Flexible circuit having overvoltage protection

• US 7,609,141 B2
• Filed: 02/26/2007
• Issued: 10/27/2009
• Est. Priority Date: 04/08/2002
• Status: Active Grant

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Littelfuse Incorporated
• Inventors: Vyas, Tushar, Harris, Edwin James, Pachla, Timothy
• Primary Examiner(s): LEE, KYUNG S
• Application Number:
  US11/679,061
• Publication Number:
  US 20070146941A1
• Time in Patent Office: 974 Days
• Field of Search: 338/21, 338/20, 338/67, 338/204, 338/312, 338/314, 296/23, 298/25, 361/111, 361/137, 257536-538
• US Class Current: 338/21
• CPC Class Codes: H01C 7/12 Overvoltage protection resistors series resistors structurally associated with spark gaps H01T1/16
• CPC Class Codes: H01G 2/14 Protection against electric or thermal overload by cooling H01G2/08
• CPC Class Codes: H02H 9/044 Physical layout, materials not provided for elsewhere varistors H01C7/12; spark-gaps H01T; Ovshinsky devices H10N70/00
• CPC Class Codes: H05K 1/0257 Overvoltage protection
• CPC Class Codes: H05K 1/0259 Electrostatic discharge [ESD] protection
• CPC Class Codes: H05K 1/0298 Multilayer circuits
• CPC Class Codes: H05K 1/0393 Flexible materials H05K1/038 takes precedence; specific organic compositions are classified in H05K1/0313 and subgroups
• CPC Class Codes: H05K 1/167 incorporating printed resistors
• CPC Class Codes: H05K 2201/0738 Use of voltage responsive materials, e.g. voltage switchable dielectric or varistor materials
• CPC Class Codes: H05K 2201/09763 Printed component having superposed conductors, but integrated in one circuit layer
• CPC Class Codes: H05K 3/28 Applying non-metallic protective coatings H05K3/0091 takes precedence; methods for intermediate insulating layers for build-up multilayer circuits H05K3/4673

Abstract

A first voltage variable material (“VVM”) includes an insulative binder, first conductive particles with a core and a shell held in the insulating binder and second conductive particles without a shell held in the insulating binder; a second VVM includes an insulating binder, first conductive particles with a core and a shell held in the insulating binder, second conductive particles without a shell held in the insulating binder, and semiconductive particles with a core and a shell held in the insulating binder; a third VVM includes only first conductive particles with a core and a shell held in the insulating binder.

Claims

1. A flexible circuit having overvoltage protection comprising:

a first flexible layer;

a plurality of signal conductors applied to the first flexible layer;

at least one ground conductor positioned adjacent to at least one of the signal conductors;

a layer of voltage variable material (“

VVM”

) applied to the plurality of signal conductors and the at least one ground conductor such that a first path through the VVM from any of the signal conductors to the at least one ground conductor is smaller than a second path through the VVM from any of the signal conductors to a closest adjacent signal conductor; and

a second flexible layer covering the signal conductors, the at least one ground conductor and the VVM, wherein the at least one ground conductor lies across the plurality of signal conductors, separated from the signal conductor by the VVM.

2. The flexible circuit of claim 1, wherein at least one of the first and second flexible layers is made of a material selected from the group consisting of:

a ribbon, mylar, polyimide and an electrically insulated film.

3. The flexible circuit of claim 1, wherein the VVM includes a binder that is pliable enough such that it can be flexed with the flexible circuit without cracking.

4. The flexible circuit of claim 1, which includes an intermediate insulation layer between at least one of:

(i) the signal conductors, (ii) the at least one ground conductor and (iii) VVM and the second flexible layer.

5. The flexible circuit of claim 4, wherein the intermediate insulative layer is made of a material selected from the group consisting of:

(i) a dry film photo-imageable coverlay, (ii) a spray liquid photo-imageable coverlay and (iii) a glob-coating.

6. The flexible circuit of claim 1, which includes a silver ink coating applied to at least one of the signal conductors, the at least one ground conductor and the VVM.

7. The flexible circuit of claim 1, wherein the VVM covers at least substantially all of an entire surface of the signal conductors and the at least one ground conductor.

8. The flexible circuit of claim 1, wherein the VVM is applied to a portion of the signal conductors and the at least one ground conductor.

9. The flexible circuit of claim 1, wherein the at least one ground conductor and the VVM are in a z-direction relationship with the plurality of signal conductors.

10. The flexible circuit of claim 1, further comprising at least one of:

(i) an internal insulating layer; and

(ii) a intermediate silver ink coating.

11. The flexible circuit of claim 1, wherein the VVM includes one of:

(i) an insulating binder, first conductive particles with a core and a shall held in the insulating binder, and second conductive particles without a shell held in the insulating binder;

(ii) an insulating binder, first conductive particles with a core and a shell held in the insulating binder, second conductive particles without a shell held in the insulating binder, and semi-conductive particles with a core and a shell held in the insulating binder; and

(iii) a insulating binder and only first conductive particles with a core and shell held in the insulating binder.

12. A flexible circuit having overvoltage protective comprising:

a first flexible layer;

a plurality of signal conductors applied to the first substrate layer;

a voltage variable material (“

VVM”

) applied to the plurality of signal conductors;

a ground conductor applied to the VVM and across the signal conductors, wherein the ground conductor extends across the signal conductors to a ground trace applied to the first flexible layer;

a first gap filled with the VVM between each adjacent signal conductor, the first gap larger than a second gap filled with the VVM between each signal conductor and the ground conductor; and

a second flexible layer covering the signal conductors, the ground conductor and the VVM.

13. The flexible circuit of claim 12, which includes at least one of:

(i) an internal insulating layer; and

(ii) a intermediate silver ink coating.

14. The flexible circuit of claim 12, further comprising a plurality of signal conductors, each signal conductor lying adjacent to one of the ground conductors, separated by the VVM.

15. A flexible circuit having overvoltage protection comprising:

a first flexible layer;

a signal conductor applied to the first flexible layer;

a second flexible layer;

a ground conductor applied to the second flexible layer; and

a voltage variable material (“

VVM”

) located between the signal and ground conductors, wherein the VVM includes one of;

(i) an insulating binder, first conductive particles with a core and a shell held in the insulating binder, and second conductive particles without a shell held in the insulating binder;

(ii) an insulating binder, first conductive particles with a core and a shell held in the insulating binder, second conductive particles without a shell held in the insulating binder, and semi-conductive particles with a core and a shell held in the insulating binder; and

(iii) a insulating binder and only first conductive particles with a core and shell held in the insulating binder.

16. The flexible circuit of claim 15, wherein at least one of the first and second flexible layers is made of a material selected from the group consisting of:

a ribbon, mylar, polyimide and an electrically insulated film.

17. The flexible circuit of claim 16, the VVM separating the signal conductors and the ground conductor by a gap, each signal conductor spaced away from an adjacent signal conductor by a distance larger than the gap.

18. The flexible circuit of claim 15, which includes a plurality of signal conductors applied to the first flexible layer.

19. A flexible circuit having overvoltage protection comprising:

a first flexible layer;

a plurality of signal conductors applied to the first flexible layer;

at least one ground conductor positioned adjacent to at least one of the signal conductors;

a layer of voltage variable material (“

VVM”

) applied to the plurality of signal conductors and the at least one ground conductor such that a first path through the VVM from any of the signal conductors to the at least one ground conductor is smaller than a second path through the VVM from any of the signal conductors to a closest adjacent signal conductor; and

a second flexible layer covering the signal conductors,

wherein the at least one ground conductor comprises a plurality of ground conductors, the VVM and each of the signal conductors in an x-y direction relationship with one of the plurality of ground conductors.

20. A flexible circuit having overvoltage protection comprising:

a first flexible layer;

a plurality of signal conductors applied to the first flexible layer;

at least one ground conductor positioned adjacent to at least one of the signal conductors;

a layer of voltage variable material (“

VVM”

) applied to the plurality of signal conductors and the at least one ground conductor such that a first path through the VVM from any of the signal conductors to the at least one ground conductor is smaller than a second path through the VVM from any of the signal conductors to a closest adjacent signal conductor; and

a second flexible layer covering the signal conductors, wherein each of the signal conductors lies adjacent to the at least one ground conductor, separated by the VVM.