JPH0462876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a conductive ink sheet for forming conductive paths on the surface of an electrically insulating material by thermal transfer printing.

[Prior Art] A method of forming a conductive path by printing on the surface of an electrically insulating material, that is, a method of obtaining a so-called printed circuit board, is a method that is conventionally well known (not shown because it is well known). , photographic negative method,
Examples include the silk screen method and the Metsuki method. However, both methods mainly involve chemical or electrochemical processing such as etching or plating, which complicates the manufacturing process, lengthens the manufacturing time, and requires chemical management. Therefore, in the urgent development trial production stage, instead of using the above methods, for example, silk screen printing using conductive ink mainly composed of fine particles of silver or copper as the printing material, or drawing with a brush etc. A conductive path was formed on the surface of the substrate.

[Problems to be solved by the invention] Conventional conductive inks require advanced technology to control the concentration of fine particles such as silver or copper, which are the main components, and the viscosity of the ink, and also require advanced techniques such as silk screen printing and brush printing. Because it is difficult to form fine conductive paths using lithography, there is a limit to increasing the degree of integration. One possible method for solving this problem is a thermal transfer printing method, for example, a method of forming conductive paths using a thermal transfer printer. Ink in ink sheets used as printing media for thermal transfer printers generally has physical properties such that it melts at temperatures of 60°C to 80°C and solidifies after adhering to the printing paper, i.e., it has a fixed melting point in the form of heating melting and cooling solidification. It is something. For example, synthetic waxes or natural waxes to which some synthetic resin is added as an agent for improving the strength of the printed image coating are mainly used. Using a conductive ink obtained by adding conductive fine particles to such an ink base material, a conductive path can be formed on a substrate by a thermal transfer printing method. However, when electronic components are soldered onto a board with conductive paths formed in this way, the conductive ink melts and spreads, making it impossible to maintain the shape of the fine conductive paths. Even if electronic components could be mounted while maintaining the shape, the adhesive strength of the conductive paths to the substrate was weak, resulting in problems such as the inability to maintain circuit function.

This invention was made in order to solve the above-mentioned problems, and is used in thermal transfer printing, which can easily form highly integrated conductive paths on a substrate. The purpose of the present invention is to obtain a conductive ink sheet capable of forming a conductive path with strong adhesion to a substrate without melting.

[Means for Solving the Problems] The conductive ink sheet according to the present invention has a conductive ink sheet prepared by kneading conductive fine particles in a thermosetting synthetic resin in a semi-cured state on a base film made of a synthetic resin. An ink layer is formed.

[Function] The conductive ink sheet of the present invention can maintain a semi-cured state for a certain period of time, so it is melted and adhered to a substrate by thermal transfer printing, and then further heated to form a three-dimensional structure and harden.

[Embodiment of the Invention] An embodiment of the present invention will be described below.
Conductive ink that can be applied to thermal transfer printing methods must have the following properties: heat-meltability that easily melts with the heat generated by the thermal head of a thermal transfer printer; heat resistance that can withstand the heat of soldering electronic components after printed wiring; It has adhesive strength that is strong enough to withstand vibrations and shocks that are normally applied when electronic components are attached, and good conductivity. First, the necessary conditions for the ink base material are that the melting point in the semi-cured state is in the range of 60°C to 110°C, and the viscosity when melted is in the range of 100 CPS to 10,000 CPS. The reason why the melting point range is limited is that if it is lower than 60°C, it will generate heat and transfer due to the pressure of the thermal head of the thermal transfer printer, and if it exceeds 110°C, excessive power is required for the thermal head, and the thermal This is because it also affects the life of the head. Next, as the conductive fine particles, for example, those having a fine particle or scale-like shape of gold, silver, copper, or nickel, and each having a particle size or thickness of 5 μm or less are suitable. However, it is not limited to a single metal, and in the case of a metal with low conductivity, it may be plated with metal such as gold or silver, and other than metals such as carbon are also suitable.

The ink base material and conductive fine particles described above are mixed in a ratio of 9 to 99 parts of the conductive fine particles to 1 part of the ink base material, and the mixture is ball-milled at room temperature or at a temperature higher than the melting temperature of the ink base material. The conductive fine particles are uniformly dispersed and kneaded using a kneading device such as a roll. Specific examples of detailed preparation materials are shown below.

Specific example 1 Bisphenol type epoxy resin (Epicote
1004, manufactured by Yuka Ciel Epoxy Co., Ltd.) 100g Diaminodiphenylsulfone 6g Butyral resin (BM resin, manufactured by Sekisui Chemical Co., Ltd.)
14g Toluene 93g Methyl ethyl ketone 93g Isopropyl alcohol 93g Silver powder (particle size 1-5 μm) 1143g Specific example 2 Unsaturated polyesterimide resin (TVB2706,
Toshiba Chemical Co., Ltd.) 100g Silver powder (particle size 1 to 5μm) 1053g To make an ink sheet from the conductive ink thus obtained, use a roll coater or gravure printing machine to print as shown in Figure 1. For example, on one side of a heat-resistant base film 1 made of polyester resin, polyimide resin, or polyamideimide resin and having a thickness of 1 to 10 μm, a conductive ink layer 2 in which conductive fine particles 3 are uniformly dispersed is applied. Apply it evenly to a thickness of 1 to 15 μm.
Thereafter, the ink sheet is completed by heat-treating the ink base material until it reaches a semi-cured state.

A heat-resistant synthetic resin film (for example, a polyester film with a thickness of 75 μm) whose surface has been chemically or electrically activated is printed by a thermal transfer printing method using the conductive ink sheet obtained as described above as a printing medium. under specified printing conditions (for example, applying 0.2 mJ/dot energy with a thermal transfer printer using a 12 dot/mm thermal head)
to transfer the conductive path pattern. At this time, the conductive ink is in a semi-hardened state, so it is easily melted by the heat of the thermal head and transferred. The transferred conductive path pattern is further heat-treated to form a three-dimensional structure and harden. The electrical resistance of the cured conductive path is 1000 to 2000 μΩ/cm, and has sufficient conductivity for practical use as an electric circuit. Furthermore, the cured conductive path has sufficient heat resistance to withstand soldering of electronic components, and adhesive strength sufficient to withstand vibrations and shocks that are normally applied when electronic components are attached. Therefore, the printed wiring board thus obtained can be applied not only to development prototypes but also to actual products.

In addition, the conductive path pattern is transferred onto the surface of the heat-resistant synthetic resin film as described above, and the conductive path pattern is retransferred onto the surface of an epoxy resin or polyimide resin substrate using a heat roll, etc., and then heat-treated to form the conductive path pattern. It is also possible to form a three-dimensional structure, and in this case also sufficient adhesive strength can be obtained.

Although the case where a conductive path is formed has been described above, it goes without saying that if a compound having an appropriate electrical resistance is used as a transfer material, a so-called printed resistance can also be formed.

[Effects of the Invention] As described above, according to the present invention, an ink sheet is made of a conductive ink that easily melts in a semi-cured state and hardens into a three-dimensional structure by further heat treatment. Therefore, a conductive path can be easily formed in a short time by a thermal transfer printing method, and after curing, a printed conductive path can be formed with sufficient strength, heat resistance, and conductivity.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conductive ink sheet for thermal transfer printed wiring according to an embodiment of the present invention. 1 is a base film, 2 is a conductive ink layer, 3
indicates conductive fine particles.

Claims (1)

[Claims] 1. A base film made of a synthetic resin, and a conductive ink layer coated on the surface of the base film and having conductive fine particles in a semi-cured thermosetting synthetic resin. Conductive ink sheet for thermal transfer printed wiring. 2. The conductive ink sheet for thermal transfer printed wiring according to claim 1, wherein the conductive fine particles are metal. 3. The conductive ink sheet for thermal transfer printed wiring according to claim 1, wherein the conductive fine particles are carbon.