JP2826422B2 - Inspection method for multilayer ceramic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a multilayer ceramic capacitor, and more specifically, to determine the presence or absence of an internal defect by measuring the frequency characteristic of equivalent series resistance with a bias voltage applied to the multilayer ceramic capacitor. Inspection method.

[0002]

2. Description of the Related Art A trouble in a manufacturing process of a multilayer ceramic capacitor (hereinafter abbreviated as MLC), particularly, a problem at the time of binder removal may cause various defects in a product and greatly affect the quality. In a mass production process, it is necessary to process many products in a short time, so that internal defects such as delamination (delamination) and minute cracks occur.

Conventionally, the detection of such internal defects such as delamination has been mainly performed by a destructive inspection method in which an MLC product is cut and the inside thereof is polished and confirmed. The application of the destructive inspection method is naturally limited to several samples in one lot, and cannot be applied to individual products.

On the other hand, non-destructive inspection methods include (a) a method of inspecting internal defects by propagating ultrasonic waves into a chip, and (b) measuring a impedance-frequency characteristic by applying a bias voltage to MLC. And the like.

A method for measuring the impedance versus frequency characteristics is disclosed in US Pat. No. 4,644,259 (Japanese Patent Laid-Open No. 61-10 / 1986).
No. 8956), the gist of which is as follows. When a bias voltage is applied to the MLC and the frequency of the AC voltage is changed to measure the impedance characteristics, the dimensions of the MLC are reduced. This causes a phenomenon in which the impedance changes at the corresponding specific frequency, that is, a standing wave. This phenomenon occurs because the chip vibrates due to the piezoelectric phenomenon caused by the AC voltage and propagates throughout the MLC.
Resonance occurs at an integral multiple of a half wavelength, and the change increases due to the resonance phenomenon, and the electric charge fluctuates due to the piezoelectric phenomenon, causing a change in impedance. Since this change in impedance is a condition inside the chip, that is, where a defect such as delamination is present, the resonance pattern is disturbed, the change is used as a reference to determine the internal defect, and a defective product and a good product, that is, an internal defect exists. Products that can not be identified.

[0006]

However, in the method using ultrasonic waves, measurement becomes difficult when the shape of the target MLC becomes small, and it is difficult to find small defects in the MLC by this method. Further, the method according to the technique disclosed in the above-mentioned U.S. Patent which measures the internal defect by measuring the impedance can detect a relatively large internal defect, but it is difficult to detect a fine internal defect.
Because, as the defect becomes finer, the impedance change corresponding to the defect shifts to the high frequency side, and as described later, the impedance change on the high frequency side has a smaller change and cannot be distinguished from a normal one. Because there is.

For example, FIG. 6 shows 3.2 × 1.6 mm, 1 μm
In the MLC of F and F characteristics, a curve is plotted showing a change in impedance (Z) and a change in equivalent series resistance (R) when a frequency is changed to a range of 1 to 10 MHz after a bias voltage of 10 V is applied. FIG. 7 is an enlarged view of the frequency range from 2 MHz to 4 MHz. As can be seen from FIG. 7, the impedance characteristic change (peak height) decreases as the frequency becomes higher. There is a characteristic, and the problem in the actual inspection process is the minute defect. Therefore, the technique of the above-mentioned US patent has a problem that the reliability is lacking.

Accordingly, an object of the present invention is to provide a simple and highly reliable method for nondestructively inspecting the quality of MLC, especially internal defects due to delamination and fine cracks existing in ceramic materials. .

[0009]

Means for Solving the Problems The present inventors have conducted research to achieve the above object, and based on the considerations described in the following (1) to (4), have been able to determine the change in the frequency characteristic due to the piezoelectric phenomenon of the MLC. Instead, the present inventors have found that it is possible to easily determine even an internal defect, particularly a minute one, if it is based on a change in the equivalent series resistance.

(1) When the MLC has piezoelectricity, the capacitor chip is displaced by applying a bias voltage, and when the displacement reaches a certain frequency, it becomes a standing wave and has a large amplitude, which is a mechanical resonance. As the frequency changes, the storage capacitance of the capacitor changes. Therefore, the impedance (Z) becomes the resonance frequency f as shown in FIG.
It is obtained as a characteristic curve having the anti-resonance frequency fr.

(2) In order to judge particularly a minute internal defect, it is necessary to consider a change in impedance characteristics at a resonance point higher than the fundamental resonance point.
As can be seen, the impedance at a higher-order resonance point tends to have a smaller change as the frequency becomes higher.

(3) On the other hand, the frequency versus the equivalent series resistance (ES
The characteristic curve of R) shows a change as shown in FIG. 8B (the dotted line is the Zf characteristic curve), and the peak of this fR characteristic curve is symmetrical with respect to the right and left, and the half width of the peak, that is, the peak It is easy to quantify by measuring the width of the frequency at half the intensity.

(4) f which can be used for determining the internal defect
The peak in the -R curve firstly appears as a fundamental wave, and peaks appear at higher frequencies such as 2, 3, 4,. Large internal defects have their effect on the fundamental wave,
Since a fine defect hardly affects the fundamental wave, it is necessary to look at a higher-order peak. Therefore, a fine defect can be determined by observing a change in a peak in a high-frequency region.

Accordingly, the present invention provides a method for inspecting an internal defect mainly including delamination present in a multilayer ceramic capacitor made of a piezoelectric material,
(A) A bias voltage is applied to the capacitor to be tested to change the frequency of the AC voltage, and the equivalent series resistance versus frequency characteristic curve obtained by measuring the equivalent series resistance of the capacitor is obtained. At the peak of the characteristic curve that appears at the frequency at which the capacitor mechanically resonates due to the piezoelectric phenomenon and at a higher frequency that is an integral multiple of this frequency, the half-width indicated by the frequency width at half the peak intensity is determined. (C) This value is compared with the half value width of the corresponding peak of the equivalent series resistance vs. frequency characteristic curve obtained from the multilayer ceramic capacitor having the same dimensions and material as the above-mentioned inspection object and having no internal defect. An object of the present invention is to provide a method for inspecting a multilayer ceramic capacitor, which comprises determining that an internal defect is present if it is large.

[0015]

Since the half width at the peak appearing in the ESR-f characteristic curve can be easily obtained, the method of the present invention quantifies the degree of the internal defect by observing the change of the ESR with respect to the frequency of the AC voltage. Can be. By comparing the obtained half-value width of the MLC to be inspected with that of the non-defective MLC, an internal defect can be detected. Further, the half-value width of a peak appearing in a higher-order frequency can be obtained, thereby obtaining the peak of the basic frequency. It is possible to detect even fine internal defects that do not affect the image quality.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1, FIG. 4 and FIG.
Impedance (Z) and equivalent series resistance (R) vs. frequency characteristics in the case of small delamination, no delamination, and large delamination in MLC with 1.6 μm and 1 μF and F characteristics 2 and 3 are schematic diagrams of micrographs showing cross sections of the MLC corresponding to FIGS. 5 and 1, respectively, and will be described below with reference to these drawings.

FIG. 1, FIG. 4 and FIG. 5 show changes in impedance and equivalent series resistance depending on the frequency in the MLC when a bias voltage of 10 V is applied, but FIG. 4 shows no delamination. , It can be seen that the degree of change in the characteristic of the equivalent series resistance is greater than that of the impedance.

On the other hand, a multilayer ceramic capacitor (ML)
C) In the characteristic curve of FIG. 5 showing the case where a large delamination 2 as shown in FIG. 2 exists in 1, both the impedance and the equivalent series resistance have a small degree of change. Internal defects due to delamination can be determined.

However, in the characteristic curve of FIG. 1 showing the case where the small delamination 2 as shown in FIG. 3 exists in the MLC 1, it is difficult to see the characteristic change in the characteristic curve of the impedance (Z). . However, in the change in the characteristic of the equivalent series resistance, for example, the peak portion at the peak indicated by the arrow A has a large peak width, and the characteristic change can be easily determined by considering the peak width.

In order to compare the peak A with the case of FIG. 4 where no delamination is present, the width of the frequency at half the peak intensity, that is, the half width was measured. 1
The peak A was 82 KHz, whereas the peak A in FIG. 1 where small delamination was present was 438 KHz.

Therefore, identification can be facilitated by comparing the half-value width of a non-defective product having no internal defect with a numerical value.

[0022]

As described above, according to the method of the present invention, the half width at the peak appearing in the ESR-f characteristic curve can be easily obtained. The half-width at the peak of the characteristic curve appearing at the fundamental frequency that resonates naturally and at the higher-order frequencies of this frequency can be numerically judged, so that not only the large internal defect but also the peak of the fundamental frequency is not affected. Such minute internal defects can be detected.

[Brief description of the drawings]

FIG. 1 is a graph showing impedance and equivalent series resistance versus frequency characteristic curves in an MLC with small delaminations.

FIG. 2 is a schematic diagram of a micrograph showing a longitudinal section of an MLC in which a large delamination exists.

FIG. 3 is a schematic diagram of a micrograph showing a longitudinal section of an MLC in which a small delamination exists.

FIG. 4 is a graph showing impedance and equivalent series resistance versus frequency characteristic curves in an MLC without delamination.

FIG. 5 is a graph showing impedance and equivalent series resistance versus frequency characteristic curves in an MLC in which a large delamination exists.

FIG. 6: Frequency change (1 to 10 MHz) in MLC
FIG. 4 is a graph showing changes in impedance (Z) and equivalent series resistance (R) with respect to the threshold voltage.

7 is a graph diagram enlarging a portion of a frequency of 2 to 4 MHz in FIG. 6;

FIG. 8A is a diagram showing a basic change in impedance with respect to a change in frequency in the MLC, and FIG. 8B is a diagram showing a basic change in equivalent series resistance with respect to a change in frequency. FIG.

[Explanation of symbols]

 1 Multilayer ceramic capacitor (MLC) 2 Delamination

Claims (1)

(57) [Claims] 1. A method for inspecting a defect existing inside a body made of a piezoelectric material of a multilayer ceramic capacitor, comprising: (a) applying an AC bias voltage to the capacitor to be inspected to change its frequency; The equivalent series resistance versus frequency characteristic curve obtained by measuring the equivalent series resistance of the capacitor is obtained. (B) The frequency at which the capacitor mechanically resonates due to the piezoelectric phenomenon and the higher order frequency that is an integral multiple of this frequency are calculated. At the peak of the characteristic curve appearing in any of the above cases, a half-width indicated by a frequency width at a half value of the peak intensity is obtained, and (c) this value is determined by the same half-width obtained from the reference multilayer ceramic capacitor. An inspection method of a multilayer ceramic capacitor having a comparing process.