JPH10335526A - Circuit substrate and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accomplish the state of low resistance and the long-term stability of the via hole conductor in a circuit substrate where the via hole conductor, containing metal powder, is formed on an insulate layer containing organic resin. SOLUTION: This circuit substrate comprises an insulating layer 1 containing at least thermosetting organic resin, a multiple layer conductive circuit layer 2 formed between the insulating layer 1 and a via hole conductor 3 containing at least metal powder 4 and used to connect the upper and the lower circuit layers 2. In this manufacturing method, the filling rate of the metal powder 4 can be increased by 65% or higher by pressing and heating the conductive paste after it is filled in the via holes. The organic resin contained in the insulating layer 1 is impregnated into the gap between the metal powder 4 formed by removing the junction material and/or the solution contained in the conductive paste, and the resin 5 is filled in the above-mentioned gap.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board which is provided with a bifocal conductor formed by filling a conductive paste containing a metal powder into an insulating layer containing an organic resin, and is suitable for a semiconductor housing package and the like, and its manufacture. It is about the method.

[0002]

2. Description of the Related Art Conventionally, a ceramic multilayer wiring board capable of high-density wiring has been widely used as a multilayer wiring board, for example, a multilayer wiring board used for a package containing a semiconductor element. This ceramic multilayer wiring board
An insulating substrate such as alumina and a paste containing a high melting point metal such as W or Mo are printed on the surface and / or inside thereof, or the paste is filled into via holes formed in the substrate and fired simultaneously with the insulating substrate. The semiconductor device includes the formed wiring conductor, and a recess for housing the semiconductor element is formed in a part of the insulating substrate, and the recess is hermetically sealed by a lid.

However, since the ceramics constituting such an insulating substrate has a hard and brittle property, chips or cracks of the ceramics are liable to be generated in a manufacturing process or a transporting process, and the hermetic sealing of the semiconductor element is difficult. There are problems such as a low manufacturing yield due to damage or a complicated manufacturing process.

Further, in a ceramic multilayer wiring board, when a conductive paste is printed on a green sheet before sintering and then sintered, shrinkage occurs, so that the resulting board has deformation such as warpage and dimensional variation. There is a problem in that it is difficult to cope with strict requirements for flatness of the substrate such as ultra-high density circuit boards and flip chips.

[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. After printing a paste containing powder on the insulating layer to form a wiring layer, and then laminating, or after lamination, form a via hole at a desired position by microdrilling or punching, etc., and apply metal to the inner wall of the hole by plating. 2. Description of the Related Art A multilayer printed wiring board has been proposed in which the upper and lower wiring layers are connected by being attached thereto.

Recently, in response to demands for multilayer printed wiring boards and finer wiring, a circuit is formed on the surface of an insulating layer containing an organic resin using a conductive paste containing a low-resistance metal such as copper. Attempts have been made to manufacture high-density multilayered wiring boards.

[0007]

However, in a conductor paste containing a low-resistance metal, a binder and a solvent are compounded in order to enhance the printability on the insulating layer and to bind the metal powder to each other. The surroundings of the metal powder are surrounded by this binder and solvent, and the contact between the metal powders is poor,
There is a problem that the resistance value is higher than that of a conductor circuit formed by ordinary copper foil or copper plating.

Therefore, after printing the conductor paste,
2. Description of the Related Art A binder and a solvent are thermally decomposed, and a printed wiring layer is pressed to be densified. However, even in the conductor wiring layer thus obtained, the binder and the solvent cannot be completely removed, and the resistivity is 7 × at most.
The resistance was about 10 ⁻⁴ Ω · cm, and it was difficult to reduce the resistance. Further, even if the binder and the solvent can be completely removed, a gap is formed between the low-resistance metal particles,
There is a problem that moisture invades from the outside into the gap, oxidizes the metal powder, and ruptures the substrate when the temperature of the substrate increases.

In view of the above, the present invention provides a circuit board in which a via-hole conductor containing a metal powder is formed on an insulating layer containing an organic resin, the circuit board having a low resistance of the bifocal conductor, and excellent long-term stability, and a method of manufacturing the same. The aim is to provide a method.

[0010]

Means for Solving the Problems As a result of repeated studies on the above-mentioned problems, the present inventors have conducted a heat treatment after filling a conductive paste containing a metal powder, a binder and a solvent into a via hole. Thus, when the binder and / or solvent in the paste is removed, a gap is inevitably formed between the metal powders. By applying pressure,
By increasing the filling rate of the metal powder and leaching the organic resin in the insulating layer into the via-hole conductor to fill the gap between the metal powders with the organic resin, the via-hole conductor has low resistance and long-term stability. The inventors have found that an excellent circuit board can be provided, and have reached the present invention.

That is, the circuit board of the present invention has a structure in which a plurality of insulating layers containing at least an organic resin are laminated, a plurality of conductive circuit layers are formed on the surface of the insulating layer and between the insulating layers, and at least a metal powder is formed. A circuit board comprising a via hole conductor for connecting the conductive circuit layers of upper and lower different layers, wherein the filling rate of the metal powder in the via hole conductor is 65% or more; An organic resin contained in the insulating layer is filled in gaps between the metal powders.

Further, as a method of manufacturing such a circuit board,
A step of forming a via hole in an uncured insulating layer containing at least an organic resin, a step of filling the via hole with a conductive paste containing a metal powder, a binder and a solvent to form a via hole conductor; Forming a conductive circuit layer on the surface of the insulating layer on which the conductive circuit is formed, laminating a plurality of insulating layers on which the conductive circuit is formed, and heating the insulating layer on which the via-hole conductor is formed by at least the step of: A step of removing the binder and / or the solvent in the conductor paste; and heating the laminated insulating layer after the heat treatment while applying pressure so that the filling rate of the metal powder in the via-hole conductor is 65% or more. After filling the via hole conductor with the organic resin in the insulating layer and filling the gap between the metal powders with the organic resin, It is characterized in that it comprises the step of fully curing the thermosetting resin in the via-hole conductor and the insulating layer.

Preferably, the organic resin contained in the uncured insulating layer has a viscosity of not less than 500 poise at a temperature of 100 ° C. or less, and has a minimum viscosity of 100 poise or less. The circuit layer is formed by forming a conductive circuit on the surface of a transfer sheet and transferring the circuit to the insulating layer by pressure.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in a schematic sectional view of FIG. 1, a circuit board according to the present invention has a plurality of insulating layers 1 containing at least a thermosetting organic resin laminated thereon, and a surface of the insulating layer 1 and an insulating layer. The conductor circuit layer 2 is formed between the layers 1, and the conductor circuit layer 2 is formed over multiple layers.

The conductor circuit layers 2 of different layers are electrically connected by via-hole conductors 3.

The thermosetting organic resin contained in the insulating layer 1 includes, for example, an epoxy resin, a triazine resin, a polybutadiene resin, a phenol resin, a fluorine resin,
Any resin generally used for circuit boards, such as diallyl phthalate resin and polyimide resin, may be used.

In the insulating layer 1, it is desirable to combine a filler with a resin in order to increase the strength of the entire substrate. As the filler to be combined with the resin, SiO
₂ , Al ₂ O ₃ , ZrO ₂ , AlN, SiC, Si ₃ N
₄ , BaTiO ₃ , SrTiO ₃ , zeolite, CaT
iO ₃ and aluminum borate particles. Further, as the insulating layer, a sheet (prepreg) in which glass fiber is impregnated with a resin, a sheet in which aramid nonwoven fabric or woven fabric is impregnated with a resin, or the like can be used.

The via-hole conductor 3 of the circuit board of the present invention forms a conductive path for electrically connecting the conductive circuit layers 2 and contains at least a metal powder.

The metal powder is preferably a low-resistance metal mainly composed of at least one or two or more alloys selected from the group consisting of copper, silver, aluminum and gold, particularly copper or an alloy containing copper. In some cases, a high-resistance metal such as a Ni—Cr alloy may be mixed or alloyed as a conductor composition for adjusting the resistance of the circuit. Further, in order to lower the resistance, a metal having a lower melting point than the low-resistance metal, for example, a low-melting metal such as solder or tin may be included in the conductor composition.

According to the present invention, the via-hole conductor has a filling rate of the metal powder in the via-hole conductor of 6%.
Another significant feature is that it is 5% or more, especially 70% or more.

The filling factor is a major factor in determining the resistivity of the via-hole conductor. If the filling ratio is lower than 65%, the resistivity of the conductor decreases.

Further, as shown in FIG. 2, the via-hole conductor according to the present invention is characterized in that the thermosetting resin 5 contained in the insulating layer 1 is filled between the metal powders 4. By filling the thermosetting resin 5, moisture does not enter from the outside to oxidize the metal powder, and the substrate is not damaged by expansion of the gap when the substrate temperature increases.

Next, a method of manufacturing a circuit board according to the present invention will be described. First, as an insulating layer, a thermosetting organic resin as described above, or a composition comprising a thermosetting organic resin and a filler is sufficiently mixed by means of a kneader, a three-roll mill, or the like. After molding into a sheet by a method, injection method, doctor blade method or the like, the thermosetting resin is semi-cured. For semi-curing, the resin may be heated to a temperature slightly lower than a temperature sufficient to completely cure the resin.

Then, via holes are formed in the semi-cured insulating layer. The formation of this via hole
A known method such as drilling, punching, sandblasting, or processing by irradiation with a carbon dioxide gas laser, a YAG laser, an excimer laser, or the like is employed.

Thereafter, a conductive paste is filled into the via hole to form a via hole conductor. The conductor paste is prepared by adding and mixing a binder and a solvent to the metal powder as described above. As a binder added to the paste, an organic resin such as cellulose is used,
The solvent may be any solvent in which the binder used can be dissolved, and for example, isopropyl alcohol, terpineol, 2-octanol, butyl carbitol acetate and the like are used.

Next, a conductive circuit layer is formed on the surface of the insulating layer on which the via-hole conductor has been formed.

As a method of forming a conductive circuit layer, a metal foil such as copper is adhered to an insulating layer with an adhesive, a resist of a circuit pattern is formed, and a metal in a non-resist region is removed by etching with an acid or the like. , Method of attaching a pre-punched metal foil, method of screen-printing a circuit pattern on the surface of an insulating layer using a conductive paste filled in the via hole, transfer of film, glass, metal plate, etc. A metal layer is formed by plating or bonding a metal foil to the surface of the medium, a conductive circuit layer is formed by etching the metal layer, and then the conductive circuit layer is transferred while pressing the transfer medium onto the insulating layer. Is adopted. Then, the plurality of insulating layers on which the via-hole conductors and the conductive circuit layers are formed as described above are aligned, and a desired number of layers are laminated and pressed.

Further, the insulating layer on which the via-hole conductor is formed is heated to decompose and remove the binder and / or the solvent in the via-hole conductor. The heating temperature at this time is appropriately adjusted depending on the types of the binder and the solvent, but is performed at a temperature at which the thermosetting resin in the insulating layer is not cured. This treatment removes the binder and / or the solvent in the via-hole conductor, so that a gap is necessarily formed between the metal powders in the via-hole conductor.

The step of decomposing and removing the binder and / or the solvent in the via-hole conductor is performed by filling the conductor paste into the via-hole of the insulating layer, immediately before forming the conductor circuit layer, or in the conductor circuit layer and the via-hole. This may be performed immediately before laminating the insulating layer on which the conductor is formed.

Thereafter, the temperature of the laminated body after the above-mentioned treatment is raised to a temperature sufficient to cure the thermosetting resin in the insulating layer while applying pressure. By this heating and pressurizing treatment, the filling rate of the metal powder in the via-hole conductor is increased, and the thermosetting resin is leached from the side wall of the via-hole conductor into the gap between the metal powders of the via-hole conductor and filled, and the curing temperature is reduced. Then, the thermosetting resin filled in the via hole conductor and the thermosetting resin in the insulating layer are completely cured.

The heating temperature at this time depends on the organic resin used, but the heating is performed at a temperature of 150 to 300 ° C. In addition, the pressure when pressing the laminate at this time is sufficient to increase the filling rate of the metal powder into the via-hole conductor and to allow the organic resin in the insulating layer to leach and fill the gap in the via-hole conductor. Pressure is applied, desirably 20 to 150 kg
/ Cm ² is applied. By setting the filling rate of the metal powder in the via-hole conductor by the heating and pressurizing treatment to 65% or more, particularly 70% or more, the resistance of the via-hole conductor can be reduced.

According to the present invention, in order to enhance the filling property of the organic resin into the gap in the via-hole conductor by the heating and pressurizing treatment, the viscosity of the thermosetting resin contained in the insulating layer at this time is set to 100. It is desirable that the temperature be 500 ° C. or less at a temperature of not more than 100 ° C.

When the viscosity at 100 ° C. or less is less than 500 poise, the resin in the insulating layer oozes into the via-hole conductor in the step of removing the binder and the solvent contained in the conductor paste, and the via-hole conductor As a result, the metal powder invades between the metal powders, thereby deteriorating the connectivity between the metal powders.Furthermore, when the resin is cured by pressurizing and heating, there is no gap in the via hole conductor. However, even if a high pressure is applied, the filling rate of the metal powder cannot be increased, and the resistivity cannot be decreased.

If the minimum viscosity is higher than 100 poise, the thermosetting resin in the insulating layer penetrates into the via-hole conductor during the process of raising the temperature to the curing temperature of the thermosetting resin in the insulating layer while applying pressure. This is because it becomes difficult to fill the gap between the metal powders. Further, even when the resin is cured at a curing temperature without applying pressure, the thermosetting resin in the insulating layer does not easily enter the via-hole conductor.

Further, in order to enhance the filling property of the organic resin into the gaps in the via-hole conductors by the heating and pressurizing treatment, the conductor circuit layer connected to the via-hole conductors is formed of a metal foil. By forming a conductive circuit layer made of a metal foil on the surface and pressing and transferring the conductive circuit layer to the insulating layer, it is possible to increase the pressure applied to the periphery of the via-hole conductor, thereby increasing the contact force between the metal powders and the via-hole. The filling rate of the metal powder in the conductor can be increased, and the resistance of the via-hole conductor can be reduced.

[0036]

EXAMPLE 60% by volume of SiO ₂ powder as a filler was mixed with various polyimide resins having the viscosity characteristics shown in Table 1 as a filler, and formed into a sheet having a thickness of 100 μm by a doctor blade method to form an insulating layer. FIG. 3 shows the relationship between the viscosity and the temperature of the polyimide resins of Sample Nos. 3 and 10.

A 20 μm beam diameter YAG
Laser light irradiation and scanning were performed to form a via hole having a diameter of 100 μm. Then, an average particle size of 5
A conductor paste prepared by mixing 1% by weight of ethyl cellulose as a binder and 6% by weight of 2-octanol as a solvent was mixed with a μm Ag-Cu alloy powder by a screen printing method.

Then, after a copper foil having a thickness of 12 μm is attached to a transfer sheet made of a PET film, a conductive circuit layer is formed by an etching method, and the insulating layer is formed to a thickness of 100 kg / cm.
^The conductor circuit layer was transferred to the insulating layer by applying a pressure of ² . Thereafter, four insulating layers produced in the same manner were laminated.

The laminate prepared as described above was subjected to heat treatment at 120 ° C. for 3 hours in nitrogen to remove the solvent in the insulating layer and the binder and the solvent in the via-hole conductor. Thereafter, the temperature was raised to the curing temperature of each resin while applying a pressure of 70 kg / cm ² , and then the curing temperature was increased to ² kg / cm 2.
After holding for a while, the thermosetting resin was completely cured to obtain a circuit board.

In the above process, after heat treatment at 120 ° C., the presence or absence of the formation of the gap between the metal powders in the via-hole conductor was observed by an SEM photograph. Also, 2
Observe the via-hole conductor after complete curing at 50 ° C,
The presence or absence of resin filling in the gap between the metal powders was observed by SEM. The results are shown in Table 1. The filling rate of the metal powder in the via-hole conductor was measured. The filling rate was determined by observing the cross section of the via-hole conductor with an SEM photograph and analyzing the area occupancy of the metal powder in the central portion of the via-hole conductor by image analysis. The resistivity of the via-hole conductor after complete curing was measured by a four-terminal method. Further, regarding the long-term stability of the via-hole conductor,
The resistivity of the via-hole conductor after being kept in an atmosphere of 85% humidity for 168 hours was measured, and the results are shown in Table 1.

For comparison, a circuit board was prepared in exactly the same manner as described above except that the circuit board was completely cured at 250 ° C. without applying pressure at the time of complete curing, and evaluated in the same manner as described above.

[0042]

[Table 1]

According to Table 1, in the examples within the scope of the present invention, a gap is formed between the metal powders in the via-hole conductor after the treatment at 120 ° C. It was confirmed that the metal powders were in strong contact with each other, the filling ratio of the metal powder was 65%, and that the gaps between the metal powders were filled with the resin. As a result, the via-hole conductor according to the present invention has an initial resistivity of not more than 3 × 10 ⁻⁵ Ω · cm, and the metal powder in the via-hole conductor is oxidized even if it is kept in a high-temperature and high-humidity state for a long time. 3 × 10 with almost no change in resistance
^-5 Ω · cm or less was achieved, and it was found to be excellent in long-term stability.

On the other hand, as a thermosetting resin constituting the insulating layer, a sample No using a resin having a viscosity at 100 ° C. or less of less than 500 poise of the organic resin contained in the uncured insulating layer. .1, 2, 3, and 4 show that the resin in the insulating layer oozes into the via-hole conductor after the treatment at 120 ° C. As a result, the resistance of the via-hole conductor was large.

In sample No. 13 having a minimum viscosity of more than 100 poise, no resin was filled in the via-hole conductor after pressurized heat treatment, and the resistance increased after heat treatment in a high-temperature and high-humidity atmosphere. The resistance of the conductor is 3.times.10.sup.- ⁵ .OMEGA.
cm or less could not be achieved.

Further, in Sample No. 14 in which no pressure treatment was performed at the time of complete curing, the filling ratio of the metal powder was low,
In addition, a gap remains in the via-hole conductor, the initial resistance exceeds 3 × 10 ⁻⁵ Ω · cm, and the resistivity is further increased by the treatment in a high-temperature and high-humidity environment.

[0047]

As described in detail above, according to the present invention,
By increasing the filling rate of the metal powder in the via-hole conductor, and filling the gap between the metal powders with a thermosetting resin in the insulating layer, the resistance of the via-hole conductor is reduced, and the penetration of moisture and high temperature of the substrate Thus, a highly reliable circuit board free from rupture or the like can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of the structure of a circuit board of the present invention.

FIG. 2 is a diagram for explaining a structure of a via-hole conductor in the circuit board of the present invention.

FIG. 3 is a diagram showing the relationship between viscosity and temperature of thermosetting resins (No. 3 and No. 10) used for an insulating layer in Examples;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating layer 2 Conductor circuit layer 3 Via-hole conductor 4 Metal powder 5 Thermosetting resin

Continuing from the front page (72) Inventor Akihiko Nishimoto 1-4-4 Yamashita-cho, Kokubu-shi, Kagoshima Prefecture Inside the Kyocera Research Institute (72) Inventor Shigeaki Fukumoto 1-4-4 Yamashita-cho, Kokubu-shi, Kagoshima Kyocera Corporation In the laboratory

Claims (4)

[Claims] An insulating layer containing at least a thermosetting organic resin, a plurality of conductive circuit layers formed on the surface of the insulating layer and between the insulating layers, and the upper and lower conductive circuit layers containing at least metal powder. In the circuit board having the via hole conductor for connecting the via holes, the filling rate of the metal powder in the via hole conductor is 65% or more, and the insulating layer is included in the gap between the metal powders in the via hole conductor. A circuit board filled with the organic resin. 2. A step of forming a via hole in an uncured insulating layer containing at least a thermosetting organic resin, and filling the via hole with a conductive paste containing a metal powder, a binder and a solvent to form a via hole conductor. Forming, forming a conductive circuit layer on the surface of the insulating layer on which the via-hole conductor is formed, laminating a plurality of insulating layers on which the conductive circuit and the via-hole conductor are formed, and forming the insulating layer A step of heating to remove at least the binder and / or the solvent in the conductor paste; and heating the laminated insulating layer after the heat treatment while applying pressure to fill the via-hole conductor with the metal powder. 6
After increasing to 5% or more, the thermosetting organic resin in the insulating layer is impregnated in the via hole conductor to fill the gap between the metal powders with the organic resin, and then the insulating layer and the via hole conductor are filled. A method for manufacturing a circuit board, comprising a step of completely curing the thermosetting resin. 3. The organic resin contained in the insulating layer has a viscosity at 100 ° C. or less in an uncured state of 500 poise or more and a minimum viscosity of 100 poise or less. 3. The method for manufacturing a circuit board according to 2. 4. The method according to claim 2, wherein the conductive circuit layer is formed by forming a conductive circuit on a surface of a transfer sheet and transferring the conductive circuit to the insulating layer by pressure.