JPS6236604B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a non-linear resistor, particularly a weir layer type voltage non-linear resistor suitable for use in a low voltage region (approximately 3 to 15 V). Voltage nonlinear resistors have traditionally been used as semiconductor elements for overvoltage protection, and SiC varistors have been put into practical use as one of them. The voltage-current characteristic is approximately I=
It is expressed as KV〓. Here, K is a constant determined by the type of material of the varistor, and α is called a nonlinear coefficient, and the larger the value of α, the better the varistor. A SiC varistor is made by baking SiC particles with a ceramic binder, and its structure uses the non-linear characteristics of the contact between particles, with SiC particles connected in series and parallel. Conventionally, SiC varistors have been used in relatively high voltage ranges, but in recent years, with the development of electronic equipment, there has been an increasing demand for SiC varistors that can be used in low voltage ranges. However, as described above, SiC varistors have a structure in which SiC particles are connected in series and parallel between electrodes, so in order to manufacture low voltage (low resistance) products, the thickness must be reduced.
However, if the thickness is made thinner, the number of particle contacts in series decreases, which increases the voltage applied to the particle contact surface, which poses a problem in terms of stability. Additionally, since SiC varistors are porous, they have problems such as weakening their strength when made thinner. In order to solve these problems, methods have been used in which a conductive substance such as carbon is added to the ceramic binder, or the ceramic is buried in carbon and then fired. However, although the SiC varistor obtained by this method does have a low resistance, its voltage-current characteristics are close to those of a linear resistor (α = 1), and its nonlinear coefficient α is small, so it is susceptible to overvoltage. The suppressing effect was small and the performance was insufficient. In addition, it is relatively easy to obtain characteristics in the low voltage range with diodes that use silicon or germanium, but unlike ceramics, it is difficult to manufacture products in various shapes, and they are expensive. It had the disadvantage of becoming obsolete, and there were naturally limits to its uses. Furthermore, there are low-voltage varistors that use titanium oxide or barium titanate semiconductor ceramic as a substrate and utilize the contact between the substrate and the electrodes. In such a varistor, a weir layer is formed between the semiconductor ceramic substrate and the electrode by forming a non-ohmic electrode as an electrode on the surface of the substrate, and this weir layer is utilized as a varistor characteristic. However, since this weir layer is a very thin layer, it has the disadvantage that if a lead wire is soldered to the electrode surface, the weir layer is destroyed and the varistor characteristics are significantly deteriorated. The present invention is intended to eliminate the above-mentioned drawbacks, and its purpose is to be suitable for use in a low voltage region (approximately 3 to 15 V), and to form an electrode between an electrode and a sintered body. It is an object of the present invention to provide a method for manufacturing a voltage nonlinear resistor that utilizes an electrical barrier and has excellent soldering resistance and pulse resistance. In other words, in order to obtain a non-linear resistor that utilizes an electrical barrier formed between electrodes and a sintered body, detailed experiments were conducted on the composition of the sintered body and the composition of the paste material applied to the surface of the body. As a result, the varistor voltage is mainly determined by the specific resistance of the element, and the solder resistance is influenced by the composition of the paste material applied to the element surface, and the pulse resistance is determined by the composition of the paste material applied to the element surface. It has become clear that this is influenced by the components contained in the sintered body. In other words, in order to obtain the desired low-voltage nonlinear resistor, the specific resistance of the sintered body must be 200Ω-cm.
For this reason, it is necessary to produce a sintered body that has low resistance and ohmic characteristics without creating an insulating phase that becomes highly resistive in the sintered body. Zinc oxide is a material that satisfies this condition.
The base composition is magnesium oxide and stannic oxide,
It has become clear that a material to which antimony oxide and niobium oxide are added as additives is extremely effective. In addition, silver powder,
It has been found that a composition consisting of copper oxide, bismuth oxide, and cobalt oxide is highly effective in preventing property deterioration due to soldering. Furthermore, it is clear that the pulse resistance is not related to the paste material applied to the surface of the element, but is greatly improved by the addition of magnesium oxide and tin oxide, which are the base composition of the sintered element. Summer. In this way, the present invention is a non-linear resistor for low voltage use, and has excellent soldering resistance and high resistance to soldering without impairing the non-linear coefficient α.
The present invention provides a voltage non-linear resistor with excellent pulse resistance, and will be explained below with reference to embodiments of the present invention. Example Semiconductor materials include zinc oxide (ZnO) 40 to 98 mol%, magnesium oxide (MgO) 1 to 50 mol%,
Antimony oxide (Sb 2 O ₃ ) as an impurity in a base composition consisting of 0.1 to 10 mol% of _stannic oxide (SnO ₂ )
and niobium oxide (Nb ₂ O ₅ ) are added in an amount of 0.1 to 6.0% by weight based on the base composition, and wet mixed for 2 to 10 hours using a ball mill to obtain a sufficiently homogeneous mixture. Next, the mixture is calcined at 500 to 1000°C for 2 to 7 hours, and 3% binder is added and granulated. At this time, a lubricant is added together with the binder if necessary.
The granulated mixture is heated to 1200-1400℃ after press molding.
Baked in the air for about 2 hours, the diameter is 8.2 mm and the thickness is 1.0 mm.
A disk-shaped sintered body of mm is obtained. On the other hand, paste materials having various composition ratios within the following range were prepared. Fine silver powder (in terms of silver) 30-91% by weight Copper or copper oxide (in terms of copper) 5-50% by weight Bismuth oxide 1-10% by weight Cobalt oxide 1-10% by weight The above composition mixture is In order to improve adhesion to the base body and facilitate application, 7 parts by weight of borosilicate glass powder was added as a low melting point glass to 100 parts by weight of the above composition mixture, and the amounts of resin and solvent were adjusted and kneaded using a roll mill. A paste material with the optimum viscosity for screen printing was created. Next, a paste material within the composition range described above is applied to both sides of the sintered body thus obtained, dried, and then baked at 600 to 850°C for 10 to 80 minutes. An ohmic electrode (eg, a silver electrode) was formed. and Pb whose eutectic point is 180℃
-The lead wires were attached using Sn-based solder. The electrical characteristics of each element were measured before and after soldering.
These results are shown in FIG. 1 and Tables 1 and 2.
Further, the measurement was carried out by applying currents of 1 mA and 10 mA to the element and measuring the voltages at both ends after 1 second as V _1nA and V _10nA . Note that the paste material and the silver electrode (ohmic electrode) can be applied at the same time and formed by one baking process. Further, the silver fine powder of the paste material may be silver oxide (Ag ₂ O) or a combination of metallic silver and silver oxide. Moreover, it goes without saying that metallic copper may be used instead of copper oxide. Table 1 shows the changes in the specific resistance of the sintered body when the composition of the sintered body was varied.

【table】

[Table] As mentioned above, in order to obtain the low voltage non-linear resistor according to the present invention, the specific resistance of the sintered body must be 200Ω-
Must be within cm. As is clear from the table, in the ZnO-SnO ₂ system and ZnO-MgO-SnO ₂ system of Samples No. 1 to 7, except for Samples No. 1 to 2, all of the sintered bodies according to the present invention have a high resistivity. It turns out that it is not suitable as such. Nos. 1 and 2 are sintered bodies that have low specific resistance and can be used as non-linear resistors for low voltage, but as will be explained later, they do not contain MgO, so they have poor pulse resistance and are not intended for this purpose. This is not desirable as a sintered body. In addition, samples No. 8 to 13 have a substrate composition of ZnO−MgO−SnO ₂ .
Sb ₂ O ₃ and Nb ₂ O ₅ were added individually. As the amount of Sb ₂ O ₃ added increases, the resistivity decreases, and when the amount added further increases, the resistivity tends to increase again. On the other hand, in the case of Nb ₂ O ₅ , as the amount added increases, the resistivity decreases, but once it decreases to a certain extent, the resistivity does not decrease as much as the amount added. Thus Sb ₂ O ₃ and
By adding Nb ₂ O ₅ , the specific resistance of the sintered body consisting of the ternary system of ZnO-MgO-SnO ₂ can be lowered. In particular, for samples No. 9, 12, and 13, the specific resistance of the sintered body was
200 Ω-cm or less, which satisfies one of the objects of the present invention, but it cannot be said to be suitable for mass production due to large variations in resistivity, and is still insufficient as a sintered body for the purpose of the present invention. I can't say that.
Nos. 15 to 39 (excluding No. 18) have a base composition of ZnO-MgO-SnO ₂ with Sb ₂ O ₃ and Nb ₂ O ₅ added simultaneously. As is clear from the table, the resistivity was significantly reduced compared to other samples when Sb ₂ O ₃ and Nb ₂ O ₅ were added alone, and a sintered body with a resistivity within the desired range was obtained. I understand. The above experimental results revealed that
Addition of MgO is effective for improving pulse resistance and lowering specific resistance, but the amount added is 50 mol%.
If it is more than that, the specific resistance will be 200 Ω-cm or more, making it unsuitable as a sintered body according to the present invention. Also 1 mol%
Below this, the pulse resistance is poor and a good nonlinear resistor cannot be obtained. When adding SnO ₂ , adding Sb ₂ O ₃ and/or Nb ₂ O ₅ at the same time produces the effect of lowering the specific resistance. And when the amount of _SnO2 added is 10 mol% or more, the specific resistance is 200Ω-cm
If the sintered body exceeds this value, it becomes unsuitable for practical use as a sintered body for a nonlinear resistor for low voltage use. Further, if it is less than 0.1 mol %, the specific resistance tends to increase and the pulse resistance tends to deteriorate, which is not preferable. If Sb ₂ O ₃ and Nb ₂ O ₅ are added in an amount of 6.0% by weight or more, the sinterability deteriorates and a desired sintered body cannot be obtained. Table 2 shows changes in electrical properties when the composition of the paste material was changed while the composition of the sintered body was kept constant.

[Table] The composition of the sintered bodies of Reference Examples 1 and 2 and Examples 1 to 14 (excluding 6 and 7) is ZnO87.4 mol%,
MgO 12 mol%, SnO ₂ 0.6 mol% Sb ₂ O ₃ and
These are sintered bodies to which 2.0% by weight of Nb ₂ O ₅ is added. In the table, the V _10nA change rate is the change rate of the characteristics after soldering with respect to the initial characteristics before soldering,
The V ₁₀ /V ₁ rate of change indicates how much the voltage ratio between V _10nA and V _1nA changes from the initial characteristics after soldering, and this voltage ratio is a value directly related to the nonlinear coefficient. The fact that this rate of change is large indicates that the characteristics after soldering are approaching those of a linear resistor. In other words, this means that the performance as a voltage non-linear resistor has deteriorated. Reference example 1 in the table has a paste material composition consisting of silver and copper oxide, and both V ₁₀ and V ₁₀ /V ₁ change rate are small values, and at first glance it seems to be a good material, but as shown in Figure 1. If a constant current of 10 mA is applied to the device and measured, the voltage across the device will drop with the measurement time (current application time). In other words, it can be said that the performance as a voltage nonlinear resistor is poor and stability is poor. In contrast, the products of the present invention (Example 1 to
14) is found to be very stable.
Reference example 2 does not contain copper, but this element has a very large V ₁₀ /V ₁ change rate, which indicates that the non-linear coefficient α becomes smaller due to soldering, making it difficult to use as a product. It has little value and cannot be considered a material suitable for practical use. However, Examples 1 to 14 consisting of paste materials within the scope of the present invention are all
It exhibits excellent soldering resistance with small V ₁₀ and V ₁₀ /V ₁ change rates. Furthermore, as described above, within the scope of this embodiment, it is an excellent voltage nonlinear resistor that also has stable characteristics as shown in FIG. However, if the copper component is added in an amount of 50% by weight or more, it becomes unstable as shown in FIG. 1 as in Reference Example 1, which is not preferable. Furthermore, if bismuth or cobalt components are added in an amount of 10% by weight or more, the V ₁₀ and V ₁₀ /V ₁ change rates will be 10% or more, resulting in significant deterioration of properties due to soldering. In addition, if the bismuth and cobalt components are less than 1% by weight and the amount of copper added is large, a voltage drop phenomenon as in Reference Example 1 will appear, and if the amount of copper added is reduced,
The rate of change in V ₁₀ and V ₁₀ /V ₁ is large and the characteristics deteriorate significantly. In Examples 5, 6, and 7, although the paste material compositions are the same, the V _10nA values of the characteristics before soldering (initial characteristics) vary greatly. This is a result of the different compositions of the semiconductor materials that serve as the substrate. This shows that the voltage can be freely varied depending on the composition of the material as needed. In addition, a pulse test was conducted to examine the pulse resistance of the product of the present invention. The test is 35μ from a DC 60V power supply.
A capacitor of F was charged, a pulse voltage was applied from the capacitor to the product of the present invention 10 times, and the rate of change in V _{10 nA} and V ₁₀ /V ₁ was determined from the initial characteristics and measurements after the pulse application. Table 3 shows the results. This table shows the pulse resistance test results when the composition of the paste material was fixed and the composition of the semiconductor element was changed. According to the results, when using the paste material and semiconductor material according to the present invention,
The average value of the V _{10 nA} change rate was 1.0%, and the average value of the V ₁₀ /V ₁ change rate was 2.9%, which were very small values. In addition, the results of pulse tests were conducted on paste materials whose composition was fixed and the semiconductor material composition was changed.
It has been revealed that when MgO and SnO ₂ are added in an amount of 1.0 mol % or more and 0.1 mol % or more, respectively, the V _{10 nA} and the V ₁₀ /V ₁ change rate become significantly smaller. i.e.
When using a zinc oxide sintered body without MgO or SnO ₂ added, the V _{10 nA} change rate is -23% on average, and the V ₁₀ /
The average value of the _V1 change rate was 29%, and there was a very large deterioration in characteristics.

[Table] As described above, the voltage nonlinear resistor according to the present invention uses zinc oxide, magnesium oxide,
Silver powder on the surface of the sintered body, which is mainly composed of tin oxide and contains antimony oxide and niobium oxide as impurities.
A paste material consisting of copper oxide, bismuth oxide, and cobalt oxide is coated and baked, and ohmic electrodes are attached to it.It is a voltage non-conductor suitable for use in the low voltage area with excellent soldering resistance and pulse resistance. It is a linear resistor, and by controlling the composition of the semiconductor material, the voltage can be freely varied and any shape can be manufactured.It has superior characteristics and costs compared to conventional resistors, making it suitable for industrial use. It has many advantages. In addition, in the examples, the processing temperature of the paste material was
If the temperature is below 600°C, the glass frit contained in the paste material will not be sufficiently melted and the adhesive force with the sintered body will be low, making it impossible to obtain desirable characteristics. 850 again
When the temperature exceeds .degree. C., the value of V _10nA increases and the pulse resistance characteristics deteriorate. This is thought to be caused by alteration of the surface of the element. Also, the processing time is 10~
Anything outside the 80 minute range is not preferred for the reasons mentioned above. Note that the upper and lower limits of the processing temperature and time are approximate values, and it goes without saying that the electrical characteristics will not suddenly deteriorate if the temperature and time are outside these ranges. It can be widely applied as an element for absorbing abnormally high voltage or stabilizing voltage in a circuit having a relatively low operating voltage such as a transistor circuit. In this example, lead wires are taken out from both sides of the disc-shaped element body, but as a special application example, a sintered ring-shaped material made of the composition of the present invention is used as a spark quenching element for a micromotor. A ring-shaped voltage non-linear electrode is formed by dividing a paste material having a composition according to the present invention on the surface of the body into pieces on the circumference in a number corresponding to the number of commutator pieces, and further forming silver electrodes so that they can be soldered to the commutator pieces. It can also be a resistor. This ring-shaped voltage nonlinear resistor is used by being inserted and fixed onto the rotor shaft of a micromotor. Thus, the present invention provides a method for manufacturing a voltage nonlinear resistor that is effective for low voltage applications.

[Brief explanation of the drawing]

FIG. 1 shows the V ₁₀ /V ₁ change rate (%) characteristics when the composition of the sintered body base of the voltage nonlinear resistor according to the present invention is kept constant and the composition of the paste material is changed. The paste material composition ratio is shown in Table 2).

Claims (1)

[Claims] 1 Oxidized as an impurity to a base component consisting of 40 to 98 mol% zinc oxide (ZnO), 1 to 50 mol% magnesium oxide (MgO), and 0.1 to 10 mol% tin oxide (SnO ₂ ). A paste material is applied and baked on the surface of a sintered body containing 0.1 to 6.0% by weight of antimony (Sb ₂ O ₃ ) and niobium oxide (Nb ₂ O ₅ ), respectively. How to make a linear resistor. 2. The paste material contains 30 to 91% by weight of fine silver powder,
Copper or copper oxide (in terms of copper) 5-50% by weight,
Bismuth oxide 1-10% by weight, cobalt oxide 1-10%
% by weight to which low melting point glass, resin, and solvent are added.