Arc extinguishing and flame-retardant coatings for electronic devices

Abstract

The present invention provides a metal oxide varistor (MOV) device that extinguishes an electric arc as quickly as possible and thereby prevents any resulting damage to connected surrounding components. [Solution] A metal oxide varistor (MOV) device 10 comprises an MOV chip 12, conductive first and second electrodes 14a and 14b arranged on both sides of the MOV chip, conductive first and second leads 15 and 16 connected to the first and second electrodes, respectively, and an arc-reducing flame-retardant coating 20 covering a portion of the MOV chip, the first and second electrodes, and the first and second leads, wherein the arc-reducing flame-retardant coating has a silicone composition formed from a filler material suspended in a silicone resin, the filler material comprising one or more of melamine, guanidine, guanine, hydantoin, allantoin, urea, melamine formaldehyde, melamine cyanurate polymer, and boric acid.

Description

Technical Field

[0001] The present disclosure generally relates to the field of electronic devices. More particularly, the present disclosure relates to an arc suppression flame retardant silicone composition for coating electronic devices that are prone to generating electric arcs and / or combustion when placed in an extreme failure state.

Background Art

[0002] When placed in a state of overcurrent, overvoltage, or overheating (collectively referred to herein as "failure states"), various types of electronic devices can become prone to generating electric arcs and / or combustion. Such devices include metal oxide varistors (MOVs), thermally protected MOVs (TMOVs), fuses, positive temperature coefficient (PTC) devices (such as PTC fuses and PTC heaters), and the like.

[0003] In the case of MOV and PTC devices, depending on the fault condition, the MOV or PTC elements within the device may overheat and burn, damaging the device and, in some cases, surrounding components. In the case of fuses and TMOVs, depending on the fault condition, the fusible elements within the device may melt or otherwise separate, interrupting the flow of current through the device. When the fusible elements separate, it may become possible for an electric arc to propagate between the separated parts of the fusible elements (for example, through evaporated residual particles between the separated parts of the fusible elements). If the electric arc is not extinguished, it may allow a considerable subsequent current to flow through the device, resulting in damage to connected components despite the fusible elements being physically open. Furthermore, the heat generated by the electric arc may burn and / or rupture the body of the device and, in some cases, damage surrounding components. Therefore, it is desirable to extinguish the electric arc as quickly as possible to prevent or mitigate any resulting damage to connected surrounding components.

[0004] This improvement may be useful with respect to these and other considerations. [Overview of the project]

[0005] This summary of the invention is provided to introduce, in a simplified form, selected from the concepts further described below, in modes for carrying out the invention. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to assist in determining the scope of the claimed subject matter.

[0006] A metal oxide varistor (MOV) device according to one embodiment of the present disclosure may include an MOV chip, conductive first and second electrodes positioned on both sides of the MOV chip, conductive first and second leads connected to the first and second electrodes, respectively, and an arc-reducing flame-retardant coating covering a portion of the MOV chip, the first and second electrodes, and the first and second leads, wherein the arc-reducing flame-retardant coating has a silicone composition formed from a filler material suspended in a silicone resin.

[0007] A thermally protected metal oxide varistor (TMOV) device according to one embodiment of the present disclosure may include a MOV chip, conductive first and second electrodes disposed on both sides of the MOV chip, a thermal cutoff (TCO) element having a conductive first lead connected to the first electrode, a conductive second lead connected to a dielectric barrier disposed on the second electrode, a first end electrically connected to the second lead on the dielectric barrier, and a second end electrically connected to the second electrode, and an arc-reducing flame-retardant coating covering the junction of the TCO element and the second electrode, wherein the arc-reducing flame-retardant coating has a silicone composition formed from a filler material suspended in a silicone resin.

[0008] A positive temperature coefficient (PTC) device according to one embodiment of the present disclosure may include a PTC element having conductive particles suspended in a non-conductive medium, conductive first and second electrodes positioned on both sides of the PTC element, conductive first and second leads connected to the first and second electrodes, respectively, and an arc-reducing flame-retardant coating covering a portion of the PTC element, the first and second electrodes, and the first and second leads, wherein the arc-reducing flame-retardant coating has a silicone composition formed from a filler material suspended in a silicone resin.

[0009] A fuse according to one embodiment of the present disclosure may include a dielectric fuse body, first and second conductive end caps positioned at both ends of the fuse body, fusible elements extending through the fuse body and electrically connected to the first and second end caps, and an arc-reducing flame-retardant coating covering the fuse body, the arc-reducing flame-retardant coating having a silicone composition formed from a filler material suspended in a silicone resin. [Brief explanation of the drawing]

[0010] [Figure 1] Figures 1A, 1B, and 1C are a series of perspective views showing a metal oxide varistor device according to one embodiment of the present disclosure.

[0011] [Figure 2] Figures 2A, 2B, and 2C are a series of perspective views showing a thermally protected metal oxide varistor device according to one embodiment of the present disclosure.

[0012] [Figure 3] Figures 3A and 3B are a series of side views showing a positive temperature coefficient device according to one embodiment of the present disclosure.

[0013] [Figure 4] Figures 4A and 4B are a series of cross-sectional views showing a fuse according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0014] Herein, exemplary embodiments of electronic devices having arc-reducing flame-retardant coatings according to the present disclosure will be described more fully below with reference to the accompanying drawings. However, electronic devices and arc-reducing flame-retardant coatings may be embodied in a number of different forms and should not be considered as being limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure may convey to those skilled in the art specific exemplary forms of electronic devices and arc-reducing flame-retardant coatings.

[0015] Referring to Figures 1A and 1B, a front view and a rear view of exemplary embodiments of the MOV device 10 according to this disclosure are shown. The MOV device 10 may include an MOV chip 12 having first and second conductive electrodes 14a, 14b positioned on either side thereof. The MOV chip 12 may be formed from any MOV composition known in the art, such as polycrystalline zinc oxide ceramic. This disclosure is not limited in this respect. The first and second electrodes 14a, 14b of the MOV device 10 may be formed from a metal having good conductivity, such as aluminum, copper, silver, or tin. This disclosure is not limited in this respect.

[0016] Although the MOV chip 12 and electrodes 14a, 14b are depicted as having a circular shape, this is not important. It is intended that one or more of the MOV chip 12 and electrodes 14a, 14b may have different shapes, such as rectangular, triangular, or irregular shapes, without departing from the scope of this disclosure.

[0017] The MOV device 10 may further include conductive first and second leads 15 and 16 connected to the first and second electrodes 14a and 14b, respectively, to facilitate the electrical connection of the MOV device 10 within the circuit. In various non-limiting embodiments, the first and second leads 15 and 16 may be electrically connected to the first and second electrodes 14a and 14b by soldering, welding, conductive adhesive, etc.

[0018] Referring to Figure 1C, the MOV device 10 may be provided with an arc-reducing flame-retardant coating 20 (hereinafter "coating 20") covering a portion of the MOV tip 12, the first and second electrodes 14a, 14b, and the first and second leads 15, 16. The coating 20 may be formed from a silicone composition formed from a filler material suspended in a silicone resin. In various embodiments, the filler material may include one or more of melamine, guanidine, guanine, hydantoin, allantoin, urea, melamine formaldehyde, melamine cyanurate polymer, boric acid, and their derivatives or mixtures, or other fillers that exhibit similar endothermic arc-extinguishing properties when burned, as described below. The filler material may be distributed substantially evenly throughout the silicone resin and may constitute 3 to 70% by weight of the silicone composition. The coating 20 may be applied to the underlying components of the MOV device 10 using any suitable method, including but not limited to dipping, jetting, and molding. This disclosure is not limited in this respect. The MOV device 10 may further include a protective dielectric shell 21 applied on the coating 20. In various embodiments, the shell 21 may be formed from epoxy and may be applied by dip or similar. This disclosure is not limited in this respect.

[0019] If an extreme fault condition (e.g., an extreme overvoltage condition) occurs in the MOV device 10, the MOV chip 12 may burn and produce a flame. The heat from the flame may cause the silicone in the coating 20 to burn and decompose. When the silicone decomposes, the filler material in the coating 20 may be exposed and may also burn due to the heat from the flame. When the filler material burns and decomposes, an endothermic chemical reaction occurs that absorbs heat and extinguishes the flame. Furthermore, byproducts of the endothermic chemical reaction may produce water, which can further extinguish the flame. Thus, when a fault condition occurs in the MOV device 10, the filler material can interfere with or extinguish the flame produced by the combustion of the MOV chip 12, thereby protecting surrounding components from damage that would normally occur if the flame were to persist.

[0020] Referring to Figures 2A and 2B, front and rear views of exemplary embodiments of a thermally protected metal oxide varistor device 100 (hereinafter referred to as "TMOV device 100") according to the present disclosure are shown. The TMOV device 100 may include an MOV chip 112 having first and second conductive electrodes 114a, 114b positioned on either side thereof. The MOV chip 112 may be formed from any MOV composition known in the art, such as zinc oxide granules embedded in ceramic. The present disclosure is not limited in this respect. The first and second electrodes 114a, 114b of the TMOV device 100 may be formed from a metal having good conductivity, including but not limited to aluminum, copper, silver, and tin. The present disclosure is not limited in this respect.

[0021] The MOV chip 112 and the first and second electrodes 114a, 114b are depicted as having a circular shape, but this is not important. It is intended that one or more of the MOV chip 112 and the first and second electrodes 114a, 114b may have different shapes, such as rectangular, triangular, or irregular shapes, without departing from the scope of this disclosure.

[0022] The TMOV device 100 may further include conductive first and second leads 115, 116 to facilitate the electrical connection of the TMOV device 100 within a circuit. The first lead 115 may be directly connected to a first electrode 114a on the front side of the MOV chip 112 by soldering, welding, conductive adhesive, etc. The second lead 116 may be connected to a dielectric barrier 117 located on the back side of the MOV chip 112 by soldering, adhesive, etc. The dielectric barrier 117 may be formed from ceramic or other dielectric material and may prevent direct electrical connection between the second lead 116 and the second electrode 114b. The TMOV device 100 may further include a thermal cutoff (TCO) element 119 having a first end electrically connected (e.g., by soldering) to the second lead 116 on the dielectric barrier 117, and a second end electrically connected (e.g., by soldering) to the second electrode 114b. The TCO element 119 may be formed from a conductive material and may be adapted to melt and separate when a predetermined temperature (e.g., 140°C to 240°C) is reached. During normal operation, the TMOV device behaves like a normal MOV device. However, if an overheating condition occurs in the TMOV device 100, the TCO element 119 melts, thereby preventing current from flowing through the TMOV device 100 and preventing further heating that could ignite the TMOV device 100 and damage to surrounding components.

[0023] Referring to FIG. 2C, the TMOV device 100 may be provided with an arc-reducing flame-retardant coating 120 (hereinafter “coating 120”) that covers the junction of the TCO element 119 and the second electrode 114b (for example, covers the solder connection between the TCO element 119 and the second electrode 114b). The coating 120 may be formed from a silicone composition formed from a filler material suspended in a silicone resin. In various embodiments, the filler material may include one or more of melamine, guanidine, guanine, hydantoin, allantoin, urea, melamine formaldehyde, melamine cyanurate polymer, boric acid, and derivatives or mixtures thereof, or other fillers that exhibit similar endothermic arc extinguishing characteristics when burned, as described below. The filler material may be distributed substantially evenly throughout the silicone resin and may occupy 3 to 70% by weight of the silicone composition. The coating 120 may be applied to the components underlying the TMOV device 100 using any suitable method, including but not limited to jetting, dispensing, printing, etc. The present disclosure is not limited in this regard.

[0024] Although not shown, the TMOV device 100 may further include a coating similar to the coating 20 described above, where such a coating may cover a part of the MOV chip 112, the first and second electrodes 114a, 114b, the dielectric barrier 117, the TCO element 119, the coating 120, and the first and second leads 115, 116. Such a coating may be formed from the silicone composition described above (a protective shell similar to the shell 21 described above may or may not be present). Alternatively, such a coating may be formed from a conventional dielectric polymer coating well known to those skilled in the art.

[0025] If a fault condition (e.g., overheating) occurs in the TMOV device 100, the TCO element 119 may melt and separate, and an electric arc may propagate across the gap remaining between the separated TCO element 119 and the second electrode 114a. The heat from the electric arc may cause the silicone in the coating 120 to burn and decompose. When the silicone decomposes, the filler material in the coating 120 may be exposed and may also burn due to the heat from the electric arc. When the filler material burns and decomposes, an endothermic chemical reaction occurs that absorbs heat, causing the electric arc to cool rapidly. Furthermore, depending on the specific arc filler material used in the coating 120, certain byproducts of the endothermic chemical reaction may be nonconductive gases (e.g., ammonia) that can interfere with the ability of the electric arc to persist. In addition, other byproducts of the endothermic chemical reaction may produce water, which can further cool the electric arc. Thus, when a fault condition occurs in the TMOV device 100, the filling material may absorb heat, release gases undesirable for maintaining the electric arc, and generate water that can further cool the electric arc, all of which can contribute to rapid arc extinguishing. Components connected to and / or located near the TMOV device 100 are thereby protected from damage that would normally occur if the electric arc were to persist.

[0026] Referring to FIG. 3A, a side view of an exemplary embodiment of a positive temperature coefficient (PTC) device 200 according to the present disclosure is shown. In various embodiments, the PTC device 200 may be a PTC fuse or a PTC heater. The present disclosure is not limited in this regard. The PTC device 200 may include a PTC element 212 having first and second conductive electrodes 214a, 214b disposed on both sides thereof. The PTC element 212 may be formed from any type of PTC material composed of conductive particles suspended in a non-conductive medium (such as a polymeric PTC material, a ceramic PTC material, etc.) and formulated to have an electrical resistance that increases as the temperature of the PTC element 212 rises. In particular, the PTC element 212 may have a predetermined “trip temperature” at which the electrical resistance of the PTC element 212 rapidly and dramatically (e.g., non-linearly) increases in order to substantially suppress the current passing therethrough. The first and second electrodes 214a, 114b of the PTC device 200 may be formed from a metal having good conductivity, such as aluminum, copper, silver, tin, etc. The present disclosure is not limited in this regard.

[0027] The PTC device 200 may further include first and second conductive leads 215, 216 respectively connected to the first and second electrodes 214a, 214b to facilitate the electrical connection of the PTC device 200 within a circuit. In various non-limiting embodiments, the first and second leads 215, 216 may be electrically connected to the first and second electrodes 214a, 214b by soldering, welding, a conductive adhesive, or the like.

[0028] Referring to Figure 3B, the PTC device 200 may be provided with an arc-reducing flame-retardant coating 220 (hereinafter referred to as "coating 220") covering a portion of the PTC element 212, the first and second electrodes 214a, 214b, and the first and second leads 215, 216. The coating 220 may be formed from a silicone composition formed from a filler material suspended in a silicone resin. In various embodiments, the filler material may include one or more of melamine, guanidine, guanine, hydantoin, allantoin, urea, melamine formaldehyde, melamine cyanurate polymer, boric acid, and derivatives or mixtures thereof, or other fillers that exhibit similar endothermic arc-extinguishing properties when burned, as described below. The filler material may be substantially evenly distributed throughout the silicone resin and may constitute 3 to 70% by weight of the silicone composition. The coating 220 may be applied to the underlying components of the PTC device 200 using any suitable method, including but not limited to dipping, jetting, and molding. The disclosure is not limited in this respect. The PTC device 200 may further include a protective dielectric shell 221 applied over the coating 220. In various embodiments, the shell 221 may be formed from epoxy and may be applied by dipping or similar. The disclosure is not limited in this respect.

[0029] If an extreme fault condition (e.g., an extreme overcurrent condition) occurs in the PTC device 200, the PTC element 212 may burn and produce a flame. The heat from the flame may cause the silicone in the coating 220 to burn and decompose. When the silicone decomposes, the filler material in the coating 220 may be exposed and may also burn due to the heat from the flame. When the filler material burns and decomposes, an endothermic chemical reaction occurs that absorbs heat and extinguishes the flame. Furthermore, by-products of the endothermic chemical reaction may produce water, which can further extinguish the flame. Thus, when a fault condition occurs in the PTC device 200, the filler material can interfere with or extinguish the flame produced by the combustion of the PTC element 212, thereby protecting surrounding components from damage that would normally occur if the flame were to persist.

[0030] Referring to Figure 4A, a cross-sectional side view of an exemplary embodiment of the fuse 300 according to the present disclosure is shown. In various embodiments, the fuse 300 may be a cartridge fuse having a tubular dielectric fuse body 312. The present disclosure is not limited thereto. In various alternative embodiments, the fuse 300 may be a surface-mount fuse or other types of fuses having a fusible element extending through a generally hollow fuse body. The fuse body 312 may be formed from an electrically insulating and preferably heat-resistant material. Examples of such materials include, but are not limited to, ceramics, glass, and glass fiber-filled melamine-formaldehyde resins.

[0031] First and second conductive end caps 315, 316 may be positioned at both ends of the fuse body 312 and may be adapted to facilitate the electrical connection of the fuse 310 in the circuit. A fusible element 324 may extend through the hollow interior of the fuse body 312 and may be connected by solder or the like to the first and second end caps 315, 316 with which it is electrically in communication. The first and second end caps 315, 316 may be formed from a conductive material including, but not limited to, copper or an alloy thereof, and may be plated with nickel or other conductive corrosion-resistant coatings. The fusible element 324 may be formed from a conductive material including, but not limited to, tin or copper, and may be configured to melt and separate when a predetermined fault condition occurs, such as an overcurrent condition in which a current exceeding a predefined maximum value flows through the fusible element 324. This maximum value is generally referred to as the "rating" of the fuse 300.

[0032] The fusible element 324 may be any type of fusible element suitable for the desired application, including but not limited to wires, corrugated strips, and wires wound around an insulating core. In various embodiments, the central portion 325 of the fusible element 324 may be narrower, narrower, perforated, or otherwise weakened relative to the other portions of the fusible element 324 to ensure that the fusible element 324 separates at the central portion 325. The disclosure is not limited in this respect.

[0033] Referring to Figure 4B, the fuse 300 may be provided with an arc-reducing flame-retardant coating 320 (hereinafter referred to as "coating 320") covering the fuse body 312. The coating 320 may be formed from a silicone composition formed from a filler material suspended in a silicone resin. In various embodiments, the filler material may include one or more of melamine, guanidine, guanine, hydantoin, allantoin, urea, melamine formaldehyde, melamine cyanurate polymer, boric acid, and derivatives or mixtures thereof, or other fillers that exhibit similar endothermic arc-extinguishing properties when burned, as described below. The filler material may be distributed substantially evenly throughout the silicone resin and may constitute 3 to 70% by weight of the silicone composition. The coating 320 may be applied to the underlying components of the fuse 300 using any suitable method, including but not limited to dipping, jetting, and molding. The disclosure is not limited in this respect. The fuse 300 may further include a protective dielectric shell 321 applied over the coating 320. In various embodiments, the shell 321 may be formed from epoxy and may be applied by jet, dispensing, or similar means. In various embodiments, the shell 321 may be omitted entirely. This disclosure is not limited in this respect.

[0034] When a fault condition (e.g., an overcurrent condition) occurs in the fuse 300, the central portion 325 of the fusible element 324 may melt and separate, and an electric arc may propagate across the gap remaining between the separated parts of the fusible element 324. In extreme cases, the electric arc may cause the fuse body 312 to burn and produce a flame. The heat from the flame may cause the silicone in the coating 320 to burn and decompose. When the silicone decomposes, the filler material in the coating 320 may be exposed and may also burn due to the heat from the flame. When the filler material burns and decomposes, an endothermic chemical reaction occurs that absorbs heat and extinguishes the flame. Furthermore, a byproduct of the endothermic chemical reaction may produce water, which can further extinguish the flame. Thus, when a fault condition occurs in the fuse 300, the filler material can obstruct or extinguish the flame produced by the burning of the fuse body 312, thereby protecting the surrounding components from damage that would normally occur if the flame were to persist.

[0035] When used herein, elements or stages described in the singular and beginning with the word "a" or "an" should be understood not to exclude multiple elements or stages unless such exclusion is expressly stated. Furthermore, references to "one embodiment" in this disclosure are not intended to be construed as excluding the existence of additional embodiments that also incorporate the described features.

[0036] While this disclosure refers to specific embodiments, many modifications, alterations, and changes can be made to the embodiments described without departing from the scope and realm of this disclosure as defined in the appended claims. Therefore, this disclosure is not limited to the embodiments described and is intended to have the entire scope defined by the following claims and their equivalents.

Claims

1. A metal oxide varistor (MOV) device, MOV chip; Conductive first and second electrodes positioned on both sides of the MOV chip; Conductive first and second leads connected to the first and second electrodes, respectively; and The MOV chip, the first and second electrodes, and a portion of the first and second leads are covered with an arc-reducing flame-retardant coating, the arc-reducing flame-retardant coating having a silicone composition formed from a filler material suspended in a silicone resin. A MOV device equipped with [a specific feature / feature].

2. The MOV device according to claim 1, wherein the filling material comprises one or more of melamine, guanidine, guanine, hydantoin, allantoin, urea, melamine formaldehyde, melamine cyanurate polymer, and boric acid.

3. The MOV device according to claim 1, wherein the filler material constitutes 3% to 70% by weight of the silicone composition.

4. The MOV device according to any one of claims 1 to 3, further comprising a protective dielectric shell applied on the arc-reducing flame-retardant coating.

5. The MOV device according to claim 4, wherein the protective dielectric shell is formed from epoxy.

6. A thermally protected metal oxide varistor (TMOV) device, MOV chip; Conductive first and second electrodes positioned on both sides of the MOV chip; A conductive first lead connected to the first electrode; A conductive second lead connected to a dielectric barrier placed on the second electrode; A thermal cutoff (TCO) element having a first end electrically connected to the second lead on the dielectric barrier and a second end electrically connected to the second electrode; and An arc-reducing flame-retardant coating covering the junction of the TCO element and the second electrode, the arc-reducing flame-retardant coating having a silicone composition formed from a filler material suspended in a silicone resin, A TMOV device equipped with the following features.

7. The TMOV device according to claim 6, wherein the TCO element is formed from a conductive material and is adapted to melt and separate when it reaches a predetermined temperature.

8. The TMOV device according to claim 6, wherein the filling material comprises one or more of melamine, guanidine, guanine, hydantoin, allantoin, urea, melamine formaldehyde, melamine cyanurate polymer, and boric acid.

9. The TMOV device according to any one of claims 6 to 8, wherein the filler material constitutes 3% to 70% by weight of the silicone composition.

10. A positive temperature coefficient (PTC) device, PTC element having conductive particles suspended in a non-conductive medium; Conductive first and second electrodes positioned on both sides of the PTC element; Conductive first and second leads connected to the first and second electrodes, respectively; and An arc-reducing flame-retardant coating covers the PTC element, the first and second electrodes, and a portion of the first and second leads, and the arc-reducing flame-retardant coating has a silicone composition formed from a filler material suspended in a silicone resin. A PTC device equipped with [a specific feature].

11. The PTC device according to claim 10, wherein the filling material comprises one or more of melamine, guanidine, guanine, hydantoin, allantoin, urea, melamine formaldehyde, melamine cyanurate polymer, and boric acid.

12. The PTC device according to claim 10, wherein the filling material constitutes 3% to 70% by weight of the silicone composition.

13. The PTC device according to any one of claims 10 to 12, further comprising a protective dielectric shell applied on the arc-reducing flame-retardant coating.

14. The PTC device according to claim 13, wherein the protective dielectric shell is formed from epoxy.

15. Dielectric fuse body; First and second conductive end caps positioned at both ends of the fuse body; A fusible element extending through the fuse body and electrically connected to the first and second conductive end caps; and The fuse body is covered with an arc-reducing flame-retardant coating, and the arc-reducing flame-retardant coating has a silicone composition formed from a filler material suspended in a silicone resin. A fuse equipped with this feature.

16. The fuse according to claim 15, wherein the filling material comprises one or more of melamine, guanidine, guanine, hydantoin, allantoin, urea, melamine formaldehyde, melamine cyanurate polymer, and boric acid.

17. The fuse according to claim 15, wherein the filling material constitutes 3% to 70% by weight of the silicone composition.

18. The fuse according to any one of claims 15 to 17, further comprising a protective dielectric shell applied on the arc-reducing flame-retardant coating.

19. The fuse according to claim 18, wherein the protective dielectric shell is formed from epoxy.

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