JP2008098300A - Zinc oxide based laminated chip varistor, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zinc oxide based laminated chip varistor wherein good insulation and sufficient resistance to a plating liquid can be obtained and which can be manufactured with good productivity. <P>SOLUTION: A protective film 13 consisting of bismuth borosilicate (ZnO-Bi<SB>2</SB>O<SB>3</SB>-SiO<SB>2</SB>-B<SB>2</SB>O<SB>3</SB>-Sb<SB>2</SB>O<SB>3</SB>) based glass is formed on the surface of a sintered chip 11 whose main component is zinc oxide (ZnO). The protective film is crystallized by the baking at a temperature between 660°C and 740°C. Thereby, the glass insulating film 13 does not erode in the plating process after protective film formation, and the zinc oxide based laminated chip varistor 10 having good insulation can be obtained with good productivity. The protective film 13 is formed to have a thickness ≤10 μm. Thereby, stable electrical characteristics of the varistor 10 can be maintained without preventing the electrical conduction between the internal electrodes 12a, 12b, 12c, 12d, 12e laminated on the sintered chips 11 respectively and the external electrodes 14a, 14b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a varistor for protecting a semiconductor element from load dump surge, ignition surge, lightning surge, electrostatic discharge (ESD), switching surge, etc. in various electric / electronic devices, and in particular, a small sized that can be surface mounted. The present invention relates to a zinc oxide-based multilayer chip varistor mainly composed of zinc oxide.

  In electric and electronic devices such as mobile phones, with the rapid increase in frequency and capacity in recent years, the circuit is protected from various surges, pulse noise, static electricity (ESD), etc., and operation stability is ensured. In addition, there is a growing need for varistors that are higher performance overvoltage protection elements in order to comply with noise regulations. Also, due to the downsizing of devices, zinc oxide multilayer chip varistors that are smaller than leaded disk varistors and can be surface mounted are often used.

In general, zinc oxide-based varistors are mainly composed of zinc oxide (ZnO) and added with bismuth oxide (Bi ₂ O ₃ ) that promotes zinc oxide grain growth and antimony oxide (Sb ₂ O ₃ ) that inhibits grain growth. Various glasses and the like are added as sintering aids. A zinc oxide-based multilayer chip varistor is configured to include external electrodes that are electrically connected to internal electrodes at both ends of a sintered body chip mainly composed of zinc oxide (ZnO) in which a plurality of internal electrodes are stacked. Yes. The external electrode is provided with a plating layer such as Ni / Sn.

Conventionally, it is known that the surface of a sintered body chip exposed between external electrodes is covered with a glass insulating film (Patent Document 1). By covering the exposed surface of the sintered body chip with this glass insulating film, there is an advantage that the insulation can be improved and the leakage current can be reduced.
JP-A-3-173402

  However, in order to cover the surface of the sintered body chip exposed between the external electrodes with the glass insulating film, it is necessary to apply glass paste to the exposed surface of the sintered body chip between the external electrodes one by one. As the varistor itself is reduced in size, it is very complicated to apply glass paste one by one, and there is a problem in productivity. Further, depending on the glass insulating film, there is a problem that it is vulnerable to an acid or alkali bath when electrolytic plating (electrode part plating) is performed. That is, if the glass insulating film is damaged by being immersed in an acid or alkali solution, in the case of a multilayer chip varistor, a problem occurs in the elongation of plating and moisture resistance.

  The present invention has been made in view of the above-described circumstances, and provides a zinc oxide-based multilayer chip varistor that has good insulation and sufficient resistance to a plating solution and can be manufactured with good productivity. With the goal.

The zinc oxide multilayer chip varistor of the present invention has bismuth borosilicate (ZnO-Bi ₂ O ₃ -SiO ₂ -B ₂ O ₃ -Sb ₂ O ₃ ) formed on the surface of a sintered chip mainly composed of zinc oxide (ZnO). ) A protective film is formed of glass. The protective film is crystallized by firing at a temperature between 660 ° C. and 740 ° C. As a result, the glass insulating film is not eroded in the plating process, which is a process after the formation of the protective film, and a protective film having good insulation can be obtained with good productivity. Further, the protective film is formed with a thickness of 10 μm or less. Thereby, stable electrical characteristics of the varistor can be maintained without impeding the conduction between the internal electrode and the external electrode laminated on the sintered body chip.

The glass composition of the protective film is as follows. As main components, zinc oxide (ZnO) 1-2 wt%, bismuth oxide (Bi ₂ O ₃ ) 50-70 wt%, silicon oxide (SiO ₂ ) 10-20 wt%, boron oxide (B ₂ O ₃ ) The composition ratio is 8 to 13 wt% and antimony oxide (Sb ₂ O ₃ ) is 0.1 to 1 wt%. Here, calcium oxide (CaO), magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), barium oxide (BaO), strontium oxide (SrO), sodium oxide (Na ₂ O) Two or more kinds of lithium oxide (Li ₂ O) and potassium oxide (K ₂ O) may be contained in an amount of 5 wt% or less. The glass insulating film of the present invention is a crystalline bismuth borosilicate glass composition having these characteristics.

It is a method for forming a glass insulating film of the present invention, but bismuth borosilicate (ZnO-Bi ₂ O ₃ —SiO ₂ —B ₂ O ₃ —Sb ₂ O ₃ ) glass 5 to 15 wt% of the above composition, glycol type A glass solution consisting of 1 wt% of a dispersant and 84 to 94 wt% of ion-exchanged water is prepared, the sintered multilayer chip varistor chip is immersed in the glass solution, and a solution film is formed on the surface of the sintered body chip. By baking at a temperature between 660 ° C and 740 ° C after drying, a crystalline bismuth borosilicate glass insulating film is formed on the surface of the sintered body chip, and then external electrodes are formed on both ends of the sintered body chip. Form. Drying is carried out at a temperature between 30 ° C. and 50 ° C. for a time between 50 minutes and 70 minutes.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an example of the structure of a zinc oxide-based multilayer chip varistor, and FIG. 2 shows the manufacturing process.

  The zinc oxide-based multilayer chip varistor 10 includes a sintered body chip 11 containing zinc oxide as a main component as a varistor material and containing additives such as antimony oxide and bismuth oxide. The sintered body chip 11 is formed by laminating a green sheet mainly composed of zinc oxide on which a conductive material paste pattern (internal electrode pattern) such as platinum (Pt) or palladium (Pd) is disposed, and cutting the green chip. And a laminated sintered chip produced by further firing. Internal electrodes 12a, 12b, 12c, 12d, and 12e are alternately stacked in a parallel plate shape inside the sintered body chip 11, and the electrode arrangement is the same as that of the multilayer capacitor. Each internal electrode is a sintered body. The external electrodes 14a and 14b disposed at both ends of the chip 11 are electrically connected.

Bismuth borosilicate (ZnO—Bi ₂ O ₃ —SiO ₂ —B ₂ O ₃ —Sb ₂ O ₃ ) -based glass insulating film (protective film) is formed on the entire surface (six sides) of the rectangular parallelepiped chip 11. 13 and the glass insulating film 13 is crystallized, and is a very thin film having a thickness of 10 μm or less. The glass insulating film 13 is made of zinc oxide (ZnO) 1 to 2 wt%, bismuth oxide (Bi ₂ O ₃ ) 50 to 70 wt%, silicon oxide (SiO ₂ ) 10 to 20 wt%, boron oxide (B ₂ O ₃ ) Is composed of 8 to 13 wt%, and antimony oxide (Sb ₂ O ₃ ) is composed of 0.1 to 1 wt%. In addition, calcium oxide (CaO), magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), barium oxide (BaO), strontium oxide (SrO), sodium oxide (Na ₂ O), lithium oxide (Li ₂ O), containing less 5 wt% of two or more of potassium oxide (K ₂ O).

  The internal electrodes 12a, 12b, 12c, 12d, and 12e are electrically connected to the left and right external electrodes 14a and 14b through the glass insulating film 13 on the end face of the sintered body 11, respectively. The external electrodes 14a and 14b have good mountability by nickel (Ni) plating, solder or tin (Sn) plating on an electrode such as silver (Ag). The glass insulating film 13 has a thickness of 10 μm or less and is extremely thin, so that a stable conduction state can be obtained without hindering electrical conduction between the external electrode and the internal electrode. Therefore, the voltage applied between the left and right external electrodes 14a, 14b is applied to the varistor sintered body portion between the electrodes 12a, 12b, 12c, 12d, 12e arranged in a parallel plate shape inside the varistor sintered body 11. Applied. In this embodiment, the varistor element is composed of four varistor sintered body layers, but the number of layers, the size, and the like are determined according to specifications. The zinc oxide-based multilayer chip varistor 10 is a surface mount type component having a size as a standard chip component such as 3.2 mm × 1.6 mm (3216 type), 2.0 mm × 1.2 mm (2012 type), for example. is there.

  The varistor is a voltage limiting function element that limits the voltage when the applied voltage exceeds a certain value, and the current suddenly flows out. The voltage limit function of the varistor protects the circuits and semiconductor elements of electrical and electronic equipment from various abnormal voltages. First, three characteristics (leakage current, limiting voltage, impulse withstand capability) and α value, which are basic characteristics of a varistor, will be described below.

(Leak current)
Leakage current usually indicates the current that flows when the maximum allowable circuit voltage is applied. That is, it is an index indicating how much current flows under a voltage environment that can be continuously applied to the external electrode when the varistor is used, and it is desirable that the number be small. On the other hand, in the evaluation, evaluation is performed with a current that flows when a voltage of 0.9 to 0.85 mm (times) of the varistor voltage, which is a more severe condition, is applied. Also in the examples of the present invention described later, evaluation is performed with a leakage current when a voltage of 0.85 mm (times) the varistor voltage is applied.

(Limit voltage)
Normally, the varistor voltage is a voltage V _{1 mA} that appears across the varistor when a current of 1 (mA) flows. In contrast, the varistor's limiting voltage is the voltages V _1A , V _2A , and V _10A that appear across the varistor when a relatively large current of about 1 (A), 2 (A), or 10 (A) flows. is there. The ratio (limit voltage / varistor voltage) with the limit voltage (V _{2A, 10A} ) to the varistor voltage (V _1mA ) is called the limit voltage ratio. The varistor is connected in parallel with the component to be protected, and shows the function to keep the circuit voltage low by using the non-linearity characteristic of the varistor against abnormal current such as static electricity (ESD). It shows that the abnormal voltage applied to the circuit to be protected is reduced.

(Impulse withstand)
Impulse withstand indicates the withstand capability of a varistor when a large impulse current such as lightning surge, ignition surge, or load dump surge enters. This withstand capability is evaluated based on the rate of change of the varistor voltage before and after applying a large current such as 500 (A) in a surge waveform.

(Α value)
In the varistor, the resistance value of the sintered body arranged between the electrodes suddenly changes depending on the voltage, and when the voltage exceeds a certain voltage, the current that has hardly flowed until then suddenly flows out. With a slight change in the varistor voltage, the current changes by a factor of ten. The non-linearity at this time (that is, the current and voltage are linearly related in Ohm's law) is called the α value, and the α value increases as the non-linearity becomes better.

  Next, the manufacturing process of the zinc oxide based multilayer chip varistor of the present invention will be described.

First, zinc oxide (ZnO), bismuth oxide (Bi ₂ O ₃ ), cobalt oxide (CoO), and manganese oxide (MnO) having a median average particle size of about 3 μm are weighed. A grain growth inhibitor such as antimony oxide (Sb ₂ O ₃ ) or chromium oxide (Cr ₂ O ₃ ) is added according to the unit varistor voltage. As a sintering aid, glass such as SiO ₂ , B ₂ O ₃ , GeO ₂ is added (step 101).
And it grind | pulverizes with a ball mill etc. and arranges a grain. Furthermore, heat treatment (calcination) is performed at about 900 ° C., the reactivity and particle size are adjusted, and the particles are pulverized again with a ball mill or the like (step 102).

Next, for example, PVB having a polymerization degree of 3000, a phthalate ester plasticizer, a polycarboxylic acid dispersant, a PEG # 600 release material, and an ethanol / toluene dilution solvent are added to prepare a slurry (step 103).
Next, the slurry is used to form a film with a doctor blade to produce a green sheet of about 10 to 100 μm (step 104).
Next, a conductive material paste such as platinum (Pt) or palladium (Pd) is screen-printed to produce an internal electrode (capacitor) pattern on the green sheet and laminated by hot pressing or the like (step 105).
Next, it is cut into chips that match the product size (for example, 3.2 mm × 1.6 mm), green chips are formed (step 106), binder removal is performed at 500 ° C. for 10 hours (step 107), and 950 to 1300 The main component is zinc oxide (ZnO) grains in which a plurality of layers of internal electrodes 12a, 12b, 12c, 12d, and 12e are laminated. The sintered body chip 11 to be formed is formed.

On the other hand, a glass solution is prepared (step 110). First, 1 to 2 wt% of zinc oxide (ZnO), 50~70wt% bismuth oxide _{(Bi 2 O 3), 10~20wt} % of silicon oxide (SiO _2), boron oxide and (B ₂ O ₃₎ 8~ 13 wt%, antimony oxide and (Sb ₂ O ₃₎ weighing 0.1 to 1 wt%. Calcium oxide (CaO), magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), barium oxide (BaO), strontium oxide (SrO), sodium oxide (Na ₂ O) , Lithium oxide (Li ₂ O), Potassium oxide (K ₂ O) 2 more than 5 wt% and further mixed, bismuth borosilicate (ZnO-Bi ₂ O ₃ -SiO ₂ -B ₂ O _3- Sb ₂ O ₃ ) glass powder material is prepared. And bismuth borosilicate (ZnO-Bi ₂ O ₃ -SiO ₂ -B ₂ O ₃ -Sb ₂ O ₃ ) glass powder 5-15 wt%, glycol dispersant 1 wt%, ion-exchanged water 84-94 wt% (Step 110).

Next, the sintered body chip is immersed in the glass solution. Actually, a large number of sintered body chips are immersed in a glass solution all at once. Thereby, the film of a glass solution adheres to the whole surface (six sides) of a sintered compact chip (step 111).
Next, the sintered body chip is dried in a # 200 mesh metal container at 40 ± 10 ° C. for 1 hr ± 10 min, the ball mill is rotated at 65 min ⁻¹ for drying (step 112), and baked at 700 ° C. for about 1 hr to obtain a glass solution. The film is crystallized into glass (step 113). Thereby, a crystalline bismuth borosilicate (ZnO—Bi ₂ O ₃ —SiO ₂ —B ₂ O ₃ —Sb ₂ O ₃ ) -based glass insulating film is formed on the six faces of the sintered body chip. As will be described later, this film thickness is 10 μm or less.

  Further, the terminal electrodes (external electrodes) 14a and 14b are formed by applying silver (Ag) or silver / palladium (Ag / Pd) paste and baking it (step 114). Then, the terminal electrode is plated in the order of a nickel (Ni) layer and a tin (Sn) layer (step 115), and electrical characteristics such as varistor voltage and leakage current are inspected and measured (step 116), and a finished product is obtained.

  Next, various examination results performed on the multilayer chip varistor manufactured in the above process will be described below.

  The test conditions for the humidity resistance load life test, which are generally considered to be the harshest conditions, are as follows: a temperature of 85 ° C, a humidity of 85RH%, a voltage of 0.85mm of the varistor voltage is applied, and the voltage change rate at 1000hrs is within ± 10% of the varistor voltage. It is required to be. Under these test conditions, deterioration of characteristics was observed in the conventional product in which the above glass protective film of 3.2 mm × 1.6 mm (L × W) size was not provided for a varistor voltage product of 50 V or more.

Here, in order to improve the varistor characteristics of the moisture resistance load life test, the following two methods are conceivable. First, it is conceivable to increase the insulation resistance of the sintered body chip, and second, to lower the ion mobility between the electrodes (for example, use of an alloy or improvement of sintered compactness). Both of the above two methods need improvement, but the insulation resistance of the first sintered body chip is particularly dominant. Therefore, there are the following two methods for increasing the insulation resistance of the first sintered body chip.
(1) Since ZnO is used as the main raw material, Li as an acceptor is added to ZnO to increase resistance.
(2) The surface of the sintered chip is coated with an insulating film to increase resistance.

  However, increasing the resistance of ZnO can increase the specific resistance of the material and reduce the cost by adding Li as an acceptor to ZnO, but the electrical characteristics of the varistor deteriorate. . On the other hand, coating an insulating film on the surface of the sintered body chip to increase the resistance does not deteriorate the electrical characteristics and can surely increase the insulation resistance of the surface of the sintered body chip. There is a problem in terms of manufacturing cost because it is necessary to coat each time.

  Therefore, the present invention immerses a large number of sintered chips in a glass solution at once and selects a glass material so that the laminated chip varistor can be sintered with good productivity (without increasing the manufacturing cost). The insulating property on the surface of the bonded chip is enhanced. That is, by immersing a large number of sintered body chips in a glass solution all at once, and drying and firing all together, a glass protective film can be formed on the entire surface of the sintered body chip with good productivity. And the characteristic of a protective film for a zinc oxide based multilayer chip varistor, such as resistance to a plating solution, can be obtained by the composition of the glass insulating film.

The examination result of the glass composition will be described. In selecting the glass composition, we examined the effect of insulation during plating, the effect on insulation resistance depending on moisture resistance, and the effect on electrical characteristics. Table 1 shows the results of the study. The sample evaluation number n was 100. Glass is B ₂ O ₃ -Bi ₂ O ₃ series, B ₂ O ₃ -Bi ₂ O ₃ -SiO ₂ series, B ₂ O ₃ -ZnO-SiO ₂ series, B ₂ O ₃ -ZnO-SiO ₂ -Bi ₂ O ₃ system, was studied _{B 2 O 3 -ZnO-SiO 2} -Bi 2 O 3 -Sb 2 O 3 system. Evaluation items were plating resistance, insulation resistance, and electrical characteristics.

In the evaluation, each item was evaluated according to the following index. “Plating resistance” indicates the probability that the insulation is impaired by plating and plating elongation occurs. “Insulation resistance” refers to the ratio of defects in characteristics as a result of performing the above-mentioned moisture resistance load life test on the plated product and performing the test for 1000 hours. “Electrical characteristics” indicate the ratio of deterioration of basic characteristics (varistor voltage, leakage current, limiting voltage, surge resistance) of the varistor before and after the formation of the glass insulating film. From the above evaluation results, the B ₂ O ₃ —ZnO—SiO ₂ —Bi ₂ O ₃ —Sb ₂ O ₃ system is optimal as the glass composition.

A glass insulating film was formed under the following conditions. Each glass shown in Table 1 was mixed with 9 wt%, polyethylene glycol 1 wt%, and ion-exchanged water 90 wt%. 100 g of the obtained glass solution was mixed with a sintered chip of a multilayer chip varistor 68V product after sintering of 2.0 mm × 1.2 mm × 1 mm and before formation of external electrodes, and then a sus-made # 200 mesh cylindrical shape The sample was transferred to a metal container, placed on a sealed ball mill frame, and dried by rotating at a rotation speed of 60 min ^-1 for 1 hr while applying heat at 40 ° C. Then, it baked in the belt furnace for each composition above the glass transition temperature. The keeping time of the firing temperature was fixed at 1 hr. A silver (Ag) external electrode was formed on the sintered chip on which the glass insulating film was formed, and Ni / Sn plating was applied to the surface.

Each product thus obtained was evaluated. As a result, the following could be confirmed. Glass with ZnO crystallized into glass showed an improvement effect with excellent insulating properties as a whole. This can be considered that the linear expansion coefficient matches the sintered body chip due to crystallization. Further, Bi ₂ O ₃ enters the glass, so that the wettability to the sintered body chip is improved and a homogeneous film can be easily formed. In addition, it is confirmed that the presence of Sb ₂ O _{3 in} a small amount increases the bondability with the Zn ₂ Sb ₇ O ₁₂ spinel phase formed on the surface of the sintered chip, resulting in a more stable insulating film. done.

These results, borosilicate bismuth _{(B 2 O-SiO 2 -Bi} 2 O 3 -SiO 2 -Sb 2 O 3) By using a glass, it has been found that can significantly improve the properties relating to moisture resistance. This glass composition is allowed in the following range.
As main components, zinc oxide (ZnO) 1-2 wt%, bismuth oxide (Bi ₂ O ₃ ) 50-70 wt%, silicon oxide (SiO ₂ ) 10-20 wt%, boron oxide (B ₂ O ₃ ) The composition ratio is 8 to 13 wt% and antimony oxide (Sb ₂ O ₃ ) is 0.1 to 1 wt%. Here, calcium oxide (CaO), magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), barium oxide (BaO), strontium oxide (SrO), sodium oxide (Na ₂ O) Two or more kinds of lithium oxide (Li ₂ O) and potassium oxide (K ₂ O) may be contained in an amount of 5 wt% or less. It is a crystalline bismuth borosilicate glass having these compositions.

  Next, the baking temperature of the glass will be examined. In the above examination, the superiority of the glass composition could be confirmed. However, a stable glass insulating film is not only determined by the composition but greatly influenced by the crystal phase determined by the baking temperature. Therefore, a comparative study was made below between the firing temperature of the glass and the finished quality of the glass insulating film. In examining the firing temperature, the thermal behavior of the glass was grasped using a thermal analyzer << Rigaku themo plus 2 >> TG-DTA, and the presence or absence of a crystalline phase was judged.

Regarding bismuth borosilicate glass, the firing temperature of the glass was changed, and the crystal phase, plating resistance, insulation resistance, and electrical characteristics were examined. The results are shown in Table 2.

  As a result, even if the composition is the same, the insulating property of the amorphous glass insulating film deteriorates due to erosion by the plating bath during plating. On the other hand, it has been found that crystalline glass is good in all of the plating resistance, insulation resistance, and electrical characteristics. For this reason, crystallization is an essential condition for forming a glass insulating film having good characteristics. Moreover, even if it was crystalline, it was confirmed that the characteristics of the sintered body chip could deteriorate regardless of the glass insulating film at a temperature of 800 ° C. or higher which causes the varistor annealing phenomenon. In the actual firing, each temperature ± 20 ° C. is set as a control temperature. That is, for example, in the case of 700 ° C., it is fired between 680 and 720 ° C. in the actual firing step. The firing time is 1 hour. From the above results, in order to form a glass insulating film having excellent moisture resistance, crystallization is the most important, and a preferable baking temperature range is 660 to 740 ° C.

  Next, the examination result of the formation method of a protective film (glass insulating film) is demonstrated. In order to form an optimum glass insulating film, there must be a process for forming a stable insulating property and a uniform insulating film even during mass production. Then, the printing method, the vapor deposition method, and the immersion method were examined about the glass insulating film formation method. The printing method has advantages such as high insulation properties and does not hinder terminal conduction, but has a problem that productivity is low because processing for each individual product is necessary. The vapor deposition method also has advantages such as good insulation and does not hinder terminal conduction, but there is also a problem that productivity is low because it is a process for each individual product. On the other hand, the dipping method can achieve good productivity because batch processing (batch processing) is possible, but there are problems such as low insulation and inhibiting terminal conduction when the film thickness is increased.

First, the optimal ratio of the glass solid content in the glass solution was examined. The sample number n was set to 100. The glass insulating film of the sample is composed of the above bismuth borosilicate (B ₂ O-SiO ₂ -Bi ₂ O ₃ -SiO ₂ -Sb ₂ O ₃ ) glass powder, 1 wt% dispersant, and ion-exchanged water as a solvent as a whole. In addition to being 100 wt%, a large number of 2.0 mm × 1.2 mm × 1.0 mm size sintered body chips were immersed to form a glass solution coating on the surface. After that, it was placed in a cylindrical container made of sus and made of # 200 mesh, placed on a sealed ball mill frame, and spin-dried at 40 ° C. and 65 min ⁻¹ . The sintered chip with the glass material attached was baked at 700 ° C for 1 hr to form a glass insulating film on the surface of the sintered chip, and then a silver (Ag) external electrode was formed, followed by Ni / Sn plating And evaluated. Table 3 shows the examination result of the ratio (%) of the glass solid content to the whole glass solution.

  Here, the “insulation failure rate” indicates the failure rate by the moisture resistance load life test. “Conductivity failure rate” indicates a conduction failure rate between the internal electrode and the external electrode. The “Abek defect rate” is an occurrence rate of defects such as fusion of sintered chips generated when a glass insulating film is baked onto a sintered chip. “Insulating film thickness” is a measurement result of the thickness of the obtained insulating film.

  From this test result, the weight ratio of the glass solid content (glass powder) to the glass solution is an optimal solid content ratio in which 5 to 15 wt% does not cause any defects. The thicker the glass insulation film, the better the insulation. However, if the glass insulation film is too thick, the continuity failure rate will increase (for example, the insulation film thickness is 16.1μm). Defects occur due to fusion between the two. In consideration of the insulation failure rate, the insulating film thickness is desirably 2.0 μm or more. Note that the glass in the insulating film does not completely cover the surface of the sintered body chip without a gap, but exists in a state of being scattered on the surface of the sintered body chip. For this reason, even if an insulating film is formed on the surface of the sintered body chip before forming the external electrode, conduction between the internal electrode and the external electrode is ensured.

  Next, the drying conditions that are the key to the glass insulating film formation process were examined. The examination results are shown in Table 4. The defective rate of insulating film formation was evaluated by the defective rate by the moisture resistance load life test with respect to the drying temperature and drying time. The number n of evaluation samples was set to 100.

  From these test results, the optimum drying conditions are a drying temperature of 30 to 50 ° C. and a drying time of 50 to 70 minutes. When the drying temperature was 30 ° C. or lower, it was not possible to dry as shown by x in the table, and the characteristics could not be evaluated by the moisture resistance load life test. Further, when the drying time was 80 min or more, chipping of the sintered body chip was always confirmed during the drying, and indicated by x. Therefore, an effective insulating protective film is formed on the surface of the sintered chip of the zinc oxide multilayer chip varistor under the above preferable process conditions, and the moisture resistance can be improved while maintaining good productivity.

  Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

It is sectional drawing of the zinc oxide laminated chip varistor of one Embodiment of this invention. It is a flowchart of the manufacturing method of the zinc oxide multilayer chip varistor of one Embodiment of this invention.

Explanation of symbols

10 Zinc Oxide Chip Chip Varistor 11 Sintered Chips 12a, 12b, 12c, 12d, 12e Internal Electrode 13 Glass Insulating Film (Protective Film)
14a, 14b External electrode

Claims (10)

On the surface of a sintered body chip composed mainly of zinc oxide (ZnO) with multiple layers of internal electrodes,
Bismuth borosilicate (ZnO-Bi ₂ O ₃ -SiO ₂ -B ₂ O ₃ -Sb ₂ O ₃ ) glass protective film, and the protective film is crystallized,
A zinc oxide-based multilayer chip varistor comprising external electrodes that are electrically connected to the internal electrodes at both ends of the sintered body chip.   2. The zinc oxide based multilayer chip varistor according to claim 1, wherein the protective film has a thickness of 10 [mu] m or less. The protective layer, 1 to 2 wt% of zinc oxide (ZnO), 50~70wt% bismuth oxide (Bi ₂ O _3), silicon oxide and (SiO ₂₎ 10~20wt%, boron oxide (B ₂ O ₃₎ The zinc oxide-based multilayer chip varistor according to claim 1, wherein the composition is composed of 8 to 13 wt% and antimony oxide (Sb ₂ O ₃ ) in a composition ratio of 0.1 to 1 wt% and is crystalline. The protective film includes calcium oxide (CaO), magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), barium oxide (BaO), strontium oxide (SrO), sodium oxide (Na ₂ O), lithium oxide (Li ₂ O), zinc oxide based multilayer chip varistor according to claim 3, characterized in that it further contains less 5 wt% of two or more of potassium oxide (K ₂ O). Zinc oxide (ZnO) and 1 to 2 wt%, 50 to 70 wt% bismuth oxide _{(Bi 2 O 3), 10~20wt} % of silicon oxide (SiO _2), boron oxide and (B ₂ O ₃₎ 8~13wt% A bismuth borosilicate glass composition comprising antimony oxide (Sb ₂ O ₃ ) at a composition ratio of 0.1 to 1 wt% and being crystalline. Calcium oxide (CaO), magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), barium oxide (BaO), strontium oxide (SrO), sodium oxide (Na ₂ O), lithium oxide The bismuth borosilicate glass composition according to claim 5, which contains 2 or more types of (Li ₂ O) and potassium oxide (K ₂ O) in an amount of 5 wt% or less. Form a green sheet mainly composed of zinc oxide (ZnO),
An internal electrode conductive material paste pattern is formed on the green sheet, the green sheets are laminated, cut to form a green chip, and then fired to form a sintered body chip.
The sintered body chip is immersed in a bismuth borosilicate (ZnO-Bi ₂ O ₃ —SiO ₂ —B ₂ O ₃ —Sb ₂ O ₃ ) glass solution, and a film of the solution is applied to the surface of the sintered body chip. By forming, drying and firing, a crystalline bismuth borosilicate (ZnO-Bi ₂ O ₃ —SiO ₂ —B ₂ O ₃ —Sb ₂ O ₃ ) glass insulating film is formed on the surface of the sintered body chip. Forming,
A method of manufacturing a zinc oxide-based multilayer chip varistor, wherein external electrodes are formed at both ends of the sintered body chip. The glass solution is bismuth borosilicate (ZnO-Bi ₂ O ₃ -SiO ₂ -B ₂ O ₃ -Sb ₂ O ₃ ) glass powder 5 to 15 wt%, glycol dispersant 1 wt%, ion-exchanged water 84 The method for producing a zinc oxide-based multilayer chip varistor according to claim 7, comprising: ˜94 wt%.   The method for manufacturing a zinc oxide-based multilayer chip varistor according to claim 7, wherein the baking of the glass insulating film is performed at a temperature between 660 ° C and 740 ° C.   The method for producing a zinc oxide-based multilayer chip varistor according to claim 7, wherein the drying is performed at a temperature between 30 ° C and 50 ° C for a time between 50 minutes and 70 minutes.

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