Surface insulation treatment method suitable for chip zinc oxide voltage-sensitive ceramic before electroplating

Abstract

The invention relates to a surface insulation treatment method suitable for chip zinc oxide voltage-sensitive ceramic before electroplating, and belongs to the technical field of special equipment or methods for manufacturing resistors. The surface insulation treatment method suitable for the chip type zinc oxide voltage-sensitive ceramic before electroplating comprises the following steps: soaking the zinc oxide voltage-sensitive ceramic in a surface treatment solution, taking out the zinc oxide voltage-sensitive ceramic, drying the zinc oxide voltage-sensitive ceramic, and performing heat treatment to obtain the chip type zinc oxide voltage-sensitive ceramic with a surface insulation layer, the surface treatment liquid comprises the following components: zinc oxide, zinc dihydrogen phosphate, sodium fluoride, bismuth nitrate, nitric acid and water. According to the treatment method, a uniform and firm insulating layer can be formed on the surface of the chip zinc oxide voltage-sensitive ceramic, and the problem of overplating of chip voltage-sensitive resistor electroplating can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of special equipment or methods for manufacturing resistors, and in particular to a surface insulation treatment method suitable for sheet-type zinc oxide varistor ceramics before electroplating. Background Art

[0002] Zinc oxide varistors feature high current density, strong voltage limiting capability, fast response speed, a wide operating voltage range, and strong energy absorption capacity. They are widely used in electronic devices for overvoltage protection, surge absorption, and voltage stabilization. Compared to plug-in zinc oxide varistors, multilayer zinc oxide varistors, with their small size and ease of automated assembly, meet the requirements for miniaturization, lightweighting, and large-scale automated production of electronic devices. However, the silver electrodes of multilayer zinc oxide varistors have poor solder resistance, necessitating electroplating of nickel and tin metals to improve solderability and resistance during surface mounting. Furthermore, because the ceramic body of multilayer zinc oxide varistors is a semiconductor, the nickel and tin metals easily deposit on the device surface during the electroplating process, resulting in a "creeping arc" phenomenon. This reduces the creeping arc distance between the two terminal electrodes and can even cause a short circuit, severely impacting the performance of the multilayer zinc oxide varistors. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] The present invention provides a method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating, which comprises the following steps:

[0006] The zinc oxide varistor ceramic is placed in a surface treatment solution for immersion treatment, taken out for drying treatment, and then heat treated to obtain a sheet-type zinc oxide varistor ceramic with a surface insulating layer;

[0007] The surface treatment liquid comprises the following components: zinc oxide, zinc dihydrogen phosphate, sodium fluoride, bismuth nitrate, nitric acid and water.

[0008] The present invention soaks the zinc oxide varistor ceramic in a surface treatment solution composed of zinc oxide, zinc dihydrogen phosphate, sodium fluoride, bismuth nitrate, nitric acid and water, so that a uniform, dense and firmly bonded insulating film layer is formed on the surface of the zinc oxide varistor during the soaking process. The insulating film layer can effectively prevent the metal Ni and metal Sn from being deposited on the surface of the zinc oxide varistor ceramic during the electroplating process to produce "creep plating", thereby improving the performance of the zinc oxide varistor.

[0009] Among them, the zinc ions and phosphate ions in the surface treatment liquid react on the surface of the zinc oxide varistor ceramic to form a phosphating film. Sodium fluoride can improve the uniformity of the phosphating film structure, and nitrate can accelerate the film formation speed of the surface treatment liquid. Nitric acid can not only prepare NO3 - / PO4 3- ratio, thereby controlling the film formation speed and providing the acidic environment required for the film formation reaction.

[0010] As a preferred embodiment of the surface insulation treatment method for sheet-type zinc oxide varistor ceramics before electroplating according to the present invention, the mass ratio of zinc oxide to zinc dihydrogen phosphate is (0.1-0.4): (1.5-4). Optionally, in parts by weight, the zinc oxide can be specifically 0.1 parts, 0.15 parts, 0.2 parts, 0.25 parts, 0.3 parts, 0.35 parts, 0.4 parts, or any two of the range values, and the zinc dihydrogen phosphate can be specifically 1.5 parts, 1.65 parts, 1.89 parts, 2 parts, 2.2 parts, 2.36 parts, 2.5 parts, 2.8 parts, 3 parts, 3.2 parts, 3.4 parts, 3.66 parts, or any two of the range values. By regulating the mass ratio of zinc oxide to zinc dihydrogen phosphate within the above range, the zinc ions and phosphate ions consumed by the treatment solution during the operation can be dynamically replenished, thereby better ensuring the stability of the treatment solution.

[0011] As a preferred embodiment of the surface insulation treatment method for sheet-type zinc oxide varistor ceramics before electroplating according to the present invention, the mass ratio of sodium fluoride to bismuth nitrate is (0.01-0.2):(0.2-1.2). Optionally, in parts by weight, the sodium fluoride can be specifically in the range of any one of 0.01 parts, 0.02 parts, 0.03 parts, 0.04 parts, 0.05 parts, 0.06 parts, 0.08 parts, 0.1 parts, 0.13 parts, 0.15 parts, 0.18 parts, and 0.2 parts, or any two of the range values, and the bismuth nitrate can be specifically in the range of any one of 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts, and 1.2 parts, or any two of the range values. By regulating the mass ratio of sodium fluoride to bismuth nitrate within the above range, good adhesion between the phosphate film and the ceramic substrate can be better ensured, and problems such as brittle cracking and easy peeling of the phosphate film can be prevented.

[0012] As a preferred embodiment of the surface insulation treatment method for sheet-type zinc oxide varistor ceramics before electroplating according to the present invention, the mass ratio of zinc dihydrogen phosphate, sodium fluoride and nitric acid is (1.5-4):(0.01-0.2):(0.1-0.5). Optionally, in parts by weight, the zinc dihydrogen phosphate can be any one of 1.5 parts, 1.65 parts, 1.89 parts, 2 parts, 2.2 parts, 2.36 parts, 2.5 parts, 2.8 parts, 3 parts, 3.2 parts, 3.4 parts, 3.66 parts, and 4 parts, or any two of the range values; the sodium fluoride can be any one of 0.01 parts, 0.02 parts, 0.03 parts, 0.04 parts, 0.05 parts, 0.06 parts, 0.08 parts, 0.1 parts, 0.13 parts, 0.15 parts, 0.18 parts, and 0.2 parts, or any two of the range values; the nitric acid can be any one of 0.1 parts, 0.15 parts, 0.2 parts, 0.25 parts, 0.3 parts, 0.35 parts, 0.4 parts, 0.45 parts, and 0.5 parts, or any two of the range values.

[0013] As a preferred embodiment of the surface insulation treatment method for zinc oxide varistor ceramics before electroplating according to the present invention, the pH value of the surface treatment solution is ≤ 5. Studies have found that the pH value of the surface treatment solution affects the solubility and reactivity of phosphates. When the pH value of the surface treatment solution is ≤ 5, it is more conducive to the surface treatment solution forming a uniform phosphate film on the surface of the zinc oxide varistor ceramic.

[0014] As a preferred embodiment of the surface insulation treatment method for sheet-type zinc oxide varistor ceramics before electroplating according to the present invention, the pH of the surface treatment solution is 1 to 5. For example, the pH of the surface treatment solution can be any one of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or any two of the ranges.

[0015] As a preferred embodiment of the surface insulation treatment method for sheet-type zinc oxide varistor ceramics before electroplating, the immersion treatment temperature is ≥40°C and the duration is ≥10 minutes. Research has found that the immersion treatment temperature and duration affect the speed, uniformity, and integrity of the phosphate film formed by the surface treatment liquid on the surface of the zinc oxide varistor ceramic. By regulating the immersion treatment temperature to ≥40°C and the duration to ≥10 minutes, not only can a suitable film formation speed be maintained and the generated grain size be smaller, but the integrity of the film formation is also improved.

[0016] As a preferred embodiment of the surface insulation treatment method for sheet-type zinc oxide varistor ceramics before electroplating according to the present invention, the immersion treatment temperature is 40 to 70° C. and the time is 10 to 40 minutes. For example, the immersion treatment temperature can be any one of 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., and 70° C., or any two of the range values, and the immersion treatment time can be any one of 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, and 40 minutes, or any two of the range values.

[0017] As a preferred embodiment of the surface insulation treatment method for zinc oxide varistor ceramics before electroplating according to the present invention, the drying treatment temperature is 80-130°C and the time is 20-30 minutes. The purpose of the drying treatment is to remove moisture from the surface of the zinc oxide varistor ceramics after the immersion treatment.

[0018] As a preferred embodiment of the present invention's method for pre-electroplating surface insulation treatment of sheet-type zinc oxide varistor ceramics, the heat treatment temperature range is 600-800°C, and the duration is 10-60 minutes. The specific temperature and duration are selected to ensure dense sintering of the phosphate film. By regulating the heat treatment temperature within this range, the bonding between the phosphate film and the zinc oxide varistor ceramic is improved, and the adhesion of the phosphate film to the surface of the zinc oxide varistor ceramic is enhanced to prevent the phosphate film from falling off. It also eliminates pores or defects in the phosphate film layer, thereby improving the structural density of the phosphate film and thereby enhancing the wear resistance and corrosion resistance of the phosphate film.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention soaks the zinc oxide varistor ceramic in a surface treatment solution composed of zinc oxide, zinc dihydrogen phosphate, sodium fluoride, bismuth nitrate, nitric acid and water, so that a uniform, dense and firmly bonded insulating film layer is formed on the surface of the zinc oxide varistor during the soaking process. The insulating film layer can effectively prevent the metal Ni and metal Sn from being deposited on the surface of the zinc oxide varistor ceramic during the electroplating process to produce "creep plating", thereby improving the performance of the zinc oxide varistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the process of the present invention for the surface insulation treatment method of sheet-type zinc oxide varistor ceramics before electroplating;

[0022] Figure 2 This is a photo of the zinc oxide varistor ceramic after electroplating in Example 1;

[0023] Figure 3 This is a photo of the zinc oxide varistor ceramic after electroplating in Example 2;

[0024] Figure 4 This is a photo of the zinc oxide varistor ceramic after electroplating in Example 3;

[0025] Figure 5 This is a photo of the zinc oxide varistor ceramic after electroplating in Example 4;

[0026] Figure 6 This is a photo of the zinc oxide varistor ceramic after electroplating in Example 5;

[0027] Figure 7 This is a photo of the zinc oxide varistor ceramic sheet after electroplating in Example 6;

[0028] Figure 8 This is a photo of the zinc oxide varistor ceramic after electroplating in Comparative Example 1;

[0029] Figure 9 This is a photo of the zinc oxide varistor ceramic after electroplating in Comparative Example 2;

[0030] Figure 10 This is a photo of the zinc oxide varistor ceramic after electroplating in Comparative Example 3;

[0031] Figure 11 This is a photo of the zinc oxide varistor ceramic after electroplating in Comparative Example 4;

[0032] Figure 12 This is a real picture of the zinc oxide varistor ceramic after electroplating in comparative example 5. DETAILED DESCRIPTION

[0033] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0034] Unless otherwise specified, other materials and reagents used in the examples can be obtained from commercial sources.

[0035] Example 1

[0036] A method for treating the surface of a sheet-type zinc oxide varistor ceramic before electroplating to provide insulation, comprising the following steps (e.g. Figure 1 shown):

[0037] S1. Prepare a surface treatment solution: add zinc oxide, zinc dihydrogen phosphate, sodium fluoride, and bismuth nitrate to deionized water in sequence and mix well. Then, add nitric acid to adjust the pH of the mixture to 2-3 to obtain a surface treatment solution. The mass ratio of zinc oxide, zinc dihydrogen phosphate, sodium fluoride, bismuth nitrate, and nitric acid is 0.2:1.89:0.06:1.18:0.31.

[0038] S2. Ultrasonic cleaning: soak the zinc oxide varistor ceramic in deionized water for 30 minutes.

[0039] S3, immersion treatment: placing the sheet-type zinc oxide varistor ceramic after ultrasonic treatment in S2 into the surface treatment solution obtained in S1, and immersing it at 55°C for 25 minutes;

[0040] S4, drying treatment: drying the zinc oxide varistor ceramic after the immersion treatment in S3 at 100°C for 25 minutes;

[0041] S5. Heat treatment: placing the sheet-type zinc oxide varistor ceramic after the drying treatment in S4 into a silver firing furnace, and heat treating it at 650° C. for 15 minutes to obtain a sheet-type zinc oxide varistor ceramic with a surface insulating layer.

[0042] Example 2 to Example 4

[0043] A method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating is the same as that of Example 1, except that the mass ratio of zinc oxide, zinc dihydrogen phosphate, sodium fluoride, bismuth nitrate and nitric acid in step S1 (preparing the surface treatment solution) is different from that in Example 1.

[0044] Example 5 to Example 6

[0045] A method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating is the same as Example 1 except that the pH of the surface treatment solution in step S1 (preparing the surface treatment solution), the temperature and time of the immersion treatment in step S3 (immersion treatment), and the temperature and time of the heat treatment in step S5 (heat treatment) are different from those in Example 1.

[0046] Comparative Examples 1 to 3

[0047] A method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating is the same as that of Example 1, except that the mass ratio of zinc oxide, zinc dihydrogen phosphate, sodium fluoride, bismuth nitrate and nitric acid in step S1 (preparing the surface treatment solution) is different from that in Example 1.

[0048] Comparative Example 4

[0049] A method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating, which is the same as Example 1 except that step S1 (preparing a surface treatment solution) is different from Example 1;

[0050] Step S1 is specifically as follows: zinc oxide, ammonium dihydrogen phosphate, sodium fluoride and bismuth nitrate are added to deionized water in sequence and mixed evenly, and then nitric acid is added to adjust the pH of the mixture to 2-3 to obtain a surface treatment solution; the mass ratio of zinc oxide, ammonium dihydrogen phosphate, sodium fluoride, bismuth nitrate and nitric acid is 0.2:1.89:0.06:1.18:0.31.

[0051] Comparative Example 5

[0052] A method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating, which is the same as Example 1 except that step S1 (preparing a surface treatment solution) is different from Example 1;

[0053] Step S1 is specifically as follows: zinc oxide, zinc sulfate, sodium fluoride and bismuth nitrate are added to deionized water in sequence and mixed evenly, and then nitric acid is added to adjust the pH of the mixture to 2-3 to obtain a surface treatment solution; the mass ratio of zinc oxide, zinc sulfate, sodium fluoride, bismuth nitrate and nitric acid is 0.2:1.89:0.06:1.18:0.31.

[0054] Table 1 Part of the reaction conditions in Examples 1 to 6 and Comparative Examples 1 to 3

[0055]

[0056] Performance Testing

[0057] The varistor voltage (V 1mA ), leakage current (I L ) and nonlinear coefficient (α), the test results are shown in Table 2.

[0058] The electroplating treatment includes the following steps: after cleaning and drying, the sheet zinc oxide varistor ceramics are placed in electroplating tanks (the electroplating solution is nickel plating solution and tin plating solution) for electroplating to obtain sheet zinc oxide varistor ceramics with nickel layer and tin layer at the product end.

[0059] Table 2 Performance test results of various embodiments and comparative examples

[0060]

[0061]

[0062] According to Table 1 and Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 and Figure 7 It can be seen that the electrodes at both ends of the chip-type zinc oxide varistor in Examples 1 to 6 are intact after electroplating, with no nickel metal or tin metal extending, and no creep plating phenomenon occurs in the middle part, indicating that the treatment method of the present invention can form a uniform and firm insulating layer on the surface of the chip-type zinc oxide varistor, which can effectively solve the problem of "creep plating" in the electroplating of chip-type varistors; at the same time, it can also be found that the electrical properties of the chip-type zinc oxide varistor before and after electroplating remain basically unchanged, indicating that the insulating layer formed on the surface of the chip-type zinc oxide varistor by the treatment method of the present invention has good corrosion resistance to the electroplating solution. In addition, according to Figure 8 、 Figure 9 、 Figure 10 、 Figure 11 and Figure 12 It can be seen that the surface treatment liquid plays a key role in the formation of the insulating layer on the surface of the chip zinc oxide varistor ceramic. Only when its components contain at least zinc oxide, zinc dihydrogen phosphate, sodium fluoride, bismuth nitrate and nitric acid at the same time can the problem of "creep plating" in the electroplating of chip varistors be effectively solved.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating, characterized in that: The following steps are involved: The zinc oxide varistor ceramic is placed in a surface treatment solution for immersion treatment, taken out for drying treatment, and then heat treated to obtain a sheet-type zinc oxide varistor ceramic with a surface insulating layer; The surface treatment liquid comprises the following components: zinc oxide, zinc dihydrogen phosphate, sodium fluoride, bismuth nitrate, nitric acid and water.

2. The method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating according to claim 1, characterized in that: The mass ratio of the zinc oxide to zinc dihydrogen phosphate is (0.1-0.4):(1.5-4).

3. The surface insulation treatment method for sheet-type zinc oxide varistor ceramics before electroplating according to claim 1, characterized in that: The mass ratio of the sodium fluoride to bismuth nitrate is (0.01-0.2):(0.2-1.2).

4. The method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating according to claim 1, characterized in that: The mass ratio of zinc dihydrogen phosphate, sodium fluoride and nitric acid is (1.5-4):(0.01-0.2):(0.1-0.5).

5. The surface insulation treatment method for sheet-type zinc oxide varistor ceramics before electroplating according to claim 1, characterized in that: The pH value of the surface treatment liquid is ≤5.

6. The method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating according to claim 5, characterized in that: The pH value of the surface treatment liquid is 1-5.

7. The method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating according to claim 1, characterized in that: The soaking treatment has a temperature of ≥40° C. and a time of ≥10 min.

8. The method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating according to claim 7, characterized in that: The soaking treatment is performed at a temperature of 40 to 70° C. and for a time of 10 to 40 minutes.

9. The method for surface insulation treatment of sheet-type zinc oxide varistor ceramics before electroplating according to claim 1, characterized in that: The drying process is performed at a temperature of 80 to 130° C. and for a time of 20 to 30 minutes.

10. The surface insulation treatment method for sheet-type zinc oxide varistor ceramics before electroplating according to claim 1, characterized in that: The heat treatment temperature is 600-800° C. and the time is 10-30 minutes.

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