JPH11103142A - Wiring board and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wiring board at low cost and which has high conductivity, and the manufacturing method. SOLUTION: A wiring board formed of conductor wiring layers 2 containing copper powders in the mean particle diameter of 3-10 μm coated with at least one kind of metal selected from among Al, Au, Cd, Cr, Ni, Pb, Sn, Th, Ti, Tl, Zn, Zr, in an insulating substrate 1 containing at least an organic resin and on the surface or inside of the substrate 1, is impressed with a pulse current of a thickness of 1-2,000 A/cm<2> and a pulse width of 0.01-1000 msec so that neckparts 8 made of an alloy of copper and a coating metal are formed in the contact parts between the metal coated copper powders for lowering the resistance.

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 particularly to an improvement in lowering the resistance of a conductor wiring layer.

[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, in a conductive paste containing a low-resistance metal, a resin is mixed in order to improve the printability on the insulator and to bond the metal powder to each other. 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 low resistivity to some extent and can be obtained at a lower cost than silver, but is inconvenient to handle, for example, it needs to be stored by a special method because its surface is easily oxidized.

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

However, even when these silver-coated copper powders are used, a resin of 3% by weight or more per total solid content is required to bind these powders,
This resin component intervenes in the contact portion between the powders, increasing the contact resistance, not reducing the specific resistance of the conductor wiring layer, and further causing migration due to the presence of silver alone. 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.

SUMMARY OF THE INVENTION An object of the present invention is to provide a wiring board having a conductor wiring layer which is inexpensive and has high conductivity without causing the above-mentioned drawbacks, and a method of manufacturing the same.

[0010]

Means for Solving the Problems The present inventor has studied the above problems and found that Al, Au, Cd, Cr,
A copper powder coated with at least one metal selected from the group consisting of Ni, Pb, Sn, Th, Ti, Tl, Zn, and Zr and having an average particle diameter of 3 to 10 μm is used, and is formed using this powder. A heat treatment is applied to the conductive wiring layer at a high pressure to bring the powders into pressure contact with each other, and by applying a pulse current to the conductive wiring layer, a discharge is caused in the vicinity of the contact between the metal powders, and electric power is generated. By removing the resin and oxides on the surface of the coated metal that prevented the conduction and simultaneously welding the powders together to form the contact part with an alloy of the coated metal and copper, the migration of the wiring layer was reduced without the occurrence of silver migration. Since it can be remarkably reduced, it was found that this can form a highly reliable conductor wiring layer that can respond to the demand for ultra-fine and precise multilayer printed wiring boards. It was.

That is, the wiring board of the present invention comprises an insulating substrate containing an organic resin, and Al, Au, Cd, Cr, Ni, Pb, Sn, T, on the surface and / or inside of the insulating substrate.
h, a wiring board on which a conductor wiring layer containing a copper powder having an average particle diameter of 3 to 10 μm formed by coating at least one metal selected from the group consisting of Ti, Tl, Zn, and Zr is provided, A neck portion made of an alloy of copper and the coating metal is formed at a contact portion between the metal coating copper powder of the conductor wiring layer, and in particular, the thickness of the metal coating layer is 0.1
１1 μm.

Further, according to the method for manufacturing a wiring board of the present invention, an insulating substrate containing an organic resin, and Al, Au, Cd, Cr, Ni, Pb, S
n, Th, Ti, Tl, Zn, Zr, having an average particle diameter of 3 to 10 coated with at least one metal selected from the group consisting of
After forming a conductor wiring layer containing copper powder of μm, a pulse current is applied to the conductor wiring layer to weld a contact portion between the coated copper powder and a neck portion made of an alloy of the coated metal and copper. Wherein the current density of the applied pulse current is 1 to 2000 A / cm ² ,
The pulse width is 0.01 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 the insulating substrate 1 or between the insulating layers, and a through-hole conductor or a via-hole conductor 4 for connecting the wiring circuit layers 3 of 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 bismailide triazine resin, a urea resin, a melamine resin, a silicone resin, a urethane resin, an unsaturated polyester resin, an allyl resin, 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 is made of Al,
Au, Cd, Cr, Ni, Pb, Sn, Th, Ti, T
It contains copper powder coated with at least one metal selected from the group consisting of l, Zn, and Zr as a conductive material, and the thickness of the metal coating layer is preferably 0.1 to 1 μm. This is because if the thickness of the metal coating layer is less than 0.1 μm, the formation amount of the neck portion made of an alloy of the coating metal and copper is small, and it is difficult to obtain a sufficient contact area for energization. Further, when the thickness of the metal coating layer is larger than 1 μm, an alloy of the coating metal and copper is not formed in the contact portion between the powders.

In the present invention, each of the above-mentioned metal groups coated on the surface of copper powder has a property of forming an alloy with copper to become an alloy having a melting point of 900 ° C. or less. A neck portion made of an alloy of a coating metal and copper can be easily formed between powders by applying a low pulse current, and simultaneously promotes the growth of the neck portion. Can be further reduced. Among these coated metals, Al, Au, Ni, Pb, Sn, and Zn are preferable in terms of low resistance and cost.

The average particle size of the metal-coated copper powder is 3
It is necessary that the thickness be 10 to 10 μm, particularly 3 to 7 μm, and optimally 3 to 5 μm. This is because when the average particle size is smaller than 3 μm or larger than 10 μm, the printability and the filling property of the conductive paste are deteriorated and the filling density of the metal-coated copper powder is lowered, so that the resistance is increased. This is because

Further, in the conductor wiring layer of the wiring board of the present invention, a resin binder may be blended in order to establish a bond between the metal-coated copper powders. In terms of properties, cellulose resins, glycol resins such as polyethylene glycol are preferably used,
In addition, the above-described thermosetting resin or the like can be used. As the amount of the resin binder increases, it tends to increase the contact resistance by being interposed between the powders. Therefore, the content is preferably 2 parts by weight or less, particularly 0.05 to 1 part by weight. It is desirable to reduce the resistance of the layer.

The exposed surface of the conductor wiring layer in the wiring board of the present invention has excellent corrosion resistance, such as nickel or gold,
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 metal-coated copper powder 5 in the conductor wiring layer
Usually, as shown in FIG. 3, the surface of an inner core 6 made of copper is constituted by a shell 7 made of a metal 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. 2, the contact portion between the metal-coated copper powders 5, 5 is welded to form a neck portion 8, and at least the neck portion 8 has an inner portion. It is formed of an alloy of a copper component of the core 6 and a metal component of the shell 7. The width of the neck portion 8 is one of the particle size of the powder 5.
/ 5 or more is desirable for achieving low resistance.

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 wiring layer containing metal-coated copper powder is formed on the insulating layer. The conductor wiring layer to be applied may be any of 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 forming the conductor wiring layer, a conductor paste mainly composed of a metal-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 an average particle size of 3 to 10 μm, particularly 3 to 7 μm, as a solid component.
m, optimally 3-5 μm metal-coated copper powder and powder 10
2 parts by weight or less of resin binder is added to 0 part by weight, especially 0.1 part by weight
And 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.

According to the present invention, the conductor wiring layer in the wiring board thus manufactured is 40 kg / cm.
² or more, in particular by applying 60 kg / cm ² or more pressure to deform at the contact portion between the metal-coated copper powder conductor wiring layer, between the powder can be joined in a form close to a surface contact. If the pressure at this time is less than 40 kg / cm ² , the surface contact between the powders becomes insufficient, and it is difficult to reduce the resistance of the conductor wiring layer.

As a method of applying a pressure of 40 kg / cm ² or more to the conductor wiring layer, a wiring board on which the conductor wiring layer is formed is pressurized by a press or the like, It may be performed by a press machine.

In the wiring board manufactured as described above, a thin resin film exists on the surface of the metal powder in the conductive wiring layer due to the resin contained in the wiring layer, or a thin resin film exists due to oxygen in the atmosphere. An oxidized thin oxide film is formed.

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 applied to the conductor wiring layer, a plasma discharge occurs between the metal powders. This plasma removes oxide films and deposits on the surface of the metal powder, and forms a so-called welded state, so that the metal powders can come into contact with each other without inclusions that hinder 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.

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 pulse current to be applied include a current density of 1 to 2000 A / cm ² and a pulse width of 0.01 to 1000 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 00 A / cm ² , heat is partially generated and the insulating substrate may be damaged. Desirably, the energizing time of one pulse is 3 seconds or less, and the interval between pulses is 3 seconds or less. The pulse current application time is 5 seconds to 5 seconds.
Minutes, particularly 10 seconds to 1 minute.

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. The reason is that a rectangular wave is more likely to cause a discharge between powders than a sine wave and has a higher surface cleaning effect, and a pulse current is less likely to adhere to a once-cleaned powder surface with a DC current than with an AC. 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.

Further, the energization heating can be performed simultaneously with the application of the above-described 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, it is possible to realize a low resistivity of 5 × 10 ⁻⁵ Ω · cm or less. This makes it possible to provide a highly reliable wiring board that can meet the demand for ultra-fine and fine conductor wiring layers in the wiring board.

[0035]

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 metal-coated copper powder having the average particle diameter and the coating thickness of the coated metal shown in Table 1 were added to the surface of the insulating substrate, 0.2 parts by weight of cellulose, and 2-octanol 10 as a solvent. A conductive paste was prepared by mixing the paste with a weight part, a through hole having a diameter of 0.1 mm was formed, and the paste was filled in the through hole.

Next, eight insulating layers each having a conductor wiring layer formed thereon as described above were prepared, 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. Thereafter, the wiring board was manufactured by treating at 250 ° C. for 5 hours to completely cure the thermosetting resin.

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, and the results are shown in Table 1. In addition, the contact state of the metal-coated copper powder in the conductor wiring layer is observed by 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.

[0040]

[Table 1]

[0041]

[Table 2]

As is clear from the results in Tables 1 and 2, A
1, Au, Cd, Cr, Ni, Pb, Sn, Th, T
Each of the coated metals selected from the group consisting of i, Tl, Zn, and Zr exhibited a resistance value of 5 × 10 ⁻⁵ Ω · cm or less, and was effective in reducing the resistance of the conductor wiring layer.

However, the average particle size of the metal-coated copper powder is 3 to 1
Samples No. 2 to 5 of 0 μm had a resistance value of 5 × 10 ⁻⁵ Ω · cm or less, but Sample No. 1 of less than 3 μm,
For sample No. 6 larger than 10 μm, the packing density was reduced and the resistance was not reduced.

For the sample having a coating metal thickness of 0.1 to 1 μm, a low resistance value of 5 × 10 ⁻⁵ Ω · cm or less was obtained, but for the sample No having a coating metal coating thickness of less than 0.1 μm. In .11, the neck made of alloy is small and
The larger sample No. 16 did not have low resistance because the neck portion made of the alloy was small or not formed.

According to the present invention, the current density is 1 to 2000 A / cm ² and the pulse width is 0.01 to the conductor wiring layer.
~ 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 each case, both components of the coating metal and copper were detected from the neck portion, and it was found that the neck portion was an alloy of the coating metal and copper. Among them, the pulse current value is 1000
For the samples of A / cm ² or more, it was found that the surface of the non-contact portion of the metal-coated copper powder was a coating metal and a copper alloy.

[0046]

As described in detail above, according to the wiring board of the present invention, the conductor wiring layer is made of Al, Au, Cd, Cr, Ni,
Pb, Sn, Th, Ti, Tl, Zn, Zr, if formed from a copper powder having an average particle size of 3 to 10 μm coated with at least one metal selected from the group of the metal, it has excellent conductivity, By applying a pulse current, the resin or oxide on the powder surface can be removed and the contact portion between the powders can be welded, so that the specific resistance of the conductor wiring layer can be significantly reduced. 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 metal-coated copper powder in a conductor wiring layer according to the present invention.

FIG. 3 is an enlarged view of a main part for explaining a contact state of a metal-coated copper powder in a conventional conductor wiring layer.

[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 metal-coated copper powder 6 internal core 7 shell 8 neck

Claims (4)

[Claims] 1. An insulating substrate containing an organic resin, and Al, Au, Cd, Cr,
Ni, Pb, Sn, Th, Ti, Tl, Zn and Zr
A conductive wiring layer formed by coating at least one metal selected from the group consisting of a copper powder having an average particle diameter of 3 to 10 μm, wherein the metal-coated copper in the conductive wiring layer is provided. A wiring board, wherein a neck portion made of an alloy of copper and the coating metal is formed at a contact portion between the powders. 2. The metal-coated copper powder according to claim 1, wherein the metal-coated layer has a thickness of 0.1 to 1 μm.
The wiring board as described. 3. An insulating substrate containing an organic resin, and Al, Au, Cd, Cr,
Ni, Pb, Sn, Th, Ti, Tl, Zn and Zr
Forming a conductor wiring layer containing copper powder having an average particle size of 3 to 10 μm coated with at least one metal selected from the group consisting of: A method of manufacturing a wiring board, wherein a contact portion between powders is welded to form a neck portion made of an alloy of the coated metal and copper. 4. The current density of a pulse current to be applied 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