Polymer composites for overvoltage protection

• US 6,251,513 B1
• Filed: 08/19/1998
• Issued: 06/26/2001
• Est. Priority Date: 11/08/1997
• Status: Expired due to Term

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Littlefuse Incorporated
• Inventors: Rector, Louis, Hyatt, Hugh M.
• Primary Examiner(s): Le, Hoa T.
• Application Number:
  US09/136,507
• Time in Patent Office: 1,042 Days
• Field of Search: 428/323, 428/328, 428/331, 524/80, 524/495, 524/781, 524/783, 524/784, 524/785, 524/786, 524/787, 524/789, 524/847, 524/858
• US Class Current: 428/323
• CPC Class Codes: H01C 7/105 Varistor cores H01C7/12 takes precedence
• CPC Class Codes: H01C 7/12 Overvoltage protection resistors series resistors structurally associated with spark gaps H01T1/16
• CPC Class Codes: Y10T 428/25 Web or sheet containing structurally defined element or component and including a second component containing structurally defined particles
• CPC Class Codes: Y10T 428/256 Heavy metal or aluminum or compound thereof
• CPC Class Codes: Y10T 428/259 Silicic material

Abstract

A composition and devices utilizing these compositions for providing protection against electrical overstress including a matrix formed of a mixture of an insulating binder, conductive particles having an average particle size of less than 10 microns, and semiconductive particles having an average particle size of less than 10 microns. The compositions exhibit improved clamping voltages in a range of about 30 volts to greater than 2,000 volts.

Claims

1. A composition for providing protection against electrical overstress, the composition comprising:

an insulating binder;

conductive particles having an average particle size of less than 10 microns, said conductive particles being spaced by a distance of approximately 1000 angstroms or greater; and

semiconductive particles having an average particle size of less than 10 microns.

2. The composition of claim 1, wherein a volume percentage of the insulating binder is in the range of about 20-60%, a volume percentage of the conductive particles is in the range of about 5-50% and a volume percentage of the semiconductive particles is in the range of about 2-60%.

3. The composition of claim 1, wherein the insulating binder comprises a material selected from the group consisting of thermoset polymers, thermoplastic polymers, elastomers, rubbers, or polymer blends.

4. The composition of claim 1, wherein the insulating binder is cross-linked.

7. The composition of claim 1, wherein the conductive particles comprise a material selected from the group consisting of nickel, carbon black, aluminum, silver, gold, copper and graphite, zinc, iron, stainless steel, tin, brass, and alloys thereof.

8. The composition of claim 1, wherein the semiconductive particles comprise a material selected from the group consisting of oxides of bismuth, zinc, calcium, vanadium, iron, copper, magnesium and titanium;

carbides of silicon, aluminum, chromium, molybdenum, titanium, beryllium, boron, tungsten and vanadium;

nitrides of silicon, aluminum, beryllium, boron, tungsten and vanadium;

sulfides of cadmium, zinc, lead, molybdenum and silver;

titanates of barium and iron;

borides of chromium, molybdenum, niobium and tungsten; and

suicides of molybdenum and chromium.

9. The composition of claim 1, wherein the semiconductive particles comprise silicon carbide.

10. The composition of claim 1, wherein the composition has a clamping voltage of less than 100 volts.

11. The composition of claim 1, wherein the composition has a clamping voltage of less than 50 volts.

12. The composition of claim 1, wherein the semiconductive particles are comprised of a first and a second semiconductive material, the first semiconductive material being different from the second semiconductive material.

13. The composition of claim 12, wherein the semiconductive particles comprised of the first semiconductive material have an average particle size in the micron range and the semiconductive particles comprised of the second semiconductive material have an average particle size in the submicron range.

14. The composition of claim 1, wherein the conductive particles have a bulk conductivity greater than 10 (ohm-cm)⁻

1.

15. The composition of claim 1, wherein the semiconductive particles have a bulk conductivity in a range of 10 to 10⁻

6 (ohm-cm)<sup>−

1</sup>.

16. A device for protecting a circuit against electrical overstress, the device comprising the composition of claim 1.

5. The composition of 1 wherein the insulating binder comprises a silicone resin.

6. The composition of claim 5, wherein the silicone is cross-linked with a peroxide curing agent.

17. A composition for providing protection against electrical overstress, the composition comprising:

an insulative binder;

conductive particles having an average particle size of less than 10 microns;

semiconductive particles having an average particle size of less than 10 microns; and

insulative particles having an average particle size in a range of about 200 angstroms to about 1,000 angstroms.

18. The composition of claim 17, wherein the insulative particles comprise a material selected from the group consisting of oxides of iron, titanium, aluminum, zinc and copper.

19. The composition of claim 17, wherein the insulative particles comprise clay.

20. The composition of claim 17, wherein the composition has a clamping voltage of less than 100 volts.

21. The composition of claim 17, wherein the composition has a clamping voltage of less than 50 volts.

22. The composition of claim 17, wherein the conductive particles have an average particle size in a range of about 4 to about 8 microns.

23. The composition of claim 17, wherein the conductive particles have an average particle size less than 4 microns.

24. The composition of claim 17, wherein the semiconductive particles have an average particle size less than 5 microns.

25. The composition of claim 17, wherein the insulative particles have a bulk conductivity of less than 10⁻

6 (ohm-cm)<sup>−

1</sup>.

26. A device for protecting against electrical overstress, the device comprising a pair of electrodes electrically connected by a composition, the composition comprising:

an insulating binder;

conductive particles having an average particle size of less than 10 microns and a bulk conductivity of greater than 10 (ohm cm)<sup>−

1</sup>; and

semiconductive particles having an average particle size of less than 10 microns and a bulk conductivity in a range of 10 to 10<sup>−

6</sup> (ohm cm)<sup>−

1</sup>.

27. A device for protecting against electrical overstress, the device comprising a pair of electrodes electrically connected by a composition, the composition comprising:

an insulating binder;

conductive particles having an average particle size of less than 10 microns and a bulk conductivity of greater than 10 (ohm cm)<sup>−

1</sup>;

semiconductive particles having an average particle size of less than 10 microns and a bulk conductivity in a range of 10 to 10<sup>−

6</sup> (ohm cm)<sup>−

1</sup>; and

insulative particles having an average particle size in a range of about 200 angstroms to about 1,000 angstroms and a bulk conductivity less than 10<sup>−

6</sup> (ohm cm)<sup>−

1</sup>.