Electrostatic discharge multifunction resistor

• US 20030025587A1
• Filed: 07/10/2002
• Published: 02/06/2003
• Est. Priority Date: 07/10/2001
• Status: Active Grant

• Current Assignee: Littlefuse Incorporated
• Original Assignee: Littlefuse Incorporated
• Inventors: Whitney, Stephen J., Rector, Louis, Hyatt, Hugh
• Granted Patent: US 7,034,652 B2
• Time in Patent Office: Days
• US Class Current: 338/22R
• CPC Class Codes: H01C 7/105 Varistor cores H01C7/12 takes precedence
• CPC Class Codes: H01C 7/118 Carbide, e.g. SiC type
• CPC Class Codes: H01C 7/12 Overvoltage protection resistors series resistors structurally associated with spark gaps H01T1/16
• CPC Class Codes: H05K 1/0246 Termination of transmission lines
• CPC Class Codes: H05K 1/0259 Electrostatic discharge [ESD] protection
• CPC Class Codes: H05K 1/095 for polymer thick films, i.e. having a permanent organic polymeric binder
• 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 2201/10022 Non-printed resistor
• CPC Class Codes: H05K 2201/10636 Leadless chip, e.g. chip capacitor or resistor
• CPC Class Codes: H05K 3/284 for encapsulating mounted components H05K1/185 takes precedence
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

The present invention provides a multifunction resistor having an improved voltage variable material (“VVM”). More specifically, the present invention provides a polymer VVM that has been formulated with a high percentage loading of conductive and/or semiconductive particles. A known length of the relatively conductive VVM is placed between adjacent electrodes to produce a desired Ohmic normal state resistance. When an electrostatic discharge event occurs, the VVM of the multifunctional resistor becomes highly conductive and dissipates the ESD threat. One application for this “resistor” is the termination of a transmission line, which prevents unwanted reflections and distortion of high frequency signals.

Claims

1. A multifunction resistor comprising:

an insulating binder; and

conductive particles mixed with the insulating binder, wherein the conductive particles and insulative binder are provided in a quantity that yields a desired Ohmic resistance when an electrostatic discharge (“

ESD”

) event is not present, and which non-Ohmically lowers in resistivity when the ESD event is present.

2. The resistor of claim 1, which includes semiconductive particles mixed with the binder and the conductive particles.

3. The resistor of claim 2, wherein the semi-conductive particles include silicon carbide.

4. The resistor of claim 2, wherein the semi-conductive particles have a bulk conductivity in a range of 10 to 1×

10<sup>−

6</sup> (ohm-cm)<sup>−

1</sup>.

5. The resistor of claim 1, wherein the conductive particles include 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, and conducting organic materials, such as intrinsically conducting polymers.

6. The resistor of claim 1, which includes insulating particles mixed with the binder and the conductive particles.

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

1.

8. The resistor of claim 1, wherein the insulating binder includes a material selected from the group consisting of:

thermoset polymers, thermoplastic polymers, elastomers, rubbers, and polymer blends.

9. The resistor of claim 1, wherein the insulating binder includes a silicone resin.

10. The resistor of claim 1, which includes a housing that encloses the insulative binder and the conductive particles.

11. The resistor of claim 1, wherein the insulative binder is self-curable to a substrate.

12. The resistor of claim 1, wherein the insulative binder and the conductive particles are applied directly to a substrate.

13. The resistor of claim 12, which includes an encapsulant placed on the directly applied insulative binder and particles.

14. The resistor of claim 1, which is a type of resistor selected from the group consisting of:

a termination resistor and a pull-up/pull-down resistor.

15. The resistor of claim 1, which is a pull-up resistor that electrically communicates between a voltage source and an input side of a device.

16. The resistor of claim 1, wherein the desired Ohmic resistance is between 50 and 100,000 Ohms.

17. A termination resistor for a transmission line comprising:

a pair of electrodes, one electrode coupling to the transmission line and the other electrode coupling to a ground contact; and

a quantity of voltage variable material (“

VVM”

) coupling the pair of electrodes, the VVM providing a desired resistance when no electrostatic discharge (“

ESD”

) event is present, the VVM lowering in resistivity when the ESD event is present.

18. The resistor of claim 17, wherein the VVM further comprises:

an insulating binder; and

conductive particles mixed with the insulating binder, the particles having a volume percentage range of 20 to 72%.

19. The resistor of claim 17, which includes a housing that encloses the VVM.

20. The resistor of claim 17, wherein the insulative binder and the conductive particles are applied directly to a substrate.

21. The resistor of claim 17, wherein the desired resistance is between 50 and 100,000 Ohms.

22. A multifunction resistor comprising:

a quantity of a material that provides a desired resistance when an electrostatic discharge (“

ESD”

) event is not present, and which lowers in resistivity when the ESD is present; and

a ground contact that electrically communicates with the quantity of material.

23. The multifunction resistor of claim 22, wherein the material is applied directly to a substrate selected from the group consisting of:

a printed circuit board, a polyimide, a polymer and any combination of there.

24. A multifunction resistor comprising:

a resistor having a fixed resistivity and plurality of non-contacting electrodes; and

a quantity of voltage variable material (“

VVM”

) that contacts the plurality of electrodes, wherein the VVM creates a low resistivity electrical path between the electrodes when an electrostatic discharge event is present.

25. The resistor of claim 24, wherein the resistor includes a material having a fixed resistivity and the VVM electrically connects in parallel with the fixed resistivity material to the electrodes.

26. The resistor of claim 24, wherein the VVM includes at least one component selected from the group consisting of:

an insulating binder, conductive particles and semiconductive particles.

27. The resistor of claim 24, which is a type of resistor selected from the group consisting of:

a termination resistor and a pull-up/pull-down resistor.

28. The resistor of claim 24, wherein the electrodes are electrically coupled to conductive pads on a substrate.

29. The resistor of claim 28, wherein the VVM is applied directly to the substrate.

30. The resistor of claim 24, wherein the VVM is applied directly to the electrodes.