Method of manufacturing multilayer ceramic component

A method of preparing multilayer ceramic component including capacitor therein includes the steps of carrying a long ceramic green sheet along its longitudinal direction and measuring the thickness thereof while carrying the same, forming an internal electrode on the long ceramic green sheet subjected to the measurement of the thickness, punching out the long ceramic green sheet provided with the internal electrode into prescribed dimensions and stacking the punched ceramic green sheets with each other by a number obtained on the basis of the measured value of the thickness for obtaining a laminate, obtaining a ceramic sintered body by firing the laminate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of manufacturing a multilayer 
ceramic component including a capacitor, and more particularly, it relates 
to a process for a multilayer ceramic component including capacitor which 
enables acquisition of a desired electrostatic capacitance in high 
accuracy. 
2. Description of the Background Art 
In general, a multilayer ceramic capacitor is prepared through the 
following steps: 
First, a ceramic green sheet is molded from a ceramic slurry. Then, 
conductive paste is applied onto the ceramic green sheet by a method such 
as screen printing, for forming an internal electrode. Then, a plurality 
of such ceramic green sheets provided with internal electrodes are stacked 
with each other and pressurized along the direction of thickness, to 
obtain a laminate. Then, the obtained laminate is fired to provide a 
ceramic sintered body, and thereafter external electrodes are formed on 
both end surfaces of the sintered body. FIG. 6 shows an exemplary 
multilayer capacitor 30 obtained in this manner. 
As clearly understood from FIG. 6, a plurality of internal electrodes 32a 
to 32g are arranged in the multilayer ceramic capacitor 30 to overlap with 
each other through sintered body layers. The electrostatic capacitance of 
the multilayer ceramic capacitor 30 is decided by the thicknesses of the 
sintered body layers which are held between the internal electrodes 32a to 
32g, overlapping areas of the internal electrodes 32a to 32g which are 
opposed to each other through the sintered body layers, and the dielectric 
constant of dielectric ceramics forming the sintered body layers. 
In general, the sintered body layers which are held between the internal 
electrodes 32a to 32g have considerably small thicknesses of 5 .mu.m to 50 
.mu.m. In the aforementioned method, therefore, slight fluctuation of the 
thicknesses of the ceramic green sheets results in remarkable fluctuation 
of the electrostatic capacitance. In order to implement a desired 
electrostatic capacitance in the multilayer ceramic capacitor, therefore, 
it is necessary to control the thicknesses of the employed ceramic green 
sheets in high accuracy. 
In actual preparation of the multilayer ceramic capacitor, on the other 
hand, conductive patterns for forming the internal electrodes are provided 
on a mother green sheet, thereafter the mother ceramic green sheet which 
is provided with the conductive patterns is punched out into prescribed 
dimensions, and a plurality of the punched ceramic green sheets are 
stacked with each other to obtain a mother laminate, for improving mass 
productivity. Thereafter the mother laminate is cut along its thickness, 
thereby obtaining laminates for respective multilayer ceramic capacitors. 
In general, the aforementioned ceramic green sheet is molded to have an 
elongated shape by a doctor blade coater or a roll coater method. In such 
a long ceramic green sheet molded in the aforementioned method, however, 
the thickness tends to disperse depending on the molding speed or the 
viscosity of the employed ceramic slurry, and partial dispersion of the 
thickness is not negligible. 
When a multilayer ceramic capacitor is prepared in accordance with the 
conventional method, therefore, it is impossible to avoid dispersion of 
the electrostatic capacitance in the obtained ceramic green sheets. In 
order to prevent such dispersion of the electrostatic capacitance, 
therefore, the following method is employed in general: 
After ceramic green sheets provided with internal electrodes for forming 
the electrostatic capacitance are stacked with each other, an additional 
ceramic green sheet for adjusting the electrostatic capacitance is further 
stacked on the laminate in consideration of the dispersion of the 
electrostatic capacitance which may be caused in the laminate, thereby 
implementing the necessary electrostatic capacitance. 
In such a method of further stacking the additional ceramic green sheet 
provided with the electrode for adjusting the electrostatic capacitance, 
however, the preparation steps are complicated since the additional 
ceramic green sheet provided with an electrode for adjusting the 
electrostatic capacitance must be prepared, i.e., an electrode pattern for 
adjusting the electrostatic capacitance is required in addition to 
electrode patterns forming the internal electrodes. 
In addition, the thicknesses of the ceramic green sheets may be 
considerably changed with time to result in thickness fluctuation of 
several .mu.m. When a certain degree of time is required in advance of 
stacking after molding of the ceramic green sheets, therefore, it is 
necessary to change the laminate structure in response to the fluctuation 
of the thicknesses of the ceramic green sheets, in order to implement the 
target electrostatic capacitance. Thus, the method of forming the 
electrode pattern for adjusting the electrostatic capacitance still tends 
to cause an error between designed and actual electrostatic capacitances. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a process for 
a multilayer ceramic component including a capacitor therein which can 
implement a desired electrostatic capacitance in high accuracy through 
relatively simple steps, with no requirement for complicated steps of 
preparing ceramic green sheets provided with conductive plates for 
adjusting the electrostatic capacitance and stacking such ceramic green 
sheets with each other. 
According to a wide aspect of the present invention, provided is a method 
of manufacturing a multilayer ceramic component including a capacitor 
therein comprising the steps of carrying a long ceramic green sheet along 
its longitudinal direction and measuring the thickness of the long ceramic 
green sheet while carrying the same, forming an internal electrode on the 
long ceramic green sheet, punching out the long ceramic green sheet into 
ceramic green sheets of prescribed dimensions and stacking the punched 
ceramic green sheets with each other by a number obtained with reference 
to the measured value of the thickness of the long ceramic green sheet, 
pressurizing the stacked ceramic green sheets along the direction of 
thickness for forming a laminate, and obtaining a ceramic sintered body by 
firing the laminate. 
In the method of manufacturing a multilayer ceramic component including a 
capacitor therein according to the present invention, the long ceramic 
green sheet is carried along its longitudinal direction so that the steps 
of measuring the thickness, forming an internal electrode and punching out 
the long ceramic green sheet are carried out, and the punched ceramic 
green sheets are immediately stacked with each other. Therefore, a 
laminate can be obtained with no influence exerted by fluctuation of the 
thicknesses of the ceramic green sheets caused with time. 
After the actual thickness of the long ceramic green sheet is measured, the 
ceramic green sheets are stacked with each other by the number obtained in 
response to the value of the thickness, whereby a target electrostatic 
capacitance can be reliably implemented. 
Even if the long ceramic green sheet disperses in thickness, therefore, it 
is possible to reliably prepare a multilayer ceramic component including a 
capacitor having the target electrostatic capacitance in high accuracy. 
Preferably, the thickness of the long ceramic green sheet is measured in a 
plurality of portions, so that the number of the ceramic green sheets to 
be stacked with each other can be decided in higher accuracy. Thus, a 
multilayer ceramic component including a capacitor having a desired 
electrostatic capacitance can be further reliably prepared. 
According to a specific aspect of the present invention, the thickness of 
the long ceramic green sheet is preferably measured at least at the center 
of a region which is provided with the internal electrode. More 
preferably, the thickness of the long ceramic green sheet is measured not 
only at the center but on positions of longitudinal ends or at corner 
portions of the region which is provided with the internal electrode. 
Thus, it is possible to decide the number of the ceramic green sheets to 
be stacked with each other on the basis of the thickness of the long 
ceramic green sheet at the central portion of the region provided with the 
internal electrode, which remarkably influences the electrostatic 
capacitance, by measuring the thickness at least at the center of the 
region provided with the internal electrode. When the thickness of the 
long ceramic green sheet is measured on the positions of the longitudinal 
ends or at the corner portions of the region which is provided with the 
internal electrode as described above, the number of the ceramic green 
sheets to be stacked with each other can be more correctly decided. 
According to a certain preferred aspect of the present invention, the 
thickness of the long ceramic green sheet is measured by a non-contact 
measuring method. Thus, the thickness of the long ceramic green sheet can 
be readily and reliably measured without influencing the step of carrying 
the same. As to such a non-contact measuring method, a measuring method 
employing radiation can be employed, for example. In the measuring method 
employing radiation, the long ceramic green sheet is irradiated with the 
radiation so that its thickness can be decided from the amount of the 
applied radiation and the amount of excited or transmitted radiation which 
is obtained as the result of the irradiation. When the thickness of the 
long ceramic green sheet is measured through the radiation as described 
above, it is necessary to measure the thickness prior to formation of the 
internal electrode. Otherwise the thickness of the long ceramic green 
sheet cannot be correctly measured since the internal electrode contains a 
metal. 
The method of deciding the number of the ceramic green sheets to be stacked 
with each other on the basis of the thickness of the long ceramic green 
sheet which is measured in the aforementioned manner can be preferably 
carried out by a central arithmetic processing unit which is connected to 
a thickness measuring unit for measuring the thickness of the long ceramic 
green sheet and generating an electric signal in response to the 
thickness. However, such an arithmetic processing unit may not be employed 
but the number of the ceramic green sheets to be stacked with each other 
can be immediately decided in response to the measured value of the 
thickness of the long ceramic green sheet by previously obtaining the 
relation between the thickness of the long ceramic green sheet and the 
number of the ceramic green sheets to be stacked with each other. 
As hereinabove described, the method of preparing a multilayer ceramic 
component including a capacitor according to the present invention simply 
carries out the series of steps of measuring the thickness of the long 
ceramic green sheet, forming the internal electrode and punching out the 
long ceramic green sheet while carrying the long ceramic green sheet along 
its longitudinal direction, whereby the capacitor having a target 
electrostatic capacitance can be obtained in high accuracy without 
reducing working efficiency. 
The number of the ceramic green sheets to be stacked with each other is set 
with reference to the thickness of the actually carried long ceramic green 
sheet, whereby dispersion in electrostatic capacitance can be remarkably 
reduced, and the desired electrostatic capacitance can be implemented in 
high accuracy. Consequently, it is possible to extremely reduce dispersion 
in electrostatic capacitance of the capacitor in the multilayer ceramic 
component. 
Further, in a particular aspect of the present invention the multilayer 
ceramic component including a capacitor therein is a multilayer ceramic 
capacitor, wherein external electrodes are formed on end surfaces of the 
ceramic sintered body respectively. 
The foregoing and other objects, features, aspects and advantages of the 
present invention will become more apparent from the following detailed 
description of the present invention when taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a schematic block diagram for illustrating an essential part of a 
method of preparing a multilayer ceramic capacitor according to an 
embodiment of the present invention. 
Referring to FIG. 1, a molded long ceramic green sheet 9 is fed from a roll 
1 toward a take-up roll 8. The ceramic green sheet 9 is wound on the roll 
1. 
The long ceramic green sheet 9 is delivered from the roll 1 and carried 
toward the roll 8, while a sheet thickness measuring unit 2, an internal 
electrode printer 3, a drying furnace 4 and a sheet punching unit 7 are 
arranged between the rolls 1 and 8. The sheet punching unit 7 punches out 
the long ceramic green sheet 9 into ceramic green sheets of prescribed 
dimensions, so that the punched ceramic green sheets are stacked with each 
other in a mold 6. After the ceramic green sheets of the prescribed 
dimensions are punched out, the remaining part of the long ceramic green 
sheet 9 is taken up on the roll 8. The sheet thickness measuring unit 2 
and the sheet punching unit 7 are electrically connected with each other 
through a central arithmetic processing unit 5. 
The method of preparing a multilayer ceramic capacitor according to this 
embodiment is now described in more concrete terms. 
First, the long ceramic green sheet 9 is wound on the roll 1. The long 
ceramic green sheet 9 is molded by a doctor blade coater, a roll coater 
method or another method, similarly to the prior art. The long ceramic 
green sheet 9 may alternatively be formed on a base film of PET 
(polyethylene terephthalate) or the like. 
The long ceramic green sheet 9 is carried along its longitudinal direction, 
and supplied to the sheet thickness measuring unit 2. The sheet thickness 
measuring unit 2 according to this embodiment is adapted to irradiate the 
long ceramic green sheet 9 with radiation for measuring the thickness of 
the long ceramic green sheet 9 from the ratio of the amount of the applied 
radiation to the amount of excited or transmitted radiation which is 
obtained as the result of the irradiation. This sheet thickness measuring 
unit 2 measures the thickness of the long ceramic green sheet 9. The 
measured value is supplied to the central arithmetic processing unit 5 as 
described later for deciding the number of the ceramic green sheets to be 
stacked with each other, and the sheet punching unit 7 is controlled to 
punch out the long ceramic green sheet 9 into the ceramic green sheets of 
the prescribed dimensions, which in turn are stacked with each other. 
The sheet thickness measuring unit 2 may alternatively be formed by any 
unit in place of that employing radiation, so far as the same can measure 
the thickness of the long ceramic green sheet 9 while carrying the same, 
without extracting a part thereof. For example, the unit 2 may be formed 
by a micrometer which presses measurers against both surfaces of the long 
ceramic green sheet 9 for measuring its thickness. 
The long ceramic green sheet 9 is preferably intermittently fed between the 
rolls 1 and 8, so that its thickness is measured while the same is 
stopped. Internal electrodes can be formed on the long ceramic green sheet 
9 during such stoppage, as described later. Thus, the thickness of the 
long ceramic green sheet 9 can be measured every formation of the internal 
electrodes, whereby the time for carrying out the steps can be prevented 
from being increased by provision of an extra time for measuring the 
thickness. 
The radiation which is employed for measuring the thickness is selected 
from X-radiation, .gamma.-radiation and .beta.-radiation, in response to 
the material for and the thickness of the long ceramic green sheet 9. 
Particularly when the long ceramic green sheet 9 is formed on a base film, 
the radiation is preferably prepared from the X-radiation or the 
.gamma.-radiation which is hardly influenced by the material for the base 
film etc. 
Thereafter the long ceramic green sheet 9 which is subjected to the 
measurement of its thickness is fed to the next step of forming the 
internal electrodes, so that the internal electrode printer 3 applies 
conductive paste 10 onto the long ceramic green sheet 9 by screen 
printing. Thus, the conductive paste 10 is printed onto the long ceramic 
green sheet 9 in a prescribed pattern (see FIG. 2). 
Then, the long ceramic green sheet 9 which is coated with the conductive 
paste 10 is introduced into and dried in the drying furnace 4. Drying 
conditions, which are varied with the type of a solvent employed for the 
conductive paste 10, are properly set in the ranges of about 70.degree. to 
150.degree. C. and 30 sec. to 10 minutes, in general. 
Thereafter the long ceramic green sheet 9 which is provided with the 
internal electrodes is punched out into prescribed dimensions by the sheet 
punching unit 7 along the portions provided with the internal electrodes. 
When the long ceramic green sheet 9 is formed on a base film, only the 
long ceramic green sheet 9 may be punched out. Thereafter the punched 
ceramic green sheets are vacuum-sucked by a suction head of the sheet 
punching unit 7, for example, moved along arrow in FIG. 1, and stacked 
with each other in the mold 6. The remaining part of the long ceramic 
green sheet 9 is taken up on the roll 8. 
The step of punching out the long ceramic green sheet 9 and stacking the 
punched ceramic green sheets with each other is carried out by punching 
out the long ceramic green sheet 9 into sheets of prescribed dimensions by 
a number which is decided in the central arithmetic processing unit 5, and 
stacking the punched sheets with each other. Thus, a desired capacitance 
can be acquired in high accuracy. 
Assuming that the average thickness of the long ceramic green sheet 9 is 
increased to 11.0 .mu.m by 1 .mu.m with respect to a desired thickness of 
10.0 .mu.m, the acquired capacitance is reduced by about 10%. In this 
case, the number of the ceramic green sheets, which is provided with the 
internal electrodes, to be stacked with each other may be increased by 10% 
for increasing the overlapping areas of the internal electrodes holding 
dielectric ceramic layers by 10%, in order to acquire the desired 
capacitance in high accuracy. 
In order to further accurately acquire the desired capacitance, capacitance 
correction may be carried out by partially changing the overlapping areas 
of the internal electrodes holding the dielectric ceramic layers of the 
multilayer capacitor. Such capacitance correction of changing the 
overlapping areas is carried out by punching out the long ceramic green 
sheet 9 provided with the internal electrodes in slight displacement from 
normal positions and stacking the punched ceramic green sheets with each 
other thereby changing the overlapping areas of the internal electrodes 
holding the dielectric ceramic layers. 
Thereafter the stacked ceramic green sheets, which are provided with a 
number of internal electrodes in general, are pressurized along the 
direction of thickness, to obtain a mother laminate 11 shown in FIG. 3. 
Then, the mother laminate 11 is cut along its thickness, to obtain 
laminates for independent multilayer ceramic capacitors. Each laminate is 
fired to obtain a ceramic sintered body 12 shown in FIG. 4. In this 
sintered body 12, internal electrodes 10a to 10g are formed by baking of 
the conductive paste 10. Further, external electrodes 13a and 13b shown in 
FIG. 5 are formed on end surfaces 12a and 12b of the sintered body 12 by 
application and baking of conductive paste and/or plating. A multilayer 
ceramic capacitor 14 obtained in the aforementioned manner can acquire a 
desired capacitance in high accuracy. 
While the thickness of the long ceramic green sheet is measured before 
printing of the internal electrodes in the aforementioned embodiment, 
measurement accuracy can be preferably improved by necessarily carrying 
out the measurement before every printing of the internal electrodes. If 
the long ceramic green sheet less disperses in thickness, however, its 
thickness may be measured once every two or three times of printing. The 
number of times for measuring the thickness of the long ceramic green 
sheet can be reduced in this case. 
While the thickness of the long ceramic green sheet can be measured in an 
arbitrary position, the same is preferably measured at a central portion 
of the region provided with the internal electrodes shown by arrow A in 
FIG. 2. The thickness of the long ceramic green sheet is preferably 
measured at the central portion A of the region provided with the internal 
electrodes, so that the thickness can be measured in high accuracy in the 
region provided with the internal electrodes which remarkably influence 
the electrostatic capacitance. 
In addition to the central portion A of the region provided with the 
internal electrodes, the thickness is preferably measured on positions of 
both longitudinal ends of the region provided with the internal electrodes 
as shown by arrows B and C in FIG. 2, or at corner portions D to G 
thereof. The number of the positions for measuring the thickness of the 
long ceramic green sheet is preferably increased so that the thickness can 
be measured in high accuracy. In order to simplify the operation for 
calculating the number of the ceramic green sheets to be stacked with each 
other with reference to the thickness, however, the number of the 
measuring positions is preferably reduced. 
When the thickness of the long ceramic green sheet is measured through 
radiation as described above, the thickness must be measured in advance of 
printing of the internal electrodes, since the internal electrodes contain 
a metal. 
Although the present invention has been described and illustrated in 
detail, it is clearly understood that the same is by way of illustration 
and example only and is not to be taken by way of limitation, the spirit 
and scope of the present invention being limited only by the terms of the 
appended claims.