JP2762017B2 - Ceramic substrate filled with through holes and conductor paste for filling through holes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic substrate in which a conductive paste is filled in through holes, and a conductive paste for filling through holes in which the firing shrinkage is reduced as much as possible.

[0002]

2. Description of the Related Art Conventionally, ceramic substrates having wirings on both surfaces have been used for various electronic devices, and through holes have been used as a method of establishing conduction between the wirings formed on both surfaces of the substrate. Conventionally, the connection of the wiring by the through hole is performed by printing and firing a conductive film 4 on a hole wall of the through hole 1 provided in the ceramic substrate 2 by a screen printing method or the like as shown in FIG. However, there is a problem that the thickness of the corner portion from the hole wall to the wiring path on the surface of the substrate is easily reduced, resulting in poor conduction and reliability. Also, the size of the through-hole is conventionally a standard one with a small diameter of about 0.4 mm due to the wiring density, and the conductor resistance of the through-hole is limited because the amount of conductor formed on the hole wall is limited. There is a problem of growing. Due to these drawbacks, electrical connection between layers using through holes cannot be avoided in fields that require large current capacity wiring, fields that require high reliability, and fields that require high-performance signal transmission. Have been. However, downsizing of electronic devices,
As the performance is improved, a highly reliable multilayer wiring ceramic substrate capable of mounting electronic components at high density is required.

As a method of manufacturing a multilayer wiring board, a printing multilayer method and a green sheet multilayer method are known. In the case of the printing multilayer method, it is necessary to print wiring while avoiding through-holes, thereby increasing the density. Cause trouble. On the other hand, as shown in FIG. 8, in the case of a green sheet multilayer method in which green sheets 5 made of glass ceramic are laminated on a ceramic substrate 2 and fired to form high-density wiring 3 between the sheets or on the sheets. Is a hollow through hole,
There is a possibility that the laminated glass ceramic may be depressed in the through-hole and cracks may be generated around the sheet to cause inconvenience such as disconnection of the wiring provided on the sheet surface.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a ceramic substrate and a conductive paste for filling the through-hole which have solved the above-mentioned problems concerning the through-hole of the ceramic substrate. If the entire through hole is filled with a conductive material, the amount of conductor in the through hole increases and the conductor resistance decreases.
The through-hole conductor and the wiring on the ceramic substrate can be connected on the same plane, and the reliability of the connection can be improved. Also, in the green sheet multilayer method, if a conductor is filled inside the through hole, sinking into the through hole which causes cracks will be eliminated, and a highly reliable multilayer wiring board that does not cause disconnection etc. will be obtained, In addition, the printed multilayer method has an advantage that the wiring can be printed without being restricted by the positions of the holes. However, since the conductor paste used at present has a large heat shrinkage during firing, satisfactory results have not been obtained for such a ceramic substrate filled with through holes.

[0005] The present inventors have studied a conductive paste having a small heat shrinkage at the time of sintering, and found that a mixture of a specific amount of ruthenium oxide powder (RuO ₂ ) with silver powder or copper powder generally used as a conductive material is used. We found that firing shrinkage was remarkably small and the increase in conductor resistance was also small, and that this conductor paste was filled into through holes and fired. It was confirmed. The present invention is based on such findings.

[0007]

(1) A low-shrinkable conductive paste obtained by adding 0.1 to 15% by weight of ruthenium oxide powder to a conductive powder containing silver powder or copper powder as a main component is added to the conductive powder. A ceramic substrate filled with holes and fired. (2) The ceramic substrate as described in (1) above, wherein the through-holes are filled with a low-shrinkable conductive paste in which the amount of the ruthenium oxide powder added to the conductive powder is 2.5 to 15% by weight and fired. (3) To a conductive powder mainly composed of silver powder or copper powder,
A low-shrinkage conductive paste for filling through-holes, wherein 0.1 to 15% by weight of ruthenium oxide powder is added to the conductive powder. (4) The low-shrinkable conductive paste according to (3), wherein the amount of the ruthenium oxide powder added to the conductive powder is 2.5 to 15% by weight.

The ceramic substrate of the present invention is obtained by filling a through-hole with a conductive paste having low shrinkage and firing the paste. Here, the low-shrinkage conductive paste refers to a conductive paste having a small shrinkage rate during firing, and the through-hole is filled with such low-shrinkage conductive paste and fired to obtain the connection reliability of the substrate wiring. High ceramic substrate was obtained. The low-shrinkable conductor paste is obtained by adding a ruthenium oxide powder to a conductor powder containing silver powder or copper powder as a main component. As shown in Examples described later, the conductor shrinkage of the conductive paste is significantly reduced by the addition of ruthenium oxide powder.

More specifically, the firing shrinkage of the conductor paste obtained by adding ruthenium oxide powder to silver powder slightly varies depending on the content when fired at 850 ° C., but as shown in FIG. A decrease in the firing shrinkage is observed at 1% by weight, and the firing shrinkage is almost zero in the range of 2.5 to 15% by weight. Further, as shown in FIG. 3, the firing shrinkage of the conductor paste obtained by adding ruthenium oxide powder to copper powder was 0.1% as shown in FIG.
A decrease in firing shrinkage was observed at 1% by weight,
It is generally less than 10% in the range of weight%. Therefore, in the present invention, the low-shrinkable conductor paste is a paste containing silver powder as a main component, to which ruthenium oxide powder is added, in a range of 2.5 to 15% by weight at 850 ° C. Is near zero, with copper powder as the main component,
When the ruthenium oxide powder is added to this, the amount of addition is in the range of 2.5 to 15% by weight, and the firing shrinkage at 850 ° C. is generally less than 10%. As shown in FIGS. 1 and 2, the content of ruthenium oxide in the conductor paste was confirmed to be effective by adding about 0.1% by weight.
The firing shrinkage rate is remarkably reduced in the range of 2.5 to 15% by weight, but as the added amount increases, the amount of the conductive powder in the conductive paste relatively decreases, and the conductive resistance value tends to increase. . Therefore, the amount of ruthenium oxide powder added is preferably 15% by weight or less.

The conductive paste for filling a through-hole of the present invention is prepared by mixing silver powder or copper powder and ruthenium oxide powder in the above-mentioned ratio, and appropriately mixing and kneading a known binder and its solvent. Can be obtained by
Silver, copper and ruthenium oxide powders, for example, spherical,
Any shape such as a lump, a needle, and a scale can be used. Although the particle size is not particularly limited, as an example,
Silver powder having an average particle diameter of about 5 to 10 μm, copper powder having an average particle diameter of about 5 to 10 μm, and ruthenium oxide powder having an average particle diameter of about 0.5 to 2 μm are used.

As the binder, ethyl cellulose, acrylic resin and the like are used. The amount of the binder used may be an amount capable of uniformly dispersing and holding the powder and maintaining a paste state. Specifically, it is used at a ratio of about 2 to 10 parts by weight with respect to 100 parts by weight of a mixed powder composed of silver powder or copper powder and ruthenium oxide powder. Examples of the solvent include acetate and terpineol.
The amount of the solvent used depends on the type of the binder, but may be any amount that gives the conductive paste an appropriate viscosity. Specifically, it is used at a ratio of about 10 to 30 parts by weight with respect to 100 parts by weight of the binder. In addition to these binders and solvents, other additives such as fatty acid esters can be used in the same manner as in known conductor pastes, for example, for imparting appropriate fluidity to the conductor paste. Also,
A small amount of oxide particles such as glass particles may be added to further prevent heat shrinkage. Incidentally, even if palladium powder or platinum powder, which is a homologous element of ruthenium, is used in place of ruthenium oxide powder, the effect of suppressing the firing shrinkage of the conductor paste is small, and therefore, the conventionally used silver-Pd
Conductive paste or the like cannot provide the same effect as the present invention.
However, palladium powder or platinum powder may be used as the conductive powder, and ruthenium oxide powder may be added to a mixture of silver powder or copper powder.

[0012]

Examples and Comparative Examples Hereinafter, Examples and Comparative Examples will be described.
The present invention will be further described.Example 1  The conductor paste of the present invention is prepared as follows,
The firing shrinkage and the conductor resistance were evaluated.

(1)Preparation of conductor paste  First, a silver powder having an average particle size of 10 μm and a silver powder having an average particle size of 1 μm
Ruthenium oxide powder and silver powder
2.5% by weight, 5% by weight, 10% by weight,
15% by weight of powdered raw materials (4 types)
Got ready. Next, a vehicle is added to each of the above powder raw materials.
(TRD-1 manufactured by Tanaka Kikinzoku International Co., Ltd.)
In theKneadingThus, a conductor paste was obtained. What
The amount of vehicle is based on 100 parts by weight of powder raw material.
30 parts by weight. As a control, ruthenium oxide
Conductor paste consisting only of silver powder without the addition of powder
It was created in the same manner as above. These conductor pastes
(5 types), their firing shrinkage and conductor resistance
Was evaluated by the following method.

(2)Evaluation method of firing shrinkage of conductor paste  96% alumina substrate (3 inches long x 3 inches wide x 0.635 thickness
mm) conductive paste diluted with a solvent
Printing was performed on a 2 mm square using a metal mask. Then
Substrate in a clean oven at 150 ° C for 10 minutes
After drying, a 2 mm square measuring pad made of the above conductive paste
Were obtained at predetermined intervals. Then
The thickness of the conductive paste on the alumina substrate was measured.
The thickness is measured using a 2 mm square measurement pad on an alumina substrate.
8 locations were selected arbitrarily. In addition, thickness measurement
Put the alumina substrate after that in a belt type electric furnace,
After firing for 47 minutes, the thickness of the conductor on the alumina substrate after firing
Was measured. The measurement is performed at the same location as the measurement point after drying.
This was done by re-measuring. Conductor film before and after firing
The firing shrinkage was calculated from the thickness according to the following equation. Firing shrinkage
(%) = [(Film thickness before firing-film thickness after firing) / film before firing
Thickness] x 100

(3)Evaluation method of conductor resistance value of conductor paste  96% alumina substrate (3 inches long x 3 inches wide x 0.635 thickness
mm) on this substrate and use the same conductivity as for firing shrinkage.
After forming a linear pattern of body paste by printing,
After drying and baking under one condition,
Alumina substrate having a linear conductor film made of
Was. The conductor film on the surface of this alumina substrate
Tine thickness (1 location-4 points), line width (1 location-
4 points) and the resistance value (line length: 70 mm)
The conductor resistance was calculated according to the following equation. Conductor resistance (mΩ / □) = 0.7 × (R × W × t) where R is wiring resistance (Ω), W is line width (mm), and t is film thickness
(Mm) and L represent the line length (mm).

The evaluation of the firing shrinkage and the conductor resistance was performed using two alumina substrates for each of the five types of conductor pastes. The obtained results are shown in FIG. 1 (fire shrinkage) and FIG. 2 (conductor resistance value).

As is apparent from FIG. 1, the conductor paste of the comparative example comprising only the silver powder containing no ruthenium oxide shrinks by about 15% on average after firing, while containing the ruthenium oxide powder. The shrinkage ratio of the conductor paste of the present invention is almost zero, which indicates that the shape stability before and after firing is extremely good. As shown in FIG. 2, the conductor resistance gradually increases as the amount of the ruthenium oxide powder increases. However, even if the conductor contains 5% by weight, the conductor resistance is 23 mΩ / □, which is sufficient for a conductor material. Value.

[0018]Example 2  Example 1 except that copper powder (average particle size: 10 μm) was used.
Similarly, when the ruthenium oxide content is 2.5% by weight,
%, 10% and 15% by weight of conductive paste
Prepared. Also, as in Example 1, ruthenium oxide powder
Of conductor paste consisting only of copper powder without addition of
It was prepared as a control. About these conductor pastes,
In the same procedure as in Example 1, the firing shrinkage and the conductor resistance
The values were evaluated. Note that the conductor paste printed
Use a clean oven at 120 ° C for the lumina substrate.
Dry for 0 minutes. In addition, firing uses a belt type electric furnace
Then, it was performed at 920 ° C. for 60 minutes in a nitrogen atmosphere. Profit
The results obtained are shown in FIG. 3 (firing shrinkage) and FIG. 4 (conductor resistance).
Value). As is clear from FIGS. 3 and 4, the copper powder
In the case of powder, the addition of ruthenium oxide powder
In addition, the firing shrinkage is small and the conductor resistance is small.
It can be seen that a conductor paste is obtained.

[0019]Example 3  96% with multiple holes of 0.4 mm in diameter
Alumina substrate (3 inches long x 3 inches wide x 0.635 mm thick)
The ruthenium oxide content prepared in Example 1 was 2.5
Weight percent conductor paste using screen printing
Filled in the lure hole. Then, this alumina substrate
Dry for 10 minutes in a clean oven maintained at 150 ° C
After firing for 10 minutes at 850 ° C,
The conductor was filled in the through hole as shown in FIG.
An alumina substrate was obtained. Through hole of this alumina substrate
About methanol penetration test and measurement of conductor resistance.
And a visual observation of the surface and cross section thereof. What
In the penetration test, the through hole exposed on the substrate surface
Apply methanol on one side and permeate the other side
The determination was made by visual observation.

As a result, the conductor resistance between the front and back of the substrate in the through hole portion was 0.9 mΩ / □, and the conductor resistance in the through hole of the type metallized only on the wall surface of the conventional through hole having the same diameter as this example (usually 2.7 mΩ / □). ~ 4.8 mΩ /
□), the resistance was much smaller and excellent results were obtained. Further, no irregularities were observed on the surface of the through hole filling portion exposed on the substrate surface, and the wiring was in close contact with the wiring on the substrate on the same plane. Further, as a result of visual observation of the cross section, no void was observed inside the through-hole, and it was confirmed that the conductive paste adhered to the hole wall and was uniformly filled in the entire hole. The absence of defects such as voids inside the through-holes was supported by the fact that no methanol permeated into the back surface of the substrate.

[0021]Comparative Example 1  To the conductive paste made of only silver powder prepared in Example 1
Then, the same baking test as in Example 1 was performed. As a result
Is also shown in FIG. Further, in the same manner as in Example 3,
Filled in through hole of alumina substrate
Then, the same evaluation test as in Example 3 was performed on this substrate.
However, the through hole surface has
A through portion was seen, and methanol was permeated into the back surface.

[0022]Example 4  After filling the conductive paste, the glass ceramic
45kg / cm of 120μm thick green sheet made of
^TwoExcept that they were laminated at a pressure of
A sheet laminated alumina substrate having the structure shown in FIG. 6 was obtained. this
The same evaluation test as in Example 3 was performed on the substrate.
No cracks were seen on the green sheet above the through hole
No pitting occurred. In addition, through through
Conductor paste adheres tightly inside the
And no internal defects such as voids were observed.
There was no penetration.

[0023]Comparative Example 2  An alumina substrate having a through hole having the same diameter as that of Example 4 was used.
Used, consisting of only the silver powder prepared in Example 1 on the substrate
Filled with conventional conductor paste, and the same thickness as in Example 4.
By stacking only ceramic sheets at the same pressure,
Thus, a sheet laminated alumina substrate having the structure shown in FIG. 6 was obtained.
The same evaluation test as in Example 3 was performed on this substrate.
At this time, the sheet surface is hollow at the through hole,
Cracks were observed near the depression.

[0024]

As described above, according to the present invention,
A conductor paste having a significantly smaller firing shrinkage ratio and excellent shape stability before and after firing is provided. By filling this conductive paste into through-holes, a ceramic having high reliability of connection between wiring on the substrate surface and through-hole conductors is provided. A substrate is obtained. In addition, since the inside of the through hole is filled with a conductor pace, when manufacturing a multilayer wiring ceramic in which green sheets are laminated, defects such as cracks do not occur in the portion covering the through hole and high reliability without inconvenience such as disconnection Wiring can be built on sheets. Furthermore, since the conductor paste having a low conductor resistance fills the inside of the through-hole, the amount of conductor in the through-hole is increased as compared with the conventional through-hole in which the wall surface is metallized, and the conductor resistance of the through-hole is significantly improved. . Due to the decrease in the conductor resistance value, the diameter of the through hole can be reduced, and the wiring density can be improved. Therefore, the present invention can be applied not only to through holes but also to via holes.

[Brief description of the drawings]

FIG. 1 is a graph showing firing shrinkage of a conductive paste of Example 1.

FIG. 2 is a graph showing a conductor resistance value of the conductor paste of Example 1.

FIG. 3 is a graph showing a firing shrinkage rate of a conductive paste of Example 2.

FIG. 4 is a graph showing a conductor resistance value of the conductor paste of Example 2.

FIG. 5 is a cross-sectional view of a ceramic substrate having through holes filled with a conductive paste according to the present invention.

FIG. 6 is a cross-sectional view showing another ceramic substrate having through holes filled with the conductive paste according to the present invention.

FIG. 7 is a cross-sectional view of a conventional ceramic substrate in which a conductive paste is not filled in through holes.

FIG. 8 is a cross-sectional view showing another example of a conventional ceramic substrate in which a through-hole is not filled with a conductive paste.

[Explanation of symbols]

1-through hole, 2-ceramic substrate, 3-
Wiring, 4-conductor film, 5-glass ceramic laminated with green sheet, 6-corner

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Minoru Ebata 383 Aiki-cho, Matsuto-shi, Ishikawa Nikko Corporation (72) Inventor Kiyoshi Mizushima 383 Aiki-cho, Matsuto-shi, Ishikawa Nikko Corporation (56) References JP-A-3-112191 (JP, A) JP-A-5-81922 (JP, A) JP-A-4-97594 (JP, A) JP-A-6-103811 (JP, A) JP-A-5-314810 (JP, A) International Publication 91/4650 (WO, A)

Claims (4)

(57) [Claims] 1. A through-hole is filled with a low-shrinkage conductive paste obtained by adding 0.1 to 15% by weight of ruthenium oxide powder to a conductive powder containing silver powder or copper powder as a main component. , Fired ceramic substrate. 2. The ceramic substrate according to claim 1, wherein the through-holes are filled with a low-shrinkable conductive paste in which the amount of the ruthenium oxide powder added to the conductive powder is 2.5 to 15% by weight and fired. 3. A low-shrinkable conductive paste for filling through holes, comprising a conductive powder containing silver powder or copper powder as a main component and 0.1 to 15% by weight of ruthenium oxide powder added to the conductive powder. 4. The low-shrinkable conductive paste according to claim 3, wherein the amount of the ruthenium oxide powder added to the conductive powder is 2.5 to 15% by weight.