Zinc oxide varistor with aluminum electrode and preparation method thereof

Abstract

The invention discloses a zinc oxide pressure-sensitive resistor for aluminum electrodes and a preparation method thereof. The zinc oxide pressure-sensitive resistor comprises a ZnO ceramic matrix, electrodes and an electrode leading-out wire, wherein the ZnO ceramic matrix has a lamellar structure; the electrodes are arranged on the two surfaces of the ZnO ceramic matrix and are connected with the electrode leading-out wire; the electrodes are aluminum electrodes; electric interconnection between an electrode leading-out wire and an electrode application welding solder is realized by adoptingan ultrasonic assisted welding way; the welding solder is one or more of multi-element Sn-based alloys with added active ingredients Ti, Zr and V and rare earth elements. Compared with only adoptionof silver paste or copper paste or multilayered composite base metal electrodes, the zinc oxide pressure-sensitive resistor for the aluminum electrodes disclosed by the invention has the advantages that the preparation cost of the electrodes is greatly reduced, the zinc oxide pressure-sensitive resistor has more excellent electric performance, the production efficiency is higher, a production process is green and environmentally friendly, and a cleaning process is eliminated.

Description

Technical field [0001] The invention relates to an overvoltage protection semiconductor element, in particular to a zinc oxide varistor using low-cost Al to make aluminum electrodes and a preparation method thereof. Background technique [0002] Zinc oxide varistor is often used as a typical electronic ceramic component and widely used in various electronic circuits and power systems because of its excellent nonlinear characteristics and strong surge resistance. The preparation process of industrial varistor is as follows: production of varistor ZnO ceramic substrate → upper electrode → welding, encapsulation, curing → finished product inspection; surface metallization (upper electrode) is the production and manufacturing process of zinc oxide varistor Necessary link in the. At present, the process of screen printing silver paste is commonly used in the industry, and then the process of preparing silver electrode by high-temperature infiltration. The significant defect of this p...

AI Technical Summary

Problems solved by technology

Compared with the traditional screen-printed silver electrode, the disadvantages of this technology are: ①The cost reduction is very small, especially when it is produced in small batches, the average cost is even higher than the cost of the screen-printed silver electrode ZnO varistor; ②Process flow Complex, screen-printed copper paste electrodes need to maintain high purity N during sintering 2 atmosphere to prevent the oxidation of the copper paste during the sintering process; ③ same as the silk screen printing silver paste electrode process, there are also problems such as environmental pollution

[0008] Chinese invention patent application CN103247362A discloses a base metal composite electrode for electronic ceramic components and its preparation method; the application uses a thermal spraying process to prepare a composite base metal electrode layer, that is, a layer of aluminum electrode is sprayed on the ceramic substrate, and then the aluminum A layer of copper electrode is sprayed on the electrode as a welding layer. This technology can reduce the production cost of the electrode to a certain extent without reducing the electrical performance of the ZnO varistor, but there are still some obvious shortcomings: First, the application uses Multi-layer composite base metal electrode structure, that is, the first base metal electrode layer is prepared on the surface of the ceramic substrate as a transition layer. To realize the interconnection between electrodes and electrode lead-out wires, the method adopted in this application is to spray the second base metal copper electrode layer on the first base metal electrode layer as a solderable layer. However, this double-layer composite electrode structure will make the electrode preparation process It is more complicated, energy consumption is large, and production efficiency is low; secondly, the preparation process of the multi-layer composite base metal electrode layer mentioned in the application is prepared by flipping the sample on one side, that is, only one side of the ceramic substrate can be prepared at a time. Electrode preparation is carried out on the surface. In this way, the sample needs to be turned over 3 times to prepare two layers of base metal electrodes on both sides. This will inevitably greatly affect production efficiency and increase labor costs. Secondly, in order to realize the interconnection between the welding layer and the electrode lead-out wire To achieve high reliability, it is necessary to ensure that the second base metal copper electrode completely covers the area to be welded on the first base metal electrode layer. In actual production, the average thickness of the sprayed copper electrode layer must be controlled above 50um to ensure that the copper electrode layer can be completely Covering the aluminum electrodes, however, the use of this excessive copper electrode material makes the cost of the entire electrode preparation sharply increased. The calculation shows that if the technology shown in this application is used to prepare ZnO varistors with Al / Cu electrodes each 50um thick , then only from the perspective of material cost, the ratio of the cost of spraying Cu electrode layer to the cost of spraying Al electrode layer is 8:1

However, in the field of metal soldering, aluminum and its alloys have extremely poor solderability due to their dense oxide film on the surface. Currently, the existing low-temperature solders for welding aluminum and its alloys are mainly Sn-based flux-cored solder wires. And solder paste, there is a remarkable feature that the matching flux is very active

However, for the sprayed Al electrode, because it is melted at high temperature, sputtered, and deposited on the ZnO ceramic substrate, its oxidation degree is much higher than that of the aluminum plate, and the surface of the sprayed aluminum electrode is rougher and porous, so As a result, conventional aluminum solder is not suitable for welding sprayed aluminum electrodes. The main reason is: on the one hand, for the high oxidation problem of the aluminum electrode layer, the existing aluminum welding flux is not active enough, and the solder hardly wets on the aluminum electrode after melting. Wet; on the other hand, for the ZnO ceramic substrate, the activity of the existing aluminum welding flux is too high, which will damage the ceramic substrate during the welding process.

[0010] At present, the method of ultrasonic-assisted brazing of aluminum or aluminum alloy is applied to butt or lap welding between aluminum and aluminum, and aluminum or aluminum alloy is a conventional aluminum sheet or bar, and aluminum or aluminum alloy needs to be welded before welding. The surface is cleaned, and the brazing material is ordinary Sn-Zn-based solder, which has poor wettability, easy oxidation, and poor corrosion resistance. Ultrasonic brazing takes a long time and the joint strength after welding also lower issues

As for the ZnO varistor sprayed aluminum electrode, due to the rough structure and high oxidation rate of the aluminum electrode itself, it is difficult for the commonly used ultrasonic welding technology to effectively solve the welding problem between the sprayed aluminum electrode and the lead wire.

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