JPH114060A - Method for forming wiring on ceramic board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming interconnection on a ceramic board without using a means of photolithography or sputtering, in which a conductive interconnection having a minute interconnection width of not more than 50 μm can be readily formed on a ceramic green sheet or a burned ceramic substrate, without contaminating the green sheet or the fired substrate. SOLUTION: A laser beam 2 is irradiated on a sheet material 1 made of a resin film or a metallic plate to form an opening 5 for forming an interconnection. This sheet material 1 is fixed by being either thermo-compressed for bonding to a ceramic green sheet 3 or by applying an adhesive thereto for bonding to a burned ceramics substrate. Then, the opening 5 of the fixed sheet material 1 is embedded with a conductive paste 4 and dried, followed by separating the sheet material 1 from the green sheet 3 or the substrate, and is finally subjected to firing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a wiring on a ceramic substrate for mounting a semiconductor element, and more particularly to a method for forming a wiring on a multilayer ceramic substrate. More specifically, the present invention relates to a method for forming a ceramic substrate wiring capable of forming fine wiring having a line width of 50 μm or less on a ceramic green sheet or a fired ceramic substrate.

[0002]

2. Description of the Related Art Wiring on a ceramic substrate is generally performed by screen printing a conductive paste. The conductor paste is a paste (ink) formed by mixing fine metal powder with a binder resin and a solvent.

In the screen printing method, a mask having an opening (hole) of a predetermined wiring pattern is placed on a fired ceramic substrate or an unfired green sheet, and a conductive paste is filled into the opening of the mask using a squeegee. After the conductor paste is dried if necessary, the mask is removed and the conductor paste is fired. As a result, a metallic conductor wiring is formed on the ceramic substrate. In the case of a green sheet, the conductor paste and the green sheet are usually sintered simultaneously by firing.

A mask used for screen printing is called a screen mask or a mesh mask, and is usually formed by forming a thin film having an opening of a predetermined wiring pattern on a metal or resin mesh. This thin film is formed using a photosensitive emulsion or from a metal foil.
Instead of using a mesh, a thin metal plate having an opening of a predetermined wiring pattern formed by a technique such as etching or the like is used in part as a mask as it is.

[0005]

With the recent miniaturization and high integration of LSIs, ICs, etc., it is necessary to reduce the wiring width and the wiring interval of the ceramic substrate.
However, in the wiring formation by the screen printing method described above,
The limit of the conductor wiring width is 100 μm, and when trying to form wiring smaller than 100 μm (for example, 50 μm or less),
When printing screens, there will be a "printer" or "blurred"
Further, variation in wiring width also increases, and disconnection particularly easily occurs.

Several methods for forming fine conductor wiring have been proposed so far. For example, JP-A-63-265493
In other publications, a method of forming a wiring by a photolithography method or a sputtering method has been proposed. Although this method is excellent in terms of miniaturization of wiring, it is difficult to commercialize from the viewpoints of productivity and cost, because the wiring forming process is complicated or requires a large-scale apparatus.

Japanese Patent Application Laid-Open No. 54-79473 discloses a method of forming a wiring pattern using a laser. In this method, a support film used for forming a green sheet is irradiated with a laser to form an opening in only the support film or in both the support film and the green sheet, and a conductive paste is embedded in the opening, and the support film is formed. Is to be peeled off. It is described that if the opening penetrates the green sheet, formation and filling of through holes can be achieved simultaneously in addition to conductor wiring.

The method disclosed in Japanese Patent Application Laid-Open No. 54-79473 is advantageous in cost because it does not require the production of a mask, and has the advantage that the width of the wiring can be reduced by using a laser aperture. However, since the laser processing is performed while the support film is stuck to the green sheet, it is difficult to selectively form an opening only in the support film, and a hole is formed so as to completely penetrate the support film. The missing or incomplete holes in the green sheet beneath it can only produce unreliable products. Also, since the conductor wiring and the through hole have different shapes, it is impossible to simultaneously form the conductor wiring and the through hole by laser processing the support film and the green sheet by this method.

Furthermore, according to the method described in this publication, the support film is easily peeled off by the heat of the laser during the laser processing, so that the conductive paste adheres also to the part that was peeled off when the conductive paste was filled, and the shape of the wiring collapsed. It becomes difficult to form fine wiring. Furthermore, the support film is melted or decomposed by heat during laser processing, but at that time, carbide may remain on the support film,
In the firing process, pores are formed, which has an adverse effect on the green sheet, such as a decrease in reliability.

Japanese Patent Application Laid-Open No. 55-118654 discloses that a photosensitive film laminated on a mylar film is provided with an opening for forming a conductive circuit by exposure and development through a mask, and a conductive paste is formed in the opening. After embedding, a green sheet is formed on a photosensitive film, a through-hole is further opened by a laser, a conductor paste is embedded in the green sheet, and then the above-mentioned films are peeled off. Has been proposed.

Although this method can achieve both the formation and filling of the conductor wiring and the through hole, the process is very complicated because of the use of the photolithography method, and the equipment and material costs are high. Furthermore, during laser processing, a melt or decomposition residue of the green sheet or film adheres to the surroundings, and has the same adverse effect on the green sheet as described above.

An object of the present invention is to provide a method for forming a wiring on a ceramic substrate which can easily and reliably form a fine conductive wiring having a wiring width of 50 μm or less without using a method such as photolithography or sputtering. That is.

Another object of the present invention is to form a wiring pattern on a green sheet or a fired ceramic substrate by using laser processing. However, the residue of laser processing does not adhere to the green sheet or the ceramic substrate. It is an object of the present invention to provide a method for forming a wiring on a ceramic substrate, which eliminates the adverse effects of the method.

[0014]

The above object is achieved by the following and the present invention. A sheet material having an opening for forming a wiring formed by laser processing is fixed to a ceramic green sheet by thermocompression bonding, a conductive paste is embedded in the opening of the fixed sheet material, and after drying, the sheet material is peeled off from the green sheet. Forming a wiring on a ceramic substrate.

A sheet material having an opening for forming wiring formed by laser processing and having an adhesive applied to one side is fixed to the ceramic substrate via the adhesive, and the opening of the fixed sheet material is provided. A method for forming wiring on a ceramic substrate, comprising: embedding a conductive paste in a ceramic substrate; and drying the sheet material from the ceramic substrate after drying.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for forming a wiring on a ceramic substrate according to the present invention can be applied irrespective of the type of the ceramic substrate or the conductive paste. Therefore, the material and composition of the ceramic and the conductive paste are not particularly limited.

As the material of the ceramic substrate, in addition to various high-temperature sinterable ceramic materials such as alumina, aluminum nitride, mullite, cordierite, and the like, glass ceramics, 1100 ° C. or less, preferably 1000 A low-temperature sintering type ceramic material that can be fired at a temperature of not more than ° C. is also applicable.

In the present invention, a conductive paste pattern can be formed on both the ceramic substrate before firing (ie, the ceramic green sheet) and the ceramic substrate after firing. The green sheet used in the method of the present invention is not particularly limited, and can be formed by any conventionally known method or composition.

When applied to a ceramic green sheet, a conductive paste of a type suitable for the firing temperature of the ceramic material to be used is selected. That is, when the ceramic material is of a high-temperature sintering type, Mo, W, Mo-
It is necessary to use a paste containing high melting point metal powder such as Mn. On the other hand, when the ceramic material is a low-temperature sintering type, Cu paste, Ag, Au, Ag-Pd
It is possible to use such a noble metal paste.

In order to form fine wiring, it is advantageous that the conductive paste has a good binder removal property and that the printed paste does not drop when the conductive paste is embedded. In that sense, as a binder for the conductor paste, a cellulose-based binder generally used conventionally has been used.
It is more preferable to use an acrylic resin, polypropylene, polycarbonate, or the like having good binder removal properties than (eg, ethyl cellulose). Further, from the viewpoint of preventing print dripping, it is desirable that the viscosity of the conductive paste be in the range of 10,000 to 50,000 cps. Conductor paste is metal fine powder,
In addition to the binder and the solvent, other components such as a glass frit may be contained.

According to the present invention, instead of the mask having openings formed corresponding to the wiring patterns used in the conventional screen printing method, such openings are formed by laser processing with a suitable material such as resin or metal. Is used for forming a conductive paste pattern by thermocompression bonding to a green sheet or fixing to a ceramic substrate via an adhesive.

Hereinafter, the method of the present invention for forming a conductive paste pattern on a ceramic green sheet will be described.
This will be described in detail with reference to FIG.

First, a sheet material 1 having an appropriate thickness is prepared. The thickness of the sheet material determines the thickness of the conductive paste, and thus the thickness of the wiring pattern to be formed.
The conductor paste is considerably thick in the thickness direction (Z direction) during firing.
(Example: about 20 to 40%) Since the sheet material 1 shrinks, the thickness of the sheet material 1 is determined in consideration of the desired thickness of the wiring pattern and the shrinkage rate in the Z direction at the time of firing.

In the present invention, the sheet material 1 having the opening formed thereon is thermocompression-bonded to the green sheet 3 and then the conductive paste 4 is formed.
Is embedded in the opening, so that the conductive paste can be uniformly and reliably embedded even when the opening is deep. Therefore, it is possible to form a thicker conductor wiring pattern than before. Therefore, the thickness of the sheet material 1 can be from about 10 μm to a maximum of about 1000 μm, and may be appropriately selected according to the strength and flexibility of the material.

The material of the sheet material 1 is not particularly limited as long as it can be laser-processed with high precision and has heat resistance and strength enough to withstand the subsequent thermocompression bonding or squeegee embedding of the conductive paste. Metal. In the case of a resin, a resin that does not generate a toxic gas by laser processing is preferable. As the resinous sheet material, a thermoplastic resin film such as polyolefin such as polyethylene and polypropylene, polyester, polyamide and polyvinyl acetate is preferable, but a thermosetting resin film can also be used. As described later, a green sheet that does not soften or melt under thermocompression bonding conditions is used. Suitable examples of metallic sheet materials include copper, aluminum, stainless steel,
Molybdenum, tungsten, and the like can be given.

The sheet material 1 is irradiated with a laser 2 in a pattern to form an opening 5 for forming a wiring corresponding to a desired wiring pattern in the sheet material [FIG. 1 (a)]. Laser pattern irradiation can be achieved by known control means such as moving a sheet material on an XY moving table. The type of laser may be selected in consideration of the material of the sheet material 1, and for example, a YAG laser, a CO ₂ laser, an excimer laser, or the like can be used.

When the sheet material 1 is a resin film,
To enhance laser energy absorption, a small amount of a dye having an absorption maximum near the laser wavelength (eg, a cyanine dye) may be contained in the resin film. Thereby, the irradiation amount of the laser can be reduced. Since only the sheet material 1 is laser-processed alone, the residue does not adhere to the green sheet, so that adverse effects on the green sheet can be avoided.

The width of the opening formed in the sheet material by laser processing is not particularly limited, but is preferably
It is 30-100 μm, more preferably 30-50 μm. In the present invention, it was impossible with the conventional screen printing method,
Even in such an opening having a small line width, a conductor wiring can be formed without disconnection.

Next, the sheet material 1 in which the wiring forming openings 5 of the predetermined pattern are formed is fixed to the green sheet 3 by thermocompression bonding [FIG. 1 (b)]. The green sheet 3 contains a binder, and as can be seen from lamination by thermocompression bonding when forming a multilayer, other materials can be fixed by thermocompression bonding involving a binder.

In the thermocompression bonding, the green sheet 3 and the sheet material 1 may be overlapped and heated under pressure. The thermocompression bonding conditions may be determined according to the type of the binder in the green sheet, and may be the same as, for example, the conditions used when laminating the green sheets. However, since the sheet material 1 is later peeled off, it is not preferable to strongly bond the sheet material 1 and the green sheet 3, and it is preferable that the heating time under pressure is short, for example, 1 minute or less.

When the sheet material is a resin film, if the resin film is softened and melted during the thermocompression bonding, the shape of the opening formed in the film is broken. Therefore, when a thermoplastic resin film is used, the thermocompression bonding conditions are set so that the binder in the green sheet is softened and melted, but the resin film is not melted and softened.

Although not shown, the green sheet 3
It may have a through hole. In this case, it is preferable to fill the through-hole with the conductive paste first and then heat-press the sheet material 1.

Thereafter, a conductive paste 4 is embedded in the opening of the sheet material 1 which has been thermocompression bonded to the green sheet 3 [FIG. 1 (c)]. This operation may be performed using a squeegee in the same manner as in conventional screen printing. Since the sheet material 1 acting as a mask is thermocompression-bonded to the green sheet 3, there is no gap at the interface between the sheet material around the opening and the green sheet, and they are in close contact. As a result, the conductive paste can be uniformly and completely filled into every corner of the opening, and since there is no protrusion at the interface, the outline is clear even in a narrow and / or deep opening, and the disconnection is prevented. The conductor paste can be embedded so as not to occur.

Next, the green sheet 3 is dried to remove the solvent in the conductor paste 4 and, if necessary, the solvent remaining in the green sheet 3, and to remove the stickiness of the conductor paste to remove the next sheet material 1. Facilitates peeling.
If the drying is not performed, the sheet material is hardly peeled off, and the wiring may be broken at the time of peeling. The drying temperature may be selected according to the composition of the conductor paste or the green sheet, particularly the solvent used. It is preferable that the drying temperature is not so high as to melt the binder in the green sheet or the conductive paste. Preferred drying temperature is 80-140 ° C
Is within the range.

Thereafter, the sheet material 1 is replaced with the green sheet 3
When peeled off, the wiring pattern of the conductive paste 4 remains on the green sheet [FIG. 1 (d)]. Peeled sheet material 1
Can often be reused at least several times as a mask. In that case, this sheet material is thermo-compressed to another green sheet, embedded with conductor paste, dried,
The sheet material is peeled off.

The thus obtained green sheet having the wiring pattern of the conductive paste is fired in the same manner as the green sheet having the wiring pattern formed by the conventional screen printing method to obtain a ceramic substrate. As we all know,
When a multilayer ceramic substrate is formed, two or more green sheets on which a wiring pattern of a conductive paste is formed are laminated by thermocompression bonding, and then fired. The sintering may be carried out in the same manner as in the prior art. If desired, the sintering may be performed while pressing in the thickness (Z) direction. The firing atmosphere is a non-oxidizing atmosphere when the metal in the conductor paste is copper, but is not particularly limited in other cases, and may be air firing.

When wiring is formed on a fired ceramic substrate instead of a green sheet according to the present invention, basically the same steps as above are performed. However, since the ceramic substrate does not contain a binder, the binder is not used. The fixing of the sheet material by thermocompression bonding, which was possible with the contained green sheet, cannot be adopted. Therefore, an adhesive is used for fixing the sheet material to the substrate.

That is, in this case, an adhesive is applied in advance to one surface of a sheet material having an opening for forming a wiring formed by laser processing. When the adhesive is applied to the ceramic substrate, the adhesive remains under the wiring, so the adhesive is applied to the opened sheet material. The application of the pressure-sensitive adhesive to the sheet material may be performed before or after the laser processing of the sheet material. After the application, the adhesive is dried while heating as necessary to remove the solvent used for applying the adhesive.

The pressure-sensitive adhesive, which is also called a pressure-sensitive adhesive, is an adhesive that can be adhered with a light pressure such as a finger pressure and that can be peeled off without staining the surface to be adhered, and is used for various kinds of adhesive tapes. Adhesives are roughly classified into rubber-based adhesives containing natural rubber or synthetic rubber, and acrylic-based adhesives containing an acrylic copolymer as a main component, and any of the adhesives can be used in the present invention.

The amount of the adhesive to be applied may be any as long as it can be fixed, and may be the same as the amount of an ordinary adhesive tape to be applied. An opening for forming wiring is formed by laser processing, and a sheet material coated with an adhesive before or after the laser processing is fixed to the ceramic substrate via the adhesive. This fixation can be achieved by simply placing the sheet material on the substrate with the pressure-sensitive adhesive applied surface facing downward, and pressing lightly from above. The ceramic substrate may be a single layer or a multilayer.

The conductor paste is buried in the opening of the sheet material fixed to the ceramic substrate in the same manner as described above, and after the conductor paste is dried and the sheet material is peeled off, the wiring pattern of the conductor paste remains on the ceramic substrate. . Since the adhesive was used for fixing, the sheet material could be easily peeled off from the ceramic substrate,
The adhesive residue hardly adheres to the ceramic substrate.
Even if the pressure-sensitive adhesive residue remains on the substrate, there is no inconvenience because the adhesive residue is lost during the subsequent firing of the conductor paste.

Also in this case, the sheet material coated with the adhesive can be reused about several times if the adhesive action of the adhesive remains. The firing may be performed under conditions that allow the conductive paste on the ceramic substrate to be sintered, and the firing atmosphere is appropriately selected as described above according to the type of metal in the conductive paste.

[0043]

Example: 100 parts of alumina powder having an average particle size of 2 μm, 10 parts of sintering aid (SiO ₂ ), binder (acrylic resin)
12 parts, 3 parts of a plasticizer (dibutyl phthalate), and 100 parts of a solvent (toluene) (both parts by weight) were mixed and mixed in a ball mill for about 10 hours to form a slurry. After removing bubbles in the slurry, the slurry was taped by a doctor blade method, dried at 100 ° C., and then cut into 70 mm square to produce a 150 μm thick green sheet.

As a sheet material, a polyethylene film having a thickness of 20 μm and a copper plate having a thickness of 20 μm were prepared, and each was cut into a 70 mm square. Using a YAG laser, each of the sheet materials was formed with 10 openings each having a width of 100 μm or 40 μm and a length of 50 mm for forming wiring.

The sheet material having the opening formed thereon is placed on the green sheet, and heated at about 90 ° C. and 70 k using a hot press.
Thermocompression bonding was performed for 30 seconds at g / cm ² . Next, a viscosity of 50,000 cps was applied to the opening of the sheet material solidified on the green sheet.
Was embedded with a squeegee and dried at 90 ° C. for 10 minutes.
Thereafter, the sheet material (polyethylene film or copper plate) was peeled off by hand to obtain a green sheet on which a wiring pattern of the conductive paste was formed.

The wiring pattern on the green sheet was observed with an optical microscope. As a result, there was no disconnection of the wiring, and a clear conductive paste wiring having a clear outline and no protrusion was formed on the green sheet.

Further, in order to confirm the disconnection of the green sheet on which the wiring pattern is formed after firing, the green sheet is laminated on another green sheet having through holes filled with tungsten paste by thermocompression bonding. And N ₂ + H ₂ + H ₂ O in a mixed gas atmosphere at 1500 ° C. for 1 hour. After firing, the wiring was electrically checked for disconnection, but no disconnection was found.

When the peeled polyethylene film and the copper plate were used again to form a wiring pattern of the conductive paste on another green sheet in the same manner as described above, two times with the polyethylene film and three times with the copper plate. Even when reused, the same clean wiring as in the first use could be formed.

On the other hand, as a comparative example, wiring was formed from the same tungsten paste as above by screen printing on the same green sheet as above using a mesh mask having wiring openings of the same shape as above. The presence or absence of disconnection was confirmed with an optical microscope. In this case, a wiring having a width of 100 μm could be formed without disconnection, but it was difficult to form a wiring having a width of 40 μm, and disconnection was confirmed in all the wirings.

[0050]

According to the method of the present invention, a photolithography method or a sputtering method is not used, and a relatively simple method is used. The outline is clear, there is no break, and the line width is 100 μm or less, particularly 50 μm or less. Wiring can be easily formed on a ceramic green sheet or a ceramic (fired) substrate. Also, since the laser processing of the sheet material is performed before fixing to the green sheet or the ceramic substrate, the green sheet and the ceramic substrate are not damaged, and the residue of the laser processing does not adversely affect the green sheet or the substrate. In addition, there is no performance deterioration of the substrate due to laser processing. Further, since the laser-processed sheet material can be reused several times, cost reduction is expected.

[Brief description of the drawings]

FIGS. 1A to 1D are explanatory views showing one example of a wiring forming method according to the present invention.

[Explanation of symbols]

 1: Sheet material (film or metal plate) 2: Laser 3: Green sheet 4: Conductive paste 5: Opening

Claims (2)

[Claims] 1. A sheet material having an opening for forming a wiring formed by laser processing is fixed to a ceramic green sheet by thermocompression bonding, a conductive paste is embedded in the opening of the fixed sheet material, and after drying, the sheet material is dried. A method for forming wiring on a ceramic substrate, comprising: 2. A sheet material having an opening for forming wiring formed by laser processing and having an adhesive applied to one side thereof is fixed to a ceramic substrate via the adhesive, and the fixed sheet material is A method for forming wiring on a ceramic substrate, comprising: embedding a conductive paste in an opening; and drying the sheet material from the ceramic substrate after drying.