Manufacturing method of ceramic electronic components and its manufacturing equipment

A manufacturing method for manufacturing ceramic electronic components, includes steps of forming a stack body by stacking ceramic green sheets and conductive layers on top of each other, punching a frame into the stack body and holding the frame in the stack body, locating a pressing force applying member inside the frame and, while the frame is held in the stack body, applying a pressing force to a portion of the stack body located inside the frame by causing the pressing force applying member located inside the frame to press against the portion of the stack body located inside the frame, to thereby form a high-density structure inside the frame while preventing the high-density structure from deforming outwardly beyond the frame. The stack body can be heated to reduce the required pressing force, and an elastic member may be provided to make the pressing force uniform.

TECHNICAL FIELD

The present invention relates to a method of manufacturing ceramic electronic components such as a multilayer ceramic capacitor and the like, and manufacturing equipment therefor.

BACKGROUND ART

Many methods for manufacturing ceramic electronic components have been known and a description is made here of a typical method of manufacturing multilayer ceramic capacitors.

First, a powder of such dielectric materials as barium titanate and the like is added with an organic binder, plasticizer, solvent and the like and the resulting mixture is kneaded and made into a slurry. Then, the slurry is coated using a doctor blade method or the like and dried to produce a ceramic green sheet. Next, a conductive paste mainly composed of a metal is printed on the ceramic green sheet by a screen printing method or the like and dried to form a conductive layer, thereby allowing an active layer sheet to be prepared. Aside from above, a cover layer sheet composed only of a ceramic green sheet, which has no conductive layer formed thereon, is prepared.

AsFIG. 12shows, according to a prior art process of stacking multilayer ceramic capacitors, adhesive layer102is disposed on supporting plate101and a plurality of cover layer sheets are stacked thereon. Further, on top of that, an active layer sheet is superimposed, thus putting together a ceramic green sheet and a conductive layer to form a stack structure. The step of superimposing an active layer sheet is repeated a predetermined number of times and further a plurality of cover layer sheets are again stacked on top of the plurality of active layer sheets to realize stack body103. When the active layer sheets are stacked on top of each other, the stacking is performed in such a manner that a plurality of rectangular patterns of respective conductive layers, each acting as an internal electrode, are staggered alternately from layer to layer by a predetermined distance in the length direction of the rectangular pattern.

In the step of forming a high-density structure by pressing, a pressing force is applied to stack body103to have respective ceramic green sheets and conductive layers pressed against one another to form a one-piece structure. In the prior art step of forming a high-density structure by pressing, a uniaxial press with flat lower die111and flat upper die112arranged in parallel with each other is used. Stack body103as composed on supporting plate101via adhesive layer102is disposed on lower die111and a pressing force is applied via upper die112to form a high-density structure of stack body103.

Next, the high-density structure of stack body103is cut into pieces, each having a desired configuration, and separated from adhesive layer102on supporting plate101, to produce green chips. The green chips are sintered and external electrodes are provided on each respective chip to complete a multilayer ceramic capacitor.

The aforementioned step of forming a high-density structure by pressing is a very important step to prevent a failure due to structural defects such as delamination and the like from occurring. When the extent of adhesive joining between respective ceramic green sheets and conductive layers is insufficient, it is likely to cause a failure due to structural defects. Therefore, in order to establish the densifying condition to a sufficient extent, it is necessary for a pressing force to be uniformly and sufficiently applied to stack body103, thereby allowing respective ceramic green sheets to be deformed in the thickness direction thereof and to be pressed against each other to realize an excellent density condition.

However, when a ceramic green sheet has a pressing force applied thereto or is exposed to a temperature and a pressure needed for densifying, the ceramic green sheet is deformed not only in the thickness direction thereof but also in the direction parallel to the surface thereof. This means that the periphery of stack body103tends to expand outwards, thereby causing a distortion in the shape of the conductive layer. As a result, when stack body103is cut into pieces, a failure due to disconnection and a failure due to poor characteristics are caused. These problems are likely to be multiplied as the step-wise difference in level due to missing of a conductive layer is increased because increasing numbers of the conductive layers are involved and/or the thickness of a ceramic green sheet is small, thereby making the ratio of the thickness of conductive layers occupying in the thickness of stack body103more significant.

Therefore, various proposals have been made with respect to a method for preventing the deformation of a stack body from occurring when a pressing force is applied thereto. For example, in the Japanese Patent Application Unexamined Publication Nos. H5-175072 and 2001-23844, disclosed methods include:

A) a method for forming a high-density structure by first applying a pressing force to the periphery on the surface of a stack body by means of a peripheral section die and then applying a pressing force to the inner part below the surface of the stack body by means of a central section die;

B) a method for applying a higher pressing force to a stack body by means of a peripheral section die than the pressing force applied to the stack body by means of a central section die; and

C) a method for applying a pressing force to a stack body placed in an elastic framework by means of a uniaxial rubber press.

Even according to the methods A and B, however, when the step-wise difference in level due to missing of a conductive layer is large, a plastic deformation of a ceramic green sheet takes place not only in the thickness direction but also in the direction parallel to the surface of the ceramic green sheet. As a result, the stack body expands at the outer periphery thereof to cause a distortion in the shape of the conductive layer.

Even according to the method C, it is necessary for the dimensions of the stack body to match the inner dimensions of the elastic framework with a high degree of precision and even a little difference in the dimensions allows the deformation of the stack body to occur.

SUMMARY OF THE INVENTION

A manufacturing method of ceramic electronic components according to the present invention comprises the step of applying a pressing force to a stack body formed by stacking ceramic green sheets and conductive layers on top of each other alternately to form a one-piece high-density structure of ceramic green sheets and conductive layers, in which a frame is installed to be held inside the stack body and a pressing force is applied to a pressing force applying member located inside of the frame. Manufacturing equipment of ceramic electronic components according to the present invention comprises a lower die, a pressing force applying member and a frame provided to surround the outer periphery of the pressing force applying member for applying a pressing force to a stack body formed by stacking ceramic green sheets and conductive layers on top of each other alternately, in which the tip of the frame is shaped like a blade.

DETAILED DESCRIPTION OF THE INVENTION

Next, a description is given to various exemplary embodiments of the present invention with reference to the drawings. With respect to descriptions made of objects structured in a manner similar to one another, the same reference symbols are used in common.

A description is made of exemplary embodiment 1 with reference toFIG. 1throughFIG. 5.

First, ceramic green sheet3composed of a ceramic powder, which is mainly formed of barium titanate, and an organic binder is formed on a base film to prepare a first sheet. Meanwhile, a second sheet is prepared by having conductive layer4deposited on ceramic green sheet3. This process is performed according to a screen printing method by the use of a metallic paste mainly composed of nickel to form conductive layer4on ceramic green sheet3of the first sheet in a desired pattern, and is followed by a drying step. At this time, the thickness of ceramic green sheet3is made about 10 μm and the thickness of conductive layer4is made about 2.5 μm.

Next, a stacking process is described. AsFIG. 5shows, adhesive sheet2is first formed on supporting plate1. Adhesive sheet2plays an important role in making supporting plate1integral with stack body5and has adhesion to both stack body5and supporting plate1. The adhesion is strong enough to prevent stack body5and supporting plate1from coming off from each other. However, when the integral structure of stack body5and supporting plate1is cut into pieces, it is necessary for the composing elements of each respective piece to be separated from each other. Therefore, the adhesion between stack body5and supporting plate1is arranged to disappear when heated to temperatures higher than a predetermined temperature.

Then, after the first sheet is transfer printed by bonding on top of adhesive sheet2on supporting plate1by an application of heat and pressure via the base film, the base film is eliminated by peeling off. This process is repeated to have 20 sheets of the first sheet stacked on top of each other, resulting in a cover layer.

Subsequently, after the second sheet is transfer printed by bonding on top of the cover layer by placing the second sheet on the cover layer in such a manner as that side of conductive layer4touches the cover layer and applying heat and pressure via the base film, the base film is eliminated by peeling off. This process of transfer printing the second sheet by bonding is repeated 150 times.

Additionally, 20 sheets of the first sheet are stacked on top of each other to form a cover layer on the stacked second sheets, thus obtaining stack body5as shown inFIG. 5.

Next, the manufacturing equipment as shown inFIG. 4is described. Frame12of the manufacturing equipment is provided so as to surround the outer periphery of pressing force applying member13with almost no gaps left therebetween. In order for frame12to have the function of cutting stack body5, the surface of frame12at the side of pressing force applying member13is aligned in parallel to the side surface of pressing force applying member13and the tip of frame12is shaped like a sharp blade which is angled outwardly. Heaters14and15are buried in lower die11and pressing force applying member13, respectively, for heating an object to be pressed. In order to secure the object to be pressed, lower die11has a suction function for fixing the object to be pressed by suction.

Next, a step of forming a high-density structure by pressing is described with reference toFIG. 1throughFIG. 3.

AsFIG. 1shows, stack body5fixed on supporting plate1by means of adhesive sheet2is disposed on lower die11of the manufacturing equipment at a predetermined position. And, on the upper surface of stack body5is disposed a polyethyleneterephthalate film6(referred to as a “film”, hereafter) of 35 μm thickness.

Then, asFIG. 2shows, frame12is moved down by hydraulic pressure and punched into stack body5, and stops when the tip of frame12touches adhesive sheet2. After that, pressing force applying member13is moved down by hydraulic pressure and presses stack body5inside of frame12asFIG. 3shows. At this time, the temperatures of lower die11and pressing force applying member13are kept at 80° C. by heaters14and15, respectively. Stack body5is pressed for 60 seconds under the pressure of 50 MPa.

Subsequently, the hydraulic pressure is reduced to 1 MPa while pressing force applying member13is stopped after moving down.

While stack body5is being held, frame12is moved up by hydraulic pressure to have frame12separated from stack body5. Then, pressing force applying member13is moved up by hydraulic pressure to have pressing force applying member13separated from stack body5.

Next, stack body5formed into a high-density structure by pressing is removed from lower die11of the manufacturing equipment together with supporting plate1and adhesive sheet2, and stack body5is cut to the required dimensions. Afterwards, stack body5cut apart together with supporting plate1and adhesive sheet2is heated to 150° C. to be separated from adhesive sheet2, thereby producing many pieces of green chips. After subjecting the green chips to a binder eliminating treatment in nitrogen gas, the green chips are sintered in a mixed atmosphere of nitrogen and hydrogen gases, in which nickel is prevented from oxidation, with the temperatures thereof increased to 1300° C., thereby obtaining sintered bodies of the chips.

Each of the sintered bodies is treated with chamfering to have the inner electrode exposed to both end surfaces thereof. After an electrode paste mainly composed of copper is applied to both end surfaces and also to side surfaces of each respective sintered body, the sintered bodies are exposed in a nitrogen atmosphere at 800° C. to form electrodes. External electrodes composed of nickel are formed on the electrodes by applying nickel plating thereto and solder is formed on nickel by applying solder plating thereto, thereby producing multilayer ceramic capacitors in exemplary embodiment 1 of the present invention.

By conducting an inspection of the internal structure of the respective multilayer ceramic capacitors produced in exemplary embodiment 1 through a microscopic observation of cross-sections of the capacitors, failures due to structural defects such as a disconnection defect caused by displacement of conductive layers, interlayer stripping, delamination and the like are not observed at all. Electrical characteristics of the multilayer ceramic capacitors are also excellent.

In the step of forming a high-density structure by pressing stack body5according to a method of manufacturing multilayer ceramic capacitors in exemplary embodiment 1 of the present invention, a pressing force is applied to stack body5by pressing force applying member13located inside of frame12while frame12is punched into stack body5. Accordingly, since a pressing force is applied to stack body5while stack body5is securely held by frame12in such a manner that no gaps are created between frame12and the peripheral side surfaces of stack body5, no deformations of stack body5in the directions parallel to the surface thereof are created, thereby eliminating the possibility of causing deformations of conductive layer4due to a strain imposed thereto and allowing stack bodies with an excellent cladding structure to be realized. As a result, when the stack bodies are fired to produce sintered bodies, ceramic electronic components produced by the use of such sintered bodies exhibit no failures due to disconnection, structural defects and defective electrical characteristics and are produced at a good yield rate.

Since heaters14and15are employed in exemplary embodiment 1 to apply a pressing force to stack body5while heat is applied thereto, stack body5is softened due to the heat application and, even when a pressing force is small in comparison with the case where a pressing force is applied at ordinary temperatures, a stack body with a sufficiently excellent cladding condition can be realized. Since the conditions for realizing a cladding structure with a pressing force application can be set up by both factors of temperature and pressing force, there is a wide range of freedom to adopt appropriate conditions for realizing a cladding structure by pressing in accordance with the properties of ceramic green sheets that constitute a stack body.

Further, a pressing force is applied to stack body5via film6disposed on the upper surface thereof, thereby preventing the pressure application surface of pressing force applying member13from sticking to stack body5to facilitate the separation from each other. In addition, the adhesion of dirt and dust to stack body5is prevented.

The manufacturing equipment used in exemplary embodiment 1 employs frame12that surrounds the outer periphery of pressure applying member13and the tip of frame12is shaped like a blade. By the use of the manufacturing equipment thus structured, it is made possible for the manufacturing method in exemplary embodiment 1 of the present invention to be put into practice, with the method featuring a pressing force being applied to stack body5via pressing force applying member13while frame12is pressed into stack body5and held securely therein.

Also, the manufacturing equipment used in exemplary embodiment 1 allows pressing force applying member13and frame12to move independently, thereby making it possible for frame12to appropriately adjust to the necessary extent and force of pressing thereof into stack body5and for pressing force applying member13to adjust the pressing force and the like in accordance with the thickness and properties of the object to be pressed, i.e., stack body5.

Furthermore, since frame12is installed in such a manner that no gaps are left between frame12and pressing force applying member13, there is no possibility for stack body5to get into gaps between frame12and pressing force member13, thereby eliminating the cause of stack body5being deformed in shape at the time of applying a pressing force to stack body5via pressing force applying member13.

The tip of frame12is shaped like a blade in such a manner that the inner surface of frame12at the side of pressing force applying member13is aligned in parallel to the side surface of pressing force applying member13. Therefore, when frame12is pressed into stack body5, no extra force is imposed to stack body5located at the inner side of frame12in the direction parallel to the surface of stack body5, thereby preventing stack body5from being lifted and/or deformed.

The advantages as described above are applicable to the case where ceramic green sheets are thin and even the case where the number of ceramic green sheets and the number of conductive layers are multiplied.

FIG. 6is a cross-sectional view of manufacturing equipment for manufacturing ceramic electronic components employed in the step of forming a high-density structure by pressing in exemplary embodiment 2 of the present invention.

The difference between exemplary embodiment 2 and exemplary embodiment 1 is in the structure of the manufacturing equipment employed. AsFIG. 6shows, the manufacturing equipment in exemplary embodiment 2 of the present invention has the pressure application surface on the end part of pressing force applying member23composed of elastic body26to apply a pressing force uniformly to an object to be pressed. A high-temperature-resistant rubber material is employed as elastic body26. Alternatively, a flat plate composed of a rigid body via a spring support can be used or a piston-type structure with a gas enclosed can be employed. Except for the foregoing, the manufacturing equipment in the present exemplary embodiment is the same as the one ofFIG. 4used in exemplary embodiment 1.

Next, steps of a manufacturing method for manufacturing ceramic electronic components in exemplary embodiment 2 of the present invention are described.

First, stack body5is prepared in the same manner as in exemplary embodiment 1.

With respect to the step of forming a high-density structure by applying a pressing force to stack body5, the drawing for describing the step is omitted since the ascending/descending movement of frame22and pressing force applying member23at the time of forming a high-density structure by applying a pressing force to stack body5is similar to that shown for exemplary embodiment 1. And, the step of disposing stack body5on lower die21at a predetermined position thereof and also disposing a polyethyleneterephthalate film on the upper surface of stack body5is also similar to that of exemplary embodiment 1 as shown inFIG. 6.

Then, frame22is moved down by hydraulic pressure and pressed into stack body5. The movement of frame22comes to a stop when the tip thereof touches adhesive sheet2. Thereafter, pressing force applying member23of the manufacturing equipment is moved down by hydraulic pressure to press stack body inside of frame22. At this time, heaters24and25maintain the temperatures of lower die21and pressing force applying member23at 80° C. and pressing force applying member23presses stack body5for 60 seconds with a pressing force of 30 MPa.

Subsequently, the hydraulic pressure is reduced to 1 MPa while pressing force applying member23is stopped after moving down. While stack body5is held, frame22is moved up by hydraulic pressure to have frame22separated from stack body5. Then, pressing force applying member23is moved up by hydraulic pressure to have pressing force applying member23separated from stack body5. Next, stack body5formed into a high-density structure by pressing is removed from lower die21together with supporting plate1and adhesive sheet2.

In the same way as in exemplary embodiment 1, stack body5is cut apart into pieces of green chips. The green chips are sintered, and are then provided with external electrodes, thus producing multilayer ceramic capacitors in exemplary embodiment 2 of the present invention.

Upon conducting an inspection of the internal structure of the multilayer ceramic capacitors produced in exemplary embodiment 2 through a microscopic observation of cross-sections of the capacitors, failures due to structural defects such as disconnection defects caused by displacement of conductive layers, delamination and the like are not observed at all. Electrical characteristics of the multilayer ceramic capacitors are also excellent.

The manufacturing equipment in exemplary embodiment 2 of the present invention has the pressure application surface on the end part of pressing force applying member23provided with elastic body26. Accordingly, the adverse effects caused by irregularities on the surface of an object to be pressed, i.e., stack body5due to the existence of conductive layer4are absorbed by elastic body26, thereby allowing a uniform pressing force to be applied to stack body5. The pressing force applied to stack body5in exemplary embodiment 2 is small in magnitude when compared with exemplary embodiment 1, resulting in an elimination of such a problem as deformations of stack body5and yet providing an excellent densifying condition of the stack body.

As a result, ceramic electronic components exhibiting no failures due to disconnection defects, structural defects and defective electrical characteristics are produced with a good yield rate.

FIG. 7is a cross-sectional view of the manufacturing equipment of ceramic electronic components employed in the step of forming a high-density structure by pressing in exemplary embodiment 3 of the present invention.FIG. 8throughFIG. 11are cross-sectional views for describing the step of forming a high-density structure by applying a pressing force to a stack body in exemplary embodiment 3 of the present invention.

Exemplary embodiment 3 differs from exemplary embodiment 1 and exemplary embodiment 2 in the structure of the manufacturing equipment employed and the ascending/descending movement of frame32and pressing force applying member33at the time of forming a high-density structure by pressing. AsFIG. 7shows, the manufacturing equipment for manufacturing ceramic electronic components in exemplary embodiment 3 is structured to allow the space inside vacuum chamber37to be kept under a reduced pressure by exhausting air through air outlet38. Accordingly, an application of a pressing force to a stack body in an atmosphere under a reduced pressure facilitates the exhaustion of gasses contained in the stack body, thereby allowing the stack body to realize an excellent densifying condition. Except for the foregoing, the manufacturing equipment in the present exemplary embodiment is structured in the same way as the manufacturing equipment ofFIG. 6used in exemplary embodiment 2.

Next, steps of a manufacturing method for manufacturing ceramic electronic components in exemplary embodiment 3 of the present invention are described.

First, stack body5as shown inFIG. 3is prepared in the same manner as in exemplary embodiment 1.

Then, asFIG. 8shows, stack body5is disposed on lower die31at a predetermined position and film6is disposed on the upper surface of stack body5. These steps are the same as in exemplary embodiment 1. And, air is exhausted through air outlet38of vacuum chamber37to reduce the atmospheric pressure inside vacuum chamber37to 13 hPa, thereby allowing gasses contained inside of stack body5to be exhausted.

Subsequently, while the atmospheric pressure inside of vacuum chamber37is kept at 13 hPa, pressing force applying member33of the manufacturing equipment is moved down by hydraulic pressure and stops the motion of moving down at a position where a small pressing force of 1 MPa is still being applied to stack body5. Thus, asFIG. 9shows, elastic body36attached to the end part of pressing force applying member33holds stack body5in place.

Next, asFIG. 10shows, frame32is moved down by hydraulic pressure and pressed into stack body5and stops the motion of moving down at a position where the tip of frame32touches adhesive sheet2. Thereafter, the pressing force of pressing force applying member33is increased by hydraulic pressure and stack body5inside of frame32is pressed asFIG. 11shows. At this time, heaters34and35keep the temperatures of lower die31and pressing force applying member33at 80° C. and a pressing force of 30 MPa is applied to stack body5for 30 seconds.

Then, while the downward motion of pressing force applying member33is stopped, the hydraulic pressure is reduced to 1 MPa. While stack body5is being held down, frame32is moved up by hydraulic pressure to have frame32separated from stack body5. Thereafter, pressing force applying member33is moved up by hydraulic pressure to be separated from stack body5. And, air is introduced through air inlet39to return the pressure inside of vacuum chamber37to barometric pressure, and stack body5formed into a high-density structure by pressing is removed together with supporting plate1and adhesive sheet2from lower die31of the pressing force applying setup.

In the same way as in exemplary embodiment 1, stack body5is cut apart into pieces of green chips. The green chips are sintered, and are then provided with external electrodes, thus producing multilayer ceramic capacitors in exemplary embodiment 3 of the present invention

By conducting an inspection of the internal structure of the multilayer ceramic capacitors produced in exemplary embodiment 2 through a microscopic observation of cross-sections of the capacitors, failures due to structural defects such as disconnection defects caused by displacement of conductive layers, delamination and the like are not observed at all. Electrical characteristics of the multilayer ceramic capacitors are also excellent.

With respect to a manufacturing method for manufacturing multilayer ceramic capacitors in exemplary embodiment 3 of the present invention, an application of a pressing force to stack body5under a reduced atmospheric pressure facilitates the elimination of gasses contained inside of stack body5, thereby allowing the adhesion between ceramic green sheets to be achieved easily. Although the application of a pressing force to stack body5is conducted in a short period of time in exemplary embodiment 3 when compared with exemplary embodiment 2, such problems as deformed stack bodies are not observed and a very excellent high-density structure of the stack body is realized. As a result, ceramic electronic components exhibiting no failures due to disconnection defects, structural defects and defective electrical characteristics are produced with a good yield rate.

In addition, frame32is punched into stack body5by means of pressing force applying member33with stack body5held in place, and then a pressing force is applied to stack body5via pressing force applying member33, thereby allowing stack body5to be fixed in position by means of pressing force applying member33and also to be prevented from being lifted or delaminated when the air inside of vacuum chamber37is exhausted to create the state of a reduction in atmospheric pressure. Even when frame32is punched into stack body5, lifting or deformation of stack body5is not caused.

With respect to a method of stacking layers on top of each other to produce stack body5in exemplary embodiment 1 through exemplary embodiment 3, a description is given of a method comprising the steps of transferring by adhesion ceramic green sheet3onto adhesive sheet2on supporting plate1via a base film by applying heat and pressure and eliminating the base film by peeling off. The present invention is equally effective in the case of forming a high-density structure by applying a pressing force to a stack body, which is produced according to a stacking method different from the aforementioned transfer stacking method.

Although a description is given of preparations of multilayer ceramic capacitors in exemplary embodiment 1 through exemplary embodiment 3, the present invention is equally effective in the case of producing a stack body formed by stacking ceramic green sheets and conductive layers on top of each other and used in ceramic electronic components such as multilayer coils, multilayer varistors, multilayer thermisters, ceramic multilayer substrates and the like.

INDUSTRIAL APPLICABILITY

As described above, the present invention deals with a manufacturing method for manufacturing ceramic electronic components, in which the process of forming a cladding structure by applying a pressing force to a stack body formed by stacking ceramic green sheets and conductive layers on top of each other comprises the steps of punching a frame into the stack body and keeping the frame in the stack body, and applying a pressing force to the stack body via a pressing force applying member located inside of the frame. According to this method, a pressing force can be applied to the stack body held and fixed in position by the frame in such a way that there are no gaps created at all between the frame and the peripheral side surfaces of the stack body. Therefore, even when a sufficiently strong pressing force is applied to the stack body to form a high-density structure, the stack body can be prevented from being deformed in the direction parallel to the surface thereof, thereby realizing a reduction in disconnection failures and also in performance failures. After the resulting stack bodies are sintered, ceramic electronic components free of structural defects and failures in electrical performance can be produced with an excellent yield rate by using the sintered bodies.

The present invention also deals with manufacturing equipment comprising a lower die, a pressing force applying member and a frame provided so as to surround the peripheral side surfaces of the pressing force applying member for the purpose of pressing an object to be pressed, in which the tip of the frame is shaped like a blade. By the use of the manufacturing equipment, a manufacturing method for manufacturing ceramic electronic components is made possible. This method comprises applying a pressing force to a stack body via a pressing force applying member located inside of a frame while the frame is punched into the stack body and kept therein.