JPH10178249A - Wiring board and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remarkably reduce the specific resistance of conductor wiring layers by constituting the layers of the particles of a low-resistance metal and a thermosetting resin and press-contacting the particles with each other through the cure shrinkage of the resin by thermally curing the resin and, at the same time, discharge-welding the contacting sections of the particles to each other by impressing a pulselike current. SOLUTION: In an insulating layer 1 containing at least an organic resin, via hole conductors 3 in which metallic particles of copper, silver, aluminum, gold, etc., are coupled with each other with a thermosetting resin are formed by filling up via holes with conductor paste containing the metallic particles and thermosetting resin and coupling the particles with each other by curing the thermosetting resin. Then the contacting sections of the metallic particles are discharge-welded to each other by impressing a pulselike current upon the conductors 3. Thereafter, the specific resistances of the conductors 3 are reduced by electrically heating the conductors 3 after or simultaneously with the discharge-welding process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board suitable for a package for accommodating a semiconductor element and the like, wherein a via-hole conductor mainly composed of a metal such as copper is provided in an insulating layer containing an organic resin. It is about the method.

[0002]

2. Description of the Related Art Conventionally, as a multilayer wiring board used for a wiring board, for example, a package for housing a semiconductor element, a multilayer having an insulating layer such as alumina and a wiring layer made of a high melting point metal such as W and Mo. Ceramic wiring boards are often used, but since such ceramic multilayer wiring boards are hard and brittle, they are susceptible to chipping or cracking of the ceramics in the manufacturing process or the transporting process, and also require sintering. When the metallized ink is printed on the previous green sheet, and the printed sheets are laminated and sintered, there is a problem that the substrate obtained by the firing is liable to be deformed such as warpage or dimensional variation, and the circuit There has been a problem that it is not possible to sufficiently cope with strict requirements for the flatness of the substrate such as ultra-high density of the substrate and flip chips.

Therefore, recently, a copper foil is bonded to the surface of an insulating layer containing an organic resin and then etched to form a fine circuit, or an ink containing a metal powder such as copper is printed on the insulating layer. After forming a wiring layer by laminating this, or after lamination, a hole is drilled for a via at a desired position by microdrilling or punching, and a metal is adhered to the inner wall of the via by a plating method to form a wiring layer. Connecting and multilayering is performed. Also, as the insulating layer,
In order to increase the strength, a substrate in which a powdery or fibrous inorganic filler is dispersed in an organic resin has also been proposed. A multi-layer substrate having a large number of semiconductor elements mounted on an insulating layer made of these composite materials has been proposed. Chip module (MC
M) etc. are also being considered.

[0004] In response to the demands for multilayer printed circuit boards, ultra-fine wiring, and precision as described above, the method of plating the inner walls of via-hole conductors has limited the design of the via-hole conductors. Because of the above restrictions,
Attempts have been made to produce high-density multi-layered wiring boards without restriction by filling the via-hole conductors with a conductive paste containing a metal such as copper in the via holes as in the case of the ceramic multilayer substrate. I have.

[0005]

However, since the conductive paste containing a metal is mixed with an organic resin in order to improve the printability on the insulating layer and to bind the metal powders to each other, the contact of the powders with the powders is not improved. Since the organic resin easily intervenes at the interface, there is a problem that the resistance value is higher than that obtained by plating the inner wall of the via hole. For this reason, various improvements have been made, such as heating and decomposing the resin component after filling the conductive paste, and further, conducting electric heating to the filled via-hole conductor. However, even in the via-hole conductor obtained in this way, it is not possible to completely remove the resin component or dirt, or even if the resin component can be removed, an oxide film or the like existing on the surface of metal particles such as Cu is removed. At present, it is difficult to reduce the resistance because it is at most about 7 × 10 ⁻⁴ Ω-cm even if the resistance is reduced without being removed.
There is a disadvantage that it is difficult to increase the density.

[0006]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that a via paste is filled with a conductive paste containing a metal such as copper and a thermosetting resin. After the conductor is formed, the thermosetting resin is thermoset to cause the metal powders to be pressed against each other by a shrinkage action at the time of hardening, and a pulse current is applied to the via-hole conductor to thereby make contact between the metal particles. We found that the resin and oxide on the surface of the metal particles, which caused electrical discharge and prevented electrical conduction, could be welded together with the particles at the same time, resulting in a marked reduction in the resistance of the via-hole conductor. It has been found that a highly reliable wiring board that can meet the demand for ultra-fine and refined substrates can be formed.

That is, the wiring board of the present invention is a wiring board in which a via-hole conductor containing a metal powder is disposed in an insulating layer containing at least an organic resin, wherein the metal powder in the via-hole conductor is thermoset. Are connected to each other by the conductive resin, and the contact portion between the metal powders is characterized by being subjected to discharge welding, and in particular, the metal powder is selected from a group of copper, silver, aluminum, and gold. At least one kind, and the specific resistance of the via-hole conductor is reduced to 1 × 10 ⁻⁵ Ω-cm or less.

Further, as a method of manufacturing such a wiring board, a step of forming a via hole in at least an insulating layer containing an organic resin, a step of filling a conductive paste containing a metal powder and a thermosetting resin into the via hole, Curing the conductive paste to form a via-hole conductor in which the metal powders are bonded to each other with a thermosetting resin; and applying a pulse current to the via-hole conductor to discharge-weld a contact portion between the metal powders. And a step of performing

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a wiring board according to the present invention has insulating layers 1 laminated in multiple layers, and a conductor wiring layer 2 is formed on the surface or between the insulating layers 1. In each conductor wiring layer 2, different layers of conductor wiring layers are electrically connected by the via hole conductor 3.

The insulating layer 1 is made of an insulating material containing at least an organic resin. Examples of the organic resin include a thermosetting polyphenylene ether resin, a bismaleide triazine resin, an epoxy resin, a polyimide resin, a fluorine resin, a phenol resin, and the like. Organic resin and the like.

Further, in the insulating layer 1, it is desirable to compound an inorganic filler with an organic resin 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
O ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ , AlN, Si
C, BaTiO ₃ , SrTiO ₃ , zeolite, CaT
Known materials such as iO ₃ and aluminum borate can be used, and a sheet (prepreg) in which a glass cloth is impregnated with a resin may be used. The filler has an average particle diameter of 20 μm or less, particularly 10 μm or less, and optimally 7 μm or less.
m, an average aspect ratio of 2 or more, in particular, 5 or more, fibrous or flat, or woven fabric. In the composite material of the organic resin and the inorganic filler, it is appropriate that the organic resin and the inorganic filler are compounded in a volume ratio of 15:85 to 50:50.

The conductive wiring layer 2 forms a conductive path for electrically connecting electronic components such as semiconductor elements mounted on a wiring board to each other or to the outside. For example, copper, silver, It contains a low-resistance metal mainly composed of at least one or two or more alloys selected from the group consisting of aluminum and gold. Particularly, copper or an alloy containing copper is most desirable. In some cases, a high-resistance metal such as a Ni—Cr alloy may be mixed or alloyed as the conductor composition for adjusting the resistance of the circuit. Further, in order to reduce the resistance of the wiring layer, a metal having a lower melting point than the low-resistance metal, for example, a low-melting metal such as solder or tin is used in an amount of 2 to 20% by weight in the metal component in the conductor composition. May be included.

The conductor wiring layer 2 is formed by a metal foil made of the above-mentioned metal or an alloy containing the above-mentioned metal, or by metal plating, or by printing and applying a conductor paste as described later by screen printing or the like. Is what is done.

The via-hole conductor 3 is also formed on the conductor wiring layer 2.
However, according to the present invention, the via-hole conductor 3 contains a powder of a low-resistance metal. This via hole conductor 3
Is desirably 0.5 to 50 μm in average particle size. If the average particle size is smaller than 0.5 μm, the contact resistance between the metal powders tends to increase and the resistance of the via-hole conductor tends to increase, and if the average particle size exceeds 50 μm, it tends to be difficult to reduce the resistance of the via-hole conductor. It is in.

The via-hole conductor of the present invention contains a thermosetting resin in addition to the above-mentioned metals in order to bond the metal powders. As this thermosetting resin,
The same thermosetting resin as the insulating layer is used. The thermosetting resin has a function of bonding the metal powders in a state where they contact each other and bonding a low-resistance metal to the inside of the via hole.

Further, the thermosetting resin has a function of bringing metal powders into pressure contact with each other by a stress generated by curing shrinkage due to a contraction effect at the time of thermosetting. In order to generate such stress due to curing shrinkage, the volume shrinkage during curing may be adjusted to 1% or more depending on the type and content of the thermosetting resin used, as described later.

If the content of the organic resin is less than 5% by volume, it is difficult to firmly bind the metal powders to each other.
If it is difficult to firmly adhere the low-resistance metal to the insulating layer, if it exceeds 40% by volume, the resin will be interposed between the metal powders, making it difficult to bring the powders into sufficient contact with each other. Resistance tends to increase. Therefore, the thermosetting resin in the via-hole conductor,
It is preferably from 5 to 40% by volume, particularly preferably from 10 to 30% by volume.

Furthermore, according to the present invention, the via-hole conductor is formed by an aggregate of the above-mentioned metal powders. Generally, the surface of these metal powders reacts with oxygen in the atmosphere to form an oxide film. . Such an organic resin for bonding between the oxide film and the powder prevents the conduction between the metal powders. On the other hand, according to the via-hole conductor of the present invention, the contact portion between the adjacent metal powders is discharge-welded, whereby the particles are directly interposed without interposing an oxide film or an organic resin between the particles. To be connected, a low-resistance via-hole conductor is formed.

Further, the via-hole conductor is excellent in corrosion resistance of nickel or gold on the exposed surface of the insulating layer, and has good bonding properties with electronic components such as semiconductor elements and connection with a wiring layer of an external electric circuit board. By forming a metal having excellent properties in a thickness of 1 to 20 μm by a plating method, it is possible to effectively prevent the via-hole conductor from being oxidized and corroded, and to provide an electric component of the via-hole conductor or an external electric circuit board. Electrical connection with the semiconductor device can be made easily and firmly.

According to the method of manufacturing a wiring board of the present invention, first, an insulating layer containing an organic resin is manufactured. This insulating layer
Using a thermosetting resin as described above, or a thermosetting resin and an inorganic filler, a suitable curing agent, a solvent is added and mixed to form a slurry, which is a doctor blade method, a calendar roll method, It is formed into a sheet by a rolling method or the like. Alternatively, it is produced by heating and curing the material to be semi-cured or completely cured. In addition, other than the above, a prepreg or the like can be used as the insulating layer. Next, via holes are formed in the sheet-like molded body by a microdrill, a laser, or the like, and the via holes are filled with a conductive paste containing a metal powder and a thermosetting resin to form via-hole conductors. At this time, as the conductive paste used at this time, the above-mentioned low-resistance metal and the above-mentioned thermosetting resin are used, and the thermosetting resin content is 5 to 4%.
It is blended in an amount of 0% by volume, especially 10 to 30% by volume. The paste contains an appropriate curing agent and a solvent.

Further, a conductor wiring layer is formed on the surface of the sheet-like molded body. As a method for forming the conductor wiring layer, a method in which a metal foil is adhered to the surface of the sheet-shaped molded body, and then formed into a conductor pattern by a photoresist method or the like,
There is a method of forming by a metal plating method, or a method of printing and forming a conductive paste containing a metal powder as described above by a known printing method such as a screen printing method or a gravure printing method.

The thickness of the formed conductor wiring layer is 10 to 35.
μm is appropriate.

Next, the above-mentioned sheet-shaped molded product is
By heating at a temperature of 00 ° C. for 1 to 60 minutes, the thermosetting resin contained in the via-hole conductor, the thermosetting resin in the sheet-shaped molded product, or the thermosetting resin in the conductor wiring layer is cured. At this time, since the thermosetting resin shrinks simultaneously with curing, the metal powders in the via-hole conductors can be pressed against each other, and the resistance between the metal powders can be reduced. The volume shrinkage at this time is desirably 1% or more, preferably 1 to 20%, and more preferably 2 to 15% by volume. This is because if the volumetric shrinkage is less than 1%, the pressing force between the metal powders in the via-hole conductors tends to be insufficient, and if the volumetric shrinkage exceeds 20%, cracks and the like may occur in the conductor wiring layer. is there.

Such a volume shrinkage tends to increase as the content of the thermosetting resin increases, or the shrinkage differs depending on the type of the resin. In particular, bisphenol type epoxy resin, bisphenol F type Since thermosetting resins such as epoxy resin, novolak type epoxy resin, imide resin, alicyclic epoxy resin, amine type epoxy resin, and glycidyl esterified epoxy resin have a large volume shrinkage, the types of these thermosetting resins and It can be appropriately adjusted depending on the content. Further, in order to increase the volume shrinkage, the pressure may be increased by 5 to 300 kg / cm ² at the time of the effect.

The curing of the thermosetting resin in the via-hole conductor may be performed before the formation of the conductor wiring layer.
After laminating the sheet-like molded body on which the conductor wiring layer and the via-hole conductor are formed in multiple layers, the laminate can be heated and cured.

In the via-hole conductor of the wiring board manufactured as described above, a thin resin film exists on the surface of the metal powder due to the organic resin contained in the conductor, or the metal powder is oxidized by oxygen in the atmosphere. A thin oxide film is formed.

Therefore, according to the present invention, the resistance of the via-hole conductor is reduced by applying a pulse current to the via-hole conductor in the wiring board manufactured as described above. When a pulse current is applied to the via hole conductor, a discharge occurs between the metal particles. This plasma removes oxide films and deposits on the surface of the metal particles, forming a so-called welded state, so that the metal particles can come into contact with each other without inclusions that hinder the conductivity. As a result, This makes it possible to form a low-resistance via-hole conductor that could not be achieved only by electric heating. The application of the pulse current can be performed by pressing the plate electrode against the substrate on which the via-hole conductor is formed at a pressure of 10 kg / cm ² or more.

Further, by controlling the pulse current applied to the via-hole conductor, a reduction in resistance of 1 × 10 ⁻⁵ Ω-cm or less can be realized. As the optimum conditions, a voltage of 1 to 200 V, an energizing time of one pulse of 3 seconds or less, and a pulse interval of 3 seconds or less are favorably used.
When the voltage is less than 1 V, it is difficult to remove an oxide film and an organic resin existing at the interface between the metal powders without discharge welding, and
If the voltage exceeds 00V, heat is partially generated and the insulating layer may be damaged. On the other hand, if the energizing time of one pulse exceeds 3 seconds, the processing time for electric discharge welding becomes long, and if the pulse interval exceeds 3 seconds, the processing time becomes long and is not practical. Desirably, both the energizing time and pulse interval of one pulse are 0.5 seconds or less, and optimally 0.02 to 0.1 seconds.

The pulse current value is set to
m ² per 10~5000A are suitable.

The pulse current is desirably a rectangular wave. Although a sine wave or the like is used, a rectangular wave is most effective. Further, it is desirable that the pulse current is a DC pulse. This is because a rectangular wave is more likely to cause discharge between particles than a sine wave, and has a higher surface cleaning effect.Pulse current is less likely to cause dirt and the like to adhere to the once-cleaned particle surface than to alternating current. It is.

Further, according to the present invention, after the application of the pulse current, the via hole conductor is subjected to a heat treatment by energization, so that the resistance of the via hole conductor can be further reduced. The energization treatment may be either DC or AC of 100 to 6000 A per 100 cm ² of the substrate,
The heating temperature by energization is suitably in the range of 100 to 350 ° C. If the temperature at this time is lower than 100 ° C., the effect of lowering the electric resistance is small, and if it is higher than 350 ° C., the organic resin constituting the insulating layer and the conductor wiring layer may be decomposed. The contact heating between the metal powders generates heat by the energization heating, so that the bonding force between the powders can be further increased.

This 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.

The application of the pulse current and the heating treatment are not limited to the via-hole conductor, and the same effect can be exerted by applying the pulse current to the conductor wiring layer printed and formed with the conductor paste.

[0034]

【Example】

Example 1 A slurry was prepared by mixing 65 vol% of substantially spherical silicon oxide having an average particle diameter of about 5 μm, 35 vol% of a phenol resin, and a curing agent, and using this slurry, a slurry was applied on a carrier sheet by a doctor blade method. And dried at a temperature of 50 ° C. for 60 minutes to a thickness of 200 μm and a size of 200 m
An m-square semi-cured insulating layer was formed, and a via hole having a diameter of 200 μm was formed by punching.

Next, a conductive paste composed of 75% by volume of copper powder having an average particle diameter of 4 μm and 25% by volume of a bisphenol-type epoxy resin was filled in the via holes of the insulating layer. Further, using a paste having the same composition, a land having a diameter of 300 μm is printed on the front and back exposed portions of the via hole by a screen printing method, which is dried and semi-cured at a temperature of 80 ° C. for 10 minutes, and then heated at a temperature of 150 ° C. for 1 hour. Then, the insulating layer and the conductive paste were thermally cured to prepare wiring boards (sample Nos. 3 to 13) having via-hole conductors in the insulating layer. The volume shrinkage of the used conductor paste under the above curing conditions was 5%.

A pulse current is applied between the land portions of the via-hole conductors to the obtained wiring board under the conditions shown in Table 1, and a current is applied to some of the boards under the conditions shown in Table 1. went. Then, the specific resistance of the conductor wiring layer in the wiring board after these treatments was measured, and the result was shown in Table 1.
It was shown to.

Example 2 A slurry was prepared by mixing 70% by volume of substantially spherical silicon oxide having an average particle size of about 5 μm, 30% by volume of a novolak type epoxy resin and a curing agent, and using this slurry by a doctor blade method. This was applied on a carrier sheet and dried at a temperature of 60 ° C. for 60 minutes to form a semi-cured insulating layer having a thickness of 200 μm and a size of 200 mm square, and a via hole having a diameter of 100 μm was formed by punching.

Next, a conductive paste composed of 70% by volume of copper powder having an average particle diameter of 1 μm and 30% by volume of novolak type epoxy resin was filled in the via holes of the insulating layer. Furthermore, using a paste of the same composition, a land having a diameter of 300 μm is printed on the front and back exposed portions of the via hole by a screen printing method, and this is dried and cured at a temperature of 100 ° C. for 30 minutes, and then heated at a temperature of 150 ° C. for 30 minutes. Then, the insulating layer and the conductive paste were thermally cured to prepare wiring boards (sample Nos. 14 and 15) having via-hole conductors in the insulating layer.
In addition, the volume shrinkage rate of the used conductor paste under the above curing conditions was 8%.

The obtained wiring board was subjected to a pulse current application and / or an electric heating treatment in the same manner as in Example 1, and the specific resistance of the conductor wiring layer was measured for the obtained wiring board. The results are shown in Table 1.

Example 3 A slurry was prepared by further mixing a curing agent with 50% by volume of substantially spherical silicon oxide having an average particle size of about 5 μm and 50% by volume of an imide resin, and using this slurry, a doctor blade method was used. On a carrier sheet by using
Dry for 30 minutes at a temperature of 100 μm and a size of 20
A 0 mm square semi-cured insulating layer was formed, and a via hole having a diameter of 75 μm was formed by punching.

Next, copper powder 75 having an average particle size of 0.7 μm
A conductor paste consisting of 25% by volume and 25% by volume of an imide resin was filled in the via hole of the insulating layer. Further, a land having a diameter of 200 μm was printed on the front and back exposed portions of the via holes by a screen printing method using a paste having the same composition, and this was dried and semi-cured at a temperature of 150 ° C. for 60 minutes.
By heating at a temperature of 30 ° C. for 30 minutes to thermally cure the insulating layer and the conductive paste, wiring boards having via-hole conductors in the insulating layer (Sample Nos. 16 and 17) were produced. The volume shrinkage of the used conductor paste under the above curing conditions was 2%.

The obtained wiring board was subjected to a pulse current application and / or a heating treatment in the same manner as in Example 1, and the specific resistance of the conductor wiring layer was measured for the obtained wiring board. The results are shown in Table 1.

Comparative Example A via paste of the insulating layer prepared in Example 1 was filled with a conductor paste composed of 93% by volume of copper powder having an average particle diameter of 5 μm and 7% by volume of cellulol.
Using a paste of the same composition, a land having a diameter of 300 μm was printed on the front and back exposed portions of the via holes by a screen printing method, and this was dried and semi-cured at a temperature of 70 ° C. for 30 minutes.
Heating was performed at a temperature of 150 ° C. for 1 hour to thermally cure the insulating layer and the conductive paste, thereby producing a wiring board (sample No. 18) having a via-hole conductor in the insulating layer. The conductor paste used had a volume shrinkage of 0.2% under the above curing conditions.
It was below.

The obtained wiring board was subjected to a pulse current application and / or an electric heating treatment in the same manner as in Example 1, and the specific resistance of the conductor wiring layer was measured for the obtained wiring board. The results are shown in Table 1.

[0045]

[Table 1]

According to the results shown in Table 1, the sample no. In 1, the resistivity of the conductive wiring layer was 7 × ^{10 -5} Ω-cm, Sample No.2 was subjected to energization heat treatment thereto, 5 × 10 ^-5 Ω-
The resistance decreased to cm.

On the other hand, when a pulse current is applied according to the present invention, the specific resistance of each of the conductor wiring layers becomes 4 × 10
^-5 Ω-cm or less, and in particular, the samples having a volumetric shrinkage of 1% or more during curing of the conductive wiring layer achieved a specific resistance of 2 × 10 ^-5 Ω-cm or less. Voltage 10
１８18 V, pulse energization time 0.01 to 0.2 second, pulse interval 0.01 to 0.2 second, all 9.5 × 10 ^-6
It could be reduced to Ω-cm. Further, in each of the samples subjected to the heating treatment in addition to the application of the pulse current, 1 × 10 ⁻⁵ Ω-cm or less was achieved.

[0048]

As described in detail above, according to the wiring board of the present invention, the conductor wiring layer is made of a low-resistance metal and a thermosetting resin, and the powders are pressed against each other by curing shrinkage during thermosetting. Since the contact portion between the powders can be discharge-welded by applying a pulse current, the specific resistance of the conductor wiring layer can be significantly reduced. This makes it possible to manufacture a wiring board that can sufficiently cope with miniaturization and high density of the wiring layer.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a wiring board of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating layer 2 Conductor wiring layer 3 Via-hole conductor

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shuichi Tateno 1-4-4 Yamashita-cho, Kokubu-shi, Kagoshima Inside the Kyocera Research Institute

Claims (6)

[Claims] 1. A wiring board having a via-hole conductor containing metal powder disposed in an insulating layer containing at least an organic resin, wherein the metal powder in the via-hole conductor is bonded to each other by a thermosetting resin. And a contact portion between the metal powders is welded. 2. The metal powder comprises copper, silver, aluminum,
2. The wiring board according to claim 1, wherein the wiring board is at least one selected from the group consisting of gold. 3. The via-hole conductor has a specific resistance of 1 × 10 ^−5.
The wiring board according to claim 1 or 2, wherein the resistance is equal to or less than Ω-cm. 4. A step of forming a via hole in an insulating layer containing at least an organic resin, a step of filling a conductive paste containing a metal powder and a thermosetting resin in the via hole, and curing the conductive paste. Forming a via hole conductor formed by bonding metal powders to each other with a thermosetting resin; and applying a pulse current to the via hole conductor to discharge-weld a contact portion between the metal powders. A method for manufacturing a wiring board, comprising: 5. The method according to claim 4, wherein the via-hole conductor is subjected to an electric heating process after or simultaneously with the discharge welding step. 6. The method according to claim 5, wherein the specific resistance of the via-hole conductor after application of the pulse current is 1 × 10 ⁻⁵ Ω-cm or less.