JP2004241432A - Multilayered ceramic board and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayered ceramic board which is capable of preventing a plating solution from penetrating into a surface electrode and a viahole so as not to deteriorate its electric properties. <P>SOLUTION: The surface electrode and the viahole formed on the outer layer of a laminate are covered with a dense metal foil of high density so as to prevent the plating solution from penetrating into them. <P>COPYRIGHT: (C)2004,JPO&NCIPI

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]
TECHNICAL FIELD 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 step.
[0002]
[Prior art]
In recent years, there has been an increasing demand for a multilayer ceramic substrate on which a semiconductor element such as an IC or an LSI, which has been operating at a higher frequency and a higher density, to stabilize the quality so as not to impair the electrical characteristics.
[0003]
A multilayer ceramic substrate is generally manufactured as follows, for example, as described in Patent Document 1.
[0004]
First, a slurry obtained by mixing a low-temperature sintering 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 step for removing the binder is performed on the green laminate obtained by laminating a plurality of ceramic green sheets and pressing in the laminating direction, and then a firing step. Finally, in order to enable soldering for mounting semiconductor elements such as ICs and LSIs, a plating step of covering a surface electrode formed on the outer surface of the fired laminate with a plating film is performed. .
[0005]
[Patent Document 1]
Japanese Patent Application 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, wiring conductors such as electrodes and via-hole conductors are formed 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, the solvent is volatilized in the drying step, and the resin and the additive are thermally decomposed or decomposed in the firing step. 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 a 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 even after the product is completed. And short-circuits between layers occur.
[0007]
Therefore, 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 method, which can solve the above-described problems.
[0008]
[Means for Solving the Problems]
The present invention is firstly directed to a multilayer ceramic substrate having a laminate 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, In order to solve the technical problem of the present invention, the following features are provided.
[0009]
That is, in the multilayer ceramic substrate according to the present invention, at least a part of the surface electrode is covered with a metal foil, and then the surface electrode and the metal foil are covered with a plating film.
[0010]
According to the present invention, preferably, a via-hole conductor is formed in the ceramic layer, and an end of the via-hole conductor is covered with the surface electrode, and a portion of the surface electrode corresponding to the end of the via-hole conductor is provided. The present invention is also directed to a multilayer ceramic substrate, at least a part of which is covered with the metal foil.
[0011]
The aforementioned metal foil preferably covers all of the surface electrodes.
[0012]
The aforementioned metal foil is preferably made of 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-mentioned technical problem.
[0014]
First, a ceramic green sheet preparing step of preparing a ceramic green sheet is performed.
[0015]
Next, an electrode forming step of forming an electrode on the ceramic green sheet using a conductive paste is performed.
[0016]
Next, a metal foil forming step of covering at least a part of the surface electrode formed on the predetermined ceramic green sheet with a metal foil is performed.
[0017]
Next, a laminating step of laminating a plurality of the ceramic sheets using the predetermined ceramic green sheet as an outer layer to obtain a laminate is performed.
[0018]
Next, a firing step of firing the laminate is performed.
[0019]
Next, a plating step of covering the surface electrode and the metal foil formed on the outer surface of the fired laminate with a plating film is performed.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a multilayer ceramic substrate 11 of the present invention. The multilayer ceramic substrate 11 includes a laminate 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 an 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 formed so as to cover the surface electrode 14 and the metal foil 15.
[0021]
It should be noted that the illustrated multilayer ceramic substrate 11 is illustrated in a simplified manner in order to avoid complication of the drawing. Actual multilayer ceramic substrates include those in which a larger number of ceramic layers are stacked, those in which a large number of electrodes and a large number of via holes are formed, and the like.
[0022]
FIG. 2 shows a method of 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 contains a low-temperature sintered ceramic material in order to enable simultaneous firing with a metal foil 15 such as copper in a firing step described later.
[0024]
The ceramic green sheet 21 is made of, for example, a mixture of powders of barium oxide, silicon oxide, alumina, calcium oxide and boron oxide, a binder of polyvinyl butyral, a plasticizer of di-n-butyl phthalate, toluene and The paste (slurry) obtained by mixing a solvent composed of propylene alcohol can be formed into a sheet by a doctor blade method or the like, and dried to obtain a sheet.
[0025]
As the low-temperature sintering ceramic material contained in the ceramic green sheet 21, in addition to a material that produces glass at the time of firing, a sintering aid such as glass, copper oxide, or magnesium oxide is previously contained, so that a lower temperature sintered ceramic material can be obtained. The composition may be such that it can be sintered. Further, the binder, the plasticizer, and the solvent contained in the ceramic green sheet 21 may be other than those described above.
[0026]
Further, on the ceramic green sheet 21, an inorganic substance having a composition different from that of the low-temperature sintering ceramic, for example, alumina, mullite, aluminum nitride, glass ceramic, zirconia, anorthite, forsterite, and cordierite, has a softening point of 780 ° C. A paste (slurry) in which borosilicate glass powder having a diameter of 1.5 μm is added and mixed so as to have a concentration of 15 to 60 vol% may be applied. The glass to be added to the inorganic substance may be any one that has a viscosity of 106.7 Pa · s-1 or less at the firing temperature or lower and fills the gap between the inorganic powders and densifies it. Crystallized glass that increases in viscosity after being converted, or an oxide mixture in which a liquid phase is generated just before the end of firing may be used. Further, at 850 to 950 ° C., which is the temperature range in which the ceramic green sheet 21 is shrunk, the material does not work too much as a sintering aid for the inorganic layer, nor does the viscosity decrease too much until it flows out of the inorganic layer. Should be fine.
[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 the inorganic material is formed into a sheet.
[0028]
Next, as shown in FIG. 2B, the electrodes 18 are formed on the ceramic green sheet 21 by a screen printing method or the like. 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 step described later. 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, and Ag / Pt as a conductive paste, and the mixture is stirred and kneaded with a raikai machine and three rolls. Use the prepared 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 free from coarse powder or extreme agglomerated powder are desirable. The organic vehicle is a mixture of a binder resin and a solvent, and is not particularly limited. Ethyl cellulose, acrylic resin, polyvinyl butyral, methacrylic resin and the like are used as the binder resin, and terpineol, butyl carbitol, and butyl carbyl are used as the solvent. Tall acetate, alcohols, etc. are used. Further, various dispersants, plasticizers and activators may be added as necessary. Further, 0 to 70% of glass frit, metal oxide such as Cu2O, ceramic powder or resin powder may be added to measure shrinkage matching with ceramic. 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 for a predetermined ceramic green sheet 22 to be an outer layer of the laminate in a laminating step 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 pasted in order on a base film, and masked with a glass substrate on which a predetermined circuit pattern is formed. After the development, the metal foil 15 is formed by etching with ammonium peroxodisulfate, ferric chloride, and the like, and subsequently removing the resist. The effect of the present invention can be further improved by using copper for the metal foil 15, but in addition, silver, nickel, palladium, tungsten, gold, platinum, or the like may be used as a main component.
[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, and the surface wiring conductor 17 is formed. At this time, in order to enhance the adhesiveness 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 may be roughened to such an extent that the high-frequency characteristics do not cause a problem. Further, preferably, in order to enhance the adhesion between the metal foil 15 and a plating film 16 formed in a plating step to be described later, both surfaces of the metal foil 15 may be roughened to such a degree that high frequency characteristics do not cause a problem. When transferring, it is preferable to apply pressure of about 100 kg / cm 2 and press-contact. Further, if a resin adhesive which is burned off by firing is applied to the metal foil 15 in advance, adhesion to the surface electrode 14 at the time of 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 contact at least the surface electrode 14 existing on the predetermined ceramic green sheet 22. Further, when the metal foil 15 is transferred so as to cover the entire surface electrode 14, the effect of the present invention can be further improved.
[0032]
Next, as shown in FIG. 2D, a ceramic green sheet 21 on which the electrodes 18 are formed is disposed in an inner layer, and a predetermined ceramic green sheet 22 on which a surface wiring conductor 17 is formed is disposed in an outer layer. A plurality of inner ceramic green sheets 21 are laminated and thermocompression bonded at a temperature of 80 ° C. and a pressure of 200 kg / cm 2 to form a green laminate 19. The green laminate 19 is fired in a reducing atmosphere at a temperature of 900 ° C. for one hour to obtain a desired multilayer ceramic substrate. The metal foil 15 may be formed after the ceramic green sheets 21 on which the electrodes 18 are formed are arranged in an inner layer and an outer layer, laminated and fired. However, in this case, after forming the metal foil 15, it is necessary to fire again at a temperature 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. For such Ni plating, about 0.5 to 10 μm is deposited at a temperature of 50 ° C. to 100 ° C. using an aqueous solution containing NiSO 4, copper sulfate, tartaric acid, sodium hydroxide, formaldehyde, or the like as an electroless plating solution. Therefore, it is immersed in a plating bath solution of pH 4 to 5 for about 5 to 150 minutes. After the precipitation, water washing is performed. Subsequently, in the Au plating, in order to precipitate about 0.01 to 5.0 μm using an aqueous solution containing AuCN as a main component or the like, it is immersed in a plating bath solution of pH 7 to 8 for about 5 to 150 minutes. After the precipitation, water washing 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 hardly enter the inside of the surface electrode 14 made of the sintered body, During use after commercialization, conduction becomes poor, and short-circuiting between layers hardly occurs.
[0035]
FIG. 3 shows a manufacturing method for implementing a via-hole conductor forming step in addition to the manufacturing method shown in FIG. 3, elements corresponding to the elements shown in FIG. 2 are denoted by the same reference numerals, and redundant description will be 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 by a punch to penetrate the ceramic green sheet 21, 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 by a three-roll mill. And a kneaded 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 free from coarse powder or extreme agglomerated powder are desirable. The organic vehicle is a mixture of a binder resin and a solvent, and is not particularly limited. Ethyl cellulose, acrylic resin, polyvinyl butyral, methacryl 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. Further, various dispersants, plasticizers and activators may be added as necessary. Further, in order to measure shrinkage matching with ceramic, glass frit, metal oxide such as Cu ₂ O, ceramic powder or resin powder may be added in an amount of 0 to 70%. The paste viscosity may be 50 to 700 Pa · s-1 in consideration of printability.
[0038]
Next, as shown in FIG. 3B, an electrode 18 is formed on the ceramic green sheet 21 by a screen printing method or the like so as to cover an end of the via hole conductor 31 formed on the ceramic green sheet 21. In addition, the surface electrode 14 is similarly formed so as to cover the end of the via-hole conductor 31 with respect to the predetermined ceramic green sheet 22 which is to be the outer layer of the laminate in the lamination step described later. The forming method and the materials used are the same as those 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 laminate in a laminating step to be described later. 17 is formed. The forming method and the materials used are the same as those in the manufacturing method of FIG. At this time, the effect of the present invention can be obtained by covering at least a part of the surface electrode 14 corresponding to the end of the via-hole conductor 31 in the surface electrode 14, but if the metal foil 15 is transferred so as to cover the entire surface electrode 14, Thus, the effects of the present invention can be further improved.
[0040]
Next, as shown in FIG. 3D, a ceramic green sheet 21 on which the electrodes 18 are formed is disposed in an inner layer, and a predetermined ceramic green sheet 22 on which a surface wiring conductor 17 is formed is disposed in an outer layer. Then, a plurality of inner ceramic green sheets 21 are laminated and thermocompression-bonded to form a green laminate 19. The green laminate 19 is fired in a reducing atmosphere at a temperature of 900 ° C. for one hour to obtain a desired ceramic multilayer substrate. The laminating method and the firing method are the same as those in 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 the materials used are the same as those in the manufacturing method of FIG.
[0042]
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 or the inside of the surface electrode 14 made of a sintered body or the inside of the via hole conductor 31 is formed. Water is less likely to penetrate, and conduction becomes poor during use after commercialization, and short-circuiting between layers is less likely to occur.
[0043]
FIG. 4 is a view for explaining a modification of the laminating step in the manufacturing method of FIGS. 2 and 3 when the non-shrinkage process using the outer constraining layer 32 is applied. 4, elements corresponding to the elements shown in FIGS. 2 and 3 are denoted by the same reference numerals, and redundant description will be omitted.
[0044]
Referring to FIG. 4, the firing step is performed with the outer constraining layer 32 disposed so as to sandwich the raw laminate 19 in the laminating direction. The outer constraining layer 32 is formed by adding a suitable binder and a solvent to a shrinkage-suppressing inorganic material powder that does not sinter at the sintering temperature of the ceramic material powder contained in the ceramic green sheet 21 and mixing the resulting slurry into a sheet. It is obtained by molding into a.
[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, for example, 1000 ° C. or less, the shrinkage suppressing material contained in the outer constraining layer 32 is used. As the inorganic material powder, for example, at least one of alumina, mullite, aluminum nitride, zirconia, anorthite, forsterite and cordierite is preferably used.
[0046]
Since the shrinkage-suppressing inorganic material powder 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. Therefore, the shrinkage suppressing action of the outer constraining layer 32 is exerted on the raw laminate 19, and the raw laminate 19 contracts in the thickness direction, but shrinks 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 laminated body after sintering 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 can be increased. It 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 modification of the ceramic green sheet preparing step in the manufacturing method of FIGS. 2 and 3, a non-shrinkage-free layer is provided not only on the outer ceramic green sheet of the green laminate 19 but also on each inner ceramic green sheet layer. 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 of 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 of FIG. 3 (e) by a digital multimeter, and left for 100 hours in a steady state.
[0052]
Next, the insulation resistance of a sample after 100 hours was measured by a digital multimeter, and a sample showing a resistance value of 1 × 109Ω or less was regarded as a defect, and 1,000 samples were measured under each condition to determine a defect rate. The above were rejected.
[0053]
Table 1 summarizes the evaluation results of this experiment.
[0054]
[Table 1]

[0055]
Samples marked with * in the table are outside the scope of the present invention. For example, when the surface electrode was not covered with the metal foil, 12% of the layers were short-circuited between the layers, and thus were rejected.
On the other hand, in the range of the present invention, the copper foil and the silver foil both did not cause interlayer short-circuiting, or even if they did, one out of 1,000 foils, which sufficiently satisfied the desired characteristics.
[0056]
【The invention's effect】
As described above, according to the present invention, since the surface wiring conductor formed on the outer layer of the laminate is covered with the dense and dense metal foil, the inside of the surface electrode or the via hole conductor made of a sintered body is formed. The plating solution and water are less likely to penetrate into the substrate, making it less conductive during use after commercialization and short-circuiting between layers.
[0057]
Therefore, a multilayer ceramic substrate manufactured using the same does not impair the electrical characteristics, and the manufacturing method thereof can be suitable for forming a high-frequency circuit that requires stable quality.
[Brief description of the drawings]
FIG. 1 is a sectional view of a multilayer ceramic substrate obtained by the present invention.
FIG. 2 is a cross-sectional view illustrating a method for manufacturing 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 a manufacturing method performed after FIG.
FIG. 4 is a cross-sectional view illustrating 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]
11 multilayer ceramic substrate 12 ceramic layer 13 laminated body 14 surface electrode 15 metal foil (circuit pattern)
Reference Signs List 16 plating film 17 surface wiring conductor 18 electrode 19 raw laminate 21 ceramic green sheet 22 predetermined ceramic green sheet 31 located on the outer layer of the laminate ... via hole conductor 32 ... outer constraining layer

Claims (6)

In a multilayer ceramic substrate having a ceramic substrate including a plurality of stacked ceramic layers and a surface electrode formed of a conductive paste on an outer surface of the ceramic substrate,
At least a part of the surface electrode is covered with a metal foil,
A multilayer ceramic substrate, wherein the surface electrode and the metal foil are covered with a plating film. A via hole conductor is formed in the ceramic layer,
An end of the via-hole conductor is covered by the surface electrode,
2. The multilayer ceramic substrate according to claim 1, wherein at least a part of the surface electrode corresponding to an end of the via-hole conductor is covered with the metal foil. 3. The multilayer ceramic substrate according to claim 1, wherein the entire surface electrode is covered with the metal foil. The multilayer ceramic substrate according to any one of claims 1 to 3, wherein the metal foil is copper. A ceramic green sheet preparation step of preparing a ceramic green sheet,
An electrode forming step of forming an electrode on the ceramic green sheet using a conductive paste,
A metal foil forming step of covering at least a part of the surface electrode formed on the predetermined ceramic green sheet with a metal foil,
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 manufacturing a multilayer ceramic substrate, comprising: a plating step of covering the surface electrode formed on the outer surface of the fired laminate and the metal foil with a plating film. After the ceramic green sheet preparation step, further comprising a via hole conductor forming step of forming a through hole in the thickness direction with respect to the ceramic green sheet, filling a conductive paste to form a via hole conductor,
In the electrode forming step, the surface electrode formed on a predetermined ceramic green sheet is formed so as to cover an end of the via-hole conductor,
In the metal foil forming step, at least a part of a part corresponding to an end of the via-hole conductor among the surface electrodes formed on a predetermined ceramic green sheet is covered with the metal foil. Item 6. The method for manufacturing a multilayer ceramic substrate according to Item 5.

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