Wiring substrate

Abstract

A substrate is provided on which wires can be formed satisfactorily using a dispersion liquid of metal microparticles without causing disconnection or short circuit. The wiring substrate comprises a substrate, an organic membrane formed on the substrate, and a metal wire formed on the organic membrane. An arithmetic mean deviation Ra of the profile of the surface of the organic membrane where the metal wire is formed is not less than 60 nm and not more than 5×10−2 D, where D is the width of the metal wire. The contact angle with respect to water on the surface of the organic membrane where the metal wire is formed is not less than 110°.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The invention relates to a wiring substrate on which metal wires are formed. [0003] 2. Description of Related Art [0004] Wiring substrates are used in many products, including OA equipment such as personal computers, printers, scanners, and various types of memory; household appliances such as television sets, audio equipment, cleaners, refrigerators, microwave ovens, and rice cookers; and transportation means such as automobiles, trains, ships, and airplanes. Metal wires are formed on such wiring substrates, and LSIs, ICs, transistors, diodes, capacitors, and resistors, for example, are mounted in accordance with the metal wires. [0005] While the wiring substrates are in many cases formed by plating, methods have recently been disclosed whereby metal wires are formed by drawing or depicting them using a dispersion liquid of metal microparticles and then subjecting the drawn wires to heating or other processes. Exam...

AI Technical Summary

Benefits of technology

[0011] In accordance with a technology disclosed in Non-Patent Document 1, (1) the surface of a substrate is rendered liquid-repellent, and then a portion where a wire is to be drawn is irradiated with a laser so as to lower the liquid repellency at the irradiated portion, followed by the formation of a wire using an ink-jet head; or (2) a groove is provided in a portion where a wire is to be drawn, and an ink-jet head is aimed at the groove to draw a wire. These techniques help alleviate the problems of the spreading of the dispersion liquid and disconnection to some extent.

[0013] It is therefore an object of the invention to provide a wiring substrate and a method of manufacturing the same whereby the undesired spreading of metal microparticles and disconnection during the formation of a metal wire using metal microparticles can be prevented and a superior mass productivity can be obtained.

[0014] As a result of analysis of the surface states of various substrates in an attempt to achieve the aforementioned object of the invention, it has been found that by using a substrate provided with appropriate surface pits and projections and with an appropriate level of liquid repellency, the spreading of metal wires to a greater degree than is desired and disconnection can be prevented.

[0015] As a first means of achieving the aforementioned object, the invention provides a wiring substrate comprising a substrate, an organic membrane formed on the substrate, and a metal wire formed on the organic membrane, wherein a mean deviation Ra of the profile of the surface of the organic membrane where the metal wire is formed is not less than 60 nm and not more than 5×10−2 D, where D is the width of the metal wire, and wherein the contact angle with respect to water on the surface of the organic membrane where the metal wire is formed is not less than 110°. It is experimentally presumed that this first means enables a desired metal wire pattern to be formed for the following reasons. Namely, by thus providing the organic membrane in which the metal wire is formed with an appropriate degree of liquid repellency, the excessive spreading of the dispersion liquid of metal microparticles on the organic membrane can be controlled. At the same time, by providing the surface of the organic membrane with appropriate pits and projections, the dispersion liquid of metal microparticles can permeate the pits and projections such that its liquid movement can be controlled, in an anchoring effect provided by the pits and projections.

[0038] In accordance with the invention, it is possible to form desired fine wires on the substrate by drawing a wire pattern on the surface thereof using a dispersion liquid of metal microparticles by an inkjet method, for example, instead of carrying out processes such as resist layer formation, exposure, and etching. The invention can thus provide a wiring substrate that has an excellent mass productivity, and a method of manufacturing the same.

Problems solved by technology

When drawing a wire on a substrate by coating it with a dispersion liquid of metal microparticles, if the liquid repellency of the substrate is not sufficient, the dispersion liquid of metal microparticles could spread further than is necessary, thereby failing to draw a wire of desired width.

Conversely, if the liquid repellency is too high, the droplet of the dispersion liquid that has been dropped on the substrate could be repelled, possibly resulting in a disconnection, particularly when the intended wire is a long one.

However, although a desired wire can be drawn according to this method immediately after the application of the dispersion liquid to the substrate, as the dispersion medium evaporates, the surface tension of the liquid changes such that the liquid could spread further than is necessary, or be repelled by the substrate surface, resulting in a disconnection.

However, both methods require a highly accurate processing of the portion where a wire is to be formed, and a high positioning accuracy during the drawing using the ink-jet head, which naturally call for complicated process steps.

Thus, these methods still have mass-productivity problems in terms of time and cost.

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