JP3757211B2 - Wiring board and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wiring board and a manufacturing method thereof, and is particularly suitable for use in a manufacturing method of a ceramic substrate.
[0002]
[Prior art]
In recent years, in wireless information communication devices such as mobile phones, Bluetooth, and other mobile devices, it has been desired to communicate high-capacity signals such as voice, images, data, and the like at higher speeds at higher frequencies. In order to realize such a wireless information communication device, it is important to reduce the conductor loss and dielectric loss (tan δ) of the wiring board at high frequencies.
[0003]
Here, the conductor loss is determined by the electrical resistance of the conductor material, and the smaller the electrical resistance, the smaller the conductor loss. Therefore, in order to communicate a large capacity signal at a higher speed, silver or copper is used for the wiring on the board. It is effective to use a conductor material having a low electrical resistance such as gold. Further, the value of the dielectric loss varies depending on the material. Generally, the dielectric loss value of the ceramic material is about 1/10 of that of the resin material.
[0004]
Based on such a background, as a wiring board in a wireless information communication apparatus, a ceramic board formed of a conductive wiring such as gold, silver, copper or the like having a small electric resistance is becoming mainstream. Development of wiring boards in ceramics) is progressing.
[0005]
[Patent Document 1]
JP-A-6-13756 [Patent Document 2]
JP-A-10-106350 [Patent Document 3]
JP-A-11-3617 [0006]
[Problems to be solved by the invention]
However, the above-described wiring substrate is formed by forming a wiring pattern on a ceramic raw sheet (hereinafter referred to as a green sheet) using a conductor paste made of a conductor having a small electrical resistance, and firing these simultaneously. However, at this time, the behavior of the firing shrinkage rate between the conductor and the ceramics is greatly different, and as a result, there is a problem that stress is generated at the interface between the conductor and the ceramics to cause cracks and the like.
[0007]
Therefore, for the purpose of adjusting the difference in behavior in the firing shrinkage ratio between the conductor and the ceramic, adding ceramics such as glass, alumina, and magnesia to the conductor paste has been performed. Since it is an insulator, the resistance value of the conductor wiring is increased.
[0008]
The present invention has been made in view of the above-described problems, and a wiring board that prevents defects such as cracks occurring at the interface between the wiring board and the conductor wiring without increasing the resistance value of the conductor wiring, and a method for manufacturing the same It aims at realizing.
[0009]
[Means for Solving the Problems]
As a result of intensive studies, the present inventor has conceived the following aspects of the invention.
[0011]
The method for manufacturing a wiring board according to the present invention includes a step of filling a via hole formed in a substrate with a conductive paste formed by mixing silver oxide with conductive powder, and forming a wiring pattern made of the conductive paste on the substrate. And heating the conductor paste at a temperature equal to or higher than the reduction temperature of silver oxide to form a conductor containing silver reduced from silver oxide in the wiring pattern forming portion of the substrate and the via hole. It is a feature.
[0012]
The wiring board of the present invention is a wiring board having a wiring layer in which a wiring pattern and a via are formed on the board, and the wiring pattern and the via heat the substrate at a temperature equal to or higher than a reduction temperature of silver oxide. It is formed and contains silver reduced from silver oxide, and does not contain an insulator.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
-Outline of the present invention-
The present inventor has achieved a conflicting request of forming a conductor wiring having a low electrical resistance and avoiding stress generated at the interface between the ceramic and the conductor by making the firing shrinkage rate of the green sheet and the conductor paste the same or similar. Accordingly, the inventors have arrived at the gist of the invention described below.
[0014]
In the present invention, silver oxide is used as an additive for adjusting the firing shrinkage rate of the conductor paste. Here, FIG. 1 shows a thermodynamic equilibrium diagram showing oxidation / reduction behavior of each metal. As shown in FIG. 1, the oxidation / reduction behavior of silver is as follows. In the atmosphere of 1 atm, the temperature of about 200 ° C. is used as a boundary, and the silver oxide is in a stable state at a temperature lower than that. Then silver becomes stable. That is, silver oxide undergoes a reduction transformation to silver at a temperature of 200 ° C. or higher.
[0015]
FIG. 2 is a characteristic diagram showing measurement results of pure silver paste, silver paste added with silver oxide, and ceramics by thermomechanical analysis (TMA).
As shown in the measurement result of FIG. 2, in the pure silver paste, the shrinkage depending on the temperature does not occur, and when the temperature becomes about 450 ° C. or more, the difference in the shrinkage rate with the ceramic becomes large. On the other hand, the silver paste to which silver oxide is added shrinks depending on the temperature, but the shrinkage shows the same behavior as ceramics, and there is almost no difference in the shrinkage rate at the firing temperature. From this result, it can be seen that the addition of silver oxide to the conductor paste can reduce the difference in shrinkage with ceramics.
[0016]
3 and 4 are characteristic diagrams showing the experimental results of the silver oxide reduction reaction. From the measurement result of differential thermal analysis (TG-DTA) by weight reduction shown in FIG. 3, endothermic reaction and weight reduction are seen at a temperature around 480 ° C. This is because silver is generated by the reduction reaction of silver oxide, and the weight is reduced. Theoretically, the weight loss is about 7% from the atomic weight.
[0017]
Further, from the measurement result of X-ray diffraction shown in FIG. 4, it can be seen that silver oxide is present up to 300 ° C., but silver is present instead of silver oxide at a temperature of 500 ° C. or higher. This indicates that the silver oxide was reduced to silver between 300 ° C and 500 ° C. Here, the reduction temperature of silver oxide is theoretically about 200 ° C. as shown in FIG. 1, but in the experiment, the reduction temperature is about 450 ° C. as shown in FIGS. Yes.
[0018]
From the measurement results shown in FIGS. 3 and 4, in firing ceramics, the firing temperature is higher than the reduction temperature of silver oxide, preferably 500 ° C. or higher, so that the conductor wiring is formed of silver or an alloy containing silver. Therefore, the resistance value of the conductor wiring is not increased.
In other words, by adding silver oxide to the conductor paste, the difference in shrinkage between the conductor paste and ceramics is reduced during firing, and a conductor wiring with low electrical resistance is formed to transform into silver after firing. can do.
[0019]
-Specific embodiment to which the gist of the present invention is applied-
Next, an embodiment based on the gist of the wiring board and the manufacturing method thereof of the present invention will be described. In the present embodiment, a multilayer ceramic substrate will be described as an example of the wiring substrate.
[0020]
FIG. 5 is a schematic view showing a method of manufacturing a multilayer ceramic substrate in the order of steps.
First, in step S1 shown in FIG. 5A, an alumina powder having an average particle size of about 5 μm is mixed with a raw material powder prepared by mixing 20 vol% and a borosilicate glass powder having an average particle size of about 3 μm. 8% by weight of PVB resin and 3% by weight of dibutyl phthalate as a plasticizer are added, and acetone is added as a solvent, and a powder is prepared using a ball mill for about 20 hours to produce a milky slurry 1.
[0021]
Subsequently, in step S2 shown in FIG. 5 (b), the milky slurry 1 produced in step S1 is passed between the doctor blade 2 and the belt 3 by the doctor blade method to have a predetermined thickness. The green sheet 4 is formed.
[0022]
Subsequently, in step S3 shown in FIG. 5 (c), the green sheet 4 formed in step S2 is subjected to regular punching to produce a green sheet substrate 5 having a predetermined shape. Thereafter, via holes are formed in the green sheet substrate 5.
[0023]
On the other hand, step S4 shown in FIG. 5D is a process for generating a conductor paste for pattern printing on the green sheet substrate 5.
Specifically, a silver powder having an average particle diameter of about 0.5 μm and a silver oxide powder having an average particle diameter of about 1.5 μm and a silver powder of about 10 wt% are prepared, Ethyl cellulose and acetone are added, and terpineol is added while evaporating the acetone solvent component using a rough machine to prepare a powder, thereby producing a conductor paste 6. Here, this conductor paste 6 was mixed and dispersed using a three-roll mill, and the viscosity was set to 300 Pa · S (3,000 poise).
[0024]
Subsequently, in step S5 shown in FIG. 5 (e), the via paste formed in the green sheet substrate 5 is filled with the conductor paste 6, and screen printing using the conductor paste 6 is performed, thereby the green sheet substrate. A wiring pattern 7 is formed on the surface of 5.
[0025]
Subsequently, in step S6 shown in FIG. 5 (f), a plurality of green sheet substrates 5 on which various wiring patterns 7 are formed are overlapped, and a temperature of 80 ° C. and a pressure of 30 MPa are applied for 30 minutes. Laminate. At this time, the PVB resin contained in the green sheet substrate 5 serves as a glue for interlayer adhesion at the time of lamination.
[0026]
Subsequently, in step S7 shown in FIG. 5G, a temperature of 900 ° C. is given to the laminated green sheet substrate 5 in the atmosphere for 2 hours to disperse the PVB resin, and the conductive metal of the wiring pattern 7 A multilayer ceramic substrate 8 is formed by firing together with the green sheet substrate 5.
[0027]
In the present embodiment, an example in which silver powder is used for the conductor paste 6 is shown, but the present invention is not limited to this, for example, a conductor metal such as gold, copper, tungsten, molybdenum, nickel, It is also possible to apply alloys based on these metals. Moreover, in the silver oxide of this embodiment, it is desirable for achieving the effect that the purity is 90% or more and the average grain size is 50 μm or less.
[0028]
In the present embodiment, although an example of using the silver (I) oxide of Ag ₂ O as silver oxide, present invention is not limited thereto, by reducing to metallic silver during firing From the viewpoint of phase transformation, AgO silver oxide (II) can also be applied.
[0029]
-Evaluation result of multilayer ceramic substrate in this embodiment-
FIG. 6 is a diagram showing characteristics of a multilayer ceramic substrate manufactured using various conductive pastes by applying the above-described manufacturing method.
Here, the multilayer ceramic substrate shown in the conventional method 1 is manufactured using a pure silver paste, and the multilayer ceramic substrate shown in the conventional method 2 uses a silver paste to which a low melting point glass is added. The manufactured multilayer ceramic substrate of this embodiment is manufactured using a silver paste to which silver oxide is added.
[0030]
Since the multilayer ceramic substrate in the conventional method 1 uses a pure silver paste, the electrical resistance of the conductor layer is very small and good, but the difference in shrinkage between the ceramic and the conductor during firing is very large. For this reason, delamination and cracks are generated in the interlayer portion of the multilayer ceramic substrate.
[0031]
Since the multilayer ceramic substrate in the conventional method 2 uses a silver paste to which low melting point glass for adjusting shrinkage during firing is used, the difference in shrinkage between the ceramic and the conductor during firing is very small. The delamination and cracks are not generated in the interlayer part of the multilayer ceramic substrate, but the added low-melting glass is an insulator, so that the electric resistance of the conductor layer becomes very large.
[0032]
On the other hand, since the multilayer ceramic substrate of this embodiment uses a silver paste to which silver oxide is added, as can be seen from the characteristic diagram shown in FIG. 2, the difference in shrinkage between the ceramic and the conductor during firing is different. Is very small, and delamination and cracks are not generated in the interlayer part of the multilayer ceramic substrate. Furthermore, since the reduction temperature of silver oxide is very low, the resistance value of the formed conductor layer is very small due to reduction from silver oxide to silver during firing.
[0033]
From the evaluation result of the multilayer ceramic substrate shown in FIG. 6, the effectiveness of the method for manufacturing the multilayer ceramic substrate in the present embodiment could be confirmed.
[0034]
Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.
[0035]
(Supplementary note 1) A step of mixing a conductor powder with silver oxide to produce a conductor paste;
And a step of heating the conductor paste at a temperature equal to or higher than the reduction temperature of silver oxide to form a conductor containing silver reduced from the silver oxide.
[0036]
(Additional remark 2) The said conductor powder contains at least 1 sort (s) among gold | metal | money, silver, copper, or the alloy in these metals, The manufacturing method of the conductor of Additional remark 1 characterized by the above-mentioned.
[0037]
(Additional remark 3) The said conductor paste is heated at 500 degreeC or more, The manufacturing method of the conductor of Additional remark 1 or 2 characterized by the above-mentioned.
[0038]
(Additional remark 4) The average particle diameter of silver oxide is 50 micrometers or less, The manufacturing method of the conductor of any one of Additional remarks 1-3 characterized by the above-mentioned.
[0039]
(Additional remark 5) The manufacturing method of the conductor of any one of Additional remark 1-4 characterized by the purity of silver oxide being 90% or more.
[0040]
(Additional remark 6) The process of forming a wiring pattern in a board | substrate using the conductor paste produced | generated by mixing silver oxide with conductor powder,
Heating the substrate at a temperature equal to or higher than the reduction temperature of silver oxide, and forming a wiring layer made of a conductor containing silver reduced from silver oxide on the substrate.
[0041]
(Additional remark 7) The said board | substrate is the manufacturing method of the wiring board of Additional remark 6 characterized by the shrinkage | contraction rate depending on temperature being the same as that of the said conductor paste, or similar.
[0042]
(Additional remark 8) The said board | substrate is formed with ceramics, The manufacturing method of the wiring board of Additional remark 6 or 7 characterized by the above-mentioned.
[0043]
(Additional remark 9) The said conductor powder contains at least 1 sort (s) among gold, silver, copper, or the alloy in these metals, The wiring board of any one of Additional remark 6-8 characterized by the above-mentioned. Production method.
[0044]
(Additional remark 10) The said board | substrate is heated at 500 degreeC or more, The manufacturing method of the wiring board of any one of Additional remark 6-9 characterized by the above-mentioned.
[0045]
(Additional remark 11) The manufacturing method of the wiring board of any one of Additional remark 6-10 characterized by the average particle diameter of silver oxide being 50 micrometers or less.
[0046]
(Additional remark 12) The manufacturing method of the wiring board of any one of additional marks 6-11 characterized by the purity of silver oxide being 90% or more.
[0047]
(Additional remark 13) The said wiring pattern is formed by screen printing, The manufacturing method of the wiring board of any one of Additional remark 6-12 characterized by the above-mentioned.
[0048]
(Supplementary note 14) a substrate;
A wiring board, wherein the board is formed by heating the board at a temperature equal to or higher than a reduction temperature of silver oxide, and the board has a wiring layer made of a conductor containing silver reduced from silver oxide.
[0049]
(Additional remark 15) The said board | substrate is the wiring board of Additional remark 14 characterized by the shrinkage | contraction rate depending on temperature being the same as that of the said conductor paste, or similar.
[0050]
(Additional remark 16) The said board | substrate is formed with ceramics, The wiring board of Additional remark 14 or 15 characterized by the above-mentioned.
[0051]
(Supplementary Note 17) The wiring layer is formed of an alloy of silver and gold or copper reduced from silver oxide, or an alloy of silver and gold or copper reduced from silver oxide. The wiring board according to any one of appendices 14 to 16.
[0052]
【The invention's effect】
According to the present invention, it is possible to prevent problems such as cracks occurring at the interface between the substrate and the conductor wiring without increasing the resistance value of the conductor wiring.
[Brief description of the drawings]
FIG. 1 is a thermodynamic equilibrium diagram showing oxidation / reduction behavior of each metal.
FIG. 2 is a characteristic diagram showing measurement results of pure silver paste, silver paste added with silver oxide, and ceramics by thermomechanical analysis (TMA).
FIG. 3 is a characteristic diagram showing experimental results of a reduction reaction of silver oxide.
FIG. 4 is a characteristic diagram showing experimental results of silver oxide reduction reaction.
FIG. 5 is a schematic view showing a method of manufacturing a multilayer ceramic substrate according to an embodiment of the present invention in the order of steps.
FIG. 6 is a view showing characteristics of a multilayer ceramic substrate manufactured using various conductor pastes.
[Explanation of symbols]
1 Slurry 2 Doctor blade 3 Belt 4 Green sheet 5 Green sheet substrate 6 Conductive paste 7 Wiring pattern 8 Multilayer ceramic substrate

Claims (8)

Filling a via hole formed in the substrate with a conductive paste obtained by mixing silver oxide with conductive powder;
Forming a wiring pattern made of the conductive paste on the substrate;
Heating the conductive paste at a temperature equal to or higher than the reduction temperature of silver oxide, and forming a conductor containing silver reduced from silver oxide in the wiring pattern forming portion and the via hole of the substrate. A method for manufacturing a wiring board.   The method for manufacturing a wiring board according to claim 1, wherein the substrate has a temperature-dependent shrinkage rate that is the same as or similar to that of the conductor paste.   The method for manufacturing a wiring board according to claim 1, wherein the substrate is made of ceramics.   The method for manufacturing a wiring board according to claim 1, wherein the conductor powder includes at least one of gold, silver, copper, and alloys of these metals. A wiring board having a wiring layer in which wiring patterns and vias are formed on the board,
The wiring pattern and the via are formed by heating the substrate at a temperature equal to or higher than the reduction temperature of silver oxide, and contain silver reduced from silver oxide and do not contain an insulator. A characteristic wiring board.   The wiring board according to claim 5, wherein the board has a shrinkage rate depending on temperature that is the same as or similar to that of the conductor paste used to form the wiring pattern and the via.   The wiring board according to claim 5, wherein the board is made of ceramics.   6. The wiring layer is formed of an alloy of silver and gold or copper reduced from silver oxide, or an alloy of silver and gold or copper reduced from silver oxide. The wiring board according to any one of?

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