JPH0897013A - Zinc oxide varistor and manufacture thereof - Google Patents

Abstract

PURPOSE: To improve the nonlinearity of voltage by a method wherein lead borosilicate glass frit, containing at least a metal oxide selected from lanthanoids, is diffused into a varistor element from the surface of a fired varistor element. CONSTITUTION: The prescribed quantity of PbO, B2 O3 , SiO2 and La2 O3 is mixed and pulverized by a ball mill, the mixture is melted in a platinum crucible at 1000 to 1500 deg.C, and it is vitrified by quenching. Then, the vitrified material is finely powdered and lead borosilicate glass frit is obtained. The glass frit (5.0wt.%) is mixed to silver paste which is formed by dissolving silver powder (65.0wt.%) into the vehicle (30.0wt.%) formed by dissolving ethyl cellusose into butyl carbitol}, and the electrode material for zinc oxide varistor is manufactured. The electrode material is screen-printed on both surfaces of a disc-shaped zinc oxide varistor sintered element 1 of 13mm in diameter and 1.5mm in thickness in such a manner that diameter of 10mm is obtained, baked at 800 deg.C for ten minutes, and an electrode 2 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc oxide varistor used for protecting various electronic devices from abnormally high voltage and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, highly integrated control circuits for consumer and industrial equipment have been rapidly developed.

Since the semiconductor electronic components used in these control circuits are destroyed when an abnormally high voltage (surge) is applied, it is essential to take measures against them. Varistors are generally used as a countermeasure. Among them, zinc oxide varistors are widely used for protecting various electronic devices from abnormally high voltage because of their excellent voltage nonlinearity and surge absorbing ability.

Conventionally, a zinc oxide varistor in which at least two electrodes are provided on the surface of a varistor element containing zinc oxide as a main component is widely known. The material of the electrode is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-290104, and its contents are as follows.

That is, lead borosilicate glass containing 50.0 to 85.0% by weight of PbO, 10.0 to 30.0% by weight of B ₂ O _{3 and} 5.0 to 25.0% by weight of SiO _2. The powder was weighed 5.0% by weight, and the vehicle in which ethylcellulose was dissolved in butyl carbitol (30.0% by weight) was used.
%) Was kneaded with Ag powder (65.0% by weight) to prepare a silver paste, which was used as an electrode material for a zinc oxide varistor.

Then, this electrode material was applied to the surface of the burned varistor element and heated to form an electrode.

[0007]

Although the above-mentioned zinc oxide varistor has excellent voltage nonlinearity as described above, this zinc oxide varistor has been demanded to save energy and improve efficiency in various electronic devices in recent years. There has been further demand for improved voltage nonlinearity for varistors.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a zinc oxide varistor which meets the above-mentioned requirements and has further improved voltage nonlinearity.

[0009]

In order to achieve this object, the present invention provides a lead borosilicate glass containing at least one element selected from lanthanoids from the surface of a varistor element that has been fired. It is diffused in the device.

[0010]

With the above-mentioned structure, the elements forming the lead borosilicate glass containing the lanthanoid element are present at the grain boundaries between the zinc oxide particles forming the varistor element. As a result, the resistance value of the grain boundary between the zinc oxide particles becomes high, and the leakage current flowing between the electrodes by that much before reaching the varistor voltage decreases, and as a conclusion, a zinc oxide varistor with improved voltage nonlinearity is obtained. Be done.

[0011]

EXAMPLE In this example, the characteristics of the electrode material are
I have it. That is, in this embodiment, the silver pace is
Use a mixture of lead borosilicate glass frit
These are described in detail below. First,
The adjustment of the glass frit will be described. Below (Table 1)
According to the composition table of PbO, B₂O₃, SiO₂, La₂O ₃To
Weigh a specified amount and crush it with a ball mill at the same time
After that, the temperature of the platinum crucible is adjusted to 1000 ° C to 1500 ° C.
It was melted under temperature conditions and rapidly cooled to vitrify. This glass
Coarsely crushed and then finely crushed with a ball mill to produce lead borosilicate
I got a glass frit. On the other hand, the conventional lead borosilicate glass
Glass as glass name A in (Table 1) as a frit
Frit (70.0% by weight of PbO, B₂O₃Is 15.0
Wt%, SiO₂Glass free of 15.0% by weight
Was prepared by the same method. Where glass transition
The point (Tg) was measured using a thermal analyzer.

[0012]

[Table 1]

Next, this lead borosilicate glass frit was weighed in an amount of 5.0% by weight and placed in a silver paste (vehicle in which ethylcellulose was dissolved in butylcarbitol (30.0% by weight)) as described above. Silver powder (6 by weight)
5.0%) was melted and kneaded to prepare an electrode material for zinc oxide varistor.

In order to evaluate the electrode material for a zinc oxide varistor manufactured as described above, bismuth oxide (Bi ₂ O ₃ ),
Cobalt oxide (Co ₃ O ₄ ), manganese oxide (Mn
O ₂ ), nickel oxide (NiO), titanium oxide (Ti
0.5 mol% of O ₂ ) and antimony oxide (Sb ₂
O ₃ ), chromium oxide (Cr ₂ O ₃ ) 0.1 mol%, Al ₂ O ₃ 0.005 mol%, and the balance zinc oxide (Z
nO) zinc oxide varistor sintered body (varistor element 1 in FIG. 3, disk-shaped diameter 13 mm, thickness 1.5 mm)
Prepared. The electrode material for zinc oxide varistor was screen-printed to have a diameter of 10 mm on both sides of this sintered body,
The electrode 2 shown in FIG. 3 was formed by baking at 0 ° C. for 10 minutes.
Next, after fixing the upper end of the lead wire 3 shown in FIG. 2 by soldering, the outer periphery of the varistor element 1 is covered with an epoxy-based insulating resin 4
The outer periphery was covered with and a sample was obtained in which only the lower end of the lead wire 3 was drawn out of the insulating resin 4 as shown in FIG.

When the surface of the varistor element 1 is coated with the above electrode material and then heated, the lead borosilicate glass containing lanthanum oxide in the electrode material penetrates into the varistor element 1 to obtain the effects described below. It is something to demonstrate.

Of the sample thus obtained

[0017]

[Outer 1]

The limiting voltage ratio (V _50A / V _1mA ) and surge current withstanding characteristics are shown in (Table 2) below.

The voltage ratio and the limiting voltage ratio were obtained by measuring with a DC constant current power supply. The surge current withstand characteristic is obtained by applying a shock current having a standard waveform of 8/20 μS and a peak value of 2500 A twice, and measuring the rate of change of the varistor voltage (V _{1 mA} ). The value is smaller than that of Sample 1 of the conventional example. Is preferred. In the above embodiment, the number of samples is 1 for each lot.
It is 0.

Further, the above

[0021]

[Outside 2]

Shows a voltage non-linearity, and the smaller the voltage ratio than the sample 1 of the conventional example, the smaller the leakage current until reaching the varistor voltage. That is, the V _{1 m A} indicates the voltage (varistor voltage) when a 1mA current flows between the electrodes 2,

[0023]

[Outside 3]

Those having a small value of are those in which a large amount of leakage current flows from a low voltage, which is not preferable.

[0025]

[Table 2]

From the above (Table 1) and (Table 2), the voltage ratio (voltage nonlinearity) of the content of lanthanum oxide (La ₂ O ₃ ) contained in the lead borosilicate glass frit in the electrode material for zinc oxide varistor is shown. Characteristics), limiting voltage ratio, and surge current withstand characteristics.

When the content of La ₂ O ₃ is 0.1% by weight or more, the voltage ratio (voltage nonlinearity) becomes good. Also, 3
If it is more than 0.0% by weight, the glass transition point (Tg) becomes high and it is difficult to diffuse into the varistor element 1, and the surge current withstand characteristic deteriorates. Therefore, L in lead borosilicate glass
It can be seen that the a ₂ O ₃ content of 0.1 to 30.0% by weight is a necessary condition.

On the other hand, characteristics such as surge current withstand capability are La ₂
In addition to the O ₃ content, PbO, B ₂ O ₃ , and SiO ₂ are affected, and therefore their composition must be considered.

Then, based on (Table 1) and (Table 2), the influence of the constituent components of the lead borosilicate glass contained in the electrode material on various characteristics will be considered. The glass of the composition system having a PbO content of less than 40.0% by weight has a high glass transition point, and the diffusivity of the glass is too small, and the glass remains on the surface of the electrode 2 and the solder wettability deteriorates. A glass having a composition system in which the PbO content is more than 80.0% by weight has a low glass transition point, the fluidity of the glass is too large, and the electrode adhesion strength is lowered, resulting in lack of reliability. In the composition system in which the content of B ₂ O ₃ is less than 5.0% by weight, the voltage ratio (voltage nonlinearity) is poor.
Further, in a composition system in which the content of B ₂ O ₃ is larger than 30.0% by weight, the surge current withstand characteristic is poor.

Further, in the composition system in which the content of SiO ₂ is less than 5.0% by weight, the surge current withstanding characteristic is poor,
Even in a composition system in which the content of SiO ₂ is more than 30.0% by weight, the surge current withstand characteristic deteriorates.

From the above results, the composition of the glass component of the electrode material for zinc oxide varistor has PbO of 40.0 to 80.
0 wt%, B ₂ O ₃ is 5.0 to 30.0 wt%, SiO ₂
Is 5.0 to 30.0 wt% and La ₂ O ₃ is 0.1 to 30.
It can be seen that the range of 0% by weight is optimum.

Next, the same evaluation was performed for lead borosilicate glass frits containing other lanthanoid elements.

The following (Table 3) and (Table 4) are lanthanum oxide.
(La₂O₃) Instead of cerium oxide (CeO₂) Is used
And (Table 5) and (Table 6) are praseodymium oxide.
(Pr₆O₁₁) Is used, and (Table 7) and (Table
8) is neodymium oxide (Nd)₂O₃), (Table
9) and (Table 10) are samarium oxide (Sm₂O₃) Is used
(Table 11) and (Table 12) are europium oxide.
(Eu₂O₃) Is used, (Table 13), (Table 14)
Gadolinium oxide (Gd₂O₃), (Table 1
5) and (Table 16) are terbium oxide (Tb)._FourO₇) Is used
(Table 17) and (Table 18) are dysprosium oxide
(Dy₂O₃) Is used, (Table 19) and (Table 20) are
Holmium oxide (Ho₂O₃) Is used (Table 2
1) and (Table 22) are erbium oxide (Er).₂O₃) Is used
(Table 23) and (Table 24) are thulium oxide (Tm
₂O₃) Is used, (Table 25) and (Table 26)
Ytterbium (Yb ₂O₃) Is used (Table 27),
(Table 28) shows lutetium oxide (Lu₂O₃) Is used
Shows the characteristics of.

[0034]

[Table 3]

[0035]

[Table 4]

[0036]

[Table 5]

[0037]

[Table 6]

[0038]

[Table 7]

[0039]

[Table 8]

[0040]

[Table 9]

[0041]

[Table 10]

[0042]

[Table 11]

[0043]

[Table 12]

[0044]

[Table 13]

[0045]

[Table 14]

[0046]

[Table 15]

[0047]

[Table 16]

[0048]

[Table 17]

[0049]

[Table 18]

[0050]

[Table 19]

[0051]

[Table 20]

[0052]

[Table 21]

[0053]

[Table 22]

[0054]

[Table 23]

[0055]

[Table 24]

[0056]

[Table 25]

[0057]

[Table 26]

[0058]

[Table 27]

[0059]

[Table 28]

In each case, the voltage ratio (voltage non-linearity) is good when the amount of the metal oxide of each lanthanoid is 0.1% by weight or more. If it is more than 30.0% by weight, the surge current withstand characteristic deteriorates.

In the present invention, lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide, lutetium oxide, oxide. Lead, boron oxide, and silicon oxide are added to La ₂ O ₃ , Ce.
_{O 2, Pr 6 O 11,} Nd 2 O 3, Sm 2 O 3, Eu 2 O 3, Gd
₂ O ₃ , Tb ₄ O ₇ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm
₂ O ₃ , Yb ₂ O ₃ , Lu ₂ O ₃ , PbO, B ₂ O ₃ , SiO ₂
However, it was confirmed that the same effect could be obtained by using other oxides.

Furthermore, in the above embodiment, the lead paste borosilicate glass frit is kneaded in the silver paste and applied to the varistor element 1 to form the electrode 2. When the electrode 2 is baked, the lead borosilicate glass frit is added. The elements that diffuse the constituent elements into the varistor element 1 are shown. However, the present invention is not limited to this, and a paste containing a lead borosilicate glass frit is applied to the surface of the varistor element 1 after firing before the formation of the electrode 2 and heated in that state to heat the lead borosilicate based material. Even if the elements forming the glass frit are infiltrated into the varistor element 1 and then the electrode 2 is formed by using the silver paste containing no lead borosilicate glass frit, the same effect on the voltage ratio (voltage nonlinearity) is obtained. Was obtained.

The electrode material for forming the electrode 2 is not limited to the silver paste, but may be formed of another metal paste such as palladium.

Furthermore, in the present embodiment, ZnO, Bi ₂ O ₃ , Co ₃ O ₄ , MnO ₂ , NiO, and S were used as sintered bodies for evaluation.
A zinc oxide varistor of the system consisting of b ₂ O ₃ , Cr ₂ O ₃ and Al ₂ O ₃ was used, but Pr ₆ O ₁₁ , CaO, BaO, Mg
Even if the electrode material for a zinc oxide varistor according to the present invention is applied to a zinc oxide varistor containing O, K ₂ O, SiO _2, etc., the effect remains the same.

[0065]

As described above, the lead borosilicate glass frit containing at least one metal oxide selected from the lanthanoids of the present invention is diffused into the varistor element from the surface of the burned varistor element. This makes it possible to obtain a zinc oxide varistor with improved voltage nonlinearity. If the voltage non-linearity is improved in this way, the amount of leakage current is small, so that it is possible to save energy and improve efficiency in various electronic devices used.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of a zinc oxide varistor of the present invention.

FIG. 2 is a sectional view of the zinc oxide varistor shown in FIG.

3 is a sectional view showing a varistor element of the zinc oxide varistor shown in FIG.

[Explanation of symbols]

 1 Varistor element 2 Electrode 3 Lead wire 4 Insulating resin

Claims (6)

[Claims] 1. A lead borosilicate glass containing a varistor element containing zinc oxide as a main component and at least two electrodes provided on the varistor element, and containing at least one element selected from lanthanoids. A zinc oxide varistor which is diffused into the varistor element from the surface of the burned varistor element. 2. A lead borosilicate glass containing lanthanoid
The metal oxide of at least one element selected from
La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃，
Eu₂O₃, Gd₂O₃, Tb_FourO₇, Dy₂O₃, Ho₂O₃，
Er₂O₃, Tm ₂O₃, Yb₂O₃, Lu₂O₃Converted to the form
0.1 to 30.0% by weight contained in the contract
A zinc oxide varistor according to claim 1. 3. The lead borosilicate glass is lead oxide containing Pb.
Converted to O, 40.0 to 80.0% by weight, boron oxide is B
₂O₃5.0 to 30.0% by weight, silicon oxide is S
iO₂5.0-15.0% by weight, Lanta Noi
Metal oxidation of at least one element selected from
Things are La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂
O₃, Eu₂O₃, Gd₂O₃, Tb_FourO₇, Dy₂O₃, Ho₂
O₃, Er ₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃Converted to
And 0.1 to 30.0% by weight is included.
Item 2. A zinc oxide varistor according to item 1. 4. A lead borosilicate-based glass containing at least one element selected from lanthanoids is applied to the surface of the varistor element and then heated, and the lead borosilicate-based glass is baked in the varistor element. 1. A method for producing a zinc oxide varistor, which comprises diffusing into. 5. A lead borosilicate glass containing at least one element selected from lanthanoids is diffused into the varistor element from the surface of the burned varistor element,
The method for manufacturing a zinc oxide varistor according to claim 4, wherein at least two electrodes are provided on the varistor element after that. 6. A lead borosilicate glass containing at least one element selected from lanthanoids is added to an electrode paste, and then this electrode paste is applied to the surface of a fired varistor element, and thereafter, A method for manufacturing a zinc oxide varistor, which comprises baking to form an electrode.