JP2000114724A - Multilayer wiring board - Google Patents

Abstract

(57) [Problem] To provide a multilayer wiring board formed by co-firing with an insulating substrate made of aluminum oxide ceramics, including copper, and having a low-resistance surface wiring layer and an internal wiring layer without wiring bleeding. provide. The insulating substrate includes a ceramic insulating substrate, a surface wiring layer and an internal wiring layer formed inside and on the surface of the insulating substrate by simultaneous firing with the insulating substrate.
The surface wiring layer 2a contains 10 to 70% by volume of copper and 30 to 90% by volume of tungsten and / or molybdenum, and the internal wiring layer 2b contains 20 to 80% by volume of copper, tungsten and / or molybdenum. 20 to 80% by volume
And the copper content in the internal wiring layer 2b is larger than that of the surface wiring layer 2a. The surface wiring layer 2a has a sheet resistance of 8 mΩ / □ or less, It is desirable that the layer 2b has a sheet resistance of 6 mΩ / □ or less, and further, a metal layer 4 is formed by plating on the surface of the surface wiring layer 2a by plating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring substrate using ceramics such as aluminum oxide as an insulating substrate, and more particularly to a wiring substrate made of a low-resistance conductor containing copper as a main component and formed by co-firing with the insulating substrate. The present invention relates to a multilayer wiring board having a surface and an internal wiring layer provided.

[0002]

2. Description of the Related Art In recent years, the heat generated from a semiconductor device tends to increase with the increase in the degree of integration of a semiconductor element. Therefore, the heat generated to eliminate malfunction of the semiconductor device due to the heat can be released to the outside of the device. There is a need for a simple wiring board. On the other hand, as for the electrical characteristics, a delay in signal becomes a problem due to an increase in operation speed, and it is required to use a conductor having a small conductor loss, that is, a low resistance conductor.

Conventionally, as a wiring substrate on which such a semiconductor element is mounted, from the viewpoint of reliability, an insulating substrate made of alumina ceramics and a wiring layer made of a refractory metal such as tungsten or molybdenum on the surface or inside thereof are used. Are often used.

However, a wiring layer made of a metal having a high melting point, which has been widely used, can reduce the resistance to at most about 8 mΩ / □. The surface wiring layer can be made to have a low wiring resistance by applying Au plating or the like, but the internal wiring layer should be subjected to plating treatment or the like after the simultaneous baking with the insulating substrate, like the surface wiring layer. Not be able to
It was difficult to reduce the resistance of the wiring layer.

On the other hand, in recent years, a multilayer wiring board using so-called glass ceramics as an insulating substrate has been proposed, in which a surface and an internal wiring layer can be formed by simultaneous firing with a low-resistance conductor such as copper or silver. I have. However, the thermal conductivity of glass ceramics is at most several W / m · K.
To a very low degree, it was difficult to solve the thermal problem.

Therefore, as a method for solving the thermal problem and the electrical problem at the same time, an aluminum oxide ceramics is used as an insulating substrate, and a copper or a conductor layer obtained by combining copper and tungsten or molybdenum is used simultaneously with the insulating substrate. A method of forming by firing is disclosed in Japanese Patent Application Laid-Open No. 8-8502.
, Japanese Patent Application Laid-Open No. 7-15101 and Japanese Patent No. 2666744.

[0007]

However, Japanese Patent Application Laid-Open No. 8-8502 discloses a method in which aluminum oxide is fired at a high temperature of 1600 ° C. or more in order to densify aluminum oxide. When the tungsten conductor layer is fired, the rapid sintering of tungsten and molybdenum progresses to form large agglomerated particles. And the like, there is a problem that the shape retention of the surface wiring layer shape is reduced and the resistance is increased due to the non-uniformity of the structure. Moreover, the copper component in the wiring layer
Since it diffuses into the ceramics of the insulating substrate during firing and the insulation between the wiring layers deteriorates, it is difficult to form a fine wiring layer at a high density.

According to Japanese Patent Application Laid-Open No. 7-15101,
For the surface wiring layer, once all the wiring layers are disposed inside the insulating substrate and simultaneously fired, the insulating layer on the surface is polished and removed by polishing or the like to expose the internal wiring layer to the surface, or after firing. A surface wiring layer is formed on the surface of the wiring substrate by a thick film method or a thin film method. Therefore, a polishing process, a thick film forming process, a thin film forming process, and the like are indispensable processes for forming a surface wiring layer, so that there are many manufacturing processes, and there are problems such as a reduction in yield and an increase in cost. there were.

Further, Japanese Patent No. 2,666,744 discloses that a fine alumina powder having an average particle size of 5 to 50 nm is used as a ceramic powder for forming an insulating substrate, so that a low resistance material such as gold, silver, and copper is used. Simultaneous sintering of the insulating substrate and low-resistance metal has been achieved by approaching the firing temperature of the metal, but such fine powders are extremely difficult to handle and costly, resulting in mass production. However, there is a problem that the cost is high.

Further, when a surface wiring layer formed by simultaneous firing on the surface of the insulating substrate is formed by a wiring layer containing a large amount of copper, molten copper flows out during firing and bleeding occurs, and the shape of the wiring layer is maintained. Properties are remarkably reduced, and fine wiring cannot be formed. For this reason, it is necessary to add a large amount of tungsten, molybdenum, or the like to the wiring layer on the surface. However, as the amount of tungsten or molybdenum increases, the sheet resistance also increases.
There is a problem that the effect of containing copper cannot be sufficiently expected.

Accordingly, the present invention provides a multi-layer wiring board which is formed by co-firing with an insulating substrate made of aluminum oxide ceramics, includes copper, and has a low-resistance surface wiring layer and an internal wiring layer without wiring bleeding. The purpose is to provide.

[0012]

Means for Solving the Problems The present inventors have repeatedly studied the above problems in a multilayer wiring board using ceramics as an insulating substrate, and as a result, it has been found that the shape of the wiring layer can be maintained for the surface wiring layer. Is important, an appropriate amount of tungsten and / or molybdenum is contained, and since the internal wiring layer is sandwiched from above and below by the insulating substrate, it has excellent shape retention compared to the surface wiring layer. The present inventors have found that the object can be achieved by lowering the sheet resistance by increasing the content of copper than that of the layer, and have reached the present invention.

That is, the multilayer wiring board of the present invention comprises a ceramic insulating substrate, and a surface wiring layer and an internal wiring layer formed inside and on the surface of the insulating substrate by simultaneous firing with the insulating substrate, The surface wiring layer is made of copper,
70% by volume, 3% tungsten and / or molybdenum
0 to 90% by volume, and the internal wiring layer contains 20 to 80% by volume of copper and 20 to 80% by volume of tungsten and / or molybdenum, and the copper in the internal wiring layer The content is larger than that of the surface wiring layer.

The surface wiring layer has a sheet resistance of 8
It is desirable that the sheet resistance be not more than mΩ / □, and that a metal layer be formed on the surface of the surface wiring layer by plating to thereby have a sheet resistance of not more than 6 mΩ / □.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view showing an embodiment of a multilayer wiring board according to the present invention. The multilayer wiring board of FIG. 1 has a plurality of insulating layers 1 made of ceramics.
The surface wiring layer 2a is provided on the surface of the insulating substrate 1 on which the a, 1b, and 1c are laminated, and the internal wiring layer 2 is provided between the insulating layers 1a, 1b, and 1c.
b is provided.

According to the present invention, the surface wiring layer 2a and the internal wiring layer 2b are made of copper and tungsten (W) and / or
Alternatively, the surface wiring layer 2a is made of a conductor mainly composed of a composite material with molybdenum (Mo).
The internal wiring layer 2b is formed by simultaneous firing with the insulating substrate 1.

The wiring layers of each layer are electrically connected by via-hole conductors 3 formed so as to penetrate the insulating layer. It is desirable that the via-hole conductor 3 is also formed by simultaneous firing using the same conductive material as the surface wiring layer 2a and the internal wiring layer 2b.

Further, a metal layer 4 is formed on the surface of the surface wiring layer 2a by electroless plating or electrolytic plating in order to prevent corrosion due to oxidation, wire bonding properties, wettability with solder, and reduce the resistance of the wiring layer. And the like. As the metal layer 4, Au, Cu, Ti,
At least one selected from the group consisting of Ni and Pd is desirable, and it is particularly desirable that the outermost surface is made of Au.

(Wiring Layer) The surface wiring layer 2a and the internal wiring layer 2b contain 10 to 80% by volume of copper and 20 to 90% by volume of W and / or Mo. When the copper content in the internal wiring layer 2b is
It is a great feature that the amount of copper in the surface wiring layer 2a is smaller than that in the internal wiring layer 2b. This is because the copper content in the surface wiring layer 2a is determined in terms of sheet resistance and the shape retention of the wiring layer, and the surface of the surface wiring layer 2a has a metal layer 4 such as a plating layer. Although the sheet resistance can be reduced by the formation, a plating layer or the like cannot be formed in the internal wiring layer 2b, so that the resistance of the internal wiring layer becomes higher than the surface.

Therefore, according to the present invention, the internal wiring layer 2b
The copper content in the surface wiring layer 2a is smaller than that of the internal wiring layer 2b, whereby the shape retention of the surface wiring layer 2a can be maintained and fine wiring can be formed. In addition, the resistance of the surface wiring layer 2a on which the metal layer 4 is applied by plating or the like and the resistance of the internal wiring layer 2b on which the metal layer such as plating cannot be applied can be controlled to the same level.

More specifically, in order to reduce the resistance of the wiring layer, maintain co-sinterability with the insulating substrate 1 and maintain the shape of the surface wiring layer, the surface wiring layer 2a is made of copper. volume%,
In particular, 40 to 60% by volume, W and / or Mo is 30 to 30% by volume.
It is necessary to contain 90% by volume, particularly 40 to 60% by volume, and it is particularly desirable that the sheet resistance is 8 mΩ / □ or less.

This is because the amount of copper in the surface wiring layer 2a is 1
If the amount is less than 0% by volume and the amount of W or Mo is more than 90% by volume, the resistance of the surface wiring layer becomes high, and the amount of copper becomes 7%.
If it is more than 0% by volume and the amount of W or Mo is less than 30% by volume, the shape retention of the surface wiring layer is reduced, and the surface wiring layer 2a
In this case, bleeding or the like occurs, the surface wiring layer is agglomerated by the molten copper, and disconnection occurs, and the wiring layer is separated due to a difference in thermal expansion coefficient between the insulating substrate and the wiring layer.

Further, in order to reduce the resistance of the wiring layer together with the surface wiring layer 2a containing W and / or Mo, the metal layer 4 deposited on the surface of the surface wiring layer 2a may be a single layer or a plurality of layers. It is desirable that the plating layer be formed with a thickness of 0.5 to 10 μm. In particular, a preferable structure of the plating layer is N in order to improve the adhesion to the surface wiring layer 2a.
It is desirable to form a metal selected from the group consisting of i, Cu, Pd, and Ti in a single layer or a plurality of layers, and further form an Au plating layer thereon.

On the other hand, the internal wiring layer 2b is
% By volume, especially 50-80% by volume, W and / or Mo
At a ratio of 20 to 80% by volume, particularly 20 to 50% by volume, and particularly desirably a sheet resistance of 6 mΩ / □ or less.

This is because the internal wiring layer 2b has a copper content of 20%.
If the amount is less than 80% by volume, the resistance cannot be reduced to 6 mΩ / □ or less.
If the content is more than 0% by volume and the amount of W or Mo is less than 20% by volume, the shape of the internal wiring layer is poor, and the molten copper diffuses between the insulating layers to be reduced. This is because the resistance increases.

In the present invention, at least in the surface wiring layer 2a, W and / or Mo are dispersed and contained in a matrix made of copper as spherical or sintered particles of several particles having an average particle diameter of 1 to 10 μm. It is desirable to have. When the average particle size is smaller than 1.0 μm, the shape retention of the surface wiring layer 2a is deteriorated, the structure becomes porous, and the resistance of the wiring layer becomes high.
If the thickness exceeds μm, the copper matrix may be separated by W or Mo particles and the resistance of the wiring layer may increase, or the copper component may be separated to cause bleeding. In addition, W and / or Mo have an average particle diameter of 1.3-5.
Most preferably, it is dispersed in a size of μm, especially 1.3 to 3 μm.

Further, in order to improve the adhesion to the insulating substrate 1, the main component of the ceramic constituting the insulating substrate or the ceramic having the same composition as the composition of the insulating substrate is provided in the surface wiring layer 2a and the internal wiring layer 2b. Ingredients 0.05-2
It is also possible to contain it at a volume percentage.

In the wiring board of the present invention, the copper component in the surface wiring layer 2a and the internal wiring layer 2b may diffuse into the insulating substrate 1 by simultaneous firing at a temperature exceeding the melting point of copper. According to the invention, it is desirable that the diffusion distance of copper into the ceramics of the insulating substrate 1 around the wiring layer containing at least copper is 20 μm or less, particularly 10 μm or less. This is because the diffusion distance of copper into ceramics is 20μ.
If it exceeds m, the insulation between the wiring layers is reduced, and the reliability as a wiring substrate is reduced. By setting the copper diffusion distance to 20 μm or less,
The minimum distance between wiring layers formed on the same plane is 10
High-density wiring of 0 μm or less, particularly 90 μm or less can be achieved. Also, as shown in FIG. 1, when a plurality of via-hole conductors 3 are formed in one insulating layer, the minimum distance between the via-hole conductors 3 is also 100 μm or less, particularly 90 μm or less for the same reason as described above. Can be controlled.

Further, the wiring substrate of the present invention is fired by controlling the firing temperature and atmosphere as described later, so that the average surface roughness Ra of the surface of the insulating substrate 1 is 1 μm or less, particularly 0.7 μm or less. It is possible to form a surface having excellent smoothness. As a result, when the surface wiring layer 2a is formed on the surface of the insulating substrate 1, it is also a major feature that it is not necessary to perform a polishing process on the surface of the insulating substrate 1.

(Insulating substrate) In the present invention, the insulating substrate 1
Has a thermal conductivity of 10 W / m · K or more, especially 15 W
/ MK or more, strength 200MPa or more, especially 300M
Ceramics having Pa or higher, especially ceramics having high thermal conductivity and high strength include aluminum oxide (Al
₂ O ₃ ), aluminum nitride (AlN), silicon nitride (S
i ₃ N ₄₎ but the like, in achieving shape retention co-sintering and surface wiring layer of the surface wiring layers and internal wiring layer containing copper, ceramic mainly containing aluminum oxide Is most desirable.

More specifically, aluminum oxide ceramics have high thermal conductivity and high strength, and have a relative density of 9%.
It is desirably composed of a high-density body of 5% or more, particularly 97% or more, and more preferably 99% or more.

According to the present invention, in order to achieve shape retention by simultaneous sintering with the surface wiring layer 2a and the internal wiring layer 2b, 12
It is desirable to fire at a low temperature of 00 to 1500 ° C, and according to the present invention, it is necessary to densify to a relative density of 95% or more even at such a low temperature.

From such a viewpoint, the insulating substrate 1 of the present invention contains aluminum oxide in a proportion of 90% by weight or more, and in order to enhance the sinterability at the above-mentioned firing temperature, a Mn compound is used as a second component. Desirably, the content is 2.0 to 6.0% by weight in terms of MnO ₂ . That is, when the amount of the Mn compound is less than 2.0% by weight, it is 1200 to 150%.
This is because densification at 0 ° C. is difficult, and if it is more than 6.0% by weight, the insulating property of the insulating substrate 1 is reduced. Optimal range of the Mn compound is 3-5 wt% at MnO ₂ basis.

In order to enhance the simultaneous sintering property of the insulating substrate 1 with SiO ₂ and alkaline earth element oxides such as MgO, CaO, and SrO as the third component, together with the copper-containing conductor, It is desirable that the total content be 0.4 to 8% by weight. Further, as a fourth component, W, Mo,
A metal such as Cr may be contained as a coloring component in a proportion of 2% by weight or less.

The components other than the aluminum oxide are present as an amorphous phase or a crystal phase at the grain boundaries of the aluminum oxide main crystal phase. However, in order to enhance the thermal conductivity, a crystal containing an auxiliary component in the grain boundaries is required. Desirably, a phase is formed.

The aluminum oxide main crystal phase forming the insulating substrate 1 exists as granular or columnar crystals, and the average crystal grain size of these main crystal phases is 1.5 to 5.0.
μm is desirable. When the main crystal phase is composed of columnar crystals, the average crystal grain size is based on the minor axis diameter. When the average crystal grain size of the main crystal phase is smaller than 1.5 μm, it is difficult to increase the thermal conductivity, and the average grain size is 5.0 μm.
This is because if it is larger than μm, it is difficult to obtain sufficient strength required when used as a substrate material.

(Manufacturing Method) Next, a method of manufacturing a wiring board according to the present invention will be specifically described in the case where a ceramic mainly containing aluminum oxide is used as an insulating substrate. First, in order to form an insulating substrate, as an aluminum oxide raw material powder which is a main component of the oxide ceramic, the average particle diameter is 0.5 to 2.5 μm, particularly 0.5 to 2.5 μm.
A 2.0 μm powder is used. This means that the average particle size is 0.5
If it is smaller than μm, handling of the powder is difficult, and the cost of the powder becomes high.
This is because firing at a temperature of 00 ° C. or less becomes difficult.

Then, MnO ₂ is added as a _second component to the aluminum oxide powder at a ratio of 2.0 to 6.0% by weight, particularly 3.0 to 5.0% by weight. Further, as the third component, SiO ₂ , MgO, Ca,
0.4 to 8% by weight of O, SrO powder and the like, and as a fourth component, a metal powder or oxide powder of a transition metal such as W, Mo, Cr or the like as a coloring component at a ratio of 2% by weight or less in terms of metal. Added. In addition, in addition to the oxide powder, the above oxide may be added as a carbonate, nitrate, acetate, or the like which can form an oxide by firing.

Then, a sheet-like molded body for forming an insulating layer is prepared using the mixed powder. The sheet-shaped molded body can be produced by a well-known molding method.
For example, after a slurry is prepared by adding an organic binder or a solvent to the mixed powder, a sheet is formed by a doctor blade method, or an organic binder is added to the mixed powder, and a sheet having a predetermined thickness is formed by press molding, rolling, or the like. Body can be made.

With respect to the sheet-like molded product thus produced, 10 to 80% by volume of copper powder having an average particle size of 1 to 10 μm, and 20 to 90% by volume of tungsten and / or molybdenum having an average particle size of 1 to 10 μm. A conductor paste containing a percentage by volume is prepared, and the paste is printed and applied to each sheet-like molded body by a technique such as screen printing or gravure printing.

At this time, as the conductor paste for forming the surface wiring layer, the conductor component composition is copper at 10 to 70% by volume, W and / or Mo at 30 to 90% by volume, and the conductor for internal wiring layer formation. The paste preferably contains 20 to 80% by volume of copper and 20 to 80% by volume of W and / or Mo.

When a via-hole conductor is formed, a via-hole having a diameter of 50 to 250 μm is formed in the sheet-like molded body by a microdrill, a laser, or the like, and the above-mentioned surface wiring layer forming layer is formed in the via-hole. Alternatively, a conductive paste for forming an internal wiring layer is filled.

In these conductor pastes, in order to enhance the adhesion to the insulating layer, 0.05 to 2% by volume of aluminum oxide powder or the same composition powder as the oxide ceramic component forming the insulating layer is used. It is also possible to add in the ratio of.

Thereafter, the sheet-like molded body on which the conductive paste was applied by printing was aligned and laminated and pressed, and the laminated body was fired in a non-oxidizing atmosphere at a maximum firing temperature of 1200 to 1500 ° C. The firing is performed under the following conditions.

If the firing temperature at this time is lower than 1200 ° C., the aluminum oxide insulating substrate cannot be densified to a relative density of 95% or more when ordinary raw materials are used, and the thermal conductivity and the strength are reduced. If the temperature is higher than ℃, sintering of W or Mo itself proceeds, and a uniform structure with copper cannot be maintained. In addition, the grain size of the main crystal phase of the oxide ceramics increases, abnormal grain growth occurs, and the diffusion speed increases as the length of the grain boundary, which is the path when copper diffuses into the ceramics, decreases. This is because it is difficult to suppress the diffusion distance to 30 μm or less. Preferably, from 1250 to 1400
The range of ° C is good.

It is desirable that the non-oxidizing atmosphere at the time of this firing be nitrogen or a mixed atmosphere of nitrogen and hydrogen. In particular, in order to suppress the diffusion of copper in the wiring layer, hydrogen and hydrogen are used. Dew point + 10 ° C or less including nitrogen, especially-
It is desirable that the atmosphere be a non-oxidizing atmosphere of 10 ° C. or less. Note that an inert gas such as an argon gas may be mixed into this atmosphere, if desired. If the dew point during firing is higher than + 10 ° C., the oxide ceramic reacts with moisture in the atmosphere during firing to form an oxide film, and this oxide film reacts with copper of the copper-containing conductor, resulting in a low conductor. This not only hinders resistance but also promotes copper diffusion.

Thereafter, the co-fired surface wiring layer 2a of the wiring board is subjected to at least one selected from the group consisting of Au, Cu, Ti, Ni and Pd by electroless plating or electrolytic plating as described above. One kind of metal layer is used for 0.1.
It is formed with a thickness of 5 to 10 μm.

Further, Fe-
When a metal fitting made of Ni-Co, Cu-W, or the like is attached, it can be joined to the metal layer using a solder such as a eutectic solder.

[0049]

EXAMPLE An aluminum oxide powder (average particle size 1.8 μm)
m), 4% by weight of MnO ₂ , 3% by weight of SiO ₂ , and 0.5% by weight of MgO were added and mixed, and then an acrylic binder was used as an organic resin (binder) for molding. After preparing a slurry by mixing toluene as a solvent, the thickness is 250 μm by a doctor blade method.
Into a sheet. Then, the hole diameter 1
A 20 μm via hole was formed.

Next, using copper powder having an average particle size of 5 μm and W powder or Mo powder having an average particle size of 0.8 to 12 μm, Tables 1 and 2 were used for an internal wiring layer and a surface wiring layer.
And an acrylic binder was used as a solvent to prepare a conductor paste.

Then, the above-mentioned conductor paste was printed and applied on the sheet-like molded body, and the via-hole conductor of each sheet-like molded body was also filled with the above-mentioned conductor paste for an internal wiring layer. Each sheet-like molded body produced as described above was aligned and laminated and pressed to prepare a laminate in which the sheet-like molded body coated with the surface wiring layer conductor paste was the uppermost layer. Thereafter, the laminate is degreased in an oxygen-containing atmosphere (N ₂ + O ₂ or in the air) substantially free of moisture.
Firing was performed at a temperature of 300 ° C. in a nitrogen-hydrogen mixed atmosphere having a dew point of −10 ° C.

Then, various metal layers as shown in Table 1 were formed on the surface wiring layer by electrolytic plating.

Separately, the relative density was measured by Archimedes method for a sintered body obtained by firing a laminate of sheet-like molded bodies to which the paste was not applied under the same conditions as described above. %, The thermal conductivity (thickness: 3 mm) was 18 W / m · K, and the volume resistivity was 10 ¹⁴ Ω-cm or more by a laser flash method.

The conductor resistance, length, width, and thickness of the wiring were measured for the surface wiring layer, the internal wiring layer, and the surface wiring layer on which the metal layer was formed, and then the conductor having a thickness of 15 μm was formed. The converted sheet resistance (mΩ / □) was calculated. In addition, the appearance of the wiring board was inspected, and the occurrence of bleeding of the surface wiring layer and the presence or absence of peeling of the surface wiring layer were observed. Result is,
The results are shown in Table 1.

[0055]

[Table 1]

As shown in Table 1, in the composition of the surface wiring layer, in Sample No. 1 in which the Cu content of the wiring layer was less than 10% by volume, the conductor resistance after plating was larger than 8 mΩ / □. Also, the sample No. 11 having more than 70% by volume,
In No. 12, the shape retention of the wiring deteriorated, the structure became uneven, the sheet resistance became 8 mΩ / □ or more, and bleeding and partial peeling of the surface wiring layer were observed.
In Sample No. 12 in which the Cu content of the wiring layer was more than 80% by volume in the composition of the internal wiring layer, the sheet resistance of the internal wiring layer was higher than 6 mΩ / □. In Sample No. 2 in which the Cu content was not higher than that in the surface wiring layer, the sheet resistance was not lower than that in the surface wiring layer after plating.

In the wiring board of the present invention, E
In PMA (X-ray microanalyzer) analysis, the distance from the end of the wiring layer to the outermost part of the region where the copper element is detected in the same plane was measured at 10 places.
The average diffusion distance of copper in each wiring layer was 20 μm or less, indicating good characteristics.

[0058]

As described in detail above, according to the wiring board of the present invention, a wiring layer containing low-resistance copper is formed on at least the surface of an insulating substrate made of aluminum oxide ceramic having high thermal conductivity by simultaneous firing. Thus, a highly reliable, high-density, low-resistance wiring layer can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of a multilayer wiring board of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 1a, 1b, 1c Insulating layer 2a Surface wiring layer 2b Internal wiring layer 3 Via hole conductor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5E346 AA12 AA15 AA35 AA43 BB01 CC17 CC19 CC32 CC35 CC36 CC38 DD02 DD13 DD22 DD34 EE24 FF18 GG02 GG06 GG08 GG09 GG10 HH02

Claims (4)

[Claims] 1. A ceramic insulating substrate comprising: a ceramic insulating substrate; and a surface wiring layer and an internal wiring layer formed inside and on the surface of the insulating substrate by simultaneous firing with the insulating substrate. 10 to 70% by volume, tungsten and / or
Or containing molybdenum in a proportion of 30 to 90% by volume,
The internal wiring layer contains 20 to 80% by volume of copper and 20 to 80% by volume of tungsten and / or molybdenum, and the content of copper in the internal wiring layer is larger than that of the surface wiring layer. A multilayer wiring board characterized by the above-mentioned. 2. The sheet resistance of said surface wiring layer is 8 mΩ / □.
2. The multilayer wiring board according to claim 1, wherein: 3. A method according to claim 1, wherein a metal layer is formed on the surface of said surface wiring layer by plating.
The multilayer wiring board as described in the above. 4. The multilayer wiring board according to claim 1, wherein a sheet resistance of the surface wiring layer on which the internal wiring layer and the metal layer are formed is 6 mΩ / □ or less.