JPH11150005A - Ceramic barrister and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a plating layer from being formed at a part except an electrode part, without adding new processes at operating barrel plating for forming a barrier layer and a soldered plating layer on the surface of an electrode. SOLUTION: When the stoichiometric composition of a spinel powder is expressed by ZnXSbYOZ, a mixed powder obtained by adjusting Sb into stoichiometric ratio excess within the range of B/A=1.0-1.25 by using ZnX as an A site and SbY as a B site is burned in a temperature within a range of 1,000-1,200 deg.C so that the spinel power can be generated. Then, a ceramic burned body is embedded in this spinel powder, and sintered in a temperature within the range of 1,000-1,200 deg.C, so that a high resistance spinel layer 7 can be formed on the surface of a semiconductor ceramic part 1. After the high resistance spinel layer 7 formed at an electrode forming part has been mechanically removed, an outside electrode 3 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic varistor and a method for manufacturing the same, and more particularly, to a technique for increasing the resistance of a surface except for an electrode portion.

[0002]

2. Description of the Related Art A ceramic varistor is a varistor formed by firing a varistor composition material such as ZnO. As shown in FIGS. 5 and 6, a multilayer chip type for surface mounting and a discrete varistor are used. There are types of ceramic varistors. Hereinafter, each type of ceramic varistor will be described with reference to FIGS. 5 and 6.

First, as shown in FIG. 5, a multilayer chip type ceramic varistor for surface mounting is composed of a semiconductor ceramic portion 1 mainly composed of ZnO or the like and a plurality of internal electrodes 2 formed therein. The varistor has a laminated structure as follows. A pair of external electrodes 3 is provided at an external lead-out portion of the internal electrode 2. Then, at the time of mounting on the substrate surface, the external electrodes 3 are soldered to the substrate pattern. In such a laminated chip type ceramic varistor, the internal electrode 2 and the external electrode 3 are generally formed of a metal fired film mainly composed of Ag or Ag / Pd.

As shown in FIG. 6, a discrete type ceramic varistor for surface mounting is made of ZnO.
This is a varistor comprising a semiconductor ceramic portion 1 mainly composed of the above-mentioned components, and a pair of opposed electrodes 4 provided on both sides thereof. At the time of mounting on the surface of the substrate, a metal wire 5 previously solder-plated on the surface of the counter electrode 4 is soldered (solder layer 6). In addition,
In such a discrete-type ceramic varistor, the counter electrode 4 is generally formed from a material containing Ag as a main component.

[0005]

However, in the above-mentioned conventional ceramic varistors for surface mounting, there is a possibility that solder erosion and Ag migration may occur during soldering. This will be described below.

First, in a multilayer chip type ceramic varistor, since the material of the external electrode 3 is mainly composed of Ag or Ag / Pd, solder erosion of the external electrode 3 occurs at the time of soldering. Therefore, in such a varistor, it is difficult to apply a flow type soldering process in which the external electrode material is exposed to a high-temperature molten solder flow, and it is difficult to improve the efficiency of soldering. The main component of the external electrode 3 is Ag or Ag.
/ Pd, there is a possibility that Ag migration may occur between opposing electrodes under the condition of intervening humidity.

Next, since the discrete type ceramic varistor is soldered to the substrate via the metal wire 5 pre-soldered, unlike the laminated chip type, there is no possibility of solder erosion. However, since the main component of the counter electrode 4 is Ag,
Ag migration may occur between opposing electrodes as in the stacked chip type.

[0008] In order to prevent such electrode erosion and Ag migration between opposing electrodes in a multilayer chip type or discrete type ceramic varistor, soldering is generally performed on a substrate. A method of forming a solder plating layer on the surface of an electrode (external electrode 3 in FIG. 5) or an electrode for soldering a metal wire (counter electrode 4 in FIG. 6) via a barrier layer is conceivable. That is, first, the entire surface of the electrode is covered with Ni or copper, a Ni layer or a copper layer serving as a barrier layer for protecting the electrode against solder is formed, and further, a solder layer is formed on the Ni layer or the copper layer. This is a method for forming a solder plating layer for improving the attachment property.

Here, in order to form the Ni layer, the Cu layer, and the solder plating layer, barrel plating is generally performed. However, in the ceramic varistor, since the ceramic portion is a semiconductor ceramic, when such barrel plating is performed, the Ni layer, the Cu layer, and the solder plating layer are formed over the entire surface including the ceramic surface other than the electrodes. As a result, there is a problem that the electrodes facing each other are short-circuited.

On the other hand, in order to prevent formation of a plating layer on the surface of the semiconductor ceramic portion of the varistor, a film that can be removed after barrel plating is formed only on the surface of the semiconductor ceramic portion in advance, and after plating is completed, A method of removing is also conceivable. However, this method requires a step of forming a removable film limited to the ceramic portion and a step of removing after the plating is completed, which increases the cost and impairs mass productivity, and is not practical.

Although there is a possibility of solder erosion during soldering and migration between opposing electrodes for the reasons described above, the external electrodes of the multilayer chip type ceramic varistor for surface mounting are made of Ag or Ag. Ag /
In fact, a material mainly composed of Pd is used, and a material mainly composed of Ag is used for a counter electrode of a discrete type ceramic varistor for surface mounting.

The present invention has been proposed in order to solve the problems of the prior art as described above, and a first object of the present invention is to prevent a problem such as a short circuit between opposing electrodes from occurring. An object of the present invention is to provide a high-quality ceramic varistor that can effectively prevent solder erosion of electrodes and Ag migration between opposing electrodes during soldering, and are advantageous in terms of cost and mass productivity. And
In order to achieve such an object, specifically, at the time of barrel plating for forming a barrier layer and a solder plating layer on the surface of the electrode, a portion other than the electrode portion is added without adding a new process. The purpose is to prevent the formation of a plating layer.

A second object of the present invention is to provide an excellent manufacturing method capable of efficiently manufacturing such a high-quality ceramic varistor and advantageous in terms of cost and mass productivity. is there.

[0014]

Means for Solving the Problems In order to solve the above problems, the invention according to claim 1 comprises a ceramic portion obtained by firing a varistor composition material and an electrode portion provided on the surface thereof. The ceramic varistor is characterized in that the surface of the ceramic portion excluding the electrode portion is covered with a high resistance layer having a spinel structure containing Zn and Sb as main components.

According to this configuration, the following operation can be obtained. That is, the high-resistance layer having a spinel structure containing Zn and Sb as main components has a sufficiently high resistance value. By providing such a high resistance layer on the surface of the ceramic part except for the electrode part, the plating layer is formed on the part other than the electrode part at the time of barrel plating for forming a barrier layer and a solder plating layer on the surface of the electrode. The formation of the barrier layer and the solder plating layer can be easily and reliably formed only on the surface of the electrode portion by preventing the formation of the barrier layer and the solder plating layer. Therefore, the barrier layer and the solder plating layer can effectively prevent solder erosion of the electrodes during soldering and generation of Ag migration between the opposed electrodes without causing a problem such as a short circuit between the opposed electrodes.

According to a second aspect of the present invention, a varistor composition material is formed to form a formed body, and the formed body is fired to form a ceramic portion, and an electrode portion is formed on a part of the surface of the ceramic portion. In the method for manufacturing a ceramic varistor provided, at any time from the firing of the molded body to after completion of the firing, the molded body is embedded in a spinel powder containing Zn and Sb as a main component and fired. I have.

According to this configuration, the high-resistance layer can be easily formed without complicating the process simply by embedding and sintering the compact in the spinel powder containing Zn and Sb as main components at any time. Can be formed. That is, as described in the first aspect of the present invention, by providing a high resistance layer on the surface of the ceramic portion excluding the electrode portion, at the time of barrel plating for forming a barrier layer and a solder plating layer on the surface of the electrode, A plating layer is prevented from being formed on a portion other than the electrode portion, and the barrier layer and the solder plating layer can be easily and reliably formed only on the surface of the electrode portion.

According to a third aspect of the present invention, in the manufacturing method of the second aspect, the temperature at which the compact is embedded in the spinel powder and fired is in the range of 1000 to 1200 ° C. It is characterized by.

According to this configuration, by firing the spinel powder at an appropriate temperature, a high-quality, high-resistance layer can be efficiently produced at a sufficient production rate.

The invention according to claim 4 is the invention according to claim 2 or 3.
When expressed in the production method according the spinel powder, a stoichiometric composition in Zn _X Sb _Y O _Z in, Zn _X
B / A = 1.0 where A is site A and Sb _Y is site B
It is characterized in that Sb is adjusted to have a stoichiometric excess in the range of １．２1.25.

According to this configuration, a high-resistance layer having a sufficient thickness can be formed by using a spinel powder having an appropriate B / A site ratio.

According to a fifth aspect of the present invention, in the manufacturing method according to any one of the second to fourth aspects, the spinel powder comprises a mixed powder containing Zn and Sb as a main component in a quantity of 1000.
It is characterized by being produced by firing at a temperature in the range of ~ 1200 ° C.

According to this configuration, by firing a mixed powder containing Zn and Sb as main components at an appropriate temperature, a high-quality spinel powder can be efficiently produced at a sufficient production rate.

[0024]

Embodiments [1. Manufacturing Process of Ceramic Varistor] An example of a manufacturing process of a ceramic varistor to which the present invention is applied will be described below. Here, the manufacturing process of the ceramic varistor according to the present invention includes a process of generating a spinel powder and a process of forming a high-resistance spinel layer (high-resistance layer having a spinel structure). Hereinafter, these steps and conditions thereof will be described in detail. [1-1. Production process of spinel powder and its conditions]
While the stoichiometric composition of the spinel powder is Zn ₇ Sb ₂ O ₁₂ and the B / A site ratio in the case where Zn _X is A site and Sb _Y is B site is gradually changed, deionization is performed by a ball mill. By mixing with water, mixed powders of ZnO and Sb ₂ O ₃ having various composition ratios which differ stepwise were prepared. Next, this mixed powder was baked for 4 hours while changing the calcination temperature stepwise to produce Zn and Sb spinel powder.

At this point, as an example, for the mixed powder having a B / A site ratio of 1.10, the firing temperature when producing the spinel powder is changed stepwise from 950 to 1300 ° C. When the reaction product was examined by the powder X-ray diffraction method, the results shown in the following Table 1 were obtained.

[0026]

[Table 1]

As can be seen from this table, the firing temperature is 10
If it is less than 00 ° C., there are unreacted materials ZnO and SbO _X. When the sintering temperature is in the range of 1000 ° C. to 1200 ° C., unreacted ZnO and SbO _X do not exist, but when the sintering temperature exceeds 1200 ° C., the unreacted substance of ZnO alone exists again. Become.

The result of this investigation can be determined as follows.
In other words, when the firing temperature is lower than 1000 ° C., the firing rate is too low and the generation rate is slow, and the spinel powder cannot be sufficiently generated in the firing time of 4 hours.
It is believed that unreacted materials ZnO and SbO _X is present. When the firing temperature reaches 1300 ° C., the firing temperature is too high, so that
Is considered to evaporate and unreacted ZnO alone is generated again. On the other hand, if the firing temperature is 10
In the case of 00 ° C to 1200 ° C, it is considered that high-quality spinel powder can be efficiently produced at a sufficient production rate because the firing temperature is appropriate.

From the above, it can be seen that it is desirable that the sintering temperature at the time of producing the spinel powder be in the range of 1000 ° C. to 1200 ° C. [1-2. Step of Forming High-Resistance Spinel Layer and Conditions] Next, 3.2 × 2.5 × 1.0 (mm) is laminated on the spinel powder by using the spinel powder prepared in the above-described step. Embedded chip type ceramic fired body
It was baked at 50 ° C. for 4 hours, and as shown in FIG. 1, a high-resistance spinel layer 7 was formed on the surface of the semiconductor ceramic portion 1 of the varistor.

FIGS. 2 and 3 show the high-resistance spinel layer 7 formed in this manner. In particular, the high-resistance spinel layer 7 is embedded and baked in a spinel powder having a B / A site ratio of Zn and Sb spinel of 1.10. FIG. 5 is a photograph showing a state of a surface and a cross section of a high-resistance spinel layer 7 formed as described above.

As shown in FIGS. 2 and 3, a very dense high-resistance spinel layer 7 having a thickness of about 60 μm or more is formed. Further, when the resistance value of the high resistance spinel layer 7 was measured, it was confirmed that a sufficiently high resistance value on the order of 10 ⁹ (Ωcm) was obtained.

Further, in order to examine the relationship between the high resistance spinel layer 7 generated as described above and the B / A site ratio of the spinel powder for burying and firing, the B / A site ratio was set to 0.
A mixed powder having a stepwise change in the range of 95 to 1.30 was produced, and calcined at 1050 ° C. for 4 hours to produce a spinel powder having a B / A site ratio stepwise different. Then, similarly to the above, 3.2 × 2.5 ×
A 1.0 (mm) laminated chip type ceramic fired body was embedded and fired at 1050 ° C. for 4 hours to form a high-resistance spinel layer 7 on the surface of the semiconductor ceramic portion 1 of the varistor as shown in FIG. . When the relationship between the B / A site ratio of the spinel powder for burying and firing and the thickness (μm) of the formed high-resistance spinel layer 7 was examined, the results shown in Table 2 below were obtained. Was done.

[0033]

[Table 2]

As can be seen from this table, if the B / A site ratio of the spinel powder is less than 1.0, a sufficiently high resistance spinel layer cannot be formed on the surface of the ceramic fired body.
When the B / A site ratio is in the range of 1.0 to 1.25, the thickness of the high-resistance spinel layer increases as the B / A site ratio increases. If it exceeds, the thickness of the formed high resistance spinel layer does not increase, and the effect of increasing the B / A site ratio is lost.

From the results of this investigation, it was found that spinel powder B / A
It is understood that the site ratio is desirably in the range of 1.0 to 1.25. [1-3. External Electrode Forming Step] Further, following the above-described step of forming the high-resistance spinel layer 7, the high-resistance spinel layer 7 formed at the electrode forming portion of the fired ceramic body is polished, blasted, or the like by mechanical means. After the removal, a pair of external electrodes 3 containing Ag or Ag / Pd as a main component were formed as in the conventional case. FIG. 1 shows a varistor completed in this way. [2. Operation / Effect] According to the manufacturing process described above and the varistor completed thereby, the following operation / effect can be obtained.

First, in producing the spinel powder,
As described above, it is desirable that the firing temperature be in the range of 1000 to 1200 ° C., whereby a high-quality spinel powder can be efficiently produced at a sufficient production rate. Similarly, the firing temperature when forming the high-resistance spinel layer using the spinel powder thus obtained is desirably in the range of 1000 to 1200 ° C., whereby a sufficient A high-quality, high-resistance spinel layer can be efficiently formed at a generation rate. Furthermore, the site ratio of the spinel powder is set to 1.0 to
It is desirable that the thickness be in the range of 1.25, so that a high-resistance spinel layer having a sufficient thickness can be formed.

As described above, the high-resistance spinel layer 7 generated under the above-described conditions has a thickness of 10 ⁹ (Ωc
m) Since such a high-resistance spinel layer 7 is provided on the surface of the semiconductor ceramic part 1 except for the electrode part because of having a sufficiently high resistance value on the order, a barrier layer and a solder are formed on the surface of the external electrode 3 during barrel plating. A plating layer can be formed favorably. That is, at the time of barrel plating, a plating layer is prevented from being formed on a portion other than the external electrode 3, and a barrier layer such as a Ni layer or a copper layer and a solder plating layer can be easily and only provided on the surface of the external electrode 3. It can be formed reliably. Therefore, the barrier layer and the solder plating layer can effectively prevent the solder erosion of the external electrodes 3 and the occurrence of Ag migration between the opposing external electrodes 3 without causing a problem such as a short circuit between the opposing external electrodes 3. . Furthermore, since the occurrence of solder erosion of the external electrodes 3 can be prevented in this manner, a flow-type soldering process can be applied, and the efficiency of soldering can be improved. Therefore, it is advantageous in terms of cost and mass productivity.

According to the above-described manufacturing process, Zn and S
By simply embedding and firing a ceramic fired body in a spinel powder containing b as a main component, a high-resistance spinel layer can be easily formed without complicating the process. Therefore, this point is also advantageous in terms of cost and mass productivity. [3. Other Embodiments] It should be noted that the present invention is not limited to the above-described embodiment, but can be similarly applied to a discrete type ceramic varistor as shown in FIG. An effect can be obtained. Further, in the present invention, the firing temperature and firing time during the formation of the spinel powder and the formation of the high-resistance spinel layer,
Alternatively, specific production conditions such as the B / A site ratio of the spinel powder can be appropriately selected. For example, in the above-described embodiment, the case where the ceramic fired body is embedded in the spinel powder and fired to form the high-resistance spinel layer is described. It is also possible to carry out at the stage of firing the molded body made of the varistor composition material before performing.
That is, in the present invention, the time of forming the high-resistance spinel layer can be arbitrarily selected from the time of firing the molded body to the time after completion of firing. Further, the present invention is similarly applicable to various ceramic varistors having various ratings and dimensions and shapes, and similarly excellent functions and effects can be obtained.

[0039]

As described above, according to the present invention, by covering the surface of the ceramic portion except for the electrode portion with the high resistance layer having a spinel structure containing Zn and Sb as main components, the other portions than the electrode portion can be obtained. Prevents the formation of plating layers on parts,
The barrier layer and the solder plating layer can be easily and reliably formed only on the surface of the electrode portion. Therefore, it is possible to effectively prevent the solder erosion of the electrodes and the occurrence of Ag migration between the opposed electrodes by the barrier layer and the solder plating layer, without causing a problem such as a short circuit between the opposed electrodes, thereby reducing cost and cost. A high-quality ceramic varistor that is advantageous in terms of mass productivity can be provided.

Further, the high-quality ceramic varistor as described above can be manufactured efficiently without complicating the process only by embedding and firing the compact in a spinel powder containing Zn and Sb as main components. It is possible to provide an excellent manufacturing method which is advantageous in terms of cost and mass productivity.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing an example of a multilayer chip type ceramic varistor according to the present invention.

FIG. 2 is a photograph showing an example of a surface state of a high resistance spinel layer formed according to the present invention.

FIG. 3 is a photograph showing an example of a cross-sectional state of a high-resistance spinel layer formed according to the present invention.

FIG. 4 is a sectional view schematically showing an example of a discrete type ceramic varistor according to the present invention.

FIG. 5 is a cross-sectional view schematically showing an example of a laminated chip type ceramic varistor according to the related art.

FIG. 6 is a cross-sectional view schematically showing one example of a discrete type ceramic varistor according to the related art.

[Description of Signs] 1 ... Semiconductor ceramic part 2 ... Internal electrode 3 ... External electrode 4 ... Counter electrode 5 ... Metal wire 6 ... Solder layer 7 ... High resistance spinel layer

Claims (5)

[Claims] 1. A ceramic varistor comprising a ceramic portion obtained by firing a varistor composition material and an electrode portion provided on the surface thereof, wherein the surface of the ceramic portion excluding the electrode portion has Zn and S
A ceramic varistor characterized by being covered with a high-resistance layer having a spinel structure containing b as a main component. 2. A varistor composition material is molded to form a molded body, and the molded body is fired to form a ceramic part, and an electrode part is provided on a part of the surface of the ceramic part to manufacture a ceramic varistor. A method for manufacturing a ceramic varistor, comprising: embedding a compact in a spinel powder containing Zn and Sb as a main component and calcining the compact at any time from the firing of the compact to the completion of the firing. 3. The method for producing a ceramic varistor according to claim 2, wherein a temperature at which the compact is embedded and baked in the spinel powder is in a range of 1000 to 1200 ° C. 4. The spinel powder, when its stoichiometric composition is represented by Zn _x Sb _Y O _Z , Zn _x is an A site,
4. The ceramic varistor according to claim 2, wherein Sb _Y is a B site, and Sb is adjusted to have a stoichiometric excess in the range of B / A = 1.0 to 1.25. Production method. 5. The spinel powder according to claim 2, wherein the spinel powder is produced by firing a mixed powder containing Zn and Sb as main components at a temperature in the range of 1000 to 1200 ° C. A method for manufacturing a ceramic varistor according to any one of the preceding claims.