JPH04242004A - Manufacture of conductive copper paste - Google Patents

Abstract

PURPOSE:To improve conductivity and conductive stability so as to enhance a shielding effect by blending a thermosetting resin and other additives with metal powder after previous reaction of the metal powder with a reducing agent or a metal surface active resin. CONSTITUTION:After reaction of copper powder with an organic carboxylic acid such as an oxalic acid and fumaric acid having a reducing property, an abietic acid isomer such as gum rosin and wood rosin, and a quinone group such as hydroquinone, a thermosetting resin such as a liquid phenol resin, a dispersant such as isopropyltriisostearoyltitanate, or a coupling agent such as epoxy silane is blended therewith. Consequently, it is possible to obtain paste excellent in conductivity and conductive stability necessary for an electromagnetic wave shield and employable for a countermeasure of an electromagnetic shield and a circuit forming material for a printed circuit board.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a copper paste composition containing copper powder and having good conductivity. After forming a conductive circuit, a copper paste has excellent conductivity by heating and curing, or a coating film is formed by screen printing on a printed circuit board such as the above-mentioned board, and then heating and curing to achieve good conductivity, i.e. The present invention relates to a method for producing a conductive copper paste suitable for enhancing the shielding effect of unnecessary conductive waves generated from a circuit board.

0002

[Prior Art] Conductive copper paste (hereinafter referred to as copper paste) has attracted attention as a conductor for circuit boards as an alternative to expensive conductive silver paste (hereinafter referred to as silver paste). It is also attracting attention as a conductor for shielding substrates (hereinafter referred to as shielding substrates).

[0003] Paste compositions containing copper powder and phenolic resin as a binder are known as copper pastes, but since copper is inherently more easily oxidized than silver, copper pastes have difficulty maintaining conductivity over a long period of time. There is a problem with that. That is, copper is oxidized during the curing process after screen printing, and as a measure to prevent such oxidation, for example, Japanese Patent Laid-Open No. 61-3154 and Japanese Patent Laid-Open No. 63
-286477 is known, and it is certainly good as a conductor for circuit boards. However, when attempting to further improve the conductivity, it is difficult to use only the above method.

By the way, when shielding unnecessary radiation, ie, electromagnetic interference, it is well known that the so-called electromagnetic wave shielding effect is caused by reflection and absorption by the shielding material. That is, Donald. R. J. According to White's theoretical consideration of shielding effect (SE),

000
5]

[Math 1] is proposed.

[0006] Therefore, the present inventors focused on the fact that the shielding effect can be enhanced by improving the specific conductivity of the copper paste composition, as is clear from the above equation, and conducted studies.

[0007]

[Problems to be Solved by the Invention] As a result of intensive studies to improve these drawbacks of copper paste, the object of the present invention is to apply a reducing agent to metal powder (copper powder) in advance in the process of manufacturing copper paste. Another object of the present invention is to provide a copper paste composition suitable for electromagnetic shielding boards or circuits that has good conductivity and stable conductivity even during component mounting processes by reacting with a metal surface active resin.

[0008]

[Means for Solving the Problems] In the process of producing copper paste, the present invention involves reacting metal powder with a reducing agent or metal surface active resin in advance, and then kneading thermosetting resin and other additives. This is a method for producing a conductive copper paste characterized by the following.

The reducing agent or metal surface active resin used in the present invention is an organic carboxylic acid, a rosin-based substance, a quinone, etc. The organic carboxylic acid includes oxalic acid, fumaric acid, maleic acid, and succinic acid, which have reducing properties. , malic acid and the like are preferred. As the rosin-based substance, those containing abietic acid isomers as a main component, such as gum rosin, wood rosin, and copal, are preferable. Further, as the quinones, hydroquinone, catechol, or alkyl and/or alkenyl substituted products thereof are preferable. Furthermore, in order to react with metallic copper powder in advance, it is necessary to uniformly cover the surface of the copper powder, so it is preferable that the reducing agent and metal surface active agent be in a liquid form dissolved in a solvent or in a liquid form themselves. Even when powder is unavoidably used, the particle size is preferably 50 μm or less because of the need for uniform dispersion.

[0010] Furthermore, the metallic copper powder used in the present invention can be a commercially available product as it is, and the shape can be scale-like, resin-like, spherical, etc. Although any of them can be used, resin-like electrolytic copper powder is particularly preferred. Further, the particle size is not particularly limited, but in the case of a copper paste having good screen printing properties, it is preferable that the particle size is as fine as possible.

[0011] The thermosetting resins used in the present invention include phenolic resins, alkyd resins, amino resins,
Unsaturated polyester resin, epoxy resin, urethane resin, etc. can be used. Furthermore, other additives include isopropyl triisostearoyl titanate (Ajinomoto Co., Ltd.)
Dispersants such as Blen Act KP-TTS (manufactured by Co., Ltd.) and coupling agents such as epoxy silane are known.

The amount of reducing agent and metal surface active resin used in the present invention is preferably 1 to 30 parts by weight per 100 parts by weight of copper powder, and the amount of thermosetting resin is preferably 1 to 30 parts by weight per 100 parts by weight of copper powder. ~20 parts by weight is preferred.

[0013] This is because if the reducing agent and metal surface active resin are less than 1 part by weight per 100 parts by weight of copper powder, the oxide film of the copper powder will not be removed sufficiently and the conductivity will be poor. On the other hand, if it exceeds 30 parts by weight, the copper powders will not come into contact with each other, resulting in poor conductivity. Furthermore, if the amount of thermosetting resin is less than 1 part by weight per 100 parts by weight of copper powder, the adhesion of the copper powder will decrease, causing blistering in the soldering heat resistance. Moreover, if it is 20 parts by weight or more, the amount of resin between the copper powder increases and the conductivity becomes poor.

[0014]

[Examples] The present invention will be explained in more detail by Examples below.

[Example] After reacting the following blended compositions with stirring for about 8 hours, ○1 liquid resol type phenolic resin (manufactured by Sumitomo Durez Co., Ltd. "PR-5")
1833” resin content 65%) 15 parts ○2
Organic titanate compound (manufactured by Ajinomoto Co., Inc.)
Brain Act KR-TTS)
1.5 parts were added and kneaded with an ink roll to obtain a paste.

[0016]

[Table 1]

Next, after screen printing an ultraviolet curing solder resist for an undercoat on the phenol resin substrate on which electrode portions have been formed in advance, 120W, 2 lamps, 3.
UV curing was performed at 1 m/min. On top of that, the copper paste prepared above was screen printed and cured at 160°C for 30 minutes, and then a thermosetting solder resist for overcoat was screen printed and cured at 150°C for 30 minutes. I got it.

Regarding the obtained evaluation board, the resistance value was measured from the initial value and the value after high temperature and high humidity treatment at 60°C x 90% RH. The occurrence of blisters on the printed surface of the substrate was observed when bath float treatment was performed.

[Comparative Example] Electrolytic copper powder, reducing agent, solvent, resol type phenolic resin, and organic titanate compound were mixed at the same time in the mixing ratios of Examples 1 to 3, and ink roll kneading was carried out to obtain Comparative Examples 1 to 3. A paste was obtained. Next, an evaluation board was created in the same manner as in the example. The obtained substrate was evaluated in the same manner as in the examples.

The results are shown in Table 2, and it is clear that the composition obtained in this example is excellent in conductivity, conductivity stability, and soldering heat resistance after humidification.

[0021]

[Table 2]

[0022]

According to the method for producing a copper paste according to the present invention, it has good conductivity and conductivity stability necessary for electromagnetic shielding, and can also be used as a paste for circuits. Furthermore, it has stable workability in the component mounting process, that is, excellent solder heat resistance after humidification, and is an extremely useful manufacturing method as a material for electromagnetic shielding of printed circuit boards and for circuit creation.

Claims (1)

[Claims] [Claim 1] In the process of manufacturing copper paste,
A method for producing a conductive copper paste, which comprises reacting metal powder with a reducing agent or a metal surface active resin in advance, and then adding a thermosetting resin and other additives.