Protection device and metal oxide varistor device
By employing a multi-layer coating design with a soft inner layer and a hard outer layer on the MOV, the durability and VOC emission issues of high-temperature MOV coatings are solved, achieving reliability and low VOC emissions in high-temperature environments.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- DONGGUAN LITTELFUSE ELECTRONICS CO LTD
- Filing Date
- 2025-03-31
- Publication Date
- 2026-05-19
AI Technical Summary
Existing metal oxide varistors (MOV) coating materials have poor performance in humidity and temperature cycling tests in high-temperature applications, and the high solvent content of traditional materials leads to high VOC emissions.
It adopts a two-layer design, with an inner layer of soft low-VOC or VOC-free material such as RTV silicone rubber, and an outer layer of hard low-VOC material such as epoxy resin, silicone resin, nylon or liquid crystal polymer, forming a multi-layer coating to improve durability and prevent damage.
It achieved no damage in 1000 cycles of temperature and humidity testing and other environmental tests, reduced VOC emissions, and improved the mechanical strength and reliability of MOV.
Smart Images
Figure CN224263872U_ABST
Abstract
Description
Technical Field
[0001] This disclosure generally relates to protecting electrical and electronic circuits and equipment from power surges, and more specifically, to next-generation low-VOC, high-temperature coating solutions for MOVs and other radial chips. Background Technology
[0002] Overvoltage protection devices are used to protect electronic circuits and components from damage caused by overvoltage fault conditions. These overvoltage protection devices may include metal oxide varistors (MOVs) connected between the circuit to be protected and ground. MOVs have specific current-voltage characteristics, which allows them to be used to protect such circuits from catastrophic voltage surges. In particular, when a voltage greater than the nominal voltage or threshold voltage is applied to the device, current flows through the MOV, which generates heat. This causes the linking element to melt. Once the link melts, an open circuit is created, which prevents the MOV from catching fire.
[0003] MOVs include coatings to protect their internal components. Epoxy resin is a typical material. However, epoxy resins are limited to low-temperature applications (e.g., below 85 or 105°C) and have insufficient temperature cycling test (TCT) performance. Other materials used for high-temperature MOVs are silicone resins and phenolic resins. Although these coating materials have improved TCT performance, they involve high solvent content (e.g., about 32%) and therefore involve significant VOC emissions.
[0004] It is precisely about these and other shortcomings that the currently available information is provided. Utility Model Content
[0005] This utility model summary is provided to present a selection of concepts in a simplified form, which are further described in the detailed description below. This utility model summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to serve as an aid in determining the scope of the claimed subject matter.
[0006] In some embodiments, the protection device may include a varistor body and an inner layer surrounding the varistor body. The protection device may also include an outer layer above the inner layer, wherein the outer layer is more rigid than the inner layer.
[0007] In some embodiments, a metal oxide varistor (MOV) device may include a varistor body and an inner layer formed directly on a first main side and a second main side of the varistor body. The MOV may also include an outer layer formed directly on the inner layer, wherein the outer layer is more rigid than the inner layer.
[0008] In some embodiments, a method of coating a metal oxide varistor (MOV) device may include forming an inner layer directly on a first main side and a second main side of a varistor body, and then forming an outer layer directly on the inner layer, wherein the outer layer is harder than the inner layer. Attached Figure Description
[0009] The accompanying drawings illustrate exemplary aspects of the disclosed embodiments designed to date for practical applications of their principles, and wherein:
[0010] Figure 1A A top view of an MOV device according to an embodiment of the present disclosure is depicted;
[0011] Figure 1B Embodiments according to this disclosure are depicted. Figure 1A A cross-sectional view of the MOV;
[0012] Figure 2A A top view of an MOV device according to an embodiment of the present disclosure is depicted; and
[0013] Figure 2B Embodiments according to this disclosure are depicted. Figure 2A A cross-sectional view of the MOV.
[0014] The accompanying drawings are not necessarily to scale. The drawings are merely illustrative and not intended to depict specific parameters of this disclosure. The drawings are intended to depict typical embodiments of this disclosure and should therefore not be considered as limiting in scope. In the drawings, similar numbers denote similar elements.
[0015] Furthermore, for clarity, some elements in some figures may be omitted or not shown to scale. Cross-sectional views may be in the form of "slice" or "near-view" cross-sectional views, omitting certain background lines that would be visible in the "true" cross-sectional view for clarity. Additionally, for clarity, some reference numbers may be omitted in some figures. Detailed Implementation
[0016] The protective devices according to this disclosure will now be described more fully below with reference to the accompanying drawings, in which embodiments of the systems and methods are illustrated. However, the protective devices may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these examples are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the systems and methods to those skilled in the art.
[0017] As will be described herein, embodiments of this disclosure pertain to next-generation low-VOC, high-temperature coating solutions for MOVs and other radial chips. More specifically, this disclosure describes a “two-layer” design. The inner layer is flexible, which helps alleviate TCT thermal stress and enables two-layer coated devices to pass 1000 cycles of TCT testing without visual defects (e.g., coating cracks). Only a limited number of coating materials (such as silicone, phenolic resins, and silicone rubber) have passed 1000 cycles of TCT testing. Among these, silicone rubber is a suitable low-VOC or VOC-free option.
[0018] However, silicone rubber materials are inherently soft, which explains their effectiveness in stress relief. This softness has also been criticized when the material is used independently as a protective coating. Other materials can pass 1000-cycle TCT testing and other reliability tests, such as 8585 bias humidity, 125°C loading, and 150°C storage testing. For example, plastic materials such as liquid crystal polymers (LCPs) using injection molding processes can meet these standards. However, the very high cost of the materials and processes hinders their large-scale application in MOV products.
[0019] The outer layer, such as epoxy resin, possesses good mechanical strength and can withstand scratches, drops, and other mechanical shocks during transportation, assembly, and other processes. However, rigid outer layers (such as epoxy resin) typically exhibit poor performance in TCT and bias humidity tests, and therefore cannot be used alone for high-temperature materials. This is why a two-layer design is proposed in this disclosure. To meet long-term EHS objectives, low-VOC or VOC-free materials are preferred for both the inner and outer layers. Furthermore, the inner and outer layers should be appropriately designed and selected to match each other during the aforementioned critical environmental reliability tests and to prevent failure modes such as delamination.
[0020] Turn now Figures 1A to 1B The MOV device (hereinafter referred to as the "device") 100 according to embodiments of the present disclosure will be described in more detail. As shown, the device 100 may include a varistor body 102, which in this embodiment has a circular or disc-shaped shape. The varistor body 102 may include a first main side 104 opposite to a second main side 106. A first terminal is electrically connected to a thermal electrode along the first main side 104, while a second terminal is electrically connected to an electrode along the second main side 106.
[0021] The device 100 may further include an inner layer 110 surrounding the varistor body 102. More specifically, the inner layer 110 may be conformally formed on all sides of the varistor body 102, including directly over its first and second main sides 104, 106. In some embodiments, the inner layer 110 may be room temperature vulcanized (RTV) silicone rubber or one or more other soft UL-cured materials. The inner layer 110 may be solvent-free and may be considered low VOC, i.e., containing less than 50 grams of volatile organic compounds per liter. In alternative embodiments, the inner layer 110 may comprise multiple layers.
[0022] like Figures 2A to 2B As shown, the device 100 may further include an outer layer 116 surrounding the inner layer 110 and the varistor body 102. More specifically, the outer layer 116 may be directly conformally formed on all sides of the inner layer 110. In some embodiments, the outer layer 116 may be an epoxy resin, silicone resin, nylon, polyphenylene sulfide, or liquid crystal polymer. The outer layer 116 may be solvent-free and may be considered low-VOC. The outer layer 116 is more rigid than the inner layer 110.
[0023] In summary, the embodiments described herein provide a multilayer inner coating design comprising an outer coating over a multilayer inner coating. One or more inner layers are flexible and serve as stress-relieving layers, enabling the coating assembly to withstand 1000 cycles of TCT. A rigid outer layer is used to prevent damage to the flexible layers during transport, handling, and MOV assembly on the PCB. Both the inner and outer layer materials are low / VOC-free and contain no solvents. Furthermore, this novel coating design can pass critical environmental tests, such as bias humidity, loading, high-T storage, and TCT testing, without damage.
[0024] As used herein, elements or steps described in the singular and beginning with the word "a" or "an" should be understood to not exclude plural elements or steps unless such exclusion is explicitly stated. Furthermore, references to "one embodiment" in this disclosure are not intended to exclude the existence of additional embodiments that also include the described features.
[0025] The use of “including,” “containing,” or “having,” and variations thereof in this document means to encompass the items listed below and their equivalents, as well as additional items. Therefore, the terms “including,” “containing,” or “having,” and variations thereof are open-ended expressions and may be used interchangeably herein.
[0026] This disclosure is not limited in scope to the specific embodiments described herein. In fact, various other embodiments and modifications of this disclosure, besides those described herein, will be apparent to those skilled in the art from the foregoing description and drawings. Therefore, these other embodiments and modifications are intended to fall within the scope of this disclosure. Furthermore, this disclosure has been described herein in the context of specific implementations in specific environments for specific purposes. Those skilled in the art will recognize that its usefulness is not limited thereto, and that this disclosure can be advantageously practiced for any number of purposes in any number of environments. Therefore, the claims set forth below should be interpreted in accordance with the full breadth and spirit of this disclosure as described herein.
Claims
1. A protective device, characterized in that, include: Varistor body; The inner layer surrounding the varistor body; and An outer layer above the inner layer, wherein the outer layer is harder than the inner layer.
2. The protection device according to claim 1, characterized in that, The inner layer is made of solvent-free silicone rubber.
3. The protection device according to claim 1, characterized in that, The outer layer is made of one of the following materials: epoxy resin, silicone resin, nylon, polyphenylene sulfide, and liquid crystal polymer.
4. The protection device according to claim 1, characterized in that, The inner and outer layers contain less than 50 grams of volatile organic compounds per liter.
5. The protection device according to claim 1, characterized in that, The varistor body is a metal oxide varistor body.
6. A metal oxide varistor device, characterized in that, include: Varistor body; An inner layer formed directly on the first and second main sides of the varistor body; as well as An outer layer formed directly on top of the inner layer, wherein the outer layer is harder than the inner layer.
7. The metal oxide varistor device according to claim 6, characterized in that, The inner layer is made of solvent-free silicone rubber.
8. The metal oxide varistor device according to claim 6, characterized in that, The outer layer is made of one of the following materials: epoxy resin, silicone resin, nylon, polyphenylene sulfide, and liquid crystal polymer.
9. The metal oxide varistor device according to claim 6, characterized in that, The inner and outer layers contain less than 50 grams of volatile organic compounds per liter.