PPTC DEVICE HAVING LOW MELTING TEMPERATURE POLYMER BODY

Abstract

A fuse device may include a PPTC body; a first electrode, disposed on a first side of the PPTC body; and a second electrode, disposed on a second side of the PPTC body. The PPTC body may comprise a polymer matrix and a conductive filler, wherein the fuse device has a trip temperature of less than 120° C.

Claims

1. A fuse device, comprising: a PPTC body; a first electrode, disposed on a first side of the PPTC body; a second electrode, disposed on a second side of the PPTC body; and wherein the PPTC body comprises a polymer matrix and a conductive filler, the conductive filler comprising tungsten carbide; wherein the polymer matrix comprises a linear low-density polyethylene material having a melting temperature of approximately 100° C.

2. The fuse device of claim 1, comprising a trip temperature of 90° C.

3. The fuse device of claim 1, wherein a hold current density of the PPTC body at 25° C. ranges from 0.05 to 0.4 A/mm.sup.2.

4. The fuse device of claim 1, wherein the conductive filler comprises approximately 44% by volume fraction of the PPTC body.

5. The fuse device of claim 1, wherein a gradual increase in resistance occurs above 40° C.

6. The fuse device of claim 5, wherein an abrupt increase in resistance occurs at between 80° C. and 100° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1A and FIG. 1B illustrate a PPTC device according to embodiments of the disclosure;

[0010] FIG. 2 and FIG. 3 illustrate exemplary resistance behavior for two different PPTC formulations, according to different embodiments of the disclosure;

[0011] FIG. 4 shows a PPTC device according to various embodiments of the disclosure;

[0012] FIG. 5 shows a PPTC device according to various other embodiments of the disclosure; and

[0013] FIG. 6 show a PPTC device according to various additional embodiments of the disclosure.

DESCRIPTION OF EMBODIMENTS

[0014] The present embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. The embodiments are not to be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey their scope to those skilled in the art. In the drawings, like numbers refer to like elements throughout.

[0015] In the following description and/or claims, the terms “on,” “overlying,” “disposed on” and “over” may be used in the following description and claims. “On,” “overlying,” “disposed on” and “over” may be used to indicate that two or more elements are in direct physical contact with one another. Also, the term “on,”, “overlying,” “disposed on,” and “over”, may mean that two or more elements are not in direct contact with one another. For example, “over” may mean that one element is above another element while not contacting one another and may have another element or elements in between the two elements. Furthermore, the term “and/or” may mean “and”, it may mean “or”, it may mean “exclusive-or”, it may mean “one”, it may mean “some, but not all”, it may mean “neither”, and/or it may mean “both”, although the scope of claimed subject matter is not limited in this respect.

[0016] In various embodiments, novel device structures and materials are provided for forming a PPTC device, where the PPTC device is configured to operate as a fuse device at relatively low temperatures. In various embodiments, a low trip-temperature PPTC is formed using a select combination of a fluoropolymer and conductive filler. According to some embodiments, a PPTC device may exhibit a trip temperature of less than 150° C.

[0017] In various embodiments, a PPTC device may be constructed as shown in FIG. 1A and FIG. 1B. FIG. 1A illustrates a side cross-sectional view of a PPTC device 100, where a PPTC body 104 is disposed between a first electrode 102 and a second electrode 106, arranged on a first side and a second side, respectively. FIG. 1B illustrates a configuration of the PPTC device 100 after a first terminal 108 is joined to the first electrode 102 and a second terminal 110 is joined to the second electrode 106. According to embodiments of the disclosure, the PPTC body 104 may be formed from a relatively low melting temperature polymer as detailed below. The first electrode 102 and second electrode 106 may be formed of known metals, such as a copper foil. In some embodiments, the copper foil may be nickel plated. The first terminal 108 and second terminal 110 may also be formed of known materials, such a copper or brass. The first terminal 108 and the second terminal 110 may form a first interface 112 and second interface 114 with the first terminal 108 and second terminal 110, such as by welding. The embodiments are not limited in this context.

[0018] In some embodiments, the PPTC body may be formed using a polymer matrix such as a low melting point polyvinylidene fluoride (PVDF) polymer, an ethylene vinyl acetate (EVA) polymer, a high-density polyethylene (HDPE), a low-density polyethylene (LDPE), a linear low density polyethylene (LLDPE), or an ethylene butyl acrylate (EBA) polymer. In other embodiments, the polymer matrix may be any crystalline polyolefin polymer, olefin copolymer, or combination of the two.

[0019] In various non-limiting embodiments, the polymer matrix may comprise a PVDF material having a melting temperature below 150 C., where the volume fraction of polymer in the PPTC body 35 to 75%, wherein the conductive filler comprises a volume fraction of 25 to 65%, and wherein the volume resistivity of the conductive filler is less than 500 μΩ-cm.

[0020] In various non-limiting embodiments, the polymer matrix may comprise a polyolefin polymer, olefin copolymer, or combination of the two, where the polymer matrix has a melting temperature of 120° C. or less, where the volume fraction of polymer in the PPTC body 35 to 75%, wherein the conductive filler comprises a volume fraction of 25 to 65%, and wherein the volume resistivity of the conductive filler is less than 500 μΩ-cm.

[0021] In various non-limiting embodiments, the hold current density of the PPTC body at 25 C. may range from 0.05 to 0.4 A/mm.sup.2. The embodiments are not limited in this context.

[0022] According to some embodiments, the conductive filler of the PPTC body 104 may be formed from conductive particles having a particle size in the range of 0.1 μm to 50 μm. The embodiments are not limited in this context. In some non-limiting embodiments, the particles may be a conductive ceramic, metal boride, metal nitride, or metal carbide (e.g., Tungsten carbide, titanium carbide, titanium diboride, vanadium carbide, zirconium carbide).

[0023] In other non-limiting embodiments, the conductive particles may be a metal, such as nickel, tungsten or copper. In additional non-limiting embodiments, the conductive particles may be a metal alloy such as a nickel-copper alloy, copper-tin alloy, or other alloy. In still further embodiments, the conductive filler particles may be a carbon material, such as carbon black, graphite.

[0024] Turning now to FIG. 2 there is shown a graph plotting the resistance behavior as a function of temperature of a PPTC device, arranged according to embodiments of the disclosure. In this example, the PPTC body is formed using a special low melting point PVDF polymer material, where the melting temperature is in the range of 100° C., such as between 90° C. and 110° C. The PVDF polymer material used in this example contrasts with conventional PVDF that exhibits a melting temperature of approximately 175° C. The conductive filler used for the example of FIG. 2 is a tungsten carbide filler, at approximately 44% by volume fraction of the PPTC body. As shown in FIG. 2 a gradual and modest increase in resistance takes place above 60° C., while an abrupt increase in resistance takes place at 120° C. Accordingly, the PPTC material of FIG. 2 may be deemed to exhibit a trip temperature of 120° C.

[0025] Turning now to FIG. 3 there is shown a graph plotting the resistance behavior as a function of temperature of a PPTC device, arranged according to other embodiments of the disclosure. In this example, the PPTC body is formed using a special low melting temperature LLDPE material, where the melting temperature is in the range of 100° C. The LLDPE material used in this example contrasts with conventional PVDF that exhibits a melting temperature of approximately 175° C. The conductive filler used for the example of FIG. 3 is a tungsten carbide filler, at approximately 44% by volume fraction of the PPTC body. As shown in FIG. 3 a gradual and modest increase in resistance takes place above 40° C., while an abrupt increase in resistance takes place at approximately 80-100° C. Accordingly, the PPTC material of FIG. 3 may be deemed to exhibit a trip temperature of 90° C.

[0026] The hold current density (the ratio of the hold current of the low tripping temperature PTC materials layer at 25° C. to the area of PPTC through which current travels between opposing electrodes) of the above examples of FIG. 2 and FIG. 3 may be designed to exhibit a value between 0.05 to 0.4 A/mm.sup.2 by appropriate choice of volume fraction of conductive filler and type of conductive filler, as discussed above.

[0027] The configuration of a PPTC device may vary according to different embodiments of the disclosure. FIG. 4 presents a top plan view of a PPTC device 400, shown as radial lead PPTC, including bottom lead 404 and top lead 406, attached to opposite surfaces of a PPTC body 402. The PPTC body 402 may have first and second electrodes (not separately shown) attached to the top surface and bottom surface, respectively, as generally described above. The PPTC device 400 may be encapsulated by an encapsulant layer 410, such as an epoxy. The PPTC body 402 may be formulated generally as described above, for operation at a low trip temperature, such as below 150 C.

[0028] FIG. 5 and FIG. 6 depict side cross-sectional views of embodiments of a single layer surface mount PPTC device 500 and a double layer surface mount PPTC device 600, according to different embodiments of the disclosure. In these additional devices, the PPTC body may be formulated generally as described above, for operation at a low trip temperature, such as below 150 C. In these additional devices, the PPTC body may be formulated generally as described above, for operation at a low trip temperature, such as below 150° C. The PPTC device 500 and PPTC device 520 each have similar components, including metal electrodes 504, metal structures 506, metal foil electrode 508, PTC layer 502, insulation layer 510, and solder mask 514.

[0029] While the present embodiments have been disclosed with reference to certain embodiments, numerous modifications, alterations and changes to the described embodiments are possible while not departing from the sphere and scope of the present disclosure, as defined in the appended claims. Accordingly, the present embodiments are not to be limited to the described embodiments, and may have the full scope defined by the language of the following claims, and equivalents thereof.