LOW-PROFILE INDUCTIVE COIL AND METHOND OF MANUFACTURE
Disclosed is an inductive coil comprising a non-conductive substrate, a plurality of insulator layers laminated in a stack over the non-conductive substrate, and a plurality of conductive layers interleaved between the insulator layers. A hole passes through the conductive and insulator layers, and a magnetic core is placed in the hole and over the substrate. Each of the conductive layers includes a single-layer conductive trace coiled around the hole with an isolating gap between each turn of the conductive trace. At least one plated via passes through at least one of the insulator layers to connect traces of at least two conductive layers. The inductive coil may be a Hearing Aid Compliant (HAC) T-coil, includable in a wireless communication device, such as a cellular phone. A method of manufacturing the inductive coil is also disclosed.
1 . An inductive coil, comprising:
a non-conductive substrate;
a plurality of insulator layers laminated in a stack over the non-conductive substrate, the insulator layers having a hole formed therein;
a plurality of conductive layers interleaved between the insulator layers and having the hole formed therein, each of the conductive layers including a single-layer conductive trace coiled around the hole with an isolating gap between each turn of the conductive trace;
at least one plated via passing through at least one of the insulator layers and connecting traces on at least two conductive layers; and
a magnetic core placed in the hole, above the non-conductive substrate.
2 . The inductive coil of claim 1 , further comprising:
a cover layer attached over the insulator and conductive layers to cover the hole and the magnetic core.
3 . The inductive coil of claim 2 , wherein additional electronic components are mounted on the cover layer.
4 . The inductive coil of claim 1 , wherein the conductive trace is a metal foil.
5 . The inductive coil of claim 1 , wherein the substrate is a flexible printed circuit board.
6 . The inductive coil of claim 1 , wherein the insulator layers are an adhesive.
7 . The inductive coil of claim 6 , wherein the insulator layers are a polyimide film.
8 . The inductive coil of claim 1 , wherein the magnetic core is a ferrite core.
9 . The inductive coil of claim 1 , wherein the insulator layers are flexible printed circuit boards.
10 . The inductive coil of claim 1 , wherein the inductive coil is a Hearing Aid Compliant (HAC) T-coil.
11 . The inductive coil of claim 1 , included in a wireless communication device.
12 . The inductive coil of claim 11 , wherein the wireless communication device is a Hearing Aid Compliant (HAC) device.
13 . The inductive coil of claim 1 , wherein additional electronic components are mounted on the non-conductive substrate.
14 . A method of manufacturing an inductive coil, comprising:
(a) providing a non-conductive substrate;
(b) forming a conductive layer, having a hole, over the non-conductive substrate, the conductive layer including a single-layer conductive trace coiled around the hole with an isolating gap between each turn of the conductive trace;
(c) forming an insulator layer, having the hole, over the conductive layer;
(d) forming at least one plated via passing through the insulator layer and connecting the trace on the conductive layer;
(e) repeating (b) through (d) a predetermined number of times to form a laminated stack of interleaved conductive and insulator layers over the substrate; and
placing a magnetic core in the hole, above the non-conductive substrate.
15 . The method of claim 14 , further comprising:
attaching a cover layer over the laminated stack of interleaved insulator and conductive layers to cover the hole and the magnetic core.
16 . The method of claim 15 , further comprising:
mounting additional electronic components on the cover layer.
17 . The method of claim 14 , further comprising:
mounting additional electronic components on the substrate.
18 . The method of claim 14 , wherein the conductive trace is a metal foil.
19 . The method of claim 14 , wherein the substrate is a flexible printed circuit board.
20 . The method of claim 14 , wherein the inductive coil is a Hearing Aid Compliant (HAC) T-coil.