JPH05235549A - Manufacture of aluminum nitride multilayer board - Google Patents

Abstract

PURPOSE:To assume a high dimensional accuracy for a board by reducing a resistance of a conductor circuit of the board and to prevent a distortion of the board. CONSTITUTION:A green sheet 1 of aluminum nitride in which sintering assistant is added is molded in a sheet, and conductor circuits 3, 4 are provided on the sheet 1. Spacers of the aluminum nitride in which no assistant is added are molded in a sheet. The spacers are press-bonded on both upper and lower surfaces of the sheet 1, and baked. Then, both the spacers are removed by grinding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an aluminum nitride multilayer substrate.

[0002]

2. Description of the Related Art Conventionally, in this type of substrate manufacturing method, a green sheet is first formed from a slurry obtained by adding a sintering aid or the like to aluminum nitride powder. A conductor circuit is formed on the green sheet by a conductive metal paste containing tungsten or the like, and then a plurality of green sheets are laminated. These green sheet groups are placed in a carbon firing jig and fired at a predetermined temperature. Then, the aluminum nitride and the sintering aid react with each other to form a liquid phase composed of, for example, Al, Y, O, and as a result, each green sheet is sintered.

However, when the green sheet is fired under high temperature and high pressure, it is known that the sintered green sheet and the jig adhere to each other due to the liquid phase oozing outside the green sheet. Further, in such a case, carbon monoxide (CO) is generated by the reaction between the carbon content in the jig and the oxygen component in the liquid phase, and the carbon monoxide converts the tungsten in the inner-layer conductor circuit into a carbide to form the inner layer. It is also known to cause resistance increase in conductor circuits.

In order to avoid the problem of lowering the resistance of the inner layer conductor circuit, conventionally, spacers are closely arranged on the upper and lower surfaces of the stacked green sheet group, and guide rods are closely arranged on the periphery thereof. Then, the green sheets are fired in a state where they are not in contact with the jig. At that time, as the spacer and the guide rod, for example, those obtained by press-molding granules produced from a slurry containing aluminum nitride as a main component and not containing a sintering aid, followed by degreasing and pre-baking are used.

[0005]

However, in the conventional method, it is necessary to separately manufacture the green sheet of the sheet molded product and the spacer and the guide rod of the press molded product, which is disadvantageous in the process.

In the conventional method, the green sheet group,
When the spacers and the guide rods are arranged at predetermined positions in the jig, it is necessary to match the dimensions of the spacers and the guide rods with the dimensions of the green sheet group so that the green sheets are not distorted during the main firing. If the dimensions are not rigorously aligned, the gaps between the green sheet group, spacers, guide rods and jigs will not be eliminated, and tungsten carbide cannot be avoided.

However, when the dimensions of the spacers and the guide rods that have been press-molded are to be adjusted, it is necessary to predict the dimensional changes due to the subsequent degreasing and calcination, and it is extremely difficult to perform the dimensional adjustment strictly. It was

The present invention has been made in view of the above circumstances, and an object thereof is to reliably achieve reduction in resistance of a conductor circuit on a substrate by using a spacer whose dimensions can be easily adjusted, and to perform firing. It is an object of the present invention to provide a method for manufacturing an aluminum nitride multi-layer substrate, which can prevent distortion due to the above and ensure suitable dimensional accuracy for the substrate.

[0009]

In order to solve the above problems, the present invention uses a slurry obtained by adding a sintering aid to aluminum nitride powder in a method for manufacturing an aluminum nitride multilayer substrate having an inner layer conductor circuit. Sheet forming a green sheet, forming a conductor circuit on the green sheet, and forming a spacer sheet using a slurry in which sintering additive is not added to aluminum nitride powder,
The spacers are simultaneously pressure-bonded to the upper and lower surfaces of the green sheet on which the conductor circuit is formed, and these are fired, and then both spacers are ground and removed.

[0010]

In this method, the green sheet and the spacer are both sheet-formed products, and the densities of both are substantially the same. Therefore, the shrinkage rates when fired are substantially the same, and dimensional matching is easier than in the past. Further, since the spacers are pressure-bonded to the upper and lower surfaces of the green sheet, no gap is created between the two during firing.

Therefore, the exudation of the liquid phase is surely prevented, and the jig and the green sheet are prevented from adhering to each other through the liquid phase. As a result, the resistance of the substrate can be surely reduced, and the dimensional accuracy suitable for the substrate can be secured.

The method for manufacturing the aluminum nitride multilayer substrate of the present invention will be described below in the order of steps. Aluminum nitride (A
1N) powder is mixed with a sintering aid such as yttria (Y ₂ O ₃ ), a binder, a dispersant, a plasticizer and the like, and a slurry is prepared by kneading the mixture for a predetermined time. The slurry is adjusted to have a predetermined viscosity and then formed into a green sheet for forming a substrate by a doctor blade method or the like. At that time, the thickness of the green sheet is 10μ
m to 500 μm is preferable, and further 20 μm
It is preferably about 300 μm. Then, holes for forming via holes are mechanically provided through the green sheet by means of a drill or the like.

Next, a conductive paste containing tungsten (W) as a main component for forming a circuit is printed on the green sheet, and the paste fills the holes by this printing. Moreover, after the paste is dried, the paste is further printed on the green sheet, thereby forming a circuit pattern on the surface of the green sheet. Through each of the above steps, the conductor circuit in the via hole and the circuit pattern forming the inner layer conductor circuit are formed on the green sheet. Then, the green sheets are appropriately laminated.
In this case, the number of laminated green sheets is preferably 3 to 50 layers, and more preferably 5 to 20 layers.

Next, a method of manufacturing a spacer and a guide rod for enclosing the periphery of the laminated green sheets during the main firing and a method of arranging them will be described. When forming the spacer, a slurry having substantially the same components as the green sheet forming slurry is used. However,
Unlike the green sheet forming slurry, no sintering aid such as yttria is added to this slurry. Then, after this slurry is adjusted to a predetermined viscosity,
It is formed into a sheet according to the doctor blade method or the like.
Thereby, the spacer is obtained.

In this case, the spacer is required to have such a thickness that the liquid phase component produced during sintering does not reach the jig. However, the amount of the liquid phase produced varies depending on the firing conditions, the type of the sintering aid, the amount added, and the like. Therefore, it is preferable to appropriately adjust the thickness of the spacer in consideration of various conditions.

The spacers are arranged on both upper and lower surfaces of the green sheet group, and then a predetermined pressure is applied in the stacking direction of the green sheet group by using a laminating device or the like. By applying this pressure, the spacers are closely pressed against the green sheet group to form a green sheet laminate. Then, after the laminate is cut into a predetermined outer shape, degreasing and calcination are performed under a predetermined temperature condition.

Here, it is desirable that the densities of the green sheets and the spacers be set to be substantially equal, and it is particularly preferable that they are set to be substantially equal to each other just before the main firing.
The reason is that, when the densities of the both are in the above relationship, the degree of shrinkage during the main firing becomes approximately the same, and the accuracy of dimensional alignment is improved. Strictly speaking, the density of the spacers is preferably about 97% to 100% of the density of the green sheet.

[0018] In this case, the density of the green sheet is in the range of ^{1.5g / cm 3 ~2.5g / cm 3} , the density of the spacers of 1.8g / cm ³ ~2.2g / cm ³ range It is preferable that it is set within.

When the laminated body is arranged at a predetermined position in the jig,
A guide rod made of aluminum nitride is closely arranged around these. The guide rod is manufactured by sheet-forming a slurry that does not contain a sintering aid like the spacer-forming slurry, or by press-molding granules produced from the slurry.

In this case, the guide rod is preferably manufactured by sheet molding, and the density of the guide rod is 97% to 97% of the density of the green sheet, like the spacer.
It is preferably set to 100%. The reason for this is that the degree of shrinkage during the main firing becomes similar to each other, and the accuracy of dimensional alignment is improved.

The thickness of the guide rod after the calcination is
It should be approximately equal to the green sheet laminate. This also applies to the case where the guide rod is manufactured by press molding.

The green sheet laminate is subjected to main firing at a predetermined temperature for a predetermined time in an inert atmosphere.
At that time, it is desirable that the main firing is hot press firing. The reason for this is that when hot pressing firing is performed with the periphery of the laminate completely surrounded by a jig made of carbon, there is no shrinkage in the x and y directions (that is, two directions orthogonal to the thickness of the substrate). This is because a substrate having excellent dimensional accuracy can be obtained.

After that, the guide rod is separated from the fired green sheet laminate. Next, this laminate is subjected to a polishing treatment using a surface grinder or the like to remove the spacers on both upper and lower surfaces of the laminate. Through the above steps, a desired aluminum nitride multilayer substrate including the inner conductor circuit is manufactured.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying the method for manufacturing an aluminum nitride multilayer substrate of the present invention will be described in detail below with reference to the drawings.

An acrylic binder was added to a uniform mixed powder of 100 parts by weight of aluminum nitride (AlN) powder having an average particle size of 1.4 μm and a purity of 98.5% or more and 5 parts by weight of yttria (Y ₂ O ₃ ) powder. 13 parts by weight, 2 parts by weight of a plasticizer, 0.5 parts by weight of a dispersant and 42 parts by weight of a toluene / ethanol mixed solvent were added. Then, this mixture was mixed for 48 hours using a ball mill to prepare a slurry. After adjusting this slurry to a predetermined viscosity, a substrate forming green sheet 1 having a thickness of 0.45 mm was prepared using a doctor blade device.

Next, after mechanically forming a via hole forming hole 2 in the green sheet 1, the forming hole 2 is formed.
The inside was filled with a tungsten paste. In addition, after the paste is dried, a conductor circuit pattern 3 is further formed on the surface of the green sheet 1 with a tungsten paste,
The conductor circuit pattern 3 was dried. As a result, the conductor circuit 4 in the via hole and the conductor circuit pattern 3 which form the inner layer conductor circuit were formed on the green sheet 1.

Here, a slurry having the same composition as the slurry except that yttria powder was not included was prepared, and the slurry was adjusted to a predetermined viscosity. Thereafter, a doctor blade device was also used to form a green sheet 2 having a thickness of 0.45 mm for forming the spacer s and the guide rod g.

Next, as shown in FIG. 1, spacers s are stacked on each other in 10 layers to form a green sheet 1 on both upper and lower surfaces.
The layers were arranged layer by layer, and these 1 and s were thermocompression bonded using a laminating apparatus to form a green sheet laminate 5. Further, these were cut into a predetermined outer shape. Further, a guide rod g was formed by a laminating apparatus using the green sheet 2 so as to have a thickness substantially equal to that of the laminate 5, and the outer diameter was cut to a predetermined size. Then, the laminated body 5 and the guide rod g were degreased at 600 ° C. under vacuum conditions, and pre-baked at 1560 ° C. in a nitrogen atmosphere. As shown in Table 1, the densities of the laminated body 5 and the guide bar g before degreasing and pre-baking are 2.13 g / cm ³ and 2.08 g / cm ³ . The densities of both 5, g after degreasing and calcination are 2.24 g / cm ³ and 2.18 g / cm ³ , and the ratio of the density of the guide rod to the green sheet density is about 98%.
Is set to.

Subsequently, as shown in FIGS. 2 (a) and 2 (b), a laminated body 5 is arranged at substantially the center of the jig M, and the periphery thereof is degreased and pre-baked aluminum nitride. The manufactured guide bar g was placed closely.

This laminated body 5 was subjected to 187 under a nitrogen atmosphere.
Hot press firing was carried out at 0 ° C. and a pressure of 18.5 kg / cm ² for 3 hours. After that, the guide rod g was separated from the laminated body 5. Further, both spacers s were removed from the laminated body 5 by polishing the upper and lower surfaces of the laminated body 5 using a surface grinder (see FIG. 3).

Through the above steps, a desired aluminum nitride multilayer substrate having the inner conductor circuits 3 and 4 was obtained. In order to investigate the characteristics of the obtained substrate, the average sheet resistance (mΩ / □) of the substrate was measured. In addition, the dimensional change rate (%) in the x and y directions of the substrate before and after the main firing, that is, in two directions orthogonal to the thickness direction of the substrate was also measured. The results are shown in Table 1.

Next, a method of manufacturing a multilayer substrate of a comparative example with respect to this embodiment will be described. Also in the comparative example, a green sheet having the same thickness was formed into a sheet by using the slurry used in the example. Then, according to the procedure of the example, the conductor circuit in the via hole and the conductor circuit pattern were formed on the green sheet.

10 layers of the green sheets are stacked,
These were thermocompression bonded by a laminating device. Then, this green sheet group was cut into a predetermined shape.
On the other hand, a mixture consisting of 4 parts by weight of an acrylic binder and 64 parts by weight of a mixed solvent of toluene / ethanol was mixed in a ball mill for 48 hours, and the obtained slurry was passed through a spray dryer to form granules. A sheet-shaped spacer (thickness 0.9 mm) and a rod-shaped guide rod (thickness 5.4 mm) were formed by press-molding the granules.

The above-mentioned green sheet group, spacers and guide rods were degreased at 600 ° C. under vacuum conditions and pre-baked at 1560 ° C. in a nitrogen atmosphere. The densities of the green sheets, spacers and guide rods before and after degreasing and pre-baking are shown in Table 1, respectively. Further, the ratio of the density of the spacer and the guide bar to the density of the green sheet after degreasing and pre-baking is set to about 90%.

Subsequently, spacers were closely arranged on both upper and lower surfaces of the green sheet group, and guide rods were arranged around both of them, and these were inserted into substantially the center of the jig. Hereinafter, after subjecting the laminate to main firing according to the method and conditions of the above-described example, the spacers were ground and removed to obtain an aluminum nitride multilayer substrate.

Table 1 shows the results of the above-described measurement performed on the substrate of this comparative example.

[0037]

[Table 1]

In the embodiment, the density of the spacers s and the guide rods g is set to be substantially equal to the density of the green sheet 1, so that the dimensional matching is easier than the conventional one, which is advantageous in terms of process. .. In addition, as a result of arranging the guide bar g around the green sheet laminate 5 and performing firing, it is possible to reliably prevent the liquid phase from seeping out, and to prevent the jig M from adhering to the sintered green sheet 1. It was possible to avoid it. Therefore, as shown in Table 1, it was possible to obtain a lower average sheet resistance value in the substrate of the example than in the comparative example.

Further, since the adhesion between the spacer s and the guide rod g with respect to the green sheet 1 is improved, the dimensional change rate of the substrate before and after the main firing can be reduced to about 1/3 of the conventional rate.

Considering the above results, it is concluded that the substrate of the example has excellent characteristics as compared with the comparative example.

[0041]

As described in detail above, according to the method for manufacturing an aluminum nitride multilayer substrate of the present invention, since the spacers whose dimensions are easily aligned are used, the resistance of the conductor circuit on the substrate can be surely reduced. It is possible to obtain the excellent effect that the distortion due to firing can be prevented and the dimensional accuracy suitable for the substrate can be secured.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a state in which a spacer is laminated on a plurality of green sheets.

FIG. 2A is a plan view showing a state in which a green sheet laminate is arranged on a jig, and FIG. 2B is a schematic sectional view of FIG.

[Explanation of symbols]

1 (for substrate formation) green sheet, 3 conductor circuit pattern forming inner layer conductor circuit, 4 via hole inner conductor circuit forming inner layer conductor circuit, and s spacer.

Claims (3)

[Claims] 1. A method for manufacturing an aluminum nitride multilayer substrate having inner layer conductor circuits (3, 4), wherein a green sheet (1) is formed by using a slurry obtained by adding a sintering aid to aluminum nitride powder, and
Conductor circuits (3, 4) are formed on the green sheet (1), and spacers (s) are formed into a sheet using a slurry in which sintering aid is not added to aluminum nitride powder, and the conductor circuits (3, 4) are formed. 4) formed green sheet (1)
A method for manufacturing an aluminum nitride multilayer substrate, characterized in that the spacers (s) are simultaneously pressure-bonded to both upper and lower surfaces of the same, and these are fired, and then both spacers (s) are ground and removed. 2. The method for manufacturing an aluminum nitride multilayer substrate according to claim 1, wherein the densities of the green sheet (1) and the spacers (s) are set to be substantially equal to each other. 3. The method for manufacturing an aluminum nitride multilayer substrate according to claim 1, wherein the firing is hot press firing.