JP4530525B2 - Wiring board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wiring board having a surface wiring layer and an internal wiring layer made of a low resistance conductor.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a wiring substrate on which a semiconductor element or the like is mounted is generally a ceramic wiring substrate in which an alumina ceramic is used as an insulating base and a wiring layer made of a refractory metal such as tungsten or molybdenum is deposited on at least the surface thereof. . However, a ceramic wiring board that has been widely used conventionally has a wiring layer formed of a refractory metal such as tungsten, and the refractory metal has a high electrical resistivity (electric resistivity (20 ° C.), tungsten: 5 .5 × 10 ⁻⁶ Ω · cm, Molybdenum: 5.7 × 10 ⁻⁶ Ω · cm) Therefore, the wiring layer should have a sufficiently low resistance in order to increase the calculation speed of semiconductor elements, etc. There was a drawback that could not.
[0003]
Therefore, as a method for solving this conventional defect, the present applicant has previously described an insulating base composed of ceramics mainly composed of aluminum oxide and having a relative density of 95% or more, and copper on the surface and / or inside of the insulating base. A wiring board having a metallized layer (wiring layer) containing 10 to 70% by volume of tungsten and 30 to 90% by volume of tungsten and / or molybdenum and a method for manufacturing the same have been proposed (see Japanese Patent Laid-Open No. 2000-188453). .
[0004]
According to this wiring board, since the metallized layer (wiring layer) contains low-resistance copper, the electrical resistance of the conductor forming the wiring layer is low (electric resistivity (20 ° C.) is about 3 to 5 × 10 −6 Ω. Furthermore, since the insulating base is made of an aluminum oxide sintered body and the like, and the relative density is high and dense, the thermal conductivity can be increased.
[0005]
Such a wiring board is, for example, a plurality of sheets obtained by molding a ceramic component containing aluminum oxide as a main component and containing manganese oxide (MnO ₂ ) in a proportion of 2.0 to 6.0% by weight into a sheet shape. On the surface of the ceramic green sheet, a conductive paste containing 10 to 70% by volume of copper powder and 30 to 90% by volume of tungsten and / or molybdenum having an average particle diameter of 1 to 10 μm is printed and applied. The ceramic green sheets are laminated on top and bottom and are fired at a temperature of 1200 to 1500 ° C. in a non-oxidizing atmosphere.
[0006]
[Problems to be solved by the invention]
However, although the wiring substrate can be made to have a low resistance, the copper powder is fused at a temperature equal to or higher than the melting point of copper, which is the main component of the wiring layer. Sintering integration with respect to the wiring layer was insufficient, and the adhesive strength of the wiring layer to the insulating substrate was low. Therefore, in this wiring board, when an external force or the like is applied to the wiring layer, a gap is formed between the wiring layer on the surface of the insulating base and the insulating base due to the external force or the like, and moisture contained in the air enters the gap and enters the gap. Moisture, etc. causes oxidation and corrosion from the connection interface between the wiring layer inside the insulating substrate and the surface wiring layer to the inside of the wiring layer, resulting in poor connection between the surface wiring layer and the internal wiring layer, or corrosion. interconnection between adjacent layers with the eluted metal component had the disadvantage or electrically shorted.
[0007]
The present invention has been devised in view of the above drawbacks, and its purpose is to reduce the resistance of the wiring layer formed on the insulating substrate and to electrically connect the internal wiring layer and the surface wiring layer and between the wiring layers. An object of the present invention is to provide a wiring board excellent in long-term reliability, which can maintain long-term insulation.
[0008]
[Means for Solving the Problems]
Wiring board of the present invention, the surface and inside of the insulating substrate, tungsten and / or connecting wiring layer and said internal wiring layer and the surface wiring layer to form a surface wiring layer and the internal wiring layer made of molybdenum and copper a wiring board formed by connecting through, the insulating substrate through-hole is the connection wiring layer together is formed by laminating a plurality of insulating layers provided on each of said insulating layer of said insulating substrate is formed, and the outermost connection wiring layer located in the through hole of the outermost layer of the insulating layer between the tungsten and / or molybdenum and iron group metal, located in the through hole of the other of said insulating layer other connection wiring layer which is formed by a tungsten and / or molybdenum and copper, the outermost layer of the connection wiring layer and the other connection wiring layer, when the cross-sectional shape is a circular shape Moni, is characterized in that it is formed as overlapping or the larger concentric towards the outermost layer of the connection wiring layers to each other.
[0009]
The wiring board of the present invention, the thickness of the insulating layer of the outermost layer to form the insulating substrate, Ru 10μm to 25μm der.
[0010]
According to the wiring board of the present invention, the surface wiring layer and the internal wiring layer are made of tungsten and / or molybdenum and copper, and low resistance copper (electric resistivity (20 ° C.) is 1.7 × 10 ⁻⁶ Ω · c), each wiring layer can be made to have a low resistance corresponding to the increase in the calculation speed of the semiconductor element, the loss of the signal propagating through the wiring layer is reduced, and the semiconductor element operates normally. Can be made.
[0011]
According to the wiring board of the present invention, the surface wiring layer and the internal wiring layer are connected via the connection wiring layer formed in the through hole provided in each insulating layer of the insulating base, and the connection wiring layer Since the connection wiring layer formed in the through hole of the insulating layer located in the outermost layer is formed of tungsten and / or molybdenum and an iron group metal that adheres firmly to the insulating base , the surface wiring layer and Even if moisture enters from the gap between the insulating substrate and the moisture, the moisture does not contact the internal wiring layer, and as a result, corrosion of the internal wiring layer is effectively prevented. As a result, the connection reliability between the surface wiring layer and the internal wiring layer can be improved, and electrical insulation between adjacent wiring layers can be ensured and the long-term reliability can be improved.
[0012]
At the same time, the connection wiring layer disposed in the through hole provided in the insulating layer other than the outermost layer among the insulating layers forming the insulating base is formed of tungsten and / or molybdenum and copper to have a low resistance. As a result, the entire connection wiring layer has low resistance, and all of the surface wiring layer, internal wiring layer, and connection wiring layer have low resistance corresponding to the increase in the operation speed of the semiconductor element, and signals are propagated to each wiring layer. In this case, the loss of the propagated signal is greatly reduced, and the semiconductor element can be operated normally. Further, the outermost connection wiring layer and the other connection wiring layers have a circular cross-sectional shape, and are formed as concentric circles that overlap with each other or have a larger outermost connection wiring layer. Intrusion of moisture into the insulating base can be prevented evenly, and the long-term reliability of the wiring board can be improved.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a wiring board according to the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows an embodiment in which the wiring board of the present invention is used as a wiring board for mounting a semiconductor element. 1 is an insulating substrate formed by laminating a plurality of insulating layers 1a, and 2 is a surface wiring. Reference numerals 3 and 3 are internal wiring layers, and 4 is a connection wiring layer formed in a through-hole 5 provided in each insulating layer 1a. These insulating substrate 1, surface wiring layer 2, internal wiring layer 3, and connection wiring layer 4 Thus, the wiring substrate 7 on which the semiconductor element 6 is mounted is formed.
[0014]
According to the present invention, as shown in enlarged view in FIG. 2, the surface wiring layer 2 and the internal wiring layer 3, thereby forming a conductor composed mainly of a composite material of tungsten and / or molybdenum and copper, Of the connection wiring layer 4, the connection wiring layer 4 a located in the through hole 5 of the outermost insulating layer 1 a is formed of tungsten and / or molybdenum and an iron group metal, and in the through hole 5 of another insulating layer. The connection wiring layer 4b located at is formed of tungsten and / or molybdenum and copper.
In this embodiment, the surface wiring layer 2, the internal wiring layer 3 and the connection wiring layer 4 are formed by simultaneous firing with the insulating substrate 1.
(Insulating Base) In the present invention, the insulating base 1 functions as a base on which the semiconductor element 6 is mounted and supported, and ceramic sintering such as an aluminum oxide sintered body, an aluminum nitride sintered body, and a silicon carbide sintered body. A plurality of insulating layers 1a made of a body are stacked, and a semiconductor element 6 is mounted on the upper surface.
[0015]
In order to improve the thermal conductivity and mechanical strength of the insulating substrate 1, it is desirable that the insulating substrate 1 be composed of a highly dense body having a relative density of 95% or more.
[0016]
Furthermore, in the present invention, the insulating substrate 1 is fired at a low temperature of 1200 ° C. to 1500 ° C. in order to achieve shape retention by simultaneous firing of the surface wiring layer 2, the internal wiring layer 3 and the connection wiring layer 4. However, according to the present invention, it is desirable to densify to a relative density of 95% or higher even in such low-temperature firing.
[0017]
From this point of view, the insulating base 1 in the present invention is preferably, for example, one having aluminum oxide as a main component, specifically, one containing aluminum oxide in a proportion of 90% by weight or more. As for, it is desirable to contain a Mn compound at a ratio of 2.0 to 6.0% by weight in terms of MnO ₂ . That is, if the manganese compound is less than 2.0% by weight, densification at 1200 ° C. to 1500 ° C. is difficult to achieve, and if it exceeds 6.0% by weight, the insulating property of the insulating substrate 1 is lowered. The optimum range of the manganese compound is 3 to 5% by weight in terms of MnO ₂ .
[0018]
Further, in this insulating substrate 1, a total of 0.4 to 8% by weight of SiO ₂ and alkaline earth element oxides such as MgO, CaO and SrO are added as a third component in order to improve the low temperature sinterability. It is desirable to make it contain in the ratio.
[0019]
Further, the insulating substrate 1 may contain a metal such as W, Mo and Cr as a coloring component in a proportion of 2% by weight or less in order to improve the dielectric properties such as the coloring component and the dielectric constant.
[0020]
Components other than the above-mentioned aluminum oxide exist as an amorphous phase or a crystalline phase at the grain boundary of the aluminum oxide main crystal phase, but a crystal phase containing an auxiliary component is formed in the grain boundary in order to improve thermal conductivity. It is desirable that
[0021]
When the insulating substrate 1 is formed mainly of aluminum oxide, the aluminum oxide main crystal phase exists as a granular or columnar crystal, and the average crystal grain size of these main crystal phases is 1.5 to 5. It is desirable to be 0 μm.
[0022]
In addition, 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 achieve high thermal conductivity, and when the average grain size is larger than 5.0 μm, sufficient strength required for use as a substrate material can be obtained. This is because it becomes difficult.
[0023]
Such an insulating substrate 1 is formed by, for example, forming a slurry (sludge material) obtained by adding an organic binder or a solvent to a raw material powder mainly composed of aluminum oxide into a sheet shape by a doctor blade method or the like. This ceramic green sheet is laminated and fired at a temperature of 1200 ° C. to 1500 ° C. in a non-oxidizing atmosphere.
(Surface wiring layer and internal wiring layer)
The surface wiring layer 2 is formed in a predetermined pattern on the surface of the insulating substrate 1 and functions as an electrode pad for connecting the electrode of the semiconductor element 6 mounted on the wiring board 7 and connects the electrode of the semiconductor element 6. It acts as a conductive path connected to the wiring layer 4. Further, the internal wiring layer 3 is connected to the surface wiring layer 2 via the connection wiring layer 4 and functions as a conductive path for leading the electrode of the semiconductor element 6 to the outside.
[0024]
The surface wiring layer 2 and the internal wiring layer 3 are made by screen printing or the like on the surface of a ceramic green sheet using a conductive paste obtained by kneading tungsten and / or molybdenum powder and copper powder together with an organic solvent and a binder at a predetermined ratio. Can be formed by printing.
[0025]
The surface wiring layer 2 and the internal wiring layer 3 preferably contain 10 to 70% by volume of copper and 30 to 90% by volume of tungsten and / or molybdenum. This is to reduce the resistance of the surface wiring layer 2 and the internal wiring layer 3 and to achieve simultaneous sintering with the insulating base 1, and to maintain the preserving during the simultaneous firing of the surface wiring layer 2 in particular. If the amount of copper is less than 10% by volume and the amount of tungsten or molybdenum is more than 90% by volume, the resistance of the conductor forming the surface wiring layer 2 and the internal wiring layer 3 is high (electric resistivity is about 5%). .5 × 10 ⁻⁶ Ω · cm or more). Further, if the amount of copper is more than 70% by volume and the amount of tungsten or molybdenum is less than 30% by volume, the preserving at the time of co-firing of the surface wiring layer 2 is reduced, and the surface wiring layer 2 may be blurred. The surface wiring layer 2 is agglomerated due to the molten copper and disconnection occurs, and the surface wiring layer 2 and the internal wiring layer 3 are separated due to the difference in the number of thermal expansion systems between the insulating substrate 1, the surface wiring layer 2 and the internal wiring layer 3. This is because it occurs. The optimum composition range is 40-60% by volume of copper and 60-40% by volume of tungsten and / or molybdenum.
[0026]
In the present invention, tungsten and / or molybdenum in the surface wiring layer 2 and the internal wiring layer 3 is dispersed in a matrix made of copper as sintered particles of spherical or several particles having an average particle diameter of 1 to 10 μm. It is desirable to contain. This is because when the average particle size is smaller than 1 μm, the shape retaining property of the surface wiring layer 2 is deteriorated and the structure becomes porous, and the resistance of the surface wiring layer 2 and the internal wiring layer 3 is increased. If it exceeds the upper limit, the copper matrix is divided by tungsten or molybdenum particles, and the resistance of the surface wiring layer 2 and the internal wiring layer 3 is increased, or the copper component is separated and bleeding occurs. Most preferably, tungsten and / or molybdenum is dispersed with an average particle size of 1.3 to 5 μm, particularly 1.3 to 3 μm.
[0027]
Further, in the surface wiring layer 2 and the internal wiring layer 3, in order to improve the adhesion to the insulating substrate 1, a ratio of 0.05 to 2% by volume of alumina or ceramics having the same component as the insulating substrate 1 is used. It is also possible to contain.
[0028]
Furthermore, in the wiring board 7 of the present invention, the surface wiring layer 2 and the internal wiring layer 3 containing the copper are co-fired with the insulating substrate 1 at a temperature exceeding the melting point of copper. Although the copper component in 3 may diffuse into the insulating substrate 1, according to the present invention, the diffusion distance of copper to the ceramic around the surface wiring layer 2 containing at least copper and the internal wiring layer 3 is 20 μm. Hereinafter, it is particularly desirable that the thickness is 10 μm or less. This is because if the diffusion distance of copper into the ceramic exceeds 20 μm, the insulation between the surface wiring layers 2 and the internal wiring layers 3 is lowered during the formation of the electric circuit, and the reliability of the electric circuit is lowered.
[0029]
By setting the copper diffusion distance to 20 μm or less, the minimum distance between each wiring layer formed in the same plane of the surface wiring layer 2 and the internal wiring layer 3 is 100 μm or less, particularly a high density of 90 μm or less. Can be achieved.
[0030]
If the exposed surface of the surface wiring layer 2 is covered with a plated metal layer such as nickel, copper, or gold, the surface wiring layer 2 can be prevented from oxidative corrosion, and the surface wiring layer can be prevented. The bonding property of the bonding wire with respect to 2 and solder wettability can be improved, and at the same time, the resistance of the surface wiring layer 2 can be further reduced. Therefore, it is preferable that the exposed surface of the surface wiring layer 2 is covered with a plating metal layer (not shown) such as nickel, copper, or gold. For example, the nickel or copper plating layer has a thickness of 1 to 10 μm and gold plating. The layers are preferably deposited sequentially with a thickness of 0.3 to 3 μm.
(Connection wiring layer)
The surface wiring layer 2 and the internal wiring layer 3 are connected to each other through a connection wiring layer 4 formed by filling a predetermined conductive material in a through hole 5 provided in each insulating layer 1a. In the connection wiring layer 4, through holes are formed in a ceramic green sheet serving as each insulating layer 1 a of the insulating base 1 by a laser processing method, a mechanical punching method, or the like, and a predetermined amount is formed in the through holes. The conductive paste is printed and filled by screen printing or the like.
[0031]
According to the wiring board of the present invention, it is important that the connection wiring layer 4a located in the through hole of the outermost insulating layer of the connection wiring layer 4 is formed of tungsten and / or molybdenum and an iron group metal. is there.
[0032]
If the connection wiring layer 4a located in the through hole of the outermost insulating layer is formed of tungsten and / or molybdenum and an iron group metal, the connection wiring layer 4a is excellent in adhesive strength to the insulating substrate 1. There is almost no gap in which moisture enters between the connection wiring layer 4a and the insulating substrate 1, and moisture enters the gap formed between the surface wiring layer 2 and the insulating substrate 1 and enters the gap. Even if moisture tries to contact the internal wiring layer 3, the contact operation is effectively blocked by the connection wiring layer 4 a, which makes the connection reliability between the surface wiring layer 2 and the internal wiring layer 3 extremely good. The electrical insulation between the adjacent internal wiring layers 3 is ensured, and the long-term reliability of the wiring board 7 can be improved.
[0033]
The outermost connection wiring layer 4a is difficult to effectively prevent moisture from entering when the length in the thickness direction is less than 25 μm . Therefore, it is preferable that the outermost connection wiring layer 4a has a thickness of 25 μm or more.
[0034]
The connection wiring layer 4a of the outermost layer, when the wiring board 7 viewed from the top, by previously completely cover such cross-sectional shape other connection wiring layer 4b, to prevent moisture from entering the good good it is possible, it can be made the reliability of the wiring board 7 superior. Therefore, the outermost layer of the connection wiring layer 4a, when the wiring board 7 viewed from the top, can you other connection wiring layer 4b as cross-sectional shape such as to completely cover, in particular the outermost layer of the connection wiring layer 4a and with the other connection wiring layer 4b and together in a circular shape in cross-sectional shape, by forming a overlapping or outermost layer having a larger concentric connection wiring layer 4a together, the moisture of the insulating base 1 can be uniformly prevented from entering the interior, it can be made long-term reliability of the wiring board 7 superior.
[0035]
In addition, when forming the said connection wiring layer 4a with the surface wiring layer 2 and the internal wiring layer 3, it is necessary to make the baking temperature into the low temperature of 1200-1500 degreeC. Therefore, in the present invention, to achieve this, an iron group metal is contained in tungsten and / or molybdenum.
[0036]
By forming the connection wiring layer 4a by adding iron group metal to tungsten and / or molybdenum, the sinterability at a low temperature can be improved, and the connection wiring layer 4a can be formed by co-firing with the insulating substrate 1. it can be strengthened adhesion strength to.
[0037]
When the amount of the iron group metal is less than 0.1% by volume in terms of oxide, the connection wiring layer 4a does not progress in densification of the connection wiring layer 4a, resulting in poor sintering and adhesion strength to the insulating substrate 1. Decreases. On the other hand, if it exceeds 5% by volume, the tungsten and molybdenum particles grow abnormally and the adhesive strength with the insulating substrate 1 decreases. Therefore, the amount of the iron group metal is preferably 0.1 to 5% by volume, more preferably 0.5 to 2% by volume in terms of oxide.
[0038]
Examples of the iron group metal in the connection wiring layer 4a include iron, nickel, and cobalt. Among these, nickel is the most desirable.
[0039]
Further, the oxide equivalent amount is an amount converted in the form of Fe ₂ O _{3 for} iron (Fe), NiO for nickel (Ni), and Co ₃ O ₄ for cobalt (Co).
[0040]
Furthermore, it is also effective to add the same kind of ceramic powder as the insulating substrate 1 such as aluminum oxide in the connection wiring layer 4a in order to increase the adhesive strength with the insulating substrate 1 mainly composed of aluminum oxide or the like. is there. However, if the content is more than 45% by volume, there is a risk of causing poor sintering. Accordingly, when aluminum oxide is added to the connection wiring layer 4a, the content is particularly preferably 2 to 35% by volume.
[0041]
Of the connection wiring layer 4, it is important that the connection wiring layer 4b other than the outermost connection wiring layer 4a is formed of tungsten and / or molybdenum and copper.
[0042]
If the connection wiring layer 4b is formed of tungsten and / or molybdenum and copper, the electrical resistance of the connection wiring layer 4b becomes lower due to the inclusion of copper, and as a result, the electrical resistance of the entire connection wiring layer 4 is reduced to the surface. It is as low as the wiring layer 2 and the internal wiring layer 3 and can sufficiently cope with the increase in the calculation speed of the semiconductor element 6. Thus, the loss of the signal is greatly reduced, and the semiconductor element 6 can be operated normally.
[0043]
The other connection wiring layer 4b made of tungsten and / or molybdenum and copper can be the same as the surface wiring layer 2 and the internal wiring layer 3, and is the same as the surface wiring layer 2 and the internal wiring layer 3. The conductive paste obtained by mixing tungsten and / or molybdenum powder and copper powder is printed and filled into the through-hole 5 formed in the ceramic green sheet to be the insulating substrate 1 by screen printing or the like. It is formed by.
(Production method)
Next, an example of a method for manufacturing the wiring board 7 will be specifically described in the case where the insulating substrate 1 is made of an aluminum oxide sintered body.
[0044]
First, in order to form the insulating substrate 1, a powder having an average particle size of 0.5 μm to 2.5 μm, particularly 0.5 μm to 2.0 μm is used as the aluminum oxide raw material powder as the main component of the ceramic sintered body. . This is because if the average particle size is smaller than 0.5 μm, it is difficult to handle the powder, and the cost of the powder becomes high. If it is larger than 2.5 μm, it is difficult to fire at a temperature of 1500 ° C. or less. It is.
[0045]
Then, MnO ₂ is added to the aluminum oxide powder at a ratio of 2.0 to 8.0% by weight, particularly 3.0 to 7.0% by weight as the second component. As appropriate, as the third component, SiO ₂ . 0.4 to 8% by weight of MgO, CaO, SrO ₂ powder, etc., and 4% by weight or less in terms of metal using a metal powder or oxide powder of a transition metal such as W, Mo, Cr or the like as a color component as a fourth component Add at a rate of
[0046]
In addition to the oxide powder, the oxide may be added as carbonate, nitrate, acetate, or the like that can form an oxide by firing.
[0047]
Next, a plurality of ceramic green sheets for forming the insulating substrate 1 are produced using this mixed powder. The ceramic green sheet can be produced by a known forming method. For example, after preparing a slurry by adding an organic binder or solvent to the above mixed powder, it is formed by a doctor blade method, or an organic binder is added to the mixed powder, and a ceramic green sheet having a predetermined thickness is formed by press molding, rolling molding, etc. Can be produced.
[0048]
Further, the ceramic green sheet is formed with a through hole 5 for filling a conductive paste that will be the connection wiring layer 4 in a later step by a laser processing method, a mechanical punching method, or the like.
[0049]
For the ceramic green sheet produced in this way, first, the conductive paste to be the outermost connection wiring layer 4a is printed and filled in the through holes of the ceramic green sheet to be the outermost insulating layer by screen printing or the like. To do. The conductor paste to be the outermost connection wiring layer 4a is, for example, 0.1% iron group metal oxide powder such as nickel oxide on tungsten and / or molybdenum having an average particle size of 0.5 to 5 μm. It is produced by adding and mixing an organic binder and a solvent with respect to a solid component containing ˜5 vol% and alumina powder in a proportion of 0 to 45 vol%.
[0050]
In addition, the conductive paste to be the connection wiring layer 4b other than the outermost layer is printed and filled into the through holes of the ceramic green sheet to be the insulating layer other than the outermost layer by a screen printing method or the like. The conductive paste used as the other connection wiring layer 4b is, for example, 10 to 70% by volume of copper powder having an average particle diameter of 1 to 10 μm, particularly 40 to 60% by volume, tungsten having an average particle diameter of 1 to 10 μm, and / or Or it can produce by adding and mixing an organic binder and a solvent with respect to the solid component formed by adding molybdenum powder in the ratio of 30 to 90 volume%, especially 40 to 60 volume%.
[0051]
In the conductor paste for forming the other connection wiring layer 4b, the same composition as the aluminum oxide powder or the oxide ceramic component forming the insulating layer is used in order to improve the adhesion to the insulating substrate 1. It is also possible to add the product powder at a ratio of 0.05 to 2% by volume.
[0052]
Next, a conductive paste that becomes the surface wiring layer 2 and the internal wiring layer 3 is printed on the surface of each ceramic green sheet by screen printing, gravure printing, or the like. As the conductive paste that becomes the surface wiring layer 2 and the internal wiring layer 3, the same conductive paste as the conductive paste that becomes the other connection wiring layer 4b can be used.
[0053]
Finally, after printing, applying, and laminating and bonding the ceramic green sheets filled with the respective conductive pastes to be the surface wiring layer 2, the internal wiring layer 3, and the connection wiring layer 4, the laminate is made non-oxidizing. Baking is performed in the atmosphere under conditions where the maximum baking temperature is 1200 to 1500 ° C.
[0054]
If the firing temperature at this time is lower than 1200 ° C., when an ordinary raw material is used, the insulating base made of the aluminum oxide sintered body cannot be densified to a relative density of 95% or more, and the thermal conductivity and strength are low. If the temperature is higher than 1500 ° C., the surface wiring layer 2, the internal wiring layer 3 and the other connection wiring layer 4b are sintered with tungsten or molybdenum itself, and the uniform structure with copper cannot be maintained. It becomes difficult to maintain low resistance, and sheet resistance becomes high. In addition, the grain size of the main crystal phase of the oxide ceramics increases and abnormal grain growth occurs, and the grain boundary length, which is the path when copper diffuses into the ceramics, becomes shorter and the diffusion speed increases. This is because it becomes difficult to control the diffusion distance to 30 μm or less. The range of 1350-1450 ° C is preferred.
[0055]
In addition, the non-oxidizing atmosphere at the time of firing is preferably nitrogen or a mixed atmosphere of nitrogen and hydrogen. In particular, in order to suppress diffusion of copper in the wiring layer, hydrogen and nitrogen are included. A non-oxidizing atmosphere with a dew point of + 10 ° C. or lower, particularly −10 ° C. or lower is desirable. In addition, you may mix inert gas, such as argon gas, in this atmosphere if desired. If the dew point during firing is higher than + 10 ° C., oxide ceramics react with moisture in the atmosphere during firing to form an oxide film, and this oxide film reacts with copper in the copper-containing conductor, resulting in a low conductor. This is because it not only prevents resistance, but also promotes copper diffusion.
[0056]
Furthermore, by controlling the baking temperature and atmosphere as described above, baking can be performed with an arithmetic average roughness Ra of the surface of the insulating substrate 1 of 1 μm or less, particularly 0.7 μm or less. .
[0057]
Thus, according to the wiring board 7 of the present invention, the semiconductor element 6 is mounted on the upper surface of the insulating base 1 and each electrode of the semiconductor element 6 is electrically connected to the surface wiring layer 2 via the bonding wires 8. Then, if necessary, the semiconductor element 6 is hermetically sealed using a bowl-shaped lid made of metal or ceramic, sealing resin (not shown), or the like, thereby completing a semiconductor device as a product.
[0058]
The present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. For example, in the above embodiments, the wiring board of the present invention is replaced with a semiconductor element. Although the case where it is applied to a wiring board for mounting has been described, this may be applied to a hybrid integrated circuit board or the like.
[0059]
【The invention's effect】
According to the wiring board of the present invention, the surface wiring layer and the internal wiring layer are made of tungsten and / or molybdenum and copper, and low resistance copper (electric resistivity (20 ° C.) is 1.7 × 10 ⁻⁶ Ω · c), each wiring layer can be made to have a low resistance corresponding to the increase in the calculation speed of the semiconductor element, the loss of the signal propagating through the wiring layer is reduced, and the semiconductor element operates normally. Can be made.
[0060]
According to the wiring board of the present invention, the surface wiring layer and the internal wiring layer are connected via the connection wiring layer formed in the through hole provided in each insulating layer of the insulating base, and the connection wiring layer Of these, the connection wiring layer formed in the through hole of the insulating layer located at the outermost layer is formed of tungsten and / or molybdenum and an iron group metal that adheres firmly to the insulating base, so that it is insulated from the surface wiring layer A gap is formed between the substrate and even if moisture enters through the gap, the entered moisture does not contact the internal wiring layer and the like, and as a result, corrosion of the internal wiring layer and the like can be effectively prevented. As a result, the connection reliability between the surface wiring layer and the internal wiring layer can be improved, and the electrical insulation between adjacent wiring layers can be ensured and the long-term reliability can be improved.
.
[0061]
At the same time, the connection wiring layer disposed in the through hole provided in the insulating layer other than the outermost layer among the insulating layers forming the insulating base is formed of tungsten and / or molybdenum and copper to have a low resistance. As a result, the entire connection wiring layer has low resistance, and all of the surface wiring layer, internal wiring layer, and connection wiring layer have low resistance corresponding to the increase in the operation speed of the semiconductor element, and signals are propagated to each wiring layer. In this case, the loss of the propagated signal is greatly reduced, and the semiconductor element can be operated normally. Further, the outermost connection wiring layer and the other connection wiring layers have a circular cross-sectional shape, and are formed as concentric circles that overlap with each other or have a larger outermost connection wiring layer. Intrusion of moisture into the insulating base can be prevented evenly, and the long-term reliability of the wiring board can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a wiring board according to the present invention.
FIG. 2 is an enlarged view of a main part of the wiring board shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Insulating base | substrate 2 ... Surface wiring layer 3 ... Internal wiring layer 4 ... Connection wiring layer 4a ... Outermost connection wiring layer 4b ... Other connection wiring layers 5... Through hole 6... Semiconductor element 7... Wiring substrate 8.

Claims (1)

On the surface and inside of the insulating substrate, formed by connecting through a connecting wiring layer and said internal wiring layer and the surface wiring layer with surface wiring layer consisting of tungsten and / or molybdenum and copper and to form an internal wiring layer A wiring board,
The insulating substrate of the connection wiring layer is formed in the through hole provided in each of the insulating layers of the insulating substrate, and the outermost layer of the insulating layer with is formed by stacking a plurality of insulating layers in the outermost layer of the connection wiring layer located in the through hole with tungsten and / or molybdenum and iron group metals, other connection wiring layer located within the through hole of the other of said insulating layer and tungsten and / or molybdenum The outermost connection wiring layer and the other connection wiring layer are formed of copper and have a circular cross-sectional shape and overlap each other or the outermost connection wiring layer is larger in concentric circles. A wiring board characterized by being formed in a shape .

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