JP3948411B2 - Multilayer ceramic substrate and manufacturing method thereof - Google Patents

Description

【００５５】
表中試料番号に＊印を付したものは、本発明の範囲外である。例えば、表面電極に金属箔が覆っていないものは、層間でショートしているものが、１２％発生したため不合格である。
それに対し、本発明の範囲内のものは銅箔、銀箔いずれも層間ショートが発生しないか発生しても１０００個中１個であり、所望の特性を充分満足するものであった。
【００５６】
【発明の効果】
以上のように、本発明によれば、積層体の外層に形成された表面配線導体は密度が高く緻密な金属箔で覆われているので、焼結体でできた表面電極内部やビアホール導体内部にめっき液や水が侵入しにくくなり、製品化後の使用中に導通が不良となったり、層間のショートが起こりにくくなる。
【００５７】
したがって、これを用いて製品化される多層セラミック基板は電気的特性が損なわれず、またその製造方法は品質の安定を要求される高周波回路の形成に適したものとすることができる。
【図面の簡単な説明】
【図１】本発明で得られる多層セラミック基板の断面図である。
【図２】本発明で得られる多層セラミック基板の製造方法を示す断面図である。
【図３】本発明で得られる多層セラミック基板の製造方法を示し、図２（ａ）の後に実施される製造方法を示す断面図である。
【図４】本発明で得られる多層セラミック基板の製造方法を示し、図２（ｄ）および図３（ｄ）で示す製造方法の変形例を示す断面図である。
【符号の説明】
１１…多層セラミック基板
１２…セラミック層
１３…積層体
１４…表面電極
１５…金属箔（回路パターン）
１６…めっき膜
１７…表面配線導体
１８…電極
１９…生の積層体
２１…セラミックグリーンシート
２２…積層体の外層に位置する所定のセラミックグリーンシート
３１…ビアホール導体
３２…外側拘束層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer ceramic substrate and a method for manufacturing the same, and more particularly to an improvement for preventing a plating solution from entering a surface electrode and a via hole in a plating process.
[0002]
[Prior art]
In recent years, there has been an increasing demand for stabilizing the quality of multilayer ceramic substrates on which semiconductor elements such as ICs and LSIs with higher frequency and higher density are mounted without impairing electrical characteristics.
[0003]
As described in Patent Document 1, for example, a multilayer ceramic substrate is generally manufactured as follows.
[0004]
First, a slurry obtained by mixing a low-temperature sintered ceramic raw material powder, an organic binder, and an organic solvent is formed into a sheet by a sheet forming method such as a doctor blade method to produce a ceramic green sheet. Next, a through hole for forming a via-hole conductor is punched into the ceramic green sheet, and the through hole is filled with a conductive paste containing a metal such as copper or silver. An electrode is formed by a screen printing method or the like using a conductive paste. Next, a heating process for removing the binder is performed on the raw laminate obtained by laminating a plurality of ceramic green sheets and pressing in the laminating direction, and then a firing process. Finally, in order to enable soldering for mounting semiconductor elements such as IC and LSI, a plating process is performed in which the surface electrode formed on the outer surface of the fired laminate is covered with a plating film .
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 05-167254
[Problems to be solved by the invention]
By the way, according to the method for manufacturing a multilayer ceramic substrate as described above, the wiring conductors such as the electrodes and the via-hole conductors are made of a sintered body of a conductive paste. That is, the conductive paste contains not only the metal powder but also a resin, a solvent and other additives. In the drying process, the solvent is volatilized, and in the firing process, the resin and the additive are thermally decomposed or decomposed. Since the wiring conductor is formed by sublimation and sintering of the metal powder and a part of the additive, it is inevitable that voids and grain boundaries exist inside the wiring conductor. As a result, in the plating process performed after the firing process, a cleaning solution such as a plating solution or water enters the voids and grain boundaries and remains after the product is completed, resulting in poor conduction during use. Or problems such as short circuit between layers occur.
[0007]
Accordingly, an object of the present invention is to provide a method for manufacturing a multilayer ceramic substrate and a multilayer ceramic substrate obtained by this manufacturing method, which can solve the above-described problems.
[0008]
[Means for Solving the Problems]
The present invention is first directed to a multilayer ceramic substrate having a laminated body constituted by a plurality of laminated ceramic layers and a surface electrode formed of a conductive paste on the outer surface of the ceramic substrate, In order to solve this technical problem, the following configuration is provided.
[0009]
That is, in the multilayer ceramic substrate according to the present invention, after the via hole conductor is formed in the ceramic layer, the end portion of the via hole conductor is covered with the surface electrode, and the end of the via hole conductor is included in the surface electrode. At least a part of the part corresponding to the part is covered with a metal foil, and the surface electrode and the metal foil are covered with a plating film.
[0011]
The aforementioned metal foil preferably covers all of the surface electrodes.
[0012]
The aforementioned metal foil is preferably copper.
[0013]
The method for manufacturing a multilayer ceramic substrate according to the present invention is characterized in that the following steps are performed in order to solve the above-described technical problem.
[0014]
First, a ceramic green sheet preparation step of preparing a ceramic green sheet is performed.
[0015]
Next, an electrode forming process is performed in which an electrode is formed on the ceramic green sheet using a conductive paste.
[0016]
Next, a metal foil forming process is performed in which at least a part of the surface electrode formed on the predetermined ceramic green sheet is covered with the metal foil.
[0017]
Next, a lamination process is performed in which a plurality of ceramic sheets are laminated with the predetermined ceramic green sheet as an outer layer to obtain a laminate.
[0018]
Next, a firing step for firing the laminate is performed.
[0019]
Next, a plating step is performed in which the surface electrode and the metal foil formed on the outer surface of the fired laminate are covered with a plating film.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a multilayer ceramic substrate 11 of the present invention. The multilayer ceramic substrate 11 includes a laminated body 13 including a plurality of laminated ceramic layers 12, an electrode 18 formed on the ceramic layer 12, and a surface electrode 14 formed on the outer layer of the ceramic layer 12. A metal foil 15 is formed so as to cover the surface electrode 14, and a plating film 16 is further formed so as to cover the surface electrode 14 and the metal foil 15.
[0021]
The illustrated multilayer ceramic substrate 11 is shown in a simplified manner in order to avoid complication of the drawing. An actual multilayer ceramic substrate includes a substrate in which a larger number of ceramic layers are laminated, a substrate in which a large number of electrodes and a large number of via holes are formed.
[0022]
FIG. 2 shows a method for manufacturing the multilayer ceramic substrate 11 shown in FIG.
[0023]
First, as shown in FIG. 2A, a ceramic green sheet 21 is prepared. The ceramic green sheet 21 preferably includes a low-temperature sintered ceramic material in order to enable simultaneous firing with the metal foil 15 such as copper in a firing step described later.
[0024]
The ceramic green sheet 21 is, for example, a mixture of barium oxide, silicon oxide, alumina, calcium oxide and boron oxide powder, a binder made of polyvinyl butyral, a plasticizer made of di-n-butyl phthalate, toluene and A paste (slurry) obtained by mixing with a solvent composed of propylene alcohol can be obtained by molding into a sheet by the doctor blade method or the like and drying it.
[0025]
As the low-temperature sintered ceramic material contained in the ceramic green sheet 21, in addition to the one that glass is generated at the time of firing, by previously containing a sintering aid such as glass, copper oxide, magnesium oxide, etc., at a lower temperature. A composition that can be sintered may be used. Moreover, you may use things other than said example also about the binder, the plasticizer, and solvent which are contained in the ceramic green sheet 21. FIG.
[0026]
Further, on the ceramic green sheet 21, an inorganic material having a composition different from that of the low-temperature sintered ceramic, such as alumina, mullite, aluminum nitride, glass ceramic, zirconia, anorthite, forsterite, cordierite, and a softening point of 780 ° C .: grain You may apply the paste (slurry) which added and mixed the borosilicate glass powder of 1.5 micrometers in diameter so that it might become 15-60 vol%. The glass to be added to the inorganic material may be any glass as long as it has a viscosity of 106.7 Pa · s-1 or less at the firing temperature or less and fills the gaps between the inorganic powders. It may be a crystallized glass whose viscosity increases after it has been converted, or an oxide mixture in which a liquid phase is generated just before the end of firing. Furthermore, at a temperature range of 850 to 950 ° C. in which the ceramic green sheet 21 is contracted, the viscosity does not decrease excessively until it works as a sintering aid for the inorganic layer or flows out from the inorganic layer. If it is.
[0027]
Further, although the inorganic material is formed on the low-temperature sintered ceramic green sheet, the low-temperature sintered ceramic green sheet may be formed after forming the inorganic material into a sheet shape.
[0028]
Next, as shown in FIG. 2B, the electrode 18 is formed on the ceramic green sheet 21 by a screen printing method or the like. Further, the surface electrode 14 is similarly formed on a predetermined ceramic green sheet 22 to be an outer layer of the laminated body in a laminating process described later. At this time, a predetermined amount of an organic vehicle is added to a conductive powder mainly composed of metals such as Ag, Au, Cu, Ni, Ag / Pd, and Ag / Pt as a conductive paste, and the mixture is stirred and kneaded with a lykai machine and three rolls. Use the paste. The center particle size and particle shape of the conductive powder are not particularly limited, but those having a center particle size of 0.1 to 10 μm and no coarse powder or extreme agglomerated powder are desirable. The organic vehicle is a mixture of a binder resin and a solvent. Although not particularly limited, ethyl cellulose, acrylic resin, polyvinyl butyral, methacrylic resin, or the like is used as the binder resin. Tall acetate, alcohols, etc. are used. Moreover, you may add various dispersing agents, a plasticizer, and an activator as needed. Furthermore, in order to measure shrinkage matching with the ceramic, 0 to 70% of metal oxide such as glass frit and Cu2O, ceramic powder, and resin powder may be added. The paste viscosity may be 50 to 700 Pa · s−1 in consideration of printability.
[0029]
Next, a metal foil is formed so as to cover the surface electrode 14 with respect to a predetermined ceramic green sheet 22 to be an outer layer of the laminated body in a laminating process described later. For example, a copper foil having a conductivity of 1.0 × 10 5 Ω−1 · cm −1 or more and a photosensitive film are sequentially pasted on a base film, masked with a glass original plate on which a predetermined circuit pattern is formed, and exposed. After the development, etching is performed with ammonium peroxodisulfate or ferric chloride, and then the resist is peeled off to form the metal foil 15. Although the effect of the present invention can be further improved by using copper for the metal foil 15, it may be composed mainly of silver, nickel, palladium, tungsten, gold, platinum or the like.
[0030]
Next, as shown in FIG. 2C, the metal foil 15 is transferred to the surface electrode 14 formed on the predetermined ceramic green sheet 22 to form the surface wiring conductor 17. At this time, in order to improve the adhesion between the metal foil 15 and the surface electrode 14, the surface of the metal foil 15 to be transferred to the surface electrode 14 is preferably roughened to the extent that the high frequency characteristics do not cause a problem. Furthermore, both surfaces of the metal foil 15 are preferably roughened so as not to cause a problem with high-frequency characteristics, in order to improve the adhesion between the metal foil 15 and the plating film 16 formed in the plating process described later. Further, when transferring, it is preferable to apply a pressure of about 100 kg / cm @ 2 and press contact. Further, if a resin adhesive that is burned off by baking is applied to the metal foil 15 in advance, the adhesion with the surface electrode 14 during transfer can be obtained more strongly. Further, the transfer may be performed after forming a laminate described later.
[0031]
The metal foil 15 to be transferred is transferred so as to be in contact with at least the surface electrode 14 existing on a predetermined ceramic green sheet 22. Furthermore, if the metal foil 15 is transferred so as to cover the entire surface electrode 14, the effect of the present invention can be improved.
[0032]
Next, as shown in FIG. 2 (d), the ceramic green sheet 21 on which the electrodes 18 are formed is arranged on the inner layer, and a predetermined ceramic green sheet 22 on which the surface wiring conductor 17 is formed is arranged on the outer layer, and if necessary A plurality of inner ceramic green sheets 21 are laminated and thermocompression bonded under conditions of a temperature of 80 ° C. and a pressure of 200 kg / cm 2 to form a raw laminate 19. The raw laminate 19 is fired in a reducing atmosphere at a temperature of 900 ° C. for 1 hour to obtain a desired multilayer ceramic substrate. Note that the metal foil 15 may be formed after the ceramic green sheets 21 on which the electrodes 18 are formed are disposed in the inner layer and the outer layer, stacked, and fired. However, in this case, after forming the metal foil 15, it is necessary to fire again at a temperature equal to or lower than the melting point of the metal foil 15 so that the metal foil 15 and the surface electrode 14 are electrically connected.
[0033]
Next, as shown in FIG. 2E, a Ni and Au plating film 16 is formed so as to cover the surface electrode 14 and the metal foil 15. The Ni plating is performed by using, for example, an aqueous solution containing NiSO4, copper sulfate, tartaric acid, sodium hydroxide, formaldehyde and the like as an electroless plating solution at a temperature of 50 ° C. to 100 ° C. for about 0.5 to 10 μm. Therefore, it is immersed in a plating bath solution having a pH of 4 to 5 for about 5 to 150 minutes. After the precipitation, washing with water is performed. Subsequently, in Au plating, in order to deposit about 0.01 to 5.0 μm using an aqueous solution containing AuCN as a main component, it is immersed in a plating bath solution of pH 7 to 8 for about 5 to 150 minutes. After the precipitation, washing with water is performed.
[0034]
At this time, since the surface wiring conductor 17 formed in the outer layer is covered with the dense and dense metal foil 15, the plating solution and water are less likely to enter the inside of the surface electrode 14 made of a sintered body, Conductivity is poor during use after commercialization, and short-circuiting between layers is less likely to occur.
[0035]
FIG. 3 shows a manufacturing method for performing a via hole conductor forming step in addition to the manufacturing method shown in FIG. 3, elements corresponding to those shown in FIG. 2 are denoted by the same reference numerals, and redundant description is omitted.
[0036]
In this manufacturing method, first, as shown in FIG. 2A, a ceramic green sheet 21 is prepared.
[0037]
Next, as shown in FIG. 3A, a hole is formed so as to penetrate the ceramic green sheet 21 by a punch, and the hole is filled with a conductive paste by a screen printing method to form a via-hole conductor 31. . At this time, a predetermined amount of an organic vehicle is added to a conductive powder mainly composed of a metal such as Ag, Au, Cu, Ni, Ag / Pd, or Ag / Pt as a conductive paste, and the mixture is stirred with a reiki machine and three rolls. A kneaded paste is used. The center particle size and particle shape of the conductive powder are not particularly limited, but those having a center particle size of 0.1 to 10 μm and no coarse powder or extreme agglomerated powder are desirable. The organic vehicle is a mixture of a binder resin and a solvent, and although not particularly limited, ethyl cellulose, acrylic resin, polyvinyl butyral, methacrylic resin, or the like is used as the binder resin. As the solvent, terpineol, butyl carbitol, butyl carbitol acetate, alcohols and the like are used. Moreover, you may add various dispersing agents, a plasticizer, and an activator as needed. Further, in order to measure shrinkage matching with ceramic, 0 to 70% of metal oxide such as glass frit and Cu ₂ O, ceramic powder and resin powder may be added. The paste viscosity may be 50 to 700 Pa · s−1 in consideration of printability.
[0038]
Next, as shown in FIG. 3B, the electrode 18 is formed on the ceramic green sheet 21 by a screen printing method or the like so as to cover the end portion of the via-hole conductor 31 formed in the ceramic green sheet 21. Further, the surface electrode 14 is similarly formed so as to cover the end portion of the via-hole conductor 31 with respect to a predetermined ceramic green sheet 22 to be an outer layer of the multilayer body in a laminating process described later. The formation method and materials used are the same as in the manufacturing method of FIG.
[0039]
Next, as shown in FIG. 3C, a metal foil 15 is formed so as to cover the surface electrode 14 with respect to a predetermined ceramic green sheet 22 to be an outer layer of the laminated body in a laminating process to be described later. 17 is formed. The formation method and materials used are the same as in the manufacturing method of FIG. At this time, the metal foil 15 can obtain the effect of the present invention by covering at least a part of the surface electrode 14 corresponding to the end of the via-hole conductor 31, but if the transfer is performed so as to cover the entire surface electrode 14. Thus, the effects of the present invention can be improved.
[0040]
Next, as shown in FIG. 3 (d), the ceramic green sheet 21 on which the electrodes 18 are formed is disposed on the inner layer, and a predetermined ceramic green sheet 22 on which the surface wiring conductor 17 is formed is disposed on the outer layer. Then, a plurality of inner ceramic green sheets 21 are laminated and thermocompression bonded to form a raw laminate 19. The raw laminate 19 is fired in a reducing atmosphere at a temperature of 900 ° C. for 1 hour to obtain a desired ceramic multilayer substrate. The lamination method, firing method, and the like are the same as the manufacturing method of FIG.
[0041]
Next, as shown in FIG. 3E, a Ni and Au plating film 16 is formed so as to cover the surface electrode 14 and the metal foil 15. The plating method and materials used are the same as in the manufacturing method of FIG.
[0042]
At this time, the surface wiring conductor 17 formed in the outer layer is covered with the dense and dense metal foil 15, so that the plating solution or the like is formed inside the surface electrode 14 made of a sintered body or inside the via-hole conductor 31. Water is less likely to enter, resulting in poor continuity during use after commercialization and short circuit between layers.
[0043]
FIG. 4 is a view for explaining a modification of the laminating process in the manufacturing method of FIGS. 2 and 3 when the non-shrink process using the outer constraining layer 32 is applied. 4, elements corresponding to those shown in FIGS. 2 and 3 are denoted by the same reference numerals, and redundant description is omitted.
[0044]
If it demonstrates with reference to FIG. 4, a baking process will be implemented in the state which has arrange | positioned the outer constrained layer 32 so that the raw laminated body 19 may be pinched | interposed in the lamination direction. The outer constraining layer 32 is a sheet-like slurry obtained by adding an appropriate binder and solvent to the inorganic material powder for shrinkage suppression not sintered at the sintering temperature of the ceramic material powder contained in the ceramic green sheet 21, and mixing them. It is obtained by molding into
[0045]
As described above, when the ceramic material powder contained in the ceramic green sheet 21 is a low-temperature sintered ceramic material powder that can be sintered at a temperature of 1000 ° C. or less, for example, the shrinkage-suppressing material contained in the outer constraining layer 32 is suppressed. As the inorganic material powder, for example, at least one of alumina, mullite, aluminum nitride, zirconia, anorthite, forsterite and cordierite is advantageously used.
[0046]
Since the inorganic material powder for shrinkage suppression contained in the outer constraining layer 32 is not substantially sintered in the firing step, no substantial shrinkage occurs in the outer constraining layer 32. Accordingly, the shrinkage suppressing action by the outer constraining layer 32 is exerted on the raw laminate 19, and the raw laminate 19 contracts in the thickness direction but in the main surface direction of the ceramic green sheet 21. Is less likely to shrink.
[0047]
As a result, the dimensional accuracy of the sintered laminate shown in FIGS. 2D and 3D can be increased, and the density of the wiring provided by the surface electrode 14 and the via-hole conductor 31 is increased. Can be achieved with reliability.
[0048]
After the firing step, the outer constraining layer 32 is removed by, for example, sandblasting.
[0049]
Further, as a modified example of the ceramic green sheet preparation step in the manufacturing method of FIGS. 2 and 3, there is no shrinkage in which constraining layers are provided not only on the outer ceramic green sheet of the raw laminate 19 but also on each inner ceramic green sheet. You may apply the process.
[0050]
Next, the operation and effect of the present invention will be described based on the experimental results in the manufacturing method shown in FIG.
[0051]
First, a voltage of 5 V was applied to the surface wiring conductor 17 of the multilayer ceramic substrate obtained after the plating step shown in FIG. 3E by a digital multimeter and left for 100 hours in a steady state.
[0052]
Next, the insulation resistance of the sample after 100 hours was measured with a digital multimeter, and those having a resistance value of 1 × 10 9 Ω or less were determined to be defective. The above was rejected.
[0053]
Table 1 summarizes the evaluation results of this experiment.
[0054]
[Table 1]

[0055]
A sample number marked with * in the table is outside the scope of the present invention. For example, when the surface electrode is not covered with the metal foil, 12% of the short-circuited layers are rejected.
On the other hand, within the scope of the present invention, both the copper foil and the silver foil did not cause an interlayer short-circuit, and even when it occurred, it was 1 in 1000, and sufficiently satisfied the desired characteristics.
[0056]
【The invention's effect】
As described above, according to the present invention, the surface wiring conductor formed in the outer layer of the laminate is covered with a dense and dense metal foil, so that the inside of the surface electrode made of a sintered body or the inside of the via-hole conductor It is difficult for the plating solution or water to penetrate into the film, resulting in poor continuity during use after commercialization or short circuit between layers.
[0057]
Therefore, the multilayer ceramic substrate that is commercialized using this is not impaired in electrical characteristics, and the manufacturing method thereof can be suitable for the formation of a high-frequency circuit that requires stable quality.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a multilayer ceramic substrate obtained by the present invention.
FIG. 2 is a cross-sectional view showing a method for producing a multilayer ceramic substrate obtained by the present invention.
FIG. 3 is a cross-sectional view illustrating a method for manufacturing a multilayer ceramic substrate obtained by the present invention and illustrating the manufacturing method performed after FIG. 2 (a).
FIG. 4 is a cross-sectional view showing a method for manufacturing a multilayer ceramic substrate obtained by the present invention and showing a modification of the manufacturing method shown in FIGS. 2 (d) and 3 (d).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Multilayer ceramic substrate 12 ... Ceramic layer 13 ... Laminated body 14 ... Surface electrode 15 ... Metal foil (circuit pattern)
DESCRIPTION OF SYMBOLS 16 ... Plating film 17 ... Surface wiring conductor 18 ... Electrode 19 ... Raw laminated body 21 ... Ceramic green sheet 22 ... Predetermined ceramic green sheet 31 located in the outer layer of the laminated body ... Via-hole conductor 32 ... Outer constraining layer

Claims (4)

In a multilayer ceramic substrate having a ceramic substrate composed of a plurality of laminated ceramic layers, and a surface electrode formed by a conductive paste on the outer surface of the ceramic substrate,
Via hole conductors are formed in the ceramic layer,
The end portion of the via-hole conductor is covered with the surface electrode,
Of the surface electrode, at least a part of a portion corresponding to an end portion of the via-hole conductor is covered with a metal foil, and the surface electrode and the metal foil are covered with a plating film. , Multilayer ceramic substrate. The multilayer ceramic substrate according to claim 1, wherein all of the surface electrodes are covered with the metal foil. The multilayer ceramic substrate according to claim 1, wherein the metal foil is copper. A ceramic green sheet preparation process for preparing a ceramic green sheet;
A via hole conductor forming step of forming a through hole in the thickness direction with respect to the ceramic green sheet and filling a conductive paste to form a via hole conductor;
An electrode forming step of forming an electrode using a conductive paste on the ceramic green sheet so as to cover at least an end portion of the via-hole conductor ;
A metal foil forming step of covering at least a part of a portion corresponding to an end portion of the via-hole conductor with a metal foil among surface electrodes formed on a predetermined ceramic green sheet;
A laminating step of laminating a plurality of the ceramic sheets with the predetermined ceramic green sheet as an outer layer to obtain a laminate;
A firing step of firing the laminate;
A method for producing a multilayer ceramic substrate, comprising: the surface electrode formed on the outer surface of the fired laminate; and a plating step of covering the metal foil with a plating film.

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