JP2007059862A - Multilayer ceramic substrate and its manufacture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a multilayer ceramic substrate having superior dimensional accuracy and flatness of a bottom surface of a cavity when the multilayer ceramic substrate having the cavity is manufactured. <P>SOLUTION: A plurality of green sheets for substrate comprising a bottom-surface-forming green sheet 32 for constituting the bottom surface of the cavity and a cavity-forming green sheet for forming an opening corresponding to the cavity shape are laminated to form laminate 33. Under the condition where contraction-suppressing material green sheets 22 and 29 are laminated on the surface of the green sheet for substrate acting as an outermost layer of the laminate 33, respectively, the laminate 33 is pressed, and then calcined, and thereby the multilayer ceramic substrate 1 having the cavity 11 is formed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multilayer ceramic substrate having a cavity and a manufacturing method thereof, and more particularly to an improvement of the multilayer ceramic substrate having a cavity manufactured by applying a non-shrinkage firing method and the manufacturing method thereof.

  In the field of electronic equipment and the like, substrates for mounting electronic devices are widely used. However, in recent years, as a substrate having high reliability in response to demands for reduction in size and weight of electronic devices and multifunctional functions. A multilayer ceramic substrate has been proposed and put into practical use. A multilayer ceramic substrate is formed by laminating a plurality of ceramic layers, and by making a wiring conductor, an electronic element and the like integrally in each ceramic layer, it is possible to increase the density of the circuit substrate.

  And in the said multilayer ceramic substrate, the multilayer ceramic substrate in which the cavity (recessed part) which accommodates an electronic device was formed was put in practical use for the purpose of advancing the further miniaturization of an electronic device, a low profile, etc. In the case of such a multilayer ceramic substrate with a cavity, the electronic device can be mounted in a state where it is accommodated in the cavity, so that the above-mentioned demand can be satisfied more sufficiently and the multilayer ceramic substrate itself can be reduced in size. It is also possible to realize a low profile.

  By the way, the above-mentioned multilayer ceramic substrate is formed by laminating a plurality of green sheets to form a laminate and then firing the laminate. The green sheet is surely shrunk with the sintering in the firing step, 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 only about 0.5%.

  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, the dimensional accuracy in the in-plane direction of the multilayer ceramic substrate can be improved to about 0.05%.

  However, in the case of producing a multilayer ceramic substrate having the cavity, there is a problem in that sufficient dimensional accuracy, flatness, etc. are not necessarily obtained even if the non-shrinkage firing method as described above is applied. This is due to the fact that the restraint force for suppressing shrinkage does not act on the bottom of the cavity in the normal shrinkless firing method. If the restraining force for suppressing shrinkage does not act on the bottom of the cavity, sufficient flatness for mounting the electronic device on the bottom of the cavity cannot be ensured, which may hinder the mounting of the electronic device.

Therefore, an attempt has been made to eliminate the above-described disadvantage by disposing a shrinkage suppression sheet on the bottom surface of the cavity (see, for example, Patent Document 2). In the invention described in Patent Document 2, a shrinkage suppression sheet containing a shrinkage suppression inorganic material is formed on a carrier film, a cut having a shape corresponding to the contour of the bottom surface of the cavity is made in the shrinkage suppression sheet, and the outside of the cut In the step of laminating a ceramic green sheet for a substrate to produce a raw substrate laminate, the shrinkage suppression held on the carrier film on the substrate ceramic green sheet that gives the bottom of the cavity is removed. The baking process is carried out in a state where the sheet for transfer is transferred and the sheet for suppressing shrinkage is disposed on the bottom surface of the cavity. Accordingly, it is possible to increase the dimensional accuracy of the laminated body for a substrate after firing, to make it difficult to cause undesired distortion in the cavity, and to achieve high density of wiring with high reliability.
JP-A-10-75060 JP 2003-318309 A

  However, as in the invention described in Patent Document 2, it is difficult to completely eliminate problems such as deformation of the cavity, for example, by simply disposing the shrinkage suppression sheet on the ceramic green sheet for the substrate that gives the bottom surface of the cavity. . In particular, in the method for manufacturing a multilayer ceramic substrate, it is necessary to press a laminated body in which a plurality of green sheets are stacked. In the method for manufacturing a multilayer ceramic substrate having the cavity, the cavity opening is crushed and deformed in the pressing step. Probability is high. Also, in the firing process, a phenomenon in which the periphery of the cavity opening is raised, which may cause deformation.

  Further, as another method for producing a multilayer ceramic substrate having a cavity, it is conceivable that green sheets are laminated and fired, and then a hole is formed in the sintered laminate. However, since the sintered laminate is hard and fragile, there are many problems in terms of manufacturing cost, such as high-precision processing is difficult and expensive equipment is required.

  The present invention has been proposed in view of such conventional circumstances, and provides a multilayer ceramic substrate that realizes excellent dimensional accuracy and flatness at low cost and has a small deformation at the periphery of the cavity. Objective. Further, according to the present invention, when manufacturing a multilayer ceramic substrate having a cavity, a multilayer ceramic substrate having excellent dimensional accuracy and flatness can be manufactured easily and at low cost, and deformation such as deformation in the periphery of the cavity can be achieved. It aims at providing the manufacturing method which can also eliminate generation | occurrence | production.

  In order to achieve the above object, a multilayer ceramic substrate of the present invention is manufactured by laminating a plurality of green sheets for a substrate and then firing, and has a cavity and forms a bottom surface of the cavity. A multilayer ceramic substrate in which ceramic layers including layers are laminated and integrated, wherein a conductor pattern is formed on the bottom surface forming ceramic layer so as to straddle a peripheral edge of the bottom surface of the cavity, and the bottom surface forming ceramic A softening layer that is softened at a firing temperature at the time of firing is provided at least on the surface of the conductor pattern in a portion corresponding to a peripheral edge portion of the bottom surface on the layer.

  Also, the method for manufacturing a multilayer ceramic substrate of the present invention comprises laminating a plurality of substrate green sheets including a bottom forming green sheet constituting the bottom of the cavity and a cavity forming green sheet forming an opening corresponding to the cavity shape. A multilayer ceramic substrate having a cavity by pressing the laminate in a state in which the shrinkage-suppressing material green sheets are laminated on the surface of the substrate green sheet that is the outermost layer of the laminate, and firing the laminate. A conductive pattern is formed on the bottom surface forming green sheet so as to straddle the peripheral portion of the bottom surface of the cavity, and the peripheral portion on the bottom surface forming green sheet is formed on the bottom surface forming green sheet. Among the corresponding portions, at least the surface of the conductor pattern is softened at the firing temperature during the firing. After forming the softening layer, the bottom forming green sheet is formed so that the bottom surface of the cavity and the shrinkage suppressing material green sheet piece overlap the cavity forming green sheet in which the shrinkage suppressing material green sheet piece is embedded in the through hole. The cavity forming green sheets are laminated so that the embedding green sheets separated from the respective cavity forming green sheets are disposed on the shrinkage-suppressing material green sheet pieces so as to fill the cavities. In this state, the pressing and firing are performed, and the fired product of the embedding green sheet is removed after firing.

  As described above, the non-shrinkage firing method is performed in a state where the shrinkage-suppressing material green sheet pieces are arranged on the substrate green sheet exposed at the bottom of the cavity, so that dimensional accuracy is ensured and the cavity bottom surface Flatness is also sufficiently secured. At the same time, since the laminate is pressed with the embedded green sheet in the cavity, it can be easily pressed by a flat plate mold or the like as in the laminate without the cavity. In addition, deformation does not occur due to the collapse of the cavity opening or the rise around the cavity opening.

  By the way, in a multilayer ceramic substrate, a conductor pattern is generally formed on the bottom of the cavity or inside the multilayer ceramic substrate, but with a shrinkage-suppressing material green sheet piece arranged at the bottom of the cavity, a non-shrinkage firing method is used. If an attempt is made to manufacture a multilayer ceramic substrate in which the conductor pattern is formed so as to straddle the peripheral edge of the bottom surface of the cavity, there may be a problem that the conductor pattern is disconnected at the contact portion with the cavity side wall. This disconnection is caused by the restraining force of the shrinkage suppression material green sheet piece and the shrinkage suppression material green sheet on the lower end portion of the cavity side wall (the inner peripheral edge of the cavity formation green sheet in contact with the bottom surface formation green sheet) compared to the other portions. Because it is weak, for example, the cavity forming green sheet that forms the lower end of the cavity side wall shrinks greatly in the direction away from the center of the cavity, and the stress at that time is concentrated on the conductor pattern in contact with the lower end of the cavity side wall and the bottom forming ceramic layer Due to

  Therefore, in the present invention, a softening layer that softens at the firing temperature during firing is formed on at least the surface of the conductor pattern on the bottom surface forming ceramic layer and corresponding to the peripheral edge of the cavity bottom surface. Since the softening layer is interposed between the conductor pattern and the lower end of the side wall of the cavity, when the green sheet for forming the cavity constituting the lower end of the side wall of the cavity shrinks in the direction away from the center of the cavity during firing, The lower end of the side wall of the cavity moves so as to slide on the softened softened layer surface. Therefore, the stress concentration on the conductor pattern caused by the cavity forming green sheet contracting in the in-plane direction is alleviated by the softening layer, and disconnection of the conductor pattern on the bottom surface of the cavity is suppressed.

  Then, by removing the residue of the shrinkage suppression material green sheet, the shrinkage suppression material green sheet piece and the embedding green sheet from the fired laminate, at least the surface of the conductor pattern in the portion corresponding to the peripheral edge of the cavity. A multilayer ceramic substrate having a softening layer and having no break in the conductor pattern on the bottom surface of the cavity is obtained.

  In the present invention, the bottom surface of the cavity corresponds to all regions constituting the so-called bottom portion in the depth direction of the cavity.For example, when the cavity has a multi-stage shape, not only the bottom surface of the deepest portion but also A step surface that is shallower and has a step with respect to the bottom surface also corresponds to the bottom surface. In addition, the embedding green sheet needs to be separated from the cavity side wall forming green sheet. In this case, for example, the separation means that the notch penetrates in the thickness direction of the cavity side wall forming green sheet. In addition to the above-mentioned ones, notches that do not penetrate through the cavity side wall forming green sheet in the thickness direction are included.

  According to the present invention, in the production of a multilayer ceramic substrate having a cavity, it is possible to produce a multilayer ceramic substrate excellent in dimensional accuracy and flatness, and further, the cavity opening is crushed, the bulge around the cavity opening, etc. It is possible to produce a multilayer ceramic substrate without any deformation. In addition, according to the present invention, since drilling after sintering is unnecessary, no special equipment for drilling is required, and the multilayer ceramic substrate can be manufactured easily and at low cost. is there. Furthermore, according to the present invention, it is possible to provide a multilayer ceramic substrate in which the conductor pattern exposed on the bottom surface of the cavity is not broken.

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

(First embodiment)
The multilayer ceramic substrate of the present embodiment is a multilayer ceramic substrate having a cavity (concave portion) for accommodating an electronic device or the like.

  FIGS. 1A to 1D show the simplest model example of a multilayer ceramic substrate 1 having a cavity 11. In this example, a plurality (9 layers in this case) of ceramic layers 2 to 10 are provided. Stacked and integrated. Among these ceramic layers 2 to 10, the lower two layers 2 and 3 are flat ceramic layers in which a through hole for forming a cavity is not formed, and the ceramic layer 3 serving as an upper layer among them is a bottom surface. It corresponds to the forming ceramic layer, and a part of the upper surface thereof faces the bottom of the cavity 11 to constitute the bottom surface 11a of the cavity.

  On the other hand, the remaining ceramic layers 4 to 10 stacked on the ceramic layer 3 have through holes 4a to 10a corresponding to the side walls of the cavity 11, respectively, and correspond to the cavity forming ceramic layer. The cavity 11 is configured as a predetermined space by the bottom surface 11a formed by the ceramic layer 3 and the side wall formed by connecting the through holes 4a to 10a of the ceramic layers 4 to 10.

  The opening shape of the cavity 11 is, for example, a square, but is not limited thereto, and may be an arbitrary shape such as a rectangle or an oval. However, when the opening shape of the cavity 11 is a square or a rectangle, it is preferable that the corner is rounded to have an arc shape. As a result, the stress generated at the corner can be relaxed, and inconveniences such as a crack occurring at the corner can be solved. When the non-shrinkage firing method using the shrinkage suppression sheet is employed, the side walls of the cavity 11 are drawn outward, and stress may concentrate on the corners of the opening shape of the cavity 11 to cause cracks. is there. By rounding the corners to form an arc shape, the stress concentration can be relaxed and the occurrence of cracks can be prevented. In this case, the radius of curvature R in the arc is preferably 0.05 mm or more. The curvature radius R is more preferably set according to the thickness of the shrinkage suppression sheet. For example, when the shrinkage suppression sheet has a thickness of 75 μm, the curvature radius R is set to 0.1 mm or more to cause cracks. Never occurred. When the thickness of the shrinkage suppression sheet was 250 μm, no crack was generated by setting the radius of curvature R to 0.51 mm or more.

  A conductor pattern 12 is formed on the surface of the ceramic layer 3 so as to straddle the periphery of the bottom surface 11 a of the cavity 11. One end of the conductor pattern 12 is exposed on the bottom surface 11 a of the cavity 11 and is connected to an electronic device accommodated in the cavity 11. The other end of the conductor pattern 12 is disposed between the ceramic layer 3 and the ceramic layer 4, and is connected to an internal electrode, wiring, or the like formed inside the multilayer ceramic substrate 11. FIG. 1 shows a state in which a total of four strip-like conductor patterns 12 are provided on two sides facing each other in a rectangular cavity 11 when viewed from the plane. Can be set arbitrarily. Although illustration is omitted, the bottom surface 11a of the cavity 11 may be provided with a heat radiating via hole or the like.

  In the multilayer ceramic substrate 1 of the present embodiment, the softening layer 13 is disposed on at least the surface of the conductor pattern 12 in the portion corresponding to the peripheral edge portion of the bottom surface of the cavity 11. The softening layer 13 shown in FIG. 1 is formed in a band shape that borders two sides of the peripheral surface of the bottom surface 11a of the cavity 11 where the conductor pattern 12 is provided.

  The softening layer 13 is made of a material that is softened at a firing temperature when the green sheets are laminated and then pressed and fired to obtain the multilayer ceramic substrate 1. During firing, the softened layer 13 is interposed between the cavity forming green sheet to be the cavity forming ceramic layers 4 to 10, the bottom surface forming green sheet, and the conductor pattern 12, thereby forming the cavity forming green sheet. The stress applied to the ceramic layer 3 and the conductor pattern 12 due to the contraction is relaxed, and disconnection of the conductor pattern 12 can be suppressed.

  The material constituting the softening layer 13 is required to soften at the firing temperature during firing for obtaining the multilayer ceramic substrate 1 and preferably does not react with the ceramic layer or the like. As such a material, for example, glass can be used, and it is particularly preferable to use the same type of glass as the glass contained in the ceramic layers 2 to 10. Specifically, borosilicate glass, barium borosilicate glass, strontium borosilicate glass, zinc borosilicate glass, potassium borosilicate glass, or the like can be used.

  It is desirable that the width of the outer side of the cavity 11 of the softening layer 13 is ensured to such an extent that disconnection of the conductor pattern 12 can be suppressed. Specifically, the distance A1 between the peripheral edge of the bottom surface 11a of the cavity 11 and the outer peripheral edge of the softening layer 13 is preferably 0.1 mm to 0.5 mm.

  The width of the inner side of the cavity 11 of the softening layer 13 will be described in detail later, but it is preferable that the width is as small as possible from the viewpoint of ensuring the flatness of the bottom surface 11a of the cavity 11 of the ceramic layer 3. Specifically, the distance A2 between the peripheral edge portion of the bottom surface 11a of the cavity 11 and the inner peripheral edge portion of the softening layer 13 can be set to 0.5 mm or less (excluding 0), for example. In order to reliably prevent the conductor pattern 12 from being disconnected, the distance A2 is preferably 0.05 mm to 0.5 mm, and more preferably 0.1 mm to 0.5 mm.

  Furthermore, if the film thickness of the softening layer 13 is too small, the effect of suppressing the disconnection of the conductor pattern 12 may be insufficient. Conversely, if the film thickness is too large, there may be a problem when the green sheets for substrates are laminated. Considering these, it is preferable that the film thickness of the softening layer 13 be 0.005 mm to 0.02 mm.

  By the way, in a multilayer ceramic substrate manufactured by each manufacturing method as described later, the cavity has a unique shape, and has superiority in resin sealing compared to the cavity shape of the conventional multilayer ceramic substrate. is doing. Hereinafter, the cavity shape of the multilayer ceramic substrate of this embodiment will be described.

  When producing the multilayer ceramic substrate 1, the details will be described later, but the first fitting sheet corresponding to the shrinkage-suppressing material green sheet piece, the uppermost composite green sheet, and further, the shrinkage-suppressing green sheet is used to form the substrate green sheet. Firing is performed while restraining to suppress shrinkage in the in-plane direction. In this case, since both sides of the laminate were constrained by the shrinkage-suppressing green sheets at the time of firing, each substrate green sheet should shrink only in the thickness direction and not in the surface direction after firing. It is.

  However, when observing in detail, the green sheet for a substrate near the shrinkage-suppressing green sheet (the first fitting sheet, the uppermost composite green sheet, and the shrinkage-preventing green sheet) is hardly shrunk in the surface direction, but shrinks. As it moves away from the restraining green sheet, it shrinks slightly in the surface direction. The shrinkage in the surface direction gradually increases as the distance from the shrinkage suppression green sheet increases. For this reason, when the shape of the cavity 11 is observed in detail, as shown schematically in FIG. 2, the inside of the opening is larger than the opening immediately adjacent to the shrinkage-suppressing green sheet.

  This point will be described in more detail. In the cavity 11, the opening dimension W <b> 1 in the opening 11 b is smaller than the opening dimension W <b> 2 in the midway position in the depth direction of the cavity 11. That is, the opening area at the opening 11 b of the cavity 11 is smaller than the opening area at the midway position 11 c in the depth direction of the cavity 11. In the case of this example, the opening area of the cavity 11 gradually increases until reaching the midway position 11c in the depth direction, and then gradually decreases, and the cross-sectional shape of the inner wall of the cavity 11 is substantially arcuate. Therefore, the shape of the cavity 11 is a shape in which a midway part in the depth direction bulges in an arc shape, and has the drum shape.

  The multilayer ceramic substrate 1 in which the cavity 11 has the shape as described above has a great advantage in terms of reliability because of the specific cavity shape. For example, as shown in FIG. 3, when the electronic device 40 is mounted in the cavity 11 and sealed with the resin 100, the opening 11 b of the cavity 11 is smaller than the inside as described above. The resin 100 does not fall off. In the conventional shape, when resin sealing is performed with the resin 100, the ceramic layers 2 to 10 constituting the multilayer ceramic substrate 1 and the sealing resin 100 have different coefficients of thermal expansion. There is a problem that the stopped resin 100 peels off and falls off the cavity 11. In particular, the above problem becomes remarkable due to repeated temperature changes over a long period of time. In the multilayer ceramic substrate 1, since the opening area in the opening 11b of the cavity 11 is smaller than the opening area in the midway position 11c in the depth direction of the cavity 11, the resin 100 filled in the cavity 11 and cured is Since the internal volume is large, it cannot pass through the opening 11 b of the cavity 11 and is held in the cavity 11.

  The multilayer ceramic substrate 1 having the cavity 11 having the specific shape as described above has never been realized so far, and the green sheet for the substrate is formed by the first fitting sheet, the uppermost composite green sheet, and further the shrinkage suppressing green sheet. In addition to firing while restraining, when forming the laminate before firing, leave the part separated by cutting into the part that forms the cavity, and fill it as a green sheet for embedding, press It can be formed by applying a uniform pressure when performing. The details are unknown, but it is experimentally confirmed that the cavity shape cannot be obtained simply by restraining with a shrinkage-suppressing green sheet, and can only be realized by applying the manufacturing method of the present invention. Yes.

  The multilayer ceramic substrate 1 having the above-described configuration is formed by performing the following manufacturing process. Hereinafter, the manufacturing process of the multilayer ceramic substrate of this embodiment will be described.

  The multilayer ceramic substrate 1 having the cavities 11 as described above is produced by laminating a plurality of green sheets, pressing them into a laminated body, and firing the laminate, but in order to ensure dimensional accuracy, firing is performed. It is necessary to suppress the contraction of time. In addition, it is not enough, and for example, it is necessary to eliminate deformation due to crushing of the opening of the cavity 11 during the pressing process and swelling around the opening of the cavity 11.

  Therefore, in the present embodiment, the non-shrinkage firing method is adopted, and the pressing step and the firing step are performed in a state where the green sheet for embedding is arranged in the space corresponding to the cavity so as to eliminate the crushing at the time of pressing. To do.

  The process flow of the manufacturing process of this embodiment is shown in FIG. As shown in FIG. 4, the manufacturing process of the present embodiment basically includes at least a laminated body forming step (Step S1), a firing step (Step S2), and a cavity forming step (Step S3). In addition to these, you may have a shrinkage | contraction suppression sheet | seat removal process (step S4). The laminate forming process (step S1) includes a green sheet forming process (step S11), a composite green sheet forming process (step S12), a notch forming process (step S13), a via hole forming process (step S14), and a conductor printing process (step S14). Step S15), a softening layer formation process (Step S16), a lamination process (Step S17), and a press process (Step S18) are included.

  Hereinafter, each process will be described. To produce the multilayer ceramic substrate described above, first, a green sheet forming process (step S11), which is the first process in the laminated body forming process (step S1), is performed. In this green sheet forming step (step S11), a ceramic green sheet (corresponding to a substrate green sheet) 21 shown in FIG. 5A and a shrinkage suppression material green sheet 22 shown in FIG. 5B are formed. To do. These ceramic green sheet 21 and shrinkage suppression material green sheet 22 are usually formed in close contact with the surface of a support 23 such as a plastic sheet. The plastic sheet used as the support 23 may be any sheet as long as the surface is smooth. For example, a PET (polyethylene terephthalate) sheet is preferable. The thickness of the support 23 is preferably a thickness that does not deform during the process and is easy to handle, and is generally 50 to 150 μm.

  As a method for producing the ceramic green sheet 21, for example, a ceramic powder and an organic vehicle are mixed to prepare a slurry (dielectric paste), which is prepared by a sheet forming method such as a doctor blade method, and the support 23 (PET sheet or the like). And a method of forming a film on the resin sheet). When the multilayer ceramic substrate to be manufactured is a glass ceramic substrate, a glass powder is used in addition to the ceramic powder, and a slurry obtained by mixing these with an organic vehicle may be used.

  The organic vehicle is obtained by dissolving a binder in an organic solvent, and is mainly a solvent such as terpineol, butyl carbitol, acetone, toluene, isopropyl alcohol, a binder such as ethyl cellulose or polyvinyl butyral, or di-n-butyl phthalate. It is comprised with plasticizers. The content of the organic vehicle is not particularly limited, and may be a normal content, for example, 1 to 5% by mass for the binder and 10 to 50% by mass for the solvent.

  The dielectric paste may be an organic paint containing an organic vehicle as described above, or may be a water-soluble paint in which a water-soluble binder, a dispersant, and the like are dissolved in water. Here, the water-based binder is not particularly limited, and may be appropriately selected from polyvinyl alcohol, cellulose, water-soluble acrylic resin, emulsion and the like.

  As described above, the dielectric paste includes ceramic powder, but the composition of the dielectric ceramic composition constituting the ceramic powder is arbitrary. Therefore, in producing the ceramic powder, raw materials (main component and subcomponent) may be selected according to the composition of the dielectric ceramic composition. In this case, the material forms of the main component and subcomponents that are raw materials are not particularly limited. Further, as the main component and subcomponent which are raw materials, an oxide or a compound which becomes an oxide by firing is used. In addition, as a compound which becomes an oxide by baking, carbonate, nitrate, oxalate, an organometallic compound, etc. are illustrated, for example. Of course, as a raw material, an oxide and a compound that becomes an oxide by firing may be used in combination. What is necessary is just to determine content of each component in a raw material so that it may become a composition of the said dielectric ceramic composition after baking. Moreover, the manufacturing method of the said ceramic powder is also arbitrary, For example, the powder obtained from any of the liquid phase synthesis method or the solid-phase method may be sufficient.

  When producing a glass ceramic substrate which is an LTCC substrate, as described above, ceramic powder (ceramic component) and glass powder (glass component) are used in combination. At this time, these glass component and ceramic component have a desired dielectric constant. What is necessary is just to select suitably based on a rate and baking temperature. Specifically, a combination of alumina (ceramic component: crystal phase) and silicon oxide (glass component: glass phase) that can be fired at 1000 ° C. or less to form a glass ceramic substrate can be exemplified. In addition, as the ceramic component, magnesia, spinel, silica, mullite, forsterite, steatite, cordierite, strontium feldspar, quartz, zinc silicate, zirconia, titania and the like can be used. As the glass component, borosilicate glass, borosilicate barium glass, strontium borosilicate glass, zinc borosilicate glass, potassium borosilicate glass, and the like can be used. The glass component is preferably 60 to 80% by volume, and the ceramic component as an aggregate is preferably 40 to 20% by volume. If the glass component is out of the above range, it is difficult to form a composite composition, and strength and sinterability are reduced.

  On the other hand, the method for producing the shrinkage suppression material green sheet 22 is basically the same as the method for producing the ceramic green sheet 21, but the components contained in the green sheet are different. That is, the shrinkage-suppressing material green sheet 22 is made of a shrinkage-suppressing material that does not easily shrink at the temperature at which the ceramic green sheet 21 is sintered, and is a green sheet in which its own shrinkage is suppressed. As the shrinkage-suppressing material, a composition containing at least one of quartz, cristobalite, or tridymite can be used. Or it is good also as a composition containing an alumina.

These shrinkage-suppressing materials do not sinter at the firing temperature of the ceramic component or glass component contained in the ceramic green sheet 21, or only partially sinter, and therefore shrinkage does not occur at the firing temperature of the ceramic green sheet 21. Therefore, if the shrinkage-suppressing material green sheet 22 composed of the shrinkage-suppressing material is laminated in close contact with the ceramic green sheet 21, it works to suppress shrinkage in the planar direction when the ceramic green sheet 21 is fired.

  In forming the shrinkage-suppressing material green sheet 22, a sintering aid may be included in addition to the shrinkage-suppressing material (a composition containing at least one of quartz, cristobalite, or tridymite). Similar effects can be obtained. When a sintering aid is included, the sintering aid is sintered at the firing temperature of the ceramic component or glass component, but the thermal expansion coefficient of each of the shrinkage-suppressing materials quartz, cristobalite, or tridymite is about 20ppm / ° C, about 50ppm / ° C, and about 40ppm / ° C, which are larger than ceramic components and glass components, so even if the sintering aid shrinks after firing, the dimensional changes before and after firing are offset. The shrinkage of the ceramic green sheet 21 can be suppressed.

  When a sintering aid is used in combination, examples of the sintering aid to be used include oxides that soften at a temperature lower than the sintering start temperature of the ceramic component or glass component or generate a liquid phase. When the former is used, the particles of the shrinkage-suppressing material are bonded together by softening the sintering aid, and when the latter is used, the shrinkage aid generates the liquid phase by the sintering aid Since the particle surface of the shrinkage inhibiting material reacts and the particles are bonded to each other, sintering is performed. The oxide used as a sintering aid is not particularly limited, but lead silicate aluminum glass, lead silicate alkali glass, lead silicate alkaline earth glass, lead borosilicate glass, borosilicate alkali glass, boric acid. Aluminum lead glass, lead borate alkali glass, lead borate alkaline earth glass, lead zinc borate glass, and the like can be used, and one or more of these may be selected and used.

It is also possible to use an alkali metal compound as a sintering aid. The alkali metal compound has an effect of promoting the progress of sintering of SiO ₂ . Therefore, if an alkali metal compound is added to a composition containing at least one of quartz, cristobalite, and tridymite, the shrinkage suppressing material green sheet 22 is slightly sintered as the ceramic green sheet 21 is fired. Here, although an alkali metal compound is not specifically limited, For example, lithium carbonate, potassium carbonate, sodium carbonate, lithium oxide, potassium oxide etc. can be mentioned.

  Furthermore, as a material used for the shrinkage suppression material green sheet 22, a composition containing tridymite and a hardly sinterable oxide can be used. Tridymite is a material that can change the sintering temperature in various ways by selecting the composition. However, tridymite has a large coefficient of thermal expansion, and the coefficient of thermal expansion reaches 40 ppm / ° C. depending on the temperature. For this reason, for example, there is a difference in thermal expansion from the glass ceramic material (about 3 to 10 ppm / ° C.), and the ceramic green sheet 21 may be peeled off before being sintered. In order to prevent this, an oxide that is not sintered at the firing temperature of the ceramic green sheet 21 is added to adjust the thermal expansion coefficient, thereby preventing the ceramic green sheet 21 from peeling off before sintering. The oxide that is not sintered in the firing process of the ceramic green sheet 21 is not particularly limited, and examples thereof include quartz, fused quartz, alumina, mullite, and zirconia.

  The ceramic green sheet 21 and the shrinkage suppression material green sheet 22 are produced as described above. The thickness per layer of the ceramic green sheet 21 and the shrinkage suppression material green sheet 22 is determined by the formation of via electrodes and internal electrodes described later. In consideration of the above, it is preferable that the thickness is about 20 μm to 300 μm.

  After the production of the ceramic green sheet 21 and the shrinkage suppression material green sheet 22, in the composite green sheet formation step (step S12), the composite green sheet (the ceramic green sheet and the shrinkage suppression material green sheet are combined with each other) Green sheet). The composite green sheet produced here is a first composite green sheet that is laminated immediately above the bottom surface forming green sheet and an uppermost composite green sheet that is laminated as the uppermost shrinkage suppression material green sheet.

  In order to produce the first composite green sheet 26, first, as shown in FIG. 6A, first through holes 24 are provided in the ceramic green sheet 21 produced in the green sheet forming step (step S11). The first through hole 24 may be formed, for example, by punching a predetermined portion of the ceramic green sheet 21 with a puncher die while the ceramic green sheet 21 is kept in close contact with the surface of the support 23. You may form by light, a micro drill, punching, etc. The 1st through-hole 24 is formed corresponding to a cavity shape, The shape is not specifically limited, For example, a square may be sufficient and a rectangle, circular, etc. may be sufficient.

  Next, the shrinkage-suppressing material greensheet 22 produced in the greensheet forming step (step S11) is cut on the support 23 into substantially the same shape as the first through hole 24, and the first fitting sheet 25 (shrinkage-suppressing sheet 25). It corresponds to a green sheet piece. This is fitted into the first through hole 24 of the ceramic green sheet 21 to form a first composite green sheet 26. At this time, in order to make the first composite green sheet 26 flat, it is preferable that the ceramic green sheet 21 and the first fitting sheet 25 have the same thickness.

  The manufacturing method of the uppermost composite green sheet 29 is the same as the manufacturing method of the first composite green sheet 26. In the uppermost composite green sheet 29, as shown in FIG. A through hole is provided in the sheet 22, and a ceramic green sheet piece is fitted therein. That is, the second through hole 27 corresponding to the opening of the cavity is provided in the shrinkage suppression material green sheet 22 produced in the green sheet forming step (step S11). The method of forming the second through hole 27 is the same as that of the first through hole 24 described above. Then, the ceramic green sheet 21 produced in the green sheet forming step (step S <b> 11) is cut into substantially the same shape as the second through hole 27 on the support body 23 to obtain a second fitting sheet 28. The second fitting sheet 28 is fitted into the second through hole 27 of the shrinkage suppression material green sheet 22 and peeled from the support 23 to form the uppermost composite green sheet 29. Also in this case, in order to make the uppermost composite green sheet 29 flat, it is preferable that the thicknesses of the shrinkage suppression material green sheet 22 and the second fitting sheet 28 are the same.

  In the notch forming step (step S13), notches are formed in the ceramic green sheet 21 to form a cavity forming green sheet. That is, in the notch forming step (step S13), the ceramic green sheet 21 produced in the green sheet forming step (step S11) is provided with the notches (or discontinuous portions) 31 to form the notch forming sheet 30 as shown in FIG. . The cut 31 is a discontinuous portion penetrating in the thickness direction of the ceramic green sheet 21. Note that the discontinuous portion includes those not penetrating in the thickness direction of the sheet. The notch 31 is formed in the same position and substantially the same shape as the first through hole 24 so as to overlap with the first through hole 24 when the notch forming sheet 30 is overlapped with the first composite green sheet 26 previously produced. The The notch 31 may be formed by pressing a puncher mold against a predetermined portion of the ceramic green sheet 1 while the ceramic green sheet 21 is kept in close contact with the surface of the support 23. Alternatively, it may be formed by punching or the like.

  In the cut forming step (step S13), cuts may be provided for each of the ceramic green sheets 21, or cuts may be provided collectively after two or more ceramic green sheets 21 are stacked. In any case, in the cut forming sheet 30, the portion 30a separated by the cut 31 is left as it is, and is used as a green sheet for embedding at the time of lamination and firing.

  Each of the multilayer ceramic substrates after firing, such as the first composite green sheet 26 and the cut forming sheet 30 (cavity forming green sheet) produced as described above, and the ceramic green sheet (bottom forming green sheet) constituting the bottom of the cavity, etc. Via holes, via electrodes, internal electrode patterns, and the like are formed on a ceramic green sheet (hereinafter, collectively referred to as “dielectric layer sheet”) constituting the ceramic layer. The via electrode is formed by filling and solidifying a via electrode paste by, for example, hole filling printing. The internal electrode pattern is formed, for example, by applying an internal electrode paste to a ceramic green sheet in a predetermined pattern by screen printing.

  Specifically, in the via hole forming step (step S14), a via hole that is a hole for forming a via electrode is formed in the dielectric layer sheet. The via hole is formed by laser light, micro drilling, punching or the like. When the dielectric layer sheet is irradiated with laser light, holes can be formed by sublimating the ceramic powder or binder resin of the dielectric layer sheet. The laser used is preferably a short wavelength UV-YAG laser or excimer laser. When the via hole is formed using the laser beam in this way, the diameter of the via hole can be easily reduced to 100 μm or less. Micro drilling and punching have the advantage that they can be processed at low cost, although it is difficult to reduce the diameter of the via hole compared to laser light. In any case, a minute via electrode can be formed with high accuracy by filling the via hole formed by these methods with a conductor paste.

  In the conductor printing process (step S15), the via hole formed in the via hole forming process (step S14) is filled with a conductive paste to form a via electrode. As the conductive paste, for example, a via electrode paste containing metal powder or alloy powder such as copper, silver, silver palladium, palladium, nickel or the like and adjusted to have a predetermined fluidity is used.

  In the conductor printing step (step S15), the internal electrode pattern is printed in a predetermined pattern on the surface of the dielectric layer sheet. In the conductor printing step (step S15), an internal electrode pattern (conductor pattern) is formed on the surface of the substrate green sheet. For example, as shown in FIG. 8, the conductor pattern 12 is formed on the surface of the ceramic green sheet 21 so as to straddle the peripheral portion (indicated by a dotted line in the drawing) of the region that becomes the bottom surface 11 a of the cavity 11.

  For the formation of the conductor pattern 12 and the internal electrode pattern, similarly to the conductive paste described above, for example, a metal powder or alloy powder such as copper, silver, silver palladium, palladium, nickel or the like is used, and the viscosity has a predetermined fluidity. The internal electrode paste adjusted to be used. The internal electrode paste and the via electrode paste may be made of different materials.

  In addition, since the constituent material of the dielectric layer sheet has resistance to reduction and an inexpensive base metal can be used as the conductive material, nickel or a nickel alloy may be used as the conductive material. As the nickel alloy, an alloy of nickel and one or more elements selected from manganese, chromium, cobalt and aluminum is preferable, and the content of nickel in the alloy is preferably 95% by mass or more. The via electrode and the internal electrode pattern may contain various trace components such as phosphorus (P) in an amount of about 0.1% by mass or less. Although the thickness of an internal electrode pattern is suitably determined according to a use, it is preferable that it is about 1 micrometer-15 micrometers, for example, and it is more preferable if it is about 2.5 micrometers-10 micrometers.

  The via electrode paste or the internal electrode paste is produced by kneading with the same vehicle as the dielectric paste. The vehicle content in the via electrode paste or the internal electrode paste is adjusted in the same manner as in the dielectric paste. Moreover, you may add additives, such as a dispersing agent, a plasticizer, a dielectric material, an insulator material, to a via electrode paste or an internal electrode paste as needed. The total amount added is preferably 10% by mass or less.

  In the softening layer forming step (step S16), the softening layer 13 is formed on a part of the substrate green sheet on which the conductor pattern 12 is formed in the conductor printing step (step S15), and the bottom surface forming green as shown in FIG. A sheet 32 is obtained. The softening layer 13 may be formed in at least a portion that overlaps the conductor pattern 12 in a portion corresponding to the peripheral portion of the region that becomes the bottom surface 11 a of the cavity 11 in the fired multilayer ceramic substrate 1. In FIG. 8, the softening layer 13 is formed so as to border two sides provided with the conductor pattern 12 in a peripheral portion (indicated by a dotted line in the drawing) of a region that becomes the bottom surface of the cavity 11 after firing. .

  As the material constituting the softening layer 13, any material that softens at the firing temperature when performing the firing step (step S2) described later can be used. It is also important that the material constituting the softening layer 13 is a material that does not adversely affect the conductor pattern 12, the substrate green sheet, and the like. Such a material is preferably glass, and most preferably the same glass as that used for the green sheet for the substrate is used as the softening layer 13.

  After forming the via electrode and the internal electrode pattern on each dielectric layer sheet as described above, and further forming the softening layer 13, the sheets prepared in the laminating step (step S17) are laminated to form the laminated body 33. The structure of the laminated body from this lamination process (step S17) to a shrinkage | contraction suppression sheet removal process (step S4) is shown to Fig.9 (a) from FIG.9 (d). It should be noted that the process shown in FIG. 9C and the process shown in FIG. 9D may be reversed in order or may be performed simultaneously.

  In the laminating step (step S17), as shown in FIG. 9A, the shrinkage-suppressing green sheet 22, the ceramic green sheet 21, the bottom forming green sheet 32, the first composite green sheet 26, and the cut forming sheet from the bottom layer. 30 and the uppermost composite green sheet 29 are laminated in this order.

  Each sheet may be at least one sheet or a plurality of sheets. In the case of this example, one ceramic green sheet 21 and one bottom forming green sheet 32 are laminated, and the first composite green sheet 26 and six cut forming sheets 30 are further laminated thereon. . Accordingly, these nine layers correspond to the green sheet for the substrate, and the first composite green sheet 26 and the six cut forming sheets 30 correspond to the green sheets for forming the cavity side walls. The structure of the laminated body 33 may be reversed upside down, and each sheet may be similarly laminated up and down with the shrinkage suppression green sheet 22 interposed therebetween.

  For example, when two or more cut forming sheets 30 are stacked as described above, the material of each cut forming sheet 30 may be the same, or the material of each cut forming sheet 30 may be a different material. However, in the latter case, it is preferable that the compression ratio at the time of pressing, the shrinkage rate at the time of firing, the thermal expansion coefficient, and the like be approximately equal in each cut-formed sheet 30. Thereby, the curvature of the board | substrate which arises from the difference of the compression rate, shrinkage | contraction rate, and thermal expansion coefficient of each notch formation sheet 30 can be suppressed.

The total thickness of the laminated body 33 laminated in this manner is preferably 1 mm or less in view of the demand for downsizing and low profile of the multilayer ceramic substrate. In addition, the stacked body 33 corresponds to the stacking height (the depth of the cavity) of the cavity side wall forming green sheets (six cut forming sheets 30 and the first composite green sheet 26) that are the portions constituting the cavity. ) Is set according to the dimensions of the electronic device accommodated in the cavity.

  After the laminating step (step S17), a pressing step (step S18) is performed. This pressing step (step S18) is a step of pressure-bonding the laminate 33 produced in the laminating step (step S17). Crimping is performed by placing the normal upper and lower punches in a flat mold. The pressure bonding conditions are preferably a pressure of 30 to 80 MPa and a pressure bonding time of about 10 minutes. In the present embodiment, the uppermost layer surface and the lowermost layer surface of the laminate 33 are flat surfaces, and the portion 30a separated by the notch 31 is left as it is in the portion where the cavity is formed, and this is used as an embedding green sheet. Since the shape is filled, the pressure can be uniformly applied when pressing. Therefore, unlike the prior art, the opening of the cavity is not crushed and deformed or damaged by the applied pressure.

  Next, a baking process (step S2) is performed. In the firing step (step S2), the laminate 33 that has been pressure-bonded in the pressing step (step S18) is fired. During firing, the produced laminate 33 is usually subjected to binder removal processing, and the binder removal treatment conditions in this case may be normal. After the binder removal treatment, firing is performed to form the laminated fired body 34. The atmosphere during firing is not particularly limited. In general, when a base metal such as nickel or a nickel alloy is used for the via electrode and the internal electrode pattern, a reducing atmosphere is preferable. The firing temperature is preferably 800 ° C to 1000 ° C. Conductive materials and resistive materials can be fired simultaneously, and such a multilayer ceramic substrate can be used for LTCC modules such as high-frequency superposition modules, antenna switch modules, and filter modules.

  In the laminated fired body 34 subjected to the firing step (step S2), as shown in FIG. 9B, a portion 30a inside the cut 31 of the cut forming sheet 30 protrudes from the cavity. This is due to the following reason. When the laminated body 33 is fired, the ceramic green sheet 21, the bottom surface forming green sheet 32, the first composite green sheet 26, and the cut forming sheet 30 that are dielectric layer sheets sinter and tend to shrink. At this time, the ceramic green sheet 21 is in close contact with the underlying shrinkage-suppressing green sheet 22. As described above, the shrinkage-suppressing green sheet 22 does not shrink at the firing temperature of the dielectric layer sheet. For this reason, the shrinkage | contraction of the planar direction of the ceramic green sheet 21 is suppressed. Moreover, since the outer portion 30b of the cut 31 of the cut forming sheet 30 is in close contact with the uppermost uppermost composite green sheet 29, the shrinkage is similarly suppressed. Furthermore, since the bottom surface forming green sheet 32 is in close contact with the first fitting sheet 25 of the first composite green sheet 26 at the bottom of the cavity, the shrinkage is similarly suppressed.

  On the other hand, since the inner portion 30a of the cut 31 of the cut forming sheet 30 has no sheet for suppressing shrinkage on the upper layer side, the shrinkage is not suppressed. Therefore, the inner portion 30 a of the cut 13 contracts in the planar direction and is separated from the outer portion 30 b of the cut 31. This contraction increases as the distance from the first fitting sheet 25 at the bottom of the cavity increases in the upper layer direction, and the contraction rate in the thickness direction decreases by the amount the inner portion 30a of the cut 31 contracts in the planar direction. Accordingly, the first fitting sheet 25, the second fitting sheet 28, and the portion sandwiched between them (the inner portion 30a of the cut 31) protrude from the surface of the laminated fired body 34 after firing. .

  Incidentally, for example, when the softening layer is not provided as shown in FIG. 10, there is a problem that the conductor pattern 201 arranged in a state straddling the peripheral portion of the bottom surface of the cavity is disconnected. In the bottom forming green sheet 202, the region where the first fitting sheet 203 is disposed (in the cavity bottom surface) hardly shrinks in the in-plane direction due to the strong binding force of the first fitting sheet 203, whereas the cavity The regions around the side walls (the cut forming sheet 204, the first composite green sheet 205, and the bottom forming green sheet 202) are restrained by the shrinkage suppression material green sheet 206 and the uppermost composite green sheet 207 toward the center in the stacking direction. Since the force tends to be weakened, the side wall lower end portion 208 of the cavity having a weak binding force is greatly contracted in the in-plane direction away from the cavity. As a result, stress concentrates on the peripheral edge portion of the bottom surface of the cavity, causing disconnection of the conductor pattern 201 located in this portion.

  On the other hand, in this embodiment, the green sheet for forming a cavity (the first composite sheet 26 is formed by the softened layer 13 softened at the firing temperature at the time of performing the firing step (step S2) constituting the lower end of the side wall of the cavity 11a. It is interposed between the ceramic green sheet 21) and the conductive pattern 12. For this reason, when the green sheet for cavity formation contracts in the direction away from the center of the cavity, it moves so as to slide on the surface of the softened softened layer 13, so that the stress applied to the conductor pattern 12 is relieved. Therefore, disconnection of the conductor pattern 12 can be suppressed.

  Note that the softening layer 13 is not formed on the two sides of the peripheral portion of the cavity bottom surface where the conductor pattern 12 does not exist. Therefore, the region shrinks greatly in the in-plane direction, but the conductor pattern 12 exposed on the cavity bottom surface. Will not be adversely affected.

  As described above, the first fitting sheet 25 and the second fitting sheet 28 and the portion sandwiched between them (the inner portion 30a of the cut 31) are the cut 31 of the ceramic green sheet 21 and the cut forming sheet 30. For example, the inner portion 30a of the cut 31 of the cut forming sheet 30 is completely separated from the outer portion 30b. Also, at the bottom, the first fitting sheet 25 is embrittled by firing, and the binding force at this portion is also weakened. Therefore, as shown in FIG. 9 (c), the first fitting sheet 25 and the second fitting sheet 28 filling the cavity, the portion sandwiched between them (the inner portion 30a of the cut 31), Can be removed with a small stimulus. Even when the shape of the cavity is complicated, the inner portion 30a of the cut 31 can be easily dropped. Moreover, in order to drop off the inner part 30a of the cut 31, a small force may be applied.

  That is, as shown in FIG. 9C, the first fitting sheet 25, the second fitting sheet 28, and the portion sandwiched between them (the inner portion 30a of the cut 31) are removed to form a cavity. While forming, a shrinkage | contraction suppression sheet | seat removal process (step S4) is performed as needed. In the shrinkage suppression sheet removing step (step S4), as shown in FIG. 9D, the uppermost sheet 35 and the lowermost sheet 36 of the laminated fired body 34 (shrinkage suppression material green sheet 22 and uppermost composite green sheet). 29 fired product) is removed. As a method for removing these, the laminated fired body 34 may be subjected to normal ultrasonic cleaning in a solvent, or the laminated fired body 34 may be subjected to wet blasting. Wet blasting is a method in which cleaning and surface treatment are performed simultaneously by accelerating a liquid obtained by mixing an abrasive with water with compressed air from a compressor and spraying it on a workpiece. In addition, when the shrinkage-suppressing material green sheet 22 is formed of a material such as tridymite-silica or cristobalite-silica, the main portions of the uppermost sheet 35 and the lowermost sheet 36 are naturally peeled off after firing. The remaining part should be washed.

  In addition to the above steps, a cutting step, a polishing step, etc. are performed as necessary to obtain the multilayer ceramic substrate 1 shown in FIG. In the cutting process, it may be divided by diamond scribe, and when the laminated fired body 34 is thick, it may be cut by a dicing method. The polishing process is performed by lapping, for example. Lapping is a processing method in which abrasive grains are not included in the rotating surface plate, and abrasive grains are included in the processing liquid to grind the object to be processed. Alternatively, a wet barrel method may be used.

  The electronic device 40 is mounted on the multilayer ceramic substrate 1 to be manufactured. FIG. 11 shows a state in which the electronic device 40 is mounted. As shown in FIG. 11, the electronic device 40 is accommodated in the cavity 11 of the multilayer ceramic substrate 1. The back surface of the electronic device 40 is connected to the conductor pattern 12 exposed on the surface of the cavity 11. Further, the electronic device 40 is connected to electrodes (not shown) formed on the multilayer ceramic substrate 1 by bonding wires 41. The electrodes are a surface electrode printed on the surface of the multilayer ceramic substrate 1, a via electrode, and an internal electrode printed inside the multilayer ceramic substrate 1. Thus, the multilayer ceramic substrate manufactured by the manufacturing method of this embodiment can accommodate an electronic device inside a multilayer ceramic substrate, and can satisfy the request | requirement of size reduction and low profile.

(Second Embodiment)
The second embodiment is an example in which the softening layer is formed so as to border the entire peripheral edge of the bottom surface of the cavity.

  In the first embodiment, on the side where the conductor pattern 12 does not exist at the peripheral edge of the bottom surface 11 a of the cavity 11, there is no fear of disconnection of the conductor pattern 12, and therefore no softening layer is present. For this reason, as a result of the bottom surface 11a of the cavity 11 corresponding to this portion receiving the binding force of the first fitting sheet 25, a large stress is generated at the boundary between the bottom surface 11a of the cavity 11 and the outside thereof. For example, when an internal electrode pattern is provided between the ceramic layers below the side walls of the cavity 11, the internal electrode pattern may be disconnected.

  Therefore, in this embodiment, the shape of the softening layer 13 is, for example, a frame shape that borders the entire peripheral edge of the bottom surface of the cavity 11. As shown in FIG. 12, in the multilayer ceramic substrate 45 of the present embodiment, the entire periphery of the bottom surface of the cavity 11, that is, along the lower end portion of the side wall of the cavity 11 even in the portion where the conductor pattern 12 of the cavity 11 is not formed. Thus, the softening layer 13 is disposed. The softening layer 13 is disposed between the ceramic layer 3 and the ceramic layer 4.

  In order to obtain the multilayer ceramic substrate 45 as shown in FIG. 12, in the softened layer forming step (step S16), the softened layer 13 is formed so as to border the entire periphery of the region that becomes the bottom surface of the cavity 11 after firing. The bottom surface forming green sheet 32 may be formed.

  In the multilayer ceramic substrate 45 as described above, the softening layer 13 is also disposed in a portion of the peripheral portion of the bottom surface 11 of the cavity 11 where the conductor pattern 12 is not formed. Therefore, the stress applied to the bottom surface forming green sheet by the softening layer 13 is alleviated even in the peripheral edge portion of the bottom surface 11 of the cavity 11 where the conductor pattern 12 is not formed, and as a result, the stress is disposed below the side wall of the cavity. Further, disconnection of the internal electrode pattern can be suppressed.

  FIG. 13 is a diagram illustrating an example in which the conductor pattern 12 is provided on the entire periphery of the cavity 11 having a quadrangular opening. Also in this case, the softening layer 13 is formed so as to border the entire peripheral edge of the bottom surface 11 a of the cavity 11. Further, in the multilayer ceramic substrate, for example, as shown in FIG. 14, the conductor pattern 12 may be formed on the entire bottom surface of the cavity. In either case, disconnection of the conductor pattern 12 and the internal electrode pattern exposed on the bottom surface of the cavity can be reliably suppressed.

(Third embodiment)
Hereinafter, a third embodiment will be described. The difference between this embodiment and the previous first embodiment is that the cavity is a multi-stage cavity (in this example, a two-stage two-stage bottom cavity).

  Hereinafter, a multilayer ceramic substrate having a two-step bottom cavity will be described with reference to FIG. A multilayer ceramic substrate 50 shown in FIG. 15 has a two-step bottom cavity 51, and a plurality (14 layers in this case) of ceramic layers are laminated and integrated. The ceramic layer 3 corresponds to a bottom surface forming ceramic layer, and a part of the upper surface thereof faces the bottom of the cavity, and forms the deepest bottom surface 51 a of the two-step bottom cavity 51. Of the ceramic layers constituting the multilayer ceramic substrate 50, the construction of the ceramic layers 2 to 9 is substantially the same as that of the first embodiment. A part of the ceramic layer 10 constitutes the second-stage bottom surface 51 b of the two-stage bottom cavity 51. Therefore, the ceramic layer 10 corresponds to a bottom surface forming ceramic layer. A conductor pattern 52 is provided on the surface of the ceramic layer 10.

  The ceramic layers 53 to 57 laminated on the ceramic layer 10 have through holes 53a to 57a, respectively, and correspond to cavity forming ceramic layers. By connecting the through holes 53 a to 57 a of the ceramic layers 53 to 57, side walls that define the shallower space of the two-stage bottom cavity 51 are configured.

  In the multilayer ceramic substrate 50 of the present embodiment, when the conductor pattern 52 is formed so as to straddle the peripheral portion of the bottom surface 51b on the second-stage bottom surface 51b, the second softened layer is formed on at least the surface of the conductor pattern 52 in the peripheral portion. 58 is arranged.

  When producing the multilayer ceramic substrate of the present embodiment, as will be described later, the first composite green sheet is disposed corresponding to the deepest bottom surface of the cavity, and the second bottom surface (step surface) of the cavity is provided. Correspondingly, a second composite green sheet is arranged, and further, cut-formed sheets having different sizes according to the dimensions of the cavities at each stage are laminated.

  FIG. 16 is a diagram showing in detail the cavity shape of the multilayer ceramic substrate shown in FIG. Here, in the side walls of the respective cavity parts 51c and 51d, the shrinkage in the surface direction gradually increases as the distance from the shrinkage suppression green sheet increases, and the opening dimension in each opening part is larger than the opening dimension in the midway position in the depth direction. It is getting smaller. That is, for the cavity 51c, W3 <W4, where W3 is the opening dimension of the opening and W4 is the opening dimension at the midway position in the depth direction. Similarly, for the cavity 51d, W5 <W6, where W5 is the opening dimension of the opening and W6 is the opening dimension at the midway position in the depth direction. Moreover, the cross-sectional shape of the side wall of each cavity part 51c, 51d is circular arc shape, Therefore, the shape of each cavity part 51c, 51d exhibits a so-called bowl shape.

  Note that the second and subsequent cavities (here, the cavity 51d) are not necessarily limited to the saddle shape, but have the largest opening area as shown in FIG. 17, and the opening area gradually decreases in the depth direction. It may be a shape. In this case, W5> W6 when the opening dimension of the opening is W5 and the opening dimension of the halfway position in the depth direction is W6, whereas the first-stage cavity 51c is bowl-shaped, The second-stage cavity portion 51d has a so-called bowl shape. By making the shape of the second and subsequent cavities into the hook shape, wire bonding or the like when mounting an electronic device in the cavity 51d is facilitated, and efficient device mounting becomes possible.

  In the multilayer ceramic substrate 50 of the present embodiment, as described above, in the multistage cavity 51, at least the cavity 51c has a drum-shaped shape with a larger opening area inside than the opening. It is possible to ensure the reliability of resin sealing in the cavities 51c and 51d.

  Hereinafter, a method for manufacturing the multilayer ceramic substrate 50 having the above-described configuration will be described. The difference between this embodiment and the previous first embodiment is that the cavity is a multi-stage cavity (in this example, a two-stage two-stage bottom cavity). Therefore, in order to make a two-step bottom cavity, the first composite green sheet is arranged corresponding to the deepest bottom surface of the cavity, and the second composite green is corresponded to the second bottom surface (step surface) of the cavity. Disposing the sheet and laminating cut-formed sheets with different through-hole sizes are the differences in the process.

  In the present embodiment, the second composite green sheet 43 shown in FIG. 18A is formed in the composite green sheet forming step (step S12). In the production of the second composite green sheet 43, first, a third penetration that overlaps the first through hole 24 and is larger than the first through hole 24 on the ceramic green sheet 21 produced in the green sheet forming step (step S11). A hole 44 is provided. The method for forming the third through hole 44 is the same as the method for forming the first through hole 24 described above.

  Then, the shrinkage-suppressing material green sheet 22 produced in the green sheet forming step (step S <b> 11) is cut into substantially the same shape as the third through-hole 44 to form a third fitting sheet 45 and fitted into the third through-hole 44. . Further, the fitted third fitting sheet 45 is provided with a fourth through hole 46 having the same position and the same shape as the first through hole 24, and the ceramic green sheet 21 is substantially the same as the fourth through hole 46. The second fitting sheet 28 cut into the same shape is fitted. In this way, the second composite green sheet 43 is formed. In producing the second composite green sheet 43, the second fitting sheet 28 is first fitted into the fourth through hole 46, and the third fitting sheet 45 is later fitted into the third through hole 44, contrary to the above procedure. It is good also as fitting.

  In the present embodiment, in the notch forming step (step S13), as shown in FIG. 18B, the notch forming sheet (second notch forming sheet 47) different from the notch forming sheet 30 in the first embodiment. Form. The difference between the second cut forming sheet 47 and the previous cut forming sheet 30 is that the size of the cut 48 is larger than the size of the cut 31. Specifically, in the second cut forming sheet 47, the cut 48 has substantially the same shape at the same position as the third through hole 44 of the second composite green sheet 43.

  Further, in the conductor printing step (step S15), as shown in FIG. 19, a conductor pattern 52 is formed on the surface of the uppermost cut forming sheet 30 so as to straddle the peripheral edge of the cavity bottom surface 51b, thereby forming the second bottom surface. A green sheet 53 is produced. Similarly to the first embodiment, the conductor pattern 12 is formed on the surface of the green sheet 21, and the bottom surface forming green sheet 32 is produced.

  Further, in the softening layer forming step (step S16), as shown in FIG. 19, at least the conductor pattern in the peripheral portion (indicated by the dotted line in the figure) of the region that becomes the second bottom surface 51b of the cavity 11 after firing. The second softened layer 58 is formed so as to border the two sides provided with 52.

  An example of a laminate 54 in which the sheets are laminated in the present embodiment is shown in FIG. Each layer constituting the stacked body 54 is stacked as follows in order from the bottom. That is, the shrinkage-suppressing green sheet 22, the ceramic green sheet 21, the bottom surface forming green sheet 32, the first composite green sheet 26, the cut forming sheet 30, the second bottom surface forming green sheet 53, and the second composite green sheet 43 from the bottom layer. The second cut forming sheet 47 and the uppermost composite green sheet 29 are laminated in this order. It should be noted that the number of stacked sheets is the shrinkage-suppressing green sheet 22, the bottom surface forming green sheet 32, the first composite green sheet 26, the second bottom surface forming green sheet 53, the second composite green sheet 43, and the top layer composite green. One sheet 29 is provided. Of course, a plurality of these may be used in a stacked manner. The ceramic green sheet 21, the cut forming sheet 30, and the second cut forming sheet 47 are usually used in two or more depending on the electrode pattern configuration between the layers required for the multilayer ceramic substrate and the dimensions of the electronic device mounted inside. To do. In the case of this example, one ceramic green sheet 21, five cut forming sheets 30, and four second cut forming sheets 47 are stacked. Of course, it is not restrained by this, The number of lamination | stacking of each sheet | seat is arbitrary. Moreover, the laminated body 54 may have a separate cavity on the shrinkage suppression green sheet 22 side, for example, in addition to the cavity shown in FIG.

  When the laminated body 54 is fired, a laminated fired body 55 is obtained as shown in FIG. In the laminated fired body 55, the portion 56a that has filled the cavity contracts in the planar direction and protrudes from the cavity. Then, as in the first embodiment, by removing this portion and performing the shrinkage suppression sheet removing step (step S4) as necessary, as shown in FIG. A multilayer ceramic substrate 50 having a bottom cavity 51 is completed.

  An example in which the electronic device 40 is mounted on the multilayer ceramic substrate 50 having the two-step bottom cavity 51 is shown in FIG. As shown in FIG. 21, the electronic device 40 is accommodated in the lower cavity portion and connected to the conductor pattern 12 exposed on the deepest bottom surface 11a. The electronic device 40 is connected to the conductor pattern 52 exposed on the bottom surface 51b of the upper cavity portion by the bonding wire 41. As described above, the multilayer ceramic substrate 50 manufactured by the manufacturing method of the present embodiment can accommodate the electronic device 40 and the bonding wire 41 in the multilayer ceramic substrate 50. Thereby, it can be made flat, without a bonding wire etc. protruding from the surface of a multilayer ceramic substrate. In addition, even in a multilayer ceramic substrate having a plurality of dielectric layers therein, electronic devices can be mounted with high density, and the requirements for miniaturization and low profile can be satisfied.

  Moreover, since the 2nd softening layer 58 is arrange | positioned in the conductor pattern 52 surface among the peripheral parts of the 2nd step bottom face 51b of the 2nd step bottom cavity 51, the side wall lower end part of the ceramic layers 53-57 shrink | contracts in an in-plane direction. The stress concentration on the conductor pattern 52 at the time is relaxed, and disconnection of the conductor pattern 52 can be suppressed.

  Note that, by applying the method for manufacturing a multilayer ceramic substrate of the present embodiment, a multi-stage bottom cavity having three or more bottoms can be formed inside the multilayer ceramic substrate. For example, in the laminated body forming step, the ceramic green sheet provided with substantially the same cut or discontinuity at the same position as the second through hole and the uppermost composite green sheet in order from the bottom The ceramic green sheet is provided with a fourth through-hole that overlaps the second through-hole and is larger than the second through-hole, and the shrinkage-suppressing green sheet having the same shape and the same thickness as the fourth through-hole is provided in the ceramic green sheet. The shrinkage-suppressing green sheet fitted into the fourth through hole is provided with a fifth through hole having the same position and the same shape as the second through hole, and substantially the same as the fifth through hole. A third composite green sheet in which a ceramic green sheet having the same shape and thickness is fitted into the fifth through hole, and a cut or discontinuous portion having substantially the same shape at the same position as the fourth through hole are provided. Ceramic And Nshito, and a state in which at least one is interposed overlapped respectively. And it presses in a lamination direction and forms a laminated body. Thereby, a three-stage bottom cavity can be formed through the cavity forming step.

  When the conductor pattern is formed so as to straddle the peripheral edge of the bottom surface of the third step, the softening layer is disposed at a predetermined position, as in the manufacturing process of the multilayer ceramic substrate having the two-step bottom cavity. . Thereby, disconnection of the conductor pattern formed on the bottom surface of the third stage can be suppressed.

(Fourth embodiment)
For example, in the manufacturing method of the first embodiment, depending on the layer structure of the multilayer ceramic substrate, the upper and lower shrinkage suppression forces cannot be balanced, and if drawn extremely, for example, the bottom surface of the cavity may be deformed as shown in FIG. is there. In such a case, the thickness of the shrinkage suppression material green sheet sandwiching the bottom surface may be adjusted. The present embodiment is an example in which such adjustment is performed.

  That is, as shown in FIG. 23, the thickness of the first composite green sheet 26 in which the shrinkage-suppressing material green sheet piece (first fitting sheet 25) is fitted to the cavity forming portion is adjusted. In this case, in order to correct the change in the thickness, only the thickness of the first fitting sheet 25 needs to be adjusted, but the thickness of the entire first composite green sheet may be adjusted. Or as shown in FIG. 24, you may make it adjust the thickness of the part corresponding to the cavity of the shrinkage | contraction suppression material green sheet 22. FIG. In this case, as shown in FIG. 24, the shrinkage-suppressing material green sheet 22 has a thin shrinkage-suppressing material green sheet 22a and a shrinkage-suppressing material in which a through hole is formed in the cavity forming portion and a ceramic green sheet is fitted therein. What is necessary is just to comprise by laminating | stacking the green sheet 22b. Thereby, the shrinkage | contraction suppression of the whole laminated body and the shrinkage | contraction suppression of a cavity bottom face part can be controlled separately.

  In addition, about the shrinkage | contraction suppression material green sheet 22b, although the shape (shape of a through-hole) to fit is the same as the shape of a cavity, what is necessary is just to determine in consideration of the balance of shrinkage | contraction suppression force. Similarly, the thicknesses of the first fitting sheet 25 and the shrinkage suppression material green sheets 22a and 22b may be appropriately set in consideration of the balance of the shrinkage suppression force. In addition, a fire-resistant sheet may be fitted in the through hole of the shrinkage suppression material green sheet 22b in place of the ceramic green sheet, and in this case also, pressure can be uniformly applied during pressing.

(Fifth embodiment)
This embodiment is an example in which a burnable sheet is used when the multilayer ceramic substrate 1 shown in FIG. 1 is manufactured. FIG. 25 shows a basic manufacturing process of the present embodiment. The manufacturing process mainly includes a step of laminating and pressing a green sheet that becomes a ceramic layer after firing and a green sheet for shrinkage suppression material, a step of firing the same, a step of removing the fired product of the embedding green sheet after firing, shrinkage And a step of removing the fired product of the suppressor green sheet.

  In producing the multilayer ceramic substrate, first, as shown in FIG. 25A, a plurality of ceramic green sheets are laminated as substrate green sheets according to the number of ceramic layers constituting the multilayer ceramic substrate. Here, nine ceramic green sheets 61 to 69 are laminated. Each of the ceramic green sheets 61 to 69 makes a slurry-like dielectric paste obtained by, for example, mixing ceramic powder, an organic binder, and an organic solvent, and applies this to a doctor such as a polyethylene terephthalate (PET) sheet. It is formed by forming a film by a blade method or the like. Any known ceramic powder and organic vehicle (organic binder and organic solvent) can be used.

  Here, among the ceramic green sheets 61 to 69, the lower two ceramic green sheets 61 and 62 do not require a through hole for forming a cavity, and are formed as a normal flat green sheet. Yes. Of these two ceramic green sheets 61, 62, the upper ceramic green sheet 62 corresponds to the bottom surface forming green sheet constituting the bottom surface of the cavity.

  The remaining seven ceramic green sheets 63 to 69 are laminated on the ceramic green sheet 62. The ceramic green sheets 63 to 69 have a predetermined shape corresponding to the opening shape of the cavity 11. Through holes 63a and cuts 64a to 69a are made, and portions 63b to 69b corresponding to the cavity space are separated. Therefore, these seven ceramic green sheets 63 to 69 correspond to cavity side wall forming green sheets.

  In the present embodiment, the portions 64b to 69b separated by the cuts 64a to 69a are used as embedding green sheets, except for the ceramic green sheet 63 that is in contact with the ceramic green sheet 62 constituting the bottom surface of the cavity. In addition to the above, for example, through holes corresponding to the cavities may be formed in each of the ceramic green sheets 64 to 69, and a separately formed green sheet for embedding may be fitted therein. It is advantageous to use the portions 64b to 69b separated by the notches 64a to 69a as the green sheet for embedding as described above.

  On the other hand, for the ceramic green sheet 63 in contact with the ceramic green sheet 62 constituting the bottom surface of the cavity, a through hole 63a corresponding to the cavity is formed, the ceramic green sheet in this portion is removed, and the shape of the through hole 63a is formed. The shrinkage-suppressing material green sheet piece 70a and the burnt-out sheet piece 71a matched to the above are fitted into the through-hole 63a so as to be filled. This is shown in detail in FIG.

  That is, first, as shown in FIG. 26A, a ceramic green sheet 63 is formed, and as shown in FIG. 26B, a through hole 63a corresponding to the opening shape of the cavity is formed by punching. Further, as shown in FIG. 26 (c), a shrinkage suppression material green sheet 70 is formed, and as shown in FIG. 26 (d), this is punched out so as to substantially match the shape of the through hole 63a, thereby suppressing the shrinkage. A material green sheet piece 70a is formed. Similarly, as shown in FIG. 26 (e), a burnout sheet 71 is formed, and as shown in FIG. 26 (f), this is punched out so as to substantially match the shape of the through hole 63a, and the burnout sheet 71 is formed. A piece 71a is formed. Next, as shown in FIG. 26 (g), the shrinkage-suppressing material green sheet piece 70a and the burnable sheet piece 71a are fitted into the through hole 63a of the ceramic green sheet 63 in this order to fill the through hole 63a. Form. Therefore, it is preferable to set the total thickness of the shrinkage suppression material green sheet piece 70 a and the burnable sheet piece 71 a so as to substantially match the thickness of the ceramic green sheet 63.

The shrinkage-suppressing material green sheet 70 (shrinkage-suppressing material green sheet piece 70a) is made of a material that does not shrink at the firing temperature of the ceramic green sheets 61 to 69, such as tridymite or cristobalite, quartz, fused quartz, alumina, mullite, A composition containing zirconia, aluminum nitride, boron nitride, magnesium oxide, silicon carbide, or the like is used, and these shrinkage-suppressing material green sheet pieces 71a are arranged in contact with the ceramic green sheet (in this case, the ceramic green sheet 62). In addition, by performing firing, shrinkage in the in-plane direction of the ceramic green sheet 62 is suppressed.

  For the burnout sheet 71 (burnout sheet piece 71a), a material that burns down at the firing temperature of the ceramic green sheets 61 to 69, such as a resin material, is used. In particular, it is preferable to use the same material as the organic binder contained in the ceramic green sheets 61-69. If the same material as the organic binder contained in the ceramic green sheets 61 to 69 is used for the burnable sheet 71 (burnable sheet piece 71a), the burnable sheet 71 (burnable sheet piece 71a) is surely formed during firing. Burned out. The burnable sheet piece 71a may be formed by punching out the sheet as described above, or may be formed by a printing method or the like, for example.

  As described above, the ceramic green sheets 61 to 69 are laminated, and the shrinkage-suppressing material green sheets 73 and 74 are superimposed on both surfaces, that is, the surfaces of the outermost ceramic green sheets 61 and 69. The material of the shrinkage suppression material green sheets 73 and 74 is the same as the material of the previous shrinkage suppression material green sheet 70. As for the shrinkage-suppressing material green sheet 74 disposed on the ceramic green sheet 69 side where a through hole (notch 69a) is formed corresponding to the cavity, the through hole corresponding to the cavity opening shape is the same as the ceramic green sheet 69. 74a is provided, and a ceramic green sheet for embedding 75, which is separately punched and formed therein, is fitted therein.

  The laminated state of the laminated body in which these layers are laminated is as shown in FIG. 25A, and the shrinkage-suppressing material green sheets 73 and 74 are provided on both sides of the laminated body in which a plurality of ceramic green sheets 61 to 69 are laminated. Laminated and configured to suppress shrinkage in the in-plane direction of the entire laminate. The conductor pattern 12 is formed on the surface of the ceramic green sheet 62 so as to straddle the bottom peripheral edge of the cavity. Further, the region constituting the cavity bottom surface of the ceramic green sheet 62 is in contact with the shrinkage-suppressing material green sheet piece 70a disposed in the through hole 63a of the ceramic green sheet 63, and this portion also has an in-plane direction. It is comprised so that shrinkage | contraction may be suppressed.

  The space corresponding to the cavity is usually formed as a space (concave portion) at this stage as well, but in the manufacturing method of the present embodiment, the portions 64b to 69b separated by the cuts 64a to 69a of the ceramic green sheets 64 to 69. Further, the embedding ceramic green sheet piece 75 is arranged as an embedding green sheet. When the entire shape of the laminate is viewed, it is formed as a flat laminate having no recess.

  The laminated body in which the ceramic green sheets 61 to 69 and the shrinkage suppression material green sheets 73 and 74 are laminated needs to be pressed by a pressing process prior to firing. At this time, if the concave portion corresponding to the cavity is formed, the concave portion may be crushed and the opening portion of the cavity may be deformed. In the present embodiment, a laminated body having a uniform thickness in the laminating direction is produced by the green sheet for embedding and is flattened including the cavity portion. Therefore, it is possible to press using a normal flat plate mold. It is possible to perform the pressing process by an easy means. In addition, the pressing process of the laminated body may be performed by sandwiching and pressing between the flat plate molds as described above. For example, the laminated body may be covered with a waterproof resin and the hydrostatic pressure pressing may be performed. Good.

  After the pressing step, as shown in FIG. 25 (b), the ceramic green sheets 61 to 69 are made into the ceramic layers 2 to 10 by firing. At this time, the shrinkage suppressing materials green sheets 73 and 74 are laminated. Therefore, the ceramic green sheets 61 to 69 contract only in the thickness direction and hardly contract in the in-plane direction. The shrinkage in the in-plane direction is also suppressed for the ceramic green sheet 62 exposed at the bottom of the cavity.

  Also, a green sheet for embedding (corresponding to the portions 64b to 69b separated by the cuts 64a to 69a of the ceramic green sheets 64 to 69a and the ceramic green sheet piece 75 for embedding) and the shrinkage-suppressing material embedded correspondingly to the cavity space. The burnt-out sheet piece 71a is interposed between the green sheet pieces 70a and burns out before the ceramic green sheets 61 to 69 are sintered. As a result, the restraining force of the shrinkage-suppressing material green sheet piece 70a disposed at the bottom of the cavity does not act on these embedding green sheets, and thus shrinks in the in-plane direction. As shown to b), it will become the form which protrudes from the laminated body after baking by the part which there is little shrinkage | contraction in the thickness direction. Since the restraining force does not work, the shrinkage-suppressing material green sheet piece 70a and further the ceramic green sheet 62 under it are not stressed by contracting them, and the ceramic green sheet 62 is formed by firing. The flatness or the like of the ceramic layer 3 is not impaired.

  After the firing, as shown in FIG. 25C, the fired product 76 of the embedding green sheet is removed from the cavity space. The fired product is separated from the shrinkage-suppressing material green sheet piece 70a by burning out the burnable sheet piece 71a, and can be easily removed by, for example, turning upside down.

  Finally, the residue 77 after firing of the shrinkage suppression material green sheets 73 and 74 and the shrinkage suppression material green sheet piece 70a is removed to complete the multilayer ceramic substrate 1 having the cavity 11 as shown in FIG. . The residue 77 after firing the shrinkage-suppressing material green sheets 73 and 74 and the shrinkage-suppressing material green sheet piece 70a can be easily removed by performing some kind of cleaning process, for example, easily removed by stimulation such as ultrasonic cleaning. Is possible. Therefore, an ultrasonic cleaning process in a solvent may be performed as the cleaning process. For example, when an alumina green sheet is used as the shrinkage-suppressing material green sheet, the residue 76 is not naturally peeled off. It is necessary to remove the residue 76 by polishing and washing in a blasting process or the like.

  The multilayer ceramic substrate 1 manufactured as described above has excellent dimensional accuracy, flatness of the bottom surface of the cavity, and the like, and deformation such as crushing of the cavity opening and swelling around the cavity opening does not occur. Furthermore, in the multilayer ceramic substrate 1, the disconnection of the conductor pattern 12 is suppressed by forming the softening layer 13.

(Sixth embodiment)
This embodiment is an example in which a burnable sheet is applied to manufacture of a multilayer ceramic substrate having a multi-stage (two-stage) cavity. FIG. 27 shows an embodiment applied to the manufacture of a multilayer ceramic substrate in which a two-stage cavity is formed. In this case, as shown in FIG. 27 (a), the shrinkage-suppressing material green sheets 82 and 83 are laminated on both surfaces of the ceramic green sheet laminate 81, and the shrinkage-suppressing material green is respectively provided on the bottom surface and the step surface of the cavity. Sheet pieces 84 and 85 and burnable sheet pieces 86 and 87 are arranged. Then, the pressing step and the firing step are performed in a state where the embedding green sheet 88 is arranged so as to fill the cavity space of the two-stage structure. Also in this example, the flatness of the laminate is maintained, and the pressing process is easy.

  After firing, as shown in FIG. 27 (b), the fired product 89 of the embedding green sheet protrudes from the laminate, but can be easily removed by flipping upside down, for example, as described above. Is possible. The resulting multilayer ceramic substrate 90 is as shown in FIG. 27 (c), which not only has excellent overall dimensional accuracy, but also has excellent dimensional accuracy and flatness of the bottom surface 91a and the stepped surface 91b of the cavity 91. It becomes. Further, by disposing the softening layer 13 and the second softening layer 58 on each bottom surface, it is possible to suppress disconnection of the conductor pattern 12 and the conductor pattern 52 due to contraction in the in-plane direction of the area around the cavity. In the case of the two-stage cavity 91 as described above, an electronic device is mounted on the bottom surface 91a, and a conductor pattern connected to the electronic device by a bonding wire is provided on the step surface.

(A) is a schematic plan view which shows an example of the multilayer ceramic substrate of this embodiment, (b) is a principal part enlarged plan view of (a), (c) is in XX in (a). It is a principal part schematic sectional drawing, (d) is a principal part expanded sectional view of (c). It is a figure which shows the cavity shape of the multilayer ceramic substrate shown in FIG. 1 in detail. It is a schematic sectional drawing which shows the state which sealed the electronic device in the cavity. It is a flowchart which shows the manufacturing process in 1st Embodiment. (A) is a schematic side view of a ceramic green sheet, (b) is a schematic side view of a shrinkage suppression material green sheet. (A) is a schematic plan view of a 1st composite green sheet, (b) is a schematic plan view of an uppermost composite green sheet. It is a schematic plan view of a cut formation sheet. It is a schematic plan view of the green sheet for bottom face formation. It is a principal part schematic sectional drawing which shows the manufacturing process of the multilayer ceramic substrate in 1st Embodiment, (a) is a lamination process, (b) is a baking process, (c) is a cavity formation process, (d) is shrinkage | contraction suppression. A sheet removal process is shown. It is a principal part schematic sectional drawing which shows the lamination process in the manufacturing process of the multilayer ceramic substrate in which the softening layer is not provided. It is a schematic sectional drawing which shows the mounting state of the electronic device to the multilayer ceramic substrate produced in 1st Embodiment. It is a schematic plan view which shows an example of the multilayer ceramic substrate of 2nd Embodiment. It is a schematic plan view which shows the other example of the multilayer ceramic substrate of 2nd Embodiment. It is a principal part schematic sectional drawing which shows the other example of the multilayer ceramic substrate of 2nd Embodiment. It is a principal part schematic sectional drawing which shows an example of the multilayer ceramic substrate which is a multilayer ceramic substrate in 3rd Embodiment, and has a cavity of a multistage structure. It is a figure which shows an example of the cavity shape in the multilayer ceramic substrate which has a multistage cavity. It is a figure which shows the other example of the cavity shape in the multilayer ceramic substrate which has a multistage cavity. (A) is a schematic plan view of the 2nd composite green sheet produced in 3rd Embodiment, (b) is a schematic plan view of a 2nd notch formation sheet. It is a schematic plan view of the green sheet for 2nd bottom face formation. It is a principal part schematic sectional drawing which shows the example of a manufacturing process of the multilayer ceramic substrate which has the cavity of the 2 step | paragraph structure in 3rd Embodiment, (a) shows a lamination process, (b) shows a baking process. It is a schematic sectional drawing which shows the mounting state of the electronic device on the multilayer ceramic substrate produced in 3rd Embodiment. It is a principal part schematic sectional drawing which shows the deformation | transformation in the cavity bottom face part of a multilayer ceramic substrate. It is a principal part schematic sectional drawing which shows an example of the laminated body in 4th Embodiment. It is a principal part schematic sectional drawing which shows the other structural example of the laminated body in 4th Embodiment. It is a principal part schematic sectional drawing which shows the manufacturing process of the multilayer ceramic substrate in 5th Embodiment, (a) is a lamination process, (b) is a baking process, (c) is the removal process of the baking products of the embedding green sheet. , (D) shows the completed multilayer ceramic substrate. It is a schematic perspective view which shows the application process of the shrinkage | contraction suppression material green sheet piece and burnable sheet piece to a ceramic green sheet. It is a principal part schematic sectional drawing which shows the example of a manufacturing process of the multilayer ceramic substrate which has the cavity of the 2 step | paragraph structure in 6th Embodiment, (a) is a lamination process, (b) is a baking process, (c) is a ceramic multilayer. The substrate is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multilayer ceramic substrate, 2-10 Ceramic layer, 11 Cavity, 12 Conductor pattern, 13 Softening layer, 21 Ceramic green sheet, 22 Shrinkage suppression material green sheet, 23 Support body, 24 1st through-hole, 25 1st fitting sheet , 26 1st composite green sheet, 27 2nd through-hole, 28 2nd fitting sheet, 29 top layer composite green sheet, 30 cut forming sheet, 31 cut, 32 bottom forming green sheet, 33 laminate, 34 laminate firing Body, 40 electronic device, 41 bonding wire, 43 second composite green sheet, 44 third through hole, 45 third fitting sheet, 46 fourth through hole, 47 second cut forming sheet, 48 cut, 50 multilayer ceramic substrate 51 Double cavity, 52 Conductor pattern, 53-57 Ceramic layer, 58 Softening layer, 61-69 Ceramic green sheet, 63a-69a Notch, 64b-69b Separated part (embedding green sheet), 70a Shrinkage suppression material green sheet piece, 71a Burn-out sheet piece, 73, 74 Shrinkage suppression material green sheet, 75 embedding green sheet piece, 76 fired product of embedding green sheet, 77 residue, 81 laminate, 82, 83 Shrinkage suppression material green sheet, 84, 85 Shrinkage suppression material green sheet piece, 86, 87 burnable sheet piece, 88 green sheet for embedding, 89 fired product of embedding green sheet, 90 multilayer ceramic substrate, 91 cavity, 91a bottom surface, 91b step surface

Claims (45)

A multilayer ceramic substrate produced by laminating a plurality of green sheets for a substrate and then firing, and having a cavity, and a ceramic layer including a bottom surface forming ceramic layer constituting the bottom surface of the cavity is laminated and integrated. ,
A conductor pattern is formed on the bottom surface forming ceramic layer so as to straddle the peripheral edge of the bottom surface of the cavity,
A multilayer ceramic substrate comprising a softening layer that is softened at a firing temperature at the time of firing at least on a surface of the conductor pattern in a portion corresponding to a peripheral portion of the bottom surface on the bottom surface forming ceramic layer.   The multilayer ceramic substrate according to claim 1, wherein the softened layer is formed on the entire periphery.   The multilayer ceramic substrate according to claim 1 or 2, wherein a distance between a peripheral edge portion of the bottom surface and an outer peripheral edge portion of the softening layer is 0.1 mm to 0.5 mm.   The multilayer ceramic substrate according to any one of claims 1 to 3, wherein a distance between a peripheral edge portion of the bottom surface and an inner peripheral edge portion of the softened layer is 0.5 mm or less.   The multilayer ceramic substrate according to any one of claims 1 to 4, wherein the softening layer is made of glass.   6. The multilayer ceramic substrate according to claim 5, wherein the glass is the same as the glass contained in the ceramic layer.   The multilayer ceramic substrate according to any one of claims 1 to 6, wherein an opening area at an opening of the cavity is smaller than an opening area at an intermediate position in the depth direction of the cavity.   The shape of the cavity is such that a midway part in the depth direction bulges out, and the opening area of the cavity gradually increases until reaching the midway position in the depth direction, and then gradually decreases. Item 8. The multilayer ceramic substrate according to Item 7.   9. The multilayer ceramic substrate according to claim 8, wherein the cross-sectional shape of the inner wall of the cavity is a substantially arc shape. The cavity has a multi-stage shape in which the opening size is gradually reduced in the depth direction,
In each bottom surface having a step, the bottom surface on which the conductor pattern is formed across the peripheral edge portion of the bottom surface, at least the portion corresponding to the peripheral edge portion of the bottom surface on the bottom surface forming ceramic layer constituting the bottom surface The multilayer ceramic substrate according to claim 1, wherein the softening layer is provided on a surface of the conductor pattern.   11. The multilayer ceramic substrate according to claim 10, wherein an opening area in the opening is smaller than an opening area in an intermediate position in the depth direction in at least the first-stage cavity.   The shape of the cavity portion in the first stage is a shape in which a midway portion in the depth direction bulges, and the opening area of the cavity portion gradually increases until reaching the midway position in the depth direction, and then gradually decreases. The multilayer ceramic substrate according to claim 11, wherein   13. The multilayer ceramic substrate according to claim 11, wherein in the second and subsequent cavities, the opening area in the opening is smaller than the opening area in the midway position in the depth direction.   The multilayer ceramic substrate according to claim 11 or 12, wherein the second and subsequent cavities have a shape in which the opening area gradually decreases with depth.   The multilayer ceramic substrate according to any one of claims 12 to 14, wherein a cross-sectional shape of an inner wall of each cavity portion is a substantially arc shape.   The multilayer ceramic substrate according to claim 1, wherein an electronic device is mounted in the cavity and sealed with resin. A plurality of substrate green sheets including a bottom surface forming green sheet constituting the bottom surface of the cavity and a cavity forming green sheet forming an opening corresponding to the cavity shape are laminated to form a laminate, and the outermost layer of the laminate A method for producing a multilayer ceramic substrate, in which a multilayer ceramic substrate having a cavity is formed by pressing the laminate in a state in which the shrinkage-suppressing material green sheets are laminated on the surface of the substrate green sheet to be fired,
A conductor pattern is formed on the bottom surface forming green sheet so as to straddle the peripheral edge portion of the bottom surface of the cavity, and at least on the surface of the conductor pattern among the portions corresponding to the peripheral edge portion on the bottom surface forming green sheet, After forming a softened layer that softens at the firing temperature during the firing,
Laminating a green sheet for forming a cavity in which a shrinkage-suppressing material green sheet piece is embedded in a through hole is laminated directly on the bottom-forming green sheet so that the bottom surface of the cavity and the shrinkage-suppressing material green sheet piece overlap with each other, and The pressing and baking are performed in a state where the green sheets for cavity formation are laminated so that the green sheets for embedding separated from the respective green sheets for cavity formation in a form to fill the cavities are arranged on the green sheet pieces of the shrinkage suppression material. Done
A method for producing a multilayer ceramic substrate, wherein the fired product of the green sheet for embedding is removed after firing.   The method for manufacturing a multilayer ceramic substrate according to claim 17, wherein the softening layer is formed over the entire peripheral edge of the bottom surface.   19. The multilayer ceramic substrate according to claim 17, wherein the softening layer is formed such that a distance between a peripheral edge portion of the bottom surface and an outer peripheral edge portion of the softening layer is 0.1 mm to 0.5 mm. Production method.   The multilayer ceramic according to any one of claims 17 to 19, wherein the softened layer is formed so that a distance between a peripheral edge of the bottom surface and an inner peripheral edge of the softened layer is 0.5 mm or less. A method for manufacturing a substrate.   21. The method of manufacturing a multilayer ceramic substrate according to claim 17, wherein glass is used for the softening layer.   The method for manufacturing a multilayer ceramic substrate according to claim 21, wherein the glass is the same as the glass contained in the green sheet for a substrate.   A through hole is formed in the cavity forming green sheet laminated immediately above the bottom surface forming green sheet according to the shape of the cavity, and the shrinkage suppression material green sheet piece is fitted into the through hole. The method for producing a multilayer ceramic substrate according to any one of claims 17 to 22.   24. The method of manufacturing a multilayer ceramic substrate according to claim 23, wherein the thickness of the shrinkage-suppressing material green sheet piece is set so as to substantially match the thickness of the substrate green sheet.   The cavity has a multi-stage shape in which the opening size is gradually reduced in the depth direction, and a shrinkage-suppressing material green sheet piece is disposed on each green sheet for a substrate constituting each bottom surface having a step. The method for producing a multilayer ceramic substrate according to any one of claims 17 to 24.   When arranging the shrinkage-suppressing material grease sheet piece on each bottom surface having the step, the bottom surface forming the bottom surface in which the conductor pattern is formed across the peripheral edge of the bottom surface among the bottom surfaces having the step. 26. The method for producing a multilayer ceramic substrate according to claim 25, wherein the softening layer is formed on at least a surface of the conductor pattern in a portion corresponding to the peripheral portion on the green sheet.   27. The method for producing a multilayer ceramic substrate according to any one of claims 17 to 26, wherein a burnable sheet is interposed between the shrinkage-suppressing material green sheet piece and the embedding green sheet.   A through hole is formed in the cavity forming green sheet laminated immediately above the bottom forming green sheet according to the cavity shape, and the shrinkage-suppressing material green sheet piece and the burnable sheet are fitted into the through hole. The method for producing a multilayer ceramic substrate according to claim 27.   29. The method for manufacturing a multilayer ceramic substrate according to claim 28, wherein a thickness of the shrinkage suppression material green sheet piece and the burnable sheet is set so as to substantially match a thickness of the cavity forming green sheet.   The cavity has a multi-stage shape in which the opening size is gradually reduced in the depth direction, and the shrinkage-suppressing material green sheet piece and the burnable sheet are arranged on the green sheet for the substrate constituting each bottom surface having a step. 30. The method for producing a multilayer ceramic substrate according to any one of claims 17 to 29, wherein:   The method for producing a multilayer ceramic substrate according to any one of claims 27 to 30, wherein the burnout sheet is made of a resin material.   32. The method of manufacturing a multilayer ceramic substrate according to claim 31, wherein the resin material is the same as the resin material contained in the cavity forming green sheet.   33. The multilayer ceramic substrate according to any one of claims 17 to 32, wherein a notch corresponding to a cavity shape is cut into the cavity forming green sheet, and a portion separated thereby is used as the embedding green sheet. Production method.   The through hole corresponding to a cavity shape is formed in the green sheet for cavity formation, The green sheet for embedding | punching separately punched and formed in this through hole is fitted, The any one of Claim 17-32 characterized by the above-mentioned. A method for producing a multilayer ceramic substrate.   A through hole corresponding to the shape of the cavity opening is formed in the shrinkage-suppressing material green sheet disposed on the surface of the outermost substrate green sheet on the opening side of the cavity, and the embedding green sheet is fitted therein. A method for producing a multilayer ceramic substrate according to any one of claims 17 to 34.   36. The method for manufacturing a multilayer ceramic substrate according to any one of claims 17 to 35, wherein the thickness of the shrinkage-suppressing material green sheet piece in the cavity portion is corrected.   The thickness of the green sheet for cavity formation laminated directly on the green sheet for bottom surface formation is different from the thickness of other green sheets for cavity formation, and the thickness of the shrinkage suppression material green sheet piece is reduced to the shrinkage suppression material green 37. The method for producing a multilayer ceramic substrate according to claim 36, wherein the thickness is set to be different from the thickness of the sheet.   The shrinkage-suppressing material green sheet disposed on the surface of the outermost substrate green sheet on the side opposite to the opening side of the cavity should be set so that the thickness is different between the part facing the cavity and the other part. 38. The method for producing a multilayer ceramic substrate according to claim 36 or 37.   The shrinkage-suppressing material green sheet is formed by laminating a first shrinkage-suppressing material green sheet having a predetermined thickness and a second shrinkage-suppressing material green sheet having a through hole formed in a portion facing the cavity. 40. The method of manufacturing a multilayer ceramic substrate according to claim 38, comprising:   40. The shrinkage suppression material green sheet and the shrinkage suppression material green sheet piece include at least one selected from quartz, cristobalite, and tridymite as the shrinkage suppression material. A method for producing a multilayer ceramic substrate.   41. The method for producing a multilayer ceramic substrate according to claim 40, wherein the shrinkage suppression material green sheet and the shrinkage suppression material green sheet piece are formed of a composition containing tridymite and a hardly sinterable oxide.   The method for producing a multilayer ceramic substrate according to any one of claims 17 to 41, wherein a firing temperature during the firing is 1000 ° C or lower.   43. The method for manufacturing a multilayer ceramic substrate according to any one of claims 17 to 42, wherein a cleaning step of cleaning the residue is performed after the firing.   44. The method for manufacturing a multilayer ceramic substrate according to claim 43, wherein the cleaning step is performed by ultrasonic cleaning in a solvent. 44. The method for manufacturing a multilayer ceramic substrate according to claim 43, wherein the cleaning step is performed by wet blasting.

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