JP4683269B2 - Manufacturing method of multilayer ceramic substrate - Google Patents

Description

  The present invention relates to a multilayer ceramic substrate having via holes straddling between layers and a method for manufacturing the same, and more particularly to a technique for preventing deformation of via holes due to shrinkage during firing.

  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. The multilayer ceramic substrate is formed by laminating a plurality of ceramic layers, and high-density mounting is possible by integrally forming a wiring conductor, an electronic element, and the like in each ceramic layer.

  The 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%.
JP-A-10-75060

  By the way, in a multilayer ceramic substrate, a via hole, an inner via hole or the like (hereinafter collectively referred to as a via hole) is generally formed. These via holes are formed for the purpose of conduction between the electrodes formed in the ceramic layers including both surfaces of the multilayer ceramic substrate, and further play a role such as forming an inductor and releasing heat.

  However, when it is going to form the multilayer ceramic substrate in which the said via hole was formed, even if it employ | adopts the said non-shrinkage firing method, there exists a big problem that a deformation | transformation etc. of a via hole cannot be suppressed. For example, when trying to produce a multilayer ceramic substrate having a via hole using the non-shrinkage firing method, the shrinkage restraining force in the central portion (inner layer portion) in the thickness direction of the green sheet laminate is smaller than that of the outer layer. As a result, a phenomenon occurs in which the diameter of the via hole becomes larger in the central portion in the thickness direction of the multilayer ceramic substrate than in the vicinity of the surface. When the diameter of the via hole is increased, there are problems such as unnecessarily occupying a large area, and there is a problem that the inductance is reduced when an inductor is formed. Arise.

  For a hole that is somewhat large (so-called cavity), a method of changing the size of the hole to correct the difference in shrinkage inside the hole has been proposed (for example, Japanese Patent Application Laid-Open No. 2003-224360). However, when applying to a multilayer ceramic substrate with via holes formed, for example, the silver paste filled in the through hole of the green sheet is peeled off during firing, and voids are generated inside the multilayer ceramic substrate. There is. If voids are generated inside the multilayer ceramic substrate, for example, an etching solution may enter during etching of the surface wiring layer, and this may remain in the substrate for a long time, adversely affecting reliability and the like.

  The present invention has been proposed in view of such a conventional situation, has high dimensional accuracy due to being formed by a non-shrinkage firing method, and is free from deformation of via holes and generation of voids. An object of the present invention is to provide a highly reliable multilayer ceramic substrate excellent in dimensional accuracy and a manufacturing method thereof.

In order to achieve the above-mentioned object, a method for manufacturing a multilayer ceramic substrate of the present invention comprises laminating a plurality of green sheets each having a through-hole formed at least in part and arranging a green sheet for suppressing shrinkage as an outermost layer. A method for manufacturing a multilayer ceramic substrate to be fired, wherein a conductive paste pattern serving as an electrode pad is provided around at least a part of a green sheet in which a through hole is formed, and is positioned relatively in an inner layer The sintering is performed by setting the size of the conductive paste pattern provided on the green sheet to be larger than the size of the conductive paste pattern provided on the green sheet located in the outer layer.

  When a green sheet is fired to form a ceramic layer, it always shrinks with sintering. Here, when the via hole is formed by forming the through hole in the green sheet, the contraction force acts inward in the outer peripheral portion, whereas in the vicinity of the through hole, the through hole is directed outward. The contraction force works radially. That is, contraction force acts in the direction of expanding the through hole. On the other hand, when the conductive paste pattern for forming the electrode pad is provided around the through hole and the baking is performed, the conductive paste pattern also contracts with the baking. At this time, the conductive paste pattern contracts in a direction in which the size is reduced, and a contraction force acts toward the through hole. Accordingly, by forming the conductive paste pattern around the through hole, the outward contraction force in the vicinity of the through hole of the green sheet is offset by the inward contraction force, and the through hole (via hole) It is thought that the expansion of the above is suppressed.

  However, when the shrinkage-suppressing green sheet is disposed on the outermost layer and the firing is performed, the green sheet close to the surface is strongly restrained by the shrinkage-suppressing green sheet and can hardly shrink in the in-plane direction. Since the restraining force of the shrinkage-suppressing green sheet hardly acts on the green sheet near the center in the stacking direction, a large shrinking force acts. With regard to the vicinity of the through hole, the contraction force toward the outside is small in the green sheet close to the surface, and the contraction force toward the outside is large in the green sheet near the center in the stacking direction.

  In such a case, if the conductive paste pattern (electrode pad) is formed in a uniform size and the via hole of the multilayer ceramic substrate is kept at a constant diameter, the conductive paste pattern of all layers is formed as the innermost layer. It is necessary to match the size of the conductive paste pattern, which reduces design freedom. Also, if the conductive paste pattern of each layer is made smaller in size, it cannot cope with the difference in shrinkage force, and the via hole of the multilayer ceramic substrate has, for example, a shape in which the central portion is swollen. It is difficult to obtain a predetermined shape. Therefore, in the present invention, the size of the conductive paste pattern (electrode pad) provided on the green sheet (ceramic layer) relatively positioned on the inner layer is set to the size of the conductive paste pattern (electrode pad) provided on the green sheet (ceramic layer) positioned on the outer layer. The size is larger than the size of the paste pattern (electrode pad), which corresponds to the difference in contraction force. By setting the size of the conductive paste pattern (electrode pad) as described above, the shrinkage force toward the inside is reduced in the green sheet near the surface, and in the green sheet in the portion near the center in the stacking direction. The inward contraction force increases. As a result, the shrinkage force is properly offset for each green sheet, from the part close to the surface to the part close to the center, and the shape (diameter) of the via hole is kept constant in each ceramic layer and designed. Is also secured.

  According to the present invention, a highly reliable multilayer ceramic substrate that has high dimensional accuracy due to being formed by a non-shrinkage firing method, is free from deformation of a via hole and generation of voids, and has excellent dimensional accuracy of a via hole. Can be provided. Further, according to the manufacturing method of the present invention, the shrinkage force acting on the green sheet from the inner layer close to the center to the outer layer close to the surface can be effectively eliminated by the conductive paste pattern, and has a constant diameter, deformation, etc. It is possible to form a via hole without peeling of the conductive paste due to.

  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.

  As shown in FIG. 1, the multilayer ceramic substrate 1 of the present invention is formed by laminating a plurality of ceramic layers (here, eight ceramic layers 2a to 2h) and providing via holes 3 penetrating the ceramic layers 2a to 2h. It will be. The via hole 3 is filled with the conductive material 4 remaining by firing the conductive paste, and the conductive material 4 electrically connects the wiring pattern electrodes formed in the ceramic layers 2a to 2h. And fulfills functions such as conducting heat. The cross-sectional shape of the via hole 3 is usually circular, but is not limited to this, and in order to obtain a large cross-sectional area in a limited shape space range, for example, the corners of an ellipse, an oval, a square or a rectangle are rounded. It can be made into arbitrary shapes, such as a thing and also the shape which combined these.

  In the case of the present embodiment, annular electrode pads 5 a to 5 g are formed on the surfaces of the ceramic layers 2 a to 2 g so as to surround the via holes 3 corresponding to the via holes 3, respectively. These electrode pads 5a to 5g may be formed independently of the wiring patterns, electrode patterns, etc. formed on the surfaces of the ceramic layers 2a to 2g, or may constitute a circuit and perform a predetermined function. Or in a state of being included in the electrode pattern (a state of being electrically connected to a wiring pattern, an electrode pattern, or the like).

  A characteristic of the multilayer ceramic substrate 1 of the present invention is that the electrode pads 5a to 5g are not formed to have the same size, but the size of the electrode pads 5a to 5g formed for each of the ceramic layers 2a to 2g ( (Diameter) is different. Specifically, the size of the electrode pads 5a and 5g formed on the outermost ceramic layers 2a and 2g is the smallest, and the size of the electrode pads gradually increases in the inner ceramic layer. The size of the electrode pad 5d formed on the ceramic layer 2d which is the innermost layer is the largest.

  By setting the size of the electrode pads 5a to 5g as described above, the inner diameter of the via hole 3 is constant in all the ceramic layers 2a to 2h, and no gap is generated inside the via hole 3. This is because the shrinkage of the ceramic layers 2a to 2h when the multilayer ceramic substrate 1 is manufactured is controlled by the shrinkage of the electrode pads 5a to 5g. Therefore, in the following, a method for manufacturing the multilayer ceramic substrate 1 will be described, and the shrinkage control will be described.

  In order to produce a multilayer ceramic substrate, first, green sheets that become ceramic layers after firing are prepared. The green sheet is made by forming a slurry-like dielectric paste obtained by mixing ceramic powder and an organic vehicle, and depositing this on a support such as a polyethylene terephthalate (PET) sheet by a doctor blade method or the like. Form. Any known ceramic powder and organic vehicle can be used.

  After the green sheet is formed, a through hole is formed at a predetermined position. The through holes communicate with each other after stacking to form via holes, and are usually formed as circular holes. Of course, the present invention is not limited to this, and as described above, any shape such as an ellipse, an oval, a square or a rectangle with round corners, or a combination of these may be used. In addition, for example, when the thickness of the green sheet is about 125 μm, the diameter of the through hole is set to about 0.1 mm in diameter considering the filling property of the conductive paste into the through hole. By performing pressure filling or the like, it is possible to cope with a smaller hole diameter, and conversely, a larger hole diameter may be used.

  Next, a conductive paste pattern for forming an electrode pad corresponding to the through hole of the green sheet is formed. FIG. 2 shows a state where the conductive paste pattern 13 is formed on the green sheet 11 provided with the through holes 12. When the through hole 12 is circular, the conductive paste pattern 13 is also formed concentrically around the through hole 12. When the shape of the through hole 12 is not circular, it is preferable that the shape of the conductive paste pattern 13 is also matched with the shape of the through hole 12. Further, when the conductive paste pattern 13 is formed, the inside of the through hole 12 is also filled with the conductive paste.

  The conductive paste used for forming the conductive paste pattern 13 is prepared by kneading a conductive material made of various conductive metals or alloys such as Ag, Ag-Pd alloy, Cu, Ni and an organic vehicle. is there. The organic vehicle has a binder and a solvent as main components, and the mixing ratio of the conductive material is arbitrary, but usually the binder is 1 to 15% by mass, and the solvent is 10 to 50% by mass. It is blended with the conductive material. Additives selected from various dispersants, plasticizers, and the like may be added to the conductive paste as necessary.

  After preparing the said green sheet, as shown in FIG. 3, this is piled up and it is set as a laminated body. In the case of this embodiment, the green body 11a-11h is laminated | stacked and the laminated body is comprised. At this time, the conductive paste patterns 13a to 13g for forming the electrode pads are formed on the green sheets 11a to 11g. However, the size (diameter) of the conductive paste patterns 13a to 13g is different for each of the green sheets 11a to 11g. They are formed differently. Specifically, the size of the conductive paste patterns 13a and 13g formed on the outermost green sheets 11a and 11g is the smallest, and the size of the conductive paste pattern gradually increases as it becomes the inner layer. Forming. The largest conductive paste pattern 13d is formed on the green sheet 11d in the central portion (innermost layer).

  Thus, the shrinkage | contraction suppression green sheet 14 is distribute | arranged to both sides (outermost layer) of the laminated body of the green sheet 11a-11h in which the electrically conductive paste patterns 13a-13g from which a magnitude | size differs was formed, and baking is performed. The shrinkage-suppressing green sheet 14 is made of a material that does not shrink at the firing temperature of the green sheet 11, such as tridymite or cristobalite, quartz, fused silica, alumina, mullite, zirconia, aluminum nitride, boron nitride, magnesium oxide, silicon carbide. And the like, and the laminate is sandwiched between the shrinkage-suppressing green sheets 14 and fired to suppress shrinkage of the laminate.

  FIG. 4 shows the multilayer ceramic substrate after firing in the laminated state shown in FIG. The ceramic layers 2a to 2h are shrunk with firing, but in the outermost ceramic layers 2a and 2h, the restraining force of the shrinkage-suppressing green sheet 14 is strong and hardly shrunk. On the other hand, since the ceramic layers 2d and 2e in the central portion in the stacking direction are separated from the shrinkage-suppressing green sheet 14, the binding force is weak and the ceramic layers 2d and 2e are greatly contracted. Therefore, as exaggeratedly depicted in FIG. 4, the fired laminate has a shape with a depressed central portion.

  On the other hand, the through holes 12 formed in each of the green sheets 11a to 11h are communicated with each other and remain as via holes in the fired laminate, but as described above, the conductive paste patterns 13a to 13g for forming the electrode pads are formed. By controlling the size, the size (diameter) of the through hole 12 formed in each of the green sheets 11a to 11h is kept constant, and deformation such as, for example, the central portion inflating does not occur. This is due to the following reason.

  FIG. 5 schematically shows the state of contraction force in the outermost green sheet 11a, and FIG. 6 schematically shows the state of contraction force in the central green sheet 11d. In each figure, (a) shows the contraction force of the green sheet, and (b) shows the contraction force of the conductive paste pattern.

  As shown in FIG. 5 (a), in the green sheet 11a, an inward contraction force acts on the outer periphery, and an outward contraction force acts radially around the through hole 12. However, in the green sheet 11a which is the outermost layer, since the restraining force of the shrinkage-suppressing green sheet 14 is acting on the green sheet 11a, the shrinkage force F1 is small. On the other hand, as shown in FIG. 5B, the conductive paste pattern 13 a is subjected to a contraction force F <b> 2 that is directed inward in the direction of reducing the size, that is, around the through hole 12. The contraction force F2 depends on the size of the conductive paste pattern, and is larger when the conductive paste pattern is larger and smaller when it is smaller. In the green sheet 11a shown in FIG. 5 (a), since the contraction force F1 outward in the periphery of the through hole 12 is small, by reducing the size (diameter r) of the conductive paste pattern 13a, What is necessary is just to produce the contraction force F2 which balances this.

  On the other hand, in the case of the green sheet 11d at the center of the laminated body, as shown in FIG. 6A, similar to the green sheet 11a, an inward contraction force acts on the outer periphery, and the through hole 12 Although the contraction force toward the outside works radially around the area, the contraction force F3 is larger than the contraction force F1 because the restraint force is weak because it is far from the contraction-inhibiting green sheet 14. Therefore, in this green sheet 11d, as shown in FIG. 6B, a conductive paste pattern 13d having a larger diameter R (> r) than the conductive paste pattern 13a is formed, and the large shrinkage force F3 is canceled out. Like that. By increasing the size (diameter R) of the conductive paste pattern 13d, a large contraction force F4 works and the contraction force F3 is offset.

  Based on the above ideas, by gradually increasing the size of the conductive paste patterns 13a to 13g formed on the green sheets 11a to 11g from the outer layer to the inner layer, the contraction force and the conductive paste in each of the green sheets 11a to 11g The contraction forces of the patterns 13a to 13g are balanced, and the contraction state becomes uniform. In this case, it is preferable to set the sizes of the conductive paste patterns 13a to 13g according to the shrinkage distribution of the green sheets 11a to 11g. As a result, the via hole (through hole 12) to be formed is formed in a good state with a constant diameter and no swelling of the central portion.

  For example, as shown in FIG. 7, when firing is performed in a state where the conductive paste pattern is not formed around the through-holes 12 of each green sheet 11 and sandwiched between the shrinkage-suppressing green sheets 14, as shown in FIG. In addition, the via hole is swollen after firing, and for example, the conductive material 15 filled in the via hole is peeled off and the gap K is formed.

  In the previous example, the conductive paste patterns 13a to 13g satisfying a predetermined size relationship are formed on the green sheets 11a to 11g. However, the size of the conductive paste pattern does not necessarily satisfy the relationship in all the green sheets. It does not have to be. For example, FIG. 9 shows an example in which a relatively large conductive paste pattern 13b is formed on the green sheet 11b. In a multilayer ceramic substrate, a large electrode pattern such as a ground may be formed. Even in such a case, it is only necessary that the conductive paste pattern of the other green sheet satisfies the above-mentioned size relationship, and the present invention does not exclude the case where such a large electrode pattern is inserted.

When the relatively large conductive paste pattern 13b is formed as described above, the via hole is formed in a good state as shown in FIG. 10 after firing, but as shown in FIG. 11, the green sheet 11b is formed in the green sheet 11b. shape of the through hole 12 is provided, can vary in the usual pattern portion 13b ₁ and the large-area pattern 13b ₂ side of the conductive paste pattern 13b. In such a case, the shape similar to that of the through holes formed in the other green sheets is not maintained. Strictly, the shape of the through holes 12 formed in the green sheet 13b is designed in consideration of this. There is a need.

  As described above, according to the present invention, the diameter of the via hole after firing can be made constant even when a non-shrinkage process is employed to form a highly accurate multilayer ceramic substrate. Etc. will not occur. For example, when the via hole is a heat radiating via, the columnar conductive material filled in the via hole is not thinned in the middle, and the amount of heat conduction is not reduced.

  As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention is not what is limited to these embodiment. For example, in the previous embodiment, all the via holes are formed so as to penetrate the multilayer ceramic substrate. However, as shown in FIG. 12, one side of the via hole is closed, or both sides are closed as shown in FIG. It may be. In any case, the idea regarding the size of the conductive paste pattern is the same as that of the previous embodiment, but in these cases, the shrinkage behavior is slightly complicated, so that each conductive paste is taken into consideration. It is preferable to design the pattern.

  Each green sheet (ceramic layer 2) is formed such that, for example, the opening diameter of the via hole 3 differs between the front and back surfaces of the ceramic layer 2 and the inner wall 3a of the via hole 3 has a tapered surface, as shown in FIG. As shown in FIG. 15, it is possible to chamfer the vicinity of the opening of the via hole 3 to form an arcuate curved surface 3b. In the present invention, the contraction force of the green paste is offset by the contraction force of the conductive paste pattern (electrode pad). Therefore, a large force is applied to the conductive paste pattern. In such a case, if the via hole is a normal vertical hole, the conductive paste pattern is divided at the corners, and the shrinkage force of the conductive paste pattern may not work effectively. On the other hand, by making the ceramic layer 2 into the shape as shown in FIG. 14 or FIG. 15, the connection between the conductive paste in the via hole and the conductive paste pattern is strengthened, and the shrinkage force of the conductive paste pattern is ensured. It is possible to work.

  Hereinafter, specific examples to which the present invention is applied will be described based on experimental results.

  An alumina-glass dielectric material was prepared as a ceramic material for the substrate. This was mixed with an organic binder and an organic solvent, and a ceramic green sheet having a thickness of 125 μm was prepared by a doctor blade method. On the other hand, a tridymite-silica material was prepared as a shrinkage suppressing material. This was mixed with an organic binder and an organic solvent in the same manner as the ceramic material, and a 125 μm-thickness shrinkage suppression material green sheet was prepared by the doctor blade method.

  Moreover, in order to form a via hole, a through hole was formed in each ceramic green sheet. The diameter of the through hole is φ0.1 mm, and the conductive paste pattern around the through hole is φ0.2 mm, φ0.18 mm, φ0.16 mm, φ0.12 mm, φ0.1 mm in order from the center layer of the pad diameter (no pad) ) And laminated. Furthermore, shrinkage-suppressing material green sheets were laminated on both sides.

The laminate thus obtained was put into a mold having a normal upper and lower punch and pressed at 700 kg / cm ^{2 for} 7 minutes, and then fired at 900 ° C. The fired ceramic substrate generally did not shrink in the surface direction, but only in the thickness direction. However, when observing in detail, when the side wall and cavity around the substrate are installed, the laminate of the inner wall inside the cavity is slightly shrunk in the surface direction, and the central portion of the side wall is in the substrate peripheral part and inside the cavity. It was depressed. On the other hand, the inner wall inside the via hole is constrained by the electrode pad (conductive paste pattern) and has a substantially linear shape.

It is a schematic sectional drawing which shows an example of the multilayer ceramic substrate to which this invention is applied. It is a schematic perspective view which shows the formation state of the electrode pad in each ceramic layer. It is a schematic sectional drawing which shows the manufacturing method of a multilayer ceramic substrate, and shows an example of the laminated structure at the time of baking. It is a schematic sectional drawing which shows the mode of the shape change after baking. (A) is a schematic diagram which shows the shrinkage force which acts on the green sheet of an outermost layer, (b) is a schematic diagram which shows the shrinkage force which acts on an electrically conductive paste pattern. (A) is a schematic diagram which shows the shrinkage force which acts on the green sheet of an innermost layer, (b) is a schematic diagram which shows the shrinkage force which acts on an electrically conductive paste pattern. It is a schematic sectional drawing which shows an example of the laminated structure at the time of baking in the case of baking without forming an electrically conductive paste pattern. It is a schematic sectional drawing which shows the mode of the shape change after baking. It is a schematic sectional drawing which shows an example of the laminated structure at the time of baking in the case of having a conductive paste pattern having a large area. It is a schematic sectional drawing which shows the mode of the shape change after baking. It is a top view which shows the example of a shape of an electrically conductive paste pattern, and the example of the shape of the through-hole at that time. It is a schematic sectional drawing which shows the example of the via hole by which the one side was block | closed. It is a schematic sectional drawing which shows the example of the via hole with which both sides were block | closed. It is a schematic diagram which shows an example of the via hole by which the inner wall was made into the taper surface. It is a schematic diagram which shows an example of the chamfered via hole.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multilayer ceramic substrate, 2a-2h Ceramic layer, 3 Via hole, 4 Conductive material, 5a-5g Electrode pad, 11a-11h Green sheet, 12 Through-hole, 13a-13g Conductive paste pattern, 14 Shrinkage suppression green sheet, 15 Conductivity Material

Claims (7)

A method for producing a multilayer ceramic substrate comprising laminating a plurality of green sheets each having a through hole formed at least in part, and arranging and firing a shrinkage suppressing green sheet as an outermost layer,
The size of the conductive paste pattern provided in the green sheet relatively located in the inner layer is provided in at least a part of the green sheet in which the through hole is formed, and a conductive paste pattern serving as an electrode pad is provided around the through hole. A method for producing a multilayer ceramic substrate, wherein the sintering is performed with a size larger than that of a conductive paste pattern provided on a green sheet located in an outer layer. 2. The method of manufacturing a multilayer ceramic substrate according to claim 1, wherein the through holes are formed at the same position in all the green sheets. 3. The method of manufacturing a multilayer ceramic substrate according to claim 1, wherein the size of the conductive paste pattern is gradually enlarged from the outer layer toward the inner layer. 4. The method for manufacturing a multilayer ceramic substrate according to claim 3, wherein the size of the conductive paste pattern is set in accordance with the shrinkage distribution of each green sheet. In the green sheet where the through holes are formed, different opening diameter in the front and back of the green sheet, the inner wall of any one of claims 1, wherein the forming the through hole so that the tapered surface 4 For producing a multilayer ceramic substrate. 5. The method for manufacturing a multilayer ceramic substrate according to claim 1 , wherein, in the green sheet in which the through hole is formed, chamfering is performed near the opening of the through hole. The method for producing a multilayer ceramic substrate according to claim 1, wherein the firing temperature is 1000 ° C. or lower.

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