JP5462036B2 - Circuit board manufacturing method and circuit board - Google Patents

Description

  The present invention relates to a method for manufacturing a circuit board and the like, in which fine droplets of ink are ejected from an inkjet head, and droplets are landed on a required location on a substrate in accordance with a device pattern.

  In recent years, electronic components such as notebook PCs and smartphones have been required to be lighter, thinner, and smaller as electronic devices become smaller, thinner, lighter, and more functional. In particular, in order to realize a low-carbon society, it is also desired that the manufacturing process in the industry be changed to a form with less environmental load. From this point of view, technology that applies printing technology to the manufacture of electronics is attracting attention, and a new field of printed electronics is flourishing. Unlike the process of repeating film formation and etching based on the conventional photolithography technology, the printed electronics is composed of a process of applying a necessary amount of material to a necessary place. For this reason, there is little waste of material and energy consumption is also low.

  There are various printing technologies such as flexographic printing, gravure printing, and screen printing. Among them, the inkjet method can design and manufacture circuits on demand, and patterns can be created without removing materials. Because it can be formed, it is especially expected as an environmentally friendly technology.

  In the ink jet method, ink in the form of minute droplets is ejected from an ink jet head, and droplets are landed on a necessary place on a substrate in accordance with a device pattern. Ink is a liquid containing functional materials. When forming conductor wiring, silver complex ink (ink complexed with silver and dissolved in solvent) or silver nanoparticle ink (silver from several nm to several tens of nm) Ink dispersed in a solvent is generally used. The droplet-like ink ejected from the nozzle of the head flies through the space between the head and the substrate facing it, and landed on the substrate. The landed droplets flow on the substrate according to the interfacial energy between the substrate and the ink, and spread. A film-like pattern made of a functional material is obtained by evaporating the ink solvent. In the case of metal nanoparticle inks including silver, silver particles are sintered by further heat treatment, and a wiring pattern having conductivity close to a bulk can be formed.

  There are two reasons why extremely small particles of several to several tens of nm are used for the silver nanoparticle ink. One is to obtain the dispersion stability of the particles in the ink. Metals have a density as high as several to several tens of times that of solvents, so they tend to settle due to gravity and produce precipitates. Therefore, by reducing the particle size, a stable dispersion state can be realized by the effect of the viscous resistance of the solvent and the Brownian motion. Another is to lower the firing temperature. It is known that the melting point of metal particles decreases as the size of the metal particles decreases, and that the particle size drops rapidly from about 10 nm. For example, the melting point of silver is 961 ° C. in the bulk state, but it is considered to drop to about a few hundred degrees at a few dozen nm, and a silver circuit can be easily formed on a resin substrate or the like. In addition, in the ink using metal nanoparticles, it coats with the organic film so that metal nanoparticles may not sinter in ink.

  The conventional ink jet method has a problem that a fine pattern cannot be drawn because the droplets 21 that have landed on the substrate 3 are greatly wetted and spread as schematically shown in FIG. As a countermeasure against this, a technique has been adopted in which the wetting and spreading of the ink is suppressed by applying a liquid repellent treatment to the substrate surface, but the uneven wetting and spreading of the droplets called the bulge effect and the film thickness called the coffee stain phenomenon. Since nonuniformity is likely to occur, the limit of miniaturization is about 30 to 50 μm for the wiring width.

  In addition, since silver nanoparticle ink contains a large amount of organic substances such as solvents and dispersants, a large number of voids (bubble cavities) are generated in the fired silver film, and the electrical resistance is orders of magnitude higher than that of the bulk. The problem of getting high in the difference was easy to occur.

  Furthermore, there is a problem that work efficiency is low. In order to obtain a practical low resistance wiring, it is necessary to have a certain thickness of the wiring. However, in the metal nanoparticle ink, the metal content in the ink is at most about 10% by volume, and this ink is on the substrate. Therefore, a thickness of only about a submicron can be obtained only by landing one droplet. For this reason, in order to obtain a thick wiring, it was necessary to repeatedly apply the coating.

WO2009 / 076023 JP 2006-239899 A JP 2004-288517 A

  An object of the present invention is to provide an ink jet method and an ink jet apparatus capable of achieving miniaturization of metal or metal oxide film and improvement of workability in forming a wiring pattern on a substrate by the ink jet method.

  According to one aspect of the present invention, laser light is applied to a droplet of ink while a droplet of ink ejected from an inkjet head is flying or immediately after landing on a substrate. A part of the metal nanoparticles or the metal in the droplet ink is selected by selecting a wavelength included in the absorption band caused by the surface plasmon of the metal nanoparticles or metal oxide nanoparticles in the droplet ink Oxide nanoparticles are enlarged and the ink printed on the substrate is mixed with the metal nanoparticles or metal oxide nanoparticles having a small diameter and the enlarged metal nanoparticles or metal oxide nanoparticles An ink jet method is provided that is characterized by being in a state.

  According to another aspect of the present invention, the droplet-shaped ink ejected from the inkjet head is radiated to the droplet-shaped ink during the flight or immediately after landing on the substrate, and the laser beam is irradiated at that time. And selecting the wavelength included in the absorption band caused by the surface plasmon of the metal nanoparticles or metal oxide nanoparticles in the droplet-like ink, and a part of the metal nanoparticles in the droplet-like ink Alternatively, the metal oxide nanoparticles may be enlarged, and the ink printed on a substrate may be enlarged with the metal nanoparticles or metal oxide nanoparticles having a small diameter and the metal nanoparticles or metal oxide nanoparticles enlarged. The ink jet method is characterized in that the ink contains a fine particle having a particle diameter of 100 nm or less, which is a metal or a metal oxide. Theft method is provided.

  According to another aspect of the present invention, the droplet-shaped ink ejected from the inkjet head is irradiated with laser light while flying or immediately after landing on the substrate. The wavelength of the laser beam is selected as a wavelength included in the absorption band caused by the surface plasmon of the metal nanoparticle or metal oxide nanoparticle in the droplet-shaped ink, and a part of the metal in the droplet-shaped ink The metal nanoparticles or the metal oxide nanoparticles obtained by enlarging the nanoparticles or the metal oxide nanoparticles and enlarging the ink printed on the substrate with the metal nanoparticles or the metal oxide nanoparticles having a small diameter In the ink jet method, wherein the wavelength of the laser beam is in the vicinity of the absorption band peak of the metal nanoparticles or the metal oxide nanoparticles in the ink The inkjet method is provided which further characterized in Rukoto.

  According to another aspect of the present invention, the droplet-shaped ink ejected from the inkjet head is irradiated with laser light while flying or immediately after landing on the substrate. The wavelength of the laser beam is selected as a wavelength included in the absorption band caused by the surface plasmon of the metal nanoparticle or metal oxide nanoparticle in the droplet-shaped ink, and a part of the metal in the droplet-shaped ink The metal nanoparticles or the metal oxide nanoparticles obtained by enlarging the nanoparticles or the metal oxide nanoparticles and enlarging the ink printed on the substrate with the metal nanoparticles or the metal oxide nanoparticles having a small diameter An ink jet method characterized in that particles are mixed with each other, wherein the ink jet method is further characterized in that the laser light irradiation is performed for each discharged droplet.

  Still further, according to another aspect of the present invention, the droplet-shaped ink ejected from the inkjet head is irradiated with laser light while flying or immediately after landing on the substrate. The wavelength of the laser beam is selected as the wavelength included in the absorption band caused by the surface plasmon of the metal nanoparticles or metal oxide nanoparticles in the droplet ink, and a part of the ink in the droplet ink is The metal nanoparticles or the metal oxide obtained by enlarging the metal nanoparticles or the metal oxide nanoparticles and enlarging the ink printed on the substrate with the metal nanoparticles or the metal oxide nanoparticles having a small diameter The substrate provided with a circuit using an ink-jet method, characterized in that nanoparticles are mixed.

  According to another aspect of the present invention, the droplet-shaped ink ejected from the inkjet head is irradiated with laser light while flying or immediately after landing on the substrate. The wavelength of the laser beam is selected as a wavelength included in the absorption band caused by the surface plasmon of the metal nanoparticle or metal oxide nanoparticle in the droplet-shaped ink, and a part of the metal in the droplet-shaped ink The metal nanoparticles or the metal oxide nanoparticles obtained by enlarging the nanoparticles or the metal oxide nanoparticles and enlarging the ink printed on the substrate with the metal nanoparticles or the metal oxide nanoparticles having a small diameter Provided is an electronic component or an electronic device using the substrate provided with the circuit using an ink jet method characterized in that particles are mixed.

  Still further, according to another aspect of the present invention, an ink jet head for landing liquid droplet ink on the substrate, and the liquid droplet ejected from the ink jet head are flying or land on the substrate. An inkjet apparatus characterized by having a laser that irradiates laser light immediately after the operation is provided.

  According to another aspect of the present invention, an inkjet head that causes droplet-shaped ink to land on the substrate, and the droplet-shaped ink ejected from the inkjet head is flying or landed on the substrate. Immediately after having the laser that irradiates laser light, the wavelength of the laser light is a wavelength included in the absorption band caused by the surface plasmon of the metal nanoparticles or metal oxide nanoparticles in the ink The inkjet apparatus is provided.

  According to the present invention, a low resistance and fine wiring pattern can be obtained, and a thick film wiring can be easily formed.

It is a conceptual diagram of this invention. It is a graph which shows the absorptance with respect to the laser wavelength for every size of a metal nanoparticle. It is a conceptual diagram of a prior art.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. The light applied to the droplet-shaped ink is not limited to laser light, but here, description will be made using laser light.

  FIG. 1 schematically illustrates the present invention. In the present embodiment, as shown in FIG. 1, the inkjet head 1 is arranged so that ink lands on the substrate 3 on which the wiring is formed. A laser 5 that irradiates a laser beam 4 immediately after the droplet-like ink 2 containing the metal nanoparticles or metal oxide nanoparticles ejected from the ink jet head 1 has landed on the substrate 3. Be placed.

    In addition, although it is also possible for the metal nanoparticles to be conductive metal oxide nanoparticles, in the following description, in order to avoid complication, the metal nanoparticles or metal oxide nanoparticles are simply referred to as metal nanoparticles. Sometimes called particles.

  According to one aspect of the present invention, as shown in FIG. 1, which is a conceptual diagram, the laser beam 4 is emitted immediately after the droplet-like ink 2 ejected from the inkjet head 1 is flying or just after landing on the substrate 3. To do. At this time, the wavelength of the laser beam 4 is selected as the wavelength included in the absorption band caused by the surface plasmon of the metal nanoparticles, and the metal nanoparticles in the droplet-like ink 2 are combined with the adjacent particles. In this way, some of the metal nanoparticles in the ink are enlarged to make the ink printed on the substrate a mixture of fine metal nanoparticles and enlarged metal nanoparticles. To do.

  In the above description, “mixed” may include particles in which metal nanoparticles are bonded in addition to enlarged metal nanoparticles and non- enlarged metal nanoparticles.

  The significance is described next.

  Free electrons collectively vibrate inside the metal, which is called plasmon. In general, plasmons do not interact with light, but there are special plasmons that interact with light on the metal surface, which are called surface plasmons. The interaction means that the light is absorbed, and is a phenomenon that becomes remarkable in a specific wavelength band. This is shown in FIG. FIG. 2 shows how the peak of the wavelength of light absorbed by the metal nanoparticles changes depending on the size (particle size) of the metal nanoparticles (Au). In FIG. 2, the wavelength dependence of the optical absorptance when the size of the metal nanoparticles is 2 nm, 12 nm, and 50 nm, respectively, is indicated by a one-dot chain line, a solid line, and a dotted line. In FIG. 2, the wavelength of light at the absorption peak is the wavelength of the surface plasmon of the corresponding metal nanoparticle.

  Therefore, when the ink droplets are irradiated with light that interacts with the surface plasmons of the metal nanoparticles, only the metal nanoparticles of a specific size in the ink can be selectively heated. , Can enlarge easily.

  Further, since the vibration frequency of the surface plasmon varies depending on the particle size, the interaction with the laser beam becomes weaker as the particles are enlarged, and it becomes difficult to be heated. Thereby, even if it irradiates with a laser beam excessively, a metal nanoparticle does not enlarge excessively.

  Note that the vibration frequency of surface plasmons differs depending on the type of metal.

  The wavelength of light that is not absorbed by the ink solvent is preferably selected as an embodiment of the present invention. Thereby, rapid evaporation of the solvent can be prevented. For this reason, fluctuations in the flying trajectory of the droplet-like ink due to the evaporation of the solvent can be suppressed to a low level, and the landing position accuracy can be prevented from being lowered.

  As an embodiment of the present invention, it is preferable to selectively irradiate a specific liquid droplet in synchronization with the timing at which the ink is ejected. The significance of this is as follows.

  In order to reliably irradiate the droplet-shaped ink with laser light, it is preferable to make the beam diameter larger than the droplet. However, in this case, if the intensity of light is large, all the metal nanoparticles contained in one droplet may be enlarged. Therefore, for example, irradiation is performed for each droplet, such as irradiating the first droplet and not irradiating the second droplet.

  The ink that has landed on the substrate is mixed with the ink that adjoins (that is, landed immediately before) due to its fluidity, and as a result, the metal nanoparticles having different particle diameters can be mixed.

  The above means can be used in combination.

  According to the present embodiment, when the ink landed on the substrate and the substrate are heated and baked, the enlarged metal nanoparticles are present, so that a low-resistance wiring can be easily obtained. Further, the presence of fine metal nanoparticles that are not irradiated with laser light does not impair the property of “can be fired at a low temperature”. In addition, since particles with a small diameter enter and accumulate in the gaps between the enlarged particles, the ratio of organic substances is small and voids are difficult to be formed. This effect also makes it easy to obtain low resistance wiring.

  Furthermore, since the enlargement of the metal nanoparticles does not occur in the ink jet head, the dispersibility of the metal nanoparticles in the ink does not occur. Therefore, the ink is not clogged in the ink jet head.

  Furthermore, since the solvent evaporates to some extent when irradiated with light, the fluidity of the ink decreases. As a result, wetting and spreading after landing on the substrate is reduced, so that fine wiring can be obtained, and even if ink droplets are overprinted, the coffee stain phenomenon does not easily occur, so it is easy to make a thick and uniform film Can be formed.

  The “ink” applied in the present invention is exemplified below.

(1) An ink having nanoparticles dispersed in a solvent and having an average particle size of 100 nm or less is preferable. If it is larger than this, the particles will settle in the ink, causing clogging in the ink jet head. On the other hand, if the average particle size is 100 nm or more, the melting point is high, so the sintering temperature must be increased, and the substrate is thermally damaged, which is not suitable.

(2) The nanoparticle is a metal and / or alloy containing at least one of gold, silver, copper, palladium, platinum, tin, bismuth, cobalt, chromium, iron, nickel, indium, titanium, and zinc, or a metal oxide The thing containing is preferable.

(3) The nanoparticles are preferably individually coated with an organic film.

(4) The solvent is a hydrocarbon solvent such as hexane, toluene, decane, or tetradecane, or an unsaturated aliphatic alcohol such as oleyl alcohol, or a branched chain such as 2-octyldodecanol, isocetyl alcohol, or isotridecyl alcohol. It is preferable to use a fatty acid alcohol or an ester solvent such as isopropyl myristate, isostearyl palmitate, or ethyl oleate.

  In the following examples, all droplets are irradiated with a laser pulse. However, since the laser output is small and the irradiation time is short, it is estimated that only a part of the metal nanoparticles is enlarged. The flying speed of the droplet is several meters per second although it depends on the performance of the head. For this reason, even if the laser beam is changed from pulse oscillation to continuous oscillation, the irradiation time may be as short as a few microseconds.

  An Au nanoparticle ink having an average particle diameter of 5 nm was printed on a polyimide resin substrate by an ink jet method. The inkjet head used a piezo drive type and ejected approximately 6 pl of droplet-like ink at a cycle of 200 Hz. The ink-jet head is about 1 mm away from the substrate surface, and the laser beam is irradiated from the almost horizontal direction toward the middle. As the laser, a second harmonic (wavelength: 532 nm, 25 mJ / pulse) of an Nd-YAG laser was used. By adjusting the laser oscillation frequency to 100 Hz and synchronizing the ejection timing of the inkjet head, adjustment was made so that every other droplet of ink ejected from the head was irradiated with laser light. The substrate was not heated.

  When the ink landed on the substrate was observed with TEM, large particles of several tens of nm were found. As a result of investigation, this could be classified into a structure in which many fine particles were aggregated and one particle. On the other hand, such particles were not found in the ink printed by the ink jet method without irradiating the laser beam. From this, it was confirmed that aggregation and fusion (enlargement) of the metal nanoparticles in the ink proceeded by laser irradiation.

  Therefore, when Au nanoparticle ink was printed on the substrate by the ink jet method and heated at 250 ° C. for 60 minutes and sintered, a circuit pattern with a golden gloss was obtained. The electrical resistivity was about 10μΩ · cm, and a high-quality thin film about 4 times the bulk of 2.21μΩ · cm could be obtained.

  The same experiment was conducted with a laser intensity of 100 mJ / Pulse for the purpose of more efficient particle growth, and the solvent of the droplets evaporated rapidly, causing the droplets to land at a predetermined position. I can no longer let you. Therefore, by irradiating the laser beam immediately before or after landing on the substrate, variations in landing positions are eliminated.

  When the laser intensity was further increased to 300 mJ / Pulse, the droplets were scattered. From this, it was found that it is important to select the laser intensity appropriately.

  An Ag nanoparticle ink having an average particle diameter of 4 nm was printed on an epoxy substrate by an inkjet method. The inkjet head used a piezo drive type and ejected approximately 4 pl of droplet-shaped ink at a period of 200 Hz, and the laser used the second harmonic of a titanium sapphire laser (wavelength 420 nm, 8 mJ / Pulse). The oscillation frequency of the laser was 200 Hz, the same as the ejection of droplet-like ink, and all the droplets were irradiated with laser light in a substantially horizontal direction before landing on the substrate. The substrate was heated to 45 ° C.

  When the substrate on which the Ag nanoparticle ink was printed was heated at 220 ° C. for 10 minutes and sintered, a circuit pattern having a silvery gloss was obtained. This electrical resistivity was about 8μΩ · cm, and a high-quality thin film about 5 times the bulk of 1.59μΩ · cm could be obtained.

  Although all the droplets were irradiated with laser light here, it is assumed that only a part of the metal nanoparticles was enlarged because the laser output was small and the irradiation time was short. For this reason, the laser may be changed from pulse oscillation to continuous oscillation (CW).

  An Ag nanoparticle ink having an average particle diameter of 4 nm was printed on an epoxy substrate by an inkjet method. The ink jet head used an electrostatic attraction type, about 1 pl of droplet-like ink was ejected at a frequency of 1 kHz, and the laser used the second harmonic of a titanium sapphire laser (wavelength 420 nm, 5 mJ / Pulse). The laser oscillation frequency was 2 kHz, and all droplets were irradiated with laser light immediately after landing. The laser beam was applied to the droplet landed on the substrate obliquely from above. The substrate was not heated.

  When the substrate on which the Ag nanoparticle ink was printed was heated at 220 ° C. for 60 minutes and sintered, a circuit pattern having a silvery luster was obtained. This electrical resistivity was about 6μΩ · cm, and a high-quality thin film about 4 times the bulk of 1.59μΩ · cm could be obtained.

  A Cu nanoparticle ink having an average particle diameter of 16 nm was printed on a silicon substrate by an inkjet method. About 4 pl of droplet-shaped ink was ejected at a period of 200 Hz, and a dye laser (wavelength 560 nm, 40 mJ / Pulse) was used as the laser. The laser oscillation frequency was the same as that of ejecting droplet-like ink, 200 Hz, so that all droplets were irradiated with laser. The substrate was heated to 40 ° C.

When the substrate printed with the Cu nanoparticle ink was heated at 350 ° C. for 60 minutes (in the atmosphere) and 350 ° C. for 30 minutes (98% N ₂ + 2% H ₂ ), the sintering process was performed. A glossy circuit pattern was obtained. The electrical resistivity was about 20 μΩ · cm, and a high-quality thin film about 13 times as large as the bulk 1.68 μΩ · cm could be obtained.

  An ITO nanoparticle ink having an average particle diameter of 20 nm was printed on a glass substrate by an inkjet method. About 25 pl of droplet-shaped ink was ejected at a period of 1 kHz, and an OPO laser (wavelength 1500 nm, 0.3 W) was used as the laser. The laser oscillation was CW, and all droplets were irradiated with the laser. The substrate was not heated.

When the substrate on which the ITO nanoparticle ink was printed was heated at 300 ° C. for 30 minutes and sintered, a transparent circuit pattern was obtained. The sheet resistance was 500 μΩ / cm ² .

  As an embodiment, the metal nanoparticles may be indirectly heated by irradiating the substrate with laser light.

  Furthermore, it is not essential to heat the substrate.

  The laser light irradiation position and its effect will be described.

  When irradiating a laser beam before the droplet-shaped ink is flying (that is, immediately before being ejected from an inkjet nozzle and landing on the substrate), it can be irradiated under the same conditions without being affected by the surface state of the substrate. There are advantages. Further, when laser light is irradiated immediately after the droplet-shaped ink has landed on the substrate, the light transmitted through the ink is reflected on the surface of the substrate and irradiated again on the ink, so that there is an advantage that efficiency is good.

DESCRIPTION OF SYMBOLS 1 Inkjet head 2 Droplet-shaped ink 21 in flight Droplet-shaped ink landed on a substrate in the prior art 22 Droplet-shaped ink landed on a substrate in the present invention 3 Substrate 4 Laser light 5 Laser

Claims (6)

  The droplet-shaped ink ejected from the inkjet head is in flight or immediately after landing on the substrate, the laser beam is irradiated with the laser beam, and the wavelength of the laser beam is changed to the metal nano-particle in the droplet-shaped ink. Select the wavelength included in the absorption band due to the surface plasmon of the particles or metal oxide nanoparticles to enlarge a part of the metal nanoparticles or the metal oxide nanoparticles in the ink, on the substrate An ink-jet method, wherein the printed ink is mixed with the metal nanoparticles or metal oxide nanoparticles having a small diameter and the enlarged metal nanoparticles or metal oxide nanoparticles.   2. The ink jet method according to claim 1, wherein the ink contains fine particles having a particle diameter of 100 nm or less made of metal or metal oxide.   3. The ink jet method according to claim 1, wherein a wavelength of the laser beam is in the vicinity of an absorption band peak of the metal nanoparticle or metal oxide nanoparticle in the ink. .   The inkjet method according to claim 1, wherein the laser light irradiation is performed for each ejected droplet.   The board | substrate which provided the circuit with the inkjet method of any one of Claims 1-4.   An electronic component or an electronic device using the substrate according to claim 5.

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