JPH10200236A - Manufacturing method of wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the plainness of an insulation film to improve the forming accuracy of a fine wiring, by forming trenches for a circuit pattern into the insulation film, using a laser beam machine, applying a conductive paste to the insulation film, heat treating it and polishing insulation film surface. SOLUTION: A laser beam is radiated on the surface of an insulation film 3 above a first layer wiring 2 to bore vias 5, thereby exposing this wiring 2. The beam is radiated on other area of the insulation film 3 for forming a second layer wiring to form openings (trenches) 6. A conductive paste 7 contg. conductor metal particles dispersed in an org. solvent is applied to the surface of the film 3 to fill the paste 7 in the vias 5 and openings 6 and heated in a low pressure atmosphere to gasify the org. solvent in the paste 7 and bake the particles in the paste 7. Excessive baked metal particles on the surface of the film 3 are removed by polishing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a wiring board, and more particularly to a method of forming a circuit pattern.

[0002]

2. Description of the Related Art A method of manufacturing a wiring board by forming a circuit pattern using a conductive paste as a conductor does not involve chemical treatments such as plating and etching, so that additional equipment including waste liquid treatment is not required. Because of the necessity, a wiring board can be manufactured at low cost and has been widely adopted. Specific examples of a method of manufacturing a wiring board using the conductive paste include a method disclosed in Japanese Patent Application Laid-Open No. 8-37376, in addition to a known screen printing method.

[0003] A method of manufacturing a multilayer circuit board disclosed in the publication will be described with reference to FIG. FIG.
FIG. 2 is a cross-sectional view showing a manufacturing process of the multilayer circuit board disclosed in the publication. First, as shown in FIG. 2A, a first-layer wiring 2 is formed on an insulating substrate 1 made of aluminum nitride, silicon, or the like. Thereafter, an insulating film 3 having a thickness of about 20 μm is formed on the insulating substrate 1, and the first wiring 2 is covered with the insulating film 3. Insulating film 3
When a polyimide is used as the material, a liquid polyimide is spin-coated on the insulating substrate 1, which is heated and solidified to form the insulating film 3.

Thereafter, as shown in FIG. 2B, a protective film 4 made of, for example, thermoplastic polyimide and having a thickness of about 20 μm is attached on the insulating film 3. Next, FIG.
As shown in (c), the protective film 4 and the insulating film 3 on a part of the first-layer wiring 2 are irradiated with an excimer laser.
Drill holes in those irradiation areas. As a result, a via hole 5 having a size of 20 μm × 20 μm is formed in the insulating film 3.

[0005] Subsequently, the irradiation energy of the excimer laser is reduced, and the region of the protective film 4 where the second-layer wiring is to be formed is irradiated with the excimer laser. Thus, an opening (groove) 6 is formed in a portion of the protective film 4 along the second-layer wiring.

Thereafter, as shown in FIG. 2D, a conductive paste 7 made by dispersing a metal ultrafine particle of a conductor such as gold or silver palladium in an organic solvent is applied on the protective film 4, and The conductive paste 7 is filled into the via hole 5 and the opening 6. Subsequently, the insulating substrate 1 is heated in a reduced-pressure atmosphere at a temperature of about 300 ° C. to vaporize the organic solvent in the conductive paste 7 and
The ultrafine metal particles are fired to form a film.

Next, when the protective film 4 is peeled from the insulating film 3, a via 8 is formed in the via hole 5 of the insulating film 3 as shown in FIG. A second-layer wiring 9 made of a fired metal ultrafine particle is formed.

[0008]

However, in this manufacturing method, since the surface has irregularities as shown in FIG. 2E, an insulating film is further formed thereon to form a third-layer wiring. In the case of multi-layering, sufficient planarity of the insulating film cannot be obtained, and it is difficult to accurately form fine wiring. In addition, there is also a problem that even when an attempt is made to mount a component on this surface, the unevenness impairs the mountability.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and the invention according to claim 1 is directed to forming a groove for a circuit pattern in an insulating film by using a laser processing machine. And applying a conductive paste formed by dispersing ultrafine particles of a conductive substance in a solvent on the insulating film,
A method for manufacturing a wiring board, comprising: a step of removing the solvent of the conductive paste applied by heat treatment and baking ultra-fine particles of the conductive substance; and a step of polishing a surface of the insulating film. ”.

[0010]

Embodiments of the present invention will be described below with reference to FIG. FIG. 1 is a cross-sectional view illustrating a manufacturing process of a method for manufacturing a wiring board according to the present invention. The wiring board according to the present invention uses a flat insulating substrate 1 made of, for example, epoxy resin or glass fiber reinforced epoxy resin as a base. Then, as shown in FIG. 1A, a first-layer wiring 2 is formed on the surface of the insulating substrate 1. Although the details of the method of forming the first-layer wiring 2 are omitted, for example, the following method may be used. That is, a so-called copper-clad laminate in which a copper foil is previously laminated on the insulating substrate 1 is used, a dry film is attached to the copper foil, exposed to ultraviolet light through a photomask, and further exposed to a 1% aqueous sodium carbonate solution. After the development, an etching treatment is performed with an aqueous cupric chloride solution. After completion of the etching process, the dry film is peeled off to obtain the first-layer wiring 2.

Next, as shown in FIG. 1B, an insulating film 3 is applied and formed on the insulating substrate 1 on which the first-layer wiring 2 is formed. The insulating film 3 is mainly composed of a liquid resin that is hardly soluble in an oxidizing agent, and is formed by dispersing an inorganic powder that is soluble in the oxidizing agent in the resin (resin liquid). In addition, the resin (resin liquid) contains a small amount of a stress relaxing agent or an additive for imparting impact resistance during machining.

As will be described later, before applying the conductive paste 7 on the insulating film 3, harmless permanganate is mainly used without using harmful substances when chemically roughening the insulating film 3. The material of the insulating film 3 is selected in advance as follows so that the chemical roughening treatment can be performed with the oxidizing agent. When the surface of the insulating film 3 is roughened by using an oxidizing agent as described later, the inorganic powder exposed on the surface of the insulating layer 3 by the oxidizing agent dissolves out. The surface roughness of the inorganic powder (calcium carbonate) is 15 μm in consideration of the surface roughness and laser processing.
The following (average particle size: 1 μm to 5 μm, more preferably 2 μm
μm to 4 μm is good), and the content is set to 15 to 35 parts by weight, respectively.

Here, the material of the insulating film 3 will be described in more detail. Examples of the resin (resin liquid) having low solubility in an oxidizing agent include, for example, bisphenol A-based epoxy resin 100 parts by weight Curing agent 10 parts by weight. As an inorganic powder that is soluble in an oxidizing agent, calcium carbonate (average particle size: 1 μm to 5 μm)... 15 to 35 parts by weight. As a material for imparting impact resistance during machining, a stress relieving agent (polybutadiene): 10 to 20 parts by weight. As other materials, a small amount of an additive is prepared, and after a plurality of the above-mentioned materials are sufficiently diffused in a liquid state, a curtain coating method or the like is formed on the insulating substrate 1 on which the first-layer wiring 2 is formed. The insulating film 3 is formed by applying a thickness of about 50 μm to 100 μm using a screen printing method or the like, and further thermally curing it in a furnace at about 150 ° C. for about 40 minutes. In this embodiment, the thickness is set to about 75 μm.

Next, as shown in FIG. 1C, the first layer wiring 2 formed on the insulating substrate 1 and the second layer wiring 9 formed on the insulating film 3 are electrically connected. To this end, a laser beam is irradiated from a predetermined position on the surface side of the insulating film 3 above the first-layer wiring 2, a via hole 5 is formed, and the first-layer wiring 2 is exposed. Similarly, at this time, the openings (grooves) 6 are formed by irradiating the laser light to other positions on the insulating film 3 where the second-layer wirings are to be formed. It is generally said that laser light is not very suitable for inorganic substances, but here,
By setting the particle size and content of the calcium carbonate powder contained in the insulating film 3 as described above, and irradiating a laser beam under the following conditions, the via hole 5 can be easily formed.

The cross-sectional shape of the via hole 5 is such that the land on the wiring 2 side of the first layer has a small diameter and the land on the wiring 9 side of the second layer has a tapered shape with a large diameter. 5 is easily filled with the conductive paste 7. This is the same for the opening 6. This tapered shape can be realized by controlling the focal position of the laser light, controlling the pulse width, controlling the energy density of the laser light, controlling the pulse energy, and the like.

Various laser beams for processing a wiring board have been proposed, but a via hole 5 and an opening 6 are formed in the insulating film 3.
As a laser beam for forming a hole, a short pulse CO2 laser and a KrF laser can be used. Practically, a short-pulse CO2 laser is optimal because of the availability of a laser light source and the quick processing time. Here, the reason for irradiating the laser light in a pulsed manner is to apply thermal energy to the insulating film 3 without applying excessive thermal energy to the insulating film 3 to prevent thermal deformation of the insulating film 3. The pulse interval of the CO2 laser beam is set to, for example, about 0.003 to 0.02 seconds.

Also, via holes 5 and openings 6 are formed in insulating film 3.
There are a conformal mask method, a mask imaging method, a contact mask method, a direct imaging method, and the like as a laser processing method for forming a hole, and the mask imaging method and the direct imaging method are preferable.

Thus, the via hole 5 and the opening 6
Then, in order to roughen the surface of the insulating film 3 formed on the insulating substrate 1, the inner wall of the via hole 5, and the inner wall of the opening 6, an oxidizing agent mainly containing permanganate is used. Oxidizing agent treatment (chemical roughening treatment).

Here, as the oxidizing agent treatment, an aqueous solution of caustic soda, a solvent, etc. is used for lubrication in the first step, and potassium permanganate (permanganate), caustic soda, etc. An aqueous solution of sulfuric acid or another is used in the third step of pickling.

Particularly, at the time of oxidizing agent treatment (at the time of chemical roughening treatment)
As described above, the surface of the insulating film 3, the inner wall of the via hole 5, and a part of the inner wall of the opening 6 are made of a resin which is hardly soluble in the oxidizing agent and a resin which is slightly soluble in the oxidizing agent. Although the calcium carbonate shown is exposed, only the exposed calcium carbonate is potassium permanganate (permanganate)
It is easily melted and roughened.

The above-mentioned potassium permanganate (permanganate) is a harmless oxidizing agent, and has no trouble at the time of oxidizing agent treatment (at the time of chemical roughening treatment) and has a versatile treatment system. It can be used, does not need to pay attention to wastewater treatment, does not cause environmental pollution problems, and reduces running costs.

Next, as shown in FIG. 1D, a conductive paste 7 obtained by dispersing ultrafine metal particles of a conductor such as gold or silver palladium in an organic solvent is applied to the surface of the insulating film 3, The conductive paste 7 is filled into the via hole 5 and the opening 6. Subsequently, this is heated at a temperature of about 300 ° C. in a reduced-pressure atmosphere to evaporate the organic solvent in the conductive paste 7 and bake the ultrafine metal particles in the conductive paste 7.

Next, excessive burned metal ultrafine particles on the surface of the insulating film 3 are removed by polishing. This polishing is performed, for example, by buffing. Thereby, a wiring board as shown in FIG. 1E is obtained.

According to the method of manufacturing a wiring board according to the embodiment of the present invention described above, the insulating film 3 is formed by using a laser.
Since the openings 6 or via holes 5 in which the second-layer wirings 9 and vias 8 are to be formed are formed thereon, extremely high positional accuracy can be realized, and a high-density wiring pattern can be realized. Specifically, in the conventional screen printing, for example, the wiring pattern width is limited to about 250 μm and the interval between the patterns is limited to about 500 μm, whereas according to the manufacturing method according to the present embodiment, the wiring pattern width is limited. Is 100μ
m, and the interval between patterns can be 100 μm.

Further, since the conductive paste 7 is filled in the via hole 5 and the opening 6 and the burned excessive metal ultrafine particles are removed by polishing, the surface flatness can be made extremely high. Also in this regard, for example, when compared with the conventional screen printing, the flatness is 10 to 40 μm in the screen printing, whereas the flatness is 10 μm or less in the manufacturing method according to the present embodiment.

For this reason, even when another insulating film is further formed on the insulating film 3 of FIG. 1E and the processes shown in FIG. Flatness is obtained and high-precision fine wiring can be formed.
The mountability of components on the insulating film 3 is also improved. In the embodiment described above, an example in which the first-layer wiring 2 is formed by etching a copper foil laminated on the insulating substrate 1 has been described, but the wiring 2 on the insulating substrate 1 on which no copper foil is laminated is described. The opening (groove) 6 is formed directly by laser at
This may be filled with a conductive paste to perform the same processing as that of the second-layer wiring 9.

In the embodiment described here, the first-layer wiring 2 and the second-layer wiring 9 are formed on one surface of the insulating substrate 1, but the present invention is not limited to this. Needless to say, each wiring layer may be formed on both surfaces of one.

[0028]

As described above, according to the method of manufacturing a wiring board of the present invention, grooves for wiring and circuit patterns such as vias are formed on an insulating film by using a laser. Extremely high positional accuracy can be realized, a high-density fine circuit pattern can be realized, and the width and thickness of the pattern become constant, so that the conductor resistance becomes stable.

Further, after these grooves are filled with a conductive paste and heat-treated, the surface of the insulating film is polished to remove excess metal ultrafine particles, so that the flatness of the surface is extremely high. can do. For this reason, even when the substrate is multi-layered, highly accurate fine wiring can be formed, and the mountability of components on the insulating film is also improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a manufacturing process of a method for manufacturing a wiring board according to the present invention.

FIG. 2 is a sectional view showing a manufacturing process of a multilayer circuit board disclosed in Japanese Patent Application Laid-Open No. 8-37376.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 First-layer wiring 3 Insulating film 4 Protective film 5 Via hole 6 Opening 7 Conductive paste 8 Via 9 Second-layer wiring

Claims (1)

[Claims] 1. A step of forming a groove for a circuit pattern in an insulating film using a laser beam machine, and applying a conductive paste obtained by dispersing ultrafine particles of a conductive substance in a solvent on the insulating film. A method for manufacturing a wiring board, comprising: a step of removing the solvent of the conductive paste applied by heat treatment, baking ultra-fine particles of the conductive substance, and polishing a surface of the insulating film.