JPH0142611B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved multilayer voltage nonlinear resistor (hereinafter referred to as a varistor). Nowadays, there is a strong desire for high-density packaging of electronic components, and varistors are no exception to this demand.Laminated varistors, which have a laminated internal structure that can be directly soldered to various circuit boards, are now available. Proposed. However, as a conventional multilayer varistor, there is one disclosed in Japanese Patent Publication No. 58-23921. That is, as shown in FIGS. 1 and 2, the device disclosed in the publication has a laminated structure of a plurality of internal electrodes 1 and a sintered body 2 mainly composed of ZnO, and the internal electrodes 1 have a laminated structure. It has a structure in which the sintered body 2 surrounds the parts other than the external electrode part 3. However, as shown in FIG. 3, the insulation between the external electrode parts 3 of the varistor with such a configuration is the grain boundary layer part of the sintered body 2, that is, the insulation layer 5 existing between the highly conductive crystals 4 of ZnO. In order to maintain the electric field, the electric field is concentrated on the insulating layer 5, resulting in low dielectric strength and discharge deterioration on the surface of the sintered body 2. Furthermore, moisture adheres to the insulating layer 5 during humidity resistance tests and surge tests, causing discharge deterioration. The problem is that the surface of the sintered body 2 changes in quality and the leakage current in the low current region increases rapidly, resulting in poor reliability. Further, the technique disclosed in the above-mentioned publication is a means of stacking and integrating a plurality of green sheets on which internal electrodes 1 are arranged, and then sintering them. In other words, the internal electrode 1 and the raw sheet are sintered at the same time, and among the components contained in the raw sheet, bismuth in particular is diffused into the internal electrode 1 as shown in FIG. 3, and most of the internal electrode 1 is Considering that this becomes the high resistance part 6 and changes the sintering state of the internal electrode 1, which is a major factor in increasing the resistance value, the amount of bismuth added is set to 0.05 mol% or less in terms of Bi ₂ O ₃ . It is. However, due to the small amount of bismuth added, voltage nonlinearity (α)
is small, and the limiting voltage ratio (V10A/V1mA)
This had the disadvantage that the varistor characteristics themselves deteriorated, such as an increase in . The present invention has been made in view of the above points, and by making one of the front and back sides of the internal electrode contact a composition that becomes an insulator after sintering, and the insulator being located in the outermost layer, The object of the present invention is to provide a multilayer voltage nonlinear resistor that has excellent characteristics such as voltage nonlinearity, limiting voltage ratio, moisture resistance, and surge resistance. The present invention will be explained below with reference to the drawings.
That is, as shown in FIGS. 5 and 6, in a structure in which a plurality of internal electrodes 11, a varistor composition sintered body 12, and an insulating composition sintered body 13 are laminated, either the front or back of the internal electrodes 11 is The varistor composition sintered body 12 and the insulating composition are in contact with the insulating composition sintered body 13, and the outermost layer is made of the insulating composition sintered body 13, and the inner electrode 11 is connected to the external lead-out electrode 14. Sintered body 1
The structure is surrounded by 3, and to explain an example of its manufacturing method, first, zinc oxide is the main component as a raw material that becomes a sintered body with varistor function after sintering, and bismuth oxide and bismuth oxide as additives. In addition, cobalt oxide, manganese oxide, nickel oxide, chromium oxide, magnesium oxide, lead oxide,
Add two or more of aluminum oxide, titanium oxide, antimony oxide, barium oxide, silicon oxide, boron oxide, etc., mix in a ball mill, dry and calcinate at 600-950℃, then crush and combine with an organic binder. Disperse in a solvent to form a slurry. Next, this is sintered to a uniform thickness of about 10 μm to 3 mm by a doctor blade method to form a green sheet having a varistor function. On the other hand, after sintering, the main ingredient is zinc oxide as a raw material that becomes an insulator, and one or more of the zinc oxide insulating components such as copper oxide, lithium oxide, potassium oxide, and silver oxide are added as additives and processed in a ball mill. After mixing and drying
It is calcined at 600 to 950°C, then crushed and dispersed in a solvent together with an organic binder to form a slurry. Next, this is done using the doctor blade method.
After uniform sintering, a green sheet having an insulating function with a thickness of about 10 μm to 500 μm is formed. After sintering, gold is applied to both the upper and lower surfaces of the raw sheet having a varistor function.
Internal electrodes are formed by screen printing to a predetermined size using a metal paste made of platinum, palladium, silver, rhodium, or an alloy of two or more of these, and the upper and lower surfaces have the insulation function after sintering. After stacking and crimping the raw sheets, they were cut to a specified size and sintered at 900 to 1200°C for 0.5 to 8 hours to bring out the internal electrodes. Silver electrodes were applied to both ends and baked at 450 to 850°C. It is something. According to the laminated varistor having the above structure, as shown in FIG. 7, the crystal grains 15 constituting the insulating composition sintered body 13 themselves are insulators, so the electric field is dispersed over the entire surface, resulting in insulation. There is no discharge deterioration on the surface of the composition sintered body 13, and an excellent insulating effect can be exhibited, and at the same time, reliability is not lost in moisture resistance and surge tests. Furthermore, even if enough bismuth is added to the varistor composition sintered body 12 to obtain excellent varistor properties, as shown in FIG.
3, the high resistance part 16 of the internal electrode 11 due to bismuth diffusion is only on one side, and the internal electrode 11
On the side of the insulating composition sintered body 13, there is no deterioration such as an increase in resistance value, and deterioration of the limiting voltage characteristics due to the series resistance due to deterioration of the internal electrodes 11 can be completely prevented. Furthermore, the deterioration of the internal electrode 11 can be prevented by using the insulating composition sintered body 13.
By being able to prevent this on the side, it is possible to add the amount of bismuth in the varistor composition sintered body 12 far beyond 0.05 mol% to 2 mol%,
Effects that cannot be obtained with conventional structures can be obtained. Next, the effects of the present invention will be explained using examples. Example 1 Pure water was added to the raw materials weighed according to the varistor composition ratio of ~ shown in Table 1, mixed in a ball mill for 24 hours, dried the moisture, and then calcined at 600 to 950°C for 2 hours.
It is further crushed, an organic binder, a dispersant, and a solvent are added to form a slurry, which is then sintered using the doctor blade method to form a raw sheet with a thickness of 500 μm. After sintering, the upper and lower cross sections of the internal electrodes are 5 x 5 mm. 3 raw sheets printed with internal electrode material made of platinum
Laminated and crimped, punched to 8 x 10 mm, heated to 900-1250℃
Table 1 shows the conventional example (B) in which the electrodes were sintered for 2 hours, a silver electrode was applied to the lead-out part of the internal electrode as an external lead-out electrode, and then baked at 650°C.
Add pure water to the raw material weighed according to the varistor composition ratio to form a varistor composition raw sheet in the same manner as in the conventional example, and separately from the raw sheet, add pure water to the raw material weighed according to the insulator composition ratio shown in Table 1. in a ball mill
After mixing for 24 hours and drying the water, it was calcined for 2 hours at 600 to 950℃, and then crushed and an organic binder, dispersant, and solvent were added to form a slurry, which was then made into a 50 μm thick insulating composition green sheet using the doctor blade method. The varistor composition raw sheet with internal electrode material made of platinum printed on both sides of the varistor composition raw sheet was laminated and crimped with insulating composition raw sheets on the upper and lower surfaces, punched into 8 x 10 mm, and sintered at 900 to 1250°C for 2 hours. Voltage nonlinearity (α) and limiting voltage ratio (V10A/
Tables 1 and 9 of the results comparing the characteristics of V1mA)
It became as shown in the figure and Fig. 10. For convenience, Figure 10 shows (α) with respect to the amount of bismuth added.
and (V10A/V1mA) characteristics.

[Table] As is clear from Table 1 and Figures 9 and 10, the conventional example (B) has the best (α) and (V10A/V1mA) characteristics when the amount of bismuth added is 0.05 mol%.
If the bismuth content exceeds 0.05 mol%, both properties tend to deteriorate, whereas in the case of the present invention (A), the (α) and (V10A/V1mA) characteristics become better when the amount of bismuth added exceeds 0.05 mol%. trend 2.0
We demonstrated that it is possible to prevent an increase in the resistance value of the internal electrodes by controlling the bismuth diffusion to the internal electrodes while ensuring that the amount of bismuth added is sufficient to obtain excellent varistor characteristics. did. Example 2 Next, Table 2 shows the results of implementing the present invention (A) when the varistor composition was the same and the insulation composition was varied. Note that the manufacturing conditions, shape, etc. of samples ~〓〓 are as described in the explanation of the present invention (A) in Example 1.

【table】

Claims (1)

[Scope of Claims] 1. In a structure in which a plurality of internal electrodes, a varistor composition sintered body, and an insulating composition sintered body are laminated, either the front or back of the internal electrode is connected to the insulating composition sintered body. The outermost layer is made of an insulating composition sintered body, and is surrounded by the varistor composition sintered body and the insulating composition sintered body except for the portion connected to the external lead-out electrode of the internal electrode. Characteristic multilayer voltage nonlinear resistor. 2. The varistor composition sintered body contains zinc oxide as a main component and additives such as bismuth oxide, cobalt oxide, manganese oxide, nickel oxide, chromium oxide, magnesium oxide, lead oxide, aluminum oxide, titanium oxide, antimony oxide, and other additives. 2. The multilayer voltage nonlinear resistor according to claim 1, wherein the multilayer voltage nonlinear resistor is made of a material to which several types of silver, barium oxide, silicon oxide, boron oxide, etc. are added. 3 The insulating composition sintered body contains zinc oxide as a main component,
The laminated voltage nonlinear device according to claim 1 or 2, characterized in that it contains one or more additives selected from copper oxide, lithium oxide, potassium oxide, silver oxide, etc. Resistor.