JP2010192786A - Method of forming wiring conductor, and wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent metal becoming wiring conductors from scattering due to irradiation with laser beams in a method of forming the wiring conductor using a laser. <P>SOLUTION: When wiring conductors 2 buried in a base material 1 are obtained by forming a metal film 3 on the base material 1, forming grooves 6 in the base material 1 by irradiating the metal film 3 with laser beams 5 from above, filling the grooves 6 with fused metal while fusing the metal forming the metal film 3, and then cooling and solidifying the metal, a scatter prevention layer 4 having laser beam transmissivity is formed on the metal layer 3 and prevents the metal forming the metal film 3 from scattering due to the irradiation with the laser beams 5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method of forming a wiring conductor and a wiring board, and more particularly to a method of forming a wiring conductor using a laser and a wiring board including a wiring conductor formed by this method.

  In recent years, higher functionality and higher performance of electronic devices have been accelerated, and accordingly, further miniaturization is required for electronic components used in electronic devices. As a result, strict accuracy has been required for printing in the electronic component manufacturing process.

  As electronic components are miniaturized, the required print line width is also getting thinner. The current circuit formation method is mainly screen printing, but the line width is said to be 30 μm. On the other hand, there is a method using a laser as one of circuit forming methods of less than 30 μm.

  For example, in Japanese Patent Laid-Open No. 2002-261439 (Patent Document 1), a metal film (for example, a conductive paste film) is formed on an insulating sheet, a laser beam is irradiated from the metal film side, and a laser beam irradiation unit is irradiated. A method of melting a metal film and an insulating sheet with generated heat to form a via conductor in the insulating sheet is disclosed.

  When the technique described in Patent Document 1 described above is applied to the formation of a wiring conductor on a substrate, the metal film evaporates by laser ablation at the time of laser light irradiation depending on the laser output and the metal material constituting the metal film. Or metal particles contained in the metal film may scatter and a desired wiring conductor may not be formed. In particular, when the substrate is made of a high melting point material such as Si, sapphire, or alumina that requires a large amount of energy to form a groove in which the wiring conductor is embedded in the substrate, the energy of the laser beam is used to form the groove. Accordingly, a situation in which evaporation of the metal film and scattering of the metal particles are more likely to occur is brought about.

JP 2002-261439 A

  Accordingly, an object of the present invention is to provide a method of forming a wiring conductor that can solve the above-described problems.

  Another object of the present invention is to provide a wiring board provided with a wiring conductor formed by the above-described forming method.

  The method for forming a wiring conductor according to the present invention includes a step of preparing a base material, a metal film forming step of forming a metal film on the base material, and laser light in a direction from above the metal film toward the base material. A laser beam irradiation step of filling the groove with the melted metal while melting the metal constituting the metal film while evaporating the material of the base material by irradiating; And a step of cooling and solidifying the molten metal in the groove. In order to solve the above technical problem, a laser is further provided after the metal film forming step and before the laser beam irradiation step. An anti-scattering layer forming step is provided to form a light-transmitting anti-scattering layer on the metal film, and the laser light irradiation step is to prevent the metal constituting the metal film from being scattered by the laser light irradiation by the anti-scattering layer. Implemented while preventing It is characterized in Rukoto.

  In the method for forming a wiring conductor according to the present invention, typically, the scattering prevention layer is made of a solid plate such as a glass plate.

  In the case described above, when the metal film forming step includes a step of forming a conductive paste film by applying a conductive paste containing a conductive metal powder, a binder, and a solvent on a substrate, a scattering prevention layer In the forming step, before the conductive paste constituting the conductive paste film is dried, it is preferable that a solid plate serving as a scattering prevention layer is placed on the conductive paste film.

  Moreover, when the scattering prevention layer is comprised from a solid board, it is also preferable to provide the liquid with which the clearance gap between a solid board and a metal film is filled.

  In the method for forming a wiring conductor according to the present invention, the scattering prevention layer may be made of a liquid instead of the solid plate as described above.

  In the method for forming a wiring conductor according to the present invention, the laser light is preferably laser light having a pulse width of femtosecond (less than 1 picosecond) (hereinafter referred to as “femtosecond laser light”). In this case, it is preferable that the laser beam is focused on the substrate in the laser beam irradiation step.

  In the method for forming a wiring conductor according to the present invention, it is preferable to further include a step of removing the metal film remaining on the surface of the base material excluding the groove.

  The present invention is also directed to a wiring board including a wiring conductor formed by the above-described forming method.

  According to the present invention, since the scattering of the metal constituting the metal film due to the ablation at the time of laser light irradiation is suppressed by the scattering preventing layer, the wiring conductor can be stably formed with a sufficient film thickness.

  When the above-mentioned scattering prevention layer is formed of a solid plate such as a glass plate, and the metal film is provided by a conductive paste film, the conductive paste constituting the conductive paste film is dried before drying. If a solid plate serving as a scattering prevention layer is placed on the conductive paste film, the conductive paste film and the scattering prevention layer can be easily brought into close contact with each other. And if the scattering prevention layer is adhered to the metal film in this way, the metal scattering suppressing effect by the scattering prevention layer is further enhanced.

  Similarly, even if a liquid is applied on the metal film and a solid plate is placed on the metal film to fill the gap between the solid plate and the metal film, the anti-scattering layer and the metal film And the metal scattering suppression effect by the scattering prevention layer is enhanced.

  In the present invention, when femtosecond laser light is used as the laser light, the energy of the laser light can be concentrated in a desired region and the amount of energy can be adjusted with good accuracy. The groove can be formed in the substrate with high accuracy and depth accuracy, and therefore the pattern accuracy and thickness accuracy of the wiring pattern embedded in the groove can be increased. Therefore, it is easy to reduce the line width of the wiring conductor and increase the line thickness.

  As described above, when femtosecond laser light is used, when the laser light is focused on the base material in the laser light irradiation step, the energy used to form grooves in the base material is used to melt the metal film. Can be greater than the energy used. Therefore, even when a relatively large energy is required for forming the groove, such as when a wiring conductor is formed on a base material made of a high melting point material such as Si, sapphire, or alumina, the transpiration of the metal film is performed. It is possible to reduce the energy spent on

  In the present invention, if the method further comprises the step of removing the metal film remaining on the surface of the base material excluding the groove, the laser can be formed without forming a metal film with a desired pattern in advance on the base material. A desired pattern can be given to the wiring conductor only by drawing with light.

It is sectional drawing which shows sequentially the typical process with which the formation method of the wiring conductor by one Embodiment of this invention is equipped.

  As shown in FIG. 1 (6), a wiring conductor 2 in an embedded state is formed on the base material 1. Hereinafter, a method of forming the wiring conductor 2 on the substrate 1 will be described with reference to FIGS. 1 (1) to 1 (6) sequentially.

  First, as shown in FIG. 1 (1), a substrate 1 is prepared. As the base material 1, for example, a ceramic substrate such as alumina, a green sheet before firing the ceramic, an organic resin substrate such as polyimide, a single crystal substrate such as Si or sapphire, or a metal substrate such as stainless steel can be used. . The substrate 1 is preferably subjected to surface cleaning by, for example, plasma ashing or using an organic solvent such as acetone, isopropyl alcohol, methanol, ethanol, or the like, in the subsequent steps.

  Next, as shown in FIG. 1 (1), a metal film 3 is formed on the substrate 1. As the metal constituting the metal film 3, for example, Au, Ag, Cu, Ni, Fe, Al, Cr, Co, Ta, W, Ti, Pd, Pt, etc., any type of metal can be used. Can also be used. As a method for forming the metal film 3, in addition to a CVD method (chemical vapor phase method), a sputtering method, a vapor deposition method, and a plating method, a conductive metal powder, a conductive material containing a binder and a solvent for forming the metal film 3 are used. When an adhesive paste is used, a coating method such as a printing method, an ink jet method, or a spin coating method can be used. The optimum thickness of the formed metal film 3 varies depending on the type of metal and the output of laser light described later, but is preferably about 1 μm to 100 μm.

  Next, as shown in FIG. 1 (2), a scattering prevention layer 4 is formed on the metal film 3. The scattering prevention layer 4 has a laser beam transparency, but the attenuation factor of the laser beam is preferably 50% or less. Moreover, it is preferable that the scattering prevention layer 4 is a thing which does not evaporate with the heat | fever by laser beam irradiation. The scattering prevention layer 4 is typically composed of a solid plate such as a glass plate. As described above, when the metal film 3 is provided by a conductive paste film formed by applying a conductive paste on the substrate 1, before the conductive paste constituting the conductive paste film is dried, It is preferable to place a solid plate to be the scattering prevention layer 4 on the conductive paste film. This is because the adhesion between the scattering prevention layer 4 and the metal film 3 can be enhanced.

  Further, when a solid plate is used as the anti-scattering layer 4, the adhesion between the solid plate and the metal film 3 is improved by applying a liquid for filling the gap between the solid plate and the metal film 3. You may make it raise. For example, after the metal film 3 is formed, a liquid is applied thereon, and then a solid plate that becomes the scattering prevention layer 4 is placed. When this embodiment is adopted, when the metal film 3 is provided by a conductive paste film, the conductive paste constituting the conductive paste film is in an undried state even if it is already dried. May be. Further, as described above, the metal film 3 may be formed by a CVD method, a sputtering method, a vapor deposition method, a plating method, or the like.

  Further, the scattering prevention layer 4 may be provided only by liquid as long as the above-described conditions for the scattering prevention layer 4 are satisfied.

  Next, as shown in FIG. 1 (3), the laser beam 5 is irradiated through the scattering prevention layer 4 in the direction from the upper side of the metal film 3 toward the base material 1. As a result, as shown in FIG. 1 (4), the material of the base material 1 is evaporated by ablation at the portion of the base material 1 irradiated with the laser beam 5, and as a result, the groove 6 is formed. At the same time, the metal constituting the metal film 3 is melted by the heat generated by the irradiation of the laser beam 5, and the melted metal fills the groove 6. When the metal is cooled and solidified, the wiring conductor 2 is formed along the groove 6.

  In the laser light irradiation process described above, the scattering prevention layer 4 acts to prevent the metal constituting the metal film 3 from scattering due to the irradiation of the laser light 5.

  The conditions such as the type, frequency, and pulse width of the laser beam 5 described above are set in a range in which the groove 6 is formed on the substrate 1 by ablation and the metal constituting the metal film 3 is melted by heat. Further, the output (energy) of the laser beam 5 is set so that the lower limit value is that which can ablate the substrate 1, and the upper limit is that in which the metal film 3 is not substantially evaporated.

In the above-described process, the laser light 5 is not limited in kind, such as YAG laser light, CO ₂ laser light, excimer laser light, and fiber laser light, but it is particularly preferable to use femtosecond laser light. This is because with the femtosecond laser light, the energy of the laser light 5 can be concentrated in a desired region, and the amount of energy can be adjusted with good accuracy.

  When femtosecond laser light is used, the laser light 5 is preferably focused on the substrate 1. Thereby, the energy used for forming the groove 6 in the substrate 1 can be made larger than the energy used for melting the metal film 3. That is, ablation is more likely to occur in the base material 1 and, on the other hand, in the metal film 3 that is out of focus, energy is not concentrated, so thermal melting is more likely to occur rather than ablation. Therefore, even if the substrate 1 is made of a high melting point material such as Si, sapphire, or alumina that requires relatively large energy for forming the groove 6, the groove 6 can be efficiently formed, and the metal film The metal constituting 3 can be efficiently melted and filled into the groove 6 without substantially evaporating.

  Next, as shown in FIG. 1 (5), the scattering prevention layer 4 is removed, and then, as shown in FIG. 1 (6), the metal film remaining on the surface of the base material 1 excluding the grooves 6 is removed. 3 is removed. When the metal film 3 is made of a conductive paste film, the excess metal film 3 can be easily removed with an organic solvent. In this case, since the wiring conductor 2 embedded in the groove 6 is in a sintered state, it is not removed by the solvent. In addition, if removal with a solvent is possible in this way, a subsequent polishing step becomes unnecessary. The removal of the scattering prevention layer 4 may be performed simultaneously with the removal of the remaining metal film 3.

  In this way, the wiring conductor 2 is formed on the substrate 1. When the base material 1 is what forms at least a part of a wiring board, for example, when the above-described steps are finished, a wiring board including the wiring conductor 2 is obtained.

  Although the present invention has been described with reference to the embodiment shown in FIG. 1, various other modifications are possible within the scope of the present invention.

  For example, in the step of forming the metal film 3 on the base material 1, in the illustrated embodiment, the metal film 3 is formed over almost the entire surface on the one main surface of the base material 1, but in the region where the formation of the wiring conductor 2 is planned. Only the metal film 3 may be formed. In this way, it is possible to save the metal material consumed for forming the wiring conductor 2.

  Next, examples carried out according to the present invention will be described.

  First, a Si substrate (manufactured by Ferrotec Co., Ltd., thickness 0.38 mm) was used as a base material. Then, the surface of this Si substrate was cleaned with isopropyl alcohol.

  Next, Ag nano paste (viscosity 20 Pa · s) manufactured by Namics Co., Ltd. was applied on the Si substrate with a spin coater (1000 rpm · 30 seconds) to obtain a metal film made of a conductive paste having a thickness of about 10 μm.

  Next, after drying the conductive paste constituting the metal film, a cover glass (thickness 0.15 mm) made by Matsunami Glass, which becomes a scattering prevention layer, was placed on the metal film.

  Next, femtosecond laser light was irradiated from above the metal film through the cover glass. As the femtosecond laser beam, one having a repetition frequency of 1 kHz, a wavelength of 800 nm, and an output of 10 mW was used, and the focus was set on the base material, and the scanning speed was set to 0.1 mm / second. By this laser light irradiation, formation of grooves on the Si substrate, filling of the grooves with metal, and metal sintering were completed at the same time.

  Next, the cover glass was removed, and then the Si substrate was dipped in acetone and further subjected to ultrasonic cleaning to remove excess paste remaining in portions other than the grooves. Thus, a desired wiring conductor was formed on the Si substrate.

  Next, the cross-sectional part of the wiring conductor was observed with an electron microscope, and the thickness T of the wiring conductor (see FIG. 1 (6)) was obtained. In addition, as thickness T, the protrusion height from the base-material surface of a wiring conductor was measured. The results are shown in Table 1 below.

  Example 2 is different from Example 1 in that the anti-scattering layer is composed of only a liquid, and a solvent (texanol) contained in the conductive paste is used as the liquid. For other points, the wiring conductor was formed in the same manner as in Example 1, and the thickness T of the wiring conductor was determined. The results are also shown in Table 1.

  In Example 3, as compared with Example 1, before placing the cover glass serving as the anti-scattering layer on the metal film, the solvent (texanol) used in Example 2 was applied on the metal film, on which The difference is that a cover glass is placed. For other points, the wiring conductor was formed in the same manner as in Example 1, and the thickness T of the wiring conductor was determined. The results are also shown in Table 1.

  In Example 4, as compared with Example 1, in the stage where the cover glass serving as a scattering prevention layer is placed on the metal film, the conductive paste constituting the metal film is left in an undried state without being dried. The difference is that the glass is placed on an undried conductive paste film. For other points, the wiring conductor was formed in the same manner as in Example 1, and the thickness T of the wiring conductor was determined. The results are also shown in Table 1.

  As can be seen from Table 1, Example 2 is superior to Example 1, Example 3 is superior to Example 2, and Example 4 is superior to Example 3.

  That is, as in Example 1, when the anti-scattering layer is composed only of a solid cover glass, if the particle size of the metal particles contained in the metal film is small, the metal particles are between the metal film and the cover glass. As in Example 2, the scattering prevention layer is made liquid so that the adhesion between the scattering prevention layer and the metal film surface is improved, and the scattering of metal particles contained in the metal film is effectively suppressed. Is done. As a result, the thickness T of the formed wiring conductor can be made thicker in the second embodiment than in the first embodiment.

  Next, in the case of Example 2, the scattering prevention layer itself made of a liquid is evaporated to some extent by the irradiation of laser light, but as in Example 3, by placing a cover glass on it, The liquid can remain under the cover glass without evaporating or splashing. As a result, according to the third embodiment, the thickness T of the wiring conductor can be made larger than that of the second embodiment. Therefore, according to Example 3, it can be said that even a base material made of a material that requires a high laser output upon groove formation can be used.

  Next, according to Example 4, the highest adhesion is obtained between the metal film and the cover glass, and the metal particles themselves are less likely to be scattered. As a result, the thickness T of the wiring conductor can be increased. Moreover, according to Example 4, since it is not necessary to dry the electrically conductive paste which comprises a metal film, cost reduction and labor saving can be anticipated.

DESCRIPTION OF SYMBOLS 1 Base material 2 Wiring conductor 3 Metal film 4 Anti-scattering layer 5 Laser beam 6 Groove

Claims (10)

Preparing a substrate;
Forming a metal film on the substrate, and forming a metal film;
By irradiating a laser beam in a direction from above the metal film toward the base material, the material of the base material was evaporated while forming a groove in the base material, and the metal film was configured. A laser beam irradiation step of filling the groove with the molten metal while melting the metal;
Cooling and solidifying the molten metal in the groove, and
After the metal film forming step, and before the laser light irradiation step, a scattering prevention layer forming step for forming a scattering prevention layer having laser light transmittance on the metal film,
The laser light irradiation step is performed while preventing scattering of the metal constituting the metal film by laser light irradiation by the scattering prevention layer.
A method of forming a wiring conductor.   The method for forming a wiring conductor according to claim 1, wherein the scattering prevention layer is made of a solid plate.   The method for forming a wiring conductor according to claim 2, wherein the solid plate is made of a glass plate.   The metal film forming step includes a step of forming a conductive paste film by applying a conductive paste containing a conductive metal powder, a binder and a solvent on the substrate, and the scattering prevention layer forming step includes the step of The method for forming a wiring conductor according to claim 2, further comprising a step of placing the solid plate on the conductive paste film before the conductive paste constituting the conductive paste film is dried.   The method for forming a wiring conductor according to claim 2, further comprising a step of applying a liquid for filling a gap between the solid plate and the metal film.   The method for forming a wiring conductor according to claim 1, wherein the scattering prevention layer is made of a liquid.   The method for forming a wiring board according to claim 1, wherein the laser beam is a laser beam having a pulse width of femtoseconds.   The method of forming a wiring conductor according to claim 7, wherein the laser light is focused on the base material in the laser light irradiation step.   The method of forming a wiring conductor according to claim 1, further comprising a step of removing the metal film remaining on the surface of the base material excluding the groove.   A wiring board comprising a wiring conductor formed by the forming method according to claim 1.

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