JPH09124382A - Production of ceramic substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for baking a ceramic substrate in a short time at a temperature lower than the conventional baking temperature without deteriorating the properties of ceramic and a metallized layer. SOLUTION: A surface of a formed ceramic 3 such as alumina, aluminum nitride, silicon nitride, silicon carbide, mullite or glass ceramic is coated with a metallizing paste containing a metal such as W, Mo, Ni, Cu or Pt and the coated ceramic is irradiated with high-frequency radiations such as microwave to bake the formed ceramic 3 and the metallizing paste at the same time.

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 a ceramic substrate having a metallized layer such as wiring, and more particularly to a method for manufacturing a ceramic substrate excellent in productivity, low cost and excellent in metallizing adhesion strength. Is.

[0002]

2. Description of the Related Art Conventionally, ceramics have been used as a substrate material for a wiring circuit because they are excellent in insulation, mechanical strength, corrosion resistance, heat resistance, thermal conductivity, and dielectric strength.

Among them, a ceramic substrate on which a wiring layer is formed by metallization is particularly suitable for a CPU of a computer.
It is mainly used for some packages.

In recent years, the demand for high-performance computers has expanded at the same time as the performance and integration of CPUs have increased remarkably, and the required characteristics for packages have increased.
The requirements for delivery time, production quantity, and cost have become particularly strict.

Usually, a ceramic substrate provided with a metallized layer is first formed from a ceramic powder into, for example, a sheet shape to prepare a green sheet, which is gradually heated to a firing temperature of the ceramic in a resistance heating furnace to a constant temperature. After the temperature is lowered and sintered after holding for a period of time, a method of correcting warpage or deformation by grinding or the like, and then coating and baking a metallizing paste is known, but recently, in order to improve productivity, Before firing the ceramic molded body,
After the metallizing paste is applied and laminated in multiple layers, the metallizing layer and the ceramic molded body are simultaneously fired by heating this in a heating furnace.

[0006]

This co-firing method is excellent in terms of productivity and is an unavoidable technique for multilayering, but in order to sinter ceramics, a temperature of 900 ° C. or higher is required. It is necessary, and in particular, firing of non-oxidizing ceramics such as aluminum nitride, silicon nitride and silicon carbide requires firing at a temperature higher than 1700 ° C.

Firing at such a high temperature is apt to cause melting of the metallized metal, reaction with the ceramics, etc., and means for controlling the atmosphere is required to suppress the melting, and the ceramics and the metallized metal species are mixed. Combinations were also limited, and inexpensive metals could not be used.

In order to solve such problems, various methods have been investigated for adding a large amount of a sintering aid or prolonging the firing time to enable firing at a low temperature. Addition of a large amount of Mn changes the characteristics of the main component ceramics and lengthens the firing time, which is unsuitable from the viewpoint of mass productivity.There is currently no method for firing at low temperature while taking advantage of the characteristics of ceramics. Met.

Recently, a glass-ceramic sinter capable of firing at a firing temperature of about 1000 ° C. by compounding glass and ceramics is also known. However, even in this glass ceramics, firing at a lower temperature is desired, but it is necessary to strictly control the combination of the glass composition and the compounding with the ceramic, or the crystal phase of the glass may change due to slight changes in the firing conditions. Change, etc.
At present, it is difficult to produce a sintered body with stable characteristics at a high yield in accordance with firing at a low temperature.

Therefore, it is an object of the present invention to provide a novel manufacturing method capable of firing at a temperature lower than the conventional firing temperature and in a short time without deteriorating the characteristics of ceramics and metallized layers. Is.

[0011]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted extensive studies in the conventional method for producing a ceramic substrate having a metallized layer, particularly from the viewpoint of the firing method, and as a result, have found that a ceramic molded body coated with a metallized paste is formed. When firing, instead of the conventional resistance heating method,
It has been found that by irradiating a molded body with a high frequency wave such as microwaves to heat and calcination, it becomes possible to densify the calcination at a temperature lower than the calcination temperature by the conventional resistance heating method.

[0012]

According to the present invention, the ceramic compact coated with the metallizing paste is fired by a high-frequency heating method such as microwave, so that the ceramic compact can be compacted at a low temperature in a short time as compared with the conventional resistance heating method. And can be fired at a temperature lower than 50 to 100 ° C. as compared with the ordinary resistance heating method, and the firing time can be densified in about 0.1 to 2 hours. Further, according to the high frequency heating method, since the power consumption is low, the cost for firing can be reduced.

Due to the fact that the high-frequency heating method can densify at a temperature lower than that of the resistance heating method, the conductivity of the metallized layer has been increased by the reaction with the ceramic in the metallized layer and the oxidation reaction of the metallized layer in the simultaneous firing of the ceramic and the metallized layer. Since it is possible to fire even at low temperature, the reactivity with ceramics is suppressed, and the oxidation reaction is suppressed, so that the types of metallized layers that can be formed can be expanded, As a result, the metal can be used at a low cost from the expensive metal.

Further, the metallized layer co-fired with the ceramic molded body has an excellent effect that the adhesion to ceramics is improved as compared with the case of co-firing by the conventional resistance heating method. It is considered that this is because the ceramic anchor effect was exerted more strongly because the metallization was composed of fine crystal grains because it was fired in a short time by irradiation with high frequency.

Further, in the resistance heating method, there is a problem that uneven heating occurs due to a large temperature difference between the surface and the inside of the molded body or the temperature inside the furnace due to the presence of a heating source outside the molded body. However, according to the high frequency heating method, since the heating source is the molded body itself, there is no uneven heating and the entire molded body can be uniformly heated and sintered.

This makes it possible to reduce the manufacturing cost of the ceramic substrate having the metallized layer and improve the productivity.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The ceramic molded body in the present invention contains at least one selected from the group consisting of alumina, aluminum nitride, silicon nitride, silicon carbide, mullite, and glass ceramics as a main component.
Glass ceramics is a mixture of glass and an inorganic compound such as cristobalite, forsterite, cordierite, quartz, quartz glass, alumina, magnesia, and spinel as a filler component. The molded body is
In addition to the above-mentioned main components, known additive components may be added,
Alkaline earth metal compounds such as Ca and Sr, Group 3a element compounds of the periodic table such as Y and La, Ti, Zr, W and M
Compounds of group 4a, 5a, 6a of the periodic table such as o, Nb and V can be blended. The molded body is one obtained by molding these ceramic powders by a desired molding means. For example, in order to prepare a sheet-shaped molded body, after preparing a slurry, this is molded by a doctor blade method, or Or to form a ceramic powder into a sheet by press molding, rolling, etc., or to make a bulk body,
For example, die press, cold isostatic press, extrusion molding,
It may be molded into an arbitrary shape by injection molding or the like.

Next, a metallizing paste is applied to the surface of this ceramic molded body. The metallized paste is
W, Mo, Ag, Cu, Al, Au, Pd, Pt, Ni
At least one selected from the group consisting of W, Mo, N
The main component is at least one selected from the group consisting of i, Cu, and Pt, and an organic solvent, a dispersant, and the like are further added to and mixed with the metal component.

As the metal component in the paste, a metal that does not melt at the firing temperature of the ceramic compact to which it is applied is selected. For example, W, Mo, Ni, Pd, Pt and the like can be used for the formed body containing alumina as a main component. W, Mo, Pt, and the like are used for the non-oxide ceramics-based compacts such as aluminum nitride, silicon nitride, and silicon carbide, and Ag, for the glass-ceramics-based compacts.
Cu, Au, etc. can be adopted.

This metallizing paste is applied by printing on the surface of the ceramic molded body by a screen printing method, an offset printing method, a gravure printing method or the like.

Next, the ceramic compact coated with the metallizing paste is placed in a high frequency heating furnace and fired. FIG. 1 shows a schematic layout of a typical high-frequency heating furnace.

According to FIG. 1, a support base 2 made of ceramic or the like is installed in a firing furnace housing 1 made of stainless steel or the like, and a molded body 3 is placed on the support base 2. The support base 2 and the molded body 3 are installed in a heat insulating material 4 having a high permeability to high frequencies such as microwaves. In addition, in the firing furnace,
A desired firing atmosphere is formed through the gas introduction path 5. On the other hand, a microwave oscillator 6 is installed outside the firing furnace, and microwaves generated by the oscillator are introduced into the output window 7 of the oscillator 6, the waveguide 8 and a part of the firing furnace casing 1. The molded body 3 is directly irradiated through the window 9. A thermocouple 10 for measuring the temperature of the molded body is provided on the support 2 of the molded body, and while measuring the temperature of the molded body by the thermocouple 10, the microwave output is adjusted to a desired firing temperature. Can be set.

According to the present invention, a microwave having a frequency of 300 MHz to 300 GHz is applied to the compact by the high frequency heating furnace. A magnetron, a klystron, a gyrotron, or the like is used as a microwave oscillation source, but a single-mode millimeter wave is desirable in order to uniformly sinter ceramics.
A gyrotron that oscillates Hz is desirable. By this irradiation, the molded body is self-heated and can be uniformly sintered without any difference between inside and outside of the molded body. The firing temperature can be arbitrarily controlled by the output of microwaves, and usually 1 to
10 kW is suitable, and sintering can be performed with a firing time of about 0.1 to 2 hours.

The firing temperature in such a firing method varies depending on the main component constituting the ceramic molded body and other additives, but generally speaking, when the main component constituting the ceramic molded body is alumina, the firing temperature is from 1000 to 1,000. 1500
C., 1300 to 1600 ° C. for mullite, 1500 to 1800 ° C. for aluminum nitride, 1500 to 1800 ° C. for silicon nitride, 1600 to 2000 ° C. for silicon carbide, and glass ceramics In particular, it can be sintered and densified at a temperature of 850 to 1050 ° C.

The present invention will be described below with reference to specific experimental examples. Experimental Example Alumina (purity 92%, including SiO ₂ , CaO, MgO), mullite (purity 99%), aluminum nitride (Y
₂ O ₃ 5% by weight added product), silicon nitride (Y ₂ O ₃ 3% by weight, Al ₂ O ₃ 5% by weight), silicon carbide (B ₄ C0.5
% By weight, C 2% by weight) and glass ceramics (70% by weight borosilicate glass, 30% by weight Al ₂ O ₃ ) to which a binder, a plasticizer and a solvent have been added, and a ball mill is used for 20 hours. Mixed. The obtained slurry has a thickness of 0.05-1.
It was molded into a 5 mm tape shape.

On the other hand, to W, Mo, Ni, Pt, and Cu having a purity of 99% or more as a metallized metal, cellulose or the like was added and mixed in a ball mill for 24 hours to prepare a metallized paste. A paste was applied on the surface in the form of a wiring circuit pattern by a screen printing method, and 15 sheets of them were laminated and pressure-bonded to produce a laminated molded body having a size of 60 mm square.

Then, the laminated molded body was subjected to a degreasing treatment for 5 hours in a reducing atmosphere at 500 ° C. and then fired. For firing, tunnel furnace as heater resistance heating furnace (RH),
A batch furnace is used, and in the configuration shown in FIG. 1 as a high frequency heating furnace, a microwave oscillator using a gyrotron of 28 GHz and a maximum output of 10 KW as an oscillation source is used in a stainless steel baking furnace housing. Baked. In addition,
The firing temperature was controlled by bringing the thermocouple into contact with the compact and measuring the temperature while changing the microwave output from 1 KW to 5 KW.

Tables 1 and 2 show the temperature rising rate up to the firing temperature, firing temperature, firing time, and firing atmosphere during firing. The firing was carried out under normal pressure. After firing, the density of the ceramic was measured by the Archimedes method to calculate the relative density. The sinterability of the metallization was evaluated from the resistance value of the electrical characteristics of the metallized layer, and those having a resistance value of 3 Ωcm or less were evaluated as ◯, and those exceeding this value were evaluated as x. Further, the presence or absence of melting of the metallized layer, dimensional accuracy, warpage, capacitance, etc. were checked from the appearance inspection of the sintered body.

Further, a metal pin was brazed to the metallized layer and the metal pin was pulled vertically, and the load when the metallized layer was peeled off was evaluated as the metallized strength. The results are shown in Tables 1 and 2.

[0030]

[Table 1]

[0031]

[Table 2]

As is clear from the results of Tables 1 and 2, according to the microwave heating method as compared with the conventional resistance heating method,
It can be seen that densification can be achieved at a firing temperature lower by 50 to 100 ° C. Moreover, the heating rate up to the firing temperature is 25 ° C./min or more, which is much faster than that by the resistance heating method, so that the firing time is shortened, and the holding time at the firing temperature is 0.15 as compared with the resistance heating method. I was able to reduce it to about 1 hour.

Further, in the microwave heating method, the metallization strength was improved as compared with the resistance heating method.

According to Sample Nos. 5 to 7 in which Ni metallized alumina, according to the resistance heating method, it was necessary to heat the alumina to 1450 ° C. or higher in order to sinter the alumina. Was melted and the metallized layer could not be formed.
Since the alumina could be densified at 400 ° C., N
A good metallized layer could be formed without melting i.

Further, in Samples Nos. 13 to 15 in which a Pt metallized layer was formed on aluminum nitride, the microwave heating method was able to densify aluminum nitride even at 1600 ° C. and form a good Pt metallized layer. .

Further, when W or Mo metallization is applied to silicon nitride (Samples No. 16 to 18), or when W metallization is applied to silicon carbide (Samples No. 19 to 2).
1) In the resistance heating method, silicon nitride or silicon carbide reacts with W or Mo in the temperature range where silicon nitride or silicon carbide is densified, and the conductivity of the metallized layer is greatly reduced. It became possible to densify, and it was possible to form a good metallized layer without reaction with W or Mo.

Furthermore, according to the glass ceramics, Cu is oxidized at 900 ° C. at which the glass ceramics are densified by the resistance heating method during firing in the air, whereas by the microwave heating method, Cu is oxidized at 850 ° C. Densification was possible and Cu was not oxidized, and a good metallized layer could be formed.

[0038]

As described above in detail, according to the present invention, by adopting the high frequency heating method, the characteristics of the ceramics and the metallized layer are not changed as compared with the conventional resistance heating method. Simultaneous firing can be carried out in a short time, and moreover, selective species of the metallized layer can be expanded and the adhesion strength can be enhanced. As a result, the cost for manufacturing the ceramic substrate can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view of a high-frequency heating furnace according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Baking furnace housing 2 Support stand 3 Forming body 4 Heat insulating material 5 Gas introduction path 6 Microwave oscillator 7 Output window 8 Waveguide 9 Introduction window 10 Thermocouple

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Kimura 1-4 Yamashita-cho, Kokubun-shi, Kagoshima Kyocera Stock Company Research Institute

Claims (3)

[Claims] 1. A method of manufacturing a ceramic substrate, comprising applying a metallizing paste to the surface of a ceramic molded body, and then irradiating the molded body with a high frequency wave to heat the molded body and the metallization at the same time. . 2. A metallizing paste comprising W, Mo, Ni,
The method for producing a ceramic substrate according to claim 1, wherein at least one selected from the group consisting of Cu and Pt is contained as a main component. 3. The method for producing a ceramic substrate according to claim 1, wherein the ceramic molded body contains at least one selected from the group consisting of alumina, aluminum nitride, silicon nitride, silicon carbide, mullite and glass ceramics as a main component.