JP2010232320A - Multilayer ceramic electronic component and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer ceramic electronic component that controls the remaining resin on the surface of an underlying electrode due to resin impregnation treatment and can improve the reliability of electric connection to the underlying electrode, and to provide a method of manufacturing the same. <P>SOLUTION: The multilayer ceramic electronic component is a multilayer ceramic electronic component subjected to resin impregnation treatment, and has an element assembly 2 mainly composed of ceramics and an underlying electrode 7 formed on the element assembly 2, wherein Ra of the surface of the underlying electrode is regulated to be 6 μm or less. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a multilayer ceramic electronic component including an element body made of ceramics and a method for manufacturing the same.

  In a multilayer ceramic electronic component composed 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. An internal electrode is exposed at a predetermined position on the end face of the element body, and after forming a base electrode thereon, a Ni layer and a Sn layer are formed by plating to form a terminal electrode. This terminal electrode is soldered to an electrode provided on a predetermined wiring portion of the printed wiring board, for example.

  However, when an element body made of ceramics is immersed in a plating solution for forming the Ni layer and the Sn layer, the plating solution penetrates into minute pores existing in the element body and the base electrode, and is made of ceramics. Problems such as erosion of the element body and deposition of plated metal on the element surface occur. In addition, the plating solution that has entered the pores of the base electrode is caused by the solder that expands and melts due to the heat at the time of mounting and disperses the solder, which is caused by the plating solution that has entered the pores in the moisture resistance load test. Inconveniences such as short circuit failure due to migration. In order to prevent the occurrence of these problems, a technique has been proposed in which the pores of the element body are impregnated with a resin such as silicon (see Patent Document 1).

JP-A-5-326316

  However, as a result of detailed examination by the present inventor, when the resin impregnation treatment described in Patent Document 1 is used for a component having a large unevenness of the base electrode, not only the pores inside the base electrode but also the surface of the base electrode is used. It has been found that the problem of residual resin can occur. Due to the presence of the resin remaining on the surface of the base electrode, the plating film (terminal electrode) is interrupted, and accordingly, soldering failure occurs. In order to remove the resin adhering to the unevenness of the surface of the base electrode, it is conceived to improve the cleaning ability in the cleaning process. In this case, the resin filled in the pores inside the element body and the base electrode is also considered. There is a problem that it is removed and the embedding of pores, which is the original purpose, becomes insufficient.

  The present invention has been made in view of the above circumstances, and the object thereof is to selectively fill the pores of the element body and the base electrode with resin, and eliminate the resin residue on the surface of the base electrode other than the pores. Another object of the present invention is to provide a monolithic ceramic electronic component having good solderability and ensuring a continuity of the plating film and a method for manufacturing the same.

  In order to achieve the above object, a multilayer ceramic electronic component of the present invention is a multilayer ceramic electronic component that is subjected to resin impregnation treatment, and comprises an element body mainly made of ceramics, and a base electrode formed on the element body. And Ra on the surface of the base electrode is specified to be 6 μm or less.

  In the above configuration, since the surface roughness Ra of the surface of the base electrode is as smooth as 6 μm or less, the surface unevenness where the resin tends to remain is reduced. Therefore, the resin remaining on the surface of the base electrode by the resin impregnation process can be removed by a simple cleaning process. This makes it possible to completely remove the resin remaining on the surface of the base electrode other than the pores while filling the pores inside the element body and the base electrode with the resin, and plating the terminal electrode caused by the residual resin. Generation | occurrence | production of a non-sticking part and the fall of the solder wettability accompanying this are suppressed.

  Furthermore, in order to achieve the above object, a method for manufacturing a multilayer ceramic electronic component according to the present invention includes a step of forming a base electrode having a surface of Ra of 6 μm or less on an element body mainly made of ceramic, A step of performing a resin impregnation treatment and a step of forming a terminal electrode on the base electrode.

  For example, in the step of forming the base electrode, a conductive paste in which metal powder having an average particle diameter of 7 μm or less is dispersed is used. As a result, a base electrode having a surface with an Ra of 6 μm or less is effectively formed without additional processing (ie, without increasing the number of steps).

  According to the multilayer ceramic electronic component and the method of manufacturing the same of the present invention, by setting the Ra on the surface of the base electrode to 6 μm or less, the resin and the pores of the base electrode are filled with the resin by the resin impregnation treatment, and at the same time other than the pores Residue of the resin on the surface of the underlying electrode can be suppressed, and the reliability of electrical connection to the underlying electrode can be improved.

It is a schematic sectional drawing of the multilayer ceramic electronic component which concerns on this embodiment. It is sectional drawing which shows the manufacturing process of the multilayer ceramic electronic component which concerns on this embodiment. It is sectional drawing which shows the manufacturing process of the multilayer ceramic electronic component which concerns on this embodiment. It is sectional drawing which shows the manufacturing process of the multilayer ceramic electronic component which concerns on this embodiment. It is an expanded sectional view of the foundation electrode in the manufacturing process of the multilayer ceramic electronic component concerning this embodiment. It is an expanded sectional view of the foundation electrode in the manufacturing process of the multilayer ceramic electronic component concerning this embodiment. It is an expanded sectional view of the base electrode in the manufacturing process of the multilayer ceramic electronic component of a prior art example. It is an expanded sectional view of the base electrode in the manufacturing process of the multilayer ceramic electronic component of a prior art example. It is a figure which shows the relationship between a base electrode surface roughness and a solder wetting defect rate. It is a figure which shows the relationship between a base electrode surface roughness and a solder wetting defect rate.

  Embodiments of the present invention will be described below 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 PTC which is an example of a multilayer ceramic electronic component according to the present embodiment. The multilayer ceramic electronic component 1 has 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. More specifically, the internal electrode 3 having an end portion exposed on one side surface (end surface) of the element body 2 and the internal electrode 3 having an end portion exposed on the other side surface of the element body 2 include the element body. 2 are alternately stacked.

  Two base electrodes 7 are formed on both side surfaces of the element body 2. Each base electrode 7 is electrically connected to a group of internal electrodes 3 exposed from one side surface of the element body 2 or a group of internal electrodes 3 exposed from the other surface of the element body 2.

  In the case of the laminated PTC, the element body is a porous body mainly composed of barium titanate, and the density after sintering is 80 to 90%. In this case, open cells exist over the entire element body, and if the plating process is performed as it is, the plating solution penetrates the entire element body and the plating adheres to the entire surface of the element body. In order to avoid this, a resin such as silicon is impregnated after the base electrode is formed, and the open cells are filled with the resin. The material of the internal electrode is preferably nickel. In the case of the laminated PTC, the entire element body 2 and the base electrode 7 are filled with resin. In the case of other laminated parts having a sintered density exceeding 90%, the resin tends to be filled only in the pores on the surface of the element body.

  A terminal electrode 8 composed of a Ni layer 8a and a Sn layer 8b is further formed on the surface of the base electrode 7 by plating. These terminal electrodes 8 and, for example, electrodes on the wiring board are joined by solder or the like.

  In the present embodiment, the surface roughness Ra of the base electrode 7 is defined to be 6 μm or less. As a method for defining the surface roughness, the centerline surface roughness Ra, the maximum height Rmax, the ten-point average height Rz, and the like are known. In the present embodiment, among these, the centerline surface roughness Ra is used. Is used. Here, the centerline average roughness Ra is a value obtained by folding a roughness curve reflecting surface irregularities from the centerline and dividing the roughness and the area obtained by the centerline by the length L (μm ). The surface roughness can be measured using a laser microscope, a contact type surface roughness measuring instrument, or the like.

  Hereinafter, each component will be described. The element body 2 is made of ceramics, specifically, semiconductor ceramics or dielectric 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. In the case of the laminated PTC, the element body is mainly composed of barium titanate, and the sintered density is as low as 80 to 90% as described above, and open cells are generated on the entire surface of the element body. It is impossible to form an electrode by plating, and the manufacturing method according to this embodiment is particularly effective.

  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.

  For the internal electrode 3, for example, a material mainly composed of Ni, Cu, Pd, Ag, or Al is used in terms of enabling reliable ohmic contact with the element body 2. There is no limitation. The internal electrode 3 is formed by printing a conductive paste containing such a metal component. In the case of laminated PTC, Ni is preferably used.

  Examples of the resin in the resin-impregnated layer 5 include silicon resin, phenol resin, and epoxy resin. In addition, vinyl benzyl resin, polyvinyl benzyl ether compound resin, bismaleimide triazine resin (BT resin), polyphenyl ether ( Polyphenylene ether oxide) resin (PPE, PPO), cyanate ester resin, epoxy + active ester cured resin, polyphenylene ether resin (polyphenylene oxide resin), curable polyolefin resin, benzocyclobutene resin, polyimide resin, aromatic polyester resin, Aromatic liquid crystal polyester resin, polyphenylene sulfide resin, polyetherimide resin, polyacrylate resin, polyether ether ketone resin, fluorine resin, benzoxazine resin, etc. It is lower, but not limited to, among these, can be preferably used a silicon resin.

  The base electrode 7 functions as a base layer for forming the terminal electrode 8 by electroplating. For example, the material of the base electrode 7 is not limited, but includes, for example, Ag, Cu, Ni or the like as a metal component. In the case of the laminated PTC, a metal component obtained by adding 10 to 60% of Zn to Ag is preferably used. The base electrode 7 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 7 mainly include a glass powder (frit), an organic vehicle (binder), and a metal powder. By firing the conductive paste, the organic vehicle The base electrode 7 which volatilizes and finally contains 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.

  In the case of the laminated PTC, the base electrode 7 preferably has a two-layer structure of a first layer containing Ag and Zn or Al and a second layer made of Ag in this order from the element body 2 side. By including Zn in the first layer, good ohmic contact with the internal electrode 3 becomes possible. By forming the Ag layer as the second layer, the fixing strength of the base electrode 7 can be increased. Since unevenness tends to be formed on the surface of the first layer, a conductive paste containing silver powder having a small average particle diameter is used as the second layer in order to reduce the surface roughness of the base electrode 7. preferable.

  The terminal electrode 8 is composed of a stacked body of a Ni layer 8a and a Sn layer 8b. The Ni layer 8a functions as a barrier metal that prevents the contact of the Sn layer 8b and the base electrode 7 and prevents the base electrode 7 from being corroded by Sn, and has a thickness of, for example, about 2 μm. Further, the Sn layer 8b has a function of improving the wettability of the solder, and the thickness thereof is, for example, about 4 μm. The Ni layer 8a and the Sn layer 8b are formed using electroplating.

  Next, a method for manufacturing the multilayer ceramic electronic component 1 according to the present embodiment will be described with reference to FIGS. 2 to 4 are process diagrams showing an example of a procedure for manufacturing the multilayer ceramic electronic component 1.

  First, as shown in FIG. 2, a laminated body 4 having a laminated structure of an element body 2 and internal electrodes 3 is formed. The laminated body 4 is manufactured as follows, for example.

  That is, first, 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 by printing a conductive paste containing a metal powder containing Pd and / or Ag, a binder resin, and a solvent on the ceramic green sheet.

  Further, 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 are further pressurized 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.

  Next, as shown in FIG. 3, the base electrode 7 is formed on the side surface of the element body 2. In the formation of the base electrode 7, first, a conductive paste containing a metal powder in which Zn or Al is added to Ag as required, a solvent, and an organic binder is applied to the side surface of the element body 2. The base electrode 7 is formed by baking the paste.

  Here, in this embodiment, the base electrode 7 having a surface roughness Ra of 6 μm or less is formed. This production method is roughly classified into the following two types. That is, one method is a method of directly forming the base electrode 7 such that Ra is 6 μm or less. One method for this purpose is to use a conductive paste in which metal powder having an average particle size of 7 μm or less is dispersed. However, it is not possible to control the surface roughness only by adjusting the average particle diameter, and even if a metal powder with a small average particle diameter is used, depending on the formation conditions (viscosity paste, baking temperature, baking time, etc.), Surface roughness can be large. On the other hand, after forming the base electrode 7 with Ra of 6 μm or more, the other method is a method of post-processing to make the Ra of the base electrode surface 6 μm or less. An example of such post-processing is a polishing process such as barrel polishing.

  Next, resin impregnation treatment of the element body 2 and the base electrode 7 is performed. The resin impregnation treatment is not particularly limited as long as the resin 2 is impregnated with resin in the pores of the base body 2 and the base electrode 7. In addition to the method of impregnating the base body 2 and the base electrode 7 with the resin liquid, the base body 2 Alternatively, a method of spraying a resin liquid onto the base electrode 7 may be used. Specifically, for example, a vacuum impregnation treatment of silicon resin is performed on the element body 2 and the base electrode 7.

  This vacuum impregnation treatment is performed by immersing the chip of the element body 2 in a mixed solution of a silicon resin and a solvent in a predetermined vacuum atmosphere. Specifically, the container for storing the mixed solution is set in a desiccator, the inside of the desiccator is sucked by a vacuum pump, and the chip is taken out from the container after a predetermined time has elapsed.

  At this time, as shown in FIG. 5, after the resin impregnation, the resin 6 adheres not only inside the base electrode 7 but also on the surface of the base electrode 7. Here, in this embodiment, since the surface roughness Ra of the surface of the base electrode 7 is as smooth as 6 μm or less, there are few surface irregularities on which the resin tends to remain. Therefore, as shown in FIG. 6, the resin 6 on the surface of the base electrode 7 can be removed by simply performing a simple cleaning process. At this time, the resin filled in the pores of the element body remains as it is. . The cleaning process is not limited, but the chip may be immersed in a container containing an organic solvent such as toluene for several tens of seconds.

  On the other hand, as shown in FIG. 7, when the surface of the base electrode 7a is rough, even if the cleaning process is performed to remove the resin 6a attached to the surface of the base electrode 7a, as shown in FIG. Resin 6a remains in the recess of base electrode 7a. The problems caused by the residual resin 6a are as described above. It is possible to completely remove the resin on the electrode by strengthening the cleaning conditions even when the surface of the base electrode has large irregularities, but in this case the resin filled in the pores of the element body is also partially Removed.

  After the cleaning process, a drying process is performed at a predetermined temperature. Thereby, the resin that has entered the pores of the element body 2 is cured (see FIG. 4). Further, as shown in FIG. 6, the surface of the base electrode 7 can be kept clean. In this way, voids, microcracks, and the like in the surface layer of the element body 2 made of ceramics are filled with the resin 6, and a surface layer having high corrosion resistance against the plating solution is formed.

  Next, the Ni layer 8a and the Sn layer 8b are sequentially deposited on the surface of the base electrode 7 by electroplating to form the terminal electrode 8 (see FIG. 1). For example, in the formation of the Ni layer 8a, a barrel plating method is adopted, and 2 μm of Ni is deposited using a watt bath. Further, in the formation of the Sn layer 8b, a barrel plating method is adopted, and Sn is deposited by 4 μm using a neutral tin plating bath.

  The multilayer ceramic electronic component 1 formed as described above is used by soldering its terminal electrode 8 to a predetermined wiring portion of the wiring board.

  According to the multilayer ceramic electronic component 1 and the method for manufacturing the same according to the above-described embodiment, since the Ra of the surface of the base electrode 7 is as smooth as 6 μm or less, the element body 2 and the base electrode 7 are thin. It is possible to remove the resin 6 adhering to the surface of the base electrode by a simple cleaning process while filling the holes with the resin. As a result, a good plating film (terminal electrode 8) can be formed on the base electrode 7 while preventing the plating solution from penetrating into the element body 2 and the base electrode 7, and solder to the terminal electrode 8 can be formed. The wettability can be improved. Therefore, the highly reliable multilayer ceramic electronic component 1 can be manufactured.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
Base electrodes 7 of 1608 size ceramic electronic components (chips) were formed to have various surface roughnesses, and classified into 10 ranks with 1 μm intervals as shown in Table 1. Further, in order to form the base electrode of each surface roughness rank, in this example, a conductive paste containing silver powder having an average particle diameter shown in Table 1 was applied to the element body 2, and this conductive paste was applied. Firing was performed in air at 600 ° C. for 10 minutes. The average particle size of the silver powder was obtained by taking an SEM image of 10 particles, calculating the area of each particle, and calculating the diameter of a circle having the same area as this average value. The surface roughness was measured with a laser microscope (KEYENCE, VK-9500). 100 chips were taken out from each rank, vacuum impregnated with silicon resin, washed with toluene for 30 seconds, dried and cured, and then electroplated on the base electrode 7 with a 2 μm Ni layer 8a and a 3 μm Sn layer. 8b was formed. Thereafter, each chip was soldered to a printed circuit board, and the number of chips with poor solder wetting was examined. Here, the chip with poor solder wettability is a chip having a contact angle of 90 degrees or more between the terminal electrode 8 and the solder surface after soldering. The results are summarized in Table 1 and FIG.

  As shown in Table 1 and FIG. 9, it was found that the higher the surface roughness of the base electrode, the higher the solder wettability rate. In order to suppress the solder wetting defect rate to about 10%, the surface roughness Ra of the base electrode is preferably 6 μm or less, and more preferably 5 μm or less, the solder wetting defect rate being 5% or less. Further, in order to make the surface roughness Ra of the base electrode 6 μm or less, it is preferable to use a conductive paste in which silver powder having an average particle diameter of 7 μm or less is dispersed, and the surface roughness Ra of the base electrode is made 5 μm or less. For this purpose, it has also been found preferable to use a conductive paste in which silver powder having an average particle size of 6 μm or less is dispersed.

(Example 2)
In Example 1, the tip (9 ≦ Ra <10) having the base electrode 7 having the largest surface roughness is barrel-polished to reduce the surface roughness of the base electrode 7, and chips having the same rank are assigned to each rank. 100 were manufactured and the same experiment as Example 1 was conducted. The results are summarized in Table 2 and FIG.

  As shown in Table 2 and FIG. 10, as in Example 1, it was found that the lower the surface roughness of the base electrode, the higher the solder wetting defect rate. Thereby, it was confirmed that the same result was obtained irrespective of the adjustment method of the electrode surface roughness.

(Comparative Example 1)
A base electrode 7 having a surface roughness Ra and an average of 7.2 μm was formed on a 1.6 × 0.8 × 0.8 mm size ceramic PTC chip in which the internal electrode 3 is Ni. The base electrode 7 was formed by applying a conductive paste containing 70% silver powder with an average particle diameter of 0.25 μm and 30% Zn powder with an average particle diameter of 7.1 μm and firing at 600 ° C. in air. . The chip was vacuum impregnated with silicon resin, washed with toluene for 30 seconds, and then dried and cured, and then a 2 μm Ni layer 8a and a 3 μm Sn layer 8b were formed by electroplating. Thereafter, each chip was soldered to a printed circuit board, and the number of chips with poor solder wetting was examined. Here, the chip with poor solder wettability is a chip having a contact angle of 90 degrees or more between the terminal electrode and the solder surface after soldering. In this case, the solder wetting defect rate was 32% (n = 100).

Example 3
Base electrodes 7 having a surface roughness Ra of 1.8 μm on average were formed on both ends of a 1.6 × 0.8 × 0.8 mm size ceramic PTC chip in which the internal electrode 3 was Ni. The base electrode 7 is formed by first applying the same conductive paste as in Comparative Example 1 including 70% silver powder having an average particle diameter of 0.25 μm and 30% Zn powder having an average particle diameter of 7.1 μm, and further averaging the same. A conductive paste made of 100% silver powder having a particle size of 0.21 μm was applied and baked in air at 600 ° C. for 10 minutes. The chip was vacuum impregnated with silicon resin, washed with toluene for 30 seconds, and cured to form a 2 μm Ni layer 8a and a 3 μm Sn layer 8b by electroplating. After that, each chip was soldered to the printed circuit board and the number of chips with poor solder wetting was examined. Here, the chip with poor solder wettability is a chip having a contact angle of 90 degrees or more between the terminal electrode 8 and the solder surface after soldering. In this case, the solder wetting defect rate was 0% (n = 100).

  The present invention includes a thermistor, a capacitor, an inductor, a LTCC (Low Temperature Co-fired Ceramics), a varistor, a multilayer ceramic electronic component composed of a composite part thereof, and a device, an apparatus, a system, a facility, and the like including the same, and It can be widely used for their production.

  DESCRIPTION OF SYMBOLS 1 ... Multilayer ceramic electronic component, 2 ... Element body, 3 ... Internal electrode, 4 ... Laminate, 6, 6a ... Resin, 7 ... Base electrode, 8 ... Terminal electrode, 8a ... Ni layer, 8b ... Sn layer.

Claims (4)

A multilayer ceramic electronic component subjected to resin impregnation treatment,
An element made mainly of ceramics,
A base electrode formed on the element body;
Ra of the surface of the base electrode is specified to be 6 μm or less,
Multilayer ceramic electronic components. The multilayer ceramic electronic component is a PTC thermistor.
The multilayer ceramic electronic component according to claim 1. Forming a base electrode having a surface with an Ra of 5 μm or less on an element body mainly made of ceramic;
Performing a resin impregnation treatment on the element;
Forming a terminal electrode on the base electrode;
A method of manufacturing a multilayer ceramic electronic component having In the step of forming the base electrode, a conductive paste in which metal powder having an average particle size of 7 μm or less is dispersed is used.
The manufacturing method of the multilayer ceramic electronic component of Claim 3.

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