JPS58134496A - Method of producing printed circuit board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a printed wiring board in which a predetermined circuit pattern is formed using a conductive paste on an insulating substrate, and a relatively large current can be supplied to the pattern. , relates to a method of manufacturing a printed wiring board suitable for use in flexible board-to-board connections as cables, signal lines, connectors, etc. of information processing machines such as personal computers, computer terminals, and copying machines. The wiring board printed with the adhesive paste is
As shown in the figure, a conductive metal layer 2 such as copper or AI is formed on a substrate l, and a conductive paste 8 such as carbon paste, silver paste or gold paste is coated on the metal layer, or It is constructed by printing conductive paste 8 directly on the substrate 1 as shown in FIG.

Conventionally, in wiring boards printed with such conductive paste, since the conductive paste (for example, carbon paste) does not originally contain a solvent, it is necessary to use a solvent such as thinner or alcohol to lower the viscosity. . Since such a solvent-based conductive paste is thermosetting, foaming of the solvent during heat curing, foaming due to printing, foaming due to gas generation during the curing reaction, or irregularities on the surface of the conductive paste depending on the viscosity of the paste, The surface condition of the paste becomes quite rough due to dust, foreign matter contamination, and non-uniformity of the paste material. For example, when the paste is printed and dried to a thickness of about 15 μm,
There was a drawback that needle-like irregularities of about 4 to 6 μm (max. 10 μm) on average were generated on the paste surface, which caused an increase in contact resistance.

Therefore, conventionally, wiring boards printed with such conductive paste cannot be used as printed wiring boards that require a relatively large current (on the order of mA) to flow, because a voltage drop occurs at the mutual contact surface. Carbon paste wiring boards are not suitable for use due to their low power consumption.
However, it has only been used for key switch contacts of desktop calculators (for example, Japanese Utility Model Publication No. 56-1ul1) and wiring circuits using C-MOS LSIs with extremely low current consumption.

In addition, in order to reduce the contact resistance at the contact points of such carbon paste printed wiring, it is possible to select paste materials with specific resistance and viscosity in mind, and to control paste drying conditions such as temperature and curing time. However, contact resistance□
゛I was able to lower my honor sufficiently a, '#lC'k [IIE A6. :gate,. □Ka1 possible.

In addition, instead of a conductive paste printed wiring board, it is possible to use a conductive adhesive such as conductive rubber or hot-melt agent, but the contact resistance cannot be ignored in soldering unlike in connection, and therefore Problems such as the connection between the liquid crystal display (LCD) and the substrate were extremely limited.

The present invention eliminates the various drawbacks of the conventional conductive paste printed circuit boards mentioned above, and is suitable for use in cables, signal lines, or connectors of information processing machines such as computer terminals and copying machines, which supply relatively large currents. It is an object of the present invention to provide a method for manufacturing a printed wiring board that can optimally reduce contact resistance.

An embodiment of the present invention will be described below with reference to the drawings. Third
4 and 4 show that in the conductive paste printed wiring board of FIG. 1 and FIG. 3. Physically polish the surface with rolling rollers, puff polishing, etc. Yo Q ” C-jl knee 7, table.

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□. , 8, ゎ2, It was confirmed that when pressure is applied with a load of 0 kg/mm2, the unevenness is suppressed to about 2 mm or less, and the contact resistance is reduced to I/6 of that without conventional surface treatment. Furthermore, it is believed that a thin local insulating layer formed on the surface of conventional conductive pastes by resin components, impurities, oxides, etc. is one of the reasons for the increase in contact resistance.
The above-described surface treatment according to the invention can eliminate this drawback and reduce the contact resistance.

FIGS. 5 and 6 illustrate the case of connecting a substrate 5 on which aluminum wiring 4 is applied to a conductive paste 3, comparing the conventional example and the present invention, respectively.

In the figure, in the case of the conventional example shown in Fig. 5, the surface is rough, so the contact area is small and the contact resistance is large, but in the example of the present invention shown in Fig. 6, the contact area increases and the contact resistance value can be reduced. will be easily understood.

In this way, the present invention has a structure that can be applied to a printed wiring board with a relatively large current (for example, on the order of mA), and it is of course useful for circuit wiring such as conventional low-power key switch contact circuits. Needless to say, it can be used. Furthermore, if a flexible printed circuit board (FPC) such as a plastic base film is used as the insulating substrate, it becomes extremely suitable for wiring cables, signal lines, connectors, etc. Furthermore, there is no need to manage the selection of paste materials or paste drying conditions, etc., and it is possible to reduce variations in contact resistance, providing a printed wiring board with high reliability and good electrical characteristics without voltage drop at contact areas. In practical terms, the effect is great.

[Brief explanation of the drawing]

1 and 2 are sectional views of a conventional conductive paste printed wiring board, 3 and 4 are sectional views of a printed wiring board manufactured according to the present invention, and 5 and 6 are sectional views of a conventional conductive paste printed wiring board. FIG. 2 is a cross-sectional view for explaining the printed wiring board of the invention. 1: Insulating substrate, 2: Conductive layer, 3: Conductive paste. Agent Patent Attorney Aihiko Fuku (2 others) Figure 1 Figure 3 Figure 5 Figure 2 Figure 4v4 6111I

Claims (1)

[Claims] 1. A printed wiring board that can form a predetermined circuit pattern on an insulating substrate using a conductive paste and supply a relatively large current to the pattern, the conductive paste formed on the substrate. A method for manufacturing a printed wiring board, characterized in that the contact resistance at the board contact portion is reduced by smoothing the surface of the printed wiring board.