JPH1197849A - Wiring board and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wiring board provided with a conductor circuit, having high conductivity at low cost and a superior migration-resistance, and its manufacturing method. SOLUTION: There are formed an insulating board 1 containing at least an organic resin, a wiring circuit layer 3 composed of mixed powder or alloy powder which have a mean particle size of 3 to 10 μm and contain, as a metal component, copper as a main component and 1 to 30 wt.% of silver, 0.1 to 15 wt.% of palladium wt.% or 0.1 to 25 wt.% of platinum and a conductor circuit 2 such as a via hole conductor 4 or the like. Thereafter, a pulse current is applied to the conductor circuit 2, and a contact part between powder particles is welded to form a neck part composed of an alloy containing at least silver and at least one kind of palladium or platinum.

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, wherein a conductive wiring layer containing a metal powder is formed on at least the surface and / or inside of an insulating substrate containing an organic resin. The present invention relates to a manufacturing method, and more particularly to improvement in resistance to migration of a conductive wiring layer and migration resistance.

[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 ceramic provided with an insulating layer such as alumina and a wiring layer made of a high melting point metal such as W and Mo. Wiring boards are often used, but such ceramic wiring boards are hard and brittle, so that in the manufacturing process or the transporting process, chipping or cracking of the ceramic is likely to occur, and also before sintering. When a metallized paste is printed on a green sheet, and the printed sheets are laminated and sintered, there is a problem that a substrate obtained by sintering is liable to be deformed such as warpage or dimensional variation, etc. However, there is a problem that it is not possible to sufficiently cope with strict requirements for flatness of a substrate such as ultra-high density and flip chips.

[0003] Therefore, recently, a copper foil is adhered to the surface of an insulating layer containing a resin and then etched to form a substrate on which a fine circuit is formed, or a paste containing a metal powder such as copper is printed on the insulating layer. After forming the wiring layer by laminating,
Alternatively, a printed wiring board has been proposed in which a hole is drilled for a via at a desired position after lamination by microdrilling or punching, a metal is attached to the inner wall of the via by a plating method, and a wiring layer is connected to form a multilayer. . Further, as an insulating layer, a substrate in which a powdery or fibrous inorganic filler is dispersed with respect to a resin in order to increase the strength has been proposed. Application to a multi-chip module (MCM) on which a semiconductor element is mounted is also being studied.

[0004] In response to the demands for multi-layer printed wiring boards, ultra-fine wiring, and precision as described above, a circuit pattern is formed on a surface of an insulating layer containing a resin by using a conductive paste containing a low-resistance metal such as copper. Attempts have been made to print high-density multi-layered wiring boards in which conductive paste is filled in through holes and conductive paste is filled in through holes.

[0005]

However, since a conductive paste containing a low-resistance metal is mixed with a resin in order to enhance the printability on the insulating property and to bond the metal powders to each other, the contact of the powders is reduced. At the interface, there is a problem that the resistance value is higher than that of a circuit formed by ordinary copper foil or copper plating because a resin is easily interposed.

For this reason, silver is frequently used as a low-resistance metal in the paste. The reason why silver is used as the main conductor component is that it has the highest conductivity among metals and has higher chemical stability than a base metal such as copper. However, silver has a very high cost, and silver has a phenomenon of migration between silver wirings due to the interaction between atmospheric moisture and a DC electric field, so-called migration. There was a problem in reliability under some conditions. On the other hand, copper has a low specific resistance to some extent and can be obtained at a lower cost than silver, but its surface is easily oxidized, so it is inconvenient to handle, for example, it needs to be stored by a special method.

Therefore, in order to solve these problems,
A conductive material in which the surface of copper particles is coated with low-resistance silver to reduce the specific resistance and suppress the oxidation of the copper particles is disclosed in JP-A-56-101.
No. 739 and Japanese Patent Application Laid-Open No. 8-13837.

However, even when these silver-coated copper particles are used, a resin of 3% by weight or more per total solid content is required to bind these particles,
This resin component intervenes in the contact portion between the particles to increase the contact resistance, which has not led to a reduction in the specific resistance of the conductive wiring layer, and furthermore, the silver alone presents a problem of migration. There is.

Therefore, in order to further solve these problems, there has been proposed a conductive powder obtained by alloying or adding palladium or platinum to the silver-coated copper powder. As a result, migration resistance is improved, but there is a problem that resistance is increased at present.

Various improvements have also been made such as removing the resin component in the paste by thermal decomposition and conducting electric heating. However, these heating treatments have not been sufficiently effective. In some cases, there is a problem that the heating adversely affects the insulating layer depending on the heating.

An object of the present invention is to provide a wiring board provided with a conductor circuit which is inexpensive, has high conductivity, and has excellent migration resistance, without causing the above-mentioned disadvantages, and a method for manufacturing the same. Is what you do.

[0012]

Means for Solving the Problems As a result of repeated studies on the above problems, the present inventor has found that a mixed powder containing at least one of palladium or platinum, silver and copper as a metal component, or By forming a conductive circuit from the alloy powder and applying a pulse current to this conductive circuit, a discharge is generated near the contact between the powders, and the resin or oxide on the surface of the conductive powder that prevented the conduction of electricity At the same time, the contact portions are formed of an alloy containing at least silver and at least one of palladium and platinum by welding the powders together, so that the resistance of the wiring layer can be remarkably reduced. It is found that the migration of silver can be suppressed because the amount of silver present in the alloy can be reduced by alloying. Thinning, and found that it is possible to form a highly reliable conductor interconnect layers that can be meet the requirements of refinement.

That is, the wiring board of the present invention has at least an insulating substrate containing an organic resin, and a surface and / or inside of the insulating substrate containing copper as a main component, silver of 1 to 30% by weight, and palladium of 0.1 to 0.3% by weight. 1 to 15% by weight or 0.1 to 2% platinum
A conductor circuit is formed of metal powder having an average particle size of 3 to 10 μm, which is contained at a ratio of 5% by weight, and at least silver and palladium or platinum are contained in a contact portion between the metal powders of the conductor circuit. A neck portion made of an alloy is formed.

Further, as a method of manufacturing such a wiring board,
An insulating substrate containing at least an organic resin, and a surface and / or inside of the insulating substrate containing copper as a main component and silver of 1 to 3;
0% by weight, 0.1 to 15% by weight of palladium or 0.1 to 25% by weight of platinum having an average particle size of 3 to 5%.
After forming a conductor circuit made of a 10 μm metal powder, a pulse current is applied to the conductor circuit to weld a contact portion between the metal powders to contain at least silver and at least one of palladium and platinum. A neck portion made of an alloy is formed. The applied pulse current has a current density of 1 to 2000 A / cm.
^2. Pulse width of 0.01 to 1000 msec. It is characterized by being.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A wiring board according to the present invention is basically composed of an insulating substrate 1 and a conductor circuit 2 as shown in a schematic sectional view of FIG. The conductor circuit 2 includes a wiring circuit layer 3 formed on the surface of an insulating substrate or between insulating layers, and a through-hole conductor or a via-hole conductor 4 for connecting the wiring circuit layers 3 in different layers.

The insulating substrate 1 according to the present invention is made of a thermosetting resin having electrical properties, heat resistance and mechanical strength as an insulating material, for example, aramid resin, phenol resin, epoxy resin, imide resin, fluorine resin, A phenylene ether resin, a bismireimide triazine resin, a urea resin, a melamine resin, a silicone resin, a urethane resin, an unsaturated polyester resin, an allyl resin and the like are included alone or in combination.

In the insulating substrate 1, a filler can be compounded with an organic resin in order to increase the strength of the entire insulating substrate or wiring substrate. SiO ₂ , Al ₂
O ₃ , ZrO ₂ , TiO ₂ , AlN, SiC, BaTi
Inorganic fillers such as O ₃ , SrTiO ₃ , zeolite, CaTiO ₃ , and aluminum borate are preferably used. Further, a nonwoven fabric or a woven fabric made of glass or aramid resin may be used by impregnating the above resin. The organic resin and the filler are in a volume ratio of 15:85 to 50: 5.
Suitably, the compound is formed in a ratio of 0. Among them, a mixture of an epoxy resin, an imide resin, a phenylene ether resin, and a nonwoven fabric of silica or aramid is most preferable in terms of workability and strength of the insulating layer.

According to the present invention, the conductor circuit 2 comprises copper as a main component, 1 to 30% by weight of silver, particularly 3 to 10% by weight, and 0.1 to 15% by weight of palladium, particularly 0.3 to 30% by weight. 10% by weight, or 0.1 to 25% by weight of platinum, especially 0.3 to 1%
A mixed powder or an alloy powder containing 0% by weight is contained as a metal powder. Here, the content of silver is limited to the above range. When the content is less than 1% by weight, oxidation resistance is deteriorated similarly to the conventional copper powder, and when the content is more than 30% by weight, migration of silver occurs. It is.

If the amount of palladium or platinum is less than 0.1% by weight, the effect of suppressing the migration of silver is reduced. If the amount of palladium is more than 15% by weight,
Alternatively, if the amount of platinum is more than 25% by weight, the resistance becomes high in any case.
Exceeding the weight percent is not desirable because the oxidation resistance deteriorates.

According to the metal powder of the present invention, the above-mentioned metal components composed of at least three components may be all alloyed or may be composed of a mixed powder. For example, powder coated with silver on the surface of copper powder, palladium or platinum powder can be added and mixed, but it is better that palladium or platinum maintain the bond with silver of the silver-coated copper powder, for example, The surface of the silver-coated copper powder can be coated with palladium or platinum by a plating method or coprecipitation powder, or can be used as a mechanical alloy powder. In particular, it is desirable to form a coating layer made of an alloy of silver and palladium or platinum on the surface of the copper powder.

The average particle size of the metal powder is 3 to 10 μm.
m, especially 3 to 7 μm, optimally 3 to 5 μm. This means that the average particle size is smaller than 3 μm,
Otherwise, when the thickness is larger than 10 μm, the printability and the filling property of the conductive paste are deteriorated, and the resistance is increased due to the decrease in the filling density of the metal powder. When palladium or platinum is mixed as a powder, the average particle size of the palladium or platinum powder is preferably 3 μm or less. This is because if the average particle size exceeds 3 μm, it becomes difficult to uniformly mix a small amount of palladium or platinum.

The metal powder in the present invention contains copper, silver,
As a metal component other than palladium or platinum, for example, Fe, Co, Ni or the like may be contained in a total amount of 10% by weight or less.

In the conductor circuit of the wiring board according to the present invention, a resin binder may be blended in order to bond the metal powders.
In terms of printability, cellulose resins and glycol resins such as polyethylene glycol are preferably used.
The aforementioned thermosetting resin or the like used for forming the insulating substrate can also be used. As the amount of the resin binder increases, the amount of the resin binder tends to increase between the powders and increase the contact resistance.
It is desirable that the amount be not more than 5 parts by weight, particularly 0.05 to 1 part by weight, in order to reduce the printability and the resistance of the conductor circuit.

The exposed surface of the conductor circuit of the wiring board of the present invention has excellent corrosion resistance such as nickel and gold, and has good bonding properties with electronic components such as semiconductor elements and connection with the wiring layer of the external electric circuit board. By forming a metal having excellent performance in a thickness of 1 to 20 μm by plating, it is possible to effectively prevent the conductive circuit from being oxidized and corroded, and to provide an electric component of the conductive circuit or an external electric circuit board. And easy and robust electrical connection.

According to the present invention, it is important that a neck portion is formed at a contact portion between metal powders, and it is important that the neck portion is formed of at least silver and an alloy of palladium or platinum. It is. The width of the neck portion is desirably at least 1/5 of the particle size of the metal powder in order to achieve a low resistance. And this neck part
Also, in the non-contact portion between the powder, at least silver,
It is desirable from the viewpoint of migration resistance that palladium or platinum is alloyed and silver is not present alone.

According to the method for manufacturing a wiring board of the present invention, first, a thermosetting resin as described above, or a thermoplastic resin and an inorganic filler, and an appropriate curing agent,
A slurry is formed by adding and mixing a solvent, and the slurry is formed into a sheet by a doctor blade method, a calender roll method, a rolling method, or the like to form an insulating layer. If desired, this is heated and cured 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, a conductor circuit containing a metal powder is formed on the insulating layer. The conductor circuit to be applied may be a wiring circuit layer formed on the surface of the insulating substrate or between the insulating layers, and / or a via-hole conductor or a through-hole conductor connecting the wiring circuit layers. When a conductive circuit is formed, a conductive paste mainly composed of a metal powder is printed to a thickness of 10 to 35 μm by a known printing method such as a screen printing method or a gravure printing method. When a via-hole conductor or a through-hole conductor is formed, a via-hole or a through-hole is formed in an insulating layer, and the hole is filled with a conductive paste.

The conductor paste used at this time is a solid component containing the metal powder and a resin binder in an amount of 2 parts by weight or less, particularly 0.05 to 1 part by weight, per 100 parts by weight of the metal powder.
Parts by weight, and further contains a suitable solvent and the like.
In some cases, the composition may contain an appropriate curing agent.

In the case of multi-layering, for example, a plurality of insulating layers in which a conductor circuit is formed by a conductor paste are laminated and pressure-bonded at a pressure of 30 kg / cm ² or less. This crimping is desirably performed in a state where the conductor circuit is softened, and when the resin binder is a thermosetting resin, the insulating layer can be adhered by laminating and crimping in a semi-cured state. Can be laminated with an adhesive between insulating layers.

In the wiring board manufactured in this manner, a thin resin film exists on the surface of the metal powder in the conductive circuit due to the resin contained in the wiring layer, or the metal powder is oxidized by oxygen in the atmosphere. A thin oxide film is formed. In the case of silver-coated copper powder, a single layer of silver is present on the surface, and silver migration easily occurs. Furthermore, in the case of silver-coated copper powder in which palladium or platinum is compounded, migration of silver is slightly suppressed, but the resistance is increased because of the presence of impurities.

Therefore, according to the present invention, a pulse current is applied to the conductor circuit in the wiring board manufactured as described above. When a pulse current is continuously applied to this wiring layer, a plasma discharge is generated between the metal particles. The plasma removes oxide films and deposits on the surface of the metal particles, resulting in a so-called welded state, whereby the metal particles can come into contact with each other without inclusions that impede the conductivity. It is possible to form a low-resistance wiring layer, which has not been achieved only by itself, without adversely affecting the surrounding insulating layer.

Further, according to the present invention, as described above, the contact portion between the silver-coated copper powders is in a welded state, so that a low resistance can be achieved, and at the same time, a state in which at least the contact portion is alloyed is obtained. As a result, silver present alone can be reduced, and the migration resistance can be increased.

The pulse current is applied by pressing electrodes on both ends of the conductor circuit to which the current is applied to apply the pulse current. The optimum conditions for the pulse current to be applied include a current density of 1 to 2000 A / cm ² and a pulse width of 0.01 to 10
00 ms. Is preferably used, and the current density is 1 A /
If it is lower than ² cm ² , it is difficult to remove an oxide film or resin existing at the interface between the metal powders without welding, and it is 2,000 A /
If it exceeds cm ² , heat may be partially generated to damage the insulating substrate. Further, it is preferable that the energizing time of one pulse be 3 seconds or less. Preferably, the pulse current is applied for 5 seconds to 5 minutes, particularly 10 seconds to 1 minute.

It is desirable that the pulse current is 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. The reason is that a rectangular wave is more likely to cause discharge between particles than a sine wave, has a higher surface cleaning effect, and a pulse current is less likely to cause dirt or the like to adhere to a once-cleaned particle surface than to an alternating current. is there.

Further, after the application of the pulse current, the wiring layer is subjected to a heat treatment by energization, whereby the resistance of the wiring layer can be further reduced. The energization treatment may be DC or AC with a current density of 1 to 4000 A / cm ² , and 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 exceeds 350 ° C., the resin constituting the insulating layer and the conductor circuit 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 heating can be performed simultaneously with the application of the pulse current. 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.

By controlling the pulse current applied to the above-described conductor circuit, it is possible to reduce the specific resistance to 5 × 10 ⁻⁵ Ω · cm or less. Further, according to the present invention, the wiring board manufactured by the above-described manufacturing method can apply a DC voltage of 5 V at 130 ° C. and 85% relative humidity in a comb pattern having a line width of 0.5 mm and a gap of 0.4 mm, for example. Insulation resistance after application for 100 hours is 5 × 10 ¹³ Ω · cm
It is possible to provide a highly reliable wiring board that exhibits the above-described excellent migration resistance and that can meet the demand for ultra-fine and precise conductor circuits in the wiring board.

[0038]

【Example】

Example 1 A slurry was prepared using 70% by volume of substantially spherical silicon oxide having an average particle diameter of about 5 μm and 30% by volume of an imide resin, and the slurry was applied to a carrier sheet by a doctor blade method. After drying at a temperature of 50 ° C. for 60 minutes, an insulating layer having a thickness of 120 μm was completed.

Next, a metal powder having the average particle diameter and the contents of silver, palladium and platinum shown in Table 1 on the surface of the insulating substrate, that is, a powder obtained by plating palladium or platinum on the surface of a silver-coated copper powder 100 parts by weight, cellulose 0.
A conductive paste was prepared by mixing 2 parts by weight and 10 parts by weight of 2-octanol as a solvent, and a comb pattern having a line width of 0.5 mm and a gap of 0.4 mm was printed by a screen printing method. Further, a through hole having a diameter of 0.1 mm was formed in one part, and the paste was filled in the hole. The content of the metal component in the metal powder is determined by ICP
Measured by emission spectroscopy.

Next, eight layers of insulating layers on which the conductor circuits were formed as described above were prepared, aligned, and laminated and pressed. And set this laminate in the press machine,
A pressure of 50 kg / cm ² was applied. Further, the paste was heated to 120 ° C. to volatilize and remove the organic solvent in the paste. Thereafter, the substrate was treated at 250 ° C. for 5 hours to completely cure the thermosetting resin, thereby producing a wiring board. (Samples Nos. 1 to 39) A pulse current was applied to the obtained wiring board at the extremes of the conductor circuit at the current density and pulse width shown in Table 1 for 30 seconds. Note that the interval between the pulses was the same as the pulse width. Some of the substrates were further heated by energization under the conditions shown in Table 1.

Then, the initial volume specific resistance of the conductor circuit in the wiring board after these treatments and the insulation resistance between the comb tooth patterns after applying a DC voltage of 5 V at 130 ° C. and 85% relative humidity for 100 hours were measured. The results are shown in Table 1. In addition, the contact state of the silver-coated copper powder on the conductor circuit was observed with a scanning electron micrograph (SEM) to confirm the presence or absence of welding, and the ratio of the neck width formed by welding to the particle size of the metal powder was measured. The average was determined.

Example 2 A wiring board was produced in exactly the same manner as described above, except that the conductive composite powder of Example 1 was replaced with a conductive alloy powder composed of copper, silver, palladium or platinum and having the composition shown in Table 3. Was prepared and evaluated similarly. (Sample Nos. 40 to 4
8)

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

As is clear from the results of Tables 1 to 3, the sample No. 8 having a silver content of less than 1% by weight has a large specific resistance, and the sample No. 33 having a silver content of more than 30% by weight has a high specific resistance. The resistance between the wirings decreased due to the migration.
In Sample No. 10 in which at least one of palladium and platinum was less than 0.1% by weight, migration could not be prevented, and the resistance between wirings was reduced. The sample No. 20 containing palladium exceeding 15% by weight and the platinum containing 25%
In the sample No. 26 in which the weight% is exceeded, the specific resistance of the wiring layer increased in each case.

Further, in Sample No. 4 to which no pulse current was applied even though the composition of the present invention was satisfied, no neck portion was formed at all, and in Sample No. 5 subjected to only current heating, the neck was slightly formed. Although formed, it did not reach the point where an alloy of silver and palladium or platinum was produced. As a result, in any case, the effect of suppressing the migration of silver was insufficient, and the resistance between wirings was reduced. Furthermore, the average particle size is 3 μm
Samples Nos. 1 to 3 smaller than Samples Nos. 34 to 36 over 10 µm all had large specific resistances.

In contrast to these comparative examples, all the products of the present invention were measured by an X-ray microanalyzer (EPMA) and found that a neck portion containing copper, silver, palladium or platinum was formed between the powders. Excellent resistance to migration with a specific resistance of the wiring circuit layer of 5 × 10 ⁻⁵ Ω · cm or less and an insulation resistance of 5 × 10 ¹³ Ω · cm or more after application of high temperature and high humidity voltage. showed that.

[0049]

As described in detail above, the wiring board of the present invention comprises a conductive circuit formed of a powder containing copper, silver, palladium or platinum in a specific ratio as a metal component, and applying a pulse current thereto. By applying the resin, the resin or oxide on the powder surface can be removed and a neck portion can be formed at the contact portion between the powders, so that the specific resistance of the conductor circuit can be significantly reduced. Furthermore, the metal component is silver,
Since it is composited with copper, palladium or platinum, it has high conductivity and excellent migration resistance. This makes it possible to provide a highly reliable wiring board which can sufficiently cope with the miniaturization and high density of the wiring circuit and can meet the demands for ultra-fine and high precision.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view for explaining a basic structure of a wiring board according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating board 2 Conductor circuit 3 Wiring circuit layer 4 Through-hole conductor / via-hole conductor

Claims (3)

[Claims] 1. An insulating substrate containing at least an organic resin and a surface and / or inside of the insulating substrate containing copper as a main component, silver of 1 to 30% by weight, palladium of 0.1 to 15% by weight or platinum. Is formed from a metal powder containing 0.1 to 25% by weight and having an average particle size of 3 to 10 μm, and at least silver, palladium or A wiring board, wherein a neck portion made of an alloy containing platinum is formed. 2. An insulating substrate containing at least an organic resin, and 1-30% by weight of silver, 0.1-15% by weight of palladium or platinum on a surface and / or inside of the insulating substrate, the main component being copper. Is formed from a metal powder containing 0.1 to 25% by weight and having an average particle size of 3 to 10 μm, and a pulse current is applied to the conductor circuit to make contact portions between the metal powders. Is welded to form a neck made of an alloy containing at least silver and at least one of palladium and platinum. 3. The current density of the applied pulse current is 1 to 20.
00 A / cm ² , pulse width of 0.01 to 1000 mse
c. 4. The method for manufacturing a wiring board according to claim 3, wherein