JP3411160B2 - Conductive composition and wiring 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 composition suitable for forming a wiring layer of a circuit board or the like, and in particular, it is applied to the surface of an insulating substrate containing an organic resin to form a wiring layer. The present invention relates to a suitable composition, and further relates to a wiring board using the same.

[0002]

2. Description of the Related Art Conventionally, a so-called printed board having a conductor layer formed on the surface of an insulating board containing a thermosetting resin such as epoxy resin or phenol resin has been applied to a circuit board or a package mounted with a semiconductor element. There is.

As a method of forming a wiring layer on such a printed board, a method of forming a wiring circuit by adhering a copper foil on the surface of an insulating substrate and then etching the copper foil, or a method of forming a wiring circuit has been used. A method of transferring a copper foil to an insulating substrate, a method of forming a circuit on the surface of the insulating substrate by a metal plating method, and the like are used.

With the increase in the number of wiring boards, the electrical connection between layers is made by through holes. The through holes are formed by drilling a hole in the insulating substrate and then plating the inner walls of the holes. Is common.

However, since it is difficult to form through holes between arbitrary layers by the above method,
There is a problem that the density of the wiring layer cannot be improved.

To solve this problem, the wiring layer is
A method of applying a conductor paste prepared by mixing a metal powder such as silver, copper, solder or the like and an organic resin for bonding to the surface of an insulating substrate or filling a through hole and laminating it is known.
No. 01739, JP-B-58-49966, JP-A-8-
No. 138437 is proposed.

[0007]

However, the conventional conductor paste must contain an organic resin for bonding as an essential component in order to improve the connection between metal particles and the adhesion of the wiring layer to the insulating substrate. Is required,
The electric resistance of the wiring layer formed by such a conductor paste was at most 1 × 10 ⁻⁴ Ω-cm.

Further, for reducing the resistance of the wiring layer, silver powder is suitable as the metal powder, but since silver causes migration, there is a problem that short-circuiting occurs between wirings when the wiring density becomes high. It was Therefore, Japanese Patent Publication Sho-58-49
In 966 and Japanese Patent Laid-Open No. 8-138437, it is proposed that bismuth oxide is mixed with copper powder coated with silver, or flake-shaped silver powder is mixed to prevent migration. Resistance is 1 × 10 ^-4 Ω
It is as high as -cm, and has migration resistance when the line width exceeds 1 mm, but it is not completely satisfactory for wiring having a line width of 1 mm or less.

[0009]

Means for Solving the Problems As a result of extensive studies on the above problems, the present inventors have found that metal particles constituting a conductive composition, together with relatively coarse particles having a particle size of 6 to 10 μm, When a wiring layer is formed using this conductive composition by mixing an appropriate amount of fine particles of 1 μm or less that can be filled in the voids between the coarse particles, the wiring layer has a structure in which metal particles are densely filled. It has been found that the electrical resistance of the wiring layer can be remarkably reduced as a result of being formed of a structure and the addition amount of the binding organic resin for binding the metal particles to each other can be made extremely small. Moreover, in the above-mentioned constitution, it was found that the use of the copper particles having the surface coated with silver as the metal particles is excellent in the migration resistance and the low resistance at the same time, and has reached the present invention.

That is, the conductive composition of the present invention comprises 98.8-99.9% by weight of metal particles and 0.1-0.1% of a binding organic resin.
1.2% by weight, and the metal particles are 50 to 90% by weight of coarse particles having a particle size of 6 to 10 μm and 10 to 50% by weight of fine particles having a particle size of 1 μm or less with respect to the total amount of the metal particles. It is characterized by including.

The wiring board of the present invention comprises an insulating substrate containing at least an organic resin, and a wiring layer made of a conductive composition deposited on the surface of the insulating board. The metal particles are composed of 98.8 to 99.9% by weight and the binding organic resin 0.1 to 1.2% by weight, and the metal particles form coarse particles having a particle size of 6 to 10 μm with respect to the total amount of the metal particles. Fine particles with 50 to 90% by weight and a particle size of 1 μm or less
It is characterized by being constituted by a ratio of 50% by weight.

In the above invention, silver-coated copper particles are used as the metal particles, and a resin decomposable at 200 ° C. is used as the binding organic resin.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in more detail with reference to the drawings. The conductive composition of the present invention is used for forming a wiring layer of a circuit board, and particularly used for a wiring layer formed on the surface or inside of an insulating substrate. The wiring layer is used as a circuit formed on the surface or between layers of an insulating substrate in a multilayer wiring board, or as an interlayer connection conductor such as a via hole or a through hole formed in each layer.

This conductive composition is composed of metal particles and a binding organic resin as components. As the metal particles, conventionally known metal particles suitable for forming a wiring layer are used. Particularly, for reducing the resistance, Ag,
Cu, Au and the like are preferably used. Among them, as will be described later, copper particles coated with silver have a low resistance,
It is most preferable in terms of low cost and migration resistance.

The major feature of the conductive composition of the present invention is that the metal particles are, first of all, 6 to 10 μm in particle diameter with respect to the total amount of the metal particles.
50 to 90% by weight of coarse particles of m and 10 to 50% by weight of fine particles having a particle diameter of 1 μm or less. this is,
This is important for improving the filling property of the metal particles when the wiring layer is formed. In other words, by using the metal particles arranged in this manner, the fine particles 2 enter the voids formed between the coarse particles 1 as shown in the structure chart of FIG. Since the metal particles are in close contact with each other, the resistance as a conductor can be reduced.

Therefore, when the amount of the coarse particles exceeds 90% by weight and the amount of the fine particles is less than 10% by weight, the filling property of the metal particles is deteriorated and the resistance cannot be reduced, and the amount of the coarse particles is 50% by weight. % And the amount of fine particles exceeds 50% by weight, the resistance becomes high.

Desirably, the coarse particles are 65 to 85% by weight, and the fine particles are 15 to 35% by weight. The particle sizes of the coarse particles and the fine particles described above mean the maximum particle size. Further, it is desirable that the above-mentioned coarse particles and fine particles occupy 90% by weight or more of the total metal particles in total.

In the conductive composition of the present invention, it is also great that the binding organic resin is blended in an extremely small amount of 0.1 to 1.2% by weight with respect to the metal particles arranged as described above. It is a feature. That is, by arranging the metal particles as described above, the amount of the binding organic resin can be reduced, and when the amount of the binding organic resin is less than 0.1% by weight, the metal particles are firmly connected, This is because it becomes difficult to bond the wiring layer to the insulating substrate, and if it exceeds 1.2% by weight, the resistance increases. Desirably, the amount of the binding organic resin is 0.2 to 1.0% by weight, and further 0.3 to 0.8% by weight.
Is.

The binding organic resin used here is a thermoplastic resin such as an acrylic resin, a methacrylic resin, a vinyl resin, a carbonate resin, or a cellulose, a thermosetting resin such as an epoxy resin, a phenol resin, or an unsaturated polyester resin. However, a resin such as ethyl cellulose, which can be thermally decomposed by heating at 200 ° C. or lower, is particularly preferable.

Next, a wiring board using the above conductive composition will be described. FIG. 2 is a cross-sectional view for explaining a typical structure of a multilayer wiring board. The wiring board is composed of an insulating substrate 3 and a wiring layer 4, and the wiring layer 4 is composed of a circuit layer 4A formed on the substrate surface and between layers and a conductor (through hole) 4B connecting the layers.

In this multilayer wiring board, a material known as a highly insulating material for a circuit board is used as the insulating substrate. In particular, according to the wiring board of the present invention, at least the organic substrate is used as the insulating substrate. It contains a resin as a constituent. Specifically, PPE (polyphenylene ether), BT resin (bismaleide triazine),
Thermosetting resin or thermoplastic resin such as epoxy resin, phenol resin, polyimide resin, or fluorine resin is used. Further, in order to increase the strength of the insulating substrate, a composite of the above organic resin and an inorganic filler is also used. As the inorganic filler, SiO ₂ , Al ₂
O ₃ , ZrO ₂ , TiO ₂ , AlN, SiC, BaTi
O ₃ , SrTiO ₃ , zeolite, CaTiO ₃ , aluminum borate, etc. are used, and the shape of this filler is a substantially spherical particle having an average particle size of 20 μm or less, particularly 10 μm or less, or an average aspect ratio of 2 or more. A fibrous material, a flat material, and a woven material are also used. In the composite material of organic resin and inorganic filler, the volume ratio of organic resin: inorganic filler is 15: 85-5.
It is desirable to be compounded at a ratio of 0:50.

According to the wiring board, the wiring layer 4 is formed of the conductive composition. Of these, the circuit layer 4A is preferably formed to have a thickness of 50 to 200 μm, and the hole diameter of the interlayer connecting conductor (through hole) 4B is preferably 75 to 200 μm.

Next, a method of manufacturing the above wiring board will be described. First, a conductive paste is prepared using the conductive composition. The conductor paste is the conductive composition 1 described above.
The viscosity was adjusted to 500 to 1000 poises by adding 8 to 20 parts by weight of an organic solvent such as 2-octanol, terpineol, ethylene carbitol, carbitol acetate, and butyl cellosolve to 100 parts by weight of the composition. is there. In the paste, in addition to the above components,
It is also possible to add corrosion inhibitors such as benzothiazole and benzimidazole.

Next, the conductor paste prepared as described above is applied to a wiring pattern on an insulating sheet containing an organic resin. Specifically, in order to print a circuit pattern on the surface of the insulating sheet using a screen printing method, a gravure printing method, or to form a through hole, a hole having a predetermined diameter is formed in the insulating sheet by drilling or punching. The conductor paste is filled in the holes. At this time, when the insulating sheet contains a thermosetting resin, the insulating sheet is preferably in a semi-cured state.

After the conductor paste is applied to the plurality of insulating sheets in this manner, they are aligned and laminated and pressure-bonded. Then, after applying the laminate to the pattern, 1
Heat treatment is performed at 00 to 250 ° C. This heat treatment is for removing the solvent in the conductor paste and adjusting the amount of the organic resin, but the heating can also completely cure the thermosetting resin. By this heat treatment, the content of the binder organic resin in the wiring layer can be adjusted and the adhesiveness between the insulating sheets can be improved. If the temperature is lower than 100 ° C., the above effect cannot be exhibited.
If the temperature is higher than 50 ° C, the organic resin in the insulating sheet may be decomposed by heat.

According to this heat treatment, when the organic resin in the conductive composition forming the wiring layer is a resin that can be thermally decomposed at 200 ° C. or lower, this organic resin content is removed, but In order to maintain the connection between the metal particles and the adhesion of the wiring layer to the insulating substrate, it is necessary to treat the organic resin so that the content of the organic resin remains 0.1% by weight or more.

Further, according to the present invention, in order to reduce the resistance of the wiring layer in the wiring board, it is best to form the metal particles in the wiring layer by silver particles. Cause migration. Therefore, in the present invention, as the metal particles, first, copper particles whose surfaces are coated with silver are used. The copper particles can be easily coated with silver by a technique such as plating. The amount of silver coated on the copper particles is appropriately 1 to 40% by weight based on the copper particles.
Then, by arranging the silver-coated copper particles as described above, the occurrence of migration can be suppressed. The effect of suppressing this migration greatly changes depending on the particle size distribution of the metal particles, and as is clear from the examples described later, the migration resistance is more excellent as the amount of coarse particles is larger, but the resistance is different between coarse particles and fine particles. By arranging the grains in the above range, the resistance can be reduced.

As described above, according to the present invention, the resistance can be reduced by mixing the metal particles in the conductive composition in an appropriate amount with the coarse particles and the fine particles. Moreover, migration resistance can also be improved by using the copper particles coated with silver as the metal particles while carrying out such grain distribution.

[0029]

【Example】

Example 1 As the metal particles in the conductive composition, the average particle size is 8 μm.
The copper powder A and the copper powder B having an average particle diameter of 0.8 μm were prepared. The copper powders A and B are arranged in a particle size to measure the particle size distribution,
The weight ratio of particles having a particle size of 6 to 10 μm and particles having a particle size of 1 μm or less to all metal particles was calculated, and metal particles having various particle size distributions shown in Table 1 were adjusted. Then, a conductive composition was prepared by adding cellulose to the metal particles in a ratio shown in Table 1.

Next, 15 parts by weight of 2-octanol as a solvent was added to 100 parts by weight of this conductive composition and mixed in a ball mill for 5 hours to prepare a conductor paste.

Then, this conductor paste was screen-printed on the surface of an insulating sheet in which spherical silica and a polyimide resin were mixed in a volume ratio of 30:70, and the paste was filled in a through hole having a diameter of 0.15 mm. .
After that, the insulating sheets filled with this paste printed and aligned are aligned and laminated to each other at a pressure of 50 kg / cm ² for 200-
A wiring board was manufactured by heating at 250 ° C. for 3 hours and thermocompression bonding with curing of the insulating board.

With respect to the obtained wiring board, the electric resistance of the wiring layer was measured by the DC 4-terminal method. The results are shown in Table 1.

As the evaluation of the migration resistance, a line width of 10 is obtained by the same method as described above as shown in FIG.
Wirings of 0 μm were formed at intervals of 1000 μm. Then, with a voltage of 250 V applied between both wirings, the resistance between the lines was measured after holding for 1000 hours in an atmosphere of a temperature of 65 ° C. and a humidity of 95%. The results are shown in Table 1.

[0034]

[Table 1]

As is clear from the results shown in Table 1, the particle size is 6 to
Particles having a particle size of 10 μm and particles having a particle size of 1 μm or less arranged according to the present invention had lower resistance than the other samples, and all achieved 10 × 10 ⁻⁵ Ω-cm or less. In this example using copper particles, migration did not substantially occur.

Example 2 8 to 11 wt% as metal particles in the conductive composition
Copper powder with an average particle size of 8 μm coated with silver, 27-33
A copper powder having an average particle size of 0.8 μm and coated with silver in weight% was prepared.

These powders were arranged in a particle size distribution to measure the particle size distribution, and the weight ratio of particles having a particle size of 6 to 10 μm and particles having a particle size of 1 μm or less to all metal particles was calculated. A distribution of metal particles was prepared. Then, a conductive composition was prepared by mixing cellulose with the metal particles in a ratio shown in Table 2.

Further, a silver powder having an average particle size of 9 μm and a silver powder having an average particle size of 0.8 μm were prepared, and the powder was used for grain distribution. Metal particles were prepared. Then, a conductive composition was prepared by mixing cellulose with the metal particles in a ratio shown in Table 2.

Using this conductive composition, a multilayer wiring board was prepared in exactly the same manner as in Example 1, and the resistance of the wiring layer was measured by the DC 4-terminal method. The migration resistance was evaluated in the same manner as in Example 1, and the results are shown in Table 2.

[0040]

[Table 2]

From the results of Table 2, it can be seen that the resistance can be reduced by arranging particles according to the present invention.
Further, when evaluated from the viewpoint of migration resistance, in the experiment of this example, when the silver powder was used, the resistance was low and good, but the occurrence of migration was remarkable. On the other hand, the use of copper particles coated with silver dramatically improved the migration resistance.

Further, by virtue of this grain distribution, although the amount of the binding organic resin is as small as 0.1 to 1.2% by weight, the metal particles are firmly connected to each other and the adhesion of the wiring layer to the insulating substrate is high. There was no problem at 1.0 kg / cm ² or more.
When the amount of the binding organic resin exceeds 1.2% by weight, the resistance is extremely reduced, and when the amount of the resin is less than 0.1% by weight, the connection between the particles is not sufficient, and the metal particles are not separated from the wiring layer. As the particles shattered, the resistance of the wiring layer also increased.

[0043]

As described in detail above, the conductive composition of the present invention can reduce the resistance when forming a wiring layer of a wiring board, and particularly, copper particles coated with silver are used as metal particles. By using it, it is possible to reduce resistance and enhance migration resistance.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a texture structure of a conductive composition of the present invention.

FIG. 2 is a sectional view for explaining a typical structure of the wiring board of the present invention.

FIG. 3 is a diagram for explaining a wiring structure used for evaluation of migration resistance in an example of the present invention.

[Explanation of symbols]

1 coarse particles 2 fine particles 3 insulating substrate 4 wiring layers 4A circuit layer 4B through hole

─────────────────────────────────────────────────── --- Continuation of front page (56) Reference JP-A-7-331360 (JP, A) JP-A-6-295616 (JP, A) JP-A-7-166072 (JP, A) JP-A-56- 101739 (JP, A) JP 8-138437 (JP, A) JP 4-65011 (JP, A) JP 9-120711 (JP, A) JP 58-49966 (JP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01B 1/00-1/24

Claims (4)

(57) [Claims] 1. Metal particles 98.8 to 99.9% by weight and a binding organic resin 0.1 to 1.2% by weight, said metal particles having a particle size of 6 to 6 relative to the total amount of the metal particles. 50 to 90% by weight of coarse particles of 10 μm and 1 of fine particles having a particle diameter of 1 μm or less
A conductive composition comprising 0 to 50% by weight. 2. The electrically conductive composition according to claim 1, wherein the metal particles are copper particles coated with silver. 3. A wiring board comprising a wiring layer made of a conductive composition deposited on the surface of an insulating substrate containing at least an organic resin, wherein the conductive composition comprises metal particles 98.
8 to 99.9% by weight, and a binding organic resin 0.1 to 1.2
The metal particles are composed of 50 to 90% by weight of coarse particles having a particle size of 6 to 10 μm and 10 to 50% by weight of fine particles having a particle size of 1 μm or less with respect to the total amount of the metal particles. A wiring board characterized by the above. 4. The wiring board according to claim 3, wherein the metal particles are copper particles coated with silver.