JPH09237957A - Alumina circuit board and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reliable circuit board, using as its insulating substrate alumina ceramic containing blackening agent, and, even after electroless plating, free from plate sticking to its portions where the plate is undesirable. SOLUTION: A conductor paste containing either or both of W and Mo as the main components is applied to a molded body that contains Al2 O3 as the main component and 0.01-5wt.% of at least one element selected from Mo, W and Nb in terms of metal, and, in some cases, has carbon powder added. The workpiece is then fired in a non-oxidizing atmosphere to obtain a board 1 made of black ceramic, the total amount of carbon of which is 0.005-3wt.%. Thereafter, an electroless plating layer 3 of Ni, Au or the like is formed on the surface of the conductor layer 2 on the board 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board in which a black alumina ceramic suitable for a multilayer wiring board, a package for housing a semiconductor element, etc. is used as an insulating board and an electroless plating layer is formed on the surface of a conductor layer. And its manufacturing method.

[0002]

2. Description of the Related Art Conventionally, alumina-based ceramics have been widely used as insulating substrates such as multilayer wiring boards and semiconductor element housing packages because they are excellent in high insulation resistance and chemical resistance. Properties required for the alumina ceramics used as such an insulating substrate include thermal properties such as heat resistance, mechanical properties such as strength, chemical properties such as corrosion resistance, and electromagnetic properties such as conductivity. . In addition to these properties, a black appearance is also preferable. This is because if it is black, it is easy to find even a small amount of dust, and if it is black, the part can be clearly identified when it is worn or damaged, and it can be marked with a laser. This is because the visibility at the time of optically wire-bonding can be improved.
In addition, black has a profound feeling and is excellent in aesthetics.

Such black alumina ceramics have conventionally been used as blackening agents for Cr, Nb, W and M.
It is produced by adding an oxide such as o and firing at a temperature of 1300 ° C. or higher after molding.
No. 23532, Japanese Examined Patent Publication No. 61-12868, JP-A-1
No. -282147.

On the other hand, in the circuit board, a plating layer is formed on the surface of the conductor layer in order to prevent oxidation of the conductor and to reduce the resistance. Recently, the plating layer is formed by electroless plating. Is being done. In this electroless plating method, a substrate on which a conductor layer is formed is immersed in a plating solution to form a plating layer on the surface of the conductor layer by utilizing the difference in ionization tendency of metal.

[0005]

However, when plating is performed by the electroless plating method, if a compound such as W or Mo is contained as a blackening agent in the alumina-based ceramics, especially when firing the ceramics. When firing in a non-oxidizing atmosphere at the time of co-firing with a conductor such as W or Mo, the blackening agent on the surface of the ceramic is reduced by the reducing action of the atmosphere and deposited as a metal. In addition to the layers, there is a problem that a plating layer is formed even on the surface of the deposited metal.

Such an unnecessary adhesion phenomenon of plating on the layers other than the conductor layer has become a serious problem that impairs the reliability of the circuit as the distance between the conductor layers becomes narrower due to the higher density of the electric circuit.

Therefore, the present invention provides a highly reliable circuit board which does not cause unnecessary plating adhesion even by electroless plating in a circuit board using an alumina ceramic containing a blackening agent as an insulating substrate. That is the purpose.

[0008]

As a result of repeated studies on the above problems, the present inventor found that a certain amount of carbon was contained in alumina ceramics containing a blackening agent to achieve electroless plating. The present inventors have found that the reducing action in a liquid can be suppressed, and thus unnecessary plating can be prevented from adhering to the present invention.

That is, the alumina-based circuit board of the present invention is
l ₂ O ₃ as a main component, Mo, at least one of 0.01 to 5 wt% in terms of metal selected from the group consisting of W and Nb,
Further, on the surface of the insulating substrate made of black ceramics containing carbon in a proportion of 0.005 to 3% by weight in the total amount,
The present invention is characterized in that a conductor layer mainly containing at least one of W and Mo is formed, and an electroless plating layer is further formed on the surface of the conductor layer.

Further, according to the method for producing an alumina circuit board of the present invention, at least one metal selected from the group consisting of Mo, W and Nb, or a compound thereof, in terms of metal, is added to Al ₂ O ₃ . A non-oxidizing atmosphere is obtained by applying a conductor paste mainly containing at least one of W and Mo to the surface of a sheet-shaped compact containing 0.01 to 5% by weight, and optionally 3% by weight or less of carbon powder. After firing in, a substrate having a conductor layer formed on the surface of an insulating substrate made of black ceramics having a total carbon content of 0.005 to 3% by weight is prepared, and then the surface of the conductor layer is electroless plated by an electroless plating method. It is characterized in that a plating layer is formed.

In the above structure, Cr or a Cr compound is further added as a blackening agent, and Cr is contained in the ceramic in a proportion of 0.03 to 1.5% by weight in terms of metal. It is what

[0012]

According to the alumina-based circuit board of the present invention, in the alumina-based ceramic of the insulating substrate, together with the blackening agent,
By containing a certain amount of carbon, the generated metal is carbonized by the carbon in the ceramic by the reducing action of the electroless plating solution, the ionization tendency thereof is lowered, and the adhesion of the plating can be suppressed. as a result,
It is possible to prevent unnecessary plating from adhering to portions other than the conductor layer, and it is possible to form a highly reliable circuit while having a black color. Therefore, due to high-density wiring, the distance between wiring layers is 2
00 μm or less, especially 100 μm or less, further 50 μm
According to the configuration of the present invention, a highly reliable circuit can be formed even when the interval becomes narrower than the following.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The alumina-based circuit board of the present invention is
As shown in FIG. 1, an insulating substrate 1 made of alumina ceramics, a conductor layer 2 is formed on at least the surface of the insulating substrate 1, and a plating layer 3 is further formed on the surface of the conductor layer 2. .

According to the present invention, the above-mentioned alumina-based ceramic is mainly composed of Al ₂ O ₃ and contains at least one selected from the group consisting of Mo, W and Nb in an amount of 0.01 to 5% by weight in terms of metal, especially The content is 0.5 to 3% by weight. These additives are for so-called blackening. If the content of these additives is less than 0.01% by weight, the blackening is insufficient, and if it exceeds 5% by weight, the electrical insulation is deteriorated. , Because it cannot be used as a circuit board.

A preferred embodiment for blackening is Cr
In an amount of 0.03 to 1.5% by weight in terms of metal and at least one of Nb, Mo and W in an amount of 0.5 to 3% by weight in terms of metal, and the total amount is 1 to 4% by weight. It is better to prepare it so that it becomes%. This is because a deep black color is obtained by the above combination. However, if the amount of Cr exceeds 1.5% by weight, the sinterability tends to decrease, the number of voids tends to increase, and the strength tends to decrease.
This is because if at least one of Mo and W exceeds 3% by weight, the electrical insulation tends to decrease.

Further, in the present invention, the total amount of carbon in the alumina ceramics is 0.005 to 3% by weight,
It is particularly important that the content is 0.01 to 2% by weight. The reason why the total carbon amount is limited to the above range is that if less than 0.005% by weight, unnecessary plating adhesion cannot be improved and 3% by weight
This is because the voids increase in the ceramics and the strength decreases when it exceeds. This carbon exists as free carbon in the ceramics or includes carbon content in the metal carbide.

Further, the alumina-based ceramics of the present invention contains Si, Mg and Ca as sintering aid components.
In order to improve the sinterability, it is desirable to contain at least one of the above in a ratio of 0.1 to 8% by weight in terms of oxide. However, if it exceeds 8% by weight, the glass component in the ceramics becomes excessive and voids increase, and the strength tends to decrease.

Further, in the circuit board of the present invention, the conductor layer formed on the surface of the insulating substrate made of alumina ceramics is at least one of W and Mo.
It is a seed and is formed with a thickness of 5 to 20 μm. Further, as the electroless plating layer formed on the surface of this conductor layer,
It is composed of at least one metal selected from Ni, Au, Co and Cr, and is 0.05 to 3 μm on the surface of the conductor layer.
It is formed with a thickness of m.

In order to produce the alumina-based ceramics of the present invention, first, Al ₂ O ₃ powder is mixed with Mo,
0.01 or more of at least one metal selected from the group consisting of W and Nb, or an oxide or carbide thereof, in terms of metal.
~ 5% by weight. Also, if desired, Si
0.1 to 8% by weight of at least one of O ₂ , MgO and CaO, and 0.03 in terms of metal of oxide or carbide of Cr.
~ 1.5 wt% added.

Then, a molding aid such as an organic binder is further added to the mixture, and the mixture is mixed with a desired molding means,
For example, a doctor blade method, a rolling method, a die press, a cold isostatic press, an extrusion molding, or the like is used to form an arbitrary shape.

Next, this molded body is decomposed and removed by a molding aid such as an organic binder in a humidified nitrogen-hydrogen mixed atmosphere at 200 to 500 ° C., and then in a nitrogen-hydrogen mixed atmosphere at 1400 to 1600 ° C. By calcination, the relative density can be densified to 96% or more.

According to the present invention, it is necessary to contain carbon in a proportion of 0.005 to 3% by weight in the finally obtained sintered body. For that purpose, at least one kind of metal carbide selected from the group of Cr, Mo, W and Nb is added as an additive at the time of forming a molded body, or carbon powder is added at a ratio of 3% by weight or less to control. To do. Further, although the molding aid is usually completely removed, it can also be controlled by controlling the decomposition and removal step and the residual carbon amount in the decomposition and removal of the added organic binder.
Further, in order to manufacture a circuit board having a conductor layer, a circuit pattern is coated with a metallized ink such as Mo-Mn on the surface of the alumina-based ceramic board manufactured as described above and baked at 1300 to 1500 ° C. Or,
Desirably, a metallized ink mainly composed of a metal such as W or Mo is applied to a circuit pattern on the surface of the above-mentioned alumina-based molded body, and if desired after multi-layer pressure bonding, it is heated at 1350 to 1650 ° C in a non-oxidizing atmosphere such as nitrogen. A circuit board having a conductor layer can be produced by co-firing with a metallizing ink at a temperature of about 0.5 to 5 hours.

After that, the circuit board obtained as described above is dipped in an electroless plating solution containing a plating metal such as Ni or Au to form a plating layer only on the conductor layer. You can

[0024]

[Example] As a raw material powder, Al ₂ having an average particle size of 1 μm
₃ % by weight of SiO ₂ as a sintering aid to O ₃ powder,
1% by weight of CaO and 2% by weight of MgO were added, and a metal or compound of Table 1 was used as a blackening agent, and further carbon powder was used in some cases. Polyethylene glycol was added as a binder, mixed by a ball mill, and tape-molded. The thickness of the tape molded body after firing W metallized ink into a circuit pattern is 15 μm.
It was screen printed so that Then, the sheet-shaped compact was debindered in a humidified nitrogen-hydrogen mixed atmosphere at 250 to 500 ° C., and was further fired in a nitrogen-hydrogen mixed atmosphere at 1550 ° C. for 2 hours. After that, this substrate is immersed in an electroless plating solution to form 0.5μ on the surface of the conductor layer.
An Au plating layer having a thickness of m was formed.

Further, in order to measure the physical properties such as strength of the alumina-based ceramics, the mixed powder described above was used in an amount of 6 × 4 × 50.
After press-molding to a size of mm, it was fired at the same temperature as above to produce a sintered body.

[0026]

[Table 1]

With respect to the obtained sintered body, the relative density was measured by the Archimedes method, and the three-point bending bending strength was measured based on JIS3081, and the total carbon amount in the ceramics was measured by the carbon analyzer. In addition, the insulation resistance of the ceramics itself was measured to examine the color tone of the ceramics. Further, on the circuit board, adhesion of plating between the conductor lines in the circuit pattern after electroless plating was observed. The results are shown in Table 2.

[0028]

[Table 2]

According to the results shown in Tables 1 and 2, the total carbon content was 0.
In Sample No. 1 with less than 005 wt%, many adhesion of plating other than the conductor layer was observed, and in Sample No. 7 with more than 3 wt%, strength was low and insulation resistance was 10 ¹² Ω-cm.
It became smaller and was not suitable as an insulating substrate.
Further, the total amount of Mo, W and Nb as a blackening agent is 5
Samples Nos. 11, 16 and 18 in which the content was more than 10% by weight had problems such as a decrease in strength and the deposition of plating on unnecessary portions. Further, in Sample No. 19 in which the total amount was less than 0.01% by weight, good blackening could not be achieved.

In contrast to these comparative examples, the products of the present invention have high strength of 45 kg / mm ² or more, insulation resistance of 10 ¹³ Ω-cm or more, black to black purple, and electroless. No adhesion of plating to the parts other than the conductor layer due to plating was observed.

[0031]

As described in detail above, the alumina-based circuit board of the present invention is black and has physical properties such as high strength and high electric insulation, and unnecessary plating adhesion between conductive lines in electroless plating. As a result, it is possible to provide a board having excellent productivity with few defects even in the manufacture of a circuit board having fine wiring.

[Brief description of drawings]

FIG. 1 is a schematic view of a circuit board of the present invention.

[Explanation of symbols]

 1 Insulating substrate 2 Conductor layer 3 Plating layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location // H05K 1/03 610 H01L 23/14 M

Claims (4)

[Claims] 1. Mainly composed of Al ₂ O ₃ , Mo, W and N
At least one selected from the group b is 0.0 in terms of metal.
1 to 5% by weight, and a conductor layer mainly containing at least one of W and Mo is formed on the surface of an insulating substrate made of black ceramics containing carbon in an amount of 0.005 to 3% by weight in the total amount. An alumina-based circuit board, further comprising an electroless plating layer formed on the surface of the conductor layer. 2. The alumina circuit board according to claim 1, wherein the ceramic further contains Cr in a ratio of 0.03 to 1.5% by weight in terms of metal. _3. Mo, W and Nb with respect to Al ₂ O ₃ .
0.01 to 5% by weight of metal, or at least one metal selected from the group
To 3 wt% (including 0) of the sheet-shaped molded body is coated with a conductive paste containing at least one of W and Mo and baked in a non-oxidizing atmosphere to obtain a total carbon content. Of 0.005 to 3% by weight of black ceramics on which a conductor layer is formed on the surface of the substrate, and then a plating layer is formed on the surface of the conductor layer by electroless plating. And a method for manufacturing an alumina circuit board. 4. The method for producing an alumina-based circuit board according to claim 3, wherein the molded body further contains Cr in a proportion of 0.03 to 1.5% by weight in terms of metal.