JPH05159621A - Conductive paste - Google Patents

Abstract

(57) [Abstract] [Purpose] In a conductor paste used for a multilayer ceramic wiring substrate having copper as an internal electrode, the purpose is to facilitate the reduction of CuO to Cu, shorten the reduction treatment time, and reduce the process cost. To do. [Constitution] A conductive paste obtained by adding glass frit and MgO in addition to CuO and at least one of H ₂ SO ₄ , HNO ₃ , and H ₃ PO ₄ is suitable for the internal electrode layer 1, Further, as additives, Al ₂ O ₃ and SnO
_A conductive paste obtained by adding at least one of ₂ , ₂ , TiO ₂ and MnO ₂ is suitable for the pierhole electrode 3. Of the paste constituents, H ₂ SO ₄ , HNO ₃ ,
The effect of H ₃ PO ₄ promotes the reducibility to Cu.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste for a circuit board, and more particularly to a conductive paste used as an electrode material for a low temperature multilayer ceramic wiring board (hereinafter abbreviated as MLC) and a via hole electrode material. It is a thing.

[0002]

2. Description of the Related Art As a conductor composition applied to a ceramic dielectric substrate, there are cases where a noble metal such as Au and Ag / Pd is used and a case where a base metal such as W, Mo, Ni and Cu is used. In particular, MLC is one in which an organic binder and a solvent are added to this metal material to form a paste, which is screen-printed on an insulating substrate such as alumina and baked to form a conductor pattern. In addition, in MLC, in addition to these conductor pastes, a method in which a ceramic or glass powder as an insulating material is dispersed in a solvent in which an organic binder is dissolved to form a multi-layer, and the insulating powder, the organic binder, and the like are used. There is a method in which a pattern formed of the conductor paste is laminated on a green sheet to form a multilayer.
Focusing on the metal conductor materials used for these, Au,
Although Ag / Pd can be fired in air, it is expensive because it is a precious metal. On the other hand, W, Ni, and Cu are base metals and are inexpensive, but the firing atmosphere must be a reducing atmosphere or a neutral atmosphere. In addition, W and Mo are fired at a high temperature of 1500 ° C or higher. Further, from the viewpoint of reliability, Au has a problem of solder erosion, and Ag / Pd has a problem of high migration and conductor resistance. Therefore, Cu has come to be used, which is inexpensive, has low electric resistance, and has good solderability.

For example, US Pat. No. 4,072,771 discloses the composition of a Cu paste, which is also disclosed in JP-A-56-933.
It is also disclosed in Japanese Patent Publication No. 96. The former describes a composition containing a glass frit in Cu powder, and the latter a composition containing a glass frit.

However, there are problems in using Cu. This is because the firing of the dielectric substrate by the Cu electrode reduces or becomes a neutral atmosphere, and it becomes difficult to decompose and remove the organic binder in the paste. This is because the oxygen concentration in nitrogen is low, so that the binder does not decompose and remains in the form of carbon, which adversely affects the metallization performance. On the other hand, when the oxygen concentration is high, the Cu electrode is oxidized and diffused into the dielectric to stop functioning as an electrode. Therefore, the firing is performed by supplying a small amount of oxygen in a nitrogen atmosphere while controlling it. Then, the remaining carbon reacts with the copper oxide to generate blisters in the electrode layer or cause a deterioration in matching between the electrode and the dielectric. As described above, the Cu paste has many problems in using the organic binder.

Therefore, in recent years, CuO has been used as a starting material for conductor materials.
A new Cu electrode multi-layer ceramic substrate manufacturing method has been developed. That is, C on the ceramic green sheet
After forming a wiring pattern with the uO conductor composition and stacking the layers, the CuO conductor composition is heat-treated in an oxidizing atmosphere.
And a step of thermally decomposing organic residues in the ceramic green sheet, a step of reducing to Cu metal by heat treatment in a reducing atmosphere, and a step of firing a ceramic substrate in a nitrogen atmosphere, For example, it is disclosed in JP-A-61-26293, US Pat. No. 4,795,512, and US Pat. No. 4,863,683. According to this method for producing a ceramic laminate, the organic binder in the insulating substrate and the paste can be easily decomposed and removed, and good Cu metallization can be obtained.

The conductor composition used in the method for producing the ceramic laminate is CuO powder, glass frit for increasing the adhesive strength, and Mg for preventing the conductor from shrinking.
Japanese Patent Application No. 2-86564 discloses that a conductor paste containing an inorganic vehicle such as O, Al ₂ O ₃ , SnO ₂ , TiO ₂ , and MnO ₂ and an organic vehicle is used.

[0007]

However, in the above structure, CuO in the conductor paste is replaced with metal Cu in order to form the internal electrodes and via holes of the MLC.
The following problems occurred when returning to. (1) CuO
Since the easiness of reduction to Cu differs depending on the particle size of the powder, C
The conditions of the reduction process must be changed depending on the lot of uO paste. (2) If the reduction temperature cannot be set high due to the composition of the ceramic green sheet, the hydrogen concentration must be increased and the reduction treatment time must be lengthened in order to reduce CuO. It is an economy.

The present invention solves the above problems by using Cu
It is an object of the present invention to provide a conductive paste for internal electrodes and a conductive paste for via holes, which both have a good reducing property from O to Cu, and are provided together.

[0009]

In order to solve the above problems, the conductive paste of the present invention is an organic paste composed of a glass frit in addition to CuO powder, an inorganic component containing MgO powder, and at least an organic binder and a solvent. Vehicle components,
At least one of H ₂ SO ₄ , HNO ₃ , and H ₃ PO _{4 is used} , and the other conductive paste includes CuO powder, glass frit, MgO powder, and Al.
₂ O ₃ , SnO ₂ , TiO ₂ , MnO ₂ containing at least one inorganic component, at least an organic binder and an organic vehicle component composed of a solvent, H ₂ SO ₄ , H
It is composed of at least one of NO ₃ and H ₃ PO ₄ .

In particular, the former conductive paste is suitable for internal electrodes, and the latter is suitable for via-hole electrodes.

[0011]

The present invention facilitates the reduction of CuO to Cu in the reduction step by using the CuO paste having the above-described structure for producing a ceramic laminate, facilitating the setting of reduction conditions and the consumption of hydrogen. The amount can be reduced, the processing time can be shortened, and the cost can be reduced. CuO of the present invention
The paste is glass frit and MgO in addition to CuO.
Alternatively, Al ₂ O ₃ , SnO ₂ , TiO ₂ , Mn
Add at least one kind of O ₂ and further add H ₂ SO
It can be obtained by adding at least one of ₄ , HNO ₃ and H ₃ PO ₄ . This CuO paste is mainly applied to a multilayer ceramic wiring board (MLC) or the like as a ceramic laminated body.
Can be easily reduced to Cu.

Of the additives contained in the conductive paste of the present invention, MgO was found as a result of various studies to have an effect of inhibiting the sinterability of Cu powder. In other words, when the Cu powder after the reduction process has an earlier sintering timing than the substrate material, a gap is generated between the ceramic and the Cu layer,
Although it caused cracks in the ceramic layer,
By adding MgO, the sintering reaction occurs near the sintering temperature of the substrate material, and the CuO composition of the present invention does not cause the above problems. At this time, if the addition amount of MgO is 3% by weight or more, the sintering timing is too late, which causes cracking in the ceramic layer. Desirably 0.
5 to 3% is good.

Al ₂ O ₃ , SnO ₂ , TiO ₂ ,
By simultaneously adding an additive such as MnO _2, the volumetric shrinkage of the electrode layer after sintering becomes almost the same as that of the ceramic substrate material. As a result, good metallization can be obtained in the electrode layer such as a via hole, and a via hole with good performance can be formed. Further, when the total amount of these additives is 3% by weight or less, the volume shrinkage of the electrode layer cannot be suppressed, so that a void is formed in the gap between the via hole and the ceramic layer. On the other hand, when the content is 20% by weight or more, the contraction of the conductor layer is too small, the matching property with the sintered body deteriorates, and the impedance of the conductor layer remarkably increases, which is not preferable. Desirably, 10 to 15% by weight of the additive is good.

As a result of various studies, it was found that additives such as H ₂ SO ₄ , HNO ₃ and H ₃ PO ₄ promote the reduction reaction of CuO to Cu in a hydrogen / nitrogen mixed atmosphere. Therefore, by adding at least one of these additives, it becomes possible to reduce CuO at a lower temperature, a shorter time, and a lower hydrogen concentration. Further, when the amount of these additives is 0.05 wt% or less with respect to the total amount of paste, there is no effect of promoting the reducing property of CuO. On the other hand, when the content is 5% by weight or more, the sinterability of the conductor after reduction is deteriorated and the conductor resistance is also deteriorated. Desirably, 0.1 to 2.0% by weight is good.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A multilayer ceramic wiring board according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a multilayer ceramic wiring board according to an embodiment of the present invention. In FIG. 1, 1 is an internal electrode layer, 2 is a dielectric layer, and 3 is a via hole electrode.

The material used for the multilayer ceramic wiring board is borosilicate glass (Corning
7059) was mixed with alumina powder as a ceramic component in a weight ratio of 50:50. Next, using the substrate material powder as an inorganic component, polybutyl butyral as an organic binder, di-n-butyl phthalate as a plasticizer, and a mixed solution of toluene and isopropyl alcohol as a solvent (30 pairs:
70 weight ratio) was mixed to form a slurry.

After sufficiently mixing this slurry, a green sheet was formed on the organic film by the doctor blade method. The film thickness after drying was about 200. A via hole is punched in this green sheet with a mold if necessary. The via hole diameter was 0.2 mmφ.

Next, the conductive paste inorganic composition was used as the internal electrode paste, including cupric oxide powder (average particle size: 3 μm).
m) is added with glass frit for obtaining adhesive strength, MgO for suppressing Cu sintering, and Al ₂ O ₃ is added as an additive for preventing via hole cavities in the paste for via hole electrodes. A mixture having a composition such as 1 was used.

The method for producing the conductive paste is as follows: a vehicle in which terpineol, which is an organic binder, is dissolved in an inorganic powder having the above composition, and H ₂ SO ₄ , HNO ₃ , and H ₃ PO ₄ which accelerates the reduction of CuO. In addition,
It is kneaded by a three-stage roll until it has an appropriate viscosity. The conductive paste thus obtained is printed on the green sheet by a screen printing method, dried and then laminated by applying heat and pressure by a desired number of layers. A wiring pattern as shown in FIG. 2 was printed on the surface layer of the green sheet laminate to measure the reducing property and the sheet resistance value of the conductor paste. In FIG. 2, 4 is the surface of the green sheet laminate, 5 is a sheet resistance measurement pattern, and 6 is a paste reducibility evaluation pattern.

After that, as a binder removal step, in the air
Heat treated for 30 minutes. The binder removal temperature was 600 ° C. Next, as a reduction step, reduction treatment was performed for 1 hour at a temperature of 250 ° C. to 450 ° C. in a nitrogen atmosphere containing 10% of hydrogen. And finally, it was baked for 10 minutes in a nitrogen atmosphere. The firing temperature was 900 ° C. Each heat treatment was automatically performed in a mesh belt furnace.

The reducibility of CuO to Cu after the reduction treatment was evaluated by the appearance change of the pattern 6 on the surface of the laminate and the X-ray diffraction measurement. For the evaluation by X-ray diffraction measurement, pattern 6 after reduction treatment was measured by X-ray diffraction, and Cu in the paste was 100%, 90% or more, 90% to 70%, less than 70% from the peak intensity ratio of CuO. It was represented by the evaluation of A, B, C, and D in four stages. The sheet resistance value (converted to a film thickness of 10 μm) of the conductor after firing the paste was calculated from the resistance value of the wiring pattern 5. The metallization performance of the internal electrode portion and the via hole electrode portion of the completed MLC substrate was relatively evaluated by measuring the resistance value of one wiring formed by the internal electrode pattern and the via.

The above results are shown in Table 1. As is clear from the resistance value and Cu reduction rate shown in Table 1, H ₂ SO ₄ , H
It can be seen that CuO can be reduced to Cu at a lower reduction temperature by adding NO ₃ and H ₃ PO ₄ . In this way, the reducing property of CuO to Cu is changed to H ₂
It is clear that the addition of SO ₄ , HNO ₃ and H ₃ PO ₄ is effective.

[0023]

[Table 1]

Particularly in the case of the present embodiment, the conductive paste added with MgO is suitable for the internal electrode of the MLC, and the other additive added with Al ₂ O ₃ is the conductive paste for filling the via hole. As is the best.

[0025]

As described above, the CuO paste of the present invention contains, in addition to CuO, glass frit and MgO, or at least one of Al ₂ O ₃ , SnO ₂ , TiO ₂ and MnO _2. , Further H ₂ SO ₄ , HN
By adding at least one of O ₃ and H ₃ PO ₄ , it becomes easy to reduce CuO to Cu, facilitating the setting of reducing conditions, reducing the amount of hydrogen consumed, and shortening the processing time.
A cost reduction can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of internal electrodes and via holes of an MLC manufactured using a conductive paste according to an example of the present invention.

FIG. 2 is a surface view of a green sheet laminate for explaining a sheet resistance measurement pattern and a reducibility evaluation pattern of a conductive paste according to an example of the present invention.

[Explanation of symbols]

 1 Internal Electrode Layer 2 Dielectric Layer 3 Via Hole Electrode 4 Surface of Green Sheet Laminate 5 Sheet Resistance Measurement Pattern 6 Reducibility Evaluation Pattern

Claims (2)

[Claims] 1. An inorganic component containing 87.0 to 99.4% by weight of CuO powder, 0.5 to 10.0% by weight of glass frit and 0 to 3.0% by weight of MgO powder, an organic vehicle component comprising at least an organic binder and a solvent, and H ₂ SO ₄ , HNO ₃ ,
A conductive paste comprising at least one of H ₃ PO _{4 in} an amount of 0.05 to 5.00% by weight based on the total amount. 2. CuO powder 67.0 to 96.4% by weight, glass frit 0.5 to 10.0% by weight, MgO powder 0 to 3.0% by weight, and further Al ₂ O ₃ , SnO ₂ , TiO ₂ , MnO ₂
An inorganic component containing at least one kind of 3.0 to 20.0 wt% of the organic vehicle component consisting of at least an organic binder and a solvent, at least one of the total amount of _{H 2 SO 4, HNO 3,} H 3 PO 4 0.05 Conductive paste characterized by comprising ~ 5.00% by weight.