JPH0511152B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a conductive copper paste composition having good electrical conductivity over a long period of time, and more specifically,
Conductive material suitable for circuit board conductors that maintains good conductivity over a long period of time by being applied by screen printing onto circuit boards such as paper/phenol resin boards, glass/epoxy resin boards, etc. and then heated and cured. The present invention relates to copper paste compositions. <Conventional technology> Conductive copper paste (hereinafter referred to as copper paste)
is attracting attention as a conductor for circuit boards that can replace expensive conductive silver paste (hereinafter referred to as silver paste). As such a copper paste, there is a paste composition containing copper powder and a thermosetting resin such as a phenolic resin as a binder, but since copper is essentially more easily oxidized than silver, it is cheaper than silver paste, but on the other hand, Copper pastes have problems in maintaining conductivity over long periods of time. As a countermeasure against such oxidation, it has been proposed to add an anthracene derivative to the copper paste, but this is still not sufficient in terms of maintaining good conductivity over a long period of time. Additionally, it has been proposed to add an organic titanium compound to the copper paste as a countermeasure against oxidation, but there is a problem with the stability of the organic titanium compound itself, and it is difficult to maintain very good conductivity over a long period of time. It is still not enough in this respect. <Problems to be Solved by the Invention> The present invention has been made in view of the above-mentioned points. An object of the present invention is to provide a copper paste composition with improved chemical properties. <Means for solving the problems> The present invention uses a specific copper powder with excellent oxidation resistance,
The above objective is achieved by blending with specific amounts of thermosetting resin, unsaturated fatty acids, etc. That is, in the present invention, 15 to 45 parts by weight of a thermosetting resin and It is characterized by containing 0.5 to 7 parts by weight of an unsaturated fatty acid or an alkali metal salt thereof. <Function and Examples> The copper powder of the present invention has a dendritic shape, an average particle size of 2 to 20 μm, and a bulk density of 1 g/cc or more. If the copper powder does not meet the above conditions, that is, if the shape is spherical, flaky, or scaly, or if the average particle size is less than 2 μm or more than 20 μm. Moreover, the bulk density is 1g/
If it is less than cc, the oxidation resistance is poor and a copper paste composition with sufficient properties in terms of maintaining good conductivity over a long period of time cannot be obtained. Thermosetting resins used in the present invention include phenolic resins, epoxy resins, and polyester resins, and act as binders. The blending ratio of this thermosetting resin is 100% copper powder
The amount is 15 to 45 parts by weight, preferably 20 to 40 parts by weight. When the amount of this thermosetting resin is less than 15 parts by weight, the absolute amount of binder is insufficient, resulting in poor fluidity of the resulting composition and poor printability, as well as oxidation of copper powder during heat curing. This leads to a decrease in conductivity. On the other hand, even if it exceeds 45 parts by weight, the absolute amount of copper powder is insufficient and good conductivity cannot be obtained. The unsaturated fatty acid or its alkali metal salt used in the present invention acts as a weak reducing agent and prevents oxidation of the copper powder, thereby contributing to maintaining conductivity. Promotes the dispersion of the particles and provides a coating film with good conductivity. Examples of the unsaturated fatty acids include oleic acid and linoleic acid, and examples of their alkali metal salts include sodium salts and potassium salts. It is also possible to use vegetable oils containing 60% or more of unsaturated fatty acids, such as soybean oil, sesame oil, olive oil, and safflower oil. The blending ratio of the unsaturated fatty acid or its alkali metal salt is 0.5 to 7 parts by weight, preferably 2 to 6 parts by weight, based on 100 parts by weight of the copper powder. When this blending ratio is less than 0.5 parts by weight, the dispersion of the copper powder in the binder is poor and the conductivity decreases, and when it exceeds 7 parts by weight, the dispersibility does not improve commensurate with the blending amount. Not only is this not possible, but it also reduces the conductivity of the resulting coating film. The copper paste composition of the present invention can be easily obtained by mixing and kneading the copper powder, thermosetting resin, unsaturated fatty acid or alkali metal salt thereof. As a method for producing a circuit board using the above-described copper paste composition of the present invention, a conventional method can be used. For example, a copper paste composition may be applied to a paper/phenol resin substrate, a glass/epoxy resin substrate, etc. by a screen printing method, and then heated and cured. Next, the composition of the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Examples 1 to 4: Comparative Examples 1 to 5 Copper powder having the format, average particle size, and bulk density shown in Tables 1 and 2 was mixed with a thermosetting resin, an unsaturated fatty acid, or an alkali metal salt thereof, and kneaded. A copper paste composition was prepared. The obtained copper paste composition was applied in the form of a strip (width 2 mm, thickness 35-45 μm) between electrodes (60 mm spacing) on a glass epoxy resin substrate.
The conductor was screen printed and cured by heating at 150°C for 60 minutes, and the specific volume resistivity was measured using a digital multimeter. Furthermore, in order to confirm whether conductivity that can withstand long-term use can be obtained, we conducted a humidity test (40°C x 95°C) as an oxidation accelerated test.
%RH for 500 hours), and the change in volume resistivity (hereinafter referred to as resistance change rate) was measured. The results are shown in Tables 1 and 2, respectively. Note that the volume resistivity was calculated based on the following formula. Volume specific resistivity (Ωcm) = R×t×W/L R: Resistance value between electrodes (Ω) t: Thickness of coating film (cm) W: Width of coating film (cm) L: Distance between electrodes (cm) Furthermore, the printability of each composition was determined from workability. The results are shown in Tables 1 and 2, respectively.
The judgment criteria are as follows. 〇: Good printability △: Printable for the time being Resistivity (Ωcm), rate of change in resistance after wet test (%), and printability were investigated. The results are shown in Table 3.

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[Table] Itotitanate <Effect> From the examples and comparative examples, specific shapes, particle sizes,
It can be seen that when the specific binder and unsaturated fatty acid or alkali metal salt thereof for copper powder having bulk density are within the scope of the present invention, good conductivity can be maintained for a long period of time without impairing printability. On the other hand, conventional copper paste compositions containing reducing agents such as anthracene are not durable enough for long-term use, as is clear from the wet test results. In particular, when any one of the shape, average particle size, and bulk density of the copper powder is outside the scope of the present invention, the good conductivity of the copper paste composition can be maintained for a long period of time even if a reducing agent is added. Can not do it.

Claims (1)

[Claims] 1 The shape is dendritic and the average particle size is 2 to 20μ
15 to 45 parts by weight of a thermosetting resin and an unsaturated fatty acid or an alkali metal salt thereof per 100 parts by weight of copper powder having a bulk density of 1 g/cc or more.
A conductive copper paste composition comprising 0.5 to 7 parts by weight.