JPH1154864A - Printed circuit board and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed circuit board provided with a conductor wiring layer, having high conductivity and superior anti-migration characteristic at low cost, and its manufacture. SOLUTION: This printed circuit board has an insulation board containing at least an organic resin on the front side of which and/or inside of which a conductor wiring layer is formed, containing silver-coated copper powder that is coated with 1-30 wt.% of silver and whose average particle diameter is 3-10 μm. In this case, a pulse current whose current density is 1-2000 A/cm<2> and whose pulse width is 0.01-1000 msec is applied to the conductor wiring layer, to form a neck part consisting of a silver-copper alloy to contact parts among the silver-coated copper powders 5, 5, and then thereby to enhance low resistance and anti-migration performance.

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 and increases the contact resistance, which has not led to a reduction in the specific resistance of the conductor wiring layer, and furthermore, the presence of silver alone causes migration. There is a current situation. In addition, various improvements have been made, such as heat decomposition of this resin component and conducting electric heating.However, sufficient effects have not been obtained in these heat treatments, and in some cases, depending on the heating, There were problems such as adverse effects on the insulating layer.

An object of the present invention is to provide a wiring board having a conductor wiring layer which is inexpensive, has high conductivity, and has excellent migration resistance, without causing the above-mentioned disadvantages, and a method of manufacturing the same. It is assumed that.

[0010]

Means for Solving the Problems As a result of repeated studies on the above problems, the present inventor has used silver-coated copper powder containing a predetermined amount of silver as a main conductor component for forming a conductor wiring layer, A heat treatment is applied to the conductor wiring layer formed using this powder at a high pressure to bring the particles into pressure contact with each other,
By applying a pulse current to the conductor wiring layer,
Discharge occurs near the point of contact between metal particles, removing the resin and oxide on the surface of the silver-coated copper powder that was preventing electrical conduction and simultaneously welding the particles together to form a contact part with an alloy of silver and copper It has been found that the resistance of the wiring layer can be remarkably reduced, and that the amount of silver present alone can be reduced by alloying, so that migration due to silver can be suppressed. It has been found that it is possible to form a highly reliable conductor wiring layer that can respond to the demand for the realization.

That is, the wiring board of the present invention has an insulating substrate containing at least an organic resin, and the surface and / or inside of the insulating substrate is coated with 1 to 30% by weight of silver and has an average particle size of 3 to 10 μm. A wiring substrate on which a conductor wiring layer containing silver-coated copper powder is formed, wherein a neck portion made of a silver-copper alloy is formed at a contact portion between the silver-coated copper powders of the conductor wiring layer. That is.

Further, in the method for producing a wiring board according to the present invention, the surface and / or inside of an insulating substrate containing at least an organic resin is coated with 1 to 30% by weight of silver and has an average particle size of 3 to 3%.
After forming a conductor wiring layer containing 10 μm silver-coated copper powder, applying a pulse current to the conductor wiring layer, welding the contact portion between the silver-coated copper powder and converting it to a silver-copper alloy. In particular, the current density of the applied pulse current is 1 to 2000 A / cm ² , and the pulse width is 0.0
1 to 1000 msec. It is characterized by being.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A wiring board according to the present invention is basically composed of an insulating substrate 1 and a conductor wiring layer 2, as shown in a schematic sectional view of FIG. The conductor wiring layer 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 between different wiring circuit layers 3.

The insulating substrate in 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 resins, imide resins, fluororesins, phenylene ether resins, bismaleide triazine resins, urea resins, melamine resins, silicone resins, urethane resins, unsaturated polyester resins, allyl resins, and the like, alone or in combination.

In the above-mentioned insulating substrate, 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, BaTiO
₃ , inorganic fillers such as 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 preferably compounded in a volume ratio of 15:85 to 50:50. Among these,
In terms of workability, strength and the like of the insulating layer, a mixture of an epoxy resin, an imide resin, a phenylene ether resin, and a silica or aramid nonwoven fabric is most desirable.

According to the present invention, the conductor wiring layer 2 contains silver-coated copper powder as a conductor material. The silver-coated copper particles contain 1 to 30% by weight of silver, preferably 1 to 15% by weight of the total amount.
It is necessary to contain it in a proportion of weight%. This is because when the silver coating amount is less than 1% by weight, the oxidation resistance is deteriorated as in the case of the conventional copper powder, and when the silver content is more than 30% by weight, silver migration is likely to occur.

The silver-coated copper powder has an average particle size of 3 to
It needs to be 10 μm, especially 3 to 8 μm, optimally 3 to 7 μm. This is because when the average particle diameter is smaller than 3 μm or larger than 10 μm, the printability and filling property of the conductive paste are all deteriorated,
This is because the resistance increases due to a decrease in the packing density of the silver-coated copper particles. In the silver-coated copper powder, metal particles other than copper and silver, for example, Fe, Co,
Ni or the like may be contained in a total amount of 10% by weight or less.

Further, a resin binder may be blended in the conductor wiring layer of the wiring board of the present invention in order to obtain a bond between the silver-coated copper particles. Glycol resins such as cellulose and polyethylene glycol are preferably used in terms of properties, but the above-mentioned thermosetting resins and the like can also be used.
As the amount of the resin binder increases, the contact resistance tends to increase due to interposition between the particles, so that the printability is preferably 2 parts by weight or less, particularly 0.05 to 1 part by weight. In addition, it is desirable to reduce the resistance of the conductor wiring layer.

The exposed surface of the conductor wiring layer of the wiring board of the present invention has excellent corrosion resistance of nickel, gold, etc.
In addition, a metal having excellent bonding properties with electronic components such as semiconductor elements and connectivity with a wiring layer of an external electric circuit board is formed in a thickness of 1 to 20 μm by plating so that the conductive wiring layer is oxidized. Corrosion can be effectively prevented, and electrical connection of the conductor wiring layer to an electric component or an external electric circuit board can be easily and firmly made.

The silver-coated copper powder 5 in the conductor wiring layer is
Usually, as shown in FIG. 2, a surface of an inner core 6 made of copper is constituted by a shell 7 made of silver having a predetermined thickness, and the powders 5 are in point contact with each other. On the other hand, according to the present invention, as shown in FIG.
The neck portion 8 is formed by welding the contact portion between them, and at least the neck portion 8 is formed of a silver-copper alloy alloyed with the copper component of the inner core 6 and the silver component of the shell 7. The width L of the neck portion 8 is desirably at least 1/5 of the particle size of the powder 5 in order to achieve low resistance. In addition, the neck portion 8 is formed of a silver-copper alloy film in which the copper component is mixed in the shell on the powder surface even in the non-contact portion between the powders, in view of the migration resistance. Is desirable.

According to the method for manufacturing a wiring board of the present invention, first, a thermosetting resin or a thermoplastic resin and an inorganic filler as described above are used, and an appropriate curing agent is added thereto.
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 wiring layer containing silver-coated copper powder is formed on the insulating layer. As the applicable conductor wiring layer,
Either a via-hole conductor or a through-hole conductor connecting the wiring circuit layers formed on the surface of the insulating substrate or between the insulating layers and / or the wiring circuit layers may be used. When forming the conductor wiring layer, a conductor paste mainly composed of silver-coated copper 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 conductive paste used at this time has a mean particle size of 3 to 10 μm, particularly 3 to 7 μm, as a solid component.
m, optimally 3-5 μm silver-coated copper powder and powder 100
2 parts by weight or less, particularly 0.0
5 to 1 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 each having a conductor wiring layer 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 wiring layer 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, Further, they can be laminated with an adhesive interposed between the insulating layers.

In the wiring board thus manufactured, a thin resin film exists on the surface of the metal powder in the conductor wiring layer due to the resin contained in the wiring layer, or the metal powder in the conductive wiring layer is exposed to oxygen in the atmosphere. An oxidized 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.

Therefore, according to the present invention, a pulse current is applied to the conductor wiring layer in the wiring board manufactured as described above. When a pulse current is continuously applied to the 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, the contact portion between the silver-coated copper powders is in a welded state as described above, and at the same time, silver and copper are alloyed at least in the contact portion. The amount of silver produced decreases, and the migration resistance can be improved.

The pulse current is applied by pressing the electrodes against both ends of the conductor wiring layer to which the current is applied to apply the pulse current. The optimum conditions for the applied pulse current are as follows: current density is 1 to 2000 A / cm ² , and pulse width is 0.01 to 1
000 msec. If the current density is lower than 1 A / cm ² , it is difficult to remove the oxide film and resin existing at the interface between the metal powders without welding,
If it exceeds 0 A / cm ² , heat is partially generated and the insulating substrate may be damaged. Also, preferably,
Pulse interval by pulse train is 0.01 to 1000 mse
c. And current is applied for 5 seconds to 5 minutes,
0 seconds to 1 minute is desirable.

It is desirable that the shape of one pulse of the pulse current in the low frequency region be 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 is higher than 350 ° C., the 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.

The current 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 conductor wiring layer, the specific resistance is reduced to 5 × 10 ⁻⁵ or less, particularly to 3 × 10 ⁻⁵ Ω · cm or less when the silver content is 5% by weight or more. Can be realized. 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 1 × 10 ¹³ Ω · cm
As described above, especially when the silver content is 15% by weight or less, 6 × 10 ¹³ Ω · c
m, which can provide a highly reliable wiring board that can meet the demand for ultra-fine and precise conductor wiring layers in the wiring board.

[0033]

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

Next, 99.8 parts by weight of silver-coated copper powder having an average particle size and silver content shown in Table 1, 0.2 parts by weight of cellulose, and 10 parts by weight of 2-octanol as a solvent were provided on the surface of the insulating substrate. A conductive paste was prepared by mixing the above-mentioned parts and a comb-tooth 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.

Next, eight insulating layers on which the conductor wiring layers were formed as described above were prepared, and the resultant was aligned and laminated and pressed. Then, the laminate was set in a press machine, and a pressure of 50 kg / cm ² was applied. Further 120
C. to remove the organic solvent in the paste. After that, the substrate was treated at 250 ° C. for 5 hours to completely cure the thermosetting resin, thereby producing a wiring board.

A pulse current was applied to the obtained wiring board at the extremes of the conductor wiring layer 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. Also, for some substrates,
Electric heating was performed under the conditions shown in Table 1.

Then, the initial volume resistivity of the conductor wiring layer in the wiring board after these treatments was measured at 130 ° C. and 85%
The insulation resistance between the comb patterns after applying a DC voltage of 5 V to the relative humidity for 100 hours was measured, and the results are shown in Table 1. In addition, the contact state of the silver-coated copper powder in the conductor wiring layer is 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 is measured. The average was calculated.

[0038]

[Table 1]

As is clear from the results shown in Table 1, the sample No. having a silver content in the silver-coated copper powder of less than 1% by weight was used.
Sample No. 6 has a specific resistance of more than 5 × 10 ⁻⁵ Ω-cm, and in Sample No. 25 containing more than 30% by weight, the resistance after energization treatment at high temperature and high humidity was reduced by migration. Sample No. 1 having an average particle size smaller than 3 μm was used.
３3, or sample No. 20３2 larger than 10 μm
Sample No. 2 had a large specific resistance.

Further, according to the present invention, the current density is 1 to 2000 A / cm ² and the pulse width is 0.01
~ 1000 msec. In the other samples of the present invention to which the pulse current was applied, neck growth due to welding at the contact portion between the powders was observed from SEM observation. Further, as a result of analyzing the components of the neck portion by EPMA (X-ray microanalyzer) for each sample in which the growth of the neck was observed,
In both cases, both silver and copper components are detected from the neck,
It was found that the neck was made of a silver-copper alloy. In addition, it was found that among the samples having a pulse current value of 1000 A / cm ² or more, the silver-copper alloy was formed also on the surface of the non-contact portion between the silver-coated copper powders.

Each of these samples of the present invention has a low initial resistivity of 5 × 10 ⁻⁵ Ω-cm or less in the conductor wiring layer, and has a low inter-wiring resistance after voltage application in high temperature and high humidity. It exhibited excellent migration resistance with a resistance of 1 × 10 ¹³ Ω-cm or more.

[0042]

As described in detail above, according to the wiring board of the present invention, since the conductive wiring layer is formed of silver-coated copper powder, it has excellent conductivity. Since the resin or oxide on the surface can be removed and the contact portion between the particles can be welded, the specific resistance of the conductor wiring layer can be significantly reduced. Furthermore, since the contact portion between the silver-coated copper particles is alloyed, migration resistance is also excellent. As a result, a highly reliable wiring board that can sufficiently cope with the miniaturization and high density of the wiring layer and can meet the demands for ultrafineness and precision can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a wiring board of the present invention.

FIG. 2 is an enlarged view of a main part for describing a contact state of silver-coated copper powder in a conductor wiring layer according to the present invention.

FIG. 3 is an enlarged view of a main part for describing a contact state of silver-coated copper powder in a conductor wiring layer in the related art.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 insulating substrate 2 conductor wiring layer 3 wiring circuit layer 4 through-hole conductor / via-hole conductor 5 silver-coated copper powder 6 internal core 7 shell 8 neck

Claims (3)

[Claims] An insulating substrate containing at least an organic resin, and a silver-coated copper powder coated on a surface and / or inside of the insulating substrate and coated with silver of 1 to 30% by weight and having an average particle size of 3 to 10 μm. A wiring board having a conductor wiring layer formed thereon, wherein a neck portion made of a silver-copper alloy is formed at a contact portion between the silver-coated copper powders of the conductor wiring layer. 2. An insulating substrate containing at least an organic resin, and a silver-coated copper powder coated on the surface and / or inside of the insulating substrate with 1 to 30% by weight of silver and having an average particle size of 3 to 10 μm. A method of manufacturing a wiring board, comprising: forming a conductive wiring layer, applying a pulse current to the conductive wiring layer, and welding a contact portion between the silver-coated copper powders to form a silver-copper alloy. 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. 3. The method for manufacturing a wiring board according to claim 2, wherein: