JPH04221878A - Thick film circuit board and its manufacturing method - Google Patents

Abstract

PURPOSE:To provide a circuit board manufacturing method by which a lower conductor film formed on a thick film circuit board having a structure of two wiring lines crossing through an insulating film thereon is effectively isolated from an external field, and migration does not occur and which is simpler than prior art inexpensively. CONSTITUTION:A lower conductor film 2 of Ag paste is formed at an intersection of two wiring lines on an alumina board 1, a glass insulating film 3 is formed on the upper surface of the lower conductor film except at least two edge regions, the lower film exposed from the insulating film is covered, for example, with a vitreous conductive film 7 for a thick film resistor of RuO2 paste, a first wiring line 4 of Cu paste is so formed as to be superposed on the conductive film, and a second wiring line 5 of Cu paste is so formed as to pass over the upper surface of the insulating film.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] On the surface, the present invention comprises:
The present invention relates to a thick film wiring board having a structure in which wiring lines made of two thick film conductors intersect with an insulating film in between, and a method for forming the same.

0002

2. Description of the Related Art A thick film wiring board as described above is known, for example, one obtained as follows. First, a ceramic substrate 1 such as an alumina substrate is prepared, and an Ag-based paste such as Ag/Pd paste is screen printed on the surface of the ceramic substrate 1 in a rectangular shape.
A rectangular lower conductor film 2 is formed by baking at 50°C (
Figure 4). Next, a glass paste is screen printed on the upper surface of this lower conductor film 2 and baked in air to form a glass insulating film 3.
form. At this time, the glass insulating film 3 is formed so that two opposing end edges of the lower conductive film 2 are exposed in a band shape (FIG. 5).

Next, using Cu paste, a pair of thick film conductor lines (after firing, the first Wiring lines 4) are formed by screen printing so as to extend in opposite directions (FIG. 6), and at the same time, another thick film conductor line (after baking, a second wiring line is formed) passing over the glass insulating film. Line 5) is formed by screen printing Cu paste in the same manner as described above (FIG. 7), and is fired at about 600° C. in an N2 atmosphere. At this time, the pair of thick film conductor lines are short-circuited to each other using the lower conductor film as an intermediary, thereby forming one wiring line.

[0004]Furthermore, at 500°C in an N2 atmosphere,
A glass paste that can be fired is prepared, and this glass paste is screen printed so as to cover the lower conductor film 2 exposed in the gap between the glass insulating film 3 and the first wiring line. Here, the reason for using a glass paste that can be fired in an N2 atmosphere as mentioned above is that if a glass paste that can be fired in air is actually fired in air, the wiring line formed from Cu paste will be oxidized. This is to be done. Thereafter, the overcoat film 6 is formed by firing in an N2 atmosphere under the conditions described above (FIG. 8).
A thick film wiring board is completed. Note that FIG. 9 is a diagram showing a cross section taken along line A-A' in FIG.

The reason why the exposed lower conductor film 2 is sealed by forming the overcoat film 6 is that the Ag-based material constituting the lower conductor film has low moisture resistance. This is because if it is not formed, a phenomenon (migration) occurs in which ionized metal from the lower conductor film is eluted toward the electrode or wiring at a higher potential than the lower conductor film. The arrows in FIG. 10 indicate the traveling direction of Ag ions during migration due to such elution of Ag ions.

[0006] Also, in the above formation process, Cu paste is used instead of the glass paste, screen printed and fired to cover the entire lower conductor film, wiring lines are formed, and the lower conductor film is sealed. Even if (Fig. 11
), the thick film conductor obtained by firing the Cu paste lacks density and is spongy, so moisture reaches the lower conductor film, metal ions are eluted from the lower conductor film, and the ions are further removed. There have been cases where it has penetrated the Cu wiring line and gone out, making it impossible to prevent migration.

[0007]

[Problems to be Solved by the Invention] However, in the above-mentioned prior art, in the above-mentioned N2 atmosphere, 500
Glass pastes that can be fired at °C are expensive and have been a cause of increased manufacturing costs for thick film wiring boards. There was also the problem that the number of man-hours increased due to the formation of the overcoat film.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and provide a thick film wiring board having a structure that reliably isolates the lower conductor film from the outside world and which does not cause migration. It is an object of the present invention to provide a method for easily manufacturing the thick film wiring board.

[0009]

[Means for Solving the Problems] As a result of research to achieve the above object, the present inventor formed a lower conductive film on a substrate, formed a glass insulating film thereon, and then formed a glass insulating film exposed from the insulating film. By covering the edge region of the lower conductor film with a glassy conductive film for thick film resistors and forming one wiring line through the conductive film, the migration can be prevented. Regarding the conduction between the lower conductive film and the wiring line, if the area where the wiring line and the lower conductive film face each other is designed to be sufficiently large compared to the thickness of the conductive film sandwiched between them, the resistance component of the conductive film can be reduced. The present invention was achieved by discovering that this can be ignored.

That is, the present invention provides a thick film wiring board having a structure in which two wiring lines intersect with each other with an insulating film on the surface of the substrate, and where the intersection of the two wiring lines is a lower conductor film formed on a substrate; an insulating film formed to cover the upper surface of the lower conductor film so that only two opposing edges of the lower conductor film are exposed; and exposed edges of the lower conductor film. The conductive layer was formed so as to be electrically connected to the vitreous conductive film formed on the upper conductive film and the lower conductive film so that each end portion overlapped with the two edges of the lower conductive film covered with the conductive film. A thick film wiring board characterized by having a structure consisting of a pair of first wiring lines and a second wiring line formed to pass through the upper surface of the insulating film; and the glassy conductive film The above-mentioned thick film wiring board, which is formed using a paste-like resistive material by a thick film process;
In a method for forming a thick film wiring board having a structure in which two wiring lines are present, a lower conductor film is formed on the substrate at the intersection of the two wiring lines, and a lower conductor film is formed on the substrate except for the two edge regions. After forming a glass insulating film that covers the entire surface of the film, the edge area of the lower conductive film exposed from the glass insulating film is completely covered with a glassy conductive film for thick film resistors, so that each end forming a pair of first wiring lines electrically connected by the lower conductive film so as to overlap the glassy conductive film formed on the exposed edge of the conductive film, and simultaneously passing through the upper surface of the insulating film; A method for forming a thick film wiring board, characterized in that a second wiring line is formed so as to form a second wiring line; It is something.

[0011]

[Operation] As seen in FIG. 1 showing a cross section of a thick film wiring board according to an embodiment of the present invention, due to the denseness of the vitreous conductive film 7 formed to cover the lower conductive film 2, , it is possible to reliably isolate moisture such as moisture from the outside air, and prevent migration from occurring. In addition, by using an existing paste-like resistive material such as RuO2 used in thick film resistors as the glassy conductive film, it is possible to manufacture the film at low cost without increasing the number of steps in the manufacturing process.

Furthermore, as is clear from FIG. 1, the conductive film 7 is sandwiched between the wiring line 4 and the lower conductive film 2 so as to separate them from each other. Therefore, this conductive film is RuO2
When the main component is a thick film resistor, a resistance component is interposed between the two that should be short-circuited, but the area of the opposing portion of the wiring line and the lower conductor film is
By designing the conductive film to have a sufficiently large thickness, the resistance component can be made negligibly small.

[0013]

EXAMPLE The process of forming a thick film wiring board which is an example of the present invention will be described below.

A 96% alumina substrate was prepared, and a rectangular Ag/Pd paste was screen printed on the surface of the substrate. Next, this substrate was baked in air at about 850° C. for about 10 minutes to form a lower conductor film.

Next, a glass paste was screen printed on the upper surface of the lower conductor film except for edge portions of a certain width at both ends, and the glass paste was baked in air to form a glass insulating film. Next, a RuO2 paste for thick film resistors is screen printed on a predetermined position on the substrate, and at the same time, the same R is applied to the area exposed from the glass insulating film on the upper surface of the lower conductor film.
Screen printing with uO2 paste was performed and fired in air.

Furthermore, by screen printing Cu paste, a pair of thick film wiring lines are formed on both sides of the lower conductor film, facing each other with the lower conductor film in between, and extending in opposite directions. RuO2 formed on the film
At the same time, another thick film wiring line passing over the glass insulating film was formed by screen printing with Cu paste in the same manner as above, and N2 The product was baked in an atmosphere at about 600°C for about 5 minutes to complete the production of a thick film wiring board.

[0017]

[Effects of the Invention] As is clear from the examples, the thick film wiring board of the present invention can reliably isolate the lower conductor film from the outside world, and therefore does not cause migration and does not require the use of expensive glass paste. This method is simpler and less costly than conventional methods, as it does not require any overcoat film formation process.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view for explaining a thick film wiring board in one embodiment of the present invention.

FIG. 2 is a diagram showing a cross section along a second wiring line of a thick film wiring board according to an embodiment of the present invention.

FIG. 3 is a diagram showing a cross section along a first wiring line of a thick film wiring board according to an embodiment of the present invention.

FIG. 4 is a plan view showing a lower conductor film formed on a substrate.

FIG. 5 is a plan view showing a glass insulating film formed on a lower conductor film.

FIG. 6 is a plan view showing first wiring lines provided oppositely so that each end overlaps with an exposed edge of a lower conductor film.

FIG. 7 is a plan view showing a second wiring line passing over a glass insulating film.

FIG. 8 is a plan view showing a conventional overcoat film for covering the lower conductor film exposed in the gap between the glass insulating film and the first wiring line.

9 is a sectional view taken along line AA' in FIG. 8;

FIG. 10 is a plan view showing the traveling direction of Ag ions during migration from the lower conductor film when no overcoat film is formed in the conventional method.

FIG. 11 is a cross-sectional view of a conventional method in which a lower conductor film is sealed with Cu paste instead of an overcoat film using glass paste.

[Explanation of symbols]

１‥‥Substrate 2. Lower conductor film 3.Glass insulation film 4..First wiring line 5. Second wiring line 6.Overcoat film 7. Glassy conductive film

Claims (4)

[Claims] 1. A thick film wiring board having a structure in which two wiring lines intersect with each other with an insulating film on the surface of the substrate, wherein the crossing portion of the two wiring lines is formed on the substrate. an insulating film formed to cover the upper surface of the lower conductive film so that only two opposing edges of the lower conductive film are exposed; a vitreous conductive film, and a pair of first conductive films formed so as to be electrically connected by the lower conductive film so that each end overlaps two edges of the lower conductive film covered with the conductive film. A thick film wiring board having a structure comprising a wiring line and a second wiring line formed to pass through the upper surface of the insulating film. 2. The glassy conductive film is formed of a paste-like resistive material by a thick film process.
The thick film wiring board described above. 3. In a method for forming a thick film wiring board having a structure in which two wiring lines intersect with each other with an insulating film on the surface of the substrate, the crossing portion of the two wiring lines is formed on the substrate. After forming a lower conductor film and forming a glass insulating film that covers the entire surface of the lower conductor film except for its two edge regions, the edge region of the lower conductor film exposed from the glass insulating film is covered with a thick film resistor. completely coated with a glassy conductive film for
forming a pair of first wiring lines electrically connected by the lower conductive film such that each end overlaps the glassy conductive film formed on the exposed edge of the lower conductive film; A method for forming a thick film wiring board, comprising forming a second wiring line so as to pass through the upper surface of the film. 4. The method of claim 3, wherein the glassy conductive film is formed by a thick film process of a pasty resistive material.