JP2003217990A - Method for screening laminated ceramic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for screening a laminated ceramic capacitor, in which the number of lamination is relatively high, with few wrong distinguishing between a non-defective product and a defective product. <P>SOLUTION: A laminated ceramic capacitor is sampled in each lot to measure the insulation resistance. From the average value in each lot of the measured insulation resistance, a threshold which determines the quality of the insulation resistance of the laminated ceramic capacitor is decided in each lot. From the threshold determined in each lot, the quality of the insulation resistance of the laminated ceramic capacitor is determined in each lot. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for screening a monolithic ceramic capacitor, and more particularly to a method for screening a monolithic ceramic capacitor which determines the quality of a monolithic ceramic capacitor having a relatively large number of dielectric layers, for example, more than 200 dielectric layers. .

[0002]

2. Description of the Related Art A screening method based on the electrical characteristics of a monolithic ceramic capacitor usually applies a withstand voltage three times or more the rated voltage to a monolithic ceramic capacitor as a sample to destroy a sample having a defect or The insulation resistance is deteriorated, then the insulation resistance is measured, and the good product and the defective product are sorted according to the magnitude of the insulation resistance. In this case, those having a magnitude of insulation resistance equal to or smaller than a specific value are removed as defective products. The threshold values for determining the quality of the insulation resistance are normally fixed to predetermined values as long as they have the same product name, for example, the same item or the same structural design and acquired capacity. The samples having the above-mentioned defects in the monolithic ceramic capacitor include those having a low insulation resistance over a plurality of dielectric layers and those having a few dots or plane defects having a low insulation resistance. .
The most difficult sample to be screened from among those having such defects is a mode in which only one specific layer has a lower insulation resistance than the normal layer. In addition, in our research, it has been found that the defects that hinder the reliability of the monolithic ceramic capacitor are most often in this mode.
By the way, when the number of laminated dielectric layers is relatively small in the monolithic ceramic capacitor, even if there is a monolithic ceramic capacitor having a defect in only one layer as described above, the insulation resistance between the good product and the defective product is large. Since they are different, screening is easy. An example of the relationship between the number of laminated dielectric layers and the insulation resistance is shown in the graph of FIG. 1 for the good and defective monolithic ceramic capacitors. Figure 1
From the graph of (1), when the number of laminated layers is relatively small, for example, 200 layers or less, the difference in insulation resistance between the good product and the defective product is very large. Therefore, for the laminated ceramic capacitors manufactured in a plurality of manufacturing lots, It can be seen that even if the average insulation resistance of each lot fluctuates, it is not necessary to change the threshold value for judging the quality. Further, the samples having defects in the monolithic ceramic capacitor are not all subject to dielectric breakdown at the time of withstanding voltage, and may have outliers with respect to the normal sample distribution. However, when the number of laminated dielectric layers of a monolithic ceramic capacitor is small, the difference in insulation resistance between a good product and a defective product is very different.Therefore, the standard value is used as a threshold value to select the good product and the defective product. It is enough.

[0003]

However, with the recent increase in capacity, the number of laminated dielectric layers of the monolithic ceramic capacitor continues to increase. Even if there is a defective layer having the same reliability problem as the number of stacked layers increases, the overall insulation resistance is determined by the parallel connection of the non-defective layer and the defective layer. For example, as shown in the graph of FIG. In addition, the difference in insulation resistance between the good product and the defective product becomes smaller and smaller. Further, even when the number of laminated dielectric layers of the monolithic ceramic capacitor is the same, if the insulation resistance of the non-defective layer changes, the insulation resistance of the non-defective product and that of the non-defective product change. For example, when considering a laminated ceramic capacitor in which the number of laminated layers is about 300 and one defective layer is included, when the insulation resistance of the non-defective layer changes by 10%, for example, the overall insulation resistance also changes to the variation of the insulation resistance of the non-defective layer. Fluctuates with it. Originally, if the difference in insulation resistance between the non-defective product and the defective product is large, this fluctuation does not matter, but if the number of stacked layers is as large as 500, as shown in the graph of FIG. It will be a size that cannot be ignored. FIG. 2 is a graph showing an example of the relationship between the average insulation resistance of a lot and the threshold value when the insulation resistance between lots varies for a good product and a defective product of a multilayer ceramic capacitor having 500 laminated layers. From the graph in Figure 2,
If the threshold value is an intermediate value between the insulation resistance of a good product and the insulation resistance of a defective product in the lot with a change rate of insulation resistance of -20%, the difference between the lots with a change rate of insulation resistance of + 20% Insulation resistance of non-defective product becomes larger than the threshold,
On the contrary, when the threshold value is an intermediate value between the insulation resistance of the good product and the insulation resistance of the defective product in the lot in which the insulation resistance change rate is + 20%, the insulation resistance change rate is -20%. It can be seen that the insulation resistance of non-defective products in the lot is smaller than the threshold value. Therefore, if monolithic ceramic capacitors with a large number of laminated layers and a small difference in insulation resistance between good products and defective products are selected with the same threshold value, if the insulation resistance between manufacturing lots fluctuates, it may be different depending on the lot. There is a high possibility that an error occurs when a good product is mistaken for a good product and mixes with a good product, and conversely, an error that a good product mixes with a defective product occurs, and accurate screening may not be possible.

Therefore, a main object of the present invention is to provide a method for screening a multilayer ceramic capacitor in which misidentification of a good product and a bad product of a multilayer ceramic capacitor having a relatively large number of stacked layers is small.

[0005]

A method for screening a laminated ceramic capacitor according to the present invention is a method for screening a laminated ceramic capacitor in which the quality of the laminated ceramic capacitor is judged according to the size of the insulation resistance. For each lot, the step of measuring the insulation resistance of the sampled ceramic capacitor, the step of determining the threshold value for judging the insulation resistance of the laminated ceramic capacitor from the measured insulation resistance for each lot, and Including the step of determining the quality of the insulation resistance of the multilayer ceramic capacitor for each lot from the determined threshold value,
This is a screening method for a laminated ceramic capacitor. In the multilayer ceramic capacitor screening method according to the present invention, the step of determining the threshold value for each lot includes, for example, the step of determining the threshold value for each lot from the measured average value of the insulation resistance for each lot.

In the multilayer ceramic capacitor screening method according to the present invention, the multilayer ceramic capacitors are sampled for each lot, the insulation resistance is measured, and the threshold value suitable for each lot is determined for each lot. It enables accurate screening of insulation resistance with few errors.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments of the invention with reference to the drawings.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION (Example) FIG. 3 shows a typical example of the insulation resistance of a manufacturing lot of a monolithic ceramic capacitor in mass production for a certain period. FIG. 3 is a diagram showing the distribution of the insulation resistance between the representative lot of the group having a large insulation resistance and the representative lot of the group having a small insulation resistance during the sampling period of the monolithic ceramic capacitor. The objects to be sampled are products having the same product name and manufactured under the same conditions except that the manufacturing time is different. The number of laminated dielectric layers of this product is 350, the thickness of the dielectric layers is 3 μm, and the acquired capacitance is 10 μF. The standard value of the insulation resistance (IR) of this product is 100 MΩ, and in FIG. 3, the lower limit of the vertical axis (logIR) of the graph is 8.
Hit 0.

In this embodiment, the data of the insulation resistance shown in FIG. 3 is acquired before the screening by the insulation resistance of the monolithic ceramic capacitor, and the average value of the insulation resistance and the statistical amount of the variation are obtained for each lot. In addition, in FIG.
Insulation resistance is shown in common logarithm.

Next, in the case of a lot, the threshold value was set to 8.25 in common logarithm, and screening was performed by insulation resistance, and the product was divided into two parts, one above the threshold and one below the threshold. . In the case of a lot, the threshold value was set to 8.10 in common logarithm, and screening was performed by insulation resistance, and the product was similarly divided into two that were above the threshold value and below the threshold value. In the case of a lot, a product having a lot threshold value or more was divided into two, one having a lot threshold value or more and the other having a lot threshold value or more.

Further, the insulation resistance is measured again for the products having a divided value lower than the threshold value, and in the case of a lot, those having a value of 8.10 or more and less than 8.25 and 8.00 or more and 8. Less than 10 and less than 8.00 were classified, and in the case of lots, it was classified into 8.00 to less than 8.10 and less than 8.00.

The above operation was repeated for several lots in each of the low-insulation lot group and the high-insulation lot group. The number of products obtained by classifying in this way,
The denominator of the fraction is shown in Table 1.

[0013]

[Table 1]

The products classified by the insulation resistance as described above were subjected to a high temperature load test in which a voltage twice the rated voltage was applied at 125 ° C., and data for 2000 hours were acquired. The results are shown in Table 1. The denominator of the fraction shown in Table 1 is the number of products classified by the above-mentioned insulation resistance and represents the number of products put into the high temperature load test. The fractional numerator shown in Table 1 is the number of defective products by 2000 hours in the high temperature load test.

As is clear from Table 1, neither of the lot groups had defects from the products judged to have the insulation resistance equal to or higher than the threshold value of the first screening. However, in the case of the product having the insulation resistance of 8.10 or more and less than 8.25, the defect occurs in the lot, whereas the defect does not occur in the lot. Products with insulation resistance in this range are included in the main distribution of the lot in the case of a lot, but are outliers in the case of a lot. That is, it indicates that the reliability of the product is not determined by the absolute insulation resistance.

Therefore, when a multilayer ceramic capacitor having a relatively large number of laminated layers is sorted by insulation resistance, if all lots are sorted by the threshold value of lots, it means that lots are excessively sorted. . On the other hand, if the lots are selected according to the threshold value, an error of mixing defects into non-defective products will be made to the lots in terms of reliability.

That is, when a multilayer ceramic capacitor having a relatively large number of laminated layers is selected by insulation resistance, a statistical amount for the insulation resistance of a lot to be selected is obtained in advance, and the statistical value is regarded as appropriate. By calculating a possible threshold value and starting selection, screening with a low error rate becomes possible. This reasonable threshold value can be easily obtained by forming an approximate expression from the statistical amount obtained in advance. Further, the appropriate threshold value can be theoretically obtained by making assumptions such as normality based on the average value and variation of the target lot. In any case, if the threshold value of the insulation resistance is changed individually for each lot based on the previously obtained statistics for each lot, it is possible to carry out screening that minimizes the number of defective products and the reverse errors. Becomes

Therefore, according to the above-described embodiment, it is possible to minimize the error of mixing a defective product into a good product in the screening by the insulation resistance. Also,
Since it is possible to reduce the excessive selection in which a defective product is mixed with a defective product, it is possible to perform screening while maintaining a high yield. Further, according to the above-described embodiment, since the system is such that the statistical amount is obtained by one piece of equipment, the threshold value is set, and the screening is performed, the error of the insulation resistance between the pieces of equipment can be eliminated. It enables stable screening with a further reduced error rate.

The threshold value for each lot in the above embodiment is an example, and in the present invention, if the standard value of the insulation resistance of the laminated ceramic capacitor to be screened is changed, the threshold value for each lot is also changed. It may change to another value.

Further, in the above-described embodiment, the product having the threshold value or more is determined as a good product, and the product having the threshold value or less is determined as a defective product. Then, those below the threshold value may be determined as defective products.

[0021]

According to the present invention, it is possible to obtain a method for screening a laminated ceramic capacitor in which there is little error in distinguishing between a good product and a defective product of a laminated ceramic capacitor having a relatively large number of laminated layers.

[Brief description of drawings]

FIG. 1 is a graph showing an example of the relationship between the number of laminated dielectric layers and the insulation resistance for good and defective multilayer ceramic capacitors.

FIG. 2 is a graph showing an example of the relationship between the average insulation resistance of a lot and the threshold value when the insulation resistance between lots varies for a good product and a defective product of a multilayer ceramic capacitor having 500 laminated sheets.

FIG. 3 is a diagram showing a distribution of insulation resistance between a representative lot of a group having a large insulation resistance and a representative lot of a group having a small insulation resistance during a sampling period of a laminated ceramic capacitor.

Claims (2)

[Claims] 1. A method of screening a laminated ceramic capacitor for judging the quality of the laminated ceramic capacitor according to the magnitude of the insulation resistance, the method comprising sampling the laminated ceramic capacitor for each lot, and measuring the insulation resistance of the sampled ceramic capacitor. And a step of determining a threshold value for judging whether the insulation resistance of the multilayer ceramic capacitor is good or bad from the measured insulation resistance for each lot, and an insulation of the multilayer ceramic capacitor from the threshold value determined for each lot. A method for screening a multilayer ceramic capacitor, comprising the step of judging the quality of resistance for each lot. 2. The step of determining the threshold value for each lot includes the step of determining the threshold value for each lot from an average value of the measured insulation resistance for each lot. A method for screening a monolithic ceramic capacitor as described in.