KR20070079548A - Conductive paste and multi-layer printed circuit board using the same - Google Patents

Abstract

A conductive paste and a multi-layer printed circuit board having the same are provided to prevent a crevice or a crack from being formed between a wiring pattern and the ceramic PCB by forming a conductive portion through the conductive paste. A conductive paste contains a binder component and an organic dissolvent. The binder is made of conductive powders and an organic chemical. The conductive powders contain silver powders and silver oxide powders. An average diameter of the silver powder is between 0.3 and 10.0 um. The conductive powders contain the silver oxide powder 0.1 - 15.0 w%. The silver powders are selected from AgO2 powders and AgO powders. The conductive paste is used for forming a conductor portion of a multi-layer PCB(4).

Description

Conductive paste and multi-layer printed circuit board using the same

1 is a cross-sectional view of an example of a low temperature fired ceramic multilayer circuit board.

2 is a diagram illustrating an example of a wiring pattern by screen printing.

3 is a diagram illustrating a method for evaluating substrate warpage.

**** Explanation of symbols on the main parts of the drawing *****

1: wiring pattern

2: beer hall

3: ceramic green sheet

4: ceramic substrate

5: surface plate

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste used as a conductor material for ceramic multilayer circuit boards used in the manufacture of high density wiring circuit boards, and a ceramic multilayer circuit board formed by forming a conductor portion using the conductive paste.

Ceramic multilayer circuit boards are widely used as high density wiring circuit boards. Ceramic multilayer circuit boards are generally manufactured by ceramic green sheet lamination, for example, in the following order.

First, via holes are formed in a plurality of ceramic green sheets for interlayer connection by punching, laser processing, and the like, and then conductive paste is applied to the via holes of each ceramic green sheet by hole filling printing. The via conductor was formed to form a via conductor, and then a wiring pattern was formed on each ceramic green sheet by using a conductive paste, by screen printing, or the like. Further, the plurality of ceramic green sheets were laminated and pressed, and the laminate was fired. Ceramic multilayer circuit boards have been manufactured.

Ceramic multilayer circuit boards currently used are roughly divided into high temperature calcined ceramic multilayer circuit boards fired at 1300 ° C. or higher, such as alumina, and low temperature calcined ceramic multilayer circuit boards fired at about 1000 ° C. or lower.

Mo, W and the like are used as conductor materials for high-temperature calcined ceramic multilayer circuit boards. However, when these metals are used, they must be fired in a reducing atmosphere or an inert atmosphere, and the electrical resistance of these metals is relatively high.

On the other hand, Ag, Ag-Pt, Ag-Pd and the like having low electrical resistance are used as the conductor material for low-temperature calcined ceramic multilayer circuit boards. These metals have excellent electrical characteristics and have the advantage of being calcined in air.

However, even in low-temperature calcined ceramic multilayer circuit boards that can be fired in air, when the binder component of the conductive paste contained in a large amount in the green sheet cannot be removed before firing of the substrate, the organic compound forming the binder is fired in the substrate. At this time, it becomes a gas and evaporates, and a gap and a crack may generate | occur | produce between the wiring pattern which consists of electroconductive paste, and a ceramic substrate. Therefore, in order to avoid such a problem, in the conventional low-temperature calcined ceramic multilayer circuit board manufacturing process, after removing the binder component to sufficiently remove the binder component before firing the substrate for several hours to several ten hours, the substrate is baked. Was doing.

However, since a long time debinding process significantly reduces productivity and causes a significant cost increase, Patent Documents 1 and 2 propose conductive pastes having improved debinding properties by employing a binder component that is easy to thermally decompose. have.

That is, Patent Document 1 discloses a conductive paste containing an acrylic resin and an alkyd resin as a binder component, that is, 2 to 4 parts by weight of acrylic resin and 1 part by weight of alkyd resin.

Further, Patent Document 2 at a shear rate of 0.2 sec ^-1 and a viscosity in a η, when the weight average molecular weight of the organic compound to form a binder by Ma, 0 <Ma range of <10, ^10, if Ma> Mc Disclosed is a conductive paste containing a binder component in which? is proportional to Ma ⁿ (where n> 1) and Ma? Mc, where a value Mc exists such that? is proportional to Ma.

Patent Document 1: Japanese Patent Application Laid-Open No. 5-234424

Patent Document 2: Japanese Patent Application Laid-Open No. 2000-76931

However, since the acrylic resin used as the binder component of the conductive paste of Patent Literature 1 has strong spinability and adhesiveness, a wiring pattern can be formed using the conductive paste containing the binder component. At this time, the shape of the screen mesh is easily transferred to the wiring pattern, and as a result, irregularities may occur on the wiring pattern surface. In particular, in the case of forming a fine wiring pattern having a line width of about 20 to 100 µm, the unevenness of the pattern surface causes the pattern to be disconnected during firing of the substrate and is a fatal defect.

Moreover, in the case of the electrically conductive paste of patent document 2, it is necessary to use the binder component determined by the special relationship of a viscosity and molecular weight, and very troublesome preparation is needed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and its object is not to cause cracks or cracks between the wiring pattern and the ceramic substrate even when the conductor paste and the ceramic green sheet are fired at the same time. It is to provide a ceramic multilayer circuit board formed by forming a conductive portion using a conductive paste that can easily obtain a substrate and the conductive paste.

In order to achieve the above object, the conductive paste of the present invention is characterized in that the conductive paste contains a conductive powder, a binder component made of an organic compound, and an organic solvent, wherein the conductive paste contains silver powder and silver oxide powder. .

It is preferable that the average particle diameter of silver powder exists in the range of 0.3-10.0 micrometers.

It is preferable to contain 0.1-15.0 weight% of silver oxide powders.

The silver oxide powder is preferably selected from Ag ₂ O powder and AgO powder.

It is preferable to form the conductor portion of the ceramic multilayer circuit board using the conductive paste.

The electrically conductive paste of this invention contains silver powder and silver oxide powder as electroconductive powder, and silver oxide produces the following reaction at about 400 degreeC.

2Ag ₂ O → 4Ag + O ₂

2AgO → 2Ag + O ₂

That is, since silver oxide causes a reduction reaction at about 400 ° C., oxygen (O ₂ ) generated as a result of the reduction reaction is carried out by performing a heat treatment (de-binder treatment) at a temperature at which the silver oxide causes a reduction reaction before firing the substrate. The organic compound which is a binder component is decomposed and debinding is promoted. As a result, gaps or cracks hardly occur between the wiring pattern and the substrate during firing of the subsequent substrate, and a highly reliable ceramic multilayer circuit board can be obtained.

In this case, when the average particle diameter of silver powder is less than 0.3 micrometer, printing of the wiring pattern of fine line width is possible, but there exists a defect which causes small shrinkage at the time of baking, and is easy to disconnect. On the other hand, when the average particle diameter of silver powder exceeds 10.0 micrometers, there exists a defect which becomes difficult to print the wiring pattern of the fine line width which has a line width of 100 micrometers or less, and a line space | interval. Therefore, by making the average particle diameter of silver powder into 0.3-10.0 micrometers, the wiring pattern of a fine line width can be formed without disconnection at the time of baking. In addition, in this application, an average particle diameter means the particle diameter in 50 volume% in the cumulative graph when the arithmetic mean value of the long diameter and short diameter of a powder is measured with the laser diffraction type particle size distribution measuring apparatus by a microtrack company.

If the silver oxide powder is less than 0.1% by weight, the effect as an oxygen source for the thermal decomposition of the binder component cannot be sufficiently expected. On the other hand, when silver oxide powder exceeds 15.0 weight%, there exists a defect which a mismatch with the shrinkage rate at the time of sintering of a ceramic substrate and a conductor, and a board curvature generate | occur | produce. Therefore, by containing 0.1-15.0 weight% of silver oxide powders, such a defect does not exist and a binder removal promoting effect can fully be expected. As the silver oxide powder, either the Ag ₂ O powder or the AgO powder can be expected to have a debinding promoting effect, so either one can be used alone, but both Ag ₂ O powder and AgO powder can be used in combination.

When the conductive portion of the ceramic multilayer circuit board is formed using the conductive paste, no gaps or cracks occur between the wiring pattern and the ceramic substrate, and a highly reliable ceramic multilayer circuit board can be obtained.

Next, an example of a method of forming a conductor portion of a low-temperature calcined ceramic multilayer circuit board using the conductive paste of the present invention will be described in the process sequence.

(1) forming of low temperature calcined ceramic green sheet

The green sheet of the low-temperature calcined ceramic is tape molded by the doctor blade method or the like. At this time, as the low-temperature calcined ceramic, for example, a mixture of 50 to 65% by weight of CaO-SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -based glass and 35 to 50% by weight of alumina can be used. In addition, low-temperature calcined ceramic materials such as a mixture of PbO-SiO ₂ -B ₂ O ₃ -based glass and alumina, MgO-Al ₂ O ₃ -SiO ₂ -B ₂ O ₃ -based glass, cozelite-based crystallized glass It can also be used.

(2) cutting of green sheets and formation of via holes

Next, after cutting the tape-shaped low-temperature calcined ceramic green sheet to a predetermined dimension, the via hole is punched at a predetermined position.

(3) Filling the conductive paste in the via hole and printing the wiring pattern

Next, the filling by the conductive paste hole filling method of the via hole and the printing of the wiring pattern by the conductive paste onto the ceramic green sheet are performed.

In the silver conductive paste used at this time, a general blending ratio may be employed for the blending ratio of the conductive powder composed of silver powder and silver oxide powder and the organic solution obtained by dissolving a binder component in an organic solvent. For example, it can be set as (70/30) <(conductive powder / organic solution) <(90/10) by weight ratio. If the conductive powder is less than 70 parts by weight (organic solution is more than 30 parts by weight), sufficient conductivity cannot be ensured. On the other hand, if the conductive powder is more than 90 parts by weight (organic solution is less than 10 parts by weight), an appropriate paste viscosity is obtained. It is not obtained because it is not obtained and the work efficiency of filling the via hole and printing the wiring pattern is lowered.

Preferable blending of the conductive paste for achieving the effect of the present invention and obtaining good electrical properties is that when the total is 100 parts by weight, 55 to 89.9 parts by weight of silver powder, 0.1 to 15.0 parts by weight of silver oxide powder, and organic solution 10 to 30 parts by weight, and the silver oxide powder blend ratio is better than the silver powder, so the effect of the particle size of the silver oxide on the electrical properties is considered to be relatively small compared to the silver powder. In order to form a pattern, it is preferable to make it the range of 0.3-10.0 micrometers so that the average particle diameter of silver oxide powder may be the same as silver powder.

Although it does not limit as a binder component which comprises an organic solution, Ethyl cellulose is used, As an organic solvent, Ethyl calbitol acetate, Butyl calbitol acetate, Terpineol etc. can be used.

For example, an electrically conductive paste can be obtained by fully kneading and disperse | distributing the thing which added 20 weight part of organic solutions which melt | dissolved ethyl cellulose in terpineol with respect to 80 weight part of said electroconductive powders using a three roll apparatus. .

The silver powder contained in the conductive paste for wiring pattern printing and the silver powder contained in the conductive paste for via hole filling do not necessarily have to use the same one, and the former silver powder has a relatively small particle diameter (0.3 to 3.0 µm). The latter silver powder may be made into a relatively large particle size (3.0 to 10.0 µm). In this way, the paste using the silver powder of small particle size can form fine wiring, and the paste using the silver powder of large particle size has the effect which can be made low in cost.

In order to improve the adhesion between the conductive paste and the ceramic substrate, the glass component may be contained in the conductive paste in an amount of 0.1% by weight or more. However, when the glass component is added in excess of 1.0% by weight, the solder wettability may deteriorate. It is preferable to add a predetermined amount of glass components as needed.

In addition, in order to improve solder corrosion resistance, the conductive paste may contain 0.1 wt% or more of Pt powder or Pd powder, but the effect is saturated even when Pt powder or Pd powder is added in excess of 0.5 parts by weight. On the other hand, since it raises a manufacturing cost, it is preferable to add a predetermined amount Pt powder or Pd powder as needed.

(4) lamination and crimping

After the conductive paste filling of the via hole and the printing of the wiring pattern are finished, the green sheets of each layer are laminated and crimped to be integrated.

(5) Debinding Treatment

Before firing the laminate, the laminate is heated to about 400 to 450 ° C. for 1 to 2 hours to thermally decompose and remove the binder component made of the organic compound by oxygen generated as a result of the reduction reaction of silver oxide. Ratio in the case of a silver oxide powder for a binder to promote including both of Ag ₂ O powder and AgO powder, Ag ₂ O powder is 20 parts by weight of an AgO powder is 80 parts by weight of Ag ₂ O powder from 80 parts by weight, the ratio And AgO powder is preferably included in the range of the proportion of 20 parts by weight.

(6) firing

The de-bindered laminate can be baked at a firing peak temperature of 800 to 950 ° C. (preferably around 900 ° C.) and baked under conditions maintained at the peak temperature for 20 to 60 minutes to obtain a low temperature fired ceramic multilayer circuit board.

1 is a cross-sectional view of an example of a low-temperature calcined ceramic multilayer circuit board manufactured through the above process, 1 is a wiring pattern, 2 is a via hole filled with a conductive paste, and 3 is a ceramic green sheet.

In addition, the alumina green sheet may be laminated and pressed on both sides of the green sheet laminate in the firing step, fired at 800 to 950 ° C. while being pressed, and after the firing, the alumina green sheet may be removed to manufacture a low temperature calcined ceramic multilayer circuit board. have. By doing in this way, curvature of a board | substrate and conductor peeling resulting from the difference of the heat shrinkage behavior of a conductor and a ceramic can be suppressed.

Hereinafter, although the Example of this invention is described, this invention is not limited to the following Example, A change and correction are possible suitably in the range which does not deviate from the technical scope of this invention.

The silver powder, the silver oxide powder, and the organic solution which melt | dissolved ethylene cellulose in terpineol which were mix | blended like the description of Table 1 were knead | mixed and disperse | distributed using three roll apparatuses, and the electrically conductive paste which showed the average particle diameter shown in Table 1 below A ceramic green sheet having a square shape (1 inch X 1 inch X 300 μm thick) formed by mixing 60% by weight of CaO-Al ₂ O ₃ -SiO ₂ -B ₂ O ₃ glass and 40% by weight of alumina. Used.

Then, after forming the wiring pattern as shown in Fig. 2 by screen printing using the conductive paste on the ceramic green sheet, in a belt-type firing furnace in the air atmosphere conditions maintained at 400 ℃ for one hour After the heat treatment was carried out, the mixture was cooled to room temperature, and then fired in an atmosphere atmosphere of a peak temperature of 890 ° C. and a peak temperature holding time of 20 minutes in the same belt type firing furnace. In the resultant ceramic circuit board, the gap between the wiring pattern, the board, and the board warpage were evaluated. In Fig. 2, L denotes a line width and S denotes a line interval. In addition, evaluation of the clearance gap of a wiring pattern, board | substrate, and board | substrate which are described later in Table 1 is based on the evaluation method as demonstrated below.

As a method for evaluating the gap between the wiring pattern and the substrate, the ceramic substrate after firing was placed on a surface plate and visually observed. As a result, no gap was recognized between the substrate and the substrate in the entire wiring pattern. (Symbol ○), the gap between the substrate is recognized in the partial region of the wiring pattern as 'a little gap' (symbol Δ), and the gap between the substrate and the substrate is almost the entire area of the wiring pattern. What was perceived was 'with gaps' (symbol X).

As a method of evaluating substrate warpage, as shown in FIG. 3, the ceramic substrate 4 after firing is placed on the surface plate 5, and the lower surface 4a of the substrate 4 and the upper surface 5a of the surface plate 5. The gap maximum value h is measured by a gap gauge, and the gap maximum value h is 20 µm or less as 'good' (symbol ○), and the gap maximum value h is 25 µm to 35 µm. Defective '(symbol DELTA), and the space | interval maximum value h was set to 50 micrometers or more as "badness" (symbol X). It is a favorable level practically suitable that the said gap maximum value h is 20 micrometers or less.

As shown in Table 1, the first embodiment to the eleventh embodiment of the present invention is a ceramic circuit board having a high level and high reliability, with no gap between the wiring pattern and the substrate, and practically suitable for warping of the substrate.

However, according to Comparative Examples 1 to 5, since Ag ₂ O is not blended with the conductive paste, the binder component cannot be thermally decomposed before firing of the substrate, and the binder component becomes a gas at the time of firing of the substrate and evaporates. A gap occurred between the wiring pattern and the substrate and warpage was also seen in the substrate.

In Comparative Example 6, since Ag ₂ O was excessively added to the conductive paste, the binder component could be thermally decomposed and removed prior to firing of the substrate, while no gap was formed between the wiring pattern and the substrate. Inconsistency was observed in the sintering timing and shrinkage ratio of, and warpage occurred in the substrate.

In Comparative Example 7, Ag ₂ O was blended into the conductive paste, but since the amount of the mixture was small, the amount of binder removal by thermal decomposition before firing of the substrate was small. A gap occurred between the substrates.

Further, in the case of Comparative Example 6 and Comparative Example 7, the same results as above were obtained even in the case of using AgO in place of the Ag ₂ O.

When the conductor portion of the ceramic multilayer circuit board is formed using the conductive paste of the present invention, a gap or crack does not occur between the wiring pattern and the ceramic substrate, and a highly reliable ceramic multilayer circuit board can be obtained.

Claims (5)

In the electrically conductive paste containing electroconductive powder, the binder component which consists of organic compounds, and an organic solvent, A conductive paste containing silver powder and silver oxide powder as the conductive powder. The electrically conductive paste of Claim 1 in which the average particle diameter of silver powder exists in the range of 0.3-10.0 micrometers. The electrically conductive paste of Claim 1 or 2 containing 0.1-15.0 weight% of silver oxide powders. The conductive paste according to any one of claims 1 to 3, wherein the silver oxide powder is selected from Ag ₂ O powder and AgO powder. A ceramic multilayer circuit board formed by forming a conductor portion using the conductive paste of any one of claims 1 to 4.

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