DIRECT APPLICATION VOLTAGE VARIABLE MATERIAL

• US 20070139848A1
• Filed: 02/26/2007
• Published: 06/21/2007
• Est. Priority Date: 04/08/2002
• Status: Active Grant

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Littelfuse Incorporated
• Inventors: Vyas, Tushar, Pachla, Timothy, Harris, Edwin
• Granted Patent: US 7,843,308 B2
• Time in Patent Office: Days
• US Class Current: 361/118
• 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 voltage variable material (“

VVM”

) comprising;

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.

2. The VVM of claim 1, wherein the insulating binder has a characteristic selected from the group consisting of:

(i) including a polymer resin, (ii) being dissolved in a solvent and thickened with an agent, (iii) being self-curable, (iv) including silicone and (v) any combination thereof.

3. The VVM of claim 1, wherein at least one of the first and second conductive particles has a bulk conductivity greater than 10 (ohm-cm)⁻

1.

4. The VVM of claim 1, wherein at least one of the first and second conductive particles is made of a material selected from the group consisting of:

nickel, carbon black, aluminum, silver, gold, copper, graphite, tungsten, zinc, iron, stainless steel, tin, brass, zirconium, iopium, titanium and any combination thereof.

5. The VVM of claim 1, wherein the shell of the first conductive particles includes an oxide layer.

6. The VVM of claim 1, wherein the second conductive particles are agglomerated from smaller conductive particles.

7. The VVM of claim 6, wherein the smaller conductive particles have an average size on the order of nanometers.

8. The VVM of claim 6, wherein the second conductive particles are (i) substantially spherical or (ii) at least slightly elongated.

9. The VVM of claim 1, wherein the first conductive particles have an average size of about 0.1 to about fifty microns.

10. The VVM of claim 1, wherein the second conductive particles have an average size of about 0.02 microns to about 5 microns.

11. The VVM of claim 1, wherein the shell on the first conductive particles has an average thickness on the order of nanometers.

12. The VVM of claim 1, wherein the first conductive particles are provided in a concentration of about 35% to about 80% by volume.

13. The VVM of claim 1, which includes at least one additional type of particle selected from the group consisting of:

insulative particles, semiconductive particles and doped semiconductive particles.

14. A voltage variable material (“

VVM”

) comprising;

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.

15. The VVM of claim 14, wherein the core of the semiconductive particles includes a material selected from the group consisting of:

silicon, silicon carbide, barium titanate, boron nitride, boron phosphide, cadmium phosphide, germanium, indium phosphide, magnesium oxide, silicon, zinc oxide, zinc sulfide, and any combination thereof.

16. The VVM of claim 14, wherein the semiconductive particles have a conductivity of about 10 to 10⁻

6 (ohm-cm)<sup>−

1</sup>.

17. The VVM of claim 14, wherein the semiconductive particles have an average size of about 0.3 to about 30 microns.

18. The VVM of claim 14, wherein the shell of the semiconductive particles has at least one characteristic selected from the group consisting of:

being insulative, having an average thickness of about 100 to 10,000 Å

, including silicon dioxide, including epitaxial silicon and including glass.

19. The VVM of claim 14, wherein the semiconductive particles are doped with a dopant material.

20. A voltage variable material (“

VVM”

) comprising;

an insulating binder;

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

21. The VVM of claim 20, wherein the insulating binder has a characteristic selected from the group consisting of:

(i) including a polymer resin, (ii) being dissolved in a solvent and thickened with an agent, (iii) being self-curable, (iv) including silicone and (v) any combination thereof.

22. The VVM of claim 20, wherein the core of the conductive particles is made of a material selected from the group consisting of:

copper, aluminum and aluminum nitride.

23. The VVM of claim 20, wherein the shell includes silica or an oxide layer.

24. The VVM of claim 20, wherein the conductive particles have an average size of about 2 to about twenty microns.

25. The VVM of claim 20, wherein the shell has an average thickness on the order of nanometers.

26. The VVM of claim 20, wherein the conductive particles are provided in a concentration of about 35% to about 75% by volume.