JP2005170769A - Method for producing ceramic substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a ceramic substrate by which warping or the like of the ceramic substrate can be surely reduced, and slippage and movement of the ceramic substrate being treated from a setter can be prevented. <P>SOLUTION: When a piezoelectric ceramic substrate is produced, a dense zirconia setter 2 on which a ceramic green 1 is mounted is prepared. Then, recessed and projected parts 3 for releasing fine substances generated at the time of heating the ceramic green 1 from the zirconia setter 2 side in such a state that the ceramic green 1 is mounted are formed on the mounting surface of the zirconia setter 2. The ceramic green 1 is obtained by adding a binder or the like to a piezoelectric ceramic powder and forming. The obtained ceramic green 1 is mounted on the mounting surface of the zirconia setter 2, and the debinding of the ceramic green 1 is performed. After that, the ceramic green 1 mounted on the mounting surface of the zirconia setter 2 is directly fired. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a ceramic substrate used for an electronic ceramic component or the like.

As a conventional method for manufacturing a ceramic substrate, for example, a method described in Patent Document 1 is known. In the method described in this document, an organic binder or the like is added to a ceramic material to form a green sheet, and then the green sheet is placed on a setter and appropriately placed in a heating furnace in a state where the entire green sheet is surrounded by a ceramic material. The warping of the substrate is reduced by removing the binder and firing the green sheet.
JP-A-1-282157

  However, according to the above-described prior art method, depending on the material of the ceramic substrate, the following problems may occur, and thus the substrate warpage and undulation may not be eliminated.

  That is, it is desirable that all the binder, solvent, and the like in the green be removed after the binder removal treatment of the green sheet, but in practice, a part of the binder remains in the green as a carbon component. This residual carbon is gasified at the time of firing the green sheet, which is a subsequent process, and in that case, the oxide in the green may be reduced. At this time, depending on the element, evaporation occurs at the time of reduction, so that the element leaves the green, and as a result, a part of the substrate composition may be different from the desired one. Such a defect occurs remarkably when, for example, ZnO is contained in the green, and this causes warping of the substrate.

  Also, as a problem other than the warpage of the substrate, when a dense setter with polished surface is used, the gas that escapes from the back surface of the green sheet (the surface on the setter side) out of the gas generated during binder removal Therefore, when the green sheet is thin and small, the green sheet is lifted from the setter, and the green sheet may be displaced. For this reason, the green sheet may fall off from the setter, and scratches or deformation may occur on the back surface of the green sheet.

  An object of the present invention is to provide a method of manufacturing a ceramic substrate that can reliably reduce warpage of the ceramic substrate and prevent the ceramic substrate being processed from being displaced relative to the setter.

  The present invention relates to a method of manufacturing a ceramic substrate by firing ceramic green to manufacture a ceramic substrate, and a material for releasing a material generated when the ceramic green is heated in a state where the ceramic green is placed from the ceramic green A step of preparing a setter having a mounting surface on which relief irregularities are formed, a step of forming a ceramic green containing a binder, a ceramic green placed on the mounting surface of the setter, and a binder removal of the ceramic green And a step of firing the ceramic green while the ceramic green is placed on the mounting surface of the setter after the binder removal of the ceramic green.

  By using a setter having a material escape irregularity formed on the mounting surface in this manner, by removing the ceramic green binder and firing, in the state where the ceramic green is placed on the mounting surface of the setter, The contact area with the ceramic green is reduced. For this reason, in the ceramic green binder removal process, the burnout of the binder easily escapes from the back surface (the surface on the setter side) of the ceramic green, so that the so-called binder removal property is improved. For this reason, the carbon component remaining in the ceramic green after the binder removal is reduced. Therefore, in the firing process of the ceramic green, evaporation of elements caused by reduction of oxide in the ceramic green when residual carbon is gasified can be suppressed. Thereby, since the uniformity of the composition of the ceramic substrate obtained by firing is improved, warpage of the ceramic substrate can be reliably reduced.

  Further, in the ceramic green binder removal process, the escape of the gas generated on the back surface of the ceramic green is improved by the material escape irregularities, so that the ceramic green can be prevented from lifting from the setter. Furthermore, when firing a ceramic green with the setter on which the ceramic green is placed in a closed furnace, the difference in heating speed between the setter and the ceramic green is reduced by the uneven part for material escape. It is prevented that the gas to be entrained on the back surface of the ceramic green and the ceramic green is lifted from the setter. Accordingly, it is possible to prevent the ceramic green from moving with respect to the setter during removal of the ceramic green from the binder and during firing.

  Preferably, as the setter, a material escape concavo-convex portion formed so that the center line average roughness Ra of the mounting surface is 1 to 20 μm is used. By forming such an uneven portion for escaping the material on the setting surface of the setter, binder burnout and gas generated in the ceramic green can be effectively released from the setter side. In addition, when the ceramic green is fired, the pattern of the material escape uneven portion is prevented from being transferred to the back surface of the ceramic green. For this reason, when a ceramic substrate obtained by firing is commercialized, it is not necessary to perform mechanical processing such as polishing on the ceramic substrate.

  At this time, it may further include a step of forming an external electrode on the ceramic substrate without subjecting the ceramic substrate obtained by firing the ceramic green to mechanical processing. Thus, when forming the external electrode on the ceramic substrate, it is not necessary to perform polishing or the like on the ceramic substrate, so that the manufacturing process of the ceramic substrate can be simplified.

  Preferably, the setter is made of a mold having projections and depressions for forming the material escape projections and depressions. Thereby, the setter which has an uneven | corrugated | grooved part can be produced easily and cheaply compared with the case where the mounting surface of a setter is roughened by blasting or grinding | polishing with polishing powder, for example. Further, since it is not necessary to perform mechanical processing on the setter as in blast processing, the setter is maintained at high strength, and processing waste or the like does not remain on the setting surface of the setter.

  Further, preferably, the ceramic green is formed of a material containing lead, and the ceramic green is fired in a state where the setter on which the ceramic green is placed is placed in a closed furnace. Thereby, a piezoelectric ceramic substrate containing lead can be easily obtained. Moreover, it is possible to suppress the evaporation of lead by firing the ceramic green in a closed furnace.

  According to the present invention, a setter having a mounting surface on which a material escape uneven part for releasing a material generated when the ceramic green is heated in a state where the ceramic green is placed is formed. Since the ceramic green binder and firing are performed, warping and undulation of the ceramic substrate can be surely reduced, and the ceramic substrate (ceramic green) being processed can be prevented from shifting relative to the setter.

  Hereinafter, a preferred embodiment of a method for producing a ceramic substrate according to the present invention will be described in detail with reference to the drawings.

  In the present embodiment, a piezoelectric ceramic substrate whose main component is lead titanate or lead zirconate titanate is manufactured. The piezoelectric ceramic substrate is applied to various products such as a ceramic oscillator, a ceramic filter, a piezoelectric buzzer, a piezoelectric sensor, and a piezoelectric actuator.

When manufacturing such a piezoelectric ceramic substrate, first, as shown in FIGS. 1 and 2, a zirconia setter 2 on which a sheet-like ceramic green 1 is placed is prepared. The zirconia setter 2 desirably has a denseness such that the porosity is less than 3%, preferably less than 1%. As a material for the zirconia setter 2, it is desirable to use, for example, a material obtained by adding yttria (Y ₂ O ₃ ) to zirconium oxide and stabilizing it in order to enhance durability. In addition to Y ₂ O ₃ , calcia (CaO), magnesia (MgO), ceria (CeO ₂ ) and the like can be used as the stabilizer.

  As shown in FIG. 3, the placement surface of the zirconia setter 2 is for releasing a substance generated in the ceramic green 1 from the zirconia setter 2 side when the ceramic green 1 is heated in a state where the ceramic green 1 is placed. The material escape uneven portion 3 is formed. The substance referred to here is a burnout of a binder generated when the ceramic green 1 described later is removed, a gas generated when the ceramic green 1 described later is fired, or the like.

  The material escape uneven portion 3 is configured such that the center line average roughness Ra of the mounting surface of the zirconia setter 2 is preferably 1 to 20 μm, more preferably 2 to 6 μm. The centerline average roughness Ra is the surface roughness specified in JIS B0601, and the roughness curve is folded from the centerline, and the area obtained by the roughness curve and the centerline is the length. The value divided by.

The zirconia setter 2 having such a minute material escape concavo-convex portion 3 is made as follows using a mold (not shown). That is, first, the surface of the mold to be used is subjected to uneven processing so as to have the above-mentioned center line average roughness Ra. Then, by pressing the zirconia powder stabilized with an additive such as Y ₂ O ₃ by the mold, minute irregularities are formed on the surface of the powder molded body. Thereafter, the powder compact is fired to obtain a zirconia setter 2 having a mounting surface on which the material escape uneven portions 3 are provided. If necessary, a binder may be added to the zirconia powder to perform molding, and the binder of the powder molded body may be removed before firing.

  By producing the zirconia setter 2 using a mold in this way, the concavo-convex part 3 for escaping the material is made smaller than when the mounting surface of the setter is roughened by, for example, blasting using a projection material. The zirconia setter 2 can be easily and inexpensively made. In addition, since the powder molded body is not subjected to mechanical processing such as polishing or blasting after the powder molded body is fired, processing waste or the like is attached to the mounting surface of the zirconia setter 2 or the zirconia setter 2 Can be prevented from being distorted.

The ceramic green 1 is made of a ternary piezoelectric ceramic having a composition of PbTiO ₃ —PbZrO ₃ —Pb (Zn1 / 3 Nb2 / 3) O ₃ , for example. A ceramic green 1 is obtained by adding an organic binder, an organic solvent, or the like to a piezoelectric ceramic powder made of such a material to form a slurry or paste, and forming a sheet by a doctor blade method or the like. The ceramic green 1 is made of a laminated body in which a plurality of sheets on which internal electrode patterns are formed, for example.

  Next, a plurality (10 in this case) of such ceramic greens 1 are placed on the placement surface of the zirconia setter 2 as shown in FIGS. 1 and 2, and the binder contained in the ceramic green 1 is removed. So-called debinding (degreasing) is performed. When the binder used at the time of molding is gasified from the ceramic green 1 during firing to be described later, the firing atmosphere is disturbed and the firing of the ceramic green 1 is caused. Therefore, the ceramic green 1 is removed before firing. Yes. As the binder removal processing, the ceramic green 1 is heated at a temperature of 400 ° C., for example, and is stabilized for 10 hours, for example.

  Next, the ceramic green 1 is fired while the ceramic green 1 is placed on the mounting surface of the zirconia setter 2. Specifically, as shown in FIGS. 4 and 5, a plurality of zirconia setters 2 on which ceramic binders 1 having been subjected to binder removal processing are placed are stacked via columnar zirconia spacers 4. The zirconia spacer 4 is placed at four corners on the zirconia setter 2. Then, a zirconia setter 2A on which the ceramic green 1 is not placed is stacked on the top of these zirconia setters 2 with a zirconia spacer 4 interposed therebetween. The zirconia setter 2A preferably has the same structure as the zirconia setter 2 on which the ceramic green 1 is placed. At this time, the interval between the zirconia setters 2 is adjusted by changing the length of the zirconia spacer 4. The zirconia spacer 4 is preferably formed of the same material as the zirconia setters 2 and 2A.

  Subsequently, the zirconia setters 2 and 2A loaded in multiple stages as described above are housed in a closed firing furnace 5, and each ceramic green 1 is fired. At this time, the ceramic green 1 is heated at a temperature of 1050 ° C., for example, and is stabilized for 3 hours, for example. Since the ceramic green 1 is placed in the firing furnace 5 and fired as described above, the lead contained in the ceramic green 1 can be prevented from evaporating. In order to reliably suppress the evaporation of lead, lead oxide powder may be put in the firing furnace 5. By performing such firing, a piezoelectric ceramic substrate is obtained.

  Thereafter, as shown in FIG. 6, external electrodes 7 are formed on the upper surface of the fired piezoelectric ceramic substrate 6. Here, since the material escape uneven portion 3 formed on the mounting surface of the zirconia setter 2 is a fine minute unevenness, the pattern of the material escape uneven portion 3 is not transferred to the lower surface of the piezoelectric ceramic substrate 6. Almost no. Therefore, the external electrode 7 can be formed on the piezoelectric ceramic substrate 6 without subjecting the piezoelectric ceramic substrate 6 to mechanical processing such as polishing. Of course, it is not necessary to polish the piezoelectric ceramic substrate 6 after forming the external electrodes 7 on the piezoelectric ceramic substrate 6.

  At this time, Ag paste is applied to the upper surface of the piezoelectric ceramic substrate 6, and the piezoelectric ceramic substrate 6 is baked at 700 ° C., for example, to form the external electrode 7. As a material for the external electrode 7, Au, Cu, or the like can be used in addition to Ag. In addition, the external electrode 7 can be formed by sputtering, electroless plating, or the like in addition to baking.

  By the way, if a part of the binder is not completely removed and remains in the ceramic green 1 as a carbon component in the step of removing the binder of the ceramic green 1, the residual carbon is formed during the subsequent firing process of the ceramic green 1. It becomes easy to come out after gasification. At this time, residual carbon may reduce the oxide (ZnO) in the ceramic green 1, and in this case, Zn evaporates from the ceramic green 1. The composition of 1 will be different. As a result, the shrinkage rate of the ceramic green 1 changes between the front surface side and the back surface side of the ceramic green 1, and as a result, warpage or undulation of the piezoelectric ceramic substrate 6 may occur.

  In order to improve the binder removal property of the ceramic green 1, it is conceivable to use a porous setter. However, when ceramic green is placed on the same porous setter after firing and firing is performed, lead (Pb) in the ceramic green 1 is absorbed by the porous setter and the back side of the ceramic green 1 (the setter side) ), It becomes difficult to maintain the soaking property and the soaking atmosphere property, and uneven firing of the ceramic green 1 occurs. As a result, even if the piezoelectric ceramic substrate is not warped, the substrate may not be able to obtain desired characteristics.

  In addition, it is conceivable that after removing the binder using a porous setter, the ceramic green 1 is replaced with a dense setter. However, since the ceramic green 1 from which the binder has been removed has low retention, the transfer of the ceramic green 1 is low. The ceramic green 1 may be damaged during loading.

  On the other hand, in this embodiment, since the zirconia setter 2 having a placement surface on which the minute material escape uneven portion 3 is formed is used, the ceramic green 1 is placed on the placement surface of the zirconia setter 2. Sometimes, the contact area between the zirconia setter 2 and the ceramic green 1 becomes small. For this reason, during the binder removal processing of the ceramic green 1, binder burnout (carbon) is easily removed from the back surface (surface on the zirconia setter 2 side) of the ceramic green 1, so that the binder removal property is improved. Therefore, the carbon remaining in the ceramic green 1 is reduced during the firing process of the ceramic green 1. In addition, when the slightly remaining carbon is gasified during the firing process, the gas easily escapes from the back surface of the ceramic green 1. As a result, Zn that evaporates due to the residual carbon reducing oxides in the ceramic green 1 is reduced, so that it is possible to suppress a difference in composition between the front side and the back side of the ceramic green 1.

  In addition, since the dense zirconia setter 2 that does not easily react to lead is used, lead in the ceramic green 1 is hardly absorbed by the zirconia setter 2 during the firing process of the ceramic green 1. Further, when the ceramic green 1 is placed on the mounting surface of the zirconia setter 2, the contact area between the zirconia setter 2 and the ceramic green 1 becomes small as described above. As a result, the uniformity of heat and atmosphere is improved between the front surface side and the back surface side of the ceramic green 1, so that firing unevenness of the ceramic green 1 is reduced.

  As described above, since the shrinkage rate of the ceramic green 1 is substantially uniform as a whole, warpage, undulation, and the like of the piezoelectric ceramic substrate 6 are reliably reduced, and the piezoelectric ceramic substrate 6 having desired characteristics can be obtained.

  Furthermore, by forming minute substance escape irregularities 3 on the mounting surface of the zirconia setter 2, it is possible to improve the escape of gas generated on the back surface of the ceramic green 1 during the binder removal processing of the ceramic green 1. The ceramic green 1 is prevented from floating above the zirconia setter 2. Further, when the ceramic green 1 is fired, a difference in the heating speed between the ceramic green 1 and the zirconia setter 2 is reduced, so that the gas originally present in the firing furnace 5 is prevented from being caught in the back surface of the ceramic green 1. It is done. For this reason, it is prevented that the ceramic green 1 floats from the zirconia setter 2 by the entrainment effect | action of such gas.

  Therefore, it is avoided that the ceramic green 1 moves with respect to the zirconia setter 2 during the binder removal and firing of the ceramic green 1. Thereby, it is possible to prevent the ceramic green 1 from falling off the zirconia setter 2, the back surface of the ceramic green 1 being scratched, and the ceramic green 1 from being deformed.

  In addition, when the zirconia setter 2 having the material escape uneven portion 3 is manufactured, since the powder molded body is not mechanically processed after the powder molded body is fired as described above, the ceramic green 1 is fired. Occasionally, foreign matter such as processing waste does not adhere to the ceramic green 1 and the zirconia setter 2 is not cracked due to distortion of the zirconia setter 2.

  The present invention is not limited to the above embodiment. For example, although the said embodiment is about the manufacturing method of the piezoelectric ceramic substrate containing lead, it cannot be overemphasized that this invention is applicable also to other ceramic substrates. In this case, a setter made of alumina, magnesia or the like may be used.

  Moreover, although the said embodiment performs the binder removal and baking of the ceramic green which consists of a laminated body, this invention is applicable also to single layer ceramic green.

  Examples of the method for manufacturing a piezoelectric ceramic substrate according to the present invention will be described below.

[Example]
(1) As the setter, a dense zirconia setter stabilized by adding ₃ mol% to 8 mol% of yttria (Y ₂ O ₃ ) to zirconium oxide was used. The porosity of this zirconia setter is less than 3%. The size of the zirconia setter is □ 100 mm × 100 mm, and the thickness of the zirconia setter is 1.5 mm. On the surface of the zirconia setter, a material escape uneven portion is formed so that the center line average roughness Ra is preferably 2 to 6 μm.

(2) As the material of the ceramic green ceramic green composition using three-component piezoelectric ceramic _{PbTiO 3 -PbZrO 3 -Pb (Zn1 /} 3 Nb2 / 3) O 3. Piezoelectric ceramic powder made of this material is prepared by mixing raw materials in the form of oxides or carbonates with a ball mill, and after mixing and pre-baking at 900 ° C., then again by wet grinding with a ball mill. It has become.

  Ceramic green was made as follows. That is, a binder, an organic solvent, and the like are added to the prepared piezoelectric ceramic powder to form a paste, and a sheet is formed into a thickness of 50 μm by a doctor blade method. Thereafter, an internal electrode pattern was formed on the sheet by screen printing using an internal electrode paste composed of a metal of Ag / Pd = 7: 3. Thereafter, the laminated body is produced by stacking the sheets so that the number of internal electrodes becomes eight, and a press treatment is performed to form ceramic green. Then, the ceramic green was cut so that the size of the ceramic green was 15 mm × 35 mm square.

(3) Debinding The ceramic green was removed by placing 10 prepared ceramic greens on the surface of the zirconia setter (see FIGS. 1 and 2) and stabilizing at a temperature of 400 ° C. for 10 hours. .

(4) Firing After removing the binder, 10 sheets of zirconia setters on which ceramic green is placed are stacked, and further, zirconia setters on which ceramic green is not placed are stacked on top of each other to form a package of firing (FIGS. 4 and 5). reference). At this time, the gap between each zirconia setter was adjusted with a zirconia spacer. Furthermore, 10 zirconia setters loaded in this way were placed in a closed firing furnace, and each ceramic green was fired. At this time, firing was performed under the conditions of a firing temperature of 1050 ° C. and a stabilization time of 3 hours.

(5) Evaluation About 100 piezoelectric ceramic substrates obtained by firing, warpage was evaluated by a non-contact laser type three-dimensional shape measuring apparatus.

  As a result, the warp of the piezoelectric ceramic substrate was within 20 μm or less at the maximum. Further, with respect to the degree of warpage, it was not found that the piezoelectric ceramic substrate was locally warped.

  Further, when the residual carbon content of each of the 10 ceramic greens after the binder removal was analyzed using the combustion in an oxygen stream-infrared absorption method, it was relatively low at 50 to 150 ppm. Furthermore, no dent was observed on the back surface of the piezoelectric ceramic substrate. Moreover, the ceramic green did not fall off from the zirconia setter.

[Comparative example]
The setter used in the comparative example is a dense zirconia setter that has been polished after firing. That is, the material escape uneven portion as in the above-described embodiment is not formed on the mounting surface of the zirconia setter. Using such a zirconia setter, a piezoelectric ceramic substrate was produced in the same manner as described above.

  When the warpage of the 100 piezoelectric ceramic substrates thus obtained was evaluated in the same manner as described above, a warp of 100 μm at maximum occurred. Further, with respect to the occurrence of warpage, warping occurred locally at the four corners of the substrate.

  Further, when the residual carbon content of the ceramic green after the binder removal was analyzed in the same manner as described above, 1000 ppm of carbon remained. Furthermore, there was a ceramic green in which a dent that appears to be caused by polishing scraps of the zirconia setter occurred on the back surface of the substrate. There was also a ceramic green that had fallen off from the zirconia setter.

It is a top view which shows the state when performing binder removal of a ceramic green by one Embodiment of the manufacturing method of the ceramic substrate concerning this invention. It is a side view which shows a state when performing the binder removal of a ceramic green by one Embodiment of the manufacturing method of the ceramic substrate concerning this invention. It is an enlarged view of the surface of the zirconia setter shown in FIG.1 and FIG.2. It is a vertical direction sectional view showing a state when firing ceramic green according to an embodiment of a method for producing a ceramic substrate according to the present invention. It is a horizontal sectional view showing a part of a state when firing ceramic green according to an embodiment of a method for producing a ceramic substrate according to the present invention. It is a perspective view which shows the ceramic substrate finally obtained by one Embodiment of the manufacturing method of the ceramic substrate concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ceramic green, 2 ... Zirconia setter, 3 ... Material relief uneven part, 5 ... Firing furnace, 6 ... Piezoelectric ceramic substrate, 7 ... External electrode.

Claims (5)

A method for producing a ceramic substrate by firing ceramic green to produce a ceramic substrate,
Preparing a setter having a placement surface on which a material escape irregularity for allowing the material generated when the ceramic green is heated in a state where the ceramic green is placed to escape from the ceramic green;
Forming the ceramic green containing a binder;
Placing the ceramic green on the mounting surface of the setter and removing the ceramic green binder;
And a step of firing the ceramic green while the ceramic green is placed on the mounting surface of the setter after the binder removal of the ceramic green.   2. The ceramic substrate according to claim 1, wherein the setter is formed with the material relief irregularities so that the center line average roughness Ra of the mounting surface is 1 to 20 μm. Method.   3. The method of manufacturing a ceramic substrate according to claim 2, further comprising a step of forming an external electrode on the ceramic substrate without subjecting the ceramic substrate obtained by firing the ceramic green to mechanical processing. .   The method for manufacturing a ceramic substrate according to any one of claims 1 to 3, wherein the setter is made of a mold having projections and depressions for forming the projections and depressions for material escape. . The ceramic green is formed of a material containing lead,
The method for producing a ceramic substrate according to any one of claims 1 to 4, wherein the ceramic green is fired in a state where the setter on which the ceramic green is placed is placed in a closed furnace.

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