JP2001185850A - Wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problems that the resistance of a wiring layer is high and a loss or the like occurs in high frequency signal. SOLUTION: This wiring board is composed of an insulation board 1 composed of sintered ceramics having heat conductivity higher than 10 W/m.k, a wiring layer 2 composed of tungsten and/or molybdenum and copper integrally formed on the board 1 by sintering simultaneous with the board 1, and a copper plated layer 7 attached on the exposed surface of this wiring layer 2. The wiring layer 2 and the copper plated layer 7 are diffused and bonded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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] A wiring board on which such a semiconductor element is mounted is made of alumina ceramic as an insulating base, 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 at most about 8 mΩ / □.

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.

As a method for solving the thermal problem and the electrical problem at the same time, the applicant of the present invention has previously described a method in which aluminum oxide is used as a main component and a manganese compound is used in an amount of 2.0 to 6.0% in terms of MnO _2. % Relative density is 95%
% Or more of ceramics, and at least the surface of the insulating base is formed by simultaneous firing of the insulating base and copper (Cu) in an amount of 10 to 70% by volume, tungsten (W) and / or molybdenum (Mo). Is contained in a proportion of 30 to 90% by volume, and tungsten and / or molybdenum have an average particle size of 1 to 1 in a matrix made of copper.
A wiring board comprising a wiring layer dispersed and contained as 0 μm particles has been proposed (see Japanese Patent Application No. 10-244237).

According to this wiring board, the insulating base is made of an aluminum oxide sintered body or the like, and has a high relative density and a high density, so that its thermal conductivity is as high as 10 W / m · K or more.
Further, since the wiring layer contains low-resistance copper, the sheet resistance can be reduced to 8 mΩ / □ or less.

Such a wiring board is formed, for example, on the surface of a green sheet containing a ceramic component containing aluminum oxide as a main component and manganese oxide (MnO 2) at a ratio of 2.0 to 6.0% by weight. Copper powder 10-7
A conductor paste containing 0% by volume and 30 to 90% by volume of tungsten and / or molybdenum having an average particle size of 1 to 10 μm is printed and applied in a circuit pattern, and then the green sheets are laminated. It is manufactured by baking in an oxidizing atmosphere under the condition that the maximum baking temperature is 1200 to 1500 ° C.

[0008]

However, although the wiring board has a wiring layer having a sheet resistance of 8 mΩ / □, which is lower than that of the conventional product, a semiconductor element using a high-frequency signal in a millimeter wave band or a microwave band is mounted. When a high-frequency signal is propagated to the wiring layer, the electric resistance is still high, and a loss is generated in the propagated high-frequency signal.

Therefore, it is conceivable to apply a plating layer made of copper having a low electric resistance on the surface of the wiring layer.

However, when a copper plating layer is deposited on the surface of the wiring layer, the wiring layer contains a metal having poor adhesion to the copper plating layer, such as tungsten or molybdenum. The semiconductor element is bonded to the wiring layer via a low melting point brazing material such as tin-lead solder because the adhesion strength with the layer is weak, and copper is easily diffused into the low melting point brazing material such as solder. When joining the wiring layer to the wiring conductor of the external electric circuit board via the low melting point brazing material, the copper plating layer is easily diffused and absorbed by the low melting point brazing material, and Tungsten and molybdenum having poor bonding properties with the low melting point brazing material will appear, and as a result, the bonding strength of the low melting point brazing material to the wiring layer will be degraded, and the disadvantage that the reliability of bonding will be greatly reduced will be induced. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and has as its object to increase the thermal conductivity of a wiring board and to reduce the electric resistance to a small value which does not cause a problem in the propagation of high-frequency signals. It is an object of the present invention to provide a wiring board excellent in mass productivity and capable of mounting a semiconductor element using a high frequency signal in a waveband or a microwave band.

[0012]

According to the present invention, there is provided a wiring board comprising: an insulating base made of a ceramic sintered body having a thermal conductivity of 10 W / m · K or more; and an insulating base formed by simultaneous firing with the insulating base. A wiring layer made of tungsten and / or molybdenum and copper formed, and a copper plating layer applied to an exposed surface of the wiring layer; and the wiring layer and the copper plating layer are diffusion-bonded. It is characterized by having.

According to the wiring board of the present invention, the wiring board obtained by forming the insulating base with a ceramic sintered body having a thermal conductivity of 10 W / m · K or more has good thermal conductivity.
The heat of the semiconductor device can be efficiently radiated to the outside of the device, and the semiconductor device can always be kept at an appropriate temperature to operate normally and stably for a long period of time.

Further, according to the wiring board of the present invention, since the wiring layer is formed of tungsten and / or molybdenum and copper, and the surface is coated with a copper plating layer, the electric resistance becomes extremely small. As a result, high-frequency signals in the millimeter-wave band or the microwave band can be propagated with almost no loss.

Further, according to the wiring board of the present invention, since the wiring layer and the copper plating layer are diffusion bonded, the bonding strength of the copper plating layer to the wiring layer is extremely high. The copper plating layer is diffused and absorbed by the low melting point brazing material even if it is joined via a low melting point brazing material such as solder or the wiring layer is joined to the wiring conductor of the external electric circuit board via the low melting point brazing material. As a result, tungsten or molybdenum hardly appears on the surface of the wiring layer in contact with the low melting point brazing material. As a result, the bonding strength of the low melting point brazing material to the wiring layer is extremely high, and the bonding reliability is extremely good. be able to.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a wiring board according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an embodiment of a package for housing a semiconductor element using a wiring board according to the present invention, wherein 1 is an insulating base, and 2 is a wiring layer. The insulating substrate 1 and the wiring layer 2 constitute a wiring board 4 on which the semiconductor element 3 is mounted. (Insulating Substrate) In the present invention, the insulating substrate 1 acts as a substrate for mounting and supporting a semiconductor element, and has a thermal conductivity of a sintered body of aluminum oxide, a sintered body of aluminum nitride, a sintered body of silicon carbide, or the like. Is formed of a ceramic sintered body of 10 W / m · K or more.

In order to achieve the thermal conductivity and the high strength of the insulating base 1, it is desirable that the insulating base 1 is made of a dense body having a relative density of 95% or more.

Further, according to the present invention, in order to achieve the shape-retaining property by simultaneous sintering with the wiring layer 2,
It is necessary to fire at a low temperature of 200 ° C. to 1500 ° C., but 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 this point of view, the insulating substrate 1 in the present invention is, for example, one having aluminum oxide as a main component,
Specifically, a material containing aluminum oxide in a proportion of 90% by weight or more is suitably used.
It is desirable to contain the n compound in a ratio of 2.0 to 6.0% by weight in terms of MnO2. That is, when the amount of the manganese compound is less than 2.0% by weight, 1200 ° C to 1500 ° C.
Is difficult to achieve, and if it is more than 6.0% by weight, the insulating property of the insulating substrate 1 is reduced. The optimum range of the manganese compound is 3 to 5% by weight in terms of MnO2.

The insulating substrate 1 contains SiO2 and alkaline earth element oxides such as MgO, CaO and SrO as a third component in order to enhance the simultaneous sinterability with the copper-containing conductor. It is desirable that the content be 0.4 to 8% by weight.

Further, a metal such as tungsten or molybdenum may be contained as a fourth component in a proportion of 2% by weight or less as a coloring component.

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.

When the insulating substrate 1 is formed mainly of aluminum oxide, the main crystal phase of aluminum oxide exists as granular or columnar crystals. The average crystal grain size of these main crystal phases is as follows. It is desirable that the thickness be 5 to 5.0 μm.

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,
This is because it is difficult to achieve high thermal conductivity, and if the average particle size is larger than 5.0 μm, it becomes difficult to obtain a sufficient strength required when used as a substrate material. (Wiring Layer) The wiring layer 2 functions as connection pads for connecting electrodes of the semiconductor element 3 mounted on the wiring board 1 via bonding wires 5 and the like, and also serves to connect the electrodes of the semiconductor element 3 to an external electric circuit board. To a conductive path for connection to a low melting point brazing material such as tin-lead solder.

The wiring layer 2 contains 10 to 70% by volume of copper,
It is necessary to contain tungsten and / or molybdenum at a ratio of 30 to 90% by volume. This is to achieve low resistance of the wiring layer 2 and simultaneous sinterability with the insulating base 1 and to maintain shape retention of the surface wiring layer after simultaneous firing. Less than volume%,
When the amount of tungsten or molybdenum is more than 90% by volume, the sheet resistance of the wiring layer increases. In addition, when the copper amount is 70
Volume%, tungsten and molybdenum content is 30%
When the volume is less than the volume%, the shape retention of the surface wiring layer 2 after the simultaneous firing is reduced, and bleeding or the like occurs in the surface wiring layer 2 or the surface wiring layer 2 is aggregated by the molten copper. This is because disconnection occurs and the wiring layer is separated due to a difference in thermal expansion coefficient between the insulating base and the wiring layer. The optimal composition range is 40 to 60% by volume of copper and 60 to 40% by volume of tungsten and / or molybdenum.

In the present invention, the tungsten and / or molybdenum are desirably dispersed and contained in a copper matrix as spherical or aggregated particles of several particles having an average particle diameter of 1 to 10 μm. When the average particle size is smaller than 1.0 μm, the shape retention of the wiring layer 2 on the surface is deteriorated, the structure becomes porous, and the resistance of the wiring layer 2 increases. Is separated by particles of tungsten or molybdenum to increase the resistance of the wiring layer 2 or to separate the copper component to cause bleeding. Most preferably, the tungsten and / or molybdenum are dispersed with an average particle size of 1.3 to 5 μm, particularly 1.3 to 3 μm.

The wiring layer 2 contains 0.05 to 2% by volume of aluminum oxide or ceramics having the same components as the insulating substrate in order to improve the adhesion to the insulating substrate 1. It is also possible.

Further, in the wiring board 4 of the present invention,
The co-firing at a temperature exceeding the melting point of copper with aluminum oxide may cause the copper component in the wiring layer 2 to diffuse into the insulating base 1. According to the present invention, the wiring layer 2 containing at least copper It is desirable that the diffusion distance of copper into the ceramics of the insulating substrate 1 around it is 20 μm or less, particularly 10 μm or less. This is because if the diffusion distance of copper into the ceramics exceeds 20 μm, the insulation between the wiring layers 2 is reduced, and the reliability as a wiring board is reduced.

By setting the copper diffusion distance to 20 μm or less, the minimum line distance between the wiring layers 2 formed in the same plane among the wiring layers 2 is set to 100 μm or less, particularly 9 μm.
High-density wiring of 0 μm or less can be achieved. Also,
Similarly, when a plurality of via hole conductors 6 are formed in one insulating layer as shown in FIG.
The minimum separation distance therebetween can be controlled to 100 μm or less, particularly 90 μm or less for the same reason as described above.

Furthermore, the wiring substrate 4 of the present invention is fired by controlling the firing temperature and the atmosphere 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 a major feature that when the wiring layer 2 is formed on the surface of the insulating substrate 1, it is not necessary to polish the surface of the insulating substrate 1. (Method of Forming Wiring Board 1) When the wiring board 1 is made of, for example, a ceramic sintered body containing aluminum oxide as a main component, it is formed as follows. That is, (1)
First, in order to form the insulating substrate 1, as an aluminum oxide raw material powder which is a main component of the ceramic sintered body, the average particle diameter is 0.5 to 2.5 μm, particularly 0.5 μm to 2.0 μm.
Use μ powder. 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 increases. It is.

Then, MnO2 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 appropriate, as the third component, SiO2, MgO, CaO,
SrO2 powder or the like is added in an amount of 0.4 to 8% by weight, and as a fourth component, a metal powder or oxide powder of a transition metal such as W, Mo, or Cr is added as a coloring component at a ratio of 2% by weight or less in terms of metal. .

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.

Next, a sheet-like molded body for forming the insulating substrate 1 is prepared using the mixed powder. The sheet-shaped molded body can be produced by a well-known molding method. For example, a slurry is prepared by adding an organic binder or a solvent to the mixed powder, and then formed by a doctor blade method. Body can be made.

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 70% by volume, particularly 40 to 60% by volume,
A conductive paste containing 30 to 90% by volume, particularly 40 to 60% by volume of tungsten and / or molybdenum having an average particle size of 1 to 10 μm is prepared, and this paste is screen-printed on each sheet-like insulating layer. And printing by a method such as gravure printing.

In order to enhance the adhesion to the insulating layer, the conductive paste contains 0.05 to 2 volumes of aluminum oxide powder or the same composition powder as the oxide ceramic component forming the insulating layer. % Can be added.

Finally, after the sheet-shaped molded body on which the conductive paste is applied by printing is aligned and laminated and pressed, the laminated body is fired in a non-oxidizing atmosphere at a maximum firing temperature of 1200 to 1500 ° C. And sintering under the condition of temperature.

If the firing temperature 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. If the temperature is higher than ℃, sintering of tungsten or molybdenum itself proceeds, and a uniform structure with copper cannot be maintained, and if it is difficult to maintain a low resistance, the sheet resistance increases. Also,
The grain size of the main crystal phase of the oxide ceramics increases and 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, and the diffusion speed increases. This is because it becomes difficult to suppress the distance to 30 μm or less. Preferably 1250 to 140
A range of 0 ° C. is preferred.

As the non-oxidizing atmosphere at the time of this firing, it is preferable to use 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.

The wiring board 1 is, as shown in FIG.
The copper plating layer 7 is applied to the exposed surface of the wiring layer 2 so that the wiring layer 2
And the copper plating layer 7 are diffusion bonded. The wiring layer 2 and the copper plating layer 7 are substantially integrated by diffusion bonding, and the integrated layer has two regions: a region made of copper containing tungsten and / or molybdenum and a region made of substantially pure copper. It is to be constituted by.

The copper plating layer 7 acts on the wiring layer 2 of the wiring board 4 as a main conductor for transmitting electric signals,
Particularly, since the wiring layer 3 is made of low-resistance copper, the wiring layer 3 has an effect of making the electrical resistance a small value that does not cause a problem even when a high-frequency signal in a millimeter wave band or a microwave band is propagated.

The copper plating layer 7 is made of, for example, copper sulfate 10
g / liter, 30 g / liter of EDTA-2Na, 3 cc / liter of formaldehyde (37% solution), and an electroless copper plating solution composed of a small amount of bipyridyl and polyethylene glycol, etc., and the exposed surface of the wiring layer 2 was degreased. After the acid treatment, the exposed surface of the wiring layer 2 is immersed in the electroless copper plating solution for a predetermined time so that the exposed surface of the wiring layer 2 is adhered to a predetermined thickness.

Note that the wiring layer 2
Tungsten and / or molybdenum exposed on the surface of the wiring layer 2 are removed by etching with a strong alkaline solution such as an aqueous solution containing potassium hydroxide and ferricyanide as main components so that copper is mainly exposed on the surface of the wiring layer 2. It is preferable to make the deposition of the copper plating layer 7 on the surface of the wiring layer 2 easy, and at the same time, the adhesion strength of the copper plating layer 7 can be increased.

The wiring layer 2 and the copper plating layer 7
For example, after the copper plating layer 7 is applied to the surface of the wiring layer 2, the wiring board 4 is heated in a non-oxidizing atmosphere at a temperature near the melting point of copper (1092 ° C.), for example, 900
° C to 1100 ° C, more preferably 950 ° C to 1040 ° C
By heat treatment.

If the gold plating layer 8 is applied to the surface of the copper plating layer 7, the wiring layer 2 can effectively prevent the copper plating layer 7 and the wiring layer 2 from being oxidized and corroded. The wettability of the low melting point brazing material to the layer 2 can be further improved. Therefore, the wiring layer 2 has a gold plating layer 8 on the surface of the copper plating layer 7, for example, having a thickness of 0.05 mm.
It is preferable to apply the coating in a thickness of from 3 μm to 3 μm.

The gold plating layer 8 is, for example, a substitutional type comprising, as a main component, gold potassium cyanide as a gold compound and ethylenediaminetetraacetic acid as a complexing agent, and adding potassium cyanide, potassium dihydrogen phosphate and the like. A gold plating solution and a reduction type gold plating solution containing gold potassium cyanide as a gold compound and sodium borohydride as a reducing agent as main components are prepared, and the copper plating layer 7 is coated thereon. The exposed surface of the wiring layer 2 is immersed for a predetermined time in the order of the replacement-type gold plating solution and the reduction-type gold plating solution for a predetermined thickness on the copper plating layer 7.

Thus, according to the wiring board of the present invention, the semiconductor element 3 is mounted on the semiconductor element mounting portion 1 a of the insulating base 1, and each electrode of the semiconductor element 3 is electrically connected to the wiring layer 2 via the bonding wire 5. After that, a bowl-shaped lid 9 made of metal or ceramics is joined to the upper surface of the insulating base 1 via a sealing material such as glass, resin, brazing material, or the like. A semiconductor device as a product is completed by hermetically housing the semiconductor element 3 inside the container formed of the semiconductor device 3 and the semiconductor element 3 is connected to an external electric circuit via the wiring layer 2 and the like. It should be noted that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. Although applied to the package for storage, it may be applied to other uses such as a hybrid integrated circuit board.

[0047]

According to the wiring substrate of the present invention, the wiring substrate obtained by forming the insulating substrate with a ceramic sintered body having a thermal conductivity of 10 W / m · K or more has a good thermal conductivity, The heat of the device can be efficiently dissipated to the outside of the device, and the semiconductor device can always be kept at an appropriate temperature to operate normally and stably for a long period of time.

Further, according to the wiring board of the present invention, since the wiring layer is formed of tungsten and / or molybdenum and copper, and the surface is coated with a copper plating layer, the electric resistance becomes extremely small. As a result, high-frequency signals in the millimeter-wave band or the microwave band can be propagated with almost no loss.

Further, according to the wiring board of the present invention, since the wiring layer and the copper plating layer are diffusion-bonded, the bonding strength of the copper plating layer to the wiring layer is extremely high. The copper plating layer is diffused and absorbed by the low melting point brazing material even if it is joined via a low melting point brazing material such as solder or the wiring layer is joined to the wiring conductor of the external electric circuit board via the low melting point brazing material. As a result, tungsten or molybdenum hardly appears on the surface of the wiring layer in contact with the low melting point brazing material. As a result, the bonding strength of the low melting point brazing material to the wiring layer is extremely high, and the bonding reliability is extremely good. be able to.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment in which a wiring board of the present invention is applied to a semiconductor element housing package for housing a semiconductor element.

FIG. 2 is a sectional view of a main part of the wiring board of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulating base 2 ... Wiring layer 3 ... Semiconductor element 4 ... Wiring board 5 ... Bonding wire 6 ... Via hole conductor 7 ... Copper plating layer 8 Gold plating layer 9 Lid

Claims (1)

[Claims] An insulating base made of a ceramic sintered body having a thermal conductivity of 10 W / m · K or more; tungsten and / or molybdenum formed integrally with the insulating base by co-firing with the insulating base; And a copper plating layer adhered to an exposed surface of the wiring layer, wherein the wiring layer and the copper plating layer are diffusion-bonded.