JP3336315B2 - Conductive paste and printed 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 paste used for electrical connection between a printed wiring board and electronic components and via holes in the printed wiring board.

[0002]

2. Description of the Related Art Recently, awareness of environmental issues has increased,
In the field of electronics packaging, lead regulations for solder are about to advance. Therefore, there is an urgent need to develop a joining technology that does not use lead.

[0003] At present, there is no lead-free solder having the performance equivalent to that of the current eutectic solder.

[0004] Conventional conductive pastes are generally obtained by dispersing conductive particles in an insulating resin component, and after the electrodes are connected, the resin is cured and the particles are brought into contact with each other.
This is to ensure conduction of the connecting portion.

[0005]

However, the conventional conductive paste has the following problems.

First, there is a case where an insulating natural oxide film formed on a metal surface grows with time and the connection resistance increases accordingly.

Second, since metal particles having a metal exposed on the surface are used, migration may occur between adjacent electrodes when left under high temperature or high humidity conditions after connection, resulting in poor insulation. there were.

Accordingly, an object of the present invention is to provide a conductive paste having high connection reliability and insulation reliability and a printed wiring board using the same.

[0009]

According to the present invention, there is provided a conductive paste comprising conductive particles having a metal particle surface coated with a complex of the same metal as the metal particles and having no native oxide film on the metal particles. And a binder mainly composed of an insulating resin , wherein the complex has a property of melting an oxide film.
Compound of the metal particles on the surface of the metal particles
It is a conductive paste .

A printed wiring board according to the present invention is a wiring board manufactured using the above-described conductive paste according to the present invention as a conductive paste for filling via holes.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing an embodiment.

In the conductive paste of the present invention, the surface of metal particles is coated with a complex of the same metal. For example, the complex is composed of conductive particles having a monomolecular arrangement and a binder containing an insulating resin as a main component, and the complex is preferably insoluble in water.

Further, the printed wiring board of the present invention uses the conductive paste of the present invention as a conductive paste for filling a via hole.

As described above, the conductive paste of the present invention mainly comprises conductive particles whose surface is not a natural oxide film but is monomolecularly coated with a complex of the metal and an insulating resin. It is composed of a binder as a component. FIG. 1 shows a schematic view of the conductive particles of the present invention. Due to the presence of the complex 2 present on the surface of the metal particles 1, oxygen cannot enter the metal surface of the conductive particles, and the formation and growth of an insulating natural oxide film are inhibited.

This complex is insulating like a natural oxide film, but is extremely thin because it is monomolecularly arranged on the metal surface, and has poor adhesion to metal. Therefore, as shown in FIG. 2, when the conductive particles of the present invention gather, only the complex of the contact portion 4 is peeled off by the contact of the metal particles 3, and the electrical connection between the particles can be secured. The complex 5 is left in areas other than the contact portion, so that oxidation resistance is secured. Here, if the complex has an extremely thin film thickness of less than 10 nm, conduction can be ensured by contact between particles, and the connection resistance is not affected.

It is also preferable that this complex is insoluble in water, because it does not release ions and does not cause insulation failure due to migration, even if it is left under high temperature and high humidity conditions after mounting.

Next, in the above-mentioned method for producing a conductive paste, the metal particles are immersed in a solution comprising a chelating agent and a solvent, and the solvent is removed by heating. Is kneaded with a binder whose main component is. This chelating agent has a property of causing a chemical reaction with a native oxide on the metal surface to dissolve the oxide and form a complex as a reaction product. Therefore, by treating the metal particles with a solution in which a chelating agent is dissolved,
The native oxide film on the metal particles is removed and a complex film is formed instead. Since this reaction is a unimolecular reaction, the complex film is monomolecularly arranged on the surface of the metal particles. As described above, according to the present manufacturing method, a conductive paste containing conductive particles having no natural oxide film on the surface of the particles can be obtained, so that the connection resistance does not increase after components are mounted. Further, since the complex at the contact portion between the conductive particles peels off, good connection reliability can be obtained.

The chelating agent used in the production method of the present embodiment includes oxalic acid, succinic acid, anthranilic acid, galloyl gallic acid, quinaldic acid, quinoline-8-
Examples include at least one of carboxylic acid, thiourea, pyrogallol, phenylfluorone, 4-chloro-3-methyl-5-nitrobenzenesulfonic acid, and rhodamine B.

In the above-mentioned production method, when the chelating agent has a sublimability, the metal particles are immersed in a solution of the chelating agent, and then heated at about 100 ° C. to remain on the particles without forming a complex. Since the chelating agent which has been used can be removed and the thickness of the coating film on the particle surface decreases, the connection resistance after component mounting becomes further lower. Therefore, it is more preferable as the chelating agent used in the above-mentioned manufacturing method. Examples of such a chelating agent include at least one selected from the group consisting of oxalic acid, anthranilic acid, and quinoline-8-carboxylic acid. In this case, the complex formed on the metal particles is a metal salt of oxalic acid, a metal salt of anthranilic acid, or a metal salt of quinoline-8-carboxylic acid, depending on the chelating agent used.

Next, in the printed wiring board of the present invention, the conductive paste of the present invention is used as a conductive paste for filling via holes, and the connection reliability between layers can be greatly improved as compared with the related art.

If conditions other than those described in the above-mentioned method for producing a conductive paste are used, the performance of the conductive paste may deteriorate, which is not preferable in the present invention. An example will be described below.

When the chelating agent does not have the property of dissolving the metal oxide, a complex film is not formed on the surface of the conductive particles, and a natural oxide film remains to increase the connection resistance after mounting the component. Therefore, it is not preferable as the method for producing the conductive paste of the present invention.

[0023]

EXAMPLES Examples of the conductive paste of the present invention will be described.

Copper particles (average particle size 2 μm) were mixed with 5 parts by weight of a chelating agent and isopropyl alcohol 100 as a solvent.
It was immersed in a solution dissolved in parts by weight and dried at 100 ° C. for about 30 minutes to produce conductive particles. 1.8 g of the obtained conductive particles was kneaded with 0.2 g of an epoxy / acrylic resin (Loctite 3016; manufactured by Nippon Loctite) using a three-roll mill to prepare a conductive paste.

A connection reliability test (insulation resistance test and connection resistance test) was performed on the conductive paste thus prepared by the method described below. (Insulation Resistance Test) FIG. 3 is a conceptual diagram of an insulation resistance test substrate. A copper comb pattern 7 (pitch: 1.0 mm) is arranged on a glass epoxy base material 6.
And the pattern 7 are formed in a land portion 8 (the number of lands: 16 × 26,
Except for (pitch: 1.0 mm, 0.6φ), it is covered with resist. The land 8 is electrolessly plated with gold.

A conductive paste is screen-printed on the land 8 and 30 ° C. at 150 ° C. to cure the paste.
After drying for a minute, it was used as a substrate for evaluation. The substrate for evaluation was placed in a thermo-hygrostat, and after the substrate was completely brought into a thermo-hygro-atmosphere, a voltage was applied between the electrodes 9 and 10 to measure the change over time in the insulation resistance between the electrodes.

The test conditions were as follows: temperature: 85 ° C., humidity: 95%
RH, applied voltage: DC 50 V, test time: 500 hours.

The criteria for the insulation reliability evaluation are shown below.

A: Insulation resistance value is always maintained at 1010Ω or more ○: Insulation resistance value is reduced from 109Ω to less than 1010Ω ×: Insulation resistance value is reduced to less than 109Ω (Connection resistance test) The connection resistance test method is shown in FIG. . Copper electrodes 12 and 13 are arranged on a ceramic base material 11, and the surfaces of the copper electrodes 12 and 13 are electrolessly plated with gold. The conductive paste 14 causes the legs 16 and 17 of the QFP (quad flat package) 15 to
To glue on 2 and 13 and cure the paste, 1
The sample was dried at 50 ° C. for 30 minutes. This sample was placed in a thermal shock tester, and subjected to a four-terminal method under thermal shock conditions.
The change with time of the resistance value between 2, 13 and 16, 17 was measured.

The test conditions were -45 to 125 ° C. (each temperature 3
0 minutes) and 1000 cycles.

The criteria for the evaluation of connection reliability are shown below.

：: Connection resistance value is always maintained at less than 10 mΩ. ○: Connection resistance value is increased from 10 mΩ to less than 20 mΩ. X: Connection resistance value is increased to 20 mΩ or more. In this example, copper was used as metal particles. But,
Metals that normally form a natural oxide film, such as iron, nickel, zinc, and solder, may be used, and are not limited to copper. Also, epoxy / acrylic Loctite 301 is used as a resin component.
6 (manufactured by Nippon Loctite) was used, but the resin is not limited to this, as long as the resin can sufficiently secure the adhesive strength.

The test results are summarized in (Table 1).

[0034]

[Table 1]

The contents of Table 1 will be described in detail below.

(Conventional Example 1) In the case of a conventional conductive paste using silver as the conductive particles, migration occurred.

(Example 1) The conductive particles produced by using iminodiacetic acid, which dissolves an oxide film, as a chelating agent showed better insulation reliability than the conventional example. Although the connection reliability is slightly inferior to the conventional example, it is a level that can be sufficiently used in practical use.

(Example 2) The conductive particles produced by using succinic acid, which dissolves an oxide film and forms a water-insoluble complex, as a chelating agent, have higher connection reliability than the conventional example. Although slightly inferior, it is a level that can withstand practical use. On the other hand, with respect to the insulation reliability, a result superior to the case of Example 1 was obtained.

Example 3 The conductive particles produced by dissolving an oxide film as a chelating agent, forming a complex insoluble in water, and using sublimable anthranilic acid are described in Example 1. Insulation reliability as good as that of No. 2 was shown. In addition, the connection reliability was equivalent to that of the conventional example, and the results were superior to those of the first and second embodiments.

COMPARATIVE EXAMPLE When acetylacetone, which does not dissolve an oxide film, is used as a chelating agent, a natural oxide film remains on the conductive particles, and the film thickness increases with time. Happened.

As described in the above examples, when parts are connected using the conductive particles of the present invention and the conductive paste formed by the method for producing the same, despite the fact that metal is used as metal particles, Excellent results in insulation reliability and connection reliability were obtained. As a result, a highly reliable conductive paste at low cost could be provided.

Of these, Example 3 is the most preferable as the conductive particles of the present invention because connection reliability is most excellent.

In the above embodiment, isopropyl alcohol was used as a solvent. However, the present invention is not limited to this, and any other solvent that dissolves a chelating agent and evaporates at a temperature of about 100 ° C. may be used. , Ketones, esters and the like. Specific examples include ethyl alcohol, methyl alcohol, acetone, methyl ethyl ketone, butyl acetate, ethyl acetate and the like.

In the above embodiment, the heating condition was set at 100
Although the temperature was set to 30 minutes, the temperature is not limited to this as long as the solvent completely evaporates. If the temperature is lower than 60 ° C., it takes a long time for the solvent to completely evaporate. If the temperature is higher than 180 ° C., the resin of the conductive paste and the resin of the substrate may be deteriorated. For this reason, the heating conditions are 6
A condition at 0 ° C. to 200 ° C. for 15 minutes to 60 minutes is preferable.

Next, an embodiment of the printed wiring board of the present invention will be described. (Embodiment 4) FIG. 5 shows a conceptual diagram of a multilayer printed wiring board using the conductive paste of the present invention as a conductive paste for filling via holes.

The multilayer printed wiring board 18 is composed of a laminated base material 19 as an insulating base material layer, a copper foil 20 as an electrode layer, and a via-hole conductor 21 produced by curing a conductive paste.

A method for producing the conductor paste will be described. 0.8 g of spherical copper particles (average particle size: 2 μm) was immersed in a solution of 5 parts by weight of anthranilic acid dissolved in 100 parts by weight of isopropyl alcohol, and dried at 100 ° C. for about 30 minutes to produce conductive particles. 1.6 g of the obtained conductive particles
With epoxy / acrylic resin (Loctite 302)
6) It was prepared by kneading 0.4 g with three rolls.

The upper portion 21a and the lower portion 21b of the via-hole conductor 21 of the multilayer printed wiring board manufactured as described above.
Was measured by a four-terminal method, and the specific resistance of the via-hole conductor was calculated from the filling volume obtained from the thickness and the hole diameter of the substrate. As a result, the resistance was 1.5 × 10 −5 Ωcm. In addition, the multilayer printed wiring board is used at -40 ° C to 12 ° C.
The intrinsic resistance value of the via-hole conductor after holding for 1000 hours under the conditions of 5 ° C. and each temperature of 30 minutes is 1.6 × 10 −5 Ω.
cm, and there was almost no increase in the connection resistance value.
(Conventional Example 2) As a result of using conductive particles without chelating treatment instead of the conductive particles used in Example 4, 8.0 × 10 −5 Ω was obtained.
cm and a resistivity of −40 ° C. as described above.
After holding at ~ 125 ° C for 1000h, 12.4 × 10
It rose to 5 Ωcm.

In the above embodiment, the insulating base material layer
Although the printed wiring board having two layers and electrode layers has been described as an example, it goes without saying that the present invention can be applied to a printed wiring board having two or more insulating base layers and three or more electrode layers.

Further, even when a composite material of a fiber reinforcing material and a thermosetting resin or a composite material of an aramid nonwoven fabric and an epoxy resin is used as the insulating base material layer in the above embodiment, the conductive paste of the present invention can be used. By using, it is possible to prevent poor connection and poor insulation caused by moisture absorption of the resin.

The content of the conductive particles in the conductive paste of each of the above embodiments is preferably about 80 wt% to 95 wt%. This is because if it is less than 80 wt%, no conductivity is exhibited, and if it exceeds 95 wt%, the adhesive force between particles is reduced and the mechanical strength of the paste is reduced.

[0052]

As apparent from the above description, the present invention has an advantage that a conductive paste having high connection reliability and insulation reliability can be provided.

Further, the present invention has an advantage that a highly reliable printed wiring board can be manufactured by using the above-mentioned conductive paste.

[Brief description of the drawings]

FIG. 1 is a schematic view of a conductive particle according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining the function of the conductive particles of the present invention.

FIG. 3 is a view showing a substrate for insulation resistance test according to the present invention.

FIG. 4 is a diagram showing a connection resistance test method according to the present invention.

FIG. 5 is a sectional view showing a multilayer printed wiring board according to the present invention.

[Explanation of symbols]

 1, 3 metal particles 2, 5 complex 4 contacting part 6 glass epoxy base material 7 copper comb pattern 8 land portion 11 ceramic base material 12, 13 copper electrode (gold plating) 14 conductive paste 15 QFP 16, 17 lead 18 multilayer printed wiring Substrate 19 Laminated base material 20 Copper foil 21 Via-hole conductor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-268381 (JP, A) JP-A-62-198186 (JP, A) JP-A-2-122472 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) H01B 1/22 H01B 1/00 H05K 1/09 H05K 1/11

Claims (12)

(57) [Claims] 1. A method according to claim 1, wherein the surface of the metal particles is coated with a complex of the same metal as the metal particles, the conductive particles having no natural oxide film on the metal particles, and a binder mainly composed of an insulating resin. The complex has a property of melting an oxide film.
Of a chelating agent having a metal on the surface of the metal particles
A conductive paste that is a compound . 2. The conductive paste according to claim 1, wherein the complex covering the surface of the metal particles is arranged in a monomolecular manner. 3. The conductive paste according to claim 1, wherein the metal is at least one of copper, iron, nickel, zinc, and tin. 4. The conductive paste according to claim 1, wherein the complex is insoluble in water. 5. The conductive material according to claim 4, wherein the complex is at least one of a metal salt of oxalic acid, a metal salt of anthranilic acid, and a metal salt of quinoline-8-carboxylic acid. Paste. 6. The conductive paste according to claim 1, wherein the complex has a thickness of less than 10 nm. 7. The conductive material according to claim 1, wherein there are a plurality of said metal particles, and only a complex at a contact portion between said metal particles is peeled off and said metal particles are electrically connected to each other. Paste. 8. The chelating agent may be oxalic acid, succinic acid, anthranilic acid, galloyl gallic acid, quinaldic acid, quinoline-8-carboxylic acid, thiourea, pyrogallol, phenylfluorone, 4-chloro-3-methyl. -5
The conductive paste according to claim 1 , wherein the conductive paste is at least one of nitrobenzenesulfonic acid and rhodamine B. 9. A printed wiring board, which comprises using the electric connection between the conductive paste printed wiring board and the electronic component according to any of claims 1-8. 10. and at least an insulating substrate layer and second layers or more electrode layers, in via hole through the insulating base material of the electrode layers, according to any one of claims 1-8 A printed wiring board, wherein a via-hole conductor formed by filling and curing the conductive paste is formed, and the respective electrode layers are electrically connected by the via-hole conductor. Wherein said insulating substrate layer, claim 10 which is a composite of a fiber reinforcement and a thermosetting resin
A printed wiring board according to claim 1. 12. The method of claim 11, wherein the insulating base layer, according to claim 1, which is a composite of aramid nonwoven fabric and an epoxy resin
The printed wiring board according to 0 .