JPH10135632A - Method for manufacturing thick film multilayer circuit board and thick film printing screen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a printing paste from flowing around a back surface 20 of a printing mask 8 due to undulation, unevenness, etc. of a printing substrate surface in manufacturing a thick film multilayer circuit board 1. And SOLUTION: In a method for manufacturing a thick-film multilayer circuit board 1 including a step of screen-printing and firing a plurality of thick-film pastes on an insulating substrate, a print mask 8 is formed on the thick-film pastes already screen-printed and fired. The new thick film paste is screen-printed using a screen having a convex portion 13 provided on the back surface of the screen along the edge of the mask portion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thick film multilayer circuit board, and more particularly to a printing method effective when a thick film is laminated and printed on a substrate having an uneven surface. And a thick film printing screen used in the printing method.

[0002]

2. Description of the Related Art Conventionally, substrates having various structures have been used as substrates for high-density electronic circuits. One of the substrates is a via hole 5 made of a ceramic as shown in FIG.
A thick-film multilayer substrate 1 is used in which an upper conductor wiring 7 and a lower conductor wiring 3 are electrically connected through the same. Each thick film layer of the thick film multilayer substrate 1 is manufactured by patterning using a thick film paste by a screen printing method. In order to form a thick film pattern on a ceramic substrate by a screen printing method, a screen mask which has been subjected to necessary pattern processing in advance is used. When the thick film multilayer substrate 1 having the fine via holes 5 as shown in FIG. 4 is manufactured by using such a screen mask, an insulating film having an opening to become the lower conductor wiring 3, that is, a so-called via hole 5 is formed on the ceramic substrate 2 in order. 4, a method of forming a conductive via fill 6 filling the via hole and an upper conductor wiring 7 formed on the insulating film by a screen printing method is used.

Here, for example, the insulating film 4 is formed by printing and firing an insulating paste on the lower conductor wiring 3 formed on the ceramic substrate 2. In this printing, as shown in FIG. 5, a squeegee 11 to which a desired printing pressure 10 is applied moves in parallel at a constant speed while pressing a printing mask 8 for an insulating paste, which has been previously patterned, onto the ceramic substrate 2. This is performed by attaching the insulating paste 9 on the ceramic substrate 2.

[0004]

However, according to the conventional screen printing, as shown in FIG. 7 (a), the swelling of the surface of the lower conductor wiring 3 formed on the ceramic substrate 2 causes the printing mask 8 to swell. There is a case that the insulating paste 18 adheres to the back surface 20 side of the print mask 8 because a gap 19 is generated between the lower conductive wiring 3 and the lower conductor wiring 3. The waviness is generated by the trace of the mesh of the screen mask or by the difference in the squeegee printing pressure on the screen mask due to the pattern shape. The trace of the mesh is moderated to some extent by leveling or the like, but is often insufficient. The insulating paste 18 wrapped around and adhered to the back surface of the print mask 8 is pressed by the squeegee 11 to which an arbitrary printing pressure 10 is applied,
It is attached on the lower conductor wiring 3 inside the via hole.
Therefore, the resolution of the pattern of the via hole 5 is reduced.

When printing is repeatedly performed using the same printing mask continuously, as shown in FIG. 7B, the insulating paste 18 adhered to the back surface 20 of the printing mask becomes a thick film that follows in the next printing step. It may adhere to the inside of the via hole 5 of the substrate and adversely affect the formation of the via hole 5 of the subsequent thick film substrate.

Accordingly, the present invention is based on the problem that the thick film printing has already been performed, and when the screen printing is further performed on a thick film printed substrate having undulations and irregularities on the surface, the undulations and irregularities on the substrate surface are caused. And preventing the print paste from flowing to the back surface of the mask portion.

[0007]

According to the first to third aspects of the present invention, thick-film printing has already been performed.
Therefore, when screen printing is further performed on a thick film printed substrate having undulations, irregularities, etc. on the surface, a screen having a convex portion provided on the back surface of the screen along the end of the mask portion of the print mask is used. Done. As a result, the undulations or irregularities of the substrate are absorbed by the convex portions formed on the back surface of the screen during printing, and even if a large number of substrates are continuously printed using the same print mask, a stable and fine thick film is formed. A pattern is formed.

Further, the convex portion can be formed only in a predetermined portion of the opening portion of the print mask which particularly needs to prevent the paste from flowing around. For example, the convex portion is provided only along the fine pattern portion of the pattern to be printed, and is not particularly formed in a portion having a large area and not greatly affected by the print paste flowing around the back surface of the mask portion.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. In recent years, the density of the thick-film multilayer substrate has been increasing, and accordingly, it is required to cope with miniaturization of the pattern. As shown in FIG. 4, the thick film multilayer substrate 1 is formed by printing and firing a silver conductive paste on a ceramic substrate 2 to form a lower conductive wiring 3, and printing and firing an insulating paste a plurality of times to cover the lower conductive wiring 3. To form an insulating film 4. At this time, a plurality of via holes 5 are simultaneously formed at arbitrary positions in the insulating film 4. In particular, the manufacturing method according to the present invention is effectively used in forming a thick-film multilayer substrate having a via hole portion requiring miniaturization.

Next, a silver conductive paste is printed and baked so as to fill a plurality of via holes 5 formed in the insulating film 4 to form a via fill 6. Further, the upper conductor wiring 7 is formed by screen printing and firing. The diameter of the via hole is usually designed to be 300 μm.
As described above, the thick-film multilayer substrate 1 is formed by patterning various thick-film pastes by a printing technique and firing them.

In the present invention, the printing method of the thick film paste is the same as the usual method as shown in FIG. 5, in which the paste 9 is applied to a previously patterned thick film screen, and a desired printing pressure 10 is applied. The paste 9 is extruded from the opening of the print mask and transferred onto the ceramic substrate 2 by patterning by moving the thick film screen at a constant speed in parallel with the ceramic substrate 2 while pressing the thick film screen onto the ceramic substrate 2 with the squeegee 11. Is what you do.

In this embodiment, particularly, as shown in FIG. 1, a portion of the via hole of the insulating film, which is most required to be miniaturized, for example, is printed on the ceramic substrate 2 side, that is, on the screen back surface 20 side. At the end of the mask portion of the mask, a projection, that is, a convex portion 13 is formed. As a result, as shown in FIG.
Even if the undulations on the surface are absorbed by the convex portions 13 and printing is performed continuously using the same print mask 8, stable and fine via holes can be formed. The present invention is not limited to the formation of an insulating film having such via holes, but can be used for forming other thick films such as conductor wiring.

In this embodiment, FIGS. 2 (a) to 2 (c)
As shown in (1), the convex portion 13 is formed by performing pattern processing on the printing screen twice. The print mask manufacturing process and the pattern processing process are basically the same as the conventional mask manufacturing process. In the conventional mask manufacturing process, as shown in FIG. 6, first, a stainless steel mesh in which stainless steel wires 15 are braided in a lattice shape on a screen frame 14 is fixed without loosening. Next, a certain amount of the emulsion 12 is applied to the front and back of the stainless mesh. Emulsion 12
Is produced by, for example, curing polyvinyl alcohol or vinyl acetate with a diazo-based curing agent. further,
A photosensitive film 16 is formed on the upper surface of the emulsion 12, a positive film 17 on which a pattern is drawn is overlaid, exposed, and developed to form an arbitrary mask pattern.

In this embodiment, after the stainless steel mesh is fixed to the screen frame 14, first, as shown in FIG. 2A, two layers of the emulsion 12 forming a print mask portion and a convex portion are applied to the screen, respectively. I do. Next, FIG.
As shown in (b), both layers form the same pattern as the print mask pattern. Then, as shown in FIG. 2C, pattern processing of the convex portion 13 is performed on the emulsion for the convex shape. In this case, the convex portions 13 are formed so as to surround four sides of the normal print mask pattern as shown in FIG. As shown in FIG. 3, the convex portion 13 may be formed only on two opposing sides in a direction perpendicular to the traveling direction (printing direction) of the squeegee 11, for example. The same effect as in the case of forming as described above can be obtained.

The emulsion 12, as used to form a conventional thick film print mask, ie, as used in the print mask 8, has some elasticity. However, the swell of the lower conductor wiring 3 cannot be absorbed only by the emulsion in the portion where the normal pattern processing including the screen mesh is performed. Therefore, the convex portion 13 is formed locally at the end of the mask portion of the print mask by using an emulsion separately. The locally formed convex portion 13 absorbs the undulation on the surface of the lower conductor wiring 3 by appropriate elasticity.

In the present application, the shape of the convex portion is not particularly limited. The cross-sectional shape can be set to a shape that easily elastically responds to undulations and irregularities on the substrate surface. For example, in addition to the rectangular shape shown in FIGS. 1A and 1B, the shape may be substantially semicircular, triangular, or the like. Also, the height of the convex portion is not particularly limited, but it is preferable that the height of the convex portion is about 程度 of the mesh thickness in order to absorb the undulation caused by the mesh of the screen. Furthermore, the material for forming the convex portions is not particularly limited to the emulsion for forming the thick film print mask, and the method for forming the convex portions 13 is not limited to the above method. Not even.

The projections 13 formed on the back surface of the screen absorb the undulations on the surface of the lower conductor wiring 3, and the paste 18 adheres to the back surface of the print mask 8 near the pattern processing during printing. Is prevented.

[Brief description of the drawings]

FIG. 1A is a sectional view according to an embodiment of the present invention. (B) A partially enlarged view showing a printing state according to one embodiment of the present invention.

FIG. 2 is a schematic view showing a manufacturing process of the printing screen according to the present invention.

FIG. 3 is a diagram showing another example of a convex shape pattern.

FIG. 4 is a cross-sectional view of a thick film multilayer substrate.

FIG. 5 is a schematic diagram showing a normal screen printing state.

FIG. 6 is a schematic view showing a manufacturing process of a conventional printing screen.

FIG. 7A is a partially enlarged cross-sectional view showing a printing state according to a conventional method. (B) Sectional drawing which shows the printing result by the conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thick film multilayer board 2 Ceramic substrate 3 Lower conductor wiring 4 Insulating film 5 Via hole 6 Via fill 7 Upper conductor wiring 8 Print mask 9 Paste 10 Printing pressure 11 Squeegee 12 Emulsion 13 Convex part 14 Screen frame 15 Wire 16 Photosensitive film 17 Positive film 18 paste 19 gap 20 back

Claims (3)

[Claims] 1. A method for manufacturing a thick-film multilayer circuit board, comprising a step of screen-printing and firing a plurality of thick-film pastes on an insulating substrate. A new thick film paste is screen-printed using a screen having a convex portion provided on the back surface of the screen along the edge of the portion. 2. The method according to claim 1, wherein the convex portion is formed only on a predetermined portion of an end of the mask portion of the print mask. 3. A thick-film printing screen on which a printing mask is formed, wherein a convex portion is formed on an underside of the screen along an edge of a mask portion of the printing mask. screen.