JP4107437B2 - Multilayer ceramic substrate and manufacturing method thereof - Google Patents

Description

  The present invention relates to a multilayer ceramic substrate having an inner conductor such as a via-hole conductor and a method for manufacturing the same, and more particularly to a technique for preventing defects around the inner conductor.

  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 always 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 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, it is possible to improve the dimensional accuracy in the in-plane direction of the multilayer ceramic substrate to, for example, about 0.05%.

  By the way, in a multilayer ceramic substrate, it is essential to form an internal conductor such as a via-hole conductor for interlayer connection. When producing the multilayer ceramic substrate, for example, a via hole is formed and filled with a conductor paste. Firing is performed. In this case, it is known that voids (defects) are generated around the inner conductor (for example, via-hole conductor) due to a difference in heat shrinkage behavior between the conductor paste and the green sheet. Such a defect is particularly noticeable in the non-shrinkage firing method.

Therefore, techniques for eliminating such defects have been studied in various directions (see, for example, Patent Documents 2 to 4). For example, in the invention described in Patent Document 2, by using a conductive composition for a multilayer ceramic substrate containing a conductive powder such as Ag and a Mo compound or a Mo metal as the conductor composition filled in the via hole, This makes it possible to produce a multilayer ceramic substrate that does not cause defects in the vicinity of the electrode after firing. Similarly, in the invention described in Patent Document 3, the via hole conductor is composed of Ag and W, so that no gap is generated between the via hole conductor and the inner wall of the via hole. In the invention described in Patent Document 4, using conductive powder coated with a metal oxide as a conductive component of the conductive paste, by increasing the shrinkage start temperature of the conductive paste, at the time of shrinkage due to firing of the ceramic molded body, The stress which restrains this is not produced.
JP-A-10-75060 JP 2003-133745 A Japanese Patent No. 2732171 Japanese Patent No. 3589239

  However, as a result of repeated investigations by the present inventors, it is not always possible to obtain satisfactory results only by controlling the shrinkage behavior of the conductive paste itself for forming the internal conductors as described in each of the above patent documents. In particular, it has been found that defects generated around the inner conductor cannot be sufficiently suppressed when a multilayer ceramic substrate is produced by the non-shrinkage firing method. For example, as described in Patent Document 4, when the surface of the conductive powder is covered with a metal oxide, there is a risk that the electrical resistance of the internal conductor will increase significantly.

  The present invention has been proposed in view of such a conventional situation, and it is an object of the present invention to reliably eliminate defects generated around the inner conductor in the multilayer ceramic substrate having the inner conductor. It is an object of the present invention to provide a highly reliable multilayer ceramic substrate and further to provide a method for producing the same.

  The present inventors have made various studies over a long period of time in order to achieve the above-mentioned object. As a result, the inventors have come to the conclusion that the occurrence of the defects can be effectively suppressed by diffusing Ti, Zr, and Mn around the inner conductor. The present invention has been completed based on such findings.

That is, the multilayer ceramic substrate of the present invention is a multilayer ceramic substrate having a plurality of glass ceramic layers laminated and having an internal conductor, wherein the internal conductor contains Ag as a conductive material and is made of Ti or Zr. Containing at least one selected oxide, wherein the glass ceramic layer around the inner conductor contains at least one selected from Ti or Zr as a diffusing element diffused from the inner conductor, and the diffusion The region where the element is present is a region whose distance from the inner conductor is 100 μm or less, and in the region where the diffusion element is present, the content of the diffusion element in the glass ceramic layer is 0.1 mass in terms of oxide. % To 50% by mass.

In the method for producing a multilayer ceramic substrate of the present invention, a conductive pattern made of a conductive paste containing Ag as a conductive material is formed on at least a part of a plurality of glass ceramic green sheets, and then laminated and fired. A method for producing a multilayer ceramic substrate, comprising adding at least one oxide selected from Ti or Zr to the conductor paste, and surrounding at least one selected from Ti or Zr as a diffusing element during the firing Diffuse into the glass ceramic sheet,
Around the inner conductor of the glass ceramic layer, the region where the diffusing element exists is a region having a distance of 100 μm or less from the inner conductor, and in the region where the diffusing element exists, the glass ceramic layer contains the diffusing element. The amount is 0.1% by mass to 50% by mass in terms of oxide.

  When firing a multilayer ceramic substrate having an internal conductor, defects are considered to occur due to differences in thermal shrinkage between the internal conductor and the glass ceramic layer (glass ceramic green sheet). The main focus is on eliminating the difference in thermal shrinkage between the conductor and the glass ceramic layer. However, as a result of detailed studies by the present inventors, the inner conductor (for example, silver) diffuses to the surroundings at the time of firing, and the sintering start temperature of this portion of the glass ceramic decreases, resulting in heat shrinkage with other portions. It has been found that differences occur and the defects occur.

  In the present invention, at least one selected from Ti, Zr, and Mn is diffused in the glass ceramic layer around the inner conductor, thereby eliminating a decrease in sintering start temperature due to diffusion of silver or the like. Therefore, in the multilayer ceramic substrate of the present invention, there is no difference in the sintering start temperature of the glass ceramic layer around the inner conductor, and the sintering of the glass ceramic layer in the vicinity of the inner conductor starts before the other portions. Generation of voids is suppressed. In addition, when Mo and W are added to the via-hole conductor as described in Patent Documents 2 and 3, Mo and W may be diffused around the inner conductor, but Mo and W are temporarily diffused around the inner conductor. Even if it does, the fall of the sintering start temperature by Ag spreading | diffusion cannot be eliminated, but generation | occurrence | production of the space | gap resulting from this cannot fully be suppressed.

  According to the present invention, it is possible to suppress the generation of voids due to the difference in the sintering start temperature of the glass ceramic layer in the vicinity of the internal electrode, and it is possible to reliably eliminate defects generated around the internal conductor. Therefore, according to the present invention, it is possible to provide a multilayer ceramic substrate having no defects and high reliability.

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

  As shown in FIG. 1, a multilayer ceramic substrate 1 of the present invention is formed by laminating a plurality of glass ceramic layers 2 (here, four glass ceramic layers 2a to 2d) and penetrating through these glass ceramic layers 2a to 2d. An internal conductor such as a surface conductor 4 formed on both surfaces of the via-hole conductor 3 and the glass ceramic layers 2a to 2d is provided.

Each glass ceramic layers 2a~2d are those formed by firing plus the composite oxide such as alumina (Al 2 _{O 3)} having a predetermined glass composition. Here, as each oxide constituting the composite oxide having a glass composition, SiO ₂ , B ₂ O ₃ , CaO, SrO, BaO, La ₂ O ₃ , ZrO ₂ , TiO ₂ , MgO, ZnO, PbO, Li ₂ O, Na ₂ O, K ₂ O, and the like can be given, and these may be used in appropriate combination. By making each ceramic layer constituting the multilayer ceramic substrate 1 the glass ceramic layer, firing at a low temperature becomes possible.

  On the other hand, the via-hole conductor 3 among the internal conductors is formed in such a manner that the via hole formed in each of the glass ceramic layers 2a to 2d is filled with a conductive material remaining by firing of the conductive paste. Thus, the surface conductors 4 formed on the ceramic layers 2a to 2d are electrically connected to each other and functions to conduct heat are performed. The cross-sectional shape of the via-hole conductor 3 is generally 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, an elliptical shape, an oval shape, a square shape, etc. can do.

  The internal conductors such as the via-hole conductor 3 and the surface conductor 4 are all formed by firing a conductor paste. For example, when silver (Ag) is contained as a conductor, the glass-ceramic layers 2a to 2d are formed during firing. And the sintering start temperature differs between the glass ceramic layer around the inner conductor and the glass ceramic layer in other portions.

  Therefore, in the present invention, at least one selected from Ti, Zr, and Mn is diffused in the portion around the inner conductor of the glass ceramic layers 2a to 2d to eliminate the difference in the sintering start temperature.

  FIG. 2 is a diagram for explaining a mechanism of defect generation near the via-hole conductor 3. When the via hole formed in the ceramic substrate 11 to be the glass ceramic layers 2a to 2d after firing is filled with the conductor paste 12 and fired, as shown in FIG. Ag in the conductor paste 12 diffuses into the surrounding ceramic substrate 11. And in the area | region 11a in which said Ag diffused among this ceramic base 11, the sintering start temperature falls and sintering starts before the other part 11b of the ceramic base 11. FIG. At this time, in the region 11a, the sintering starts and contracts, whereas in the other portion 11b, the sintering does not start and thus does not contract, and a gap 13 is generated due to the difference between these contractions.

  When the temperature further increases, as shown in FIG. 2 (b), sintering also begins in the other part 11b of the ceramic substrate 11, and along with this, pull-in as indicated by the outward arrows begins. At this time, the sintering of the conductor paste 12 starts, and the shrinkage as shown by the arrow toward the inside occurs around the conductor paste 12, and the gap 13 is enlarged. As a result, as shown in FIG. 2C, a large gap (defect) 13 is formed around the via-hole conductor 3 formed by firing the conductor paste 12 when the sintering is completed.

  In consideration of such a defect generation mechanism, it is considered effective to suppress a decrease in the sintering start temperature of the ceramic substrate 11 around the conductor paste due to the diffusion of Ag. Ti, Zr, and Mn are highly effective in suppressing a decrease in the sintering start temperature of the ceramic substrate 11, and for example, by diffusing them around the via-hole conductor 3 and the surface conductor 4, the generation of the defects is suppressed. It is possible.

  FIG. 3 shows a state in which a diffusion region 2A is formed by diffusing at least one selected from Ti, Zr, and Mn into the glass ceramic layer 2 around the via-hole conductor 3 as a diffusing element. In the diffusion region 2A, each of the elements is diffused as a diffusion element, and functions to suppress a decrease in the sintering start temperature due to the diffusion of the Ag.

In this case, the diffusing element is considered to exist in the form of an oxide such as TiO ₂ , ZrO ₂ , MnO _2, etc., but is not limited to this and diffuses into the glass ceramic layer 2 in any form. It is sufficient that the element is diffused. Further, here, the periphery of the via-hole conductor 3 has been described as an example. However, the present invention is not limited to this, and the diffusion element may be diffused around the surface conductor 4, including the via-hole conductor 3 and the surface conductor 4. It is preferable that the diffusing element is diffused around all the inner conductors.

  If the diffusion range of the diffusing element, that is, the diffusion distance L from the via-hole conductor 3 in the diffusion region 2A is too large, the effect may be lost, and it is preferable that the diffusion range is approximately 100 μm or less. The content of the diffusing element in the diffusion region 2A is preferably 0.1% by mass to 50% by mass. If the content of the diffusing element is less than 0.1% by mass, the sintering start temperature cannot be sufficiently increased, and defects may occur. On the other hand, if the content of the diffusing element exceeds 50% by mass, the sintering start temperature of the ceramic body around the inner conductor becomes too high, and the sintering starts earlier at a part farther from the inner conductor. There is a risk of occurrence.

  The diffusing element may be included as a constituent element of the ceramic substrate. In this case, it is sufficient that the content of the diffusing element is relatively higher than the other parts around the inner conductor. . Therefore, in this case, the regulation of the content of the diffusing element (0.1% by mass to 50% by mass) is a difference in content between the periphery of the inner conductor and other parts.

  As described above, in order to diffuse the diffusing element in the glass ceramic layer around the inner conductor, for example, the diffusing element may be added to a conductor paste for forming the inner conductor and fired. Hereinafter, a method for manufacturing the multilayer ceramic substrate 1 will be described.

  In order to produce a multilayer ceramic substrate, first, as shown in FIG. 4A, glass ceramic green sheets 21a to 21d to be glass ceramic layers after firing are prepared. The glass ceramic green sheets 21a to 21d make a slurry-like dielectric paste obtained by mixing the above-mentioned oxide powder and an organic vehicle, and this is formed on a support such as a polyethylene terephthalate (PET) sheet by a doctor blade. It is formed by forming a film by a method or the like. Any known organic vehicle can be used.

  After the glass ceramic green sheets 21a to 21d are formed, through holes (via holes) are formed at predetermined positions. The front via hole is usually formed as a circular hole, and a via hole conductor is formed by filling the conductor paste 22 therein. Further, a conductive paste is printed in a predetermined pattern on the surface of each glass ceramic green sheet 21 a to 21 d to form a surface conductor pattern 23.

  The conductive paste 22 used to form the conductive paste 22 and the surface conductive pattern 23 filled in the via hole includes, for example, conductive materials made of various conductive metals and alloys such as Ag, Ag-Pd alloy, Cu, Ni, and organic vehicles. However, when Ag is used, the above-mentioned defect problem is particularly remarkable. Therefore, the application of the present invention is effective when a conductor paste using Ag as a conductive material is employed. It is.

  In the conductive paste, the organic vehicle is mainly composed of a binder and a solvent, and the mixing ratio of the conductive material is arbitrary, but the binder is usually 1 to 15% by mass, and the solvent is 10 to 50% by mass. It mix | blends with respect to an electrically-conductive material so that it may become. Additives selected from various dispersants, plasticizers and the like may be added to the conductor paste as necessary.

In the present invention, a diffusing element (Ti, Zr, Mn) is further added to the conductor paste and diffused into the glass ceramic green sheets 21a to 21d during firing. In this case, the diffusion element added to the conductive paste may be an oxide of each element (TiO ₂ , ZrO ₂ , MnO ₂ ), or may be added in a metal state. The addition amount of the diffusing element to the conductor paste is preferably set so that the diffusion amount into the glass ceramic green sheets 21a to 21d is within the above range, and the addition amount may be set in consideration of firing conditions and the like. .

  Further, in order to diffuse the diffusing elements into the glass ceramic green sheets 21a to 21d, in addition to adding the diffusing elements to the conductor paste as described above, for example, after applying a paste containing the diffusing element on the inner wall of the via hole Alternatively, a conductive paste containing a conductive material may be filled.

  After filling each glass ceramic green sheet 21a-21d with the conductor paste 22 used as an internal conductor and forming the surface conductor pattern 23, as shown in FIG.4 (b), these are piled up and it is set as a laminated body, At this time, the shrinkage-suppressing green sheets 24 are disposed as constraining layers on both sides (outermost layers) of the laminate and fired.

  The shrinkage-suppressing green sheet 24 is made of a material that does not shrink at the firing temperature of the glass ceramic green sheets 21a to 21d, such as tridymite and cristobalite, quartz, fused quartz, alumina, mullite, zirconia, aluminum nitride, boron nitride, and oxide. A composition containing magnesium, silicon carbide, or the like is used, and the laminate is sandwiched between the shrinkage-suppressing green sheets 24 and fired, whereby shrinkage in the in-plane direction of the laminate is suppressed.

  FIG. 4B is a so-called temporary stack state of a laminated body. Next, pressing is performed as shown in FIG. 4C, and baking is performed as shown in FIG. 4D. In firing, it is preferable to control the firing temperature, firing time, and the like so that the diffusion amount and diffusion distance of the diffusing element are appropriate. After firing, the glass ceramic green sheets 21a to 21d become glass ceramic layers 2a to 2d, and the conductor paste 23 in the via hole becomes the via hole conductor 3. Similarly, the surface conductor pattern 24 also becomes the surface conductor 4.

  In the firing, each of the glass ceramic green sheets 21a to 21d is shrunk with firing, but in the outermost glass ceramic green sheets 21a and 21d, the restraining force of the shrinkage-suppressing green sheet 24 acts strongly and almost shrinks. Not done. On the other hand, since the glass ceramic green sheets 21b and 21c in the central portion in the stacking direction are separated from the shrinkage-suppressing green sheet 24, their restraining force is weak and contracts to some extent. Accordingly, defects such as voids are likely to occur around the inner conductor, for example, around the via-hole conductor 3, but the diffusing element diffuses from the conductor paste 23 and the surface conductor pattern 24 into the surrounding glass ceramic green sheets 21a to 21d. And since the fall of the sintering start temperature by the spreading | diffusion of Ag which is an electrically-conductive material is suppressed, generation | occurrence | production of defects, such as the said space | gap, is suppressed reliably.

  After firing, as shown in FIG. 4E, the shrinkage-suppressing green sheet 24 is naturally peeled due to the difference in thermal expansion, and the multilayer ceramic substrate 1 of the present invention is obtained. In the obtained multilayer ceramic substrate 1, no defects are generated around the inner conductor (via-hole conductor 3 or surface conductor 4), and a highly reliable multilayer ceramic substrate can be realized.

  The defect prevention effect due to diffusion of the diffusing element is great when the above-described shrinkage-suppressing green sheet 24 is disposed and fired without shrinkage. However, the invention is not limited to this, and the shrinkage-suppressing green sheet is used. The same effect can be obtained even when not.

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

Elucidation of defect generation mechanism A through-hole was formed in a glass ceramic green sheet, and a conductive paste serving as a via-hole conductor was filled therein and fired. The material composition of the glass ceramic green sheet is SiO ₂ 32.87 mass%, B ₂ O ₃ 2.19 mass%, Al ₂ O ₃ 44.53 mass%, MgO 1.07 mass%, CaO 1.98 mass%, SrO17. .36% by mass. As the conductive paste, a conductive paste containing Ag as a conductive material was used. Firing was performed by a non-shrinkage firing method by providing a shrinkage-suppressing green sheet (constraint layer) containing α-quartz and tridymite.

  FIG. 5 is a photomicrograph showing the vicinity of the via-hole conductor after firing. A void is formed around the via-hole conductor, but this void is not formed at the interface between the via-hole conductor and the ceramic substrate, and a ceramic substrate exists between the via-hole conductor and the void. Therefore, an analysis of the composition of the ceramic substrate existing between the via-hole conductor and the gap revealed that Ag diffused from the via-hole conductor was included.

  On the other hand, Ag was added to the glass ceramic material composition to examine the difference in shrinkage. Three types were measured: the glass ceramic material composition (no Ag added), the glass ceramic material composition added with 2% by mass of Ag, and the glass ceramic material composition added with 4% by mass of Ag. When measuring the shrinkage rate, the state of shrinkage was examined while gradually raising the temperature. The results are shown in FIG. As is apparent from FIG. 6, it was found that by adding Ag, shrinkage started at a low temperature, and the sintering start temperature was lowered by diffusion of Ag into the glass ceramic substrate.

  From these measurement results, there is a difference in the sintering start temperature between the glass ceramic substrate around the inner conductor and the other portion of the glass ceramic substrate, and defects are generated by the mechanism shown in FIGS. 2 (a) to (c). Presumed to be.

Confirmation of effect by diffusion of Ti, Zr, Mn TiO ₂ , ZrO ₂ , MnO ₂ was added to a conductive paste containing Ag as a conductive material, and filled in a through hole of a glass ceramic green sheet having the same material composition as described above. . And the shrinkage | contraction suppression green sheet (constraint layer) which contains (alpha) quartz and tridymite was distribute | arranged on both sides, and it baked by the non-shrinkage baking method. The diffusion distance of the diffusion element (distance L from the via-hole conductor) in the glass ceramic layer after firing was measured, the content of the diffusion element in the diffusion region was measured, and the presence or absence of defects was further examined. Since ZrO ₂ is also included in the material composition of the glass ceramic layer, the increase in the diffusion region was measured. For comparison, the same measurement was performed when MoO ₃ or WO ₃ was added to the conductor paste. The results are shown in Table 1.

  As is apparent from Table 1, it can be seen that Ti, Zr, and Mn are diffused in the glass ceramic layer, so that the generation of defects is effectively suppressed. Such an effect is not obtained in the diffusion of Mo or W. However, when Ti is diffused, if the diffusion distance is too large or the diffusion amount is too large, defects cannot be eliminated, and therefore the diffusion distance and the diffusion amount must be appropriately controlled.

It is a schematic sectional drawing which shows an example of a multilayer ceramic substrate. (A)-(c) is a figure explaining the mechanism of a defect generation | occurrence | production. It is a schematic diagram which shows a mode that the diffusing element diffused around the via-hole conductor. It is typical sectional drawing which shows the manufacturing process of a multilayer ceramic substrate, (a) is a glass ceramics green sheet and internal conductor formation process, (b) is a temporary stacking process, (c) is a press process, (d) is a baking process. A process and (e) show the green sheet peeling process for shrinkage | contraction suppression. It is a microscope picture which shows the mode of the defect generation | occurrence | production of a via-hole conductor vicinity. It is a characteristic view which shows the change of the sintering start temperature by the spreading | diffusion of Ag.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multilayer ceramic substrate, 2a-2d glass-ceramics layer, 2A Diffusion area | region, 3 Via-hole conductor, 4 Surface conductor, 11 Glass-ceramics base, 12 Conductive paste, 13 Space | gap (defect), 21a-21d Glass-ceramic green sheet, 22 Conductive paste , 23 Surface conductor pattern, 24 Green sheet for shrinkage suppression

Claims (5)

A multilayer ceramic substrate having a plurality of glass ceramic layers laminated and an internal conductor,
The inner conductor contains Ag as a conductive material, and contains at least one oxide selected from Ti or Zr ,
The glass ceramic layer around the inner conductor contains at least one selected from Ti or Zr as a diffusing element diffused from the inner conductor,
The region where the diffusing element is present is a region having a distance of 100 μm or less from the inner conductor, and in the region where the diffusing element is present, the content of the diffusing element in the glass ceramic layer is 0. A multilayer ceramic substrate, wherein the content is 1% by mass to 50% by mass.   The multilayer ceramic substrate according to claim 1, wherein the inner conductor is a via-hole conductor.   3. The multilayer ceramic substrate according to claim 1, wherein the multilayer ceramic substrate is produced by a shrinkage suppression process. A method for producing a multilayer ceramic substrate comprising forming a conductive pattern made of a conductive paste containing Ag as a conductive material on at least a part of a plurality of glass ceramic green sheets, and laminating and firing them.
Adding at least one oxide selected from Ti or Zr to the conductor paste, and diffusing at least one selected from Ti or Zr as a diffusing element in the surrounding glass ceramic sheet during the firing;
Around the inner conductor of the glass ceramic layer, the region where the diffusing element exists is a region having a distance of 100 μm or less from the inner conductor, and in the region where the diffusing element exists, the glass ceramic layer contains the diffusing element. A method for producing a multilayer ceramic substrate, wherein the amount is 0.1% by mass to 50% by mass in terms of oxide.   The method for producing a multilayer ceramic substrate according to claim 4, wherein a green sheet for suppressing shrinkage is disposed on the outermost layer of the laminated glass ceramic sheets and the firing is performed.

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