JP3005635B2 - Conductive paste and circuit board using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste containing silver as a main component and having a reduced shrinkage during firing, and a circuit board using the same. In particular, the present invention relates to a conductor paste for forming wiring on a ceramic circuit board in an electronic component or the like requiring multilayer wiring, and a circuit board using the same.

[0002] In the present specification, the "shrinkage ratio" of a conductor paste indicates a ratio of a film thickness after firing to a film thickness when the conductor paste is printed and dried (in a state where an organic solvent is completely volatilized). 100- (film thickness after firing / film thickness after drying) × 100 (%).

[0003]

2. Description of the Related Art For example, a circuit board made of a ceramic such as alumina is often used as a circuit board in an electronic component such as a fixing heater used in a hybrid IC or a copying machine. Conventionally, as a conductive paste for forming a wiring (conductive layer) in such a ceramic circuit board, a conductive paste containing silver as a main component such as a silver paste or a silver-platinum paste has been mainly used.

[0004] The silver paste has an average particle diameter of 1 μm.
And a glass component having a softening point of about 500 ° C. in a weight ratio of about silver: glass component = about 98: 2 in order to increase the adhesion strength to the circuit board, and a paste in which these are mixed with an appropriate resin and solvent. . Further, in the silver-platinum paste, platinum particles are used as silver particles in the silver paste, and the conductor resistance value (sheet resistance value) of the obtained wiring does not become higher than a predetermined value by making the average particle size of the silver the same. Paste mixed in the range. These conductor pastes are printed and dried in a predetermined pattern on a circuit board,
The conductor layer is obtained by firing at about 850 ° C.

Japanese Patent Application Laid-Open No. 227909/1990 discloses that a conductor material for forming a conductor circuit has an average particle size of 0.1.
There has been proposed a conductive paste comprising a conductive fine powder of 1 μm or less such as silver and an organic metal compound such as an organic compound of gold.

[0006]

However, the silver particles used as a main component in the silver paste, silver-palladium paste and silver-platinum paste undergo grain growth at around 800 ° C. during firing. It has easy characteristics. The degree of the grain growth tends to increase as the particle size of the silver particles is smaller, because the contact area between the silver particles is larger and the reactivity is increased. However, in the above-described conventional conductive paste, the average particle diameter of the silver particles contained therein is adjusted to be relatively small, about 1 μm. Since the growth is easy to proceed and the particles are aggregated without gaps between the silver particles, the layer thickness of the obtained conductor layer largely shrinks from the layer thickness of the conductor paste after drying, and the shrinkage is large. . The shrinkage ratio of the silver paste, silver-palladium paste and silver-platinum paste is about 53 to 57%. Therefore, when a conductor layer is formed on a circuit board using the above-mentioned conventional conductor paste, the resulting conductor layer has reduced adhesion strength to the circuit board due to the shrinkage.

Further, the conductive paste described in the above-mentioned publication uses a conductive fine powder having an extremely fine particle diameter in order to form a fine and sharp circuit pattern, and thus has a higher shrinkage rate. Yes, the adhesion strength is reduced.

The problem of the adhesion strength due to the shrinkage of the conductor paste particularly occurs when a through hole for a multilayer wiring is provided on a circuit board or in the vicinity of the through hole. That is, since the through hole is generally formed by sublimation under a high temperature using a carbon dioxide laser, the wall surface of the through hole and the surface of the circuit board in the vicinity thereof are vitrified, and a conductive paste is printed thereon. If the conductor layer is provided by firing, a metal-glass structure that produces adhesion at the interface between the conductor layer and the circuit board is not formed well, and is formed on the surface of the circuit board that is not irradiated with laser. The adhesion is further reduced as compared to the conductor layer provided. As a result, shrinkage of the conductor paste during firing is promoted, and in the case of a through-hole conductor filling type in which the through-hole is completely buried in the conductor layer and wired, as shown in FIG.
A crescent-shaped space 4 is generated between the conductor layer 1 and the through hole 3 in the circuit board 2, which may lead to a conduction failure due to disconnection or the like.

Further, in order to alleviate the poor adhesion of the conductor layer due to the contraction of the conductor paste, the inside of the through hole of the conductor paste may be sucked from one opening of the through hole, for example, so that the film thickness after drying is reduced. Thinner (for example, 50 μm
In some cases, a method of reducing the shrinkage force during firing may be adopted. However, it is still not possible to completely suppress shrinkage of the conductive paste, and a through hole is formed by forming a conductive layer on the wall surface of the through hole and wiring. In the case of the inclusion type, as shown in FIG. 2, the conductor layer 1 becomes thin at the edge portions 3a and 3b of the through hole 3 on the front and back surfaces of the circuit board 2, which may also cause poor conduction, and furthermore, the printing conditions Management is extremely cumbersome.

According to the present invention, by suppressing the growth of silver particles, the shrinkage ratio of the conductive paste during firing is reduced, and even if the wiring (conductive layer) on the ceramic circuit board is formed by a thick layer, the disconnection occurs. It is an object of the present invention to provide a technique capable of forming a highly reliable circuit board without causing conduction failure such as the above.

[0011]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above object, and as a result, have increased the particle size of silver particles and mixed organic silicon in a silver paste for forming a conductor layer. By doing so, it has been found that the grain growth of silver particles during firing can be suppressed, and the shrinkage rate can be reduced. In addition, it has been found that, by further mixing a glass component having a high softening point into the paste as described above, the adhesion to a ceramic circuit board can be improved and the shrinkage can be further reduced.

That is, the present invention relates to the following conductive paste and circuit board.

A conductive paste for forming wiring on a ceramic circuit board, which contains silver particles and organic silicon, wherein the silver particles are adjusted to an average particle size of 3 to 5 μm, and the organic silicon is contained in an amount of 0.1 to 5 μm. A conductor paste which is adjusted to be contained in a range of 1 to 1% by weight.

A conductive paste for forming wiring on a ceramic circuit board, comprising silver particles, organic silicon and a glass component, wherein the silver particles have an average particle size of 3 to 5 μm.
m, and adjusted so that organosilicon is contained in the range of 0.1 to 1% by weight.
A conductor paste characterized in that it is adjusted so that the glass component having the above softening point is contained in the range of 1 to 1.5% by weight.

A circuit board on which a wiring is formed by the conductive paste according to claim 1.

The larger the particle size of the silver particles used in the conductor paste of the present invention is, the smaller the shrinkage rate of the conductor paste is, but the conductor resistance (sheet resistance) is smaller.
Therefore, the average particle size is about 3 μm or more, preferably about 3 to 5 μm.

The resinate paste used in the present invention includes, for example, organic silicon and the like, which generates an inorganic oxide during firing, for example, silicon oxide in the case of the above-mentioned organic silicon. Is increased, that is, as the amount of the inorganic oxide generated at the time of firing is increased, the shrinkage ratio is reduced, but if it is too large, the conductor resistance as a conductor layer (wiring) becomes too large. The content is adjusted so that the content of the inorganic oxide (silicon oxide) in the conductive layer after firing the conductive paste is about 0.05% by weight or more, more preferably about 0.1 to 1% by weight. Here, the term “organic silicon” includes a material obtained by converting Si into a resin.

As the glass component used in the present invention, a glass pulverized body such as lead glass, which is generally called a glass frit, can be preferably used, and its softening point is about 700 ° C. or more, more preferably about 750 ° C. or more. It is said. In addition, the amount of the glass component can increase the adhesion with the increase, but on the other hand, the conductor resistance is lowered. Therefore, the compounding ratio is 2% by weight in the conductor layer after firing the conductor paste. The content is adjusted so as to be contained within the range of about 1 to 1.5% by weight or less.

In the present invention, the silver particles and the resinate paste, or a mixture obtained by adding a glass component to the silver particles and the resinate paste are used as a binder such as a resin such as ethyl cellulose.
Further, the conductor paste is appropriately adjusted to a paste having an appropriate viscosity with a high boiling point organic solvent such as terpineol, butyl carbitol acetate, ethylene glycol monobutyl ether, or the like to obtain a conductive paste. At this time, if necessary, for example,
Metal particles such as palladium, platinum, gold, nickel, and titanium may be added to the silver particles as long as the conductor resistance does not exceed a predetermined value.

[0020]

According to the present invention, since the average particle size of the silver particles is about 3 μm or more, the overall surface area of the silver particles in the conductive paste is small, and accordingly, the contact area between the silver particles during firing is reduced. , The reactivity between silver particles can be reduced, and the grain growth of silver particles can be suppressed. Therefore, a decrease in volume due to firing is reduced. Further, the contained resinate paste is oxidized and decomposed during firing to precipitate an inorganic oxide, for example, silicon oxide when organic silicon is used as the resinate paste, and this inorganic oxide (silicon oxide) is interposed between the silver particles. By doing so, the contact between the metal particles is hindered, and the grain growth of the silver particles can be further suppressed. As a result, the contraction rate of the conductor paste is reduced, and the amount of the contraction rate is reduced,
The force with which the conductive paste is drawn toward the center is reduced, and the adhesive strength of the obtained wiring (conductive layer) to the ceramic circuit board can be increased.

On the other hand, since the contained glass component has a high softening point of about 700 ° C. or more, it is necessary to reduce the film loss due to unnecessary flow of glass during firing and further reduce the shrinkage ratio in the conductive paste. In addition, the formation of a good metal-glass structure at the interface with the circuit board on the ceramic circuit board can be promoted, and the adhesion to the circuit board can be further improved.

As described above, the conductor paste of the present invention has a smaller shrinkage ratio than the conventional paste, and the adhesion strength of the conductor layer when the conductor layer is formed on a ceramic circuit board is improved. In particular, when a through hole is formed in the circuit board and a wiring is formed in the through hole, it is possible to prevent connection failure such as disconnection in the through hole.

[0023]

The features of the present invention will be described in more detail with reference to the following examples.

(Example 1) Silver particles 8 having an average particle size of 3 μm
A conductor paste was prepared by mixing 7.0% by weight, 0.1% by weight of organic silicon, and 12.9% by weight of ethyl cellulose, terpineol and butyl carbitol acetate.

Example 2 Silver particles 8 having an average particle size of 3 μm
7.0% by weight, organic silicon 0.1% by weight, softening point 75
A conductor paste was prepared by mixing 1% by weight of lead glass frit at O ° C and 11.9% by weight of ethyl cellulose, terpineol and butyl carbitol acetate.

(Comparative Example) Silver particles having an average particle size of 1 μm
A conductive paste was prepared by mixing 0% by weight, 2.0% by weight of lead glass frit having a softening point of 500 ° C., and 11.0% by weight of ethyl cellulose, terpineol and butyl carbitol acetate.

The conductor pastes of Examples 1 and 2 and Comparative Example were printed on a ceramic circuit board, and were printed at 150 ° C. for 20 minutes.
And then calcined at 810 ° C. for 60 minutes. As a result, the shrinkage was 40% in Example 1, 43% in Example 2, and 55% in Comparative Example.

From the above results, it can be seen that the contraction rate of the conductive paste of the present invention is reduced by about 15% as compared with the conventional paste.

Using the conductor pastes of Examples 1 and 2 and Comparative Example, a through-hole conductor filling type and a through-hole inclusion type (drying) were formed in a through-hole having an inner diameter of 0.4 mm provided in a ceramic circuit board. Time film thickness 5
0 μm) was formed by printing, drying and firing under the same conditions as above. As a result, when the conductor pastes of Examples 1 and 2 were used, no crescent-shaped space was generated in the through hole in the case of the filling type, and the film thickness at the edge of the through hole in the case of the inclusion type. Although a good conductor layer could be formed without being extremely thin, when the conductor paste of the comparative example was used, a crescent-shaped space was generated in the through hole, or an edge portion of the through hole was formed. Often, the film thickness was reduced and disconnection was caused.

[0030]

According to the present invention, the shrinkage of the conductive paste containing silver as a main component can be greatly reduced as compared with the conventional conductive paste. Therefore, the conductor layer can be formed with a relatively large film thickness without the necessity of printing so that the dry film thickness of the conductor paste becomes thin unlike the related art, so that the conductor paste can be easily printed.

Further, since the conductor layer can be formed with a large film thickness, the conductor resistance can be reduced, and a connection failure due to disconnection at the edge portion of the through hole in the circuit board can be prevented, and the reliability of the circuit board can be reduced. Performance can be improved.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a state in which a crescent-shaped space is formed in a conductor layer in a through hole when a conductor layer is formed on a circuit board using a conventional conductor paste.

FIG. 2 is a cross-sectional view illustrating a state in which a conductor layer is disconnected at an edge portion of a through hole when a conductor layer is formed on a circuit board using a conventional conductor paste.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conductor layer 2 Ceramic circuit board 3 Through hole 3a, 3b Edge part 4 Space

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01B 1/20-1/22 C09D 5/24 H05K 1/09 H01G 4/12 358 H01G 4/30 301

Claims (3)

(57) [Claims] 1. A wiring type on a ceramic circuit board
A conductive paste for forming silver particles and organic silicon
And the silver particles are adjusted to an average particle size of 3 to 5 μm.
And the content of organic silicon is in the range of 0.1 to 1% by weight.
Conductor characterized by being adjusted to be contained
paste. 2. A wiring pattern on a ceramic circuit board.
Conductive paste for forming silver particles, organic silicon and
And a glass component, and the silver particles have an average particle size of 3 to 5 μm.
m, and 0.1 to 1 layer of organic silicon
% And adjusted to 750 ° C.
The glass component having the above softening point is 1 to 1.5% by weight.
It is characterized by being adjusted to be contained in the range
Conductor paste. 3. A conductor according to claim 1, wherein
A circuit board on which wiring is formed by paste.