JP2008186897A - Method of manufacturing multilayer ceramic substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the warpage of a multilayer ceramic substrate that is a special problem to the non-shrinkage baking method. <P>SOLUTION: This method is used to manufacture a multilayer ceramic substrate 5 by the following steps: a shrinkage suppressing sheet 2 is stacked on the outermost layer of a laminated green sheet to make a laminate 4; the laminate 4 is baked; and the baked substance 2a of the shrinkage suppressing sheet 2 is removed to complete the multilayer ceramic substrate 5. In this case, the outer periphery 4a of one main surface of the laminate 4 is crushed when forming the laminate 4, and the main surface of the crushed side is faced down and baked. Preferably, after a temporary laminated body 3 including a plurality of green sheets and the shrinkage suppressing sheet 2 is formed, it is packed in vacuum while its one main surface is still in contact with a flat plate 11, and it is pressed at hydrostatic pressure to form the laminate 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a multilayer ceramic substrate in which firing is performed in a state in which a shrinkage suppression sheet is disposed on the outermost layer of laminated green sheets.

  In the field of electronic equipment and the like, ceramic substrates for mounting electronic devices are widely used. In recent years, as a ceramic substrate having high reliability in response to requests for downsizing and weight reduction of electronic equipment and multifunctional functions. Multilayer ceramic substrates have been proposed and put into practical use. The multilayer ceramic substrate is formed by laminating a plurality of ceramic layers, and the circuit board can be densified by integrally forming a wiring conductor, an electronic element, or the like in each ceramic layer.

  The multilayer ceramic substrate is formed by laminating a plurality of green sheets, removing the binder, and firing. The green sheet is surely contracted with the sintering in the firing step or the like, which is a major factor for reducing the dimensional accuracy of the multilayer ceramic substrate. Specifically, shrinkage variation occurs with the shrinkage, and the finally obtained multilayer ceramic substrate has a dimensional accuracy of about 0.5%. Another problem is that the conductor pattern formed on the outermost surface of the multilayer ceramic substrate is displaced due to the shrinkage of the green sheet.

Under such circumstances, a so-called non-shrinkage firing method that suppresses shrinkage in the in-plane direction of the green sheet and shrinks only in the thickness direction in the firing process of the multilayer ceramic substrate has been proposed (for example, Patent Document 1). Etc.). As described in Patent Document 1 and the like, when a sheet that does not shrink even at the firing temperature is attached to a laminate of green sheets and firing is performed in this state, shrinkage in the in-plane direction is suppressed, and the thickness direction Only shrinks. According to this method, it is possible to improve the dimensional accuracy in the in-plane direction of the multilayer ceramic substrate to, for example, about 0.05%. Further, it is possible to prevent displacement of the conductor pattern on the outermost surface of the multilayer ceramic substrate.
Japanese Patent No. 3471571

  By the way, the non-shrinkage firing method described above is performed as follows. First, the temporary laminated body 103 which has arrange | positioned the shrinkage | contraction suppression sheet | seat 102 on both surfaces of the several green sheet 101 is formed, and this is press-processed with the metal mold | die 121 with a flat press surface, as shown to Fig.6 (a). As a result, as shown in FIG. 6B, a laminate 104 in which the surfaces are orthogonal to each other is obtained. As shown in FIG. 6 (c), for example, the setters 111 and 112 are fired in a state of being sandwiched from above and below, and the fired product of the shrinkage suppression sheet 102a is removed as shown in FIG. 6 (d). A ceramic substrate 105 is obtained.

  However, when the multilayer ceramic substrate 105 obtained by the above-described method is observed in detail, it can be seen that a specific deformation called warping occurs as shown in FIG. That is, in the fired multilayer ceramic substrate 105, the surface on the side facing the setter 111, that is, the lower surface is substantially flat, but the other surface, that is, the upper surface has a concavely curved shape. As a result, the height of the outer peripheral edge portion is higher on the upper surface of the multilayer ceramic substrate 105 than the central portion, but the portion where the height from the central portion (warping amount) exceeds a predetermined range is an unnecessary region. Must be cut and removed. That is, if the amount of warpage is large, it is necessary to set a large unnecessary area in the outer peripheral edge accordingly, so that there is a disadvantage that the effective substrate area is reduced.

  The present invention has been proposed in view of such conventional circumstances, and provides a method for manufacturing a multilayer ceramic substrate capable of suppressing warpage of the multilayer ceramic substrate, which is a problem peculiar to the so-called non-shrinkage firing method. The purpose is to do.

  In order to solve the above-described problem, the method for producing a multilayer ceramic substrate according to the present invention includes forming a laminate by laminating a shrinkage suppression sheet on the outermost layer of the laminated green sheets, and firing the laminate. A method of manufacturing a multilayer ceramic substrate by removing the fired product of the shrinkage suppression sheet, wherein when forming the laminate, the outer peripheral edge of at least one main surface of the laminate is crushed and crushed The firing is performed with the main surface on the side facing downward.

  In the non-shrinkage firing method of the multilayer ceramic substrate, the side surface of the green sheet is shrunk so as to be drawn inward, so that the thickness at the outer peripheral edge is larger than that at the center. As a result, in the conventional firing method, the laminated body is supported by the outer peripheral edge portion having an increased thickness and the central portion is lifted, resulting in a large warp on the upper surface side. In the present invention, the outer peripheral edge of the laminate is previously crushed, and firing is performed with the crushed main surface facing downward, so that the outer peripheral edge is prevented from lifting the laminate during firing. Is done. For this reason, the warpage amount on one surface (upper surface) of the multilayer ceramic substrate, that is, the height difference between the center portion and the outer peripheral edge portion is reduced, and as a result, an unnecessary region in the outer peripheral edge portion can be narrowed.

  According to the present invention, it is possible to suppress the occurrence of warpage, which is a problem peculiar to the so-called non-shrinkage firing method. Therefore, according to the present invention, it is possible to reduce the removal width at the outer peripheral edge of the multilayer ceramic substrate while ensuring the dimensional accuracy of the substrate and the positional accuracy of the conductor pattern, and it is possible to expand the effective substrate area. .

  Hereinafter, a method for producing a multilayer ceramic substrate to which the present invention is applied will be described in detail with reference to the drawings.

  In order to produce a multilayer ceramic substrate, first, as shown in FIG. 1A, a green sheet 1 that becomes each ceramic layer after firing is prepared. The green sheet 1 is formed by mixing a ceramic powder and an organic vehicle to form a slurry-like dielectric paste, which is formed on a support such as a polyethylene terephthalate (PET) sheet by a doctor blade method or the like. To do. When producing a glass ceramic substrate that can be fired at a low temperature as a multilayer ceramic substrate, ceramic powder and glass powder are used in combination in the dielectric paste. Any known ceramic powder, glass powder, and organic vehicle can be used.

  Conductive patterns (wiring patterns, electrode pads, via holes, etc.) are formed on the green sheet 1 in accordance with a desired circuit. Furthermore, electronic elements (inductors, capacitors, etc.) may be built in as necessary.

  The conductive pattern is formed, for example, by printing a conductive paste in a predetermined pattern, and the conductive paste used is a conductive material made of various conductive metals and alloys such as Ag, Ag-Pd alloy, Cu, and Ni. And an organic vehicle. The organic vehicle has a binder and a solvent as main components, and the mixing ratio of the conductive material is arbitrary, but usually the binder is 1 to 15% by mass, and the solvent is 10 to 50% by mass. It is blended with the conductive material. Additives selected from various dispersants, plasticizers, and the like may be added to the conductive paste as necessary.

  Moreover, the shrinkage | contraction suppression sheet | seat 2 for suppressing the shrinkage | contraction of the in-plane direction of a multilayer ceramic substrate is prepared. The shrinkage suppression sheet 2 is a material that does not shrink at the firing temperature of the green sheet 1, such as tridymite or cristobalite, and also quartz, fused quartz, alumina, mullite, zirconia, aluminum nitride, boron nitride, magnesium oxide, silicon carbide, calcium carbonate. The composition containing the above is formed into a slurry and formed by forming a film on a support such as a PET sheet by a doctor blade method or the like.

  Next, as shown in FIG. 1B, in the temporary stacking step, a plurality of green sheets 1 are stacked, and a shrinkage suppression sheet 2 is stacked on the outermost layer of the stacked green sheets 1 to form a temporary stack 3. Form.

  Next, the temporary laminate 3 is subjected to pressure treatment in the main lamination step to produce a laminate 4 having a predetermined shape. In the present embodiment, the stacking process includes a bagging process (FIG. 2A), a vacuum packing process (FIG. 2B), and a hydrostatic press process (FIG. 2C).

  In the bag filling step, as shown in FIG. 2A, the temporary laminate 3 is placed on the flat plate 11 so that one main surface of the temporary laminate 3 is in contact with the flat plate 11, and these are formed in the bag 12. Put in. The bag 12 is formed of a flexible film.

  In the vacuum packing process, as shown in FIG. 2B, the inside of the bag 12 is evacuated and sealed.

  In the hydrostatic pressure pressing step, as shown in FIG. 2C, the vacuum-packed temporary laminate 3 is subjected to pressure treatment by a hydrostatic pressure pressing device 13. It is preferable that the isostatic press 13 is a warm isostatic press (WIP) apparatus that uses a liquid at 70 ° C. to 80 ° C. as a pressure medium. By using a warm isostatic pressing apparatus, the adhesion between the sheets in the laminate 4 can be improved as compared to a cold isostatic pressing apparatus.

  Next, in the laminated body taking-out step, the laminated body 4 after the main laminating step is taken out from the bag 12 (FIG. 2D). When the laminated body 4 taken out is observed in detail, the outer peripheral edge 4a of the main surface on the side not in contact with the flat plate 11 is crushed and formed into a curved surface by an isostatic pressing process.

  Next, the laminate 4 is fired in the firing step (FIG. 2E). In the firing step, the laminate 4 is fired in a state of being placed on the setter 21 so that the crushed main surface on the outer peripheral edge 4a side faces downward. In FIG. 2 (e), the setter 22 is also disposed on the laminate 4 for firing. In the firing, the firing temperature is arbitrary. For example, when a conductive pattern using Ag as a conductive material is formed on the green sheet 1, the firing is performed at a temperature lower than the melting point of Ag (about 960 ° C.). preferable. A preferable firing temperature in this case is 850 ° C to 950 ° C.

  After firing, as shown in FIG. 2 (f), the multilayer ceramic substrate 5 is obtained by removing the fired product 2 a of the shrinkage suppression sheet 2. Due to the action of the shrinkage suppression sheets 2 disposed on both sides of the laminated green sheet 1, the green sheet 1 is restrained from shrinking in the in-plane direction and shrinks only in the thickness direction. A multilayer ceramic substrate 5 having excellent pattern positional accuracy is obtained.

  Here, when a laminated body is formed using a mold having a flat press surface as in the prior art and fired, it is presumed that the multilayer ceramic substrate is warped as follows. That is, as shown in FIG. 3A, a laminate 103 in which a plurality of green sheets 101 are laminated and a shrinkage suppression sheet 102 is arranged in the outermost layer is prepared, and firing is performed with setters 111 and 112 arranged above and below. And as shown in FIG.3 (b), both surfaces of the laminated body 103 curve in a concave shape, and the thickness in the outer periphery part of the laminated body 103 becomes larger than a center part. The reason why the thickness at the outer peripheral edge is increased is that the side surface of the green sheet 101 on which the shrinkage suppression sheet 102 is not disposed is shrunk so as to be drawn inside the laminate 103. For this reason, the center part of the laminated body 103 is supported by the outer peripheral edge part in contact with the lower setter 111 and is temporarily lifted to form a gap with the setter 111. It sinks due to its own weight over time. As a result, as shown in FIG. 3C, deformation occurs such that the upper surface side has a concave shape. Here, the upper surface of the multilayer ceramic substrate 104 reflects not only the original deformation on the upper surface but also the temporary deformation on the surface facing the setter 111. Therefore, it is estimated that the final warpage amount of the multilayer ceramic substrate 104, that is, the height difference between the central portion and the outer peripheral edge portion inevitably increases.

  On the other hand, in the present invention, as shown in FIG. 2 (d), the outer peripheral edge 4a of at least one main surface of the laminate 4 is crushed, and the outer peripheral edge is crushed as shown in FIG. 2 (e). Firing is performed with the main surface having 4a facing down. At this time, since the side surface of the green sheet 1 is contracted so as to be drawn inward, the thickness at the outer peripheral edge increases, but as shown in FIG. 4, the outer peripheral edge 4a on the crushed side is directed downward. Therefore, the laminated body 4 is not lifted by the outer peripheral edge 4a. For this reason, since no gap is generated under the laminate 3, the amount of warpage on one surface (upper surface) of the multilayer ceramic substrate is made smaller than in the conventional case, as compared with the case of firing the conventional laminate. Can do.

  In the above description, the method of crushing the outer peripheral edge 4a of the laminate 4 is exemplified by the method of vacuum-packing the temporary laminate 3 brought into contact with the flat plate 11 and then pressing it hydrostatically. As long as the outer peripheral edge of at least one of the main surfaces can be crushed, not only the above-described method but also various methods can be used.

  For example, as shown in FIG. 5A, the outer peripheral edge 4 a on one main surface side of the laminate 4 may be crushed by pressing using a mold 14. A convex portion 15 is provided on the press surface of the upper die of the mold 14 along the outer peripheral edge portion, and the outer peripheral edge portion on one main surface side of the laminate 4 is crushed as shown in FIG. A flat inclined surface is formed. As described above, even when at least one outer peripheral edge portion of the laminate is crushed by the press treatment by the mold 14, the firing is performed (FIG. 5C), and the fired product 2a of the shrinkage suppression sheet 2 is removed ( As shown in FIG. 5D, the multilayer ceramic substrate 5 having a small amount of warpage can be obtained as in the case of using the hydrostatic press.

  Further, in the above description, only the outer peripheral edge portion on one main surface side of the laminate is crushed, but the effect of the present invention can also be obtained when the outer peripheral edge portions on both main surface sides are crushed. it can.

Hereinafter, specific examples to which the present invention is applied will be described based on experimental results.
(Production of green sheets)
Alumina-glass-based dielectric material is prepared as a ceramic material, mixed with an organic binder, a plasticizer, and an organic solvent to prepare a dielectric paste, and then formed into a sheet by a doctor blade method, 56 mm in length, 65 mm in width, thickness A 125 μm green sheet was prepared.

(Preparation of shrinkage suppression sheet)
Tridymite and quartz were prepared as shrinkage suppression materials, mixed with an organic binder, a plasticizer, a dispersant and an organic solvent to prepare a shrinkage suppression material paste, and then formed into a sheet by a doctor blade method, 56 mm in length, 65 mm in width, thickness A shrinkage suppression sheet having a thickness of 125 μm was produced.

(Example)
Fifteen produced green sheets were laminated, and a shrinkage suppression sheet was arranged on each of both surfaces to form a temporary laminate. Next, the temporary laminate was placed on a flat plate, placed in a bag made of a flexible film, and vacuum packed. Next, pressure treatment was performed at a temperature of 70 ° C. using a warm isostatic press. After the pressure treatment, the laminate was taken out of the bag and observed in detail. As a result, the outer peripheral edge on the surface opposite to the flat plate was crushed to form a curved surface. Next, the obtained laminate was sandwiched from above and below by a setter and fired at 900 ° C. At this time, the laminated body was disposed so that the main surface on the side where the outer peripheral edge portion was crushed faced downward. After firing, the fired product of the shrinkage suppression sheet was removed to obtain a multilayer ceramic substrate.

(Comparative example)
The temporary laminated body was formed similarly to the said Example, and the laminated body was obtained by pressing a temporary laminated body using a metal mold | die with a flat press surface after that. The obtained laminate was fired under the same conditions as in the above example to obtain a multilayer ceramic substrate.

(Evaluation)
The amount of warpage of the multilayer ceramic substrates of the example and the comparative example was examined, and based on this, the width of the cutting margin (unnecessary region) provided along the outer peripheral edge was set. Specifically, first, the obtained multilayer ceramic substrate is placed on a flat table while maintaining the vertical direction at the time of firing, and the surface of the multilayer ceramic substrate is scanned along a diagonal line with a probe to adjust the height. Examined. Then, the center part of the substrate was set as a reference (0 μm), and the height compared to this, that is, the outside from the position where the warpage amount exceeded 20 μm was set as a cutting margin. As a result, in the example, it was necessary to set the width of the cutting allowance of the multilayer ceramic substrate to 7 mm. That is, in the example, the effective area formed inside the cutting allowance was 42 mm long and 51 mm wide. On the other hand, in the multilayer ceramic substrate of the comparative example, it was necessary to set the width of the cutting margin to 9 mm. That is, the effective area of the substrate of the comparative example was 38 mm long and 47 mm wide. From the above examination results, it was shown that the warpage at the outer peripheral edge of the substrate was improved by the method of the present invention, and the effective area of the substrate could be expanded.

It is sectional drawing which shows the outline | summary of the manufacturing method of a multilayer ceramic substrate, (a) shows a sheet | seat preparation process, (b) shows a temporary lamination process. It is a figure explaining an example of this lamination | stacking process and baking process of this invention, (a) is a bagging process, (b) is a vacuum packing process, (c) is an isostatic pressing process, (d) is a taking-out process, (E) shows a firing step, and (f) shows a shrinkage suppression sheet removing step. It is sectional drawing explaining the deformation | transformation mechanism of the laminated body in the conventional baking process, (a) is before baking, (b) is during baking, (c) shows after baking. It is a principal part expanded sectional view for demonstrating the deformation | transformation mechanism of the laminated body in the baking process of this invention. It is a figure explaining the other example of this lamination process of this invention, and a baking process, (a) is this lamination process by a die-press apparatus, (b) is a laminated body, (c) is a baking process, (d) Indicates a shrinkage suppression sheet removing step. It is sectional drawing which shows the manufacturing method of the conventional multilayer ceramic substrate, (a) is this lamination | stacking process by a die press apparatus, (b) is a laminated body, (c) is a baking process, (d) is a shrinkage | contraction suppression sheet removal. A process is shown. It is sectional drawing which shows the multilayer ceramic substrate manufactured by the conventional manufacturing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Green sheet, 2 Shrinkage suppression sheet, 3 Temporary laminated body, 4 Laminated body, 11 Multi-layer ceramic substrate, 11 Flat plate, 12 bag, 13 Hydrostatic press, 14 Mold, 15 Convex part, 21, 22 Setter

Claims (4)

A method for producing a multilayer ceramic substrate by laminating a shrinkage suppression sheet on the outermost layer of a laminated green sheet to form a laminate, firing the laminate, and then removing the fired product of the shrinkage suppression sheet. ,
A multilayer ceramic substrate characterized by crushing an outer peripheral edge portion of at least one main surface of a laminated body when forming the laminated body, and performing the firing with a principal surface on a crushed side facing downward. Production method.   After forming a temporary laminate including a plurality of the green sheets and the shrinkage suppression sheet, vacuum packing is performed in a state where one main surface of the temporary laminate is in contact with a flat plate, and the hydrostatic press is performed. 2. A method for producing a multilayer ceramic substrate according to claim 1, wherein a laminate is formed.   The method for producing a multilayer ceramic substrate according to claim 2, wherein the hydrostatic press is a warm isostatic press. After forming a temporary laminate including a plurality of the green sheets and the shrinkage suppression sheet, press processing is performed using a mold having a convex portion along the outer peripheral edge portion of the press surface to form the laminate. The method for producing a multilayer ceramic substrate according to claim 1.

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