Surface-mounted over-current protection device

Abstract

A surface-mounted over-current protection device with positive temperature coefficient (ptc) behavior is disclosed. The surface-mounted over-current protection device comprises a first metal foil, a second metal foil corresponding to the first metal foil, a ptc material layer stacked between the first metal foil and the second metal foil, a first metal electrode, a first metal conductor electrically connecting the first metal foil to the first metal electrode, a second metal electrode corresponding to the first metal electrode, a second metal conductor electrically connecting the second metal foil to the second metal electrode, and at least one insulated layer to electrically insulate the first metal electrode from the second metal electrode. The surface-mounted over-current protection device, at 25° C., indicates that a hold current thereof divided by the product of a covered area thereof and the number of the conductive composite module is at least 0.16 A/mm².

Description

CROSS-REFERENCE TO A RELATED APPLICATION

This application is a Continuation-In-Part (CIP) of U.S. patent application Ser. No. 11/478,604 filed on Jul. 3, 2006 TPC PTC material layer used in the surface-mounted over-current protection device of the present invention can contain a traditional crystalline polymer with a lower melting point (e.g., LDPE) or can contain at least one crystalline polymer, in which the crystalline polymer comprises at least one polymer with a melting point below 115° C. The above LDPE can be polymerized using Ziegler-Natta catalyst, Metallocene catalyst or other catalysts, or can be copolymerized by vinyl monomer or other monomers such as butane, hexane, octene, acrylic acid, or vinyl acetate. Sometimes, to achieve an over-current protection at high temperature or to meet a specific purpose, the compositions of the PTC material layer can totally or partially use crystalline polymers with high melting points; e.g., PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), PTFE (polytetrafluoroethylene), or PCTFE (polychlorotrifluoro-ethylene).

The above crystalline polymers can also comprise a functional group such as an acidic group, an acid anhydride group, a halide group, an amine group, an unsaturated group, an epoxide group, an alcohol group, an amide group, a metallic ion, an ester group, and acrylate group, or a salt group. In addition, an antioxidant, a cross-linking agent, a flame retardant, a water repellent, or an arc-controlling agent can be added into the PTC material layer to improve the material polarity, electric property, mechanical bonding property or other properties such as waterproofing, high-temperature resistance, cross-linking, and oxidation resistance.

The metal powder or the conductive ceramic powder used in the present invention could exhibit various types, e.g., spherical, cubic, flake, polygonal, spiky, rod, coral, nodular or filament, and exhibit various shapes e.g., high structure or low structure. In general, conductive fillers with high structure can improve the resistance repeatability of PTC material, and conductive fillers with low structure can improve the voltage endurance of PTC material.

In other embodiments of the present invention, the conductive filler with lower conductivity, e.g., carbon black or graphite, can be mixed with conductive filler with higher conductivity, e.g., metal powder or conductive ceramic powder as long as the mixture (i.e., the mixed conductive filler) exhibits a resistivity below 0.2 Ω-cm and the value of the hold current thereof divided by the product of the covered area and the number of the conductive composite modules is at least 0.16 A/mm² and at most 1 A/mm².

In addition, the PTC material layer of the surface-mounted over-current protection device of the present invention could comprise a non-conductive filler to enhance the functionality of the present invention. The non-conductive filler of the present invention is selected from: (1) an inorganic compound with the effects of flame retardant and anti-arcing; for example, zinc oxide, antimony oxide, aluminum oxide, silicon oxide, calcium carbonate, boron nitride, aluminum nitride, magnesium sulfate and barium sulfate and (2) an inorganic compound with a hydroxyl group; for example, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, and barium hydroxide. The particle size of the non-conductive filler is mainly between 0.05 μm and 50 μm and the non-conductive filler is 1% to 20% by weight of the total composition of the PTC material layer.

According to the above description, the traditional over-current protection device applied to the small-sized SMDs exhibits insufficient hold current and thus loses many practical applications. The present invention, overcoming the limitation of low hold current of the traditional over-current protection device applied to the small-sized SMDs, presents excellent resistivity (i.e., below 0.2 Ω-cm), voltage endurance (i.e., above 12V), resistance repeatability (i.e., R₁/R_i below 3), and a high hold current (i.e., with a value of Ih/(Area×N) above 0.16 A/mm²). Also, since the area of the surface-mounted over-current protection device of the present invention is smaller, more protection devices in the PTC plate can be produced. As a result, the production cost is reduced and the expected objective of the present invention can be achieved.

The methods and features of this invention have been sufficiently described in the above examples and descriptions. It should be understood that any modifications or changes without departing from the spirit of the invention are intended to be covered in the protection scope of the invention.

Claims

1. A surface-mounted over-current protection device, comprising: at least one conductive composite module, comprising:

a first metal foil;

a second metal foil; and

a ptc material layer stacked between the first metal foil and the second metal foil, exhibiting a resistivity below 0.2 Ω-cm, comprising

at least one crystalline polymer and at least one conductive filler distributed in the at least one crystalline polymer and exhibiting a resistivity below 500 μΩ-cm;

a first metal electrode electrically connected to the first metal foil;

a second metal electrode electrically connected to the second metal foil; and

at least one first insulated layer disposed between the first metal electrode and the second metal electrode to electrically insulate the first metal electrode from the second metal electrode; wherein the surface-mounted over-current protection device, at 25° C., indicates that the value of a hold current thereof divided by the product of a covered area thereof and the number of the conductive composite module is from 0.16 0.215 A/mm² to 1 A/mm².

2. The surface-mounted over-current protection device of claim 1, further comprising a first metal conductor electrically connecting the first metal foil to the first metal electrode.

3. The surface-mounted over-current protection device of claim 1, further comprising a second metal conductor electrically connecting the second metal foil to the second metal electrode.

4. The surface-mounted over-current protection device of claim 1, wherein the at least one crystalline polymer comprises polyethylene.

5. The surface-mounted over-current protection device of claim 1, wherein the conductive filler is a metal powder or a conductive ceramic powder.

6. The surface-mounted over-current protection device of claim 5, wherein the metal powder is nickel, copper, iron, tin, lead, silver, gold, platinum, or an alloy thereof.

7. The surface-mounted over-current protection device of claim 5, wherein the conductive ceramic powder is selected from the group consisting of titanium carbide, tungsten carbide, vanadium carbide, zirconium carbide, niobium carbide, tantalum carbide, molybdenum carbide, hafnium carbide, titanium boride, vanadium boride, zirconium boride, niobium boride, molybdenum boride, hafnium boride, and zirconium nitride.

8. The surface-mounted over-current protection device of claim 1, wherein the particle size distribution of the at least one conductive filler consisting essentially of 0.1 μm to 10 μm.

9. The surface mounted over-current protection device of claim 1, wherein the ptc material layer has a thickness of greater than 0.2 mm.

10. The surface mounted over-current protection device of claim 1, wherein the first metal electrode and the second metal electrode are disposed on one surface of the conductive composite module.

11. The surface mounted over-current protection device of claim 1, wherein the first metal electrode and the second metal electrode are disposed on opposite surfaces of the conductive composite module.

12. The surface mounted over-current protection device of claim 1, wherein the at least one crystalline polymer comprises high density polyethylene, low density polyethylene, polyvinylidene fluoride, polyvinyl fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, or the mixture thereof.

13. The surface-mounted over-current protection device of claim 1, further comprising non-conductive filler selected from the group consisting of zinc oxide, antimony oxide, aluminum oxide, silicon oxide, calcium carbonate, boron nitride, aluminum nitride, magnesium sulfate, barium sulfate, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, and barium hydroxide.

14. The surface mounted over-current protection device of claim 13, wherein the ptc material layer is capable of withstanding a voltage over 12 volts.

15. A surface-mounted over-current protection device, comprising:

a first conductive composite module, comprising:

a first metal foil;

a second metal foil; and

a ptc material layer stacked between the first metal foil and the second metal foil, exhibiting a resistivity below 0.2 Ω-cm, comprising at least one crystalline polymer and at least one conductive filler distributed in the at least one crystalline polymer and exhibiting a resistivity below 500 μΩ-cm;

a second conductive composite module of the same structure and material of the first conductive composite module and being superimposed on the first conductive composite module;

a first metal electrode electrically connected to the first metal foil; and

a second metal electrode electrically connected to the second metal foil;

wherein the first metal electrode is insulated from the second metal electrode;

wherein the surface-mounted over-current protection device, at 25° C. indicates that the value of a hold current thereof divided by the product of two and a covered area thereof is from 0.215 A/mm² to 1 A/mm².

16. The surface-mounted over-current protection device of claim 15, wherein a pair of first insulated layers are disposed on the first and second conductive composite modules and between the first metal electrode and the second metal electrode to electrically insulate the first metal electrode from the second metal electrode.

17. The surface-mounted over-current protection device of claim 16, wherein a second insulated layer is disposed between the first conductive composite module and the second conductive composite module.

18. The surface-mounted over-current protection device of claim 15, wherein the conductive filler is nickel, copper, iron, tin, lead, silver, gold, platinum, or an alloy thereof.

19. The surface-mounted over-current protection device of claim 15, wherein the conductive filler is selected from the group consisting of titanium carbide, tungsten carbide, vanadium carbide, zirconium carbide, niobium carbide, tantalum carbide, molybdenum carbide, hafnium carbide, titanium boride, vanadium boride, zirconium boride, niobium boride, molybdenum boride, hafnium boride, and zirconium nitride.