JP2001015869A - Wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a wiring board which is formed of a material that contains copper and is low in resistance and high in thermal conductivity and where thermal vias which are large in diameter and arranged at a narrow interval can be formed at the same time when an insulating board is formed by sintering. SOLUTION: A wiring board is equipped with an insulating board formed of ceramic whose main component is aluminum oxide and relative density is 95% or above and which contains 2.0 to 10.0 wt.% Mn in terms of Mn2O3 and thermal vias 2 provided penetrating through the insulating board so as to dissipate heat released from a heat releasing device mounted on the insulating board, where the thermal via 2 is formed of thermal good conductor which contains 10 to 60 vol.% copper and 40 to 90 vol.% tungsten and/or molybdenum, its maximum diameter is set 200 μm or above, and an interval between the adjacent thermal vias is set at 50 to 300 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring substrate which is an insulating substrate made of ceramics mainly composed of aluminum oxide, and more particularly, to a wiring substrate made of a low-resistance conductor and formed by co-firing with an insulating substrate. The present invention relates to a wiring board including a thermal via formed so as to penetrate from the front surface to the back surface of the insulating substrate in order to radiate heat generated from a heat-generating element mounted on the front surface of the substrate, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, heat generated by a semiconductor device has been increasing along with the high integration of semiconductor elements. In order to eliminate the malfunction of the semiconductor device, a wiring board capable of releasing such heat to the outside of the device is required. On the other hand, as for electrical characteristics, signal delay has become a problem due to an increase in operation speed, and it has been required to use conductors having small conductor loss, that is, low resistance.

[0003] As a wiring board on which such a semiconductor element is mounted, from the viewpoint of reliability, an alumina ceramic is used as an insulating substrate, and a wiring layer made of a refractory metal such as tungsten or molybdenum is deposited on the surface or inside thereof. The formed ceramic wiring board is frequently used. However, in a wiring layer made of a refractory metal that has been widely used, the resistance can be reduced only to about 8 mΩ / □ at most.
For this reason, the heat dissipation is also improved by bonding the heat dissipation fins or thermal vias, but a large effect cannot be obtained because the thermal conductivity of the W metallization itself is poor.

On the other hand, in recent years, a multilayer wiring board using a so-called glass ceramic which can be co-fired with copper or silver which is a low-resistance conductor has been proposed. However, the thermal conductivity of glass ceramics is at most several W / m · K.
However, it has become difficult to solve the thermal problem. To solve this problem, by forming a thermal via in the same manner as with alumina or the like, the thermal conductivity as a wiring substrate can be improved to about ten and several W / m · K.
However, in recent years, miniaturization has progressed further, and there is a situation where thermal vias alone cannot be used as a wiring substrate.

[0005] Therefore, as a method of simultaneously solving the thermal problem and the electrical problem, aluminum oxide is used.
Japanese Patent Application Laid-Open Nos. H8-8502, H7-115101, and No. 26 describe a method for forming a conductor layer formed by simultaneously sintering copper or a combination of copper and tungsten or molybdenum.
66744.

[0006]

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 molten copper component separates to the surface, causing bleeding of the surface wiring layer and the volatilization of copper In particular, when the via diameter is large, such as a thermal via, the copper dissolved during the firing is eluted, so that the thermal via cannot be formed. . In addition, there is a problem that the copper component in the conductor diffuses into the ceramics of the insulating substrate during firing and deteriorates the insulation between the wiring layers.

According to Japanese Patent Application Laid-Open No. 7-15101,
Once all the wiring layers are placed inside the insulating substrate and fired at the same time, the insulating layer on the surface is polished and removed by polishing or the like to expose the internal wiring layer to the surface. And forming a surface wiring layer 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, since the internal wirings are simultaneously fired, it is difficult to form a conductor layer such as a thermal via.

Further, Japanese Patent No. 2666744 discloses that a fine alumina powder having an average particle diameter 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, copper or the like 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.

In a conventional alumina-based wiring board, a single wiring material such as Cu, Ag, W, and Mo is used. However, due to a difference in thermal expansion between the substrate material and the via wiring material, a via and an insulating substrate are not fired after firing. Separation or substrate cracking. Therefore, the thermal via diameter is 200 at most.
In this case, the distance between adjacent vias needs to be about 300 μm or more, so that there is a limit to improvement in heat dissipation.

Accordingly, the present invention is directed to a wiring board on which a heat generating element is mounted and on which a thermal via is formed, wherein heat generated from the heat generating element can be efficiently radiated and a thermal via forming portion is provided. It is an object of the present invention to provide a wiring board which is free from cracks and the like and has excellent reliability.

[0011]

Means for Solving the Problems The inventors of the present invention have studied the above problems, and as a result, have found that in a wiring board using an oxide ceramic as an insulating substrate, a ceramic mainly containing aluminum oxide is used as an insulating substrate. The thermal via is formed of a composite conductor material of Cu and a high melting point metal such as W / Mo, and the thermal expansion of the insulating substrate and the thermal via are matched by changing the ratio. Therefore, the present inventors have found that it is possible to increase the hole diameter of the thermal via and to narrow the interval between the vias, thereby improving the heat radiation characteristics of the thermal via.

That is, the wiring board of the present invention radiates heat generated from an insulating substrate made of ceramics containing aluminum oxide as a main component and having a relative density of 95% or more, and a heat generating element mounted on the surface of the insulating substrate. A wiring board having a plurality of thermal vias formed so as to penetrate from the front surface to the back surface of the insulating substrate, the thermal vias are made of 10 to 60% by volume of copper, and 40 to 90% by volume of tungsten and / or molybdenum. And the maximum diameter of the thermal via is 2
It is characterized in that it is not less than 00 μm and the interval between adjacent thermal vias is 50 to 300 μm.

The thermal expansion coefficient of the insulating substrate and the good thermal conductor in the thermal via at 40 to 400 ° C. is 5 ppm / ° C. or less, and the thermal via has a substantially elliptical cross-sectional shape. Or the insulating substrate contains Mn in an amount of 2.0 to 10.0% by weight in terms of Mn ₂ O _3.
Is desirable.

[0014]

FIG. 1 is a schematic sectional view showing one embodiment of a wiring board according to the present invention. According to the wiring board of FIG. 1, a thermal via 2 penetrating from the front surface to the back surface is provided in an insulating substrate 1 made of ceramics mainly composed of aluminum oxide.

In the wiring board of the present invention, the insulating substrate 1
When the heat generating element 4 such as a semiconductor element is mounted directly on the upper surface of the formation portion of the thermal via 2 or via the conductor layer 3, the heat generated from the heat generating element 4 directly or Heat is transferred to the heat sink 5 and the like joined to the back surface of the insulating substrate 1 via the thermal via 2 via the thermal via.

Further, in addition to the thermal via 2, a surface wiring layer 6 a, an internal wiring layer 6 b, and a via-hole conductor 7 may be formed on the insulating substrate 1 of the wiring board. The wiring layers 6a and 6b and the via-hole conductor 7 are all formed by firing simultaneously with the insulating substrate 1.

(Insulating substrate) In the present invention, the insulating substrate 1
Is mainly composed of aluminum oxide, but is composed of a high-density body having a relative density of 95% or more, particularly 97%, and more preferably 98% or more in order to achieve the thermal conductivity and high strength of the insulating substrate. And a thermal conductivity of 1
It is desirably 0 W / m · K or more, particularly 15 W / m · K or more, and more desirably 17 W / m · K or more.

In the present invention, in order to achieve shape retention during simultaneous sintering with the thermal via 2 or the like, 1200 to 1500
It is necessary to fire at a low temperature as low as 95 ° C., but according to the present invention, even at such a low temperature, the relative density is 95%.
It is necessary to densify as described above.

From this point of view, the insulating substrate 1 according to the present invention contains aluminum oxide as a main component, and specifically contains aluminum oxide in a proportion of at least 84% by weight. As the Mn compound
It must be contained at a rate of 2.0 to 10.0% by weight in terms of ₂ O ₃ . That is, the amount of the Mn compound is 2.0% by weight.
If it is less than 1, the densification at 1200 to 1500 ° C. cannot be achieved, and if it is more than 10.0% by weight, the insulating substrate 1
This is because the insulating property of the metal decreases. The optimum range of the Mn compound is ₃ to 7% by weight in terms of Mn ₂ O ₃ .

Further, in the insulating substrate 1, SiO ₂ and alkaline earth element oxides such as MgO, CaO, and SrO are added as a third component in order to improve the simultaneous sinterability with the copper-containing conductor. At a ratio of 0.4 to 8% by weight.

Further, a metal such as W or Mo as a fourth component 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, but the crystal containing an auxiliary component in the grain boundaries to enhance the thermal conductivity. 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.

(Thermal via) On the other hand, the thermal via 3
Is 10 to 60% by volume of copper, 40 and W and / or Mo
It must be contained at a rate of ~ 90% by volume.

The ratio of copper to W and / or Mo depends on the heat dissipation of the thermal via 3, the simultaneous sintering with the insulating substrate 1, the maintenance of the shape retention after the simultaneous firing of the thermal via 3, and the insulation. It is important to match the thermal expansion characteristics with the substrate. The copper content is less than 10% by volume, and the W and Mo content is 9% by volume.
If the content is more than 0% by volume, not only the thermal conductivity of the thermal via becomes equal to and lower than W, but also a crack such as a crack occurs in the insulating substrate due to a difference in thermal expansion.

Further, when the content of copper is more than 60% by volume, W or M
If the amount of o is less than 40% by volume, the shape retention of the thermal vias after simultaneous firing is reduced, and bleeding or the like occurs in the thermal vias 3 or the thermal vias have large irregularities. A defect occurs in which the conductor in the via is missing. The optimal composition range is 30-60% by volume of copper and 40-70% by volume of W and / or Mo.

In the present invention, it is desirable that the W and / or Mo are dispersed and contained in a matrix composed of copper as spherical particles having an average particle diameter of 1 to 10 μm or sintered particles of several particles. . When the average particle size is smaller than 1.0 μm, the shape retention of the good thermal conductor in the thermal via 3 is deteriorated, the structure becomes porous, and the thermal conductivity is reduced. Is separated by the particles of W or Mo, the heat conduction path is cut off, the thermal resistance is increased, and the copper component is separated, thereby causing bleeding or the like. W and / or Mo have an average particle size of 1.3 to 5 μm, particularly 1.3 to 3 μm
Most preferably, they are dispersed in the size of

According to the present invention, the difference in thermal expansion coefficient between the insulating substrate 1 and the good thermal conductor forming the thermal via 2 at 40 to 400 ° C. is 5 ppm / ° C. or less, particularly 4 ppm.
It is desirable that: This is because the thermal expansion difference is 5pp
If the temperature is higher than m / ° C., when the thermal vias 2 to be described later are arranged at the same diameter and at intervals, the insulating substrate 1 between the thermal vias 2 may be cracked by stress caused by a difference in thermal expansion. That's why.

FIG. 2 is a plan view for explaining the arrangement of the thermal via 3. As shown in FIG. 2, the maximum diameter X of the thermal via 3 is 200 μm or more, particularly 210 μm or more, and further 250 μm or more. The distance Z between adjacent thermal vias is 50 to 300 μm, especially 50 to 290 μm.
m, and more preferably 50 to 250 μm, in order to increase the efficiency of heat dissipation in the wiring board.

That is, the maximum diameter of the thermal via is 200 μm.
Smaller, and the distance between adjacent thermal vias is 300μ
If it is larger than m, not only is it necessary to form a large number of thermal vias in a predetermined region, but also because a portion having a high thermal resistance increases locally, good heat dissipation cannot be obtained, and Induces malfunction due to heat generation. Further, when the interval between adjacent thermal vias 3 is smaller than 50 μm,
This is because cracks and the like occur in the insulating substrate 1 between the thermal vias 3.

The thermal via 2 according to the present invention comprises:
Generally, the cross section is circular, but it is desirable that the maximum diameter X and the minimum diameter Y be substantially elliptical with X> Y as shown in FIG. This is because the area occupied by the thermal vias when the thermal vias are arranged in a lattice as shown in FIG. 2 is larger in the substantially elliptical shape than in the circular shape, and the heat dissipation per unit area of the wiring board is larger. Can be increased. In particular, the ratio of the maximum diameter X / minimum diameter Y in the substantially elliptical shape is preferably 1.1 or more, particularly preferably 1.2 or more.

The surface wiring layer 6a and the internal wiring layer 6b
Also, it is desirable that the through-hole conductor 7 be formed of the same conductor as the good thermal conductor forming the thermal via 2 from the viewpoint of simultaneous sintering.

According to the wiring board of the present invention, the average surface roughness Ra of the surface of the insulating substrate 1 is 1 μm or less, particularly 0.7 μm or less by firing at a controlled firing temperature and atmosphere as described later. The surface having excellent smoothness can be formed. As a result, when the surface wiring layer 6a is formed on the surface of the insulating substrate 1, it is not necessary to perform a polishing process or the like on the surface of the insulating substrate 1.

Furthermore, in the wiring board of the present invention, the thermal via 2, the surface wiring layer 6a, the internal wiring layer 6b and the via-hole conductor 7 are simultaneously baked at a temperature exceeding the melting point of copper with aluminum oxide. May diffuse into the insulating substrate 1, but according to the present invention,
It is desirable that the diffusion distance of copper into the ceramics of the insulating substrate 1 around the conductor layer be 20 μm or less, particularly 10 μm or less. This is because if the diffusion distance of copper into the ceramic exceeds 20 μm, the insulation between the wiring layers decreases, and the reliability as a wiring substrate decreases.

(Manufacturing Method) Next, a method of manufacturing a wiring board according to the present invention will be specifically described. First, in order to form an insulating substrate, an aluminum oxide raw material powder which is a main component of oxide ceramics has an average particle size of 0.5 to 2.
5 μm, especially 0.5 to 2.0 μm powder is used. If the average particle size is smaller than 0.5 μm, it is difficult to handle the powder, and the cost of the powder is increased.
If it is larger than this, it becomes difficult to fire at a temperature of 1500 ° C. or less.

Then, ₂ to 10% by weight of MnO ₂ as a sintering aid is added to the aluminum oxide powder as appropriate.
Particularly, it is added at a ratio of 3 to 7% by weight. In addition, as appropriate,
0.4 to 8% by weight of O ₂ , MgO, CaO, SrO powder and the like, and 2% by weight or less in terms of metal as a color component using a metal powder or oxide powder of a transition metal such as W, Mo or Cr. Added.

In addition, in addition to the oxide powder, the above oxides may be added as carbonates, nitrates, acetates, etc. which can form oxides 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. Then, the diameter of this sheet-like molded body after firing by a microdrill, laser, or the like is 0.1 to
A through hole for a thermal via having a thickness of 0.3 mm is formed. Also, a through-hole for a via-hole conductor having a diameter of 50 to 250 μm may be formed at the same time.

With respect to the sheet-like molded body thus produced, as a conductor component, a copper-containing powder having an average particle diameter of 1 to 10 μm is 10 to 60% by volume, particularly 40 to 60% by volume,
W and / or Mo having an average particle size of 1 to 10 μm
A conductor paste containing a content of about 90% by volume, especially about 40% to 60% by volume is prepared, and the paste is filled into the through holes provided in each sheet-like insulating layer by a screen printing method or the like.

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 filled with the conductive paste is aligned and pressed by lamination, and the laminated body is fired in a non-oxidizing atmosphere at a maximum firing temperature of 1 ° C.
The firing is performed under the condition of a temperature of 200 to 1500 ° C.

When the surface wiring layer and the internal wiring layer are formed, the above-mentioned conductive paste is printed and applied on the surface of the sheet-like molded body by a method such as screen printing or gravure printing. Then, firing is performed in the same manner as described above.

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, so that the thermal conductivity and strength are reduced, and 1500 ° C. If the temperature is higher than 0 ° C., sintering of W or Mo itself proceeds, and a uniform structure with copper cannot be maintained.
Only the same heat dissipation can be obtained. 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 becomes difficult to suppress the diffusion distance to 20 μm or less. Preferably, the range of 1250-1400 degreeC is good.

It is preferable that the non-oxidizing atmosphere at the time of firing is 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 oxidizing atmosphere are preferable. 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.

[0045]

EXAMPLE An aluminum oxide powder (average particle size 1.8 μm)
m), Mn ₂ O ₃ was added at a ratio as shown in Tables 1 and 2, SiO ₂ was added at 3% by weight, and MgO was added at a ratio of 0.5% by weight. A slurry was prepared by mixing an acrylic binder as a forming organic resin (binder) and toluene as a solvent, and then formed into a sheet having a thickness of 250 μm by a doctor blade method. Then, the shape of the via hole after firing by a micro drill at a predetermined location is the maximum diameter X in Tables 1 and 2,
Via holes were formed so as to have a minimum diameter and an interval Z between via holes.

Next, copper powder having an average particle diameter of 5 μm and W powder or Mo powder having an average particle diameter of 0.8 to 12 μm were mixed at the ratios shown in Tables 1 and 2, and an acrylic binder was mixed. A conductor paste was prepared using acetone as a solvent.

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 wiring layer. Each sheet-like molded body produced as described above was aligned, laminated and pressed to produce a molded body laminate. Thereafter, the molded laminate is placed in an oxygen-containing atmosphere (N
₂ + O ₂ or in the air) and then Tables 1 and 2
At the firing temperature shown in Table 2 and a nitrogen-hydrogen mixed atmosphere with a dew point of -20 ° C.

The relative density of the insulating substrate in the manufactured wiring substrate was measured by the Archimedes method, and the thermal conductivity (thickness: 3 mm) was measured by the laser flash method.

The structure was observed with a scanning electron microscope, and the structure around the via hole was observed. The results are shown in Tables 1 and 2.

[0050]

[Table 1]

[0051]

[Table 2]

As shown in Tables 1 and 2, M in the insulating substrate
The content of n ₂ O ₃ is lower than 2% by weight and the relative density is 9%.
In sample No. 1 smaller than 5%, the thermal conductivity of the substrate deteriorated, the insulating property also deteriorated, and it could not be used as a wiring substrate. Also, in Sample No. 28, in which the firing temperature was low and the relative density was less than 95%, the thermal conductivity of the substrate was similarly reduced, and the thermal conductivity of the entire wiring substrate was reduced.

In the thermal via conductor, Cu
In Sample No. 8 having a content of less than 10% by volume, the thermal conductivity of the entire wiring board was smaller than 60 W / m · K. Cracks were observed on the insulating substrate. Cu
In Sample No. 16 having a content of more than 70% by volume, not only the shape retention of the conductor is deteriorated, but also the structure becomes non-uniform, the conductor is also missing in the thermal via, and bleeding and Partial peeling was also observed in the wiring layer on the surface.

In contrast to these comparative examples, according to the wiring board of the present invention, the insulating substrate has a relative density of 95% and a power density of 60 W / m ·
A thermal via having good thermal conductivity was formed by simultaneous firing, having a thermal conductivity of K or more, without causing bleeding of the thermal via and falling off of the conductor.

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.

[0056]

As described in detail above, according to the wiring board of the present invention, large-diameter and narrow-spaced thermal vias penetrating from the surface to the back of an insulating substrate made of aluminum oxide ceramic having high thermal conductivity are simultaneously fired. It can be formed as a conductor layer containing copper with low resistance, and a thermal via with high reliability and low resistance and good thermal conductivity can be formed.

[Brief description of the drawings]

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

FIG. 2 is a plan view for explaining the shape of a thermal via in the wiring board of the present invention.

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 1/11 H01L 23/36 D (72) Inventor Nariki Yamada 1-4-4 Yamashita-cho, Kokubu-shi, Kagoshima KYOCERA (72) Inventor Masanobu Ishida 1-4-4 Yamashita-cho, Kokubu-shi, Kagoshima F-term in Kyocera Research Institute (reference) 4E351 AA07 AA08 BB01 BB31 BB49 CC12 CC22 CC35 DD04 DD17 DD18 EE02 EE08 GG04 GG16 5E317 AA24 AA25 BB04 BB12 BB16 BB17 BB19 BB24 CC22 CC25 CD32 GG03 GG20 5E338 AA03 AA18 BB05 BB12 BB25 BB75 CC08 EE02 5F036 AA01 BB01 BB08 BC31 BD01 BD13

Claims (4)

[Claims] 1. An insulating substrate made of ceramics containing aluminum oxide as a main component and having a relative density of 95% or more, and a surface of the insulating substrate for radiating heat generated from a heat-generating element mounted on the surface of the insulating substrate. In a wiring board having a plurality of thermal vias formed so as to penetrate from the back to the back, the thermal vias are made of 10 to 60% by volume of copper, and 40 to 90% by volume of tungsten and / or molybdenum.
And the maximum diameter of the thermal vias is 200 μm or more, and the interval between adjacent thermal vias is 50 to 300 μm.
A wiring board, characterized in that: 2. The thermal expansion coefficient difference between the insulating substrate and the good thermal conductor in the thermal via at 40 to 400 ° C. is 5p.
2. The wiring board according to claim 1, wherein the temperature is not more than pm / ° C. 3. The wiring board according to claim 1, wherein the thermal via has a substantially elliptical cross-sectional shape. 4. The wiring substrate according to claim 1, wherein said insulating substrate contains Mn at a ratio of 2.0 to 10.0% by weight in terms of Mn ₂ O ₃ .