Geometric configuration or alignment of protective material in a gap structure for electrical devices

• US 9,053,844 B2
• Filed: 09/09/2010
• Issued: 06/09/2015
• Est. Priority Date: 09/09/2009
• Status: Active Grant

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Littelfuse Incorporated
• Inventors: Kosowsky, Lex, Fleming, Robert
• Primary Examiner(s): Fureman, Jared
• Assistant Examiner(s): Ieva, Nicholas
• Application Number:
  US12/878,344
• Publication Number:
  US 20110058291A1
• Time in Patent Office: 1,734 Days
• Field of Search: 361/56, 361/111, 361/117, 361/118, 361/120, 361/126, 361/127
• US Class Current: 1/1
• CPC Class Codes: H01C 7/10 voltage responsive, i.e. varistors
• CPC Class Codes: H01C 7/12 Overvoltage protection resistors series resistors structurally associated with spark gaps H01T1/16
• CPC Class Codes: H05K 1/0257 Overvoltage protection
• CPC Class Codes: H05K 1/0259 Electrostatic discharge [ESD] protection
• 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

Abstract

An electrical device that includes a first electrode and a second electrode that are separated from one another so as to form a gap structure. A layer of protective material spans the gap structure to contact the first electrode and the second electrode. A dimension of the gap structure, corresponding to a separation distance between the first electrode and the second electrode, is varied and includes a minimum separation distance that coincides with a critical path of the layer of protective material between the first electrode and the second electrode.

Claims

1. An electrical device comprising:

a first electrode;

a second electrode separated from the first electrode to form a gap structure;

a layer of protective material that spans the gap structure to contact the first electrode and the second electrode;

wherein the layer of protective material is (i) a dielectric in absence of a voltage that exceeds a characteristic voltage level, and (ii) a conductor with application of a voltage that exceeds a characteristic voltage level of the composition;

wherein a dimension of the gap structure, corresponding to a separation distance between the first electrode and the second electrode, is varied and includes a minimum separation distance that coincides with a critical path of the layer of protective material between the first electrode and the second electrode;

wherein the first electrode surrounds all of the second electrode, and wherein a center of the second electrode is offset relative to a center of the first electrode so as to vary the separation distance with the first electrode at different locations along the perimeter of the second electrode; and

wherein the protective material is a varistor.

2. The electrical device of claim 1, wherein one of the first or second electrodes is interconnected to a grounding element so that the first and second electrode are both electrically grounded when the layer of protective material switches from the non-conductive state.

3. The electrical device of claim 1, wherein the minimum separation distance between the first electrode and the second electrode is greater than a defect density length of the protective material.

4. The electrical device of claim 1, wherein the protective material is voltage switchable dielectric (VSD) material.

5. The electrical device of claim 1, wherein each of the second electrode and the protective material is circular or elliptical in shape, and wherein the protective material surrounds the second electrode and is geometrically offset with respect to the second electrode.

6. The electrical device of claim 1, wherein each of the first electrode and the protective material is polygonal, and the second electrode is circular or elliptical.

7. The electrical device of claim 1, wherein the first electrode is polygonal, and each of the protective material and the second electrode is circular or elliptical.

8. The electrical device of claim 1, wherein the second electrode is polygonal.

9. The electrical device of claim 1, wherein the protective material is circular or elliptical in surrounding the second electrode.

10. The electrical device of claim 1, wherein the first electrode, second electrode and protective material are arranged so that a resulting electric field from the electrical event is optimized to be non-uniform.

11. The electrical device in claim 1, wherein the electrical device is a discrete surge protector.

12. The electrical device in claim 1, wherein the electrical device is a printed circuit board or discrete semiconductor package.

13. The electrical device of claim 1, wherein the protective material protects against lightning strike.

14. The electrical device of claim 1, wherein the protective material protects against an electrostatic discharge event.

15. The electrical device of claim 7, wherein the first electrode has a triangular shape.

16. The electrical device of claim 1 wherein the dimension of the critical path is less than or equal to the span at which at least one defect in the protective material is expected.