Pham, Anh-Vu, McConnell, Stephen M.
• Granted Patent: US 7,821,374 B2
• Time in Patent Office: Days
• US Class Current: 336/69
• CPC Class Codes: H01F 17/0033 with the coil helically wound around a magnetic core
• CPC Class Codes: H01F 19/04 Transformers or mutual inductances suitable for handling frequencies considerably beyond the audio range resonant circuits H03H
• CPC Class Codes: H01F 2027/2814 with only part of the coil or of the winding in the printed circuit board, e.g. the remaining coil or winding sections can be made of wires or sheets
• CPC Class Codes: H01F 30/16 Toroidal transformers
• CPC Class Codes: H01F 41/046 structurally combined with ferromagnetic material
• CPC Class Codes: Y10T 29/4902 Electromagnet, transformer or inductor

Abstract

A method of arranging and fabricating parallel primary and secondary coils of a wideband planar transformer is provided. The spacing and width of the coils are disposed to extend the bandwidth from DC to GHz and allow for high frequency coupling when the core permeability dramatically drops and achieves low reflected energy and low loss over a wide bandwidth. A bottom mold having a pattern of hole-pairs with conductive elements inserted vertically couples to a top mold such that a middle portion of the conductive elements spans between the top and bottom molds. Dielectric material envelopes the middle portion and a displacement feature of the mold creates a vacancy. A ferrite element is deposited to the vacancy. A second top mold spans the bottom mold and dielectric material is deposited to create a molded assembly. A deposited patterned conductive coating connects the element ends to define the transformer coils.

Claims

1. A method of fabricating a wideband planar transformer comprising:

a. providing a bottom mold, wherein said bottom mold comprises a pattern of hole pairs disposed in a planar base of said bottom mold;

b. inserting conductive elements to said holes, wherein said conductive elements are disposed vertically from said planar base, whereby a bottom portion of said conductive elements are held by said bottom mold;

c. providing a first top mold, wherein said first top mold is disposed on said bottom mold forming a first mold pair, whereas said first top mold comprises conductive element receiving features and a displacement feature disposed between said conductive element receiving features, whereby a middle portion of said conductive elements spans between said first top mold and said bottom mold;

d. depositing a dielectric material to said first mold pair, wherein said dielectric material envelopes said middle portion of said conductive elements and further envelopes said displacement feature;

e. removing said first top mold, wherein a vacancy is revealed by removing said displacement feature;

f. depositing a ferrite element to said vacancy;

g. providing a second top mold to said bottom mold, wherein said second top mold and said bottom mold define a second mold pair, whereby said second top mold spans said bottom mold;

h. depositing said dielectric material to said second mold pair to create a molded assembly, wherein said dielectric material envelopes a top portion of said conductive element and envelopes said ferrite element;

i. removing said molded assembly from said second mold pair, wherein said molded assembly comprises a top surface and a bottom surface;

j. preparing said top surface and said bottom surface for receiving a pattern of conductive coatings, wherein said preparation comprises removing said top conductive element portion and said bottom conductive element portion, whereby said top surface and said bottom surface comprise said dielectric material and planed ends of said conductive element middle portion;

k. applying said conductive coating, wherein said coating is disposed to connect said middle portion conductive element ends according to a conductive pattern, wherein said conductive pattern defines a primary coil and a secondary coil of said wideband planar transformer.

2. The method of claim 1, wherein said displacement feature is a toroid shape.

4. The method of claims 1 or 3, wherein said molds comprise a mold array, whereby said methods provide an array of said transformers.

5. The method of claim 4, wherein said ferrite element is an array of said ferrite elements.

6. The method of claim 4, wherein said transformer array is diced.

7. The method of claims 1 or 3, wherein said ferrite element is a toroid shaped ferrite element, whereby said conductive element pair comprises a first element of said pair on an inside of said toroid and a second element of said pair on an outside of said toroid.

8. The method of claims 1 or 3, wherein said conductive elements are selected from a group consisting of pins and drawn wire.

9. The method of claims 1 or 3, wherein said conductive pattern comprises a pattern of generally teardrop-shape conductors arranged in a spiral pattern, whereby a narrow end of said teardrop is on an inside of said spiral and a large end of said teardrop is on an outside of said spiral.

10. The method of claims 1 or 3, wherein said surface preparation is selected from a group consisting of plasma etching, machining, grinding and lapping.

11. The method of claims 1 or 3, wherein said applying conductive coating comprises photolithography.

12. The method of claims 1 or 3 further comprises providing a center tap to said primary coil and a center tap to said secondary coil.

13. The method of claims 1 or 3 further comprises providing an electrode pair for said primary coil and providing an electrode pair for said secondary coil, wherein a first electrode of said pair is adjacent to a second electrode of said pair is on said top surface, whereas said primary coil and said secondary coil are generally parallel coils having coil spacing and coil widths optimized to control leakage inductance and winding capacitance to lower reflected energy and extend bandwidth from DC to GHz.

14. The method of claims 1 or 3 further comprising providing a solder ball grid array for combining said transformer with an integrated circuit.

3. A method of fabricating a wideband planar transformer comprising:

a. providing a bottom mold, wherein said bottom mold comprises a pattern of hole pairs disposed in a planar base of said bottom mold;

b. inserting conductive elements to said holes, wherein said conductive elements are disposed vertically from said planar base forming conductive element pairs, whereby a bottom portion of said conductive elements are held by said bottom mold;

c. inserting a standoff element to said mold bottom, wherein said standoff element is made from a dielectric material;

d. disposing a ferrite material on said standoff element, wherein said ferrite material separates said conductive element pairs;

e. providing a top mold to said bottom mold, wherein said top mold spans said bottom mold, whereby said top mold and said bottom mold define a mold pair;

f. depositing said dielectric material to said mold pair to create a molded assembly, wherein said dielectric material envelopes a top portion of said conductive element and envelopes said ferrite element and said standoff element;

g. removing said molded assembly from said mold pair, wherein said molded assembly comprises a top surface and a bottom surface;

h. preparing said top surface and said bottom surface for receiving a pattern of conductive coatings, wherein said preparation comprises making planar said assembly top surface and said bottom surface, whereby ends of said conductive elements are even with said planar surfaces;

i. applying said conductive coating, wherein said coating is disposed to connect said conductive element ends according to a conductive pattern, wherein said conductive pattern defines a primary coil and a secondary coil of said wideband planar transformer.

15. A wideband planar transformer comprising:

a. a ferrite element;

b. at least one conductive element disposed on a first side of said ferrite element;

c. at least one conductive element disposed on a second side of said ferrite element, wherein said first conductive element and said second conductive element form a pair of conductive elements;

d. a bottom pattern of conductive coating, wherein said bottom pattern is a pattern of teardrop-shape conductors, whereby said bottom teardrop-shape conductor is disposed to connect a bottom end of said first side conductive element of one said pair with a bottom end of said second side conductive element of an adjacent said pair;

e. a top pattern of conductive coating, wherein said top pattern is a pattern of said teardrop-shape coatings, whereby said top teardrop-shape conductor is disposed to connect a top end of said first side conductive element with a top end of said second side conductive element of said adjacent pair, whereas said conductive coatings and said conductive elements form a primary coil and a secondary coil around said ferrite element;

f. a first primary electrode connected to a first end of said primary coil and a second primary electrode connected to a second end of said primary coil;

g. a first secondary coil electrode connected to a first end of said secondary coil and a second secondary coil electrode connected to a second end of said secondary coil;

h. a primary coil tap connected to any coil of said primary coil;

i. a secondary coil tap connected to any coil of said secondary coil; and

j. a dielectric material enveloping said ferrite element and said coils.

16. The planar transformer of claim 15, wherein said ferrite element is selected from a group consisting of a toroid shape and a closed-loop circuitous shape, whereby said teardrop-shape conductors are arranged with a small teardrop end near a center of said ferrite element and a large teardrop end away from said center of said ferrite element.

17. The planar transformer of claim 15, wherein said conductive elements are selected from a group consisting of drawing wire and pins.

18. The planar transformer of claim 15, wherein said teardrop-shape conductive coatings form generally parallel said primary and said secondary coils with said first and said second conductive elements having coil spacing and coil widths optimized to control leakage inductance and winding capacitance to lower reflected energy and extend bandwidth from DC to GHz.