JP2000223836A - Multilayer wiring board and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce electric resistance between two via hole conductors sandwiching an internal wiring circuit layer, in a structure wherein via hole conductors formed by the filling of metal powder are connected with the upper and the lower surfaces of the internal wiring circuit layer. SOLUTION: In this multilayer wiring board, wiring circuit layers 12 composed of metal foils are formed on the surface and in the inside of an insulating board constituted by laminating a plurality of insulating layers 11a, 11b containing organic resin, and via hole conductors 13, 15 constituted by the filling of at least metal powder like copper are formed on and under the wiring circuit layer 12. Contact parts where the metal powder 14 in the via hole conductor 13 connected with the wiring circuit layer 12 is in contact with the wiring circuit layer 12 are welded. Metal powder 16 in the via hole conductors 15 connected with the wiring circuit layer 12 is connected with the wiring circuit layer 12 via solder 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, a multilayer printed wiring board is formed by bonding a copper foil to a surface of a flat plate containing an organic resin called a prepreg and then etching it to form a fine circuit.
After laminating them, a through hole is drilled at a desired position by a micro drill, a metal is adhered to the inner wall of the hole by a plating method to form a through hole conductor, and electrical connection between the layers is performed. .

However, in this method, since the through-hole conductor penetrates the entire wiring board,
When the number of through-holes increases with the increase in the number of layers, the space required for wiring cannot be secured.This has led to the demand for multilayered printed wiring boards and finer wiring due to the lighter and thinner electronic devices. On the other hand, the current situation is that conventional multilayer printed wiring boards cannot respond.

In response to these demands, a technique has been developed in which a via-hole conductor is formed in an insulating layer and then laminated to form a multilayer. Such a via-hole conductor is called an IVH (interstitial via hole).

[0005]

This via-hole conductor is produced by forming a metal film on the inner wall of the hole by using a plating technique in the same way as a general printed wiring board. Since the use of harmful chemicals may cause a problem to the environment due to a long time, the via-hole conductor may be formed by filling a metal paste containing a metal powder in the hole. Have been done.

However, the metal paste necessarily contains an organic resin in order to enhance the filling property and printability in the holes, and therefore has a lower resistance than a circuit formed by ordinary metal plating. Is high, and via-hole conductors made of metal paste have a diameter of 150 μm in particular.
With a fine via size of less than m, the resistance of the circuit was too high to be practical. For this reason, it has been proposed that after printing the conductor paste, the organic resin component is thermally decomposed, and furthermore, the via-hole conductor after printing is heated by energization to reduce the resistance of the through-hole conductor.

However, in the via-hole conductor formed by filling the metal paste in this way, the filling property tends to decrease as the diameter decreases, and the paste contains a solvent. When the paste is dried, or when the organic resin is decomposed and removed by heat treatment, many pores are generated in the holes,
Due to the generation of the pores, the resistance of the hole itself tends to increase. Even if the resistance of the via hole conductor is reduced, it is at most about 7 × 10 ⁻⁴ Ω-cm, and it is difficult to reduce the resistance of the via hole conductor. That was the current situation.

Further, when the via-hole conductor is formed by filling a metal paste, the connection with the wiring layer on the surface of the insulating layer becomes weak. If the connection is weak, there is a problem that when a temperature cycle of a low temperature and a high temperature is applied, a crack occurs inside the via-hole conductor or a crack occurs between the wiring layer and the via-hole conductor.

In view of the above, the present inventors first filled a via hole formed for one insulating layer with a metal paste to form a via hole conductor, and then formed a wiring circuit layer on the surface thereof. Further, a pulse current is applied between the via-hole conductor and the wiring circuit layer to weld a contact portion between the via-hole conductor and the wiring circuit layer, and then the insulating layers are laminated and integrated to form a connection between the via-hole conductor and the wiring circuit layer. It was proposed to reduce the connection resistance.

On the other hand, in a multilayer wiring board, via-hole conductors are formed above and below a wiring circuit layer inside an insulating substrate, and the two via-hole conductors are electrically connected to each other with the wiring circuit layer interposed therebetween. It is necessary to achieve electrical conduction.

In such a case, the step of welding the via-hole conductor and the wiring circuit layer by applying the current is basically performed by processing each layer constituting the multilayer wiring board. When the insulating layers subjected to the application treatment are laminated and integrated, the electrical connection between the via-hole conductor and the wiring circuit layer between the insulating layers becomes insufficient. Although a method of applying a current after the lamination and integration is conceivable, it has been difficult to weld the connection portions between all the wiring circuit layers and the via-hole conductors to a complicated circuit pattern in the multilayer wiring circuit.

In electrically connecting two wiring circuit layers formed with two or more insulating layers interposed therebetween, via-hole conductors formed in each insulating layer are vertically formed continuously over the two insulating layers. However, in such a case, it is difficult to reduce the connection resistance and connect the via-hole conductors formed in the respective insulating layers.

In some cases, two continuous via-hole conductors are connected via a wiring circuit layer. However, when the above-described pulse current is applied, the via-holes are stacked after the current is applied to each insulating layer. Between the conductor-wiring circuit layer and via-hole conductor, even if one via-hole conductor-wiring-circuit layer is welded to reduce the connection resistance, since the connection resistance is not welded to the other via-hole conductor, the connection is continued in the vertical direction. Thus, the reduction of the electrical resistance between the via-hole conductor, the wiring circuit layer, and the via-hole conductor thus formed has not been sufficiently achieved.

Accordingly, the present invention provides a structure in which via-hole conductors formed on the upper and lower surfaces of an internal wiring circuit layer in an insulating substrate and formed by filling metal powder are connected.
It is an object of the present invention to provide a multi-layer wiring board having two via-hole conductors having low resistance through an internal wiring circuit layer and having high reliability, and a method for manufacturing the same.

[0015]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the above-mentioned problems, and as a result, of the two via-hole conductors connected to the internal wiring circuit layer and formed by filling metal powder, The metal powder in the via hole conductor connected to one surface of the internal wiring circuit layer is welded to the internal wiring circuit layer, and the metal powder in the via hole conductor connected to the other surface and the internal wiring circuit layer are soldered. It has been found that by connecting via the internal wiring circuit layer, the resistance between the internal wiring circuit layer and two via-hole conductors connected to the internal wiring circuit layer can be reduced.

That is, a multilayer wiring board according to the present invention is a wiring circuit comprising an insulating substrate formed by laminating a plurality of insulating layers containing an organic resin, and a plurality of metal foils formed on the surface and inside of the insulating substrate. A multilayer wiring board comprising a layer and a via-hole conductor provided to electrically connect the wiring circuit layers and at least filled with metal powder.
At least one or more via-hole conductors are respectively connected to one surface and the other surface of at least one internal wiring circuit layer in the insulating substrate, and in the via-hole conductor connected to the one surface, The contact portion between the metal powder and the wiring circuit layer is welded, and the metal powder in the via-hole conductor connected to the other surface and the wiring circuit layer are connected to each other via solder. It is characterized by the following.

In the above-mentioned multilayer wiring board, the metal powder further contains at least copper.

In the method for manufacturing a multilayer wiring board according to the present invention, a step of forming a via-hole conductor by filling a conductive paste containing a metal powder into a via-hole formed in an insulating layer containing an organic resin; Forming a wiring circuit layer made of metal foil on one surface of the insulating layer having the via-hole conductor formed thereon so as to cover the via-hole conductor; and b. Forming a current between the via-hole conductor and the wiring circuit layer. C) welding a contact portion between the metal powder in the via-hole conductor and the wiring circuit layer, and soldering to an end of the via-hole conductor on the side not connected to the wiring circuit layer. A step d of applying, and the steps a to d
A step e of laminating and compressing a plurality of insulating layers on which via-hole conductors and wiring circuit layers formed through the above are formed, and a step f of heating the laminate manufactured in the step e to a temperature at which the solder melts. It is characterized by having.

In the method for manufacturing a multilayer wiring board, the current in the step (c) is set to a current density of 1 to 200.
0 A / cm ² , pulse width 0.01 to 1000 mse
c. And the metal powder contains at least copper.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method for manufacturing a multilayer wiring board according to the present invention will be specifically described with reference to the process chart of FIG. According to the method for manufacturing a multilayer wiring board of the present invention, first, FIG.
As shown in FIG. 1A, a via hole 2 is formed in a predetermined portion of an insulating layer 1 containing at least an organic resin, and the via hole 2 is filled with a metal paste containing a metal powder to form a via hole conductor 3.

The insulating layer 1 contains at least an organic resin, for example, a thermosetting resin such as PPE (polyphenylene ether), BT resin (bismaleimide triazine), epoxy resin, polyimide resin, fluorine resin, phenol resin and the like. Or a thermoplastic resin.

In the insulating layer 1, an organic resin may be combined with an inorganic filler in order to increase the strength of the insulating layer or the entire wiring board. As the inorganic filler compounded with the organic resin, Si
Known materials such as O ₂ , Al ₂ O ₃ , AlN, and SiC can be used, and a sheet (prepreg) in which a glass cloth or an aramid nonwoven fabric is impregnated with a resin may be used. In the composite material of the organic resin and the inorganic filler, the volume ratio of the organic resin: the inorganic filler is 1%.
It is appropriate that the composite is formed in a ratio of 5:85 to 50:50.

The formation of the through hole in the insulating layer is performed by punching, laser or the like on the insulating layer in an uncured state (B stage state). The diameter of the through-hole varies depending on the circuit.
It is formed with a diameter of 0 to 200 μm.

The metal paste to be filled in the through hole 2 is made of a metal powder, an organic resin and a solvent, and the metal powder is at least one or more alloys selected from the group consisting of copper, aluminum, gold and silver. It is desirable to constitute by. In particular, of these, copper is most desirable.

On the exposed surface of the through-hole conductor 3, a metal other than copper which can form an alloy having a lower melting point than copper by alloying with copper, specifically, Ag, Al, Au, C
d, Cr, Ni, Th, Ti, Tl, Zn, Pb, S
By coating at least one metal selected from the group consisting of n and In, low-temperature weldability accompanying current application, which will be described later, can be improved.

On the other hand, as the organic resin contained in the metal paste, a resin such as cellulose is used in addition to the above-mentioned thermosetting resin. In addition, the solvent is composed of a solvent in which the organic resin used can be dissolved, for example, isopropyl alcohol, terpineol, 2-octanol,
Butyl carbitol acetate (BCA) and the like. As the composition of the metal paste, 0.05 to 10 parts by weight of organic resin, especially 0.1 to 100 parts by weight of metal powder is used.
05 to 3.0 parts by weight, solvent 1 to 20 parts by weight, especially 2 to 2 parts by weight
A mixture of 15 parts by weight is suitable. In addition,
The drying treatment is performed at a temperature sufficient to evaporate the solvent, specifically, desirably at 30 to 200 ° C.

Next, as shown in FIG. 1B, a wiring circuit layer made of a metal foil is formed on one exposed end of the insulating layer 1 of the through-hole conductor 3. In FIG. 1B, a wiring circuit layer 4 made of a metal foil is formed at an end exposed on one surface of the insulating layer 1. The wiring circuit layer 4 has a thickness L which is at least 0.05 times, especially 0.1 times the thickness L of the insulating layer 1.
It is desirable that the thickness be twice or more.

This is because, as the thickness of the metal foil forming the wiring circuit layer 4 is larger, when the wiring circuit layer 4 is buried on the surface of the insulating layer 1, the compression ratio of the through-hole conductor becomes higher. This is because the filling rate of the metal powder in the hole conductor 3 can be increased. If the thickness is too large, it is difficult to bury the insulating layer in the insulating layer, and when the substrate is multilayered, the substrate may be deformed by a wiring circuit layer. From such a viewpoint, the upper limit is suitably 0.25 times.

The wiring circuit layer 4 made of a metal foil is formed by a known method. For example, after a metal foil such as copper is adhered to the surface of the insulating layer 1, a resist is applied to the wiring pattern and a non-resist forming portion is removed by etching, and then a method of removing the resist, or a method in which the copper foil is adhered. A method of forming a wiring pattern on the transfer sheet in the same manner and transferring the wiring pattern to the insulating layer 1 is adopted.

In particular, the above transfer method is advantageous in terms of productivity because the patterning of the wiring circuit layer can be performed simultaneously and simultaneously with the formation of the insulating layer.
In this transfer method, the wiring circuit layer 4 can be embedded in the surface of the insulating layer 1 by applying pressure during the transfer.

Next, as shown in FIG. 1C, the insulating layer 1 having the wiring circuit layer 4 formed on one surface as described above is sandwiched between electrodes 5 and 6 from above and below. By applying a current between the metal wires 6, the metal powder in the via-hole conductor 3 and the contact portions between the metal powder and the wiring circuit layer 4 are welded.

The optimum conditions for the pulse current to be applied at this time are as follows: a current density of 1 to 2000 A / cm ² , a current application time of one pulse of 3 seconds or less, and a pulse interval of 3 seconds or less. Is fine. Current density is 1A / c
If it is less than m ² , the effect of lowering resistance is small, and 200
If it exceeds 0 A / cm ² , heat is partially generated and the insulating layer may be damaged. Further, if the energizing time of one pulse exceeds 3 seconds, the processing time for lowering the resistance becomes long, and if the pulse interval is 3 seconds or more, the processing time becomes long and is not practical. Desirably, the energizing time of one pulse and the pulse interval are both 0.5 second or less, and most preferably 0.02 to 0.1 second.

The pulse current is desirably a rectangular wave. Although a sine wave or the like is used, a rectangular wave is most effective. Further, the pulse power supply is desirably a DC pulse power supply. That is, a square wave is better than a sine wave,
Discharge between particles is easy to occur, the surface cleaning action is high,
This is because the pulse current of the direct current is less likely to adhere to the particle surface once cleaned than the alternating current.

Further, according to the present invention, after the application of the pulse current, the through-hole conductor 3 and the wiring circuit layer 4 are subjected to a heat treatment by energization to further reduce the resistance of the through-hole conductor. Can be. The energization process
Any of direct current and alternating current with a current density of 1 to 4000 A / cm ² may be used, and the heating temperature by energization is desirably in the range of 100 to 300 ° C. The heating temperature at this time is 300 ° C
If it is higher than this, the resin having high heat resistance that forms the insulating layer is decomposed, and if it is lower than 100 ° C., the effect of further lowering the resistance is small. By this heating, the bonding between the metal particles is strengthened, and the resistance of the via-hole conductor can be reduced.

Further, the energization heating process can be performed simultaneously with the above-described pulse current application process. Specifically, when a waveform obtained by combining a DC pulse current and a DC current, that is, when a current having a rectangular waveform at the top of the DC current waveform is applied, the action of energization heating and the discharge welding action of pulse current application are simultaneously performed. Can be added.

Next, as shown in FIG. 1D, solder 7 is applied to the end of the via-hole conductor 3 on the side not connected to the wiring circuit layer 4. As the solder 7, Pb-Sn
System, Bi-Sn system, Cu-Sn system, Sn-Ag-Cu
System, Sn-Ag-Bi system and Sn-Zn system are used. Among them, those having a melting point of 139 to 290 ° C are desirable, and a group of Pb-Sn system, Bi-Sn system and Cu-Sn system is used. At least one kind of solder selected from the group consisting of

Then, a plurality of substrates prepared through the step of FIG. 1 (d) are prepared, these are aligned, heated and heated to a predetermined temperature, and a pressure is applied to laminate and integrate the substrates. By heating to a temperature at which the thermosetting resin contained therein can be completely cured to completely cure the insulating layer, the internal wiring circuit layer 8 and the surface wiring circuit layer 9 as shown in FIG. In addition, a multilayer wiring board having the via hole conductor 10 can be manufactured.

According to the above process, by applying pressure during lamination, the wiring circuit layer 4 formed on each insulating layer is embedded in the insulating layer 1 and the through-hole conductor 3 is simultaneously compressed and compressed. As a result, the filling rate of the metal powder in the through-hole conductor 3 can be increased.

The pressure applied at this time is 1 to 200 k
g / cm ² , preferably in the range of ^{20 to} 70 kg / cm ² .

The heating temperature to be applied is such that the solder in the via-hole conductor is half-melted or melted, so that the metal powder in the via-hole conductor and the wiring circuit layer on the other surface of the internal wiring circuit layer are heated. Can be firmly connected by the molten solder. The optimal heating temperature is 150 to 250 ° C.

As shown in the enlarged view of the connection portion between the internal wiring circuit layer and the via-hole conductor in FIG.
An internal wiring circuit layer 12 made of metal foil is formed inside an insulating substrate 11 made of a, 11b, and a via hole conductor 13 is formed at a connection portion with a via hole conductor 13 formed on the lower surface of the internal wiring circuit layer 12. Metal powder 1 in 13
4 and the internal wiring circuit layer 12 are welded, that is, the neck a is grown at the contact portion between the wiring circuit layer 12 made of metal foil and the metal powder 14. In addition, the neck grows not only between the wiring circuit layer 12 and the metal powder 14 but also between the metal powders 14, so that the via-hole conductor 13 and the internal wiring circuit layer 12 have a low resistance and a strong resistance. Can be connected to

At the connection portion with the via-hole conductor 15 formed on the upper surface of the internal wiring circuit layer 12, the metal powder 16 in the via-hole conductor 15 and the internal wiring circuit layer 12 are connected via the solder 17. Therefore, the via-hole conductor 15 and the internal wiring circuit layer 12 can be firmly connected with low resistance. As a result, the via-hole conductor 13 -the internal wiring circuit layer 12 -the via-hole conductor 15 can be firmly connected with low resistance. A neck b grows between the metal powders in the via-hole conductor 15 due to the current application process.

The multilayer wiring board and the method for manufacturing the multilayer wiring board of the present invention are not limited to the above-mentioned specific examples.
All changes or additions can be made without changing the gist of the present invention.

In the above example, the metal powder in the via-hole conductor connected to the other surface of the internal wiring circuit layer is connected via solder. However, this solder is used to form the via-hole conductor in advance. May be mixed in the metal paste, and in that case, when welding with the via-hole conductor on one surface of the internal wiring circuit layer, the solder melted by applying the pulse current flows from the via-hole conductor and the metal foil. It plays a role of assisting the connectivity with the wiring circuit layer, and can further reduce the connection resistance.

[0045]

EXAMPLE An evaluation board as shown in FIG. 3 was manufactured to confirm the effect of the structure of the multilayer wiring board of the present invention. According to FIG. 3, as the two-layer structure of the insulating layers 18 and 19, one internal wiring circuit layer 20 is formed inside, and wiring circuit layers 21 and 22 are formed on both surfaces of the wiring board, respectively.
A wiring board was prepared in which via-hole conductors 23 and 24 were connected to the top and bottom, respectively, and were electrically connected to the wiring circuit layers on both surfaces.

In manufacturing, first, as an insulating layer,
An imide resin is used as an organic resin, spherical silica is used as an inorganic filler, and a composition in which the volume ratio of organic resin: inorganic filler is 30:70 is used, and this is semi-cured to a thickness of 120 μm by a doctor blade method. An insulating layer in a state was formed, and a through hole having a diameter of 0.1 mm was formed at a predetermined position by punching.

Then, a metal paste obtained by mixing 100 parts by weight of copper powder coated with silver on the surface having an average particle diameter of 4 μm, 0.2 parts by weight of cellulose, and 10 parts by weight of 2-octanol was filled in the through holes. And dried at 140 ° C. for 30 minutes.

Next, a wiring circuit layer was formed by a photoresist method on the copper foil of the transfer sheet to which the copper foil having a thickness of 12 μm was adhered. Then, the transfer sheet is positioned and superimposed on the insulating layer on which the through-hole conductor has been formed.
A pressure of kg / cm ² was applied to bury the wiring circuit layer in the insulating layer. After heating to 120 ° C., the transfer sheet was peeled off to transfer the wiring circuit layer.

In forming the wiring circuit layer, the front wiring circuit layer is formed on the insulating layer 18 shown in FIG. 3, and the internal wiring circuit layer 20 and the rear wiring circuit layer are formed on the insulating layer 19 in FIG. Layers 22 were each formed.

Then, the insulating layer 1 on which the wiring circuit layer is formed
8 and 19 were respectively sandwiched between a pair of electrode plates, and current was applied under the conditions shown in Table 1. From the cross-sectional photograph of the single wiring layer after the application of the current, it was confirmed that a neck was grown and welded at the contact portion between the metal powder in the via hole conductor and the wiring circuit layer.

Thereafter, the end face of the via-hole conductor 23 on the side of the insulating layer 18 not connected to the wiring circuit layer 21 is Sn-
Pb (melting point: 183 ° C.) solder was applied.

Next, the insulating layer 1 produced as described above
8 and the insulating layer 19 are aligned with each other to obtain 20 kg / cm ²
While applying the pressure, a heat treatment was performed at 150 ° C. for 0.5 hour to laminate and integrate.

Thereafter, the laminate was heated at a temperature of 250 ° C. for 3 hours.
By holding for a time, the thermosetting resin in the insulating layer was completely cured to produce a multilayer wiring board for evaluation as shown in FIG.

With respect to the obtained multilayer wiring board for evaluation,
Surface wiring circuit layer 21 via hole conductors 23-internal wiring circuit layer 20-the initial electrical resistance R ₁ between the via-hole conductors 24 backside interconnect circuit layers 22 were measured. The relative humidity is 95%
In the atmosphere, the temperature change from -55 ° C to + 125 ° C is 1000
Measuring the conduction resistance R ₂ after repeated cycles, also to calculate the rate of change in resistance _{{(R 2 -R 1) /} R 1} × 100 (%). Table 1 shows the results.

Comparative Example 1 A multilayer wiring board (sample No. 6) was prepared in exactly the same manner as in the above example, except that no current was applied and no solder was applied. Was evaluated.

(Comparative Example 2) In the above-described embodiment, a current was applied, but the solder was not applied to the end face of the via-hole conductor.
7) was prepared, and the same evaluation was performed.

(Comparative Example 3) The same method as described above, except that the connection of the wiring circuit layer and the via-hole conductor is entirely applied to the end face of the via-hole conductor instead of applying the current in the above-described embodiment. With a multilayer wiring board (sample N
o.8), and the same evaluation was performed.

[0058]

[Table 1]

As is clear from the results in Table 1, in Comparative Example 1 in which no current was applied and no solder was applied, the resistance between the front wiring circuit layer and the rear wiring circuit layer was 8.5 × 10 ⁻⁴ Ω-cm.
It was high. In Comparative Examples 2 and 3 in which either the application of current or the application of solder was not performed, the resistance was lower than in Comparative Example 1, but it was not practically sufficient. On the other hand, all of the samples of the present invention were 8.5 × 10 ⁻⁶ Ω−.
cm or less can be realized.

[0060]

As described in detail above, according to the present invention, the contact portion between the metal powder in the via-hole conductor connected to one surface of the internal wiring circuit layer and the internal wiring circuit layer is welded, and the other is welded. The electrical resistance between the two via-hole conductors sandwiching the internal wiring circuit layer is reduced by connecting the metal powder in the via-hole conductor connected to the surface of the internal wiring circuit layer and the internal wiring circuit layer via solder, respectively. As a result, a highly reliable multilayer wiring board can be provided.

[Brief description of the drawings]

FIG. 1 is a process chart for explaining a method for manufacturing a multilayer wiring board of the present invention.

FIG. 2 is a partially enlarged cross-sectional view for explaining the structure of the multilayer wiring board of the present invention.

FIG. 3 is a schematic sectional view for explaining the structure of a multilayer wiring board for evaluation.

[Explanation of symbols]

 1, 11, 18, 19 Insulating layer 2 Via hole 3, 10, 13, 15, 23, 24 Via hole conductor 4, 21, 22 Wiring circuit layer 5, 6 Electrode 7, 17 Solder 8, 12, 20 Internal wiring circuit layer 9 Surface wiring circuit layer 14, 16 Metal powder

Claims (5)

[Claims] An insulating substrate formed by laminating a plurality of insulating layers containing an organic resin; a wiring circuit layer formed of a plurality of metal foils formed on the surface and inside of the insulating substrate; A multilayer wiring board provided for electrical connection and having via-hole conductors filled with at least metal powder, wherein one surface and the other surface of at least one internal wiring circuit layer in the insulating substrate At least one or more via-hole conductors are connected to each other, and a contact portion between the metal powder in the via-hole conductor connected to the one surface and the wiring circuit layer is welded to the other surface. A metal powder in the via hole conductor connected to the wiring circuit layer and the wiring circuit layer are connected to each other via solder. 2. The multilayer wiring board according to claim 1, wherein said metal powder contains at least copper. 3. A step a of forming a via-hole conductor by filling a conductive paste containing a metal powder into a via-hole formed in an insulating layer containing an organic resin, and one of the insulating layers on which the via-hole conductor is formed. B) applying a current between the via-hole conductor and the wiring circuit layer to form a wiring circuit layer made of a metal foil so as to cover the via-hole conductor on the surface of the via-hole conductor; A step c of welding a contact portion between the powder and the wiring circuit layer, a step d of applying solder to an end of the via-hole conductor that is not connected to the wiring circuit layer, and a step d to the step a to the step d. E) laminating and compressing a plurality of insulating layers on which via-hole conductors and wiring circuit layers are formed, and heating the laminate manufactured in step e to a temperature at which the solder melts. Method for manufacturing a multilayer wiring board, characterized by comprising the, the. 4. The method according to claim 1, wherein the current in step c is a current density of 1
2,000 A / cm ² , pulse width 0.01-1000
msec. 4. The method for manufacturing a multilayer wiring board according to claim 3, wherein the pulse current is a pulse current. 5. The method for manufacturing a multilayer wiring board according to claim 3, wherein said metal powder contains at least copper.