JP5218499B2 - Manufacturing method of ceramic multilayer electronic component - Google Patents

Description

  The present invention relates to a method for manufacturing a ceramic multilayer electronic component including an element body having ceramic as a main composition (main component).

  2. Description of the Related Art In recent years, in a ceramic multilayer electronic component made of a thermistor, a capacitor, an inductor, a LTCC (Low Temperature Co-fired Ceramics), a varistor, or a composite thereof, an internal electrode is formed inside a ceramic body. Usually, an internal electrode is exposed on the end face of the element body, and after forming a base electrode connected to the internal electrode on the end face of the element body, for example, a Ni layer and an Sn layer are formed on the base electrode by plating. A terminal electrode is formed. An element body (after sintering or firing) of a ceramic multilayer electronic component may be porous, for example, a multilayer ceramic PTC or a low dielectric constant ferrite material. When the terminal electrode is formed by plating, the plating solution enters the element body, and power is supplied from the internal electrode to adhere to the inside of the void of the element body that is a porous body, resulting in a decrease in insulation resistance (IR). There is a problem.

  As one of the techniques for solving such a problem caused by the fact that the element body is porous, a technique for covering the surface of the element body with glass has been proposed (see Patent Document 1). In the technique disclosed in Patent Document 1, a ceramic PTC element is immersed in an aqueous glass solution to form a liquid glass film, and then the glass film is fired at 600 ° C. in the atmosphere to obtain a ceramic PTC element. A glass layer is formed on the surface layer of the element body.

JP 2004-128488 A

  However, in this method, the water in the glass aqueous solution evaporates due to the heat during firing and accumulates in the voids of the porous body, which expands and breaks through the liquid glass coating and is released to the outside. There is a possibility that pinholes are generated in the fired glass layer, and the pinholes thus formed in the glass layer can become an intrusion path for the plating solution, causing an IR defect.

  Accordingly, the present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a ceramic multilayer electronic component capable of forming a glass layer without generating pinholes.

  In order to solve the above problems, a method for producing a ceramic multilayer electronic component according to the present invention includes a step of forming a glass powder layer on the surface of a sintered body mainly made of ceramics, and a predetermined firing temperature in a firing furnace. A firing step of firing the glass powder layer, and in the firing step, the pressure in the firing furnace at a predetermined firing temperature is set to 2.2 times or more of the pressure in the firing furnace at room temperature. Bake the layer.

  In the firing step, the inventors of the present invention applied the glass powder layer to the glass layer by firing the pressure in the firing furnace at the firing temperature at 2.2 times or more the pressure in the firing furnace at room temperature. It has been found that the occurrence of pinholes can be significantly suppressed. This is thought to be due to the following reasons. That is, when the porous element body is fired, the pressure of the gas inside the voids of the element element increases as the temperature rises. The glass layer at the time of firing is melted although it has a high viscosity, and when the gas pressure inside the element body increases, it is considered that a gas is blown through the glass layer and a pinhole is formed. On the other hand, in the present invention, it is considered that by increasing the pressure in the furnace at the firing temperature to a certain value or more, ejection of gas inside the void is prevented, and as a result, generation of pinholes is suppressed ( However, the action is not limited to this).

  For example, the glass powder layer is fired in a state where the atmosphere in the firing furnace is sealed. As a result, since the firing temperature of glass is usually 350 ° C. or higher, the pressure in the firing furnace at the firing temperature can be made 2.2 times or more of the pressure in the firing furnace at room temperature according to Boyle Charles' law. The generation of pinholes in the glass layer can be significantly suppressed.

  The effect of the present invention is particularly remarkable in the case of a porous body having a low sintered density of the element body. For example, the sintered density of the element body is 90% or less.

  Preferably, the baking is performed in an oxidizing gas atmosphere. As a result, the element body of the ceramic multilayer electronic component is prevented from being reduced in the firing step, and fluctuations in the characteristics of the ceramic multilayer electronic component are suppressed. Examples of the oxidizing gas include oxygen gas, mixed gas of oxygen and nitrogen, mixed gas of inert gas such as oxygen and Ar, ozone gas, NOx (x> 1), SOx (x> 2), water vapor and the like.

  According to the method for manufacturing a ceramic multilayer electronic component of the present invention, the pressure inside the firing furnace at the firing temperature is set to 2.2 times or more of the pressure inside the firing furnace at room temperature, thereby firing the void inside the element body. It is possible to prevent the generation of pinholes in the glass layer by preventing the gas from being ejected.

It is sectional drawing which shows schematic structure of the ceramic PTC element of this embodiment. It is sectional drawing which shows schematic structure of the ceramic PTC element of this embodiment. It is process drawing which shows an example of the procedure which manufactures a ceramic PTC element. It is a top view which shows the space | gap of the element body surface of a ceramic PTC element. It is process drawing which shows an example of the procedure which manufactures a ceramic PTC element. It is process drawing which shows an example of the procedure which manufactures a ceramic PTC element. It is a figure which shows the structure of a baking furnace. It is a figure which shows the relationship between the furnace pressure and the pinhole density in a calcination temperature. It is a figure which shows the relationship between the furnace pressure and the pinhole density in a calcination temperature. It is a figure which shows the relationship between the furnace pressure and the pinhole density in a calcination temperature. It is a figure which shows the relationship between the furnace pressure and the pinhole density in a calcination temperature. It is a figure which shows the relationship between the furnace pressure and the pinhole density in a calcination temperature.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the illustrated ratios. Further, the following embodiments are exemplifications for explaining the present invention, and are not intended to limit the present invention only to the embodiments. Furthermore, the present invention can be variously modified without departing from the gist thereof.

  FIG. 1 is a cross-sectional view showing a schematic structure of a ceramic multilayer electronic component. The ceramic multilayer electronic component 1 is a PTC thermistor having a multilayer body 4 including an element body 2 made of ceramics and a plurality of internal electrodes 3 formed in the element body 2. In other words, the ceramic multilayer electronic component 1 At least one unit structure in which the electrodes 3 are stacked is provided. More specifically, the internal electrodes 3 having end portions exposed on one side surface of the multilayer body 4 and the internal electrodes 3 having end portions exposed on the other side surface of the multilayer body 4 are alternately stacked. .

  A glass layer 5 is formed on the surface excluding both side surfaces of the laminate 4. Although not shown, a part of the glass component of the glass layer 5 penetrates into the surface layer of the laminate 4.

  Base electrodes 6 are provided on both side surfaces of the multilayer body 4 so as to cover those side surfaces, and each ground electrode 6 is a group of internal electrodes 3 exposed from one side surface of the multilayer body 4 or a multilayer body. 4 is electrically connected to the group of internal electrodes 3 exposed from the other surface.

  A terminal electrode 7 is further formed on the outside of the base electrode 6 by plating. These terminal electrodes 7 are joined to, for example, electrodes on the wiring board with solder or the like. Each terminal electrode 7 has, for example, a two-layer structure including a Ni layer 7a and a Sn layer 7b that are stacked from the base electrode 6 side. The Ni layer 7a functions as a barrier metal that prevents the Sn layer 7b and the base electrode 6 from contacting each other and prevents corrosion of the base electrode 6 due to Sn, and has a thickness of, for example, about 2 μm. Further, the Sn layer 7b has a function of improving the wettability of the solder, and the thickness thereof is, for example, about 4 μm.

  The element body 2 is made of ceramics, and specifically, is made of semiconductor ceramics, dielectric ceramics, and magnetic ceramics. Such a ceramic material is not limited, and examples thereof include barium titanate, strontium titanate, boron nitride, ferrite, lead zirconate titanate, silicon carbide, silicon nitride, steatite, zinc oxide, and zirconia.

  A method for synthesizing the ceramic powder used for forming the element body 2 is not particularly limited, and for example, a hydrothermal method, a hydrolysis method, a coprecipitation method, a solid phase method, a sol-gel method, or the like is used. And may be calcined as necessary.

  On the other hand, a material mainly composed of Ag, Ni, Cu, Al, or the like is used for the internal electrode 3 in terms of enabling reliable ohmic contact with the element body 2, and these alloys or It may be a composite material.

  On the other hand, the base electrode 6 is obtained, for example, by applying and baking a conductive paste on the side surface of the multilayer body 4. Examples of the conductive paste for forming the base electrode 6 mainly include a glass powder, an organic vehicle (binder), and a metal powder. By firing the conductive paste, the organic vehicle is volatilized, Finally, the base electrode 6 containing a glass component and a metal component is formed. In addition, you may add various additives, such as a viscosity modifier, an inorganic binder, and an oxidizing agent, to an electrically conductive paste as needed.

  For example, the base electrode 6 contains Ag and Zn as metal components, and this Zn is a constituent component of the internal electrode 3 such as Ni, Cu, or Al and Ag contained in the base electrode 6. By forming an alloy with both of them at the joining site, the contact resistance is reduced and the joining area between the internal electrode 3 and the base electrode 6 is increased, thereby sufficiently reducing the connection resistance. In addition, the mechanical bonding strength between the internal electrode 3 and the base electrode 6 can be increased.

  Moreover, as shown in FIG. 2, it is also preferable to make the base electrode 6 into two layers. It is preferable to form a dense base electrode layer 6b made of Ag alone on the base electrode layer 6a made of Ag and Zn. The base electrode layer 6a made of Ag and Zn layers is alloyed during firing, but at this stage, there is a tendency for voids (kerkendal voids) to occur due to the Kirkendall phenomenon. Further, the plating solution penetrates into the element body, which remains inside the porous body and causes a serious problem in reliability. When the dense base electrode layer 6b made of Ag alone is formed on the base electrode layer 6a made of Ag and Zn, the terminal electrode is formed even if a void portion having an opening is generated in the base electrode layer 6a made of Ag and Zn. It is possible to prevent the plating solution from entering the element body during plating, and it is possible to constitute a ceramic multilayer electronic component having excellent reliability. The frit amount of the base electrode layer 6b is preferably as small as possible in order to ensure denseness, and is 8% or less, more preferably 5% or less, and most preferably 3% or less. The average particle size of the silver powder is preferably 1 μm or less in order to improve the density of the electrode.

  Next, a method for manufacturing the ceramic multilayer electronic component 1 according to the present embodiment will be described with reference to FIGS. 3-6 is process drawing which shows an example of the procedure which manufactures the ceramic multilayer electronic component 1. FIG.

  First, as shown in FIG. 3, a laminated body 4 having a laminated structure of the element body 2 and the internal electrodes 3 is formed. The laminated body 4 is manufactured as follows, for example. A ceramic powder, an organic solvent, an organic binder, a plasticizer, and the like are mixed to form a ceramic slurry, and then molded by a doctor blade method to obtain a sheet-like body, a so-called ceramic green sheet. Subsequently, a pattern of the internal electrode 3 is formed on the ceramic green sheet by printing a conductive paste containing metal powder, a binder resin, and a solvent. Further, subsequently, a plurality of element bodies 2 in which the internal electrodes 3 are formed and a plurality of element bodies 2 in which the internal electrodes 3 are not formed are alternately laminated, and further pressed to obtain a laminated structure. Then, the laminated structure is divided into individual laminated bodies 4 by cutting. Thereby, the edge part of the internal electrode 3 will be in the state exposed from the side surface of the laminated body 4 after a cutting | disconnection. Next, the laminate 4 is subjected to a binder removal treatment in the air and then fired to obtain a sintered laminate 4.

  FIG. 4 is a plan view showing the surface of the element body 2. The element body 2 that is a sintered body may be porous like a multilayer ceramic PTC or a low dielectric constant ferrite element body, and a large number of voids 2a are formed on the surface and inside thereof.

  Next, as shown in FIG. 5, a glass slurry containing glass powder, a binder resin and a solvent is applied to the entire surface of the base body 2 to form a glass powder layer 5 a on the surface layer of the laminate 4.

  Subsequently, as shown in FIG. 6, the glass powder layer 5a is fired. By this firing, a dense and high-density glass layer 5 is formed on the element body 2. In the firing step of the glass powder layer 5a, the element body 2 on which the glass powder layer 5a is formed is carried into a firing furnace, the temperature in the firing furnace is increased, and the glass powder layer is fired at a predetermined firing temperature. In this embodiment, in this firing step, firing is performed by setting the pressure in the firing furnace at the firing temperature to 2.2 times or more than the pressure in the firing furnace at room temperature.

FIG. 7 is a diagram showing a schematic configuration of a firing furnace.
As shown in FIG. 7, a gas supply source 103 is connected to the firing furnace 101 via a flow rate adjustment valve 102. Further, an exhaust pump 105 is connected through a pressure adjustment valve 104. Further, the firing furnace 101 is provided with a pressure gauge 106 for measuring the pressure in the firing furnace.

  The gas supply source 103 supplies a gas having a desired pressure, and the flow rate of the gas supplied from the gas supply source 103 is adjusted by the flow rate adjusting valve 102. The gas supply source 103 preferably supplies an oxidizing gas. Examples of the oxidizing gas include oxygen gas, mixed gas of oxygen and nitrogen, mixed gas of inert gas such as oxygen and Ar, ozone gas, NOx (x> 1), SOx (x> 2), water vapor and the like.

  The exhaust pump 105 is composed of, for example, a mechanical booster pump. The amount of exhaust by the exhaust pump 105 is adjusted by adjusting the opening of the pressure adjustment valve 104.

  In the firing furnace 101 configured as described above, the pressure in the firing furnace 101 is adjusted to a desired pressure while supplying the oxidizing gas into the firing furnace 101 by adjusting the flow rate adjustment valve 102 and the pressure adjustment valve 104. .

  In the present embodiment, the glass powder layer 5a is adjusted by using the firing furnace 101 described above so that the pressure in the firing furnace at the firing temperature is equal to or higher than a certain value with respect to the pressure in the firing furnace at room temperature. Is fired to form the glass layer 5.

  As a subsequent process, after removing the glass layer 5 formed on the side surface of the element body 2, the base electrode 6 is formed on the side surface of the element body 2 (see FIG. 1). In forming the base electrode 6, a conductive paste containing metal powder, an organic binder, glass frit, and a solvent is applied to the side surface of the element body 2, dried, and then fired. By firing at this time, the organic vehicle contained in the base electrode is volatilized, and finally the base electrode 6 containing a glass component and a metal component is formed.

  Subsequently, the Ni layer 7 a and the Sn layer 7 b are sequentially deposited on the surface of the base electrode 6 by electroplating to form the terminal electrode 7. For example, in the formation of the Ni layer 7a, a barrel plating method is adopted, and Ni of 2 μm is deposited using a Watt-based bath. Further, in forming the Sn layer 7b, a barrel plating method is adopted, and Sn is deposited by 4 μm using a neutral tin plating bath. Thus, the ceramic multilayer electronic component 1 is manufactured (see FIG. 1).

  Examples of the present invention will be described below, but the present invention is not limited to these examples. In the following examples, a laminated PTC was formed as the ceramic laminated electronic component 1.

Example 1
Glass coating of laminated PTC with an outer diameter of 1.6 × 0.8 × 0.8 mm and sintered body density of 80, 85, 90, and 95% was performed with a barrel spray device of Φ200. First, a glass powder having a glass transition temperature of 450 ° C. and a softening temperature of 520 ° C. and an average particle diameter of 1.2 μm was prepared, and the glass powder and polyvinyl alcohol resin were mixed at a weight ratio of 95: 5. Further, the obtained solid component (a mixture of glass powder and polyvinyl alcohol) and a solvent were mixed at a weight ratio of 2.5: 97.5, and stirred for 16 hours by a ball mill. As the solvent, a mixture of water and ethanol at 8: 2 was used. Next, 900 g of the chip was put into a barrel spray apparatus, and a glass coating film (glass powder layer) was formed on the chip surface. The hot air temperature was 70 ° C., the barrel rotation speed was 5 rpm (circumferential speed 0.05 m / s), and the slurry discharge amount and coating time were appropriately adjusted. No chip sticking or corner exposure occurred after coating. At this time, the thickness of the glass powder layer on the flat portion of the chip surface was 7 μm on average.

Next, 100 pieces of the obtained chips were baked at 550 ° C. The rate of temperature increase and decrease is 5 deg / min, and this temperature is maintained at 550 ° C. for 10 minutes. Here, the pressure in the furnace at room temperature was set to 1 atm, and the pressure in the furnace at the firing temperature (550 ° C.) was changed from 1 to 3 atm in steps of 0.2 atm. The pressure in the furnace was linearly increased in proportion to the temperature increase, and adjusted to a specified pressure at the firing temperature. The pressure inside the furnace is adjusted by adjusting the flow rate adjusting valve 102 by adjusting the flow rate adjusting valve 102 with the pressure of the gas supply source 103 higher than the pressure inside the furnace at 550 ° C. while the exhaust pump 105 exhausts the exhaust side. This was carried out by supplying at a rate of 100 ml / min and automatically adjusting the opening of the pressure adjustment valve 104 on the exhaust side (see FIG. 7). The thickness of the glass layer after firing was 5 μm. Five chips after firing were randomly selected, and a 1 mm ² area was observed with a 500 times SEM on the flat surface of each chip, and the number of pinholes was investigated. The results are shown in Table 1 and FIG.

  As shown in Table 1 and FIG. 8, when the furnace pressure at the firing temperature / the furnace pressure at room temperature falls below 2.2, pinholes are generated, and rapidly as the furnace pressure at the firing temperature decreases. It turned out to increase. It has also been found that the occurrence of pinholes rapidly increases when the sintered density of the element body is less than 90%. The case where the pressure in the furnace at the firing temperature is 1 atm is the most well-known case where firing is performed with a part of the firing furnace open, but in this case, it has been found that pinholes are most severely generated.

  Next, the surface where the internal electrodes are exposed is subjected to blasting to remove the glass layer on this surface, and then the surface is coated with a conductive paste of Ag 60 wt%, Zn 30 wt%, and the remaining glass and baked at 500 ° C. Thus, a base electrode was formed. After that, a 2 μm Ni layer and a 4 μm Sn layer were formed on the base electrode of this chip by wet barrel plating. When the appearance of the chip after plating was examined, the sample in which the glass layer was formed under the firing conditions where pinholes occurred in the glass layer showed plating adhesion on the element body, but the sample was fired under conditions where no pinholes occurred Was not seen.

(Example 2)
In Example 1, the same examination was performed by setting the pressure in the furnace at room temperature to 0.5 atm. The results are shown in Table 2 and FIG.

  As shown in Table 2 and FIG. 9, when the furnace pressure at the firing temperature / furnace pressure at room temperature falls below 2.2 as in Example 1, a pinhole is generated, and the furnace pressure at the firing temperature is It turned out to increase rapidly as it gets smaller. It has also been found that the occurrence of pinholes rapidly increases when the sintered density of the element body is less than 90%.

(Example 3)
A laminated PTC was produced in the same manner as in Example 1 except that the firing furnace was sealed and fired in the state. In this case, the pressure in the furnace at the firing temperature was 2.8 atm. In this case, no pinholes were observed in all the laminated PTCs having a sintered density of 80, 85, 90, and 95%.

(Comparative Example 1)
A laminated PTC was produced in the same manner as in Example 1 except that the thickness of the glass layer was adjusted to 2 μm after firing. In this case, pinholes occurred in all samples. This is considered to be because, in the case of a porous body, glass is partially absorbed into the body during firing, so that the continuity of the glass layer is not guaranteed when the film thickness is 2 μm or less.

(Comparative Example 2)
The laminated PTC chip was immersed in a Na—Si—O ₂ -based glass aqueous solution for 60 minutes and then fired at 600 ° C. in the air. In this case, when the surface of the element body was observed, many fine pinholes of 1 μm or less were generated, and when the chip was wet-plated, the plating adhered to the entire surface of the element body. This is because moisture evaporates from the glass component that has penetrated into the element body during heating, but the water vapor degassing path at this time is a pinhole, and the thickness of the surface glass layer is 1 μm or less, This is thought to be due to the lack of continuity.

(Comparative Example 3)
A laminated PTC was produced in the same manner as in Example 1 except that firing was performed in vacuum. In this case, no pinhole was observed in any sample, but the resistance jump was 1.5 digits or less in all the samples after firing. This is presumably because the surface of the porous body was reduced because it was heated in vacuum.

Example 4
In Example 1, three types of glass are prepared: A: a bismuth-based softening temperature of 470 ° C., B: a zinc-based softening temperature of 570 ° C., and C: a silica-based softening temperature of 670 ° C. Firing was performed at 500 ° C., 600 ° C., and 700 ° C., respectively. The results of A are shown in Table 3 and FIG. 10, the results of B are shown in Tables 4 and 11, and the results of C are shown in Tables 5 and 12.

  As shown in Tables 3 to 5 and FIGS. 10 to 12, similar results were obtained even when the firing temperature of the glass was changed.

  As described above, the following knowledge is obtained by this example.

  By firing the pressure in the firing furnace at the firing temperature at 2.2 times or more than the pressure in the firing furnace at room temperature, the occurrence of pinholes in the glass layer can be significantly suppressed. This is thought to be due to the following reasons. When firing the porous element body, the pressure of the gas inside the voids of the element element increases as the temperature rises. The glass layer at the time of firing is melted although it has a high viscosity, and when the gas pressure inside the element body increases, it is considered that a gas is blown through the glass layer and a pinhole is formed. It is considered that by increasing the pressure in the furnace at the firing temperature to a certain value or more, the gas inside the void is prevented from being ejected and the generation of pinholes is suppressed.

  And it turned out that the effect of said Example is especially remarkable in the case of a porous body with a low sintered density of the element body.

  Furthermore, it has been found that the furnace pressure at the firing temperature is preferably 10 times or less of the furnace pressure at room temperature. When the pressure in the firing furnace at the firing temperature exceeds 10 times the pressure in the firing furnace at room temperature, the glass penetrates too deeply into the body during firing, and the glass thickness on the surface cuts down to 2 μm. This is because it will occur.

  Moreover, it turned out that the film thickness of a glass layer is larger than 2 and 10 micrometers or less are preferable. When the film thickness is 2 μm or less, pinholes increase. On the other hand, when the film thickness of the glass layer exceeds 10 μm, the thermal stress between the glass and the element body increases, and cracks may occur in the glass layer or element body. Moreover, when the film thickness of a glass layer exceeds 10 micrometers, there exists a disadvantage that productivity falls.

  The method for manufacturing a ceramic multilayer electronic component of the present invention can be widely used for manufacturing a ceramic multilayer electronic component comprising a thermistor, a capacitor, an inductor, LTCC (Low Temperature Co-fired Ceramics), a varistor, and a composite component thereof.

  DESCRIPTION OF SYMBOLS 1 ... Ceramic laminated electronic component, 2 ... Element body, 2a ... Air gap, 3 ... Internal electrode, 4 ... Laminated body (sintered body), 5a ... Glass powder layer, 5 ... Glass layer, 6 ... Base electrode, 6a ... Base Electrode layer, 6b: Base electrode layer, 7 ... Terminal electrode, 7a ... Ni layer, 7b ... Sn layer, 101 ... Firing furnace, 102 ... Flow control valve, 103 ... Gas supply source, 104 ... Pressure adjustment valve, 105 ... Exhaust Pump, 106 ... pressure gauge.

Claims (5)

Forming a glass powder layer on the surface of a sintered body mainly composed of ceramics;
A firing step of firing the glass powder layer at a predetermined firing temperature in a firing furnace;
Have
In the firing step, the pressure in the firing furnace at the predetermined firing temperature is set to 2.2 to 3 times the pressure in the firing furnace at room temperature, and the glass powder layer is fired.
Manufacturing method of ceramic multilayer electronic components. Firing the glass powder layer in a state where the atmosphere in the firing furnace is sealed,
The method for producing a ceramic multilayer electronic component according to claim 1. The sintered density of the element body is 90% or less.
The manufacturing method of the ceramic multilayer electronic component of Claim 1 or 2. Firing the glass powder layer in an oxidizing gas atmosphere;
The manufacturing method of the ceramic multilayer electronic component in any one of Claims 1-3. In the firing step, the pressure in the firing furnace is increased linearly in proportion to the temperature rise.
The manufacturing method of the ceramic multilayer electronic component in any one of Claims 1-4.

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