JPS63196672A - Carbon paste composition - Google Patents

Abstract

PURPOSE:To provide the title paste compsn. having excellent electrical conductivity and adhesion and suitable for use in forming resistors and electrically conductive circuits for printed wiring boards, hybrid boards, etc., by blending electrically conductive carbon and a binder with graphite whisker. CONSTITUTION:100pts.wt. binder (A) such as polyester, polyvinyl butyral, or epoxy resin is blended with 10-100pts.wt. electrically conductive carbon powder (B) such as furnace black or acetylene black, 5-100pts.wt. graphite whisker (C) having a diameter of 0.05 - several mu and a length of several mu - several mm and excellent electrical conductivity and thermal conductivity (e.g., electrical resistivity: about 70X10<-6>OMEGAcm, thermal conductivity: about 2,000W.cm<-1>.K<-1>) and optionally 0-80pts.wt. electrically non-conductive filler (D) such as kaolin, talc, silica or alumina. A solvent such as ethyl acetate is added thereto and the mixture is kneaded to obtain the title paste compsn. having a residual solvent content of 10-50%.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a carbon-based paste composition for forming conductor circuits and resistors used in printed wiring boards and hybrid boards.

(Prior Art) Conventionally, carbon-based paste compositions have been used for forming conductor circuits or contacts and for forming resistive elements in printed wiring boards and hybrid boards. Of course, the former requires a paste with high conductivity, and the latter requires a paste with a desired resistivity. This carbon-based paste is made of so-called carbon black, which is finely divided carbon obtained by incomplete combustion or thermal decomposition of natural gas, oil, etc., and is made of thermoplastic resin such as polyester, polyvinyl butyral, epoxy resin, phenol, etc.
It is made by mixing a thermosetting resin such as a resin as a binder.

The conductivity of the carbon-based paste is mainly adjusted by selecting the type of carbon black used and appropriately selecting the mixing ratio of carbon black and binder. Generally, in order to increase conductivity, a method is used to mix in a large amount of highly conductive carbon black, but a method of mixing silver powder, which has higher conductivity than carbon black (B, L, Ro
os-KozelProc, International
al, SympzMicroelectronics
,.

p239 (1985)) is also known. In addition, when carbon-based paste is used for forming a resistor element, the amount of conductive carbon black added may be reduced, or non-conductive fillers such as kaolinite and detsuite (Japanese Patent Laid-Open No. 61-111)
-93506), magnesium hydroxide, vermiculite (JP-A-61-93505), and organic fillers such as cross-linked polystyrene beads and benzoguanamine resinous fine powder (RF 6L-163601). A method of controlling conductivity has been adopted.

(Problems with the prior art) When using such a carbon-based paste for forming a conductive circuit, increasing the amount of carbon black added as conductive particles improves the conductivity, but the adhesion to the substrate is poor. At present, the conductivity that can be leaked while maintaining adhesion is about several tens of ohms/hole.

In addition, when using carbon black and silver powder together, several Ω/
A carbon-based paste with a resistance value as low as that of a metal can be used, but it requires the addition of a relatively large amount of expensive silver, which poses a cost problem. At the same time, there is also the problem that silver migration occurs.

(Objective of the Invention) The object of the present invention is to solve the above-mentioned conventional problems and to provide a carbon-based paste that has excellent adhesion to a substrate and has high conductivity even without containing silver. It is in. Another object of the present invention is to provide a carbon-based paste that has excellent adhesion to a substrate and has a stable resistance value.

(Structure of the Invention) In order to achieve the object of the present invention, in a carbon-based paste composition mainly composed of conductive carbon and a binder, graphite whiskers are added as conductive particles. The present invention provides a carbon-based paste composition with excellent electrical properties and stability.

``Graff-Itwhiskers are made by simultaneously vaporizing the raw material benzene and the catalyst organometallic compound.

Fine fibers are produced in the form of smoke by continuously feeding them into the reaction tube as a three-component mixed gas with a carrier gas (fluidized gas phase method), and the diameter generally varies depending on the reaction conditions. The size ranges from 0.05 to several μm and the length from several μm to several mm.

This graphite whisker has an electrical resistivity of 70 x 10 Ω (by doping with an electron acceptor (AsF5), it is possible to increase the resistance to the order of I x 10 = Ω), which is normally car yj+'
7 black 3000~50oooxlo-6Ω・(7)
or graphite powder 100 to 1000 x 10 = Ω
lower than chicken. Also, this graphite whisker is 200
It has a high thermal conductivity of 0 W-cm-' x-1,
This is also normal carbon black 1.5 W-cm-'.
x-11' or graphite powder 80~23oW-cIn-1・K
Significantly higher than ``1'' (, metallic copper (403W-rm-''
, ni-1) It has the advantage that the twist is several times higher.

The present invention is characterized by mixing such electrically and thermally conductive graphite whiskers into a carbon-based paste, and can be used without using metals such as silver powder, which are expensive and prone to migration. It is possible to spread a highly conductive paste, and when used as a carbon paste as a resistance paste, it has high thermal conductivity, and the Joule heat generated by the resistor can be dissipated well, and the binder can be localized. It is possible to prevent deterioration due to excessive heating.
A highly stable resistance element can be provided.

The carbon-based paste used in the present invention is not particularly limited, and contains conductive carbon and a binder as main components, and optionally non-conductive inorganic fillers such as kaolin, talc, silica, alumina, etc. A dispersion in an appropriate solvent is used.

The binder used in the present invention is one that has been conventionally used as a binder for carbon-based pastes, and includes, for example, thermoplastic resins such as polyester, polyvinyl butyral, and acrylic resins, and thermosetting resins such as epoxy resins and phenolic resins. .

As the conductive carbon powder, those commonly used in carbon-based pastes, such as furnace black and acetylene black, are used, and the blending amount varies depending on the intended use of the carbon-based paste, but in general, the above-mentioned binder Approximately 10 to 100 parts by weight
This is 1001 Keibu.

Kaolin is also used as a non-conductive inorganic filler.

Powders of Merck, calcium carbonate, silica, alumina, etc. are used, and the blend 1 thereof is 0 to 80 parts by weight based on the weight of the binder 1001 described above.

The carbon-based paste according to the present invention includes the binder,
It is prepared by adding a predetermined amount of graphite whiskers to conductive carbon powder and non-conductive filler, and kneading them using an appropriate solvent.

The amount of graphite whiskers added varies depending on the intended use of the leaking carbon paste, but is generally about 5 to 100 parts by weight per 100 parts by weight of the binder.

The solvent used for kneading and remaining in the paste is selected from solvents that are soluble in the binder, have appropriate evaporation properties, and have good workability, such as xylene, ethyl acetate, butyl acetate, methyl ethyl ketone, Ron, Shiv. Butyl cellosolve, butyl calpitol, etc. are common, and ordinary carbon pastes have a
Contains a solvent as a volatile component of 5096.

The carbon-based paste prepared in the above manner can be applied to a predetermined substrate, such as polyester film, glass, etc.
Epoxy laminate 1 After coating or printing on a paper-phenol laminate, ceramic substrate, alumina plate, etc., it is heat treated and solidified. The heat treatment conditions depend on the properties of the carbon paste (especially the type of binder and its solidification properties).

It is selected as appropriate depending on the purpose of use, the type of substrate to be adhered to, etc.

(Examples of the Invention) The present invention will be explained below with reference to Examples. It should be understood that the following examples illustrate the present invention, but the present invention is not limited thereto.

Example 1 Resol type phenolic resin 10 as binder
Take 0t and add graphite whiskers (Nikkiso ■
Made by Glasscar, diameter 0.2μm.

20 tons (length: 10 pm) and acetylene black 509 were kneaded together with 30 tons of butyl carpitol.

A carbon-based conductive paste was obtained through three rolls.

This carbon-based paste is printed on a ceramic substrate,
It was thermally cured at 250° C. for 5 minutes and the resistance value was measured, and the area resistance value was 120/mouth.

For comparison, the entire graphite whisker of Example 1 was replaced with Ketjen Black EC, a furnace black, and the sheet resistance value was 85 Ω/mouth. Further, for comparison, when the entire amount of graphite whiskers in Example 1 was replaced with acetylene black, the sheet resistance value was 2400/mouth.

As a carbon-based conductor paste, the effect of adding graphite whiskers was extremely large.

Example 2 Graphite whisker (manufactured by Nikkiso ■) I glass car "diameter 0.5 μm length Sa20
μm) was added.

The amount added is 10, 20, 40. Parts by weight. Butyl cellosolve was used to adjust the viscosity so that it had good screen printability.

The three types of carbon paste obtained in this way were printed on a glass epoxy resin wiring board, and
It was cured at 3 zones (100°C, 150°C, and 180°C in 10 minutes), and the resistance value was measured. As a result, T.U.
-100-5 had a resistance of 90Ω/portion, whereas the graphite whisker addition amount of 10.20.40 parts by weight resulted in a resistance of 45.28.12Ω/portion, respectively. Also, these compositions adhered well to the substrate. For comparison, when 0 parts by weight of TOUCH ENBLACK ECl was added to TU-100-5100 Seikyo 1, the carbon paste became dry.

20 parts of butyl cellosolve was added to this to make the viscosity suitable for screen printing, and this was printed and cured in the same manner as in Example 2, and the resistance value was measured. The result was 75Ω/mouth, which was a lower degree of decrease in resistance than when the same amount of graphite whiskers was added. Further, the adhesion of the Ketjenblack-added paste to the substrate was poor, and the adhesion test using cellophane tape showed a poor score of 50/100.

Example 3 Resol type 7 enol resin 10 as binder
0P, acetylene black 20F, and the same graphite whisker 102.0 as used in Example 1. Merck 702. And 50 to butyl calpitot? A carbon-based resistance paste was prepared by kneading the same.

This paste was printed on a ceramic substrate and heated to 250℃ for 5 minutes.
When the resistance value was measured after heat curing for a minute, the area resistance value was 10,500/mouth, and the adhesion to the substrate was also good. This paste has a stable resistance value Example 4 Polyester solution (solid content 50%, methyl ethyl keto/
and isophorone (mixed solvent) 1009, add Ketjen Black EC5t and Carbon Whisker 509, and add butyl calpitol to 1009? The mixture was added and kneaded to prepare a carbon-based paste according to the present invention.

The obtained carbon paste was printed on a polyester film with a thickness of 50 μm. Printing area: 2MX 100 m
A conductor pattern was formed by drying at 150° C. for 30 minutes (dry film thickness: 25 μm). The cellophane tape adhesion test (crosscut) of this conductor pattern was 100/100, and the electrical resistance was 100/portion in area resistance.

(Effects of the Invention) The carbon-based paste according to the present invention has higher conductivity than conventional carbon-based pastes and has good adhesion to various substrates, so it is suitable for printed wiring boards (flexible wiring boards) and hybrid boards. It can be used as a material for conductors, resistors, contacts, etc. (ceramic substrates), etc.

Patent applicant: Dai Iwasa Yama, representative of Asahi Chemical Research Institute Co., Ltd.

Claims (1)

[Scope of Claims] A carbon-based paste composition for forming conductive circuits and resistors, which is a mixture of conductive carbon and a binder as main components, and is characterized in that graphite whiskers are added thereto.