JP5859075B1 - Wiring board manufacturing method, wiring board, and dispersion for manufacturing wiring board - Google Patents

Abstract

A method of manufacturing a wiring board capable of obtaining a copper wiring board by a dry processing method (dry process) using copper microparticles is provided. A method of manufacturing a wiring board according to the present invention includes a method of manufacturing a wiring board in which conductive wiring is formed on an electrically insulating substrate, wherein copper microparticles, a volatile organic solvent, and A coating film forming step of obtaining a coating film by applying a dispersion liquid containing, a drying step of drying and removing the organic solvent by heat-treating the coating film, and a coating film after the drying step, in the atmosphere, A laser light irradiation step of obtaining a copper microparticle sintered film by irradiating a laser beam having a wavelength of 300 to 600 nm to sinter the copper microparticles and closely adhere to the substrate. [Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a wiring board, a wiring board, and a dispersion for manufacturing the wiring board.

  In addition to the conventional photochemical etching of copper foil and additive copper plating, a new dry process (dry process) that replaces these wet processes has recently been announced as a method for manufacturing wiring boards for electronic devices. In these dry process methods, copper nanoparticles are sintered and bulked by laser irradiation or plasma treatment of copper nanoparticles, and conductive wiring is formed on a substrate. As a wiring forming method by laser sintering or plasma processing that has already been disclosed, there are the following Patent Documents 1-7.

  Patent Document 1 (Japanese Patent Publication No. 2010-528428) discloses a method of forming a conductive film on an electrically insulating substrate, and depositing a film containing a plurality of copper nanoparticles on the surface of the substrate. And exposing at least a portion of the film to render the exposed portion conductive. Patent Document 1 describes that copper ink containing copper nanoparticles (with a diameter of less than 1000 nm) is sintered to a copper conductor using a laser (including a continuous laser and a pulse laser) for exposure. In addition, it is described that in a pulse laser, copper ink is sintered using a pulse laser of nanosecond to femtosecond.

  In Patent Document 2 (Japanese Patent Laid-Open No. 2014-57024), a support with a precursor layer having a support and a precursor layer containing copper oxide particles disposed on the support is irradiated with light. A method for producing a conductive layer comprising a reduction step of forming a conductive layer containing metallic copper by reducing the copper oxide particles, wherein the filling rate of the copper oxide particles in the precursor layer is 65% or more A method for manufacturing a conductive layer is disclosed. Patent Document 2 describes that the average particle diameter of copper oxide particles is preferably 200 nm or less, and more preferably 100 nm or less. Further, it is described that a laser beam is used as a light source used in the light irradiation process.

  Patent Document 3 (Japanese Patent No. 5507161) includes at least metal fine particles having an organic compound on the particle surface, a polymer dispersant, and a solvent, and the difference between the amine value and the acid value of the polymer dispersant (amine value − A step (a) of applying a dispersion having an acid value of 0 to 50 to a substrate to produce a coating film; and a step of irradiating the entire region or a partial region of the coating film with laser light in the atmosphere ( and b). A method for producing a coating film is disclosed. In Patent Document 3, the metal fine particles are preferably about 1 nm to 1 μm, more preferably metal fine particles having an average particle diameter in the range of 1 to 200 nm, and can be used for various purposes. Metal fine particles having an average particle diameter are more preferable, and in order to obtain finer electrodes, circuit wiring patterns and surfaces with excellent metal color tone, it is further preferable to use metal fine particles having an average particle diameter in the range of 1 to 50 nm. Preferred is described.

Patent Document 4 (Japanese Patent Laid-Open No. 2013-247060) discloses a conductive metal thick film forming material used for forming a conductive metal thick film. The material contains metal particles and metal nanoparticles used to form a conductive metal thick film, and organic substances, and exhibits a fluidity that can be applied. A conductive metal thick film forming material is applied onto a substrate. After forming the coating film of the conductive metal thick film forming material, the metal particles and the metal nanoparticles contained in the coating film are subjected to a treatment by irradiating with microwave plasma in a reducing atmosphere and firing. Thus, a conductive metal thick film forming material is disclosed, which is capable of forming a bulk conductive metal thick film.

  In Patent Document 5 (Japanese Patent Laid-Open No. 2010-87287), a coating liquid containing copper nanoparticles is printed in a pattern on a substrate to form a printed layer, and then the printed layer is baked to form a pattern. A method for manufacturing a semiconductor substrate for forming a semiconductor layer, wherein the printed layer is exposed to surface wave plasma generated by application of microwave energy in an oxygen-containing atmosphere, thereby firing the printed layer A method for manufacturing a semiconductor substrate is disclosed.

Patent Document 6 (Japanese Patent Application Laid-Open No. 2004-119686) discloses a method of forming a fine copper-based wiring pattern composed of a sintered body layer of copper nanoparticles on a substrate, and having an average particle diameter of 1 to 100 nm. And a step of drawing the coating layer of the fine wiring pattern on the substrate using a dispersion liquid containing nanoparticles having a copper oxide coating layer on the surface, which is selected within the range, and included in the coating layer Applying a treatment for reducing the surface copper oxide to the nanoparticles having a copper oxide coating layer on the surface, and further firing the nanoparticles subjected to the reduction treatment to form a sintered body layer; And the reduction treatment and the firing treatment performed in the same process,
A fine wiring pattern characterized by performing heating by selecting a heating temperature of 300 ° C. or less and exposing the nanoparticles contained in the coating layer in a plasma atmosphere generated in the presence of a reducing gas. A forming method is disclosed.

  Patent Document 7 (Japanese Patent Application Laid-Open No. 2004-218055) discloses a method of forming an electroless gold plating alternative conductive gold film using a conductive gold paste using gold ultrafine particles as a conductive medium. A step of forming a conductive gold paste coating layer on a base for forming a gold plating alternative conductive gold film, and heat-treating the formed conductive gold paste coating layer at a temperature not exceeding 300 ° C .; And a step of sintering the ultrafine gold particles contained therein, and the conductive gold paste to be used is composed of ultrafine gold particles whose average particle diameter is selected in the range of 1 to 100 nm in the organic solvent serving as the dispersion medium. The surface of the gold ultrafine particles is dispersed and coated with one or more compounds having a group containing any of nitrogen, oxygen and sulfur atoms as a group capable of coordinative bonding with the gold element. When processing, gold element Dissociation of a compound having a group containing nitrogen, oxygen, or sulfur atom as a group capable of coordinate bond from the surface of gold ultrafine particles, and a method for forming an electroless gold plating alternative conductive gold film Is disclosed.

Special table 2010-528428 JP 2014-57024 A Japanese Patent No. 5507161 JP 2013-247060 A JP 2010-87287 A JP 2004-119686 A Japanese Patent Laid-Open No. 2004-218055

  In the above prior art, copper nanoparticles are used as the copper particles, a dispersion liquid containing the copper nanoparticles is applied onto the substrate using an ink jet apparatus or the like, and the coating film is irradiated with laser or plasma to obtain a wiring substrate. ing. The reason for using copper nanoparticles is that they have high surface energy and are easily sintered by laser light or plasma irradiation. In general, it is well known that an organic compound film called a dispersant is formed on the surface of a nanoparticle in order to keep a metal nanoparticle shape having a high surface energy stable in a dispersion (in a solvent). As this dispersant, an amine-based organic compound such as polyethyleneimine or amine, or a sulfur-based organic compound such as thiol, which has high chelate bonding with copper, is used. This dispersant needs to be easily decomposed by laser irradiation, and if left, there is a possibility of increasing the electrical properties, particularly the specific resistance, of the bulk metal (copper wiring).

  In Patent Document 1, it is described that the solvent and the dispersant before laser sintering are dried at a temperature of less than 150 ° C. In practice, however, selection of a dispersant having a boiling point lower than this temperature is limited. And the dispersant may remain after laser sintering. If the dispersion does not completely burn or ablate (decompose and evaporate) by laser sintering, it can remain in the bulk copper. If the dispersant remains in the bulk copper, voids may be generated in the bulk coating and electrical characteristics may be deteriorated. For this reason, these dispersing agents need to be managed as the minimum necessary addition amount, and it is most desirable not to use a dispersing agent if possible.

  In addition, copper nanoparticles are generally produced by being collected in an organic solvent to which a dispersant has been added at the stage of being produced by a wet solution reduction method or an atomization method. Ingenuity is required, and the manufacturing cost is extremely high compared to copper microparticles.

  Furthermore, with copper nanoparticles, the film thickness that can be applied to the substrate at one time is very small compared to copper microparticles. In a wiring board using a normal copper conductor, the copper wiring film is required to have a thickness of 7 μm or more from the viewpoint of electrical characteristics. This is also intended to obtain a low high frequency characteristic impedance required in the transmission path of the wiring board. In order to obtain this required film thickness, the copper nanoparticle ink has high fluidity of the ink, and since it cannot normally be applied to a thickness of 5 μm or more, it is necessary to apply the dispersion liquid (ink) multiple times. This increases manufacturing costs.

  In view of the above circumstances, an object of the present invention is to provide a method for manufacturing a wiring board capable of obtaining a copper wiring board by a dry processing method (dry process) using copper microparticles.

  In order to achieve the above object, the present invention provides a method for manufacturing a wiring substrate in which conductive wiring is formed on an electrically insulating substrate, and the dispersion containing copper microparticles and a volatile organic solvent on the substrate. A coating film forming step for obtaining a coating film by applying a liquid, a drying step for drying and removing the organic solvent by heat-treating the coating film, and a coating film after the drying step having a wavelength of 300 to 600 nm in the atmosphere. A method of manufacturing a wiring board, comprising: a laser light irradiation step of obtaining a copper microparticle sintered film by irradiating a laser beam of To do.

  Moreover, the present invention provides a wiring board having a copper wiring on an electrically insulating substrate, wherein the copper wiring has a conductive layer obtained by sintering copper particles, and the conductive layer has a thickness of 7 μm or more. The present invention provides a wiring board characterized by the above.

  Further, the present invention is a dispersion for producing a wiring board used for forming conductive wiring on an electrically insulating substrate, and the dispersion contains copper microparticles and a volatile organic solvent. A dispersion for manufacturing a wiring board is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the wiring board which can obtain a copper wiring board by the dry-type processing method (dry process) using copper microparticles can be provided. In other words, instead of using a wet process such as chemical etching of copper foil or additive copper plating, a conductive wiring board can be formed without a photomask by printing ink containing copper microparticles and a dry process of laser sintering. Can be manufactured. The dispersion containing copper microparticles does not contain the dispersant used for nanoparticles, but uses only components that are completely decomposed by laser irradiation. Therefore, generation of voids and organic substances such as carbon (carbon) are not generated after laser sintering. A highly conductive film can be obtained without remaining. Furthermore, by using copper microparticles, it is possible to obtain a wiring layer thickness of 7 μm or more by a single ink printing.

  According to the manufacturing method of the present invention, a wiring film can be formed on a substrate (resin molded product) having various three-dimensional shapes. For example, a wiring film can be formed directly on an exterior part of an electronic device (such as a case of an IC card of a mobile phone). For this reason, the conventional built-in wiring board (printed wiring board) becomes unnecessary, and further downsizing of the electronic device can be achieved.

It is a flowchart which shows an example of the manufacturing method of the wiring board which concerns on this invention. It is a graph which shows the reflection, absorption, and transmission spectrum of a copper microparticle. It is a flowchart which shows another example of the manufacturing method of the wiring board which concerns on this invention. It is a graph which shows the reflection, absorption, and transmission spectrum of a phenol resin. It is a graph which shows the reflection, absorption, and transmission spectrum of glass epoxy resin. It is a graph which shows the reflection, absorption, and transmission spectrum of a polyimide resin. It is a flowchart which shows another example of the manufacturing method of the wiring board which concerns on this invention. It is a cross-sectional schematic diagram which shows an example of the wiring board which concerns on this invention. It is a plane schematic diagram which shows an example of the wiring board which concerns on this invention. 2 is an optical micrograph of a Cu wiring substrate of Example 1. FIG. 2 is an optical micrograph of a Cu wiring substrate of Example 1. FIG. 2 is a laser micrograph of the Cu wiring substrate of Example 1. FIG. 4 is an optical micrograph of a Cu wiring board of Example 2. 4 is an optical micrograph of a Cu wiring board of Example 3.

  The method for manufacturing a wiring board according to the present invention uses HLP (High Speed Laser Placing, registered trademark). The present inventors sinter copper microparticles by irradiating a 300 to 600 nm laser beam in the air after drying a coating film obtained by applying a dispersion containing copper microparticles on a substrate. As a result, the inventors have found that a wiring substrate that achieves adhesion and wiring resistance with a substrate equivalent to or higher than that of copper nanoparticles can be obtained, and the present invention has been completed. A wiring film obtained by sintering copper microparticles with a laser beam is a novel invention.

  Hereinafter, a manufacturing method of a wiring board and a wiring board according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments, and improvements and modifications can be added as appropriate without departing from the scope of the present invention.

[Method of manufacturing a wiring board]
FIG. 1 is a flowchart showing an example of a method for manufacturing a wiring board according to the present invention. As shown in FIG. 1, in the method for manufacturing a wiring board according to the present invention, a dispersion containing copper microparticles and a volatile organic solvent is applied (printed) onto an electrically insulating substrate 1 to produce a copper A coating film forming step (a) for obtaining a coating film 2 containing microparticles, a drying step (b) in which the coating film 2 is heated to remove volatile organic solvents in the coating film 2 by drying, A laser beam irradiation step (c) for obtaining a copper microparticle sintered film 4 by irradiating the dried coating film 3 with a laser beam 6 to sinter the copper microparticles and bring them into close contact with the substrate 1. Hereinafter, the steps (a) to (c) will be described in detail.

(A) Coating film formation process There is no limitation in particular as the electrically insulating board | substrate 1 which forms wiring, For example, the thermosetting resin, thermoplastic resin, or the modified thermosetting resin obtained by blending these, or modification | denaturation A thermoplastic resin or the like can be used. More specifically, as the thermosetting resin, a resol-type or novolac-type phenol resin, an epoxy resin, or the like can be given. Since the phenol resin and the epoxy resin cannot provide sufficient mechanical strength by themselves, a glass fiber is used as a reinforcing material, and a material obtained by impregnating the glass fiber with an uncured resin and then curing can be used. As the thermoplastic resin, polyimide resin (PI), polyamideimide resin (PAI) often used for flexible wiring boards, and liquid crystal polymer (LCP) which has been partially put into practical use in recent years can be used.

  A dispersion liquid containing copper microparticles and a volatile organic solvent is applied onto the substrate 1 to obtain a coating film 2. The copper microparticles of the present invention preferably have an average particle size of 1 to 3 μm (1 μm or more and 3 μm or less). If the thickness is less than 1 μm, the number of coatings (number of times of printing) increases as in the case of copper nanoparticles in order to increase the film thickness of the wiring film to 7 μm or more. If the thickness is larger than 3 μm, sintering is performed in the laser light irradiation process described later. It becomes difficult. The conditions of the laser beam capable of sintering copper particles having an average particle diameter of 1 to 3 μm will be described in detail later.

  One reason why the present invention uses copper microparticles is to eliminate the dispersant used in the copper nanoparticles. It is known that when metal is miniaturized, lattice strain increases and surface free energy increases. This increase in surface energy is particularly noticeable for nanoparticles with a particle size of 1-5 nm whose size is close to the lattice constant. In the case of metal microparticles, the surface energy is close to that of bulk metal, so that the surface energy is small and the use of a dispersant is unnecessary.

  In addition to the pure copper, the copper microparticles described above may be an alloy of copper and another metal element in order to improve the characteristics of the wiring film. For example, a copper-tin (Cu-Sn) alloy alloyed with tin (Sn) in order to improve strength may be used. In addition, a copper-zinc (Cu-Zn) or copper-zirconium (Cu-Zr) alloy may be used. Or you may mix microparticles, such as Sn, Zn, Zr, other than a copper microparticle. If the average particle diameter of these alloy particles is in the range of 1 to 3 μm described above, the effects of the present invention can be obtained.

  The dispersion containing copper microparticles preferably contains a volatile organic solvent and a binder and a viscosity modifier as additives in addition to the copper microparticles. As the volatile organic solvent, a solvent having a boiling point that is removed by drying in a drying step described later is used. As the additive component in the dispersion liquid, it is preferable to use a low boiling point (350 ° C. or lower) solvent or a low molecular weight (10,000 or lower) organic compound that is completely decomposed by a laser in a laser light irradiation step described later. This is because if these components are not decomposed and are present in the wiring film, voids may be generated and wiring resistance may be increased. The preferred composition of the dispersion is listed in Table 1.

  In the dispersion shown in Table 1, decanol (boiling point: 231 ° C) and castor oil (boiling point: 313) are used as viscosity modifiers in order to obtain fluidity by using ethanol having a low boiling point (boiling point: 78.3 ° C) as the main solvent. ° C.) and a small amount of ethyl cellulose (molecular weight: 1,000 to 3,000) as a binder (thickener). Ethanol is completely evaporated in the drying process after printing the dispersion described later, and other organic compounds are completely decomposed by heat and light in the laser light irradiation process described later.

  As the organic solvent, methanol (boiling point 64.5 ° C.) or the like can be used in addition to ethanol. Moreover, glycerin (boiling point 290 degreeC) etc. can be used as a viscosity modifier, Low molecular weight methylcellulose, polyvinyl alcohol, etc. with a molecular weight of 10,000 or less can be used as a binder.

  The dispersion liquid (copper microparticle paste) is applied to the substrate 1 in a desired pattern using a method capable of applying a dispersion liquid containing copper microparticles, such as a screen printing method, a doctor blade method, or a dispenser method. Apply.

(B) Drying process Next, the board | substrate 1 is heat-processed and the volatile organic solvent contained in the coating film 2 is dried and removed. Although drying is performed in the air, the drying temperature is preferably 120 ° C. or less in order to prevent oxidation of the copper microparticles. Since the volatile organic solvent (ethanol or the like) evaporates by drying the dispersion, the thickness of the coating film 3 after drying is reduced to 6 to 7% before drying. Moreover, drying can reduce time by drying under reduced pressure.

(C) Laser light irradiation step Next, the dried coating film 3 is irradiated with laser light 6 from above the printed pattern to sinter the copper microparticles in the coating film 3. In this step, components (additives and the like) other than the copper microparticles contained in the dispersion are decomposed by laser light irradiation. For laser sintering of copper microparticles, a laser beam having the most suitable wavelength is selected from the measured values of reflection, absorption and transmission spectra of the copper microparticles. FIG. 2 is a graph showing the reflection, absorption, and transmission spectra of copper microparticles (average particle size: 1 μm). As shown in FIG. 2, the copper microparticles have a high absorption rate of about 80% or more at a wavelength of 200 to 600 nm, and particularly a high absorption rate of about 95% at a wavelength of 200 to 550 nm. A sintered film of copper microparticles can be obtained by using laser light. For example, using a green laser beam having a wavelength of 532 nm is effective for sintering in a short time. In order to obtain a sintered film of copper microparticles, it is preferable to use laser light having a wavelength of 70% or more.

  For the laser power (condensed beam fluence) and the irradiation time, optimum values are selected according to the thickness of the coating film 3 after the drying process. The thicker the coating film 3 (printing layer) is, the higher the laser power is set and irradiation is performed, whereby a sintered film can be obtained up to the inside of the printing layer. The optimum irradiation time is determined according to the power of the laser beam used. The conditions of the wavelength, power, and time of the laser beam were determined by observing the presence or absence of sintering defects (voids, etc.) by observing the sintered film by, for example, SEM (Scanning Electron Microscope) after cross-section processing using FIB (Focused Ion Beam) Can be optimized. The laser beam may be a continuous wave (CW: Continuous Wave) that oscillates constantly, but by using a pulse wave (PW: Pulse Wave), a thicker and denser sintered film can be obtained. When a pulse laser is used, it is preferable that the frequency of the pulse laser beam is 10 to 300 kHz and the pulse width is 1 to 50 ns. For example, for a green laser beam of 532 nm, it is preferable to use a pulse laser having a frequency of 30 kHz and a pulse width of 6 ns.

  Metal nanoparticles with a diameter of 5-10 nm or less have a remarkable increase in surface energy (energy that the particles themselves try to agglomerate and coarsen) due to lattice strain on the particle surface, and become coarser (bulk) below the melting point. It is known. Although such a particle effect cannot be expected with copper microparticles, the present inventors have developed copper nanoparticles by using a short pulse laser, particularly in a wavelength band having an absorption rate of 70% or more of the laser light of copper microparticles. It was found that it could be similarly sintered. For example, in the case of a pulse green laser (wavelength of 532 nm) having a pulse width of 6 ns or less, it was found that a copper sintered film can be obtained in a short time of about 50 ms.

There are other advantages of using this pulse laser, for example, even when copper microparticles are oxidized during long-term storage or high-temperature storage to form cuprous oxide (Cu ₂ O), copper oxide (CuO), or the like. The present inventors have found that these copper oxides are decomposed and reduced to pure copper (Cu) by using a laser. By reducing the copper oxide to pure copper, a denser sintered copper film with fewer defects can be obtained.

  The laser irradiation process is performed in the atmosphere. In the above-described conventional plasma processing, the processing atmosphere needs to be controlled to a reducing atmosphere containing hydrogen or an inert atmosphere, but in the present invention, since it can be performed in an air atmosphere, a manufacturing process for performing plasma processing Compared with the manufacturing cost, the manufacturing cost can be reduced. Furthermore, although plasma processing takes several minutes to sinter, as described above, according to the present invention, a wiring film can be obtained in a short time of about 50 ms. Compared with this, the manufacturing cost can be reduced. For this reason, it becomes possible to make inline in the resin molding process and the wiring board manufacturing process.

  According to the above-described method for manufacturing a wiring board according to the present invention, a copper sintered film bulked with copper microparticles that do not require a dispersant can be obtained without using copper nanoparticles that require a dispersant coating.

  FIG. 3 is a flowchart showing another example of the method for manufacturing a wiring board according to the present invention. The manufacturing method shown in FIG. 3 has a substrate pretreatment step (a-1) before the coating film forming step (a) shown in FIG. In the substrate pretreatment step (a-1), a process for activating the surface of the substrate 1 by irradiation with the laser beam 5 is performed. Specifically, activation treatment (surface roughening and functional group addition) is performed on the surface of the substrate 1 using the laser light 5 having a wavelength obtained from the measured absorption spectrum values specific to these resins. Below, this activation process is explained in full detail.

Carboxyl group (—COOH), hydroxyl group (—OH) or amino group (NH ₂ ) showing high adhesion to the copper wiring film (copper microparticles) on the irradiated surface by laser light irradiation in the pretreatment step (a-1) And other functional groups are generated (exposed). Since the surface (activation treatment surface) of the substrate 1 on which such a functional group is generated (activated) becomes high temperature by the laser light irradiation step (c), it is active in the case of a thermoplastic resin. Since the temperature of the chemical treatment surface becomes Tg (glass transition temperature) or higher and the molecule flows, and the copper microparticles are taken in, the thermoplastic resin and the copper microparticles are chemically bonded. Due to this action and a mechanical anchor effect obtained by surface roughening by laser light irradiation, a copper sintered film having high adhesion to the substrate 1 can be obtained. In addition, a crystalline thermosetting resin such as a phenol resin does not exhibit thermoplasticity, but its mechanical strength decreases at a temperature of about 150 ° C. (thermal deformation temperature). When the surface temperature of the substrate rises to about this thermal deformation temperature, copper microparticles easily penetrate into the recesses of the phenolic resin whose surface has been roughened in advance, and high adhesion copper firing due to the mechanical anchor effect. A conjunctiva can be obtained. Since the substrate is cooled after the laser light irradiation and the resin shrinks, the sintered body of copper microparticles confined in the resin substrate further improves the adhesion to the substrate.

  From the above, in order to obtain an activation treatment surface, it is preferable to irradiate a laser beam having a wavelength at which the substrate 1 exhibits high absorption (absorption rate of 50% or more).

  4 to 6 are graphs showing reflection, absorption, and transmission spectra of a phenol resin, a glass epoxy resin, and a polyimide resin, respectively.

  Phenolic resins frequently used in resin molded products for automotive electronics are obtained as resins with a three-dimensional network structure by adding a basic curing agent such as hexamethylenetetramine to phenol having a hydroxyl group on the benzene ring and heat polymerization. It is done. As shown in FIG. 4, the absorption spectrum of the phenol resin shows a high absorption rate of about 90% in the entire wavelength region of 200 to 1200 nm. This shows the material characteristics as a composite material of black carbon powder or fibrous reinforcing substance and phenol resin filled in phenol resin. This high absorptance can be expected to cause surface roughening due to carbon decomposition in the phenol resin by laser irradiation, and generation of functional groups that predominate the chemical bonding properties of the phenol resin.

  Further, as shown in FIG. 5, the glass epoxy resin frequently used in the wiring board for electronic equipment has an absorption rate of 80% or more up to a wavelength of about 400 nm, but the absorption rate is 40% on the long wavelength side (500 nm or more). To a degree. For this reason, in the case of a glass epoxy substrate, it is expected that the resin is efficiently decomposed and the functional group is imparted by using a laser beam having a short wavelength.

  Further, as shown in FIG. 6, the polyimide resin exhibits maximum absorption at a wavelength of 400 nm, but decreases to an absorption rate of less than 10% at 600 nm or more.

  From the above, it is preferable to use a wavelength region in which the substrate 1 has a high absorption rate (50% or more) as the wavelength of the laser beam 5 irradiated to the substrate 1 in the pretreatment step (a-1). 1200 nm, 200 to 400 nm for glass epoxy resin, and 200 to 400 nm for polyimide film are preferable. Thus, by irradiating the substrate 1 before applying the dispersion containing copper microparticles with a laser wavelength corresponding to the type of the substrate 1 before the coating film forming step, the surface of the resin substrate is roughened and Functional group addition can be performed.

  FIG. 7 is a flowchart showing another example of the method for manufacturing a wiring board according to the present invention. The manufacturing method shown in FIG. 7 has a via hole forming step (a-2) before the coating film forming step (a) shown in FIG. In the via hole forming step (a-2), the via hole 7 is formed in the substrate 1, and the coating film 2 is formed in the via hole 7. A method for forming the via hole 7 in the substrate 1 is not particularly limited and can be formed by a drill or the like. In the coating film forming step (a), when the dispersion liquid is applied to the substrate 1, the dispersion liquid is covered by covering the opening on the side opposite to the opening of the via hole filled with the dispersion liquid with the adhesive protective tape 8. Can be filled with the dispersion without leaking. Subsequent to the drying step (b) is the same as the manufacturing method shown in FIG. Further, after the via hole forming step (a-2) and before the coating film forming step (a), the substrate pretreatment step (a-1) shown in FIG. 3 may be performed. According to the manufacturing method shown in FIG. 7, it is possible to form a wiring film having the same or better adhesion with the substrate and the electric resistance of the wiring film than the conventional one even for the via hole.

[Wiring board]
8A and 8B are schematic views showing an example of a wiring board according to the present invention. According to the above-described method for manufacturing a wiring board according to the present invention, an exterior part (resin molded product) of an electronic device having an uneven shape, for example, an IC (Integrated Circuit) card (SIM (Subscriber Identity Module) card) of a mobile phone. Conductive wiring can be formed directly on the housing. In the conventional plating method, it is impossible to plate a wiring film on a substrate having an uneven shape. On the other hand, according to the method for manufacturing a wiring board according to the present invention, a wiring film can be formed without selecting a substrate shape without requiring special materials and equipment. The uneven | corrugated size which a board | substrate has is not specifically limited, The thing of several micrometers and a thing of several mm can also be made into object.

  In a conventional method for manufacturing a wiring board by a dry process, for example, as seen in Patent Document 7 described above, an alkylamine or the like whose boiling point does not exceed 300 ° C. is used as a dispersant. And since sintering is not performed by laser but by furnace firing at about 200 ° C. for about 10 minutes, most of the dispersant remains in the sintered film. For this reason, there exists a possibility that an electrical resistance may become large several times as much as a pure metal (pure copper).

  Furthermore, the conventional copper nanoparticle ink has high fluidity, and is mainly ink jet printing. Therefore, the film thickness that can be applied at one time is about 2 μm, and when this is dried and laser sintered, the film thickness is about 0.5 μm. Usually, the electronic circuit of the wiring board is required to be 7 μm or more. Therefore, when copper nanoparticles are used, it is necessary to apply about 15 times. The wiring film that has been applied a plurality of times in this manner can recognize the application boundary by microstructural observation (cross-sectional observation by an optical microscope). On the other hand, since the wiring film of the wiring board manufactured using the manufacturing method of the wiring board according to the present invention can obtain a wiring film of 7 μm or more by one coating, the wiring film has no particular boundary.

[Dispersion for wiring board production]
The present invention provides a wiring board manufacturing dispersion (copper microparticle-containing dispersion applied to the substrate 1 in the coating film forming step (a)) in addition to the above-described wiring board manufacturing method and wiring board. Is. The composition of the dispersion is as described above. Conventionally, since a dispersion containing copper nanoparticles is used as a dispersion, a dispersion containing copper microparticles is a novel invention.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to these examples.

  A wiring board was manufactured by the manufacturing method shown in FIG. A glass epoxy resin substrate having a thickness of 1 mm and a 25 mm square was prepared as the substrate 1. A copper microparticle dispersion was printed on the substrate 1 as a coating film forming step (a) to obtain a coating film 2. The composition of the dispersion was as shown in Table 1, and the average particle size of the copper microparticles was 1 μm. As the copper microparticles, HXR-Cu, lot number 14302-D of Nippon Atomizing Co., Ltd. was used. The dispersion (copper microparticle paste) was printed on a glass epoxy resin substrate using a doctor blade so as to have a thickness of 100 μm.

  After printing, in the drying step (b), the temperature of the printed substrate was raised to 100 ° C. in the atmosphere, and a drying process was performed for 5 minutes. As a result, ethanol having a boiling point of 78.3 ° C. contained in the copper microparticle dispersion liquid evaporated and deviated.

  Next, in the laser beam irradiation step (c), the dried coating film 3 was irradiated with the laser beam 6, and the copper microparticles in the coating film 3 were sintered and adhered to the substrate 1. Irradiation was performed using a green laser 6 (wavelength: 532 nm) having a beam diameter of φ25 μm. The irradiation conditions were a frequency of 30 kHz, a laser power of 0.3 W, a pulse width of 6 ns, and a laser irradiation scanning speed of 10 mm / s.

  FIG. 9 is an optical micrograph (plan view of the substrate) of the Cu wiring substrate of Example 1. As shown in FIG. 9, the portion irradiated with the laser light is sintered with copper microparticles bulked into a line having a width of 25 μm, and the portion not irradiated with the laser light has a copper microparticle of φ1 μm. The particles remain in the printed state. 10 is an optical micrograph (cross-sectional view of the substrate) of the Cu wiring substrate of Example 1. FIG. As shown in FIG. 10, the formation of a copper sintered layer of about 7 μm in the depth direction can be confirmed. FIG. 11 is a laser micrograph (cross-sectional view of the substrate) of the Cu wiring substrate of Example 1. FIG. 11 is a laser microscope image of the cross-sectional microstructure after etching with hydrogen peroxide and ammonia water in the laser sintered portion. As shown in FIG. 11, a copper microparticle sintered layer 32 can be clearly confirmed at the center of unsintered φ1 μm copper microparticles 31. The presence of unsintered copper microparticles can be confirmed at the periphery of the copper microparticle sintered layer.

  When the adhesive tape (manufactured by Sumitomo 3M Limited, product name: Scotch (registered trademark)) was applied to the copper wiring film obtained above and peeled off, no peeling (peeling) of the copper wiring film was observed. Moreover, when the resistance value of the copper wiring film was measured by the four probe method and the specific resistance was calculated from the cross-sectional area and the wiring length in FIG. 11, a value equivalent to pure copper (1.68 μΩ · cm) could be obtained. It was. In this example, it was possible to obtain a wiring substrate having a copper wiring film having high adhesion and low electrical resistance by a dry process method using copper microparticles.

  A wiring board was manufactured by the manufacturing method shown in FIG. As the substrate 1, a phenol resin substrate having a thickness of 1 mm and a 25 mm square was prepared. This substrate 1 was irradiated with a green laser 5 having a wavelength of 532 nm as a substrate pretreatment step (a-1). For irradiation, a pulse laser having a beam diameter of 25 μm, a frequency of 30 kHz, and a pulse width of 6 ns was used. The laser power was 0.3W. The irradiation area was the entire area of 15 mm copper microparticle paste printing on which the coating film was formed in the subsequent coating film forming step (a). The scanning speed of the laser beam was 800 mm / s.

  Next, after printing the copper microparticle paste shown in Table 1 to a thickness of 100 μm with a doctor blade, in the drying step (b), the temperature of the printed board is raised to 100 ° C. in the atmosphere, and a drying process is performed for 5 minutes. went. As a result, ethanol having a boiling point of 78.3 ° C. contained in the copper microparticle paste evaporated and deviated.

  Next, in the laser beam irradiation step (c), the dried coating film 3 was irradiated with the laser beam 6, and the copper microparticles in the coating film 3 were sintered and adhered to the substrate 1. Irradiation was performed using a green laser 6 having a beam diameter of 25 μm and a wavelength of 532 nm. The irradiation conditions were a frequency of 90 kHz, a laser power of 0.9 W, a pulse width of 8 ns, and a laser irradiation scanning speed of 10 mm / s.

  12 is an optical micrograph (plan view of the substrate) of the Cu wiring substrate of Example 2. FIG. As shown in FIG. 12, copper microparticles are bulked and sintered in a laser beam width of 25 μm in the laser irradiated part, and φ1 μm copper microparticles are printed in the part not irradiated with laser. It was found that it remained as it was.

  When the peeling test using a peeling tape was performed on the copper wiring film obtained above in the same manner as in Example 1, peeling (peeling) of the copper wiring film was not observed. Moreover, when the resistance value of the copper wiring film was measured by the four-terminal method and the specific resistance was calculated from the cross-sectional area and wiring length of the wiring film, a value equivalent to pure copper (1.68 μΩ · cm) could be obtained. It was. In this example, a wiring substrate having a copper wiring film having high adhesion and low resistance could be obtained by a dry process method using copper microparticles.

  A wiring board having a wiring film formed in a via hole was manufactured by the manufacturing method shown in FIG. A through hole having a diameter of 0.4 mm was formed in a polyimide resin substrate 1 having a thickness of 38 μm by a punch hole processing die, and the through hole (via hole) 7 was filled with a copper microparticle dispersion liquid having the composition shown in Table 1. . Squeegee printing was used for filling. An adhesive protective tape 8 having a thickness of 60 μm was attached to the back surface of the via hole 7 (the opening opposite to the opening filled with the dispersion) in order to prevent leakage of the copper microparticle dispersion. A copper microparticle ink layer 2 having a thickness of 100 μm was formed on the substrate 1 on the via hole surface (opening for filling the dispersion) side with a doctor blade. As a result, the copper microparticle ink could be filled into the through hole having a diameter of 0.4 mm.

  Next, in the drying step (b), a drying treatment was performed at 100 ° C. for 1 minute. As a result, ethanol having a boiling point of 78.3 ° C. contained in the copper microparticle paste evaporated and deviated.

  Next, in the laser beam irradiation step (c), the dried coating film 3 was irradiated with the laser beam 6, and the copper microparticles in the coating film 3 were sintered and adhered to the substrate 1. Laser irradiation was performed using a green laser 5 (wavelength: wavelength 532 nm) having a beam diameter of φ25 μm. The frequency of the green laser was 150 kHz, the laser power was 2.4 W, the pulse width was 10 ns, and the laser irradiation scanning speed was 10 mm / s. FIG. 13 is an optical micrograph (plan view of the substrate) of the Cu wiring substrate of Example 3. According to the manufacturing method of the present invention, it has been demonstrated that a wiring film can be formed even for a via hole.

  As described above, according to the present invention, it has been shown that a method of manufacturing a wiring board capable of obtaining a copper wiring board by a dry processing method (dry process) using copper microparticles can be provided. According to the present invention, it is possible to obtain a wiring board having a wiring film having a wiring layer thickness of 7 μm or more with a single ink printing, and having adhesion and wiring resistance equal to or higher than those of conventional ones. It was shown that it can be provided. As described above in Examples 1, 2, and 3, after printing the copper microparticles on the entire surface of the substrate and then partially irradiating with a laser to sinter, the unsintered copper microparticles are treated with, for example, alcohol. By removing with a solvent such as, a wiring board having copper wiring on the board can be manufactured. The removed copper microparticles can be collected and used repeatedly. In addition, although the doctor blade method is used in the above embodiment, a conductive wiring board can be manufactured by a method in which, for example, a copper microparticle pattern is printed on a substrate using a screen printing method and then laser irradiation is performed. It is. In this method, a wiring board can be manufactured without removing unsintered copper microparticles.

  Note that the above-described embodiments have been specifically described in order to help understanding of the present invention, and the present invention is not limited to having all the configurations described. For example, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, a part of the configuration of each embodiment can be deleted, replaced with another configuration, or added with another configuration.

  DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Coating film, 3 ... Coating film after drying, 4 ... Sintered film, 5, 6 ... Laser beam, 7, 15 ... Via hole, 8 ... Protection tape, 11 ... Copper wiring, 12 ... Resin molding Substrate (SIM card), 13 ... flash memory, 14 ... insertion terminal, 20 ... wiring board, 31 ... unsintered copper microparticles, 32 ... sintered copper microparticles.

Claims (19)

In a method of manufacturing a wiring board in which conductive wiring is formed on an electrically insulating board,
A coating film forming step of obtaining a coating film by applying a dispersion containing copper microparticles, a volatile organic solvent, and a binder on the substrate;
A drying step in which the coating film is heated to remove the organic solvent by drying;
The coating film after the drying step is irradiated with a laser beam having a wavelength of 300 to 600 nm in the atmosphere to decompose the binder, and the copper microparticles are sintered and adhered to the substrate to obtain copper. And a laser beam irradiation step for obtaining a microparticle sintered film. Furthermore, before the coating film forming step, it has a substrate pretreatment step of irradiating the substrate with laser light,
2. The method for manufacturing a wiring board according to claim 1, wherein, in the coating film forming step, the coating film is formed at a position irradiated with laser light in the substrate pretreatment step.   3. The method of manufacturing a wiring board according to claim 2, wherein the wavelength of the laser light in the substrate pretreatment step is a wavelength at which the substrate exhibits an absorption rate of 50% or more. The laser beam in the laser beam irradiation step is a pulse laser beam, the frequency of the pulse laser beam is 10 to 300 kHz, and the pulse width is 1 to 50 ns. A method for manufacturing a wiring board according to claim 1.   5. The method of manufacturing a wiring substrate according to claim 1, wherein the copper microparticles have an average particle diameter of 1 to 3 μm. The dispersion comprises a viscosity adjusting agent as an additive,
6. The method for manufacturing a wiring board according to claim 1, wherein the additive comprises a component that is decomposed by the laser beam.   The method for manufacturing a wiring board according to claim 1, wherein the heat treatment is performed at a temperature of 120 ° C. or less in the atmosphere.   The method for manufacturing a wiring board according to any one of claims 1 to 7, wherein the substrate is a thermosetting resin, a thermoplastic resin, or a modified resin thereof. Furthermore, before the coating film forming step, having a via hole forming step of providing a via hole in the substrate,
The method for manufacturing a wiring board according to claim 1, wherein the dispersion liquid is applied to the via hole in the coating film forming step.   The method for manufacturing a wiring board according to claim 1, wherein the substrate is an exterior part of an electronic device having an uneven shape.   11. The method for manufacturing a wiring board according to claim 10, wherein the exterior component is a housing of an IC card of a mobile phone. In a wiring board having copper wiring on an electrically insulating board,
The copper wiring has a conductive layer in which copper particles are sintered,
The conductive layer state, and are thickness 7μm or more, the wiring board characterized by having a melt solidification structure.   The wiring board according to claim 12, wherein the conductive layer has no coating boundary in the film thickness direction.   The wiring board according to claim 12, wherein the board is an exterior component of an electronic device.   The wiring board according to claim 14, wherein the exterior component is a housing of an IC card of a mobile phone. A dispersion for manufacturing a wiring board used for manufacturing a wiring board having an electrically insulating substrate and conductive wiring formed on the substrate by laser sintering ,
The said dispersion liquid contains a copper microparticle, a volatile organic solvent, and a binder , The dispersion liquid for wiring board manufacture characterized by the above-mentioned.   The dispersion for manufacturing a wiring board according to claim 16, wherein the copper microparticles have an average particle diameter of 1 to 3 μm. Further comprising a viscosity modifier wherein the dispersion is an additive,
18. The wiring board manufacturing method according to claim 16, wherein each of the binder and the viscosity modifier is an organic compound having a boiling point of 350 ° C. or less and / or a molecular weight of 10,000 or less. Dispersion.   The dispersion liquid for manufacturing a wiring board according to any one of claims 16 to 18, wherein the organic solvent contains ethanol or methanol.

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