JP3633138B2 - Thick film multilayer circuit board and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thick film multilayer circuit board. In particular, a lower conductor wiring and an upper conductor wiring formed on an insulating substrate via an insulating film are electrically connected by a conductive via fill in a via hole formed in the insulating film. In particular, the present invention relates to thick film multilayer circuit boards that are connected to each other.
[0002]
[Prior art]
Conventionally, when forming a thick film multilayer circuit board by screen printing method including a printing and firing process on an insulating substrate such as a ceramic substrate, an insulating film having an opening serving as a lower conductor wiring, a so-called via hole in order on the insulating substrate, A conductive via fill filling the via hole, an upper insulating film for forming the upper portion of the via hole, and an upper conductor wiring formed on the upper insulating film are formed by a screen printing method.
[0003]
Here, regarding the formation of the via hole, the geometric shape of the via hole is preferably a simple and stable shape with no distortion or unevenness because of ease of manufacturing. Also, in order to ensure the electrical connection between the lower conductor wiring and the upper conductor wiring that are electrically connected through the via fill, the area of the lower conductor wiring exposed in the via hole and connected to the via fill should be as large as possible. desired. For this reason, conventionally, as shown in FIG. 4, there is a method of forming an insulating film by printing and baking an insulating paste in a pattern in which the lower openings of the via holes are all within the flat surface portion of the lower conductor wiring. Has been adopted. For example, a lower conductor wiring of 1.4 mm square is provided below a 1 mm square via hole.
[0004]
[Problems to be solved by the invention]
However, the following problems arise when the insulating film is formed in the conventional pattern in which the lower opening of the via hole is always within the flat surface of the lower conductor wiring by design.
[0005]
As shown in FIG. 4, the insulating paste printed on the flat portion of the lower conductor wiring 3 flows inside the via hole before being dried, thereby producing a sag 9. The sagging 9 generated on the surface of the flat lower conductor wiring covers most or all of the surface of the lower conductor wiring that should be exposed in the via hole, and the so-called via hole 5 may be crushed. For example, such sagging tends to occur particularly when the viscosity of the insulating paste is partially or wholly lowered for some reason. In such a case, even if a conductive via fill is filled in the via hole in the next step, there arises a problem that an electrical continuity failure occurs between the lower conductor wiring and the upper conductor wiring. In particular, recently, there is a demand for reducing the size of each pattern due to the necessity of high-density mounting, and accordingly, the width of the conductor wiring and the size of the via hole are also required to be reduced. The problem of sagging of the insulating paste is particularly significant in the miniaturized pattern.
[0006]
In view of this, the present invention prevents the poor conduction between the lower conductor wiring and the upper conductor wiring even when the insulating paste sag inside the via hole after the screen printing and before drying. The purpose is to.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, in the invention of claim 1, the lower conductor wiring and the upper conductor wiring are formed on the insulating film such as the ceramic substrate through the insulating film, and the lower conductor wiring and the upper conductor wiring are formed as the insulating film. In the thick film multilayer circuit board that is electrically connected through the via fill in the provided via hole, the lower opening of the via hole is connected to the end of the lower conductor wiring formed so as to have a step with the insulating substrate. It is arranged so as to extend across.
[0008]
With such a configuration, even when the insulating paste sags inside the via hole after screen printing of the insulating film, so-called collapse of the via hole can be prevented. That is, as shown in FIGS. 1A and 1B, by arranging the end 10 of the lower conductor wiring 3 so as to extend across the lower portion of the via hole 5, as shown in FIG. The sag 9 from one direction (the side where the ceramic substrate is exposed) can be made smaller than the sag 9 ′ from the other direction (the lower conductor side), and the collapse of the via hole 5 can be reduced.
[0009]
Further, as in the second aspect of the invention, in particular, by forming the lower conductor wiring with a narrow width in the lower opening of the via hole (see FIGS. 3C and 3D), both sides of the lower conductor wiring 3 are formed. In addition, the increase in the resistance value of the entire wiring can be suppressed even if the via hole portion is miniaturized.
[0010]
Furthermore, as in the invention of claim 3, the intermediate insulating film in which the via hole is provided may be a single layer. Costs can be reduced by reducing the number of times the insulating film is printed.
[0011]
Further, as in the invention of claim 4, the via fill 6 may be formed such that the upper conductor wiring is in direct contact with the lower conductor wiring when the upper conductor wiring is formed without using another conductive material. Reduction of materials and processes can be achieved.
[0012]
Further, in order to solve the above-mentioned problems, a thick film multilayer circuit board is provided with an insulating film having a via hole so that the end of the lower conductor wiring extends across the lower opening of the via hole. It is manufactured by forming.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
As shown in FIG. 1A, a thick film multilayer substrate 1 according to the present invention includes an insulating film 4, via fill 6, insulating film having an opening serving as a lower conductor wiring 3 and a via hole 5 on an insulating substrate such as a ceramic substrate 2. The film 4 and the upper conductor wiring 8 are sequentially formed by using a thick film screen printing method.
[0014]
As the ceramic substrate, a 96% alumina substrate is usually used, but beryllia, a silicon carbide (SiC) -based substrate, an aluminum nitride (AlN) substrate, or the like is used particularly when high thermal conductivity is required.
[0015]
First, the lower conductor wiring 3 made of a silver conductor paste is formed on the ceramic substrate 2 by printing and firing. After screen printing, it is left at room temperature for 5 to 15 minutes, dried at 100 to 150 ° C. for 10 to 20 minutes, and baked at 850 ° C. For the firing, a belt furnace is usually used in which the temperature profile is easily controlled and the gas after combustion is easily discharged. Instead of the silver conductor paste, a conductor paste such as a gold conductor paste, an Ag / Pd paste, or a Cu paste can be used. In particular, a gold conductor paste is preferably used when fine wiring is required, and an Ag / Pd-based paste is used when it is used under environmental conditions where migration is a problem. Although the film thickness of the lower conductor wiring 3 is not particularly limited, for example, 7 to 30 μm is appropriate in order to obtain sufficient conductivity. In particular, when it is necessary to form a sufficient level difference between the substrate and the substrate, it is preferable to form it as thick as about 15 to 30 μm.
[0016]
Next, an insulating paste is printed and fired so as to cover the lower conductor wiring 3. The insulation paste may be printed only once, but it is necessary to reliably insulate between the upper conductor wiring and the lower conductor wiring, and it is necessary to reduce the line capacity between the upper conductor wiring and the lower conductor wiring. In some cases, the insulating film 4 is formed by repeating printing and baking a plurality of times. At this time, a plurality of via holes 5 are simultaneously formed in the insulating film 4 at arbitrary locations. Although the size of the via hole 5 is not particularly limited, the diameter or width of the via hole 5 is preferably 300 μm or more in order to absorb the sagging effect of the insulating paste in the recess formed in the lower portion of the via hole. The via hole 5 is designed and arranged so that both the lower conductor wiring 3 and the ceramic substrate 2 are exposed in the lower opening. That is, the via hole 5 defined by the insulating film 4 is formed such that the end side 10 of the lower conductor wiring 3 extends across the lower opening of the via hole 5. The distance between the insulating film 4 and the edge 10 of the lower conductor wiring is determined in consideration of the thickness of the insulating film 4 and the viscosity of the insulating paste used. Under normal film forming conditions, the diameter or width of the via hole 5 should be about 1/3. In the present invention, the cross-sectional shape of the via hole 5 is not particularly limited. Although a square via hole is shown in FIG. 5, other shapes such as a circle may be used.
[0017]
Next, for example, a silver conductor paste is printed and fired so as to fill a plurality of via holes 5 formed in the insulating film 4, thereby forming the via fill 6. When the insulating film is thin, the printing / firing process of via fill 6 as a separate process is omitted, and the upper conductor wiring 8 is directly printed and fired to connect the conductive path between the lower conductor wiring 3. May be formed.
[0018]
Subsequently, as in the case of the insulating film 4, an upper insulating film 7 is formed through a printing / firing process using an insulating paste. Then, the upper conductor wiring 8 is formed on the upper insulating film 7 by printing and baking so as to be connected to the lower conductor wiring 3 through the via fill 6 in the via hole 5 using, for example, silver conductor paste.
[0019]
In the above method, as shown in FIG. 2, the via hole 5 is formed so as to straddle the end 10 of the lower conductor wiring 3 at a predetermined location of the lower conductor wiring 3. For this reason, both the lower conductor wiring 3 and the ceramic substrate 2 are exposed in the lower opening of the via hole 5. In the exposed edge 10 of the lower conductor wiring 3, a step 11 of about 15 to 30 μm is always formed between the ceramic substrate 2 and the surface of the lower conductor wiring 3 by the thickness of the lower conductor wiring 3. . Therefore, when the printed insulating paste sag inside the via hole 5 before drying, the sag 9 of the insulating paste printed at least on the exposed side of the ceramic substrate 2 (the right side in FIG. 2) 3 is a wall and is suppressed compared to the sagging 9 'from the other direction (lower conductor wiring side, left side in FIG. 2), and the via hole 5 is prevented from being crushed. As a result, as described above, the electrical connection failure between the lower conductor wiring 3 and the upper conductor wiring 8 is reduced.
[0020]
The insulating films 4, 7, the via fill 6, and the upper conductor wiring 8 are formed by screen printing, drying at 100 to 150 ° C., and baking at 850 ° C., like the lower conductor wiring 3. As the insulating substrate to be used, not only a single insulating substrate as shown in FIG. 1 but also a multilayer substrate in which electrical wiring has already been formed and the surface thereof is covered with an insulating film may be used.
[0021]
(Second embodiment)
As shown in FIGS. 3A and 3B, the lower conductor wiring 3 formed on the ceramic substrate 2 is disposed between the side walls on both sides of the insulating film 4 forming the via hole. The ends 10 of the lower conductor wiring 3 are arranged so as to face each other between the side walls of the insulating film 4 and serve as walls against sagging from the insulating films on both sides. As a result, there are two side steps at the bottom of the via hole 5 to prevent sagging of the insulating paste from the opposite two directions before drying. The via hole 5 can be prevented from being crushed even if there is some sagging from the direction of the lower conductor wiring part (vertical direction in FIG. 3). FIG. 3A is a schematic view of a cross section taken along line XX ′ of FIG.
[0022]
(Third embodiment)
FIGS. 3C and 3D show a case where the line width of the lower conductor wiring 3 is narrowed by a portion corresponding to the lower opening of the via hole 5, particularly the line width of the other lower conductor wiring 3. As in the case of FIGS. 3A and 3B, steps on both sides of the lower conductor wiring 3 can be utilized in the lower portion of the via hole 5. By making the sagging of the insulating paste from the two opposing directions along the conductor wiring smaller than the sagging from the other direction (direction of the conductor wiring), the via hole 5 can be prevented from being crushed. Since the width of the lower conductor wiring is formed thin only in the via hole 5, the influence on the resistance value of the entire lower conductor wiring is extremely small. FIG. 3B is an example in which the central portion of the lower conductor wiring 3 is thinned, and FIG. 3C is an example in which one side of the lower conductor wiring 3 is thinned.
[Brief description of the drawings]
FIG. 1A is a sectional view according to a first embodiment of the present invention.
(B) The top view of the via-hole part which concerns on this invention.
FIG. 2 is a cross-sectional view after forming an insulating paste in a via hole portion according to the present invention.
FIG. 3A is a sectional view of a via hole portion according to a second embodiment of the present invention.
(B) The top view of the via-hole part which concerns on 2nd Example of this invention.
(C) The top view of the via-hole part which concerns on 3rd Example of this invention.
(D) The top view of the via-hole part which concerns on 3rd Example of this invention.
FIG. 4 is a cross-sectional view of a via hole portion according to the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Thick film multilayer substrate 2 Ceramic substrate 3 Lower conductor wiring 4 Insulating film 5 Via hole 6 Via fill 7 Insulating film 8 Upper conductor wiring 9 Sagging 10 Edge 11 Step

Claims (7)

A thick film in which a lower conductor wiring and an upper conductor wiring are formed on an insulating substrate via an insulating film, and the lower conductor wiring and the upper conductor wiring are electrically connected through a via fill in a via hole provided in the insulating film. In the multilayer circuit board, an end side of the lower conductor wiring formed so as to have a step with the insulating substrate is disposed so as to extend across the lower opening of the via hole, and the via fill and A thick film multilayer circuit board which is in direct contact with the insulating substrate. 2. The thick film multilayer circuit board according to claim 1, wherein the lower conductor wiring is formed to have a particularly narrow width in a lower opening of the via hole. 2. The thick film multilayer circuit board according to claim 1, wherein the insulating film defining the via hole is a single layer. 2. The thick film multilayer circuit board according to claim 1, wherein the via fill is formed simultaneously with the formation of the upper conductor wiring. 2. The thick film multilayer circuit board according to claim 1, wherein the lower conductor wiring is disposed between side walls on both sides of the insulating film. A step of screen printing and baking a conductive paste for forming a lower conductor wiring on an insulating substrate, an insulating paste for forming an insulating film having a via hole, and a conductive paste for forming an upper conductor wiring; and further, in the via hole In a method for manufacturing a thick film multilayer circuit board including a step of forming a via fill that electrically connects the lower conductor wiring and the upper conductor wiring, an end side of the lower conductor wiring crosses a lower opening of the via hole. A method of manufacturing a thick film multilayer circuit board, wherein the insulating film is formed to extend , and the insulating paste is formed to expose the insulating substrate . 7. The method of manufacturing a thick film multilayer circuit board according to claim 6, wherein the via fill and the insulating substrate are in direct contact.

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