JPH09260853A - Ceramic circuit board and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the connection of a via conductor of a ceramic board with its surface conductor favorable, by providing further on an internal via conductor formed in the ceramic board a surface layer via conductor with a porosity not smaller than a specific value to be joined to the surface conductor. SOLUTION: Into a via hole 5 formed in a ceramic board 1, an internal via conductor 4a is filled. Further, a surface layer via conductor 4b with a porosity not smaller than 5% is filled into the existing portion of the via hole 5 on the internal via conductor 4a. Then, on the surface of the surface layer via conductor 4b, a surface conductor 2 containing a glass frit is formed in a joining way. Thereby, the melts of the glass frit in the surface conductor 2 can so penetrate into the existing voids not smaller than 5% in the surface vicinity of the surface layer via conductor 4b that the melts are not maldistributed on its joining plane to the surface conductor 2. Therefore, the connection of the surface layer via conductor 4b with the surface conductor 2 can be made favorable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic circuit board for electronic equipment and a method for manufacturing the same.

[0002]

2. Description of the Related Art A built-in conductor is arranged on a ceramic circuit board,
Circuit boards for electronic devices, in which this and surface conductors are joined by via conductors, are known, but in recent years there has been a strong demand for miniaturization and multi-functionalization of electronic devices, and ceramic substrates and built-in conductors have become multi-layered. Arranged multilayer circuit boards are often used. In a ceramic multi-layer circuit board, a conductor made of W and Mo is built in the ceramic, and the built-in conductor is exposed from a via provided on the surface board and formed on the surface layer.
A substrate having a structure in which a surface conductor made of a thick metal film containing u as a main component is connected via an intermediate metal layer in a via is widely used. Although both the built-in conductor and the surface conductor are manufactured by firing in a non-oxidizing atmosphere, such a substrate is a surface conductor mainly made of Ag-based or Au-based metal that can be fired in air with higher productivity. A manufacturing method for forming the has also been developed. When this firing in air is used, the built-in conductors W and Mo are oxidized, so that the connection between the built-in conductor and the surface conductor was technically difficult.

The multilayer circuit board described in Japanese Patent Publication No. 5-44200 has a structure in which built-in conductors made of W or Mo and electric insulating layers are alternately laminated on an electric insulating substrate containing alumina as a main component to form an outermost insulating layer. Is provided with a via in which the built-in conductor is exposed, the via portion is filled with a conductor material composed of a noble metal and a low-melting-point glass material that is not reduced by W or Mo, and fired, and then a surface conductor is provided thereon and fired. An object of the present invention is to provide a multilayer circuit board without deterioration of a conductor layer.

[0004]

In the present invention, as a result of examining the conventional techniques, it was found that a connection failure occurs when the surface conductor and the conductor arranged in the via are joined. The possible causes are as follows. Ag-based, Au-based, Cu
Since the surface conductor of a system or the like needs to be firmly bonded to the ceramic substrate, the surface conductor forming material generally contains glass frit. That is, the surface conductor forming material is usually composed mainly of a metal powder, an organic vehicle, and a glass frit in a paste form, which is printed on a desired circuit by a screen printing method and baked at about 850 ° C. . The glass frit joins the ceramic and metal during firing, but when joining the via conductor,
The glass frit is unnecessary, and if there is no molten frit in the via conductor, there will be a large amount of molten glass frit between the via conductor and the surface conductor, which solidifies and causes a connection failure. . Therefore, the present invention eliminates such a phenomenon and ensures good connection between the via conductor and the surface conductor to ensure excellent conductivity.

[0005]

According to the present invention, in a ceramic circuit board in which at least a via and a metal conductor are arranged on the surface, the via conductor and the surface conductor are joined to each other. A ceramic circuit board in which a surface conductor is joined to a surface layer via conductor having a porosity of 5% or more on a joint surface with the conductor.

According to the present invention, a via is formed on the surface of a ceramic substrate material, and a surface layer via conductor material for porosity of 5% or more is provided in the via at least in the vicinity of an exposed portion after firing, and the via firing is performed simultaneously. After that, a ceramic circuit, in which a surface conductor is formed by printing a circuit pattern with a conductor paste containing metal powder as a main component on which a glass frit and a binder are intermixed and firing at a predetermined portion of the surface centered on the via, is formed. It is a method of manufacturing a substrate.

In the above, the surface conductor is formed of a metal conductor material and glass frit. Al ₂ O ₃ and AlN can be used as the ceramic substrate material, but 10
A ceramic that can be fired at 00 ° C or lower is desirable. Via conductor material and surface conductive material are W, Mo, Mo-Mn,
Appropriate combinations of Ag, Ag-Pd, Ag-Pt, Au, Cu and the like can be applied. Further, as the glass frit contained in the surface conductive material, the metal material is W, Mo, Mo-Mn.
In the case of, the CaO-MgO-SiO ₂ based glass frit may also contain Ag, Ag-Pd, Ag-Pt, Au,
If it is Cu is _{PbO-SiO 2 -Al 2 O 3} -B 2 O
_{3 system, SiO 2 -CaO-Al 2 O} 3 -B 2 O 3 system and the like.

Further, the via conductor and the surface conductor are joined to each other with the porosity of the via conductor and the surface conductor to be joined to 5% or more because the melted material of the glass frit in the surface conductor is attached to the via conductor. 5% of the via conductor joint surface to prevent uneven distribution
It is designed to be able to penetrate into the above voids. If the porosity is less than 5%, a concentrated portion of the glass frit derived from the surface conductor is likely to be formed between the via conductor and the surface layer conductor,
In some cases, electrical continuity is cut off. When the porosity is 5% or more, the concentrated portion of the glass frit is not formed on the via conductor, and the electrical continuity is maintained. The maximum value of the porosity may be in the range where the upper conductor and the via conductor can be conducted.
The porosity in the present invention is defined as follows.

[0009]

[Equation 1]

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION There are the following several means for forming a structure having a porosity of 5% or more. The sintering completion temperature of the material added to the conductive paste filled in the via is higher than the sintering completion temperature of the ceramic material of the substrate. A metal material having poor sinterability is used as the conductive material of the via. Organic substances that evaporate and scatter are added to the conductive material of the via. After firing the substrate, mechanically fine holes are drilled in the via conductor surface.

[0011]

EXAMPLES Specific examples will be described below. Example 1 FIG. 1 is an explanatory diagram of a circuit board to which the present invention is applied, in which 1 is a ceramic substrate, 2 is a surface conductor, 3 is a built-in conductor, 4 is a via conductor, and 5 and 6 are other vias. As a material for the ceramic substrate 1, a low-temperature fired ceramic made of a mixture of CaO—Al ₂ O ₃ —SiO ₂ —B ₂ O ₃ glass and α-Al ₂ O ₃ at a ratio of 60:40 (weight ratio) was used. A for the surface conductor 2
was used a PbO-SiO ₂ -B ₂ O ₃ based glass frit is contained 5% g and Pd powder in a mixing ratio of 85:15 by weight. The via conductor 4 was divided into an internal via conductor 4a and a surface layer via conductor 4b as shown in an enlarged scale in FIG. 2, and 100% Ag was used as the internal via conductor 4a. As the surface layer via conductor 4b, a powder obtained by mixing Ag and Pd in a weight ratio of 90:10 was used. The via 5 inside the substrate is the same conductor as the internal via conductor 4a, and the via 6 on the opposite surface side is the surface layer via conductor 4 described above.
The same conductor as b may be applied. This surface layer via conductor material contains Pd, which has poorer sinterability than the internal via conductor material Ag, that is, it corresponds to the above-mentioned porosity of 5% or more. It is 6%.

Next, the manufacturing method will be described. Ceramic powder for the ceramic substrate 1 (average particle size 0.1 to 0.1
Polyvinyl butyral resin was mixed with a solvent (toluene) in a ball mill, and a ceramic green sheet was prepared by a doctor blade method. This was cut into a desired shape, and a via hole for obtaining conduction between layers was formed using a punching die. And
First, the material of the inner via conductor 4a was filled in the via, and the material of the surface layer via conductor 4b was further filled thereon by the printing method, and if necessary, the internal wiring (Ag 100% or the like) was formed by the screen printing method. Next, after the required number of ceramic green sheets were thermocompression bonded, they were fired at the ceramic sintering temperature (900 ° C.). The surface conductor 2 material containing glass frit is formed on the obtained sintered ceramic plate so as to be bonded to the via surface, and if necessary, resistors and the like are formed, and thereafter the sintering temperature of the surface conductor (900 Sintered at (° C) to obtain a ceramic circuit board. Via diameter 0.25m
m, wiring width 0.3 mm, and ceramic thickness 0.3 mm, the via connectivity of the product was tested.
The number of occurrences of poor connection was 0 in the test 0 times.

Example 2 The same material as in Example 1 was used as the material for the ceramic substrate 1, and the grain size was 0.5 μm as the material for the surface layer via conductor 4b.
Cu powder with 10% Al ₂ O ₃ powder added was used, and Cu powder with a particle size of 3 μm was used as the material of the internal via conductor 4a and fired at 900 ° C. The porosity of the surface layer via conductor corresponds to the above means and was 15%. To the resulting fired ceramic _{board, PbO-SiO 2 -B 2 O} 3 -CdO the Cu powder
A surface conductor 2 material containing 10 wt% of a glass frit is formed so as to be bonded to the via surface, and a resistor and the like are formed if necessary, and then the surface conductor is sintered at a temperature of 900.
The ceramic circuit board was obtained by firing at ° C. When tested in the same manner as in Example 1, the number of occurrences of connection failure was 0 after 10,000 tests.

Example 3 96% Al ₂ O ₃ was used as the material for the ceramic substrate 1, W powder was used as the material for the internal via conductor 4b, and the particle size was 10 μm.
3% by weight of the polystyrene ball was used as the surface layer via conductor 4a material, and W powder having a particle diameter of 2 μm was used.
Wirings made of W were formed if necessary and fired at 1600 ° C. The surface layer via conductor corresponded to the above means, and the porosity was 7%. To the resulting fired ceramic board, 5 wt the MgO-SiO ₂ -CaO-based glass frit W powder
% W-based surface conductor 2 material added so as to be bonded to the via surface, and after forming a resistor or the like as required, the surface conductor is sintered at a sintering temperature of 1600 ° C. to form a ceramic circuit board. Got When tested in the same manner as in Example 1, the incidence of connection failure was 0 after 10,000 tests.

Comparative Example 1 As a material for the ceramic substrate 1, CaO--Al ₂ O _{3 was used.}
-SiO ₂ at a weight ratio of -B ₂ O ₃ based glass and α-Al ₂ O ₃ with a powder mixture of 60:40, the inner conductor 3, via conductors (4, 4b, includes any 4a) grain material Diameter 0.5μ
Wiring was formed using Ag powder of m and baked at 900 ° C. The porosity of the surface layer via conductor 4b was 3%. 5% by weight of PbO—SiO ₂ —B ₂ O ₃ based glass was added to the mixture of Ag / Pd (85/15) on the obtained fired ceramic substrate.
The contained material is formed as a surface conductor 2 material so as to be bonded to the via, and after forming a resistor or the like as necessary, the conductor surface conductor is fired at a sintering temperature of 900 ° C. to form a ceramic circuit board. Obtained. When tested in the same manner as in Example 1,
The connection failure rate was 23 times in the test of 10,000 times. As a result of analyzing this defective portion, it was found that glass frit was omnipresent on the connection surface and the connection was defective.

[0016]

The present invention can provide a ceramic circuit board with a highly reliable connection between a via conductor and a surface conductor.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is an enlarged explanatory view of a joint portion between a via conductor and a surface conductor of the present invention.

[Explanation of symbols]

 1 Ceramic Substrate 2 Surface Conductor 3 Internal Conductor 4 Via Conductor 4a Internal Via Conductor 4b Surface Layer Via Conductor 5 Via 6 Via

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H05K 3/40 7511-4E H05K 3/40 Z

Claims (5)

[Claims] 1. A ceramic circuit board in which at least a via and a metal conductor are arranged on the surface, so that the via conductor and the surface conductor are joined, the via conductor formed in the ceramic substrate has a porosity at a joint surface with the surface conductor. A ceramic circuit board, wherein surface conductors are bonded to 5% or more surface layer via conductors. 2. The ceramic circuit board according to claim 1, wherein the surface conductor is formed of a metal conductor material and glass frit. 3. The ceramic circuit board according to claim 1, wherein the ceramic is a low temperature fired ceramic fired at 1000 ° C. or lower. 4. A via is formed on the surface of a ceramic substrate material, and a surface layer via conductor material for arranging at least the exposed portion in the vicinity of the exposed portion so as to have a porosity of 5% or more after firing is formed, and the via is simultaneously fired. A ceramic characterized in that a surface conductor is formed by printing a circuit pattern on a predetermined portion of the surface centered on a metal powder as a main component and printing a circuit pattern with a conductor paste made by mixing glass frit and a binder with the paste and firing the paste. Circuit board manufacturing method. 5. The method of manufacturing a ceramic circuit board according to claim 4, wherein the ceramic substrate material is a low temperature fired ceramic.