EP-4738396-A1 - ARC QUENCHING AND FLAME RETARDING COATING FOR ELECTRONIC DEVICES

EP4738396A1EP 4738396 A1EP4738396 A1EP 4738396A1EP-4738396-A1

Abstract

A metal oxide varistor (MOV) device including a MOV chip, electrically conductive first and second electrodes disposed on opposite sides of the MOV chip, electrically conductive first and second leads connected to the first and second electrodes, respectively, and an arc mitigating, flame retarding coating covering the MOV chip, the first and second electrodes, and portions of the first and second leads, the arc mitigating, flame retarding coating comprising a silicone composition formed of a filler material suspended in a silicone resin, wherein the filler material includes one or more of melamine, guanidine, guanine, hydantoin, allantoin, urea, melamine-formaldehyde, melamine-cyanurate polymer, and boric acid.

Inventors

CHEN, JIANHUA
TSANG, Chun-Kwan
DIETSCH, GORDON T.

Assignees

Littelfuse, Inc.

Dates

Publication Date: 20260506
Application Date: 20251024

Claims (15)

An arc mitigating, flame retarding coating covering for an electronic device, the coating comprising a silicone composition formed of a filler material suspended in a silicone resin.
The coating of claim 1, wherein the filler material includes one or more of melamine, guanidine, guanine, hydantoin, allantoin, urea, melamine-formaldehyde, melamine-cyanurate polymer, and boric acid.
The coating of claim 1 or 2, wherein the filler material comprises 3% to 70% by weight of the silicone composition.
The coating of any of the preceding claims, whereby on exposure to heat and flames, silicone in the composition decomposes, exposing the filler material in the coating, which in turn is burned and decomposes, whereby on decomposing the filler material undergoes an endothermic chemical reaction that absorbs heat and quells the flames.
An electronic device coated with an arc mitigating, flame retarding coating according to any of the preceding claims.
The electronic device according claim 5, being one of a metal oxide varistor (MOV), a thermally protected MOV (TMOV), a fuse, a positive temperature coefficient (PTC) fuse or a PTC heater.
The electronic device of claim 6 being a metal oxide varistor (MOV) device comprising: a MOV chip; electrically conductive first and second electrodes disposed on opposite sides of the MOV chip; and electrically conductive first and second leads connected to the first and second electrodes, respectively.
The electronic device of claim 6 being a thermally protected metal oxide varistor (TMOV) device comprising: a MOV chip; electrically conductive first and second electrodes disposed on opposite sides of the MOV chip; an electrically conductive first lead connected to the first electrode; an electrically conducive second lead connected to a dielectric barrier disposed on the second electrode; and 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; whereby the arc mitigating, flame retarding coating covers a juncture of the TCO element and the second electrode.
The electronic device of claim 6 being a positive temperature coefficient (PTC) device comprising: a PTC element comprising electrically conductive particles suspended in a non-conductive medium; electrically conductive first and second electrodes disposed on opposite sides of the PTC element; electrically conductive first and second leads connected to the first and second electrodes, respectively; whereby the arc mitigating, flame retarding coating covering the PTC element, the first and second electrodes, and portions of the first and second leads.
The PTC device of claim 9 being a heater or a fuse.
The electronic device of claim 6 being a fuse comprising a dielectric fuse body; first and second electrically conductive endcaps disposed on opposing ends of the fuse body; a fusible element extending through the fuse body and electrically connected to the first and second endcaps; whereby the arc mitigating, flame retarding coating covers the fuse body.
The electronic device of any of the preceding claims, further comprising a protective, dielectric shell applied over the arc mitigating, flame retarding coating.
The electronic device of claim 12, wherein the protective, dielectric shell is formed of epoxy.
Use of a coating according to any of the claims 1-4 for protecting an electronic device against arcing.
Process for providing an electronic device according claim 5, comprising the step of coating the device with a coating according to any of the claims 1-4.

Description

BACKGROUND Field The present disclosure relates generally to the field of electronic devices. More specifically, the present disclosure relates to an arc-quenching, flame-retarding silicone composition for coating electronic devices that are prone to electrical arcing and/or combustion when subjected to extreme fault conditions. Description of Related Art Various types of electronic devices may be prone to electrical arcing and/or combustion when subjected to overcurrent, overvoltage, or overtemperature conditions (collectively referred to herein as "fault conditions"). Such devices include metal oxide varistors (MOVs), thermally protected MOVs (TMOVs), fuses, positive temperature coefficient (PTC) devices (e.g., PTC fuses and PTC heaters), and the like. In the case of MOV and PTC devices, a fault condition may cause the MOV element or PTC element in the device to overheat and combust, damaging the device and potentially damaging surrounding components. In the case of fuses and TMOVs, a fault condition may cause the fusible element in the device to melt or otherwise separate to interrupt the flow of electrical current through the device. When the fusible element separates, it is sometimes possible for an electrical arc to propagate between the separated portions of the fusible element (e.g., through residual, vaporized particulate between the separated portions of the fusible element). If not extinguished, the electrical arc may allow significant follow-on currents to flow through the device, resulting in damage to connected components despite the physical opening of the fusible element. Moreover, heat generated by an electrical arc can burn and/or rupture the body of the device, potentially causing damage to surrounding components. It is therefore desirable to extinguish an electrical arc as quickly as possible to prevent or mitigate any damage to connected and surrounding components that might result therefrom. It is with respect to these and other considerations that the present improvements may be useful. SUMMARY This Summary is provided to introduce a selection of concepts in a simplified form further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is the summary intended as an aid in determining the scope of the claimed subject matter. The present disclosure relates to an arc mitigating, flame retarding coating covering for an electronic device, the coating comprising a silicone composition formed of a filler material suspended in a silicone resin. The filler material may include one or more of melamine, guanidine, guanine, hydantoin, allantoin, urea, melamine-formaldehyde, melamine-cyanurate polymer, and boric acid. The filler material may comprise 3% to 70% by weight of the silicone composition. On exposure to heat and flames, silicone in the composition decomposes, exposing the filler material in the coating, which in turn is burned and decomposes, whereby on decomposing the filler material undergoes an endothermic chemical reaction that absorbs heat and quells the flames. The present disclosure also relates to an electronic device coated with the arc mitigating, flame retarding coating according to any of the preceding claims. A metal oxide varistor (MOV) device in accordance with the present disclosure may include a MOV chip, electrically conductive first and second electrodes disposed on opposite sides of the MOV chip, electrically conductive first and second leads connected to the first and second electrodes, respectively, and an arc mitigating, flame retarding coating covering the MOV chip, the first and second electrodes, and portions of the first and second leads, the arc mitigating, flame retarding coating comprising a silicone composition formed of a filler material suspended in a silicone resin. A thermally protected metal oxide varistor (TMOV) in accordance with the present disclosure may include a MOV chip, electrically conductive first and second electrodes disposed on opposite sides of the MOV chip, an electrically conductive first lead connected to the first electrode, an electrically conducive second lead connected to a dielectric barrier disposed 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 mitigating, flame retarding coating covering a juncture of the TCO element and the second electrode, the arc mitigating, flame retarding coating comprising a silicone composition formed of a filler material suspended in a silicone resin. A positive temperature coefficient (PTC) device in accordance with the present disclosure may include a PTC element comprising electrically conductive particles suspended in a non-conductive medium, electrically conductive first and second electrodes disposed on opposite sides of the P