A method for preparing a surface glass insulating layer of a ZnO varistor

Abstract

This invention belongs to the field of inorganic functional ceramic materials, specifically relating to a method for preparing a glass insulating layer on the surface of a ZnO varistor. The technical solution employed in this invention includes three steps: first, protecting the silver electrode; second, chemically depositing glass powder onto the ZnO magnet; and finally, high-temperature calcination, allowing the glass powder to form a uniform glass insulating layer on the ZnO ceramic surface, while simultaneously decomposing the organic matter protecting the silver electrode. The resulting glass insulating layer only coats the ZnO ceramic surface and does not deposit on the Ag electrode surface, thus preserving the conductivity of the Ag electrode. This invention avoids the adsorption of polyelectrolytes on the silver end electrode and the deposition of glass powder in subsequent processes, ensuring that the glass insulating layer is deposited only on the ZnO ceramic body, reducing the steps required in traditional specialized equipment for removing the end electrode insulating layer. This method requires no special equipment, is low-cost, and highly efficient.

Description

Technical Field

[0001] This invention belongs to the field of inorganic functional ceramic materials, and particularly relates to the field of surface insulation treatment technology, specifically to a method for preparing a glass insulating layer on the surface of a ZnO varistor. Background Technology

[0002] ZnO varistors, as a nonlinear semiconductor material, are characterized by a nonlinear change in resistance as the external voltage increases, thus suppressing transient high voltages. Based on this characteristic, ZnO varistors are mainly used in the manufacture of zinc oxide surge arresters, overvoltage protection devices, surge protectors, and piezoelectric materials.

[0003] Multilayer ZnO varistors, as ceramic sensing elements, possess advantages such as high nonlinearity, fast response, large current and high energy handling capacity, and low limiting voltage. They serve functions such as overvoltage protection and surge absorption in circuits and are widely used in IC protection and CMOS and MOSFET device protection, covering industries such as communications, power, transportation, industrial control, automotive electronics, medical equipment, and home appliances, with a very broad development prospect.

[0004] For multilayer chip devices, the fabrication process typically involves first preparing a blank using tape casting or thick film methods, followed by sintering and silvering, and finally surface mounting. However, silver has poor solderability. To improve the solderability and solderability of multilayer chip devices during surface mounting, Ni and Sn plating layers are usually electroplated onto the silver electrodes. The main purpose of the Ni plating layer is to prevent Sn from penetrating through the Ag layer into the ceramic body of the varistor and damaging its electrical properties, acting as a bridge between the Ag and Sn layers (due to the poor adhesion between the Ag and Sn layers). Since the ceramic body of a ZnO varistor is a semiconductor, and the electric field strength is often high during chemical electroplating to improve plating efficiency, metal ions easily diffuse. Therefore, metallic Ni and Sn easily deposit on the device surface, causing a short circuit between the two terminals, making the resistor surface a conductor and rendering it unusable—a phenomenon known as "plating creep." To avoid plating creep, the ceramic body of the multilayer chip varistor coated with Ag terminal electrodes needs to be surface-insulated. After treatment, the ceramic body of the multilayer chip varistor is not only easier to electroplate, but its moisture resistance is also improved.

[0005] Currently, research on electroplating processes to overcome plating creep mainly focuses on three types: 1. Applying an organic insulating protective layer to the ceramic body surface, then removing the organic insulating layer from the terminal electrodes before electroplating. These processes require specialized equipment and have high operational requirements. Moreover, the coating of organic insulating material on the silver electrode can easily cause the device to disconnect and fail. During the electroplating process, the soft organic insulating layer is also easily damaged, leading to plating creep. 2. Using chemical treatment solutions to treat the resistor surface to generate a phosphate insulating protective layer. For example, placing a silver-fired ceramic body into a supersaturated solution of phosphoric acid can generate a zinc phosphate insulating layer on the surface. Since phosphoric acid does not react with the silver electrode, the insulating layer is only generated on the part outside the silver terminal electrode (i.e., the exposed ceramic body) (Chinese Patent CN1881486A). Chinese patent CN115101232 A discloses a chemical treatment solution with zinc dihydrogen phosphate, phosphoric acid, sodium molybdate, and surfactant as the main components, which forms an insulating layer on the surface of a varistor. The resulting insulating layer has good insulation properties, effectively preventing "plating creep," and the electrical performance of the varistor element before and after treatment changes little, making it suitable for practical production. Currently, there are few reports on zinc phosphate insulating layers, and their industrial use is still limited. A potential drawback is that the resistor must be placed in an acidic plating solution during electroplating, and the zinc phosphate coating formed by most chemical treatments corrodes quickly in the plating solution, failing to effectively protect against plating creep. A more mature industrial process involves embedding the resistor in glass powder and co-firing it to form an insulating layer. This method utilizes the principle of high-insulation layer formation through the reaction between the main components of the glass powder and the main components of the ceramic body of the chip varistor at high temperatures, forming a robust and reliable insulating layer that suppresses plating creep. This process has a good resist plating effect, but the process steps are complicated. It also requires special instruments and equipment to remove the insulating layer on the end electrode, which increases the number of process steps and the weight of the end electrode paste, thus increasing the cost.

[0006] For the glass insulation of varistors, it is of great significance to develop a simple, low-cost, and efficient method for preparing the insulating layer. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to provide a method for preparing a glass insulating layer on the surface of a ZnO varistor.

[0008] The technical solution adopted in this invention is specifically described as follows:

[0009] A method for preparing a glass insulating layer on the surface of a ZnO varistor, characterized by comprising the following steps:

[0010] (1) Immerse the multilayer ZnO varistor in organic thiol for 5-300 min and then take it out. Then immerse it in the activation solution and then immerse it in amino coupling reagent.

[0011] (2) Immerse the multilayer ZnO varistor obtained in step (1) in a glass powder suspension so that the glass powder is deposited on the surface of the resistor by electrostatic action. Take it out, wash it, and then immerse it in a positive electrolyte solution. Repeat this step at least once.

[0012] (3) The layered ZnO varistor obtained in step (2) is subjected to heat treatment at 500℃~700℃ for 30~300min to obtain a multilayered ZnO varistor with a glass insulating layer on its surface.

[0013] Preferably, the organothiol in step (1) is a long-chain thiol with the molecular formula CH3(CH2). n SH, n = 5 to 21; the concentration of the organothiol is 1 mmol / L to 0.1 mol / L, and the soaking time is 10 to 30 min.

[0014] Preferably, the long-chain thiol is one or more of dodecyl mercaptan, hexadecyl mercaptan, hexamethylene mercaptan, eicosethiol, and decyl mercaptan.

[0015] Preferably, the activation solution in step (1) is one or more of phosphoric acid, phosphate, oxalic acid, oxalate, acetic acid, and acetate, with a concentration of 5 mmol / L to 0.1 mol / L and a soaking time of 5 to 60 min.

[0016] Preferably, the solute of the amino coupling reagent in step (1) is one or more of aminopropyltrimethoxysilane, aminopropyltriethoxysilane, triethanolamine, monoethanolamine, and diethanolamine, and the solvent is water or alcohol; the concentration of the amino coupling reagent is 1 mmol / L to 0.05 mol / L, and the soaking time is 10 to 240 min.

[0017] Preferably, the concentration of the glass powder suspension in step (2) is 0.05 mg / mL to 1 mg / mL, and the soaking time is 5 to 200 min; the glass powder comprises one or more of Al2O3, SiO2, CaO, ZnO, TiO2, and K2O.

[0018] Preferably, the glass powder has a particle size of 1-3 μm. After mixing the glass powder with water, the glass powder is subjected to ultrasonic treatment for 10-60 minutes to fully disperse the glass powder, thus obtaining a glass powder suspension.

[0019] Preferably, the positive electrolyte solution in step (2) is an aqueous solution of one or more of polyethyleneimine, polyacrylamide, polyallyl ammonium chloride, and polyethyleneamine; the concentration of the positive electrolyte solution is 0.01 mg / mL to 0.5 mg / mL, and the soaking time is 5 to 200 min.

[0020] Preferably, the heat treatment temperature in step (3) is 600-680℃ and the heat treatment time is 10-40 min.

[0021] Preferably, the glass insulating layer covers only the ZnO varistor magnet portion and not the terminal Ag electrode; the thickness of the glass insulating layer is 1–10 μm.

[0022] The technical solution adopted in this invention includes three steps: first, protecting the silver electrode; second, chemically depositing glass powder on the ZnO magnet; and finally, high-temperature calcination, which allows the glass powder to form a uniform glass insulating layer on the ZnO ceramic surface, while simultaneously decomposing the organic matter protecting the silver electrode. The resulting glass insulating layer only coats the ZnO ceramic surface and does not deposit on the Ag electrode surface, thus the conductivity of the Ag electrode remains unaffected.

[0023] Step 1: The silver electrode is protected using a self-assembly method. Utilizing the specific adsorption of organothiol molecules onto Ag, a self-assembled monolayer film is formed on the Ag electrode surface, thus transforming the Ag electrode from hydrophilic to hydrophobic. This hydrophobic organic self-assembled film forms a protective layer on the Ag electrode, preventing the deposition of glass powder on the Ag electrode during subsequent liquid-phase chemical deposition.

[0024] Step 2: The deposition of glass powder on the ZnO ceramic body employs a liquid-phase layer-by-layer assembly method. First, a positively charged layer is constructed on the ZnO ceramic body. Utilizing the negatively charged nature of the glass powder, it is deposited onto the ZnO ceramic surface through electrostatic adsorption. This process can be repeated multiple times, thereby adjusting the amount of deposited glass powder, i.e., adjusting the thickness of the glass layer.

[0025] Step 3: High-temperature heat treatment. The treatment temperature is selected between the softening point of the glass powder and the melting point of the Ag electrode. After high-temperature treatment, the glass powder fuses into a film, forming a uniform and dense glass layer, while the bonding between the glass and ZnO is enhanced. In addition, the organic molecules protecting the Ag electrode decompose at high temperature, ensuring that the conductivity of the Ag electrode is not affected.

[0026] Compared with the prior art, the advanced technical effects of this invention are as follows:

[0027] (1) The present invention provides a method for preparing a glass insulating layer. By alternatingly depositing negatively charged glass powder and positively charged layers, the thickness of the insulating layer can be controlled, effectively avoiding the occurrence of "climbing" phenomenon.

[0028] (2) This invention uses organic thiol molecules to protect the silver end electrode. These protective molecules specifically adsorb onto the Ag end electrode, causing the Ag electrode to change from hydrophilic to hydrophobic. This avoids the adsorption of polyelectrolytes on the silver end electrode and the deposition of glass powder in subsequent processes, ensuring that the glass insulating layer is deposited only on the ZnO ceramic body, reducing the number of steps required for removing the end electrode insulating layer using traditional specialized equipment. This method does not require special equipment, is low in cost, and is highly efficient. Attached Figure Description

[0029] Figure 1(a) is a SEM image of the ZnO varistor with a glass insulating layer on its surface in Example 1 before heat treatment; Figure 1(b) is a SEM image of the ZnO varistor with a glass insulating layer on its surface in Example 1 after heat treatment; Figure 1(c) is a side SEM image of the ZnO varistor with a glass insulating layer on its surface in Example 1.

[0030] Figure 2 This is a side SEM image of the ZnO varistor with a glass insulating layer on its surface in Example 2.

[0031] Figure 3 (a) is an optical photograph of the comparative example after electroplating treatment; Figure 3 (b) is an optical photograph of Example 1 after electroplating treatment. Detailed Implementation

[0032] To better understand the present invention, the embodiments of the present invention will be described in detail below with reference to the examples. The examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0033] Example 1

[0034] 1) The multilayer ZnO varistor was immersed in anhydrous ethanol and ultrasonically cleaned for 5 min. After air drying, it was immersed in a 10 mmol / L dodecanethiol solution for 10 min. After cleaning and drying, it was immersed in a 0.01 mol / L phosphoric acid solution for 30 min for acidification. Finally, it was immersed in a 0.01 mol / L aminopropyltriethoxysilanol solution for 30 min to obtain a positively electroplated multilayer ZnO varistor.

[0035] 2) Prepare a 0.5 mg / ml glass powder negative electrolyte solution and sonicate for 10 min to fully disperse the glass powder. Immerse the multilayer ZnO varistor with positively charged surface obtained in 1) into the negative electrolyte solution for 30 min, remove it, and wash it 5 times with deionized water to obtain the first matrix material. Immerse the first matrix material in a 0.3 mg / ml polyacrylamide positive electrolyte solution for 30 min. The first self-assembled layer of glass insulation on the surface of the varistor is completed. Repeat the above operation 3 times to obtain a glass powder layer-by-layer self-assembled ZnO varistor. After removing and drying the varistor, place it in a muffle furnace and heat-treat it at about 600℃~680℃ for 10 min~30 min. This forms an insulating layer with a thickness of about 3 μm on the surface of the multilayer ZnO varistor, resulting in a multilayer ZnO varistor with an insulating layer on its surface.

[0036] Example 2

[0037] 1) The multilayer ZnO varistor was immersed in anhydrous ethanol and ultrasonically cleaned for 5 min. After air drying, it was immersed in a 10 mmol / L dodecanethiol solution for 10 min. After cleaning and drying, it was immersed in a 0.01 mol / L phosphoric acid solution for 30 min for acidification. Finally, it was immersed in a 0.01 mol / L aminopropyltriethoxysilanol solution for 30 min to obtain a positively electroplated multilayer ZnO varistor.

[0038] 2) Prepare a 1 mg / ml glass powder negative electrolyte solution and sonicate for 10 min to fully disperse the glass powder. Immerse the multilayer ZnO varistor with positively charged surface obtained in 1) into the negative electrolyte solution for 30 min, remove it, and wash it 5 times with deionized water to obtain the first matrix material. Immerse the first matrix material in a 0.5 mg / ml polyacrylamide positive electrolyte solution for 30 min. The first self-assembled layer of glass insulation on the surface of the varistor is completed. Repeat the above operation 5 times to obtain a glass powder layer-by-layer self-assembled ZnO varistor. After removing and drying the varistor, place it in a muffle furnace and heat-treat it at about 600℃~660℃ for 10 min~30 min. This forms an insulating layer with a thickness of about 5 μm on the surface of the multilayer ZnO varistor, resulting in a multilayer ZnO varistor with an insulating layer on its surface.

[0039] Example 3

[0040] 1) The multilayer ZnO varistor was immersed in anhydrous ethanol and ultrasonically cleaned for 5 min. After air drying, it was immersed in a 10 mmol / L hexadecyl mercaptan solution for 10 min. After cleaning and drying, it was immersed in a 0.01 mol / L phosphoric acid solution for 30 min for acidification. Finally, it was immersed in a 0.01 mol / L triethanolamine solution for 30 min to obtain a positively charged multilayer ZnO varistor.

[0041] 2) Prepare a 0.5 mg / ml glass powder negative electrolyte solution and sonicate for 10 min to fully disperse the glass powder. Immerse the multilayer ZnO varistor with positively charged surface obtained in 1) into the negative electrolyte solution for 30 min, remove it, and wash it 5 times with deionized water to obtain the first matrix material. Immerse the first matrix material in a 0.5 mg / ml polyethyleneimine positive electrolyte solution for 30 min. The first self-assembled layer of glass insulation on the surface of the varistor is completed. Repeat the above operation 10 times to obtain a glass powder layer-by-layer self-assembled ZnO varistor. After removing and drying the varistor, place it in a muffle furnace and heat-treat it at about 650℃~680℃ for 30 min. This forms an insulating layer with a thickness of about 10 μm on the surface of the multilayer ZnO varistor, resulting in a multilayer ZnO varistor with an insulating layer on its surface.

[0042] Example 4

[0043] 1) The multilayer ZnO varistor was immersed in anhydrous ethanol and ultrasonically cleaned for 5 min. After air drying, it was immersed in a 10 mmol / L hexamethylenetetramine solution for 20 min. After cleaning and drying, it was immersed in a 0.02 mol / L oxalic acid solution for 10 min for acidification. Finally, it was immersed in a 0.03 mol / L monoethanolamine solution for 60 min to obtain a positively charged multilayer ZnO varistor.

[0044] 2) Prepare a 1 mg / ml glass powder negative electrolyte solution and sonicate it for 30 min to fully disperse the glass powder. Immerse the multilayer ZnO varistor with positively charged surface obtained in 1) in the negative electrolyte solution for 1 hour. Remove it and wash it 5 times with deionized water to obtain the first matrix material. Immerse the first matrix material in a 0.3 mg / ml polyallyl ammonium chloride positive electrolyte solution for 1 hour. The first self-assembled layer of glass insulation on the surface of the varistor is completed. Repeat the above operation 3 times to obtain a glass powder layer-by-layer self-assembled ZnO varistor. After removing and drying the varistor, place it in a muffle furnace and heat-treat it at about 600℃~650℃ for 30 min. This forms an insulating layer with a thickness of about 3 μm on the surface of the multilayer ZnO varistor, resulting in a multilayer ZnO varistor with an insulating layer on its surface.

[0045] Example 5

[0046] 1) The multilayer ZnO varistor was immersed in anhydrous ethanol and ultrasonically cleaned for 5 min. After air drying, it was immersed in a 10 mmol / L eicosyl mercaptan solution for 30 min. After cleaning and drying, it was immersed in a 0.02 mol / L acetic acid solution for 5 min for acidification. Finally, it was immersed in a 0.03 mol / L diethanolamine solution for 40 min to obtain a multilayer ZnO varistor with positive surface electrostatics.

[0047] 2) Prepare a 0.6 mg / ml glass powder negative electrolyte solution and sonicate it for 30 min to fully disperse the glass powder. Immerse the multilayer ZnO varistor with positively charged surface obtained in 1) into the negative electrolyte solution for 40 min, remove it, and wash it 5 times with deionized water to obtain the first matrix material. Immerse the first matrix material in a 0.3 mg / ml polyethyleneimine positive electrolyte solution for 40 min. The first self-assembled layer of glass insulation on the surface of the varistor is completed. Repeat the above operation 4 times to obtain a glass powder layer-by-layer self-assembled ZnO varistor. After removing and drying the varistor, place it in a muffle furnace and heat-treat it at about 600℃~660℃ for 40 min. This forms an insulating layer with a thickness of about 5 μm on the surface of the multilayer ZnO varistor, resulting in a multilayer ZnO varistor with an insulating layer on its surface.

[0048] Example 6

[0049] 1) The multilayer ZnO varistor was immersed in anhydrous ethanol and ultrasonically cleaned for 5 min. After air drying, it was immersed in a 10 mmol / L eicosyl mercaptan solution for 30 min. After cleaning and drying, it was immersed in a 0.02 mol / L acetic acid solution for 5 min for acidification. Finally, it was immersed in a 0.03 mol / L diethanolamine solution for 40 min to obtain a multilayer ZnO varistor with positive surface electrostatics.

[0050] 2) Prepare a 0.6 mg / ml glass powder negative electrolyte solution and sonicate it for 30 min to fully disperse the glass powder. Immerse the multilayer ZnO varistor with positively charged surface obtained in 1) into the negative electrolyte solution for 40 min, remove it, and wash it 5 times with deionized water to obtain the first matrix material. Immerse the first matrix material in a 0.3 mg / ml polyethyleneimine positive electrolyte solution for 40 min. The first self-assembled layer of glass insulation on the surface of the varistor is completed. Repeat the above operation twice to obtain a glass powder layer-by-layer self-assembled ZnO varistor. After removing and drying the varistor, place it in a muffle furnace and heat-treat it at about 600℃~660℃ for 40 min. This forms an insulating layer with a thickness of about 3 μm on the surface of the multilayer ZnO varistor, resulting in a multilayer ZnO varistor with an insulating layer on its surface.

[0051] Example 7

[0052] 1) The multilayer ZnO varistor was immersed in anhydrous ethanol and ultrasonically cleaned for 5 min. After air drying, it was immersed in a 10 mmol / L decyl mercaptan solution for 10 min. After cleaning and drying, it was immersed in a 0.02 mol / L phosphoric acid solution for 60 min for acidification. Finally, it was immersed in a 0.03 mol / L monoethanolamine solution for 20 min to obtain a positively charged multilayer ZnO varistor.

[0053] 2) Prepare a 0.6 mg / ml glass powder negative electrolyte solution and sonicate it for 30 min to fully disperse the glass powder. Immerse the multilayer ZnO varistor with positively charged surface obtained in 1) into the negative electrolyte solution for 40 min, remove it, and wash it 5 times with deionized water to obtain the first matrix material. Immerse the first matrix material in a 0.3 mg / ml polyethyleneamine positive electrolyte solution for 40 min to complete the first self-assembled layer of glass insulation on the surface of the varistor. Repeat the above operation 5 times to obtain a glass powder layer-by-layer self-assembled ZnO varistor. After removing and drying the varistor, place it in a muffle furnace and heat-treat it at about 600℃~660℃ for 30 min. This forms an insulating layer with a thickness of about 5 μm on the surface of the multilayer ZnO varistor, resulting in a multilayer ZnO varistor with an insulating layer on its surface.

[0054] Comparative Example

[0055] Multilayer chip ZnO varistor (same as Example 1, except that the surface is not glass-insulated).

[0056] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a surface glass insulating layer of a ZnO varistor, characterized by, Includes the following steps: (1) Immerse the multilayer ZnO varistor in organic thiol for 5-300 min, then remove it, immerse it in activation solution, and then immerse it in amino coupling reagent. (2) Immerse the multilayer ZnO varistor obtained in step (1) in a glass powder suspension so that the glass powder is deposited on the surface of the resistor by electrostatic action. Take it out, wash it, and then immerse it in a positive electrolyte solution. Repeat this step at least once. (3) The multilayer chip ZnO varistor obtained in step (2) is subjected to heat treatment at 500℃~700℃ for 30~300min to obtain a multilayer chip ZnO varistor with a glass insulating layer on the surface. Step (1) the organic mercaptan is long-chain mercaptan, molecular formula is CH3(CH2) n SH, n = 5 ~ 21; The activation solution in step (1) is one or more of phosphoric acid, phosphate, oxalic acid, oxalate, acetic acid, and acetate. The solute of the amino coupling reagent in step (1) is one or more of aminopropyltrimethoxysilane, aminopropyltriethoxysilane, triethanolamine, monoethanolamine, and diethanolamine, and the solvent is water or alcohol. The glass insulating layer only covers the ceramic body of the ZnO varistor, and does not cover the terminal Ag electrode; The positive electrolyte solution in step (2) is an aqueous solution of one or more of polyethyleneimine, polyacrylamide, polyallyl ammonium chloride, and polyethyleneamine.

2. The method according to claim 1, characterized in that, The concentration of the organic thiol in step (1) is 1 mmol / L to 0.1 mol / L, and the soaking time is 10 to 30 min.

3. The method according to claim 2, characterized in that, The long-chain thiols are one or more of dodecyl mercaptan, hexadecyl mercaptan, hexamethylene mercaptan, eicosyl mercaptan, and decyl mercaptan.

4. The method according to claim 1, characterized in that, The concentration of the activation solution in step (1) is 5 mmol / L to 0.1 mol / L, and the soaking time is 5 to 60 min.

5. The method according to claim 1, characterized in that, The concentration of the amino coupling reagent in step (1) is 1 mmol / L to 0.05 mol / L, and the soaking time is 10 to 240 min.

6. The method according to claim 1, characterized in that, The concentration of the glass powder suspension in step (2) is 0.05 mg / mL to 1 mg / mL, and the soaking time is 5 to 200 min; the glass powder comprises one or more of Al2O3, SiO2, CaO, ZnO, TiO2, and K2O.

7. The method according to claim 6, characterized in that, The glass powder has a particle size of 1~3μm. After mixing the glass powder with water, it is subjected to ultrasonic treatment for 10~60min to fully disperse the glass powder, thus obtaining a glass powder suspension.

8. The method according to claim 1, characterized in that, The concentration of the positive electrolyte solution in step (2) is 0.01 mg / mL to 0.5 mg / mL, and the soaking time is 5 to 200 min.

9. The method according to claim 1, characterized in that, The thickness of the glass insulating layer is 1~10μm.

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