JPS60207396A - Circuit substrate - 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 wiring board.

In a wiring board, the main body of the board is made of a ceramic such as alumina ceramic, and one line is formed on its surface with a thick or thin film, and appropriate circuit elements are formed or loaded. It is known that the surface of the substrate body is coated with a wear-resistant and oxidation-resistant film to protect these wirings.

By the way, such a protective film is usually formed into a thin film by sputtering or vapor deposition. However, as mentioned above, when ceramic is used as the substrate body, the density of the thin film may be reduced due to the influence of its surface. Figure 1 shows an enlarged cross-sectional view of a thin film B formed on the surface of a ceramic substrate body A. As is well known, the surface of the ceramic has a particle size of about 11
1") There are countless uneven surfaces. Pus grows on this smooth surface by sputtering, etc. Under the influence of these uneven surfaces, minute gaps CB are formed near the boundaries of each uneven surface. In other words, the crystals of the film material become discontinuous with each other.

Therefore, if a growing firefly is left in a place with a lot of moisture, such as during an environmental test, it may pass through this gap C and reach the surface of the board A.This moisture may cause the wiring on the board A. etc. are eroded and become K from tq.

An object of the present invention is to improve corrosion resistance when a protective film is formed on a ceramic substrate body.

This invention applies to the surface of a protective film formed in the form of a thin film.

It is characterized by being coated with a filler that can penetrate into the minute gaps in the protective film.

Embodiments of the invention will be described with reference to the drawings. The figure shows an embodiment in which the present invention is applied to a thermal print head. Figure 2 shows the manufacturing process of the Therma V print head F. First, an alumina ceramic substrate is used as the substrate body l, and a protrusion 2 made of glaze is provided on its surface (Figure 2A). . Board body 1. A heating resistor layer 8 for printing is formed on the surface of the protrusion 2, and a conductive layer 4 for electricity supply is formed on the surface thereof, and then patterned into a predetermined pattern by a photo-etching process. In the figure, 8A is the heat generating part, and C is the energizing part for the 4A heat generating part 8A.
Figure 2B). After this, a protective film is formed on the surface of the substrate body 1 (FIG. 11.2C).

The protective film covers the entire surface including the surface of the conductive layer 4.

The end portion of the conductive layer 4 that is connected to the outside, that is, the area where the external terminal 6 (see FIG. 8) is provided is excluded.

The above configuration is not much different from conventional thermal print heads of this type. Furthermore, in the formed protective film 5, light is generated in minute gaps due to the unevenness of the surface of the ceramic substrate body! As already stated, it can be avoided. Note that another film (
For example, in the case where an oxidation-resistant P111) is present, the protective film will be affected by the unevenness of the substrate body and gaps will occur.For example, if the protective film 5 is required to have wear resistance, Tantalum oxide is suitable, and its film thickness is
It is about 5 μm thick.

In order to compensate for the existence of gaps in the protective film, in this invention,
The surface of the protective film is coated with a filler that can penetrate into this gap (FIG. 2D). The dandruff coating layer is shown. As a filler, a resin having sufficient fluidity to penetrate into the Fi gap is suitable. When applied to a thermal print head - since the coating layer 7 is also exposed to high temperatures higher than SOB, it is desirable to use a heat-resistant resin. Specifically, polyimide, Teflon, etc. are preferred, and these can be applied by printing, etc. Bye L/-
h.

When polyimide is used, its precursor is applied and the required areas are etched away.

You can also cure it. Furthermore, if the surface of the protective pJb is covered with the filler 7 with a strength greater than this filler, this filler 7 will cause fine Vim inside the protective film.

Therefore, it is impossible for moisture to penetrate into this gap from now on (therefore, the 2gw layer 0 circuit elements on the board body will not be eroded by moisture. The thickness of layer 7 is 05 to 5.
μm is sufficient.

As described in detail above, according to the present invention, even when the substrate body is made of ceramic and a protective film is formed on the surface thereof, by coating the surface with a filler, it is possible to prevent discontinuity of crystals within the protective film. Since the gaps due to corrosion are filled, corrosion due to the gaps can be reliably prevented and corrosion resistance can be improved.

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view of the substrate body and the protective film; FIG. 2 is a cross-sectional view of the manufacturing process showing an embodiment of the present invention;
FIG. 8 is a perspective view of the same. 1... Board main body, 4A... Current carrying part, 5
······Protective film. 7...Coating layer

Claims (1)

[Claims] The surface of a ceramic substrate main body having a MI-hI butter coating on the surface is covered with a thin protective film, and the wiring board is made of a ceramic material. A wiring board in which a coating layer made of a fluid filler is provided on the surface of the protective film.