JPS6058268B2 - Conductive copper paste composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to conductive copper paste compositions capable of providing conductive coatings comparable to copper paste coatings.

Silver paste has been widely used as a printed wiring material for electronic circuits.

However, in recent years, as the price of silver has soared, there has been a desire to replace it with a conductive copper paste based on cheaper copper powder. An important disadvantage of using such copper pastes is that the copper powder dispersed in the binder is susceptible to oxidation and can oxidize during storage as a paste as well as during use after film formation. This means that it is not possible to maintain a conductive coating film. For this reason, many attempts have been made to add various additives to copper paste to provide good conductivity.

Some of these attempts include phenolic compounds such as quinone or phenol, amines, phosphorus compounds, sulfur compounds, and anthracene derivatives (Japanese Patent Application Laid-Open No.
-1032 surface publication), those containing a copper compound and its reducing agent in addition to copper powder (Japanese Unexamined Patent Publication No. 51-93394), and those containing an organic titanium compound ( JP-A No. 56-36653). However, according to the research conducted by the present inventors, even with copper pastes containing these additives, the specific resistance value of the resulting coating film is at most about 10-0 Ω-a,
Its long-term stability is still insufficient. Incidentally, the specific resistance value of the coating film obtained with silver paste is about 10-'Ω-α, and in order to be able to replace this, at least 5×
It is necessary to stably provide a specific resistance of 10-”Ω-α or less.In addition to good conductivity, the conductive copper paste also has the following properties:
It is also required that soldering is possible if necessary. A conductive copper paste that meets these requirements has not yet been developed. SUMMARY OF THE INVENTION An object of the present invention is to provide a conductive copper paste composition that provides a coating film that has good conductivity and can be soldered if necessary. According to the research conducted by the present inventors, by blending unsaturated fatty acids with specific organotitanium compounds, which themselves have only a weak reducing effect, it is possible to achieve better results that cannot be obtained by adding these alone. It has now been found that copper paste compositions are provided which are capable of providing coatings with electrical conductivity and stability thereof. Moreover, since these can provide good dispersibility to the system of copper powder and thermosetting resin, it is possible to incorporate an extremely large amount of copper powder into the copper paste without impairing its coating or printing suitability.
It has therefore been found that coatings with good soldering properties can also be formed. The conductive copper paste composition of the present invention is based on such knowledge, and is based on copper powder 7.
5-μs parts by weight, 25-2 parts by weight of thermosetting resin binder (total amount of copper powder and binder is 10 parts by weight), 0.1-1 parts by weight of unsaturated fatty acids, and 4 organic parts bonded to Tl. It is characterized by comprising 0.01 to 5 parts by weight of an organic titanium compound (hereinafter abbreviated as an organic titanium compound) whose group is an unsubstituted or substituted alkoxy group or alkyloxy group.

The present invention will be explained in more detail below.

In the following description, 1% and 1 part are based on weight unless otherwise specified. As the copper powder which is the main component of the copper paste composition of the present invention, electrolytic copper powder, ring-based copper powder, etc., having a particle size of 1 to 50 μl, preferably 5 to 20 μm, are used.

If the particle size is less than 1 μm, the oxidation rate will be excessive and the resulting coating film will have poor electrical conductivity. If it exceeds 50p, the fluidity of the paste composition will be poor, the finish of the coated surface will be poor, and the screen printability will be poor, resulting in poor coating suitability. As a binder, acrylic resin,
Thermosetting resins such as epoxy resins, phenol resins, polyester resins, and xylene resins are used. Among them, novolak phenolic resins are preferably used. Thermoplastic resins do not provide good electrical conductivity. The composition of the present invention has these copper powder and thermosetting resin binder as main components, and the total amount of these components is 1 (1) part (hereinafter, the ratio of each component in the composition refers to the total amount of both components). (based on 1 (1) part), copper powder is 75~
98 parts, and the binder is 2 to 25 parts.

Good conductivity is obtained when the copper powder content is less than 75 parts, 98
If the amount exceeds 50%, the conductivity decreases and a good coating film cannot be obtained. A particularly preferred ratio of amounts for obtaining conductivity and coating properties is 80 to 9 parts of the copper powder and 10 to 2 parts of the binder. Generally, solderability improves as the amount of copper powder added increases. A range of 85 to 95 parts is preferable to provide both electrical conductivity and solderability, and a range of 88 to 9 parts is particularly preferable to provide good solderability. Unsaturated fatty acids contribute to maintaining conductivity by acting as a weak reducing agent and preventing oxidation of the copper powder, and also promote fine dispersion of the copper powder in the presence of the organic titanium compound described below, resulting in good conductivity. It is thought that it has the effect of providing a beautiful coating film.

As unsaturated fatty acids, those having 12 to 23 carbon atoms are preferably used. Those with less than 1 carbon number have poor compatibility with thermosetting resins and are difficult to form into paints, while those with more than 23 carbon atoms are difficult to obtain and are not economically viable. Among them, oleic acid and linoleic acid having 18 carbon atoms are preferred. The unsaturated fatty acid is 0.1 to 10 parts, preferably 0.5 to 5 parts.
Used within the scope of the section. If less than 0.1 part is added, the effect will be poor, and if more than 1 part is added, the conductivity of the resulting coating film will decrease, and depending on the type of thermosetting resin used, the paste composition may thicken or gel. and impairs its suitability for painting.

It is thought that the organic titanium compound, in cooperation with the unsaturated fatty acid, contributes to fine dispersion of the copper powder, protects the copper powder, imparts good conductivity, and stabilizes the copper powder.

Many organic titanium compounds hydrolyze very quickly, and when added to a paste, the paste quickly turns into a gel. For this reason, the organic titanium compound preferably has low hydrolyzability. Preferred examples of organic titanium compounds include those in which the four organic groups bonded to Ti are unsubstituted or substituted alkoxy groups or alkyloxy groups. More specifically, di-1-propoxybisacetylacetonatotitanium, di-n-butoxybis(triethanolamineto)titanium, isopropoxytriisostearoyloxytitanium, and isopropoxytri(N-aminoethylaminoethoxy)titanium. can be mentioned. These organic titanium compounds are 0
．． It is used in an amount of 0.01 to 5 parts, preferably 0.05 to 1.5 parts.

If it is less than 0.01 part, the effect of addition is poor, and if it is added in excess of 5 parts, the viscosity of the paste increases due to hydrolysis of the organic titanium compound, resulting in poor coating workability and poor solderability.

It is preferable to further add hydroquinone or a derivative thereof (hereinafter abbreviated as hydroquinones) to the copper paste composition of the present invention.

These include hydroquinone, catechol, pyrogallol, methylhydroquinone, ethylhydroquinone, propylhydroquinone, butylhydroquinone, and particularly methylhydroquinone and t-butylhydroquinone are preferably used. When these hydroquinones are added, the conductivity during coating film formation is further improved, and the stability over time under high temperature use is improved. These phenolic compounds are preferably used in an amount of 0.8 to 20 parts, particularly 2 to 15 parts. If it is less than 0.8 part, the effect of addition is poor, and 20f! When added in excess of IS, the oxidation rate of the copper powder becomes faster due to the production of peroxide.

A solvent can also be added to the copper paste composition of the present invention for viscosity adjustment to improve coating workability. Usable solvents include known solvents such as toluene, xylene, and methyl isobutyl ketone. be. The copper paste composition of the present invention can be obtained by kneading the above-mentioned components in a conventional manner using a ball mill, roll mill, etc., for example, for 30 to 6 minutes.

The obtained copper paste composition is used to form printed wiring by screen printing on a substrate by a conventional method such as screen printing, and also to connect circuit parts on the upper and lower surfaces of the substrate through through holes. In addition, within the scope of the present invention, by increasing or decreasing the content of copper powder, a paste with good solderability is printed at the ends of the circuit that need to be connected to other parts, and a paste with good solderability is printed on other parts. It can be used to print pastes with good properties. In order to maintain good electrical conductivity, the film thickness (dry) of the coating film is preferably 20 pm or more, and a range of 25 to 35 pm is particularly practical.After printing the paste, It is cured under conditions suitable for the resin, such as 120 to 180°C and 15 to 4 powder, to form a coating film and form a wiring circuit.After circuit formation, heat curing is performed to maintain conductive stability for a longer period of time. It is also effective to overcoat with a mold or ultraviolet curable resist ink.The present invention will be explained in more detail below with reference to Examples and Comparative Examples.

Example 1 80 parts of electrolytic copper powder with an average particle size of 10 pm was mixed with 33.3 parts of phenol resin (Gunei Kagakusha Co., Ltd.-104, resin concentration 6.
Paste samples 1 to 16 were obtained by kneading 6 powders in a ball mill with 0%) and additives of the types and amounts shown in Table 1 below.

Each of the above samples was screen printed on a phenolic resin substrate 1 in a strip shape of 10 mm width and 8 mm length as shown in the attached drawings, and was cured at 150° C. x 3 powder to obtain a printed coating film 2.

Next, electrodes 3 were placed at positions 10W0IL apart from both ends of the coating film 2, and the resistance of the coating film was measured using a Wheatstone bridge. The specific resistance values calculated from the obtained resistance values are also shown in Table 1 below. Looking at Table 1 above, it can be seen that the conductivity was sufficiently improved when used alone. It can be seen that an excellent conductivity improvement effect can be obtained by combining unsaturated fatty acids and organotitanium compounds, which are ineffective, and that excellent conductivity can be obtained in the SO layer by adding a phenolic compound. .

Another advantage of using these components in combination is that even if they are added alone in larger amounts, the conductive effect will not be improved and the suitability for painting will deteriorate; The effect of improving conductivity can be obtained without causing a decrease. Example 2 Among the above samples, samples 4, 8, 9, 12, and 15 were tested at 40°C x 95% R. after coating film formation. H. A moisture resistance test was conducted under the following conditions.

The results are shown in Table 2 below as a change in resistance value over time. Above table-
2, it can be seen that the coating film obtained from the conductive paste of the present invention not only has a low initial resistance value, but also has a small increase in resistance value even in a high humidity atmosphere.

Example 3 Processed.

Claims (1)

[Scope of Claims] 1 (i) 75 to 98 parts by weight of copper powder, (ii) 25 to 2 parts by weight of thermosetting resin binder (the total amount of copper powder and binder is 100 parts by weight), (iii) 0 saturated fatty acids
．． 1 to 10 parts by weight and (iv) di-i-propoxy-
selected from the group consisting of bisacetylacetonatotitanium, di-n-butoxy-bis(triethanolaminato)titanium, isopropoxy-triisostearoyloxytitanium and isopropoxy-tri(N-aminoethylaminoethoxy)titanium Organic titanium compound 0.01-5
A conductive copper paste composition comprising parts by weight. 2 (i) 75 to 98 parts by weight of copper powder, (ii) 25 to 2 parts by weight of thermosetting resin binder (total amount of copper powder and binder is 100 parts by weight), (iii) 0 unsaturated fatty acids
．． 1 to 10 parts by weight, (iv) di-i-propoxy-bisacetylacetonatotitanium, di-n-butoxy-bis(
0.05 to 5 parts by weight of an organotitanium compound selected from the group consisting of titanium, isopropoxy-triisostearoyloxytitanium, and isopropoxy-tri(N-aminoethylaminoethoxy)titanium; and (v) 0.8 phenolic compound selected from methylhydroquinone and t-butylhydroquinone
20 parts by weight of a conductive copper paste composition.