JP3495890B2 - Conductive paste composition, method for producing conductive paste composition, method for forming surface conductor, and ceramic multilayer substrate - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a conductive paste composition for forming a conductor on a substrate by firing, a method for producing the conductive paste composition, and formation of a surface layer conductor using the conductive paste composition. The present invention relates to a method and a ceramic multilayer substrate made using the conductive paste composition.

[0002]

2. Description of the Related Art In recent years, remarkable progress has been made in the field of mobile communication.
As a material suitable for use in such high frequency applications, a glass ceramic, which uses a low resistance conductor and has a low loss, has been drawing attention. This kind of glass ceramic can be fired at a low temperature of 1000 ° C. or lower, and the usual firing temperature is 840-9.
It is often in the range of 50 ° C. In the case of crystallized glass or a type in which glass and a filler are reacted, the holding time at the highest temperature during firing is, for example, 3
It is relatively long, from 0 minutes to 2 hours.

[0003]

By the way, conventionally, various noble metal materials such as silver have been used as the material of the surface layer conductor of the product using the above glass ceramic. However, including silver with a melting point of about 960 ° C,
When a precious metal material with a melting point of about 1000 ° C. is co-fired with the glass ceramic as described above, the surface conductor on the substrate becomes oversintered and the surface conductor has a porous structure. There were many. Then, in such an over-sintered state, there has been a problem that the surface layer conductor has a high resistance, the plating paste and the solder wettability are deteriorated, and the properties required for this type of conductor are significantly deteriorated. Also,
When the surface conductor with a porous structure is plated, the treatment liquid such as acid or alkali penetrates from the pores of the surface layer conductor, and the structure inside the surface layer conductor or the interface between the surface layer conductor and the substrate is invaded. There is also a problem that the adhesion strength of the conductor is significantly deteriorated.

Here, considering only to avoid oversintering of the surface conductor, a silver conductor having a good plating property is formed by firing the substrate on which the inner layer wiring is formed without the surface conductor and then secondary metallizing the surface layer. There is a way to burn. However, this increases the man-hours, which is disadvantageous in cost.
In the case of a product having a cavity, it is difficult to form a silver conductor in the cavity by secondary metallization.

If a silver-based alloy such as silver / Pd or silver / Pt is used, a surface layer conductor which does not require plating can be formed, so that the problems caused by the plating solution can be solved. However, in the method using silver / Pd, disconnection (Kirkendall effect) is likely to occur in the connection portion with the silver conductor in the inner layer due to the difference in thermal diffusion rate between them during co-firing, so cost reduction due to co-firing cannot be expected. . On the other hand, the method using silver / Pt has good connectivity with the silver conductor of the inner layer at the time of simultaneous firing, but has a problem in durability against solder other than silver-containing solder.

That is, according to the above-mentioned means, it is possible to obtain a surface layer conductor excellent in all of the characteristics such as plating, solder wetting, and adhesion strength while reducing the cost by simultaneously firing the glass ceramic substrate and the surface layer conductor. It was extremely difficult. The present invention has been made to solve the above problems, and its object is to achieve all of the characteristics such as plating paste, solder wetting, and adhesion strength even when co-firing a glass ceramic substrate and a surface layer conductor. Another object of the present invention is to provide a novel conductive paste composition capable of obtaining an excellent surface layer conductor. Another object of the present invention is to provide a method for manufacturing the conductive paste composition, a method for forming a surface layer conductor using the conductive paste composition, and a ceramic multilayer substrate manufactured using the conductive paste composition.

[0007]

Means for Solving the Problem and Effect of the Invention In order to solve this problem, the conductive paste composition of the present invention has a silver powder and an average particle size of 0.5 to 0.5 as described in claim 1.
2μm of tungsten powder, oxidation rhodium and organic
It is a mixture formed by mixing a vehicle and a paste, and contains 3 to 5% of tungsten powder and 100 to 600 ppm of rhodium oxide in a weight ratio with respect to the silver powder.

In this conductive paste composition, silver (A
g) Powder is a component that finally forms a silver conductor. The silver powder is not particularly limited as long as it is one generally used in this kind of conductive paste composition. To give a more specific example, for example, the average particle size is 1 to 10
It is preferable to use silver powder of about μm.

The tungsten (W) powder has the function of forming fine depressions on the surface of the silver conductor obtained by firing. A part of the plating film penetrates into the recess when the silver conductor surface is plated. Therefore, this serves as an anchor to improve the adhesion of the plated coating to the silver conductor. That is, the anchoring effect due to the depression appears. Further, when the plating treatment is electroless plating, in the recess formed as a result of adding tungsten, palladium nuclei serving as a catalyst are easily deposited,
It also has the effect of increasing the catalytic activity.

Here, it is important that the tungsten powder is contained in an amount of 3 to 5% by weight with respect to the silver powder. When the content of the tungsten powder is less than 3% by weight with respect to the silver powder, the adhesion of the plated coating becomes weak and the plating is liable to peel off. On the other hand,
If it exceeds 5%, the tungsten powder floats on the surface of the silver conductor, making it difficult to secure good plating properties. It is also important to use tungsten powder having an average particle size of 0.5 to 2 μm. If the average particle diameter is less than 0.5 μm, the above-mentioned depressions become too small, while if the average particle diameter exceeds 2 μm, the above-mentioned depressions become too large. In any case, the anchoring effect weakens,
The adhesion of the plated coating to the silver conductor will be reduced.

Further, rhodium oxide (Rh ₂ O ₃ ) is
It has the effect of suppressing the silver conductor obtained by firing from becoming a porous structure. Therefore, it becomes difficult for the chemical solution used for plating the surface of the silver conductor to enter the structure of the silver conductor. As a result, good adhesion of the silver conductor to the base material is maintained.

Here, it is important that the rhodium oxide is contained in a weight ratio of 100 to 600 ppm relative to the silver powder. If the rhodium oxide content is less than 100 ppm, the abnormal grain growth of the silver conductor that occurs during simultaneous firing with the substrate at 840 to 950 ° C. cannot be suppressed, and the silver conductor tends to have a porous structure. On the other hand, when the amount exceeds 600 ppm, the firing of the silver powder is excessively suppressed, and unevenness in the degree of burning occurs due to the difference in the metallized thickness, making it difficult to secure good plating properties.

Further , the components necessary for forming the paste
As an organic vehicle is added. However, organic
In addition, the addition amount and the like do not affect the essence of the present invention.

According to the conductive paste composition as described above, since it has the characteristic composition as described above,
Due to the action of each component, the formed silver conductor does not have a porous structure even when co-firing with the glass ceramic substrate. As a result, it is possible to obtain a silver conductor having excellent characteristics such as plating glue, solder wetting, and adhesion strength.

By the way, in the conductive paste composition of the present invention, as for rhodium oxide, of course, it is sufficient if powder of rhodium oxide is added, but in addition to this, it is converted into rhodium oxide by heat treatment in an oxidizing atmosphere. Such rhodium-based substances may be mixed and rhodium oxide may be produced in the mixture. As such a rhodium-based substance, for example, organic rhodium can be considered. As a conductive paste composition containing an organic rhodium, the patented invention of Japanese Patent No. 2503974 is already known.
However, in the above-mentioned patented invention, organic rhodium is contained in the conductive paste composition applied to the substrate. Therefore, especially when the content of organorhodium is 100 p
When it exceeds pm, metallization peeling is likely to occur in the step of removing the resin from the ceramic green body before firing due to organic rhodium. In addition, the thixotropy of the paste is deteriorated, which makes it difficult to screen-print the conductive paste. On the other hand, the conductive paste composition of the present invention, even if the organic rhodium is added, is subjected to heat treatment in advance, the organic rhodium in the conductive paste composition is changed to rhodium oxide, Since it is applied to the base material above, the above problems do not occur.

By the way, the conductive paste composition of the present invention can be obtained by appropriately mixing the above-mentioned main components, but more preferably, as described in claim 2, the silver powder and the rhodium oxide are used. The mixture is 200 ~
Heat treatment is performed in the range of 400 ° C. for 5 to 30 minutes, and the tungsten powder and the tungsten powder are added to the heat-treated mixture.
It is preferable that the organic vehicle is mixed.

Since such a conductive paste composition is subjected to heat treatment in a state where the silver powder and the rhodium oxide are surely in contact with each other, the silver powder and the rhodium oxide are fixed to each other in the conductive paste composition. It is a composite particle. The composite particles are mixed with other components ( tungsten powder and organic vehicle) . Therefore, other components ( tungsten powder and
The rhodium oxide in the state where the contact with the silver powder is blocked by the machine vehicle) is drastically reduced. This enhances the effect of suppressing abnormal grain growth of the silver conductor due to rhodium oxide. As a result, it is possible to more reliably prevent the silver conductor obtained by firing from having a porous structure.

As is apparent from the above description, in producing the conductive paste composition of the present invention, the method of claim 3 is used.
As described, rhodium oxide was mixed with silver powder in a weight ratio of 100 to 600 ppm with respect to silver powder, and the mixture of the silver powder and rhodium oxide was heat-treated in the range of 200 to 400 ° C. for 5 to 30 minutes, The heat-treated mixture of silver powder and rhodium oxide had an average particle size of 0.
It is advisable to mix an organic vehicle with a tungsten powder having a weight ratio of 5 to 2 μm and a weight ratio to the silver powder of 3 to 5% .

According to such a manufacturing method, an excellent conductive paste composition as described in claim 2 can be obtained. Next, the method for forming a surface layer conductor according to the present invention comprises:
As described above, a method for forming a surface layer conductor, which comprises forming a surface layer conductor having a desired shape on the surface of a base material by applying the conductive paste composition according to claim 1 or 2 onto the surface of the base material and baking the composition. Then, the firing temperature T (° C.) is 684.7 × Y in relation to the content Y (ppm) of the rhodium oxide.
It is characterized in that the firing is performed by adjusting the range of ^0.044 ≤ T ≤ 950.

Here, the upper limit of the above temperature condition is a limit due to the melting point of silver. That is, at a firing temperature higher than this upper limit, silver tends to be in a state in which it can freely flow, so that it is difficult to form a surface layer conductor that draws a desired pattern. On the other hand, the lower limit value of the temperature condition is a finding obtained by the inventor through many experiments, and clearly explains the causal relationship between the rhodium oxide content Y and the lower limit value of the firing temperature T. Is difficult

The firing temperature T usually depends on the temperature conditions required from the substrate side. On the other hand, as the content R of the rhodium oxide, an appropriate value is selected according to the area and thickness of the silver conductor. However, when the content of rhodium oxide is a certain content and the temperature condition during firing is below a certain lower limit value, the characteristics such as plating of silver conductor, solder wetting and adhesion strength may deteriorate. . Therefore, in order to select the optimum rhodium oxide content, it is necessary to consider the firing temperature as well, and such selection work has not always been easy.

Therefore, the inventor first carried out an experiment with various combinations of the rhodium oxide content Y and the firing temperature T, and plotted the relationship on a graph. As a result, the inventor has found that, as the content Y of rhodium oxide increases, unless the lower limit of the firing temperature T is increased, a silver conductor having necessary characteristics tends to be not obtained. This tendency was considered to be approximated by the relational expression T = a × Y ^b as far as it was judged from the graph. Therefore, the lower limit value of the temperature condition was calculated by regression analysis using an electronic calculator,
The above conditions were decided.

According to the surface layer conductor forming method of the present invention completed in this way, the relationship between the firing temperature and the content of rhodium oxide can be determined more easily and quickly than before, under the conditions. The silver conductor formed in step 1 has excellent characteristics such as plating paste, solder wetting, and adhesion strength.

Next, in the ceramic multilayer substrate of the present invention, as described in claim 5, the conductive paste composition according to claim 1 or 2 is printed on a ceramic green sheet and simultaneously fired, It is characterized in that a surface wiring circuit is formed.

According to this ceramic multi-layer substrate, since the silver conductor is formed by using the above-mentioned conductive paste composition of the present invention, even if co-firing is performed, it is possible to obtain characteristics such as plating glue, solder wetting and adhesion strength. An excellent silver conductor is formed. Further, in particular, as in the ceramic multilayer substrate according to claim 6, the ceramic green sheet is 840.
Those made of low-temperature fired glass ceramics that can be fired at ~ 950 ° C often require a long time especially for co-firing, and even in that case, silver excellent in all characteristics such as plating glue, solder wetting, and adhesion strength. A conductor is formed.

Further, the ceramic multi-layer substrate according to claim 7.
Like the plate, the conductive paste composition and the ceramic
The green sheet at the firing temperature T (° C.)
684.7 in relation to the rhodium content Y (ppm)
× Y ^0.044Adjust within the range of ≦ T ≦ 950 and co-fire
The optimum firing temperature and rhodium oxide content.
Since firing is performed in a state adjusted to the relationship,
Properties such as body plating, solder wetting, and adhesion strength
It will definitely be superior.

[0027]

DETAILED DESCRIPTION OF THE INVENTION

(1) Preparation of silver paste First, to 100 g of silver powder having an average particle size of 3 μm, rhodium oxide having an average particle size of 0.1 μm was added and mixed. The addition amount of rhodium oxide is 90, by weight ratio to silver powder.
100, 110, 160, 300, 500, 600, 6
Nine kinds of 50,700 ppm were used.

Subsequently, the mixture of 9 kinds of silver powders and rhodium oxide was heated in an oven furnace at a maximum temperature of 400 ° C. for 10 times.
Heat treatment was performed for one minute, and then tungsten powder having an average particle diameter of 1.3 μm was added and mixed. The amount of the tungsten powder added was 2.5, 3.5, 4.
It was set to four kinds of 5, 5.5%.

Thereafter, 5 g of ethyl cellulose and BCA (butyl carbitol acetate) 2 were used as an organic vehicle.
After adding and mixing 0 g, the mixture was kneaded with a three-roll mill to prepare a silver paste. (2) Preparation of Ceramic Green Sheet As the ceramic raw material powder, powder of alumina borosilicate glass and alumina powder were prepared. Glass powder is Si
O ₂ : 43% by weight, A1 ₂ O ₃ : 28% by weight, B
₂ O ₃ : 8% by weight, MgO: 8% by weight, CaO: 8% by weight, ZrO ₂ : 1% by weight, the respective oxide powders are mixed, melted and then rapidly cooled to a cullet shape, and further crushed. Then, an average particle diameter of 5 μm was obtained. on the other hand,
Alumina powder is a commercially available low-soda α-alumina powder,
An average particle size of 3 μm was prepared.

An ethyl methacrylate-based acrylic resin was prepared as the binder. Next, the glass powder and the alumina powder were placed in an alumina pot at a ratio of 6: 4 so that the total amount was 1000 g. Further, 200 g of MEK (methyl ethyl ketone) as a solvent, 100 g of the above acrylic resin, 50 g of DOP (dioctyl phthalate) as a plasticizer, and 5 g of a dispersant were placed in the pot and mixed for 10 hours to obtain a slurry. From this slurry, a thickness of 0.4 is obtained by a known doctor blade method.
mm ceramic green sheets were produced. (3) Preparation of sample After stacking four ceramic green sheets of (2) above, the ceramic green sheets were cut into a 60 mm square, and using the silver paste of (1) above, as shown in FIG. The 4 mm square tensile test pad 10 is attached to the ceramic green sheet 1
2 was screen printed. After drying at 120 ° C. for 10 minutes, resin was removed at 250 ° C. for 10 hours. After that, the ceramic and the silver conductor were simultaneously fired using a continuous belt furnace. The firing temperature at this time is 840, 860, 88.
7 kinds of 0,900,910,930,950 ° C,
The firing time was 30 minutes. Shrinkage rate after firing is 8
At 3%, the baking size of the tensile test pad 10 is 2
The mm square and the thickness were 20 μm. (4) Test method The following tests A to C were performed.

A. Plating Glue Test The above sample was degreased, washed with 10% sulfuric acid, immersed in a palladium chloride solution, and electroless Ni-- was placed on the tensile test pad.
P plating 3 μm, thin replacement Au plating 0.1 μm
It took m. After washing and drying, the appearance of plating was checked by visual inspection. The evaluation was evaluated as “◯” when the plating was good, “Δ” when there was partial unevenness, and “x” when there was no plating.

B. Solder Wetting Test After the above test A, the same sample was heated to 230 ° C. to 60%.
Dip in a eutectic solder bath of Sn-40% Pb for 10 seconds. After washing with ethanol, the solder wettability was checked by visual inspection. In the evaluation, good wetness was evaluated as “◯”, partial wetness was evaluated as “Δ”, and almost no wetness was evaluated as “x”.

C. Adhesion Strength Test After the above test B, as shown in FIG.
A nickel-plated copper wire 14 having a diameter of 0.8 mm was soldered. Then, the copper wire 14 fixed by the solder 16 was bent at 90 degrees with respect to the surface of the ceramic green sheet 12. In this state, the copper wire 14 was pulled in the direction of arrow P in the drawing at a speed of 20 mm / min, and the adhesion strength was measured. When the evaluation is 2 kg or more, it is considered to pass. (5) Comprehensive Evaluation First, in order to evaluate the addition amount of rhodium oxide and the firing temperature, the results of the above tests A to C when the addition amount of tungsten is 3.5% are shown in Table 1 and FIG. 3 below. . In addition, in FIG. 3, both of the tests A and B are “◯”.
In addition, the sample that became 2 kg or more in the test C was plotted as "○", and the remaining samples were plotted as "●". Further, in Table 1, the column marked with "-" has not been tested.

[0034]

[Table 1]

As is clear from Table 1 and FIG. 3, if the content of rhodium oxide is less than 100 ppm, a silver conductor having excellent characteristics cannot be obtained. This tendency becomes remarkable especially when the firing temperature is increased. It is considered that this is because the amount of rhodium oxide is too small to sufficiently suppress overfiring. On the other hand, the content of rhodium oxide is 600 pp
Even if it exceeds m, a silver conductor having excellent characteristics cannot be obtained. In particular, the tendency becomes remarkable when the firing temperature is lowered. It is considered that this is because the amount of rhodium oxide was too large and firing was suppressed too much.

Further, the firing temperature is tested with an upper limit of 950 ° C. This means that even if firing is attempted at a temperature higher than 950 ° C., silver flows to form the desired surface layer conductor. This is because it cannot be done. On the other hand, the lower limit of the firing temperature varied depending on the content of rhodium oxide. As the content Y of rhodium oxide increases, unless the lower limit of the firing temperature T is increased, it tends to be difficult to obtain a silver conductor having excellent characteristics. It is considered that this tendency can be approximated by the relational expression T = a × Y ^b as far as judged from the graph of FIG.

Therefore, the most probable relational expression passing through "o" at the lowest position in the vertical axis direction in FIG. 3 was calculated by regression analysis using an electronic computer. As a result, the following formula 1 was obtained.

[0038]

[Number 1] T = 684.7 × Y ^0.044 Incidentally, the above equation 1, on Figure 3, a curve shown by a solid line in FIG. From the above results, the content of rhodium oxide is 100 to 600 ppm, the firing temperature T is 684.7 × Y ^{0.044 in} relation to the content Y of rhodium oxide.
It is understood that the firing may be performed by adjusting the range of ≦ T ≦ 950. That is, when the above conditions are satisfied, even when the glass ceramic substrate and the surface layer conductor are co-fired, it is possible to obtain a surface layer conductor having excellent characteristics such as plating glue, solder wetting, and adhesion strength. it is conceivable that.

Next, in order to evaluate the addition amount of tungsten and the firing temperature, the addition amount of rhodium oxide was set to 300 p.
The results of the above tests A to C in the case of pm are shown in Table 2 below.

[0040]

[Table 2]

As is clear from Table 2, when the content of tungsten is less than 3%, the silver conductor has poor plating adhesion. On the other hand, if the content of tungsten exceeds 5%, the characteristics of both plating and solder wetting are adversely affected.
It should be noted that these tendencies are almost the same even if the firing temperature changes, and it is considered that the firing temperature has almost no effect.

Furthermore, the content of tungsten is 3.5%.
Comparing the ones of 4.5% and those of 4.5%, the one of 4.5% can produce a silver conductor excellent in plating paste and solder wetting in a wider firing temperature range. However, when looking at the adhesion strength under the same firing temperature condition, a tungsten content of 3.5% shows a somewhat higher value. Therefore, when these are comprehensively taken into consideration, the tungsten contents of 3.5% and 4.5% are
It is hard to say which one is superior, but at 880 ° C
When the above firing is possible, it can be said that the content of tungsten is preferably 3.5%.

Although the embodiments of the present invention have been described above, various specific forms of the embodiments of the present invention other than those described above are possible.

[Brief description of drawings]

FIG. 1 is a front view of a sample equipped with a tensile test pad produced using the conductive paste composition of the present invention.

FIG. 2 is a sectional view showing a state in which a copper wire is soldered to the sample.

FIG. 3 is a graph plotting the content of rhodium oxide on the horizontal axis and the firing temperature on the vertical axis so that the superiority or inferiority of the firing state of the silver conductor can be seen.

[Explanation of symbols]

10 ... Tension test pad, 12 ... Ceramic green sheet, 14 ... Copper wire, 16 ... Solder.

Claims (7)

(57) [Claims] 1. A silver powder, tungsten powder having an average particle diameter of 0.5 to 2 [mu] m, oxidation rhodium, and an organic vehicle are mixed
A mixture of the tungsten powder and the silver powder in a weight ratio to the silver powder.
A conductive paste composition comprising 5% and 100-600 ppm of rhodium oxide. 2. The conductive paste composition according to claim 1, wherein the mixture of the silver powder and the rhodium oxide is 200
Is 5-30 minutes heat treatment in the range of to 400 ° C., Oyo the tungsten powder for the heat treated mixture
And a mixture of the organic vehicle and a conductive paste composition. 3. Rhodium oxide is mixed with silver powder in a weight ratio of 100 to 600 ppm with respect to silver powder, and the mixture of the silver powder and rhodium oxide is mixed with 200 to 4 ppm.
Heat treatment is performed in the range of 00 ° C. for 5 to 30 minutes, and the heat-treated mixture of silver powder and rhodium oxide has an average particle diameter of 0.5 to 2 μm and a weight of silver powder.
A method for producing a conductive paste composition, which comprises mixing 3 to 5% by weight of tungsten powder with an organic vehicle . 4. A method for forming a surface layer conductor, which comprises forming a surface layer conductor having a desired shape on the surface of a base material by applying the conductive paste composition according to claim 1 or 2 onto the surface of the base material and firing the composition. The firing temperature T (° C.) at the rhodium oxide content Y (p
684.7 × Y ^0.044 ≦ T ≦ 950
The surface layer conductor forming method is characterized in that the firing is carried out by adjusting to the range. 5. A ceramic green sheet is printed with the conductive paste composition according to claim 1 or 2,
A ceramic multilayer substrate having a surface wiring circuit formed by simultaneous firing. 6. The ceramic multilayer substrate according to claim 5, wherein the ceramic green sheet is made of a low temperature fired glass ceramic capable of firing at 840 to 950 ° C. 7. The ceramic multilayer substrate according to claim 5, wherein the conductive paste composition and the ceramic green sheet have a firing temperature T (° C.) and a rhodium oxide content Y (ppm). 684.7 × Y ^0.044 ≦
A ceramic multilayer substrate, which is co-fired in a range of T ≦ 950.