JPS603149A - Manufacture of thick film circuit - Google Patents

Abstract

PURPOSE:To prevent a conductor and a conveyer from coming into contact with each other while reducing the drying and baking frequencies by a method wherein a thick film dried paste is provided on a conductor side coming into contact with a conveyer to be baked not to come into contact with the conveyer. CONSTITUTION:A conductor 2 is provided on an alumina substrate 1 by means of heating and drying a printed paste likewise another conductor 4 on the backside. A printed substrate is forwarded into a tunnel furnace by means of net-type belt 5 with the surface and backside heated by infrared beams. A hole 3 is made for connecting both side conductors with each other. The substrate coming out of the furnace is cooled down to room temperature and reversed to place both ends upon the conductor 2 for printing paste on the formed surface of the conductor 2 further heating and drying the paste to produce resistors 6a, 6b for baking. The surface coming into contact with the belt 5 in case of baking the conductor does not come into contact with the belt 5 in case of baking the resistor 6 with any incompletely baked part baked completely at this time. Through these procedures, the electric properties of conductors may be stabilized producing both side thick film circuit at less baking frequency and manufacturing space.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a method of manufacturing thick film circuits that can be used in radios, televisions, video tape recorders, and the like.

Conventional structure and problems thereof FIG. 1 shows an example of a thick film circuit. The thick film paste printed on the top and bottom surfaces of the Almite ceramic substrate 100 is dried and fired to form a first conductor 1o1, a second conductor 1o2, and so on. Resistor 103a.

1o3b is formed. 104 connects the conductor 101 on the top surface and the conductor 102 on the bottom surface formed in the through hole,
It is a meridian conductor and is a circuit board with thick film circuits formed on both sides.

Conventionally, the process of forming a double-sided thick film circuit as shown in FIG.
The process shown in Figure 2 was common. That is, first, in the surface conductor printing step biC, a conductor paste containing silver-palladium metal powder is printed on one side of the ceramic substrate 100 by a screen method.

Next, in the drying/firing step C, the conductor paste is heated and dried, and then the ceramic substrate is placed on a mesh conveyor belt and placed in a tunnel furnace equipped with an infrared lamp so that the substrate temperature reaches about 850°C. The second conductor 102 is formed by passing through for 15 minutes and firing. Next, in a front-back reversing step d, the ceramic substrate 10α is reversed so that the surface of the ceramic substrate 10α faces upward. Next, in the back conductor printing step e, a conductor paste is printed by the screen method in the same manner as in the front surface conductor printing step. At this time, the lower surface of the through ball is depressurized by a vacuum pump during printing so that the conductive paste enters the through ball. Next, a drying/firing step f is performed in the same manner as the drying/firing step C to form the first conductor 101 and the meridian conductor 104. Next, in a backside resistor printing step q, a resistor paste is printed on the conductor 101 by a screen method so that both ends overlap. After that, the resistor 103 is fired in the same drying and firing process as described above.
a, 103b were formed.

This conventional method for forming double-sided thick film circuits has been problematic because it involves many drying and firing steps and the time required for drying and firing is long. For this reason, the present inventors attempted to omit the firing step in the drying and firing process of C, but since the conductor 102 becomes the lower surface and contacts the mesh conveyor belt during firing, the air necessary for firing is not sufficient at the contact point. This resulted in incomplete firing. Even if the resistor paste was then printed and fired again, the incomplete firing could not be completely prevented because the second conductor 102 became the lower surface and came into contact with the mesh conveyor belt. Unfortunately, the process of printing, drying, and firing had to be repeated three times as in the conventional method.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned drawbacks of the conventional circuits, and makes it possible to manufacture double-sided thick film circuits with fewer drying and firing times and in a smaller space.

Structure of the Invention In view of the above-mentioned drawbacks of the conventional art, the present inventors have conducted intensive research and have arrived at the present invention. That is, according to the present invention, in a method for manufacturing a thick film circuit in which thick film conductors are formed on both sides of a substrate and a thick film resistor is formed on one side, a conductive paste is printed on both sides of the substrate, and The conductors are fired simultaneously in one process, simplifying the conductor firing process. At this time, in order to improve the incomplete firing part on the surface of the board that came into contact with the transport conveyor in the firing furnace, another thick film paste was printed on the conductor side of the board that came into contact with the transport conveyor, and after drying, At the same time as baking the other dried thick film paste, the incompletely baked portion of the conductor is baked again, making sure that the substrate surface on which the other thick film paste is printed does not come into contact with the conveyor. , which is completely fired. To explain this in more detail, there are a process of printing conductive paste on the first side of the board, a process of reversing this board, a process of printing conductive paste on the second side of this board, and a process of drying this board. and a step of baking, a step of inverting the substrate again, and a resistor paste on the first surface of the substrate.
This method of manufacturing a thick film circuit includes the steps of printing at least one paste selected from conductive paste and insulating paste, and drying and firing the substrate again.

Description of examples Next, an embodiment of the present invention will be described with reference to FIG.

FIG. 3a shows a first conductor formed by heating a conductor paste screen printed on an alumina substrate 1 and drying the solvent.

Figure 3 shows that in the next step, the top and bottom surfaces of the substrate are reversed, a conductor is printed on the surface on which no conductor has been printed using the screen printing method, the solvent is dried by heating, and a second conductor 4 is formed.
The printed circuit board is shown placed on a reticular conveyor belt 6 driven by an electric motor after forming a printed circuit board. The printed circuit board is fed into a tunnel-shaped kiln by a reticulated conveyor belt 5. The tunnel-shaped firing furnace is equipped with a plurality of near-infrared lamps above and below the reticular conveyor belt 6, and the substrate is heated by near-infrared rays from both upper and lower surfaces at a temperature of about 850° C. for 15 to 20 minutes. At this time, the second conductor 4
is sufficiently heated from above by near-infrared rays, and the firing furnace is filled with air containing sufficient oxygen, so that it is completely fired. The first conductor 2 is shaped by the reticular conveyor belt 5, so that near-infrared rays are not directly emitted and the temperature does not rise sufficiently, resulting in incomplete firing.
In some cases, the contact between the reticular conveyor belt 5 and the first conductor is still not sufficiently oxygenated, resulting in incomplete firing, but this problem will be resolved in the next step. 3 is a meridian hole that connects the first conductor and the second conductor. After being fired and leaving the furnace, the substrate is cooled to room temperature.
Move on to the next process. In the next step, shown in FIG. 3C, the upper and lower surfaces of the board are turned over again, and the resistor paste is applied onto the surface where the first conductor 2 is formed so that both ends overlap the first conductor 2. After printing by the screen printing method and drying the solvent by heating to form the resistors 6a and 6b, the resistors 6a and 6b are fired in the same manner as the firing of the conductors (first conductor and second conductor). . Here, the surface that was in contact with the mesh conveyor belt 5 during firing of the conductor is the resistor 6a.
, 6b will not come into contact with the mesh conveyor belt. Therefore, even if there is a portion that is incomplete during firing of the conductor, it will be sufficiently fired during firing of the resistors 6a and 6b, resulting in a complete fired body.

In this example, a known conductor paste consisting of palladium/silver powder, glass frit, a resin binder, and an organic solvent was used as the conductor paste. The conductive paste may be made of copper or nickel instead of the palladium/silver powder. A known resistor paste consisting of ruthenium oxide powder, glass frit, resin binder, and organic solvent was used as the resistor paste.

No, oh, printing in this invention is screen printing.

Although offset printing is practical, another method is to move the nozzle that discharges thick film paste based on pattern wiring data or resistor layout data to draw thick film paste wiring circuits or resistors directly on the board. It may be a method.

Effects of the Invention As described above, the present invention eliminates the adverse effects of the contact between the conductor and the conveyor when the conductors formed on both sides of the substrate are simultaneously fired, by adding another thick film to the surface of the conductor that is in contact with the conveyor. This problem is solved by forming a dried paste and baking it so that the surface on which the dried thick film paste is formed does not come into contact with the conveyor, which stabilizes the electrical properties of the conductor and reduces the need for double-sided thick film circuits. It can now be manufactured in just a few firings, and can be manufactured in a significantly smaller amount of space.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an example of a thick film circuit, Fig. 2 is a flowchart showing an example of the manufacturing process of a conventional double-sided thick film circuit, Figs. FIG. 3 is a cross-sectional view of a substrate during a process of a method for manufacturing a double-sided thick film circuit in an embodiment of the invention. 1.100...Substrate, 2,101...1st
conductor, 4,102... second conductor, 5...
・Mesh conveyor belt, 6a, 6b, 103a,
103b=--Resistor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 @ 3 Figure 2

Claims (2)

[Claims] (1) A step of printing a conductive paste on the first side of the substrate, a step of reversing the substrate, a step of printing the conductive paste on the second side of the substrate, and a step of drying and firing the substrate. a step of inverting the substrate again; a step of printing at least one paste selected from resistor paste, conductor paste, and insulator paste on the first side of the substrate; and drying the substrate again. and a firing process. (2) The method for manufacturing a thick film circuit according to claim 1, wherein the heat source for firing is a near-infrared lamp.