JPH04756B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a conductive paste having excellent printability, good solder adhesion, and excellent conductivity. [Technical background of the invention and its problems] Conductive paste is a paste made by mixing a specified curable resin prepolymer with a conductive substance such as copper powder. When printed and cured, the cured surface has excellent conductivity.
It can be melted and coated with solder. For this type of conductive paste, curable resin prepolymers such as phenol resins, melamine resins, xylene resins, and epoxy resins having a number average molecular weight of about 100 to 2000 are currently used to mix metal powder. Such conductive pastes are used for electrodes of electronic parts, printed circuits for conductor parts, and the like. However, in recent years, electronic parts have become lighter, thinner, shorter, smaller, higher performance, and more dense, and there are demands for various improvements in conductive pastes. That is, there is a demand for a material that has good printability, excellent solder adhesion, and favorable electrical conductivity. In reality, such a conductive paste has not yet been developed. [Object of the Invention] The present invention was made in view of the above-mentioned actual situation, and an object of the present invention is to provide a conductive paste having excellent printability, solder adhesion, and good conductivity. [Summary of the Invention] As a result of extensive research to achieve the above object, it was discovered that a conductive paste described below can achieve the object. That is, the present invention comprises (A) a curable resin which is a prepolymer having a number average molecular weight of 10,000 or more, and (B) (a) a particle size of
Flake-like copper powder of 10 μm or less and (b) particle size of 10 μm
An essential component is a conductive substance consisting of a copper/silver composite powder coated with silver on the surface of a copper powder having a diameter of 75 to 95% by weight
This is a conductive paste characterized by containing the following: Examples of the curable resin (A) which is a prepolymer having a number average molecular weight of 10,000 or more used in the present invention include phenoxy resin, polybutadiene resin, p-vinylphenol resin, epoxy-modified acrylic resin,
Examples include 1,2-polybutadiene resin and polyester resin, and these resins may be used alone or in combination of two or more. Among these resins, polybutadiene resin, p
- For vinylphenol resin or polyester resin, by blending an amino resin etherified with a lower alcohol such as methanol, ethanol, butanol, the amino resin and the resin prepolymer cause a condensation reaction, Cures into a three-dimensional network structure. Note that the above amino resin may be used by mixing or reacting with resins other than polybutadiene resins or polyester resins that are themselves curable. The reason why the number average molecular weight of the resin is set to 10,000 or more is
This is because if it is less than 10,000, high-density packing of the copper powder (B) will be impossible, and it will not become paste-like, making it unsuitable for screen printing, etc. The conductive substance (B) used in the present invention is a mixture of flaky copper powder (a) and copper/silver composite powder (b). The flaky copper powder (a) in the present invention refers to copper powder that is deformed by stamping spherical powder and has a flake shape. In addition, the copper/silver-based composite powder (b) in the present invention refers to one in which the surface of copper powder is coated with silver, such as one in which metallic silver is precipitated by substitution on the surface of copper powder using a silver complex salt solution. say. Both the flaky copper powder and the copper/silver composite powder are powders with an average particle size of 10 μm or less. In any case, if the average particle size exceeds 10 μm, it becomes difficult to pack the conductive substance at high density, and the resulting paste does not become paste-like, resulting in poor printability, which is not preferred. The ratio of metallic silver deposited on the surface of the copper powder in the copper/silver composite powder (b) is 0.3 to 20% by weight. If the precipitated proportion of metallic silver is less than 0.3% by weight, it has no effect on conductivity, and if it exceeds 20% by weight, not only will the cost increase, but the conductivity will be saturated, resulting in waste. The mixing ratio of the flaky copper powder (a) and the copper/silver composite powder (b) is 10/90 to 90/10 by weight. If the weight ratio of the flaky copper powder is less than 10, it will not form a good paste, and if it exceeds 90, the conductivity will be poor, which is not preferable. The conductive paste of the present invention consists of a curable resin (A) and a conductive substance (B), and the conductive substance (B) is [(A)+
(B)] is required to be contained in an amount of 75 to 90% by weight. If the content of the conductive substance (B) is less than 75% by weight, the solder adhesion will be poor, and if it exceeds 90% by weight, the adhesion will be poor and the coating film will be brittle, which is not preferable. These [(A)+(B)] components are mixed with a small amount of a solvent such as butyl carbitol acetate using a triple roll or the like to prepare a conductive paste. In addition to the main components (A) and (B), the components added to the conductive paste include thixotropic agents, antioxidants,
These include dispersants, surfactants, fillers, etc. The object to be coated with the conductive paste of the present invention may be a resin, an insulating substrate, a metal plate, etc., and is coated using a roll coater, screen printing, or the like. This curing is done when the resin is thermosetting resin.
Heat to 80-250℃. When the resin is composed of an amino resin and a polybutadiene resin, p-vinylphenol resin, or polyester resin, heating causes a condensation reaction between the amino resin and the hydroxyl groups of the resin prepolymer to form a three-dimensional network structure. In this process, the copper powders come into contact with each other and are connected, resulting in conductivity. Furthermore, solder can be melted on the cured surface of this coating. The hardened surface has good solder wettability, so it has excellent solder adhesion. The reason for this is not clear, but it is thought that the interaction between the amino resin as a crosslinking agent and the solder surpasses the solder repellency. Therefore, a good conductive surface can be obtained, and it can be used, for example, as a printed circuit in which various mounted products are combined. To melt and coat the cured surface of the conductive paste of the present invention with solder, it may be brought into contact with a molten solder bath, or the solder or solder cream may be heated and melted on the cured surface. [Examples of the Invention] The present invention will be specifically explained with reference to Examples. Hereinafter, "part" means "part by weight", and the present invention is not limited to this example. Example 1 30 parts of flaky electrolytic copper powder with an average particle size of 10 μm, 45 parts of 0.5% by weight silver-plated copper powder, 24 parts of phenoxy resin with a number average molecular weight of 14,000, 1 part of methyl etherified melamine resin, and as a solvent A conductive paste (A) was obtained by thoroughly kneading the mixture and 15 parts of butyl carbitol acetate using three ceramic rolls. Example 2 A conductive paste was prepared in the same manner as in Example 1, except that an isophthalic acid polyester resin with a number average molecular weight of 20,000 was used in place of the phenoxy resin in Example 1.
I got (B). Comparative Example 1 30 parts of flaky electrolytic copper powder with an average particle size of 10 μm, 45 parts of 0.5% by weight silver-plated copper powder, 25 parts of epoxy resin with a number average molecular weight of 3800, 0.5 part of imidazole crosslinking agent, and butyl carbyl as a solvent. A small amount of toll acetate was thoroughly kneaded using three rolls to obtain a conductive paste (C). Comparative Example 2 A conductive paste (D) was obtained in the same manner as in Example 2, except that 80 parts of flaky electrolytic copper powder with an average particle size of 10 μm was used as the copper powder. Using the conductive pastes obtained in Examples and Comparative Examples, a pattern with a width of 1 mm and a total length of 20 cm was printed on an epoxy laminate (trade name MEL-4 manufactured by Toshiba Chemical Corporation) using a screen printing machine with a 180 meshtron screen. . Next, the paste was cured by heating at 180° C. for 1 hour to obtain a hardened paste surface with a thickness of 20 μm. After applying solder flux to this cured surface, solder of 63% tin containing 0.5% copper was melted and adhered at 240° C., and the state of the paste, printability, solder adhesion, and conductivity were tested. The results are shown in Table 1.

[Table] [Effects of the Invention] The conductive paste of the present invention has good printability, solder adhesion, and paste condition, and has excellent conductivity, and is suitable for printed circuits and the like.

Claims (1)

[Scope of Claims] 1. (A) a curable resin that is a prepolymer with a number average molecular weight of 10,000 or more, (B) (a) flaky copper powder with a particle size of 10 μm or less, and (b) a particle size of 10 μm or less An essential component is a conductive substance consisting of a copper/silver composite powder coated with silver on the surface of copper powder, and the conductive substance (B) weighs 75 to 90% by weight relative to [(A) + (B)]. % of conductive paste. 2. The conductive paste according to claim 1, wherein the curable resin (A) comprises a prepolymer having a crosslinkable hydroxyl group and an amino resin etherified with a lower alcohol. 3 The mixing ratio [(a)/(b)] of the flaky copper powder (a) and the copper/silver composite powder (b) of the conductive substance (B) is 10/90 to
The conductive paste according to claim 1 or 2, which has a weight ratio of 90/10. 4. Any one of claims 1 to 3, wherein the copper/silver-based composite powder (b) is obtained by substituting 0.3 to 20% by weight of metallic silver on the surface of copper powder using a silver complex salt solution. Conductive paste as described in .