JP2005159250A - Cleaning method for multilayer ceramic capacitors - Google Patents

Abstract

A method for cleaning a multilayer ceramic capacitor capable of accurately measuring and controlling the amount of anions remaining in an external electrode film or at a connection portion between an external electrode film and an internal electrode layer in a short time and capable of preventing structural defects. provide.
A capacitor body 1 is formed by laminating a plurality of rectangular dielectric layers 2 with internal electrode layers 3 and 4 interposed therebetween, and internal electrode layers 3 and 4 are formed on end faces of the capacitor body 1. The external electrode films 5a and 6a that are electrically connected to each other are formed by a thick film technique, and the metal plating films 5b to 6c are deposited on the surfaces of the external electrode films 5a and 6a by a wet plating method to form a multilayer ceramic. While the process A for obtaining the capacitor 10 and the multilayer ceramic capacitor 10 obtained in the process A are boiled in the washing water 11, the anion concentration in the washing water 11 is measured by an ion chromatograph method, and the measured value becomes a predetermined value. The method of cleaning the multilayer ceramic capacitor 10 includes the step B of ending boiling cleaning at the time of reaching.
[Selection] Figure 1

Description

  The present invention relates to a method for cleaning a multilayer ceramic capacitor.

A multilayer ceramic capacitor is formed on the end face of a capacitor element body, in which a main body is composed of barium titanate (BaTiO ₃ ) and the like, and a plurality of rectangular dielectric layers are laminated via an internal electrode layer therebetween. And an external electrode film made of Ni, Cu or the like electrically connected to the internal electrode layer, and a metal plating film such as Ni plating or Sn plating deposited on the surface of the external electrode film. The external electrode film is formed by a thick film method, and the metal plating film is obtained by immersing the capacitor element body on which the external electrode film is formed by a wet plating method in a plating solution containing various ions. As a result, it is deposited on the surface of the external electrode film.

However, in the above method for forming a metal plating film, anions such as SO ₄ ²⁻ ions and Cl ^{2 −} ions contained in the plating solution remain in the external electrode film or in the connection portion between the external electrode film and the internal electrode layer. However, there has been a problem that reliability in a humidity load test is lowered. At this time, in order to measure the amount of remaining anions, when a part of each lot is actually extracted and a wet load test is performed, the measurement takes a long time and the total number measurement is impossible. There was a point.

  Accordingly, a method for cleaning a multilayer ceramic capacitor has been proposed in which the anion concentration in the cleaning liquid is measured by an ion chromatographic method while the multilayer ceramic capacitor after the formation of the metal plating film is immersed in the cleaning water (for example, Patent Documents). 1 and 2).

In addition, a method for cleaning a multilayer ceramic capacitor in which a multilayer ceramic capacitor after metal plating film formation is ultrasonically cleaned in cleaning water and an anion concentration in the cleaning liquid is measured by an ion chromatography method has been proposed (for example, (See Patent Document 3).
JP-A-5-291074 (page 3-8, FIG. 1) Japanese Patent Laid-Open No. 9-80016 (page 3-5, FIG. 1) Japanese Patent No. 30977771 (page 2-3, FIG. 2)

  However, according to the cleaning methods described in Patent Documents 1 and 2, it is possible to clean the anions remaining on the surface of the metal plating film, but in the external electrode film or in the connection portion between the external electrode film and the internal electrode layer. However, there was a limit to washing the anions remaining on the surface, and accurate measurement could not be performed.

  On the other hand, according to the cleaning method described in Patent Document 3, it is difficult to accurately control the ultrasonic cleaning time. When the ultrasonic cleaning time is too long, part of the dielectric layer is physically removed by ultrasonic cleaning. There is a problem that structural defects such as peeling between the dielectric layer and the internal electrode layer occur.

  The present invention has been devised in view of the problems as described above, and its purpose is to reduce the total amount of anions remaining in the external electrode film or in the connection portion between the external electrode film and the internal electrode layer in a short time. It is an object of the present invention to provide a method for cleaning a multilayer ceramic capacitor that can be measured and controlled with high accuracy and can prevent structural defects.

  The method for cleaning a multilayer ceramic capacitor according to the present invention forms a capacitor body by laminating a plurality of rectangular dielectric layers with an internal electrode layer therebetween, and the internal electrode layer is formed on an end surface of the capacitor body. Forming an external electrode film electrically connected to the outer electrode film by a thick film technique, and depositing a metal plating film on the surface of the external electrode film by a wet plating method to obtain a multilayer ceramic capacitor; Process B in which the multilayer ceramic capacitor obtained in Step A is boiled in washing water, the anion concentration in the washing water is measured by an ion chromatograph method, and boiling washing is terminated when the measured value reaches a predetermined value. It is characterized by including.

  In the method for cleaning a multilayer ceramic capacitor of the present invention, washing water containing a plating component remaining on the surface is applied to the multilayer ceramic capacitor boiled and washed in Step B by applying a centrifugal force at a temperature of 40 ° C. or lower. The method further includes a step C of separating and removing.

  According to the present invention, while the multilayer ceramic capacitor is boiled in the washing water, the anion concentration in the washing water is measured by an ion chromatograph method. Therefore, in the external electrode film or in the connection portion between the external electrode film and the internal electrode layer. The amount of remaining anions can be measured for all in a short time.

  Further, a part of the dielectric layer is physically scraped off, and structural defects such as peeling between the dielectric layer and the internal electrode layer are not caused.

  Furthermore, since boiling ends when the anion concentration reaches a predetermined value, the amount of remaining anions can be controlled with high accuracy, and the anions remaining in the external electrode film or at the connection between the external electrode film and the internal electrode layer Since the amount can be made a certain amount or less, it is possible to solve the problem that reliability such as a humidity load test is lowered.

  Further, according to the present invention, the step C for separating and removing the washing water containing the plating component remaining on the surface of the multilayer ceramic capacitor boiled and washed in the step B by applying a centrifugal force at a temperature of 40 ° C. or less. Further, since the conductive residual plating component attached to the surface of the multilayer ceramic capacitor is prevented from remaining as spots or spots, it is possible to effectively prevent a short circuit from occurring between the electrodes.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a method for cleaning a multilayer ceramic capacitor of the present invention. 2A and 2B are views showing the multilayer ceramic capacitor of FIG. 1, in which FIG. 2A is an external perspective view, and FIG. 2B is a longitudinal sectional view.

In the figure, a multilayer ceramic capacitor 10 is composed of a capacitor element body 1 composed of barium titanate (BaTiO ₃ ) or the like as a main component and a plurality of rectangular dielectric layers 2 laminated via internal electrode layers 3 and 4 therebetween. The external electrode films 5a and 6a made of Ni, Cu, etc., which are formed on the end face of the capacitor body 1 and electrically connected to the internal electrode layers 3 and 4, and the surfaces of the external electrode films 5a and 6a are covered. It consists of metal plating films (Ni plating 5b, 6b, Sn plating 5c, 6c) to be deposited. In the drawing, external electrode films 5a and 6a, Ni platings 5b and 6b, and Sn platings 5c and 6c are combined to form external electrodes 5 and 6.

  Hereinafter, a method for cleaning the multilayer ceramic capacitor 10 of the present invention will be described. The figure numbers are not distinguished before and after firing.

  First, a conductive paste containing metal powder to be the internal electrode layers 3 and 4 is formed on a predetermined region of the ceramic green sheet 2 to be a dielectric layer by screen printing.

  Then, such a ceramic green sheet 2 is stacked after a predetermined number of stacked layers so that the internal electrode layers 3 and 4 face each other and the internal electrode layers 3 and 4 extend to different end faces, and then cut. The unfired capacitor body 1 is fired by adding a predetermined atmosphere, temperature and time. As a result, the internal electrode layers 3 and 4 are exposed on the pair of end faces of the sintered capacitor body 1.

  Next, external electrodes 5 and 6 are formed on the pair of end faces of the capacitor body 1. Specifically, the external electrode films 5a and 6a are formed on both end surfaces of the capacitor body 1 by applying and baking a conductive paste containing base metal, borosilicate glass and an organic binder by a thick film technique.

Next, as a process A, a capacitor element body 1 in which external electrode films 5a and 6a are formed in a plating solution such as a watt bath mainly composed of NiSO ₄ , NiCl ₂ , and H ₃ BO ₃ as a wet plating method. After the Ni plating films 5b and 6b are deposited on the external electrode films 5a and 6a, the Sn plating films 5c and 6c are deposited.

  Next, as step B, after removing the plating solution adhering to the surfaces of the Sn plating films 5c and 6c, as shown in FIG. 1, the multilayer ceramic capacitor 10 after the formation of the metal plating films 5b to 6c is replaced with a water tank 12. The anion remaining inside was washed by boiling in the ultrapure water (wash water) 11 in the inside, and the anion concentration in the ultrapure water 11 was measured online by ion chromatography, and the measured value was When the predetermined value is reached, boiling cleaning is terminated. At this time, it is desirable that the washing water 11 is ultrapure water and the water tank 12 is made of quartz or the like so that the measurement by the ion chromatography method can be performed with high accuracy. Further, in order to prevent discoloration of the Sn plating films 5c and 6c, it is desirable to perform boiling after removing the plating solution adhering to the surface of the Sn plating films 5c and 6c.

  Further, the anions remaining in the external electrode films 5a and 6a and at the connection portions between the external electrode films 5a and 6a and the internal electrode layers 3 and 4 should not be completely removed, and a certain amount of anions remain. Accordingly, it is considered that the connection portion between the external electrode films 5a and 6a and the internal electrode layers 3 and 4 is ionically activated, and the connection between the external electrode films 5a and 6a and the internal electrode layers 3 and 4 is improved. That is, since the present invention ends boiling cleaning when the measured value reaches a predetermined value, anion ions are present in the external electrode films 5a, 6a or in the connection portions between the external electrode films 5a, 6a and the internal electrode layers 3, 4. Can remain in a certain amount.

  Next, as process C, centrifugal water is applied to the multilayer ceramic capacitor 10 boiled and washed in process B under a condition of 40 ° C. or less to separate and remove the washing water 11 containing the plating component remaining on the surface. Specifically, as shown in FIG. 3, a method in which the multilayer ceramic capacitor 10 is placed in a dehydration tank 13 provided with a plurality of holes 14 and rotated at a high speed is used. Thereby, it can prevent effectively that a short circuit arises between each electrode by preventing that the residual plating component which has the electroconductivity adhering to the surface of the multilayer ceramic capacitor 10 remains as a spot or a spot.

  Here, when a centrifugal force is applied under conditions exceeding 40 ° C., only the washing water 11 is dried, and the plating component remains on the surface of the capacitor body 1. It is desirable. On the other hand, when the temperature is 0 ° C. or lower, the cleaning water 11 is frozen and the cleaning water 11 containing the plating component remaining on the surface of the capacitor body 1 cannot be sufficiently separated and removed. It is desirable to apply centrifugal force.

  Further, when a centrifugal force is applied under a pressurized condition, separation and removal of the cleaning water 11 including the plating component remaining on the surface of the capacitor body 1 is inhibited, and only the cleaning water 11 is separated and removed. Because of the tendency, it is desirable to apply centrifugal force under normal pressure conditions.

  Furthermore, the multilayer ceramic capacitor 10 may be placed in a dewatering tank 13 after being placed in a mesh bag having a smaller size than the size of the multilayer ceramic capacitor 10. As a result, the size of the through hole 14 of the dewatering tank 13 can be made larger than the size of the multilayer ceramic capacitor 10, so that the separation and removal of the cleaning water 11 including the plating component becomes efficient and the multilayer ceramic capacitor 10 is placed in the bag. Since the centrifugal force is applied in a state where the multilayer ceramic capacitor 10 is put, the impact applied to the multilayer ceramic capacitor 10 can be reduced, and chipping, cracks, etc. of the multilayer ceramic capacitor 10 can be suppressed.

  Further, the process B for boiling and washing the multilayer ceramic capacitor 10 in the cleaning water 11 and the process C for separating and removing the cleaning water 11 containing the plating component remaining on the surface of the capacitor body 1 are performed in the same tank. Anyway. This simplifies the process and ensures that the cleaning water 11 containing the plating component remaining on the surface of the capacitor element body 1 is ensured without drying only the cleaning water 12 and leaving the remaining plating component as spots or spots. It can be separated and removed.

  Further, immediately before the process C for separating and removing the cleaning water 11 containing the plating component remaining on the surface of the capacitor body 1, the cleaning water 11 may be applied to the multilayer ceramic capacitor 10. The capacitor 10 may be stored in the cleaning liquid 11. Thus, even when the cleaning water 11 is partially dried and the plating component is deposited on the surface of the external electrodes 5 and 6, the plating component can be dissolved again in the cleaning water 11 and separated and removed.

  If necessary, after step C, the multilayer ceramic capacitor 10 may be dried under conditions of 80 ° C. or more × 10 minutes or more.

  It should be noted that the present invention is not limited to the above-described embodiment, and various modifications and improvements can be made without departing from the scope of the present invention.

  For example, after the boiling cleaning is performed for a certain time (for example, 1 hour), the anion concentration in the ultrapure water 11 is continuously measured by an ion chromatography method, and the external electrode films 5a and 6a or the external electrode film 5a are measured. , 6a and the internal electrode layers 3 and 4 may be indirectly measured for the amount of anions remaining at the connection portion. At this time, the anion concentration in the washing water 11 is desirably in the range of 0.01 μg to 0.08 mg per 1 g of the external electrode films 5a and 6a. That is, since the anion concentration is 0.01 μg or more per 1 g of the external electrode films 5a and 6a, the connection portion between the external electrode films 5a and 6a and the internal electrode layers 3 and 4 is ionically activated by the anions. For this reason, the connection between the external electrodes 5 and 6 and the internal electrode layers 3 and 4 is improved. On the other hand, since the anion concentration is 0.08 mg or less per 1 g of the external electrode films 5a and 6a, the reliability in a moisture load test or the like is improved. The boiling time at this time is preferably about 1 hour although it depends on the plating conditions.

  When the anion concentration is 0.08 mg or less per 1 g of the external electrode films 5a and 6a, it is shipped as a non-defective product. On the other hand, when the anion concentration exceeds 0.08 mg per 1 g of the external electrode films 5a and 6a, the anion remaining inside is washed again and the multilayer ceramic capacitor 10 is boiled again in the ultrapure water 11, The anion concentration in the pure water 11 is measured by an ion chromatography method, and these steps are repeated until the anion concentration becomes 0.08 mg or less per 1 g of the external electrode films 5a and 6a.

  On the other hand, when the anion concentration is less than 0.01 μg per 1 g of the external electrode films 5a and 6a, it remains in the external electrode films 5a and 6a or at the connection portion between the external electrode films 5a and 6a and the internal electrode layers 3 and 4. The plating conditions are changed so that the amount of anions to be performed is a certain amount or more.

  When the anion concentration exceeds 0.08 mg per 1 g of the external electrode films 5a and 6a, the ultrapure water 11 in the water tank 12 is replaced, and boiling is repeated again under the same conditions, so that the anion concentration falls within the above range. At that time, it may be shipped as a non-defective product. This eliminates the need for ultrasonic cleaning of the multilayer ceramic capacitor 10, thereby preventing structural defects more effectively.

  Further, two or more metal plating films are deposited, and plating for forming metal plating films (Ni plating films 5b and 6b in this embodiment) deposited on the external electrode films 5a and 6a. When the anion contained in the plating solution is different from the anion contained in the plating solution for forming the plating layer (Sn plating films 5c, 6c in this embodiment) deposited on the metal plating film, It is desirable to measure the amount of anions contained in the plating solution for forming the metal plating films (Ni plating films 5b and 6b in this embodiment) deposited on the external electrode films 5a and 6a. . That is, the anions contained in the plating solution for forming the Ni plating films 5b and 6b remain in the external electrode films 5a and 6a or in the connection portions between the external electrode films 5a and 6a and the internal electrode layers 3 and 4. In addition, the plating solution for forming the Sn plating films 5c and 6c is formed in the external electrode films 5a and 6a or between the external electrode films 5a and 6a and the internal electrode layers 3 and 4 due to the presence of the Ni plating films 5b and 6b. This is because the ratio of entering the connection portion is small.

  The present invention can also be applied to the case where a conductive resin is used as the external electrode films 5a and 6a.

  Furthermore, the metal plating film may be a metal plating film other than the Ni plating films 5b and 6b and the Sn plating films 5c and 6c.

  The present inventor made a capacitor body 1 after firing by laminating the dielectric layer 2 mainly composed of barium titanate and exposing the internal electrode layers 3 and 4 on a pair of end faces. External electrode films 5a and 5b electrically connected to the internal electrode layers 3 and 4 are formed on the end face of the capacitor element body 1 by a thick film method, and the surface of the external electrode films 5a and 6a is formed by a wet plating method. Ni plating films 5b and 6b and Sn plating films 5c and 6c were sequentially deposited to produce a 3225 type multilayer ceramic capacitor 10 as shown in FIG.

When the obtained multilayer ceramic capacitor 10 was boiled in 50 ml of ultrapure water 11 for 1 hour (sample numbers 1 to 10) immediately after the formation of the metal plating films 5b to 6c, ultrapure The amount of anion (SO ₄ ^2- ion) in water 11 was measured by ion chromatography. At this time, the amount of SO ₄ ²⁻ ions (mg) was converted to the amount per 1 g of the external electrode films 5a and 6a. That is, the weights of the external electrode films 5a and 6a were calculated by subtracting the weight of the capacitor element body 1 from the weight after the external electrode films 5a and 5b were formed on the end face of the capacitor element body 1 by the thick film technique. . Moreover, in order to confirm whether a part of the dielectric layer 2 was physically scraped off, the presence or absence of Ti ⁴⁺ ions in the cleaning liquid was also measured. That is, at the detection limit of the ion chromatographic method (external electrode film 5a, 6a: less than 0.001 μg per 1 g), a case where Ti ⁴⁺ ions are not detected is marked as a non-defective product, and a case where it is detected is marked as a defective product. Marked. Furthermore, the multilayer ceramic capacitor 10 was taken out of the ultrapure water 11 and subjected to a wet load test. The humidity load test is held for 1000 hours under the conditions of a temperature of 85 ° C. and a relative humidity of 85%. A sample having an insulation resistance value exceeding 40 mΩ is regarded as a non-defective product and a sample having a resistance of 40 mΩ or less is regarded as a defective product. The proportion of non-defective products was measured. As a comparative example, the same evaluation was performed when immersed in ultrapure water 11 for 1 hour (sample number 11) and when ultrasonically cleaned in ultrapure water 11 for 1 hour (sample number 12). The results are shown in Table 1.

As shown in Table 1, Ti ⁴⁺ ions were not detected in this example (sample numbers 1 to 10) boiled in ultrapure water 11 for 1 hour immediately after the formation of the metal plating films 5b to 6c. Further, when the SO ₄ ^2- ion amount in the ultrapure water 1 is 0.01 μg to 0.08 mg per 1 g of the external electrode films 5a and 6a (sample numbers 1 to 5), the defective rate in the moisture load test Becomes 0%, and when the SO ₄ ^2- ion amount exceeds 0.08 mg per 1 g of the external electrode films 5a and 6a (sample numbers 6 to 10), a defect in the moisture load test occurs, and the ultrapure By measuring the amount of SO ₄ ^2- ion in the water 1, the amount of anions remaining in the external electrode films 5 a, 6 a or in the connection portions between the external electrode films 5 a, 6 a and the internal electrode layers 3, 4 is indirectly measured. I was able to measure.

On the other hand, in the comparative example (sample number 11) immersed in ultrapure water 11 for 1 hour, even when SO ₄ ^2- ion was not detected at the detection limit of the ion chromatography method, A defect occurred, and the amount of anions remaining in the external electrode films 5a and 6a and at the connection portions between the external electrode films 5a and 6a and the internal electrode layers 3 and 4 could not be indirectly measured.

On the other hand, in the comparative example (sample number 12) that was ultrasonically cleaned in ultrapure water 11 for 1 hour, Ti ⁴⁺ ions were detected in ultrapure water 1, and a part of dielectric layer 2 was physically scraped off. It was suggested that

  Next, as Step C, by applying centrifugal force to the multilayer ceramic capacitor 10 of Sample No. 1 boiled and washed in Step B under the condition of 40 ° C. or less, the washing water 11 containing the plating component remaining on the surface is obtained. Separated and removed. Specifically, as shown in FIG. 3, 40,000 multilayer ceramic capacitors 10 are placed in a cylindrical dehydration tank 13 having a plurality of holes 14 and having a diameter of 40 cm and a depth of 30 cm, and 1000 rpm at 25 ° C. X The sample was rotated at a high speed under conditions of 6 minutes or longer (Sample No. 13). As a comparative example, the multilayer ceramic capacitor 10 of Sample No. 1 that had been boiled and washed in Step B was naturally dried at 25 ° C. (Sample No. 14). About the obtained sample, the incidence rate of a spot and a spot was confirmed by observing the capacitor | condenser body 1 surface with a metal microscope.

  As a result of the experiment, no stains or spots were observed in the present Example (Sample No. 13) in which Step C was performed after Step B. On the other hand, with respect to the comparative example (sample number 14) which was naturally dried at 25 ° C. after step B, 2% of spots and spots were generated, and a short circuit between external electrodes occurred at a rate of 0.5%.

From these results, according to the method for cleaning the multilayer ceramic capacitor 10 of the present invention, the anion concentration in the ultrapure water 11 is determined by ion chromatography while the multilayer ceramic capacitor 10 is boiled in the ultrapure water 11. In order to measure, the amount of anions remaining in the external electrode films 5a, 6a or at the connection portions between the external electrode films 5a, 6a and the internal electrode layers 3, 4 can be indirectly measured in a short time for all the dielectric layers. It was found that a part of 2 was not dissolved in the ultrapure water 11. In addition, since it further includes a step C of separating and removing the washing water 11 containing the plating component remaining on the surface by applying a centrifugal force to the boiled and washed multilayer ceramic capacitor 10 under a condition of 40 ° C. or less,
It was found that short-circuiting between the electrodes can be effectively prevented by preventing the conductive residual plating component attached to the surface of the multilayer ceramic capacitor 10 from remaining as spots or spots.

It is a figure which shows the washing | cleaning method of the multilayer ceramic capacitor of this invention. 2A and 2B are diagrams illustrating the multilayer ceramic capacitor of FIG. 1, in which FIG. 1A is an external perspective view, and FIG. It is a figure which shows the washing | cleaning method of the multilayer ceramic capacitor of this invention, and is sectional drawing which shows the process of isolate | separating and removing washing water.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Multilayer ceramic capacitor 1 ... Capacitor body 2 ... Dielectric layer 3, 4 ... Internal electrode layer 5, 6 ... External electrode 5a, 6a External electrode film 5b, 6b · Ni plating film 5c, 6c · Sn plating film 11 ··· Ultra pure water (cleaning water)
12 .... Water tank

Claims (2)

A capacitor body is formed by laminating a plurality of rectangular dielectric layers with an internal electrode layer interposed therebetween, and an external electrode film electrically connected to the internal electrode layer is formed on an end surface of the capacitor body. A step A for obtaining a multilayer ceramic capacitor by forming a thick film method and depositing a metal plating film on the surface of the external electrode film by a wet plating method;
While boiling the multilayer ceramic capacitor obtained in the step A in washing water, measuring the anion concentration in the washing water by an ion chromatography method, and ending the boiling washing when the measured value reaches a predetermined value A method for cleaning a multilayer ceramic capacitor comprising: B. The process according to claim 1, further comprising a step C of separating and removing the washing water containing plating components remaining on the surface of the multilayer ceramic capacitor boiled and washed in the step B by applying a centrifugal force under a condition of 40 ° C or lower. A method for cleaning the multilayer ceramic capacitor as described.

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