JP2000312063A - Wiring board and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To provide a high-precision via-hole conductor even when a via-hole conductor is formed by using a laser beam, without having to change the design of a wiring pattern between an incident side surface and an exit side surface. And a method of manufacturing the same. An insulating substrate made of an insulating material containing at least an organic resin, and a plurality of wiring circuit layers formed on a surface and / or inside of the insulating substrate are formed between different ones of the wiring circuit layers. In a wiring board in which at least two wiring circuit layers 3a and 3b are connected by a via-hole conductor 4a in which a via hole is filled with metal powder, the via-hole conductor 4a has a vertical cross-sectional shape having an upper bottom and a lower bottom. Multiple blocks B with trapezoidal shape
The wiring circuit layers 3a and 3b are connected to the same trapezoidal bottom side of the via-hole conductor 4a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board applied to, for example, a package for accommodating a semiconductor device, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with the development of portable information terminals and the spread of so-called mobile computing in which a computer is brought in and operated, a small, thin, and high-definition wiring board tends to be required.

Conventionally, as a wiring substrate, for example, a ceramic substrate capable of high-density wiring has been widely used as a wiring substrate used for a package for housing a semiconductor element. This ceramic wiring board is composed of an insulating substrate such as alumina and a wiring conductor made of a high melting point metal such as W or Mo formed on the surface thereof. Is housed, and the recess is hermetically sealed by the lid.

However, since the ceramics constituting the insulating substrate of such a ceramic wiring board has a hard and brittle property, chipping or cracking of the ceramics is liable to occur in a manufacturing process or a transporting process. There are problems such as a low yield because the airtightness of the sealing may be impaired. Further, since firing shrinkage is caused by firing at a high temperature, there is a problem that deformation such as warpage, dimensional variation, and the like are likely to occur in the obtained substrate.

[0005] Therefore, recently, a fine circuit is formed by etching on the surface of an insulating substrate containing an organic resin to which a copper foil is adhered, and thereafter, this substrate is laminated to form a multilayer printed circuit board or a metal such as copper. A paste containing powder is printed on an insulating layer to form a wiring layer, and then laminated, or after lamination, a via hole is formed at a desired position by a microdrill, punching, or the like, and a metal is formed in the via wall by plating. There has been proposed a printed wiring board having a multilayer structure by attaching wiring layers and connecting wiring layers.

In order to increase the strength of such a printed board, an insulating board in which a spherical or fibrous inorganic material is dispersed in an organic resin has been proposed. Further, in order to reduce the size of the wiring board, it is required to reduce the diameter of the via-hole conductor, to be able to arrange the via-hole conductor at an arbitrary position, to miniaturize the wiring, and to increase the number of layers.

In response to such demands for multilayer printed circuit boards and fine wiring, recently, a via hole has been formed in each insulating layer using a microdrill or punching, and a low resistance has been formed in the via hole. After a via paste is formed by filling a conductive paste containing a metal powder, a conductive layer is formed, and an insulating layer is laminated to form a multilayer wiring board. According to this structure, a via hole conductor can be formed at an arbitrary position, so that it is suitable for miniaturization of a circuit, and a substrate capable of finer wiring is required.

[0008]

However, in the method of forming a via hole using a microdrill or punching, the diameter of the drill or the punch is at least about 0.15 mm, which is not suitable for the required fine processing. . In particular, when drilling holes using microdrilling or punching on an insulating sheet in which a fibrous inorganic material is dispersed in an organic resin, if the diameter of the via hole becomes smaller, the drill or punching pin may be used during drilling. There was a problem that it could break in and break.

The method of forming a via hole by irradiating a laser beam is very advantageous for forming a fine hole in that the diameter of the via hole can be arbitrarily adjusted by controlling the beam diameter of the laser beam.

However, as shown in FIG. 4, when irradiating a laser beam, the via hole conductor 10 has a shape of the laser beam of the insulating layer 11 because the laser beam is condensed and irradiated by an f-θ lens or the like. The hole diameter on the entrance side 10a is large and the hole diameter on the exit side 10b is small, and the vertical cross-sectional shape is substantially trapezoidal. Therefore, a large difference occurs in the via hole diameter on both surfaces of the insulating layer 11.

Therefore, the hole exit side 10 having a small diameter is used.
In b, although the hole interval can be reduced, the incidence side 10
When the insulating layer 11 becomes thicker because the hole diameter of the hole a is larger than the emission side 10b, short-circuiting occurs between adjacent via-hole conductors on the emission side 10b,
However, there is a problem that a wiring circuit layer connected to the circuit pattern cannot be formed in an electrically insulated state, which causes a short circuit failure between circuit patterns.

On the other hand, Japanese Patent Application Laid-Open No. Hei 8-116174 proposes that the diameter of a land, which is one of the wiring circuit layers connected to the via-hole conductor, be adjusted on the incident side and the output side. I have. However, this method has a problem that even if the density can be increased on the emission side, the density cannot necessarily be increased on the incidence side having a large via hole diameter.

Further, since the wiring circuit layer connected to the via hole conductor is necessarily designed to be larger than the via hole diameter on the surface of the insulating sheet, the wiring density of the wiring circuit layer depends on the incident side via hole diameter having the larger via hole diameter. And there is a limit to high-density wiring. Such a problem with the via hole diameter has become more remarkable as the thickness of the insulating sheet increases, as the hole diameter difference between the entrance side and the exit side increases.

As described above, when a via hole formed by irradiation with a laser beam is used, the diameter of the via hole is different between the incident side and the exit side of the laser beam. It is necessary to change the design of the pattern, which hinders the degree of freedom of the design, and causes problems such as a very troublesome design.

Therefore, according to the present invention, even when a via hole conductor is formed using laser light, it is not necessary to change the design of the wiring pattern between the incident side surface and the emission side surface, and the via hole conductor is provided with high accuracy. And a method of manufacturing the same.

[0016]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventor has found that a via hole conductor formed by irradiation with laser light and having a substantially trapezoidal vertical cross-sectional shape is filled with a conductive paste in a via hole conductor. When connecting two wiring circuit layers, the via-hole conductor is formed by stacking a plurality of blocks each having a substantially trapezoidal vertical cross-sectional shape.
By connecting the two wiring circuit layers to the same bottom side of the substantially trapezoidal shape of the via hole conductor, the via hole diameter of the connection portion between the wiring circuit layer and the via hole conductor can be made substantially the same, so that the above object can be achieved. Was found.

That is, the wiring board of the present invention comprises an insulating substrate made of an insulating material containing at least an organic resin, and a plurality of wiring circuit layers formed on the surface and / or inside the insulating substrate. In a wiring board in which at least two wiring circuit layers formed between different layers among the wiring circuit layers are connected by a via-hole conductor formed by filling a metal powder in a via-hole, the via-hole conductor has a vertical cross-sectional shape of an upper bottom. And formed by a laminate of a plurality of blocks having a substantially trapezoidal shape having a lower bottom,
The two wiring circuit layers are connected to the same bottom side of the substantially trapezoidal shape in the via hole conductor. In particular, in order to achieve fine wiring, the above-mentioned 2
Preferably, each of the two wiring circuit layers is connected to the upper bottom side of the substantially trapezoidal block in the via-hole conductor. The upper base side of this substantially trapezoidal shape is the emission side of the laser beam.

Further, the wiring board has the following structure: (a) the surface of a plurality of insulating sheets made of an insulating material containing at least a thermosetting resin is irradiated with a laser beam, so that the diameter of the via hole on the incident side becomes larger than the diameter of the via hole on the emitting side. Forming a substantially trapezoidal via hole having an upper bottom and a lower bottom with a smaller vertical cross-sectional shape, and then filling the via hole with a conductive paste containing a metal powder to form a via-hole conductor; A step of laminating a plurality of insulating sheets on which via-hole conductors are formed to produce a laminate in which one of an upper bottom and a lower bottom of the via-hole conductor is exposed on a front surface and a back surface; A step of forming a wiring circuit layer on both surfaces or forming a wiring circuit layer on one surface of the laminate and then laminating it with another laminate having a wiring circuit layer formed in the same manner A step of curing the thermosetting resin by heating the laminate obtained by (d) (c),
In particular, in the step (b), it is desirable to produce a laminate in which the upper bottom side of the via-hole conductor is exposed on the front surface and the back surface.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to a schematic sectional view showing an example of the wiring board of FIG. As shown in FIG. 1, a wiring board 1 of the present invention includes an insulating board 2 including at least a plurality of insulating layers 2 a to 2 c containing an organic resin, and a wiring circuit is provided on the surface and / or inside of the insulating board 2. Layer 3 is applied. The wiring circuit layers 3 formed between different layers are electrically connected by via-hole conductors 4.

According to the present invention, FIG. 2 shows an enlarged cross-sectional view of a main part of at least one via-hole conductor 4a among the via-hole conductors 4. According to FIG. 2A, the wiring circuit layers 3a provided on the upper and lower surfaces of the insulating layer 2a,
3b are electrically connected by via-hole conductors 4a. The via-hole conductor 4a has a structure in which a plurality of blocks each having a substantially trapezoidal cross section (hereinafter, simply referred to as substantially trapezoidal blocks) are stacked.
In the shape of FIG. 2A, the wiring circuit layers 3a, 3a
The space between b is formed by two substantially trapezoidal blocks B1 and B2. And these substantially trapezoidal blocks B1 and B2 are:
Both lower bases are joined together, and the wiring circuit layers 3a, 3b are all connected to the upper base side of the substantially trapezoidal blocks B1, B2.

As another form, as shown in FIG. 2B, the substantially trapezoidal blocks B1 and B2 can be connected to each other by connecting the upper and lower bases of the wiring circuit layers 3a and 3b. It will be connected to the lower bottom side of B1 and B2,
In any case, the wiring circuit layers 3a and 3b are all connected to the lower bottoms of the substantially trapezoidal blocks B1 and B2 in the via hole conductor 4a, and the via hole diameters of the upper surface and the lower surface of the insulating layer 2a are substantially the same. be able to.

Since the via-hole conductor 4a generally has a substantially circular cross section, each substantially trapezoidal block is formed by a tapered surface having a conical side surface. In particular, the wiring circuit layers 3a and 3b are connected to the upper bottom side of the substantially trapezoidal blocks B1 and B2, and are configured as shown in FIG. 2A. 3a and 3b can be wired at high density.

Further, as another embodiment, the wiring circuit layer 3
a, 3b, the via-hole conductor 4
As shown in FIG. 2 (c), the wiring circuit layers 3a and 3b can be connected even if the distance between the wiring circuit layers 3a and 3b is increased by connecting three or more substantially trapezoidal blocks B1 to B5 as shown in FIG. Both can be formed on the surface of the via hole conductor 4a having a small hole diameter.

According to the present invention, such a via-hole conductor 4
According to the structure of a, even if the interval between the wiring circuit layers 3a and 3b, in other words, the thickness of the insulating layer 2a is any interval,
The via hole diameter of the via hole conductor can be made constant. In particular, the thickness of the insulating layer 2a is 50 μm or more,
Furthermore, a via hole with high dimensional accuracy can be formed in the insulating layer 2a having a thickness of 100 μm or more.
A via-hole conductor having a fine via-hole diameter of 75 μm or less, particularly 50 μm or less, can be formed at the connection portion 3b with the via-hole conductor 4a.

Further, the difference between the diameters of the via holes at the connection with the wiring circuit layers 3a and 3b at both ends of one via hole conductor 4a can be reduced to 5 μm or less, and even when a via hole is formed, a via hole with high dimensional accuracy can be formed. it can.

(Material of Insulating Substrate) The material constituting the insulating layer 2 contains at least an organic resin, and is an epoxy resin, a triazine resin, a polybutadiene resin, a phenol resin, a fluorine resin, a polyimide resin. For example, resin commonly used for circuit boards is used,
In particular, PPE (polyphenylene ether), BT resin (bismaleimide triazine), epoxy resin, polyimide resin, fluororesin, phenol resin, and polyamide bismaleimide resin are desirable, and in particular, a thermosetting resin that becomes a varnish at room temperature as a raw material. Is desirable.

An organic resin obtained by impregnating the above organic resin with glass fiber as a reinforcing material is also preferably used. At this time, the glass fiber is desirably contained as a woven or nonwoven fabric. In particular, in order to form a uniform via hole, it is desirable that the woven fabric is defibrated so that a part of the fibers of the woven fabric is loosened and the thickness of the woven fabric is made uniform. In addition, glass fiber
It is desirable that the insulating layer be contained in a proportion of 30 to 70% by volume.

Further, in order to increase the strength of the insulating layer 2,
An inorganic filler can be added to the organic resin. As the inorganic filler, SiO ₂ , Al ₂ O ₃ ,
AlN or the like is suitably used, and as the filler, a substantially spherical powder having an average particle diameter of 20 μm or less, particularly 10 μm or less, and optimally 7 μm or less is used. In some cases, the dielectric constant of the insulating layer 2 can be increased by using a filler having a high dielectric constant. Further, the volume ratio of the organic resin to the inorganic filler is set to 85:15 to 15: 8.
By appropriately mixing at a ratio of 5, the thermal expansion coefficient of the insulating layer 2 can be adjusted.

(Wiring Circuit Layer) On the other hand, the wiring circuit layer 3 is made of a metal foil made of a low-resistance metal such as copper, copper, aluminum, or the like.
It is formed from a conductor containing a low-resistance metal powder such as gold or silver.
From the viewpoint of lowering the resistance, it is desirable to use a metal foil.

(Via Hole Conductor) The via hole conductor 4 has, for example, at least one or two or more alloys selected from the group consisting of copper, aluminum, gold, silver and the like, and has an average particle diameter of 0.1 to 0.1. It is formed from a conductor containing a 10 μm low-resistance metal powder. As the low-resistance metal, copper or an alloy containing copper is particularly desirable. In some cases, in addition to the above metals, a high-resistance metal such as a Ni—Cr alloy may be mixed or alloyed for adjusting the resistance of the circuit. Further, in order to reduce the resistance, the conductor composition may include a metal having a lower melting point than the low-resistance metal, for example, a metal having a low melting point such as solder or tin. In addition, in addition to the low-resistance metal, an organic binder and a solvent are added to the via-hole conductor as a binder between metal powders or to improve the filling property of the metal powder.

(Multilayer Substrate Structure) Further, as a structure as a multilayer wiring substrate, it is desirable to use a glass fiber-containing insulating layer as an insulating layer from the viewpoint of improving the strength of the substrate. It is desirable to arrange an insulating layer made of a glass fiber impregnated organic resin as the inner layer, and to arrange an insulating layer made of an organic resin or a composite material made of an organic resin and an inorganic filler as the outermost layer.

Although the water absorption of the glass fiber impregnated organic resin itself is as low as 0.2%, when the glass fiber impregnated organic resin is kept in a humid atmosphere for a long time, water diffuses at the interface between the glass fiber and the organic resin.
Since the wiring circuit layer 3 is oxidized, it is desirable to use, as the outermost layer, an organic resin capable of preventing entry of moisture or a composite material including an organic resin and an inorganic filler. The thickness of the outermost layer is 40 to 300 μm, especially 10
Desirably, it is 0 to 200 μm.

(Manufacturing Method) Next, an example of a specific manufacturing method for manufacturing the wiring board of the present invention will be described with reference to FIG. For example, an organic resin or a composite composition of an organic resin and an inorganic filler is sufficiently mixed by means of a kneader or a three-roll mill, and this is rolled, extruded, injected, doctor bladed, etc. Then, at least two insulating sheets 5a and 5b are formed in the shape (FIG. 3A). Also, the thermosetting resin is semi-cured on the insulating sheets 5a and 5b as appropriate. For semi-curing, if the organic resin is a thermoplastic resin, cool the mixture mixed under heating, and if it is a thermosetting resin, heat it to a temperature lower than the temperature sufficient for complete curing. Good.

Then, via holes 6a and 6b having a diameter of about 0.05 to 0.075 mm are formed in the insulating sheets 5a and 5b by laser light.
a and 6b are filled with a conductive paste containing a metal powder to form via-hole conductors 7a and 7b (FIG. 3).
(B)).

As a laser used for forming the via holes 6a and 6b, known methods such as a carbon dioxide laser, a YAG laser and an excimer laser can be used, but a carbon dioxide laser having a sufficient energy is particularly preferable. It is. By this laser processing, as shown in FIG. 3B, a via hole having a larger via hole diameter on the laser incident side and a larger via hole diameter on the laser emitting side is inevitably formed in the insulating sheets 5a and 5b.

The conductor paste is prepared by adding 0.1 to 5 parts by weight of an organic resin such as epoxy or cellulose to 100 parts by weight of the low-resistance metal powder as described above, butyl acetate, isopropyl alcohol, octanol, terpineol, toluene, It is desirable that a solvent such as xylene has a composition of 4 to 10 parts by weight. If desired, via holes 6a,
After filling with 6b, a heat treatment may be performed at 60 to 140 ° C. to decompose and volatilize and remove the solvent and resin components in the paste.

Next, the insulating sheets 5a and 5b on which the via-hole conductors 7a and 7b are formed are laminated, and the laser beam emitting side or the laser beam incident side of the via-hole conductors 7a and 7b is placed on the front and back sides of the laminate. Exposed laminate A
Is prepared. In FIG. 3C, the laser light emitting side can be exposed by bonding the laser light incident side surfaces of the via hole conductors 7a and 7b in the insulating sheets 5a and 5b.

Then, as shown in FIG. 3D, a wiring circuit layer 8 is formed on both surfaces or one surface of the laminate A. In the figure, wiring circuit layers 8a and 8b are provided on both surfaces.
At this time, the wiring circuit layers 8a and 8b are
The via-hole conductors 7a and 7b of FIG.

The wiring circuit layer 8 is formed by: 1) attaching a metal foil such as copper to an insulating sheet with an adhesive, forming a resist of a circuit pattern, and etching away unnecessary metal by an acid or the like. 2) Attach a pre-punched metal foil to an insulating sheet. 3) Apply a conductor paste on the surface of the insulating sheet to a circuit pattern by a screen printing method or a photoresist method, and then dry. 4) Film, A known method such as forming a metal plating film or metal foil on a glass or metal plate, forming a circuit pattern by etching, and then transferring the circuit pattern while applying pressure to an insulating sheet can be employed.

As a result, the wiring circuit layers 8a and 8b formed on the upper and lower surfaces of the laminate A are electrically connected to each other by the two via-hole conductors 7a and 7b having a substantially trapezoidal longitudinal section. .

When a wiring board having a wiring circuit layer formed on both sides of an insulating layer is manufactured, the laminate A is heated to a temperature sufficient to cure the thermosetting resin, thereby forming a single substrate. Can be manufactured.

In the case of manufacturing a multilayer wiring board,
Laminates A1 to A3 produced through the above (a) to (d)
As shown in FIG. 3 (e), a multilayer wiring board can be manufactured by pressing and laminating a plurality of layers and then thermosetting similarly.

The form of the laminate A is not limited to a two-layer structure, but may be a three-layer structure as shown in FIG. 3, or a laminate of four or more layers.

As described above, by forming the via-hole conductor on the insulating layer having a thickness smaller than that of the insulating layer, the diameter of the formed via-hole and the taper of the via-hole can be reduced. Therefore, when a plurality of via-hole conductors are formed in the insulating layer, contact between adjacent via-hole conductors can be prevented, and short circuit failure between the via-hole conductors can be reduced. In addition, since the conductors are filled in the via holes formed in the individual thin insulating layers, defective filling of the conductor material is reduced as compared with the case where the conductors are collectively filled in the long via holes. As a result, the reliability of the via-hole conductor is improved, the pitch of the via-holes can be reduced, and fine wiring can be achieved.

[0045]

EXAMPLE A glass woven fabric was impregnated with a slurry (solvent toluene) containing a PPE (polyphenylene ether) resin (glass transition point of 165 to 185 ° C. as measured by coefficient of thermal expansion), dried, and dried to a thickness shown in Table 1. A prepreg of a glass fiber-impregnated insulating sheet was prepared. The content of each component was 50% by volume of PPE resin and 50% by volume of glass woven fabric.

Using a carbon dioxide gas laser as the prepreg, a via hole having a substantially trapezoidal vertical cross section was formed under the laser irradiation conditions shown in Table 1, and a copper paste containing copper powder plated with silver was filled in the hole. To form a via-hole conductor. The diameters of the via holes on the incident side and the exit side of the via hole conductor thus manufactured were measured, and are shown in Table 1.

2 to 5 sheets of this insulating sheet are
According to the above, the positions of the via holes are aligned and overlapped so that the lower bottoms of the two substantially trapezoidal shapes are joined to each other.
The film was pressurized and heated at 30 ° C. for 30 minutes to be semi-cured, thereby producing an insulating layer laminate A. The diameters of the via holes on the front side and the back side of the manufactured insulating layer laminate A were measured, and the results are shown in Table 1.

As a comparison, a via hole is formed by laser light in an insulating layer made of a single prepreg having the same thickness as the insulating layer laminate A, and a conductive paste is filled in the same manner as described above to form a via hole conductor. Then, the diameters of via holes on the front side and the back side of the insulating layer were measured in the same manner.
It was shown to.

[0049]

[Table 1]

As is clear from the results shown in Table 1, when the insulating layer is formed by a single prepreg as in the prior art, the diameter of the via hole greatly differs between the front side and the back side of the insulating layer. By forming the insulating layer with a plurality of prepregs and adjusting the laminating direction, the diameter of the via hole on the front surface side and the diameter of the via hole on the back surface side of the insulating layer can be made equal.

On the other hand, polyethylene terephthalate (PE)
T) A copper foil having a thickness of 12 μm and a surface roughness of 0.8 μm was adhered to one surface of a transfer sheet made of a resin, and then a wiring circuit layer was formed by a photoresist method. In the manufactured wiring circuit layer, the line width was 30 μm, and the distance between the wirings was 30 μm.

Then, on both sides of the laminate A according to the present invention,
The transfer sheet on which the wiring pattern is formed is overlapped and pressed, and only the transfer sheet is peeled off to transfer the wiring circuit layer,
The wiring circuit layer was embedded in the prepreg surface. And 2
The substrate was heated at 40 ° C. for 3 hours under a load of 20 kg / cm ² and completely cured to produce a wiring board.

The specific resistance of the obtained wiring board was measured by the four-terminal method. As a result, the resistance between the wiring circuit layers was 2 × 10 ⁻⁵ Ω · cm or less, showing good characteristics.

[0054]

As described above in detail, according to the present invention, a via-hole conductor for connecting between wiring circuit layers is formed by a laminate of a plurality of blocks each having a substantially trapezoidal vertical cross section having an upper bottom and a lower bottom. In addition, by connecting the two wiring circuit layers to the same bottom of the substantially trapezoidal shape of the via hole conductor, the via hole diameter at the connection portion between the two wiring circuit layers and the via hole conductor connected by the via hole conductor is substantially the same. Therefore, it is not necessary to change the design of the wiring pattern between the front surface and the back surface of the insulating layer, and a highly accurate via-hole conductor can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view for explaining an example of a wiring board of the present invention.

FIG. 2 is an enlarged sectional view of a main part of a via-hole conductor in the multilayer wiring board of FIG. 1;

FIG. 3 is a process chart for explaining a method of manufacturing a wiring board according to the present invention.

FIG. 4 is an enlarged sectional view of a main part of a via-hole conductor in a conventional wiring board.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wiring board 2, 2a-2c Insulating layer 3, 3a, 3b Wiring circuit layer 4, 4a Via hole conductor B1-B4 Block

Claims (5)

[Claims] 1. An insulating substrate comprising an insulating material containing at least an organic resin, and a plurality of wiring circuit layers formed on the surface and / or inside of the insulating substrate, wherein different ones of the wiring circuit layers are provided. A wiring board formed by connecting at least two wiring circuit layers formed by a via-hole conductor formed by filling a metal powder in a via-hole, wherein the via-hole conductor has a substantially trapezoidal vertical cross-sectional shape having an upper bottom and a lower bottom. A wiring board formed of a laminate of a plurality of blocks each having a shape, wherein the two wiring circuit layers are connected to the same bottom side of the substantially trapezoidal shape in the via-hole conductor. 2. The wiring board according to claim 1, wherein each of the two wiring circuit layers is connected to an upper bottom side of the substantially trapezoidal block in the via hole conductor. 3. The wiring board according to claim 2, wherein said via hole is formed by irradiating a laser beam, and an upper bottom side of said substantially trapezoidal shape is a laser beam emission side. 4. A longitudinal section in which the diameter of the via hole on the incident side is smaller than the diameter of the via hole on the exit side by irradiating laser light onto the surface of a plurality of insulating sheets made of an insulating material containing at least a thermosetting resin. Forming a substantially trapezoidal via hole having an upper bottom and a lower bottom, and then filling the via hole with a conductive paste containing metal powder to form a via hole conductor; and (b) forming the via hole conductor. Forming a laminate in which one of the upper and lower bottoms of the via-hole conductor is exposed on the front and back surfaces, and (c) wiring circuit layers on both surfaces of the laminate. Or forming a wiring circuit layer on one surface of the laminate, and then laminating the same with another laminate having a wiring circuit layer formed thereon,
(D) a step of heating the laminate obtained in (c) to cure the thermosetting resin, the method comprising the steps of: 5. The method of manufacturing a wiring board according to claim 4, wherein in the step (b), a laminate in which an upper bottom side of the via hole conductor is exposed on a front surface and a back surface is manufactured.