JP2009231755A - Micro-wiring fabricating method - Google Patents

Abstract

The present invention relates to a method for producing a fine wiring, in which the firing temperature of a fine wiring drawn by an ink jet printing method or the like using a conductive paste made of copper nanoparticles can be set to a temperature of 250 ° C. or less at which a resin substrate can be used. I will provide a.
A method for fabricating a fine wiring according to the present invention includes firstly oxidizing a conductive paste made of copper nanoparticles, a dispersant and a binder drawn on a substrate according to a wiring pattern, and then reducing the conductive paste. A fine wiring manufacturing method for manufacturing a fine wiring, wherein the substrate is oxidized at a temperature exceeding an oxidation start temperature required by thermal analysis in the oxidation treatment and reduction treatment of the copper nanoparticles, and at a temperature exceeding the reduction start temperature. This is performed by performing a reduction treatment of the substrate.
[Selection] Figure 3

Description

  The present invention relates to a fine wiring manufacturing method in which a conductive paste containing copper nanoparticles is used and a fine wiring or electrode is drawn on a substrate by an inkjet printing method or the like.

  The wiring of the board is generally produced by etching using a three-layer flexible board in which a copper foil is bonded to an insulator film using an adhesive, or a two-layer flexible board in which a copper coating layer is directly formed by plating. ing. Since such a manufacturing method requires many steps and takes time, a method of drawing wiring and electrodes directly on a substrate using a conductive paste by an ink-jet printing method or the like, and firing this to produce an electric wiring Has been proposed.

  For example, in Patent Document 1, when gold or silver nanoparticles are used as the conductive paste, it is expensive, and when silver nanoparticles are used, there is a problem of electro (ion) migration. A fine wiring manufacturing method using a nanoparticle conductive paste has been proposed. That is, a fine wiring pattern forming method has been proposed in which fine wiring drawn on a substrate is subjected to reduction firing in a plasma atmosphere. And according to this fine wiring pattern forming method, the reduction firing temperature can be set to 300 ° C. or lower, and an embodiment in which reduction treatment is performed at 150 ° C. and 50 ° C. is disclosed.

  In Patent Document 2, a dispersion in which a reducible metal oxide having a particle size of 200 nm or less is dispersed in an organic dispersion medium is applied to a substrate, and then fired at a temperature of 100 ° C. to 400 ° C. in an inert atmosphere. After that, a method for producing a metal film has been proposed, characterized by firing at a temperature of 80 ° C. or higher and 400 ° C. or lower in a reducing atmosphere. And the Example which fired at 250 degreeC in inert atmosphere, and then baked at 300 degreeC in a reducing atmosphere produced the metal film.

  Further, in Patent Document 3, after a metal nanoparticle dispersion is applied to a substrate, it is fired at a temperature of 100 to 600 ° C. in an oxidizing atmosphere, and then fired at a temperature of 100 to 600 ° C. in a reducing atmosphere. A method for producing a coating has been proposed. And the Example which baked at the temperature of 300 degreeC in oxidizing atmosphere, and then baked at the temperature of 300 degreeC in reducing atmosphere produced the metal film.

JP 2004-119686 A JP 2004-164876 A JP 2007-200659

  Fine wiring such as wiring and electrodes drawn using a conductive paste made of copper nanoparticles needs to be fired so as to have electrical conductivity that can be actually used as wiring. The firing temperature is desirably lower than 250 ° C. at which the resin substrate can be used. However, it is very difficult to lower the firing temperature. The fine wiring pattern forming method described in Patent Document 1 can reduce the firing temperature to 300 ° C. or lower, and also describes an embodiment in which reduction firing is actually performed at 150 ° C. or 50 ° C., which is a preferable method. However, a special apparatus such as a vacuum apparatus or a plasma generation apparatus is required, and there is a problem that productivity and economy are inferior.

  In the method for producing a metal film described in Patent Document 2, the firing temperature in the inert atmosphere and the reducing atmosphere is not higher than 300 ° C. and may be 100 ° C. Similarly, in the method for producing a metal film described in Patent Document 3, it is assumed that the firing temperature in the oxidizing atmosphere and the reducing atmosphere may be 100 ° C. instead of 300 ° C. or lower. However, Patent Documents 2 and 3 do not disclose such examples. Patent Document 2 only discloses an example in which a metal film was produced by firing at 250 ° C. in an inert atmosphere and then firing at 300 ° C. in a reducing atmosphere. Patent Document 3 only discloses an example in which a metal film is produced by firing at a temperature of 300 ° C. in an oxidizing atmosphere and then firing at a temperature of 300 ° C. in a reducing atmosphere.

  In view of such conventional problems, the present invention has a firing temperature of fine wiring drawn by an inkjet printing method or the like using a conductive paste made of copper nanoparticles, and the resin substrate can be used at 250 ° C. or lower. An object of the present invention is to provide a method for producing a fine wiring that can be set to a temperature of 5 mm.

  In the fine wiring manufacturing method according to the present invention, a conductive paste composed of copper nanoparticles, a dispersant, and a binder drawn on a substrate according to a wiring pattern is first oxidized and then reduced to prepare a fine wiring. A method for producing a fine wiring, wherein the substrate is oxidized at a temperature exceeding an oxidation start temperature required by thermal analysis in the oxidation treatment and reduction treatment of the copper nanoparticles, and the substrate is reduced at a temperature exceeding the reduction start temperature. It is implemented by doing.

  In the above invention, the thermal analysis can use a differential thermal analysis method or a thermogravimetric measurement method. When performing thermal analysis by differential thermal analysis, in the oxidation thermal analysis curve obtained by differential thermal analysis, the temperature in the temperature range indicating the end of the first exothermic peak of copper oxide formation is defined as the oxidation treatment temperature. It is preferable to perform the oxidation treatment and reduce the substrate using the temperature in the temperature range showing the maximum endotherm as the reduction treatment temperature in the reduction thermal analysis curve.

  When performing thermal analysis by differential thermal analysis, the oxidation treatment temperature is ± 10 ° C of the temperature indicating the end of the first exothermic peak of copper oxide formation in the oxidation thermal analysis curve, and the reduction treatment temperature is in the reduction thermal analysis curve. It can be ± 10 ° C of the temperature showing the maximum endotherm.

  On the other hand, when performing thermal analysis by thermogravimetry, the substrate is subjected to oxidation treatment using the oxidation temperature analysis curve determined by thermogravimetry as the oxidation treatment temperature at the temperature range indicating the inflection point for copper oxide formation. In the reduction thermal analysis curve, it is preferable to perform the substrate reduction process using the temperature in the temperature range indicating the inflection point for rapid weight reduction as the reduction process temperature.

  When performing thermal analysis by thermogravimetry, the oxidation treatment temperature is ± 10 ° C of the temperature indicating the inflection point for copper oxide formation in the oxidation thermal analysis curve, and the reduction treatment temperature is rapidly reduced in weight in the reduction thermal analysis curve. It can be set to ± 10 ° C. of the temperature indicating the bending point.

  According to the method for producing fine wiring according to the present invention, the firing temperature of the fine wiring drawn with the conductive paste using copper nanoparticles is set to a temperature that is possible even when using a resin substrate, a temperature of 250 ° C. or lower. Can do.

  The best mode for carrying out the invention will be described below. The fine wiring manufacturing method according to the present invention is drawn according to a wiring pattern on a substrate using a conductive paste composed of copper nanoparticles, a dispersant and a binder, and the drawn conductive paste is oxidized as follows: And reduction treatment. That is, first, oxidation treatment and reduction treatment of the copper nanoparticles are performed, and thermal analysis in these processes is performed. Then, the oxidation start temperature and the reduction start temperature are obtained based on the thermal analysis curve obtained by the thermal analysis, the substrate is oxidized at a temperature exceeding the obtained oxidation start temperature, and the temperature exceeding the reduction start temperature is obtained. The substrate is reduced. Thereby, the oxidation treatment and the reduction treatment can be performed at the lowest possible temperature, and the treatment temperature of the oxidation treatment and the reduction treatment can be lowered.

The oxidation treatment temperature and the reduction treatment temperature in the present invention will be described with reference to the drawings. FIG. 1 is a graph showing the results of a thermal analysis test when copper nanoparticles are oxidized, and FIG. 2 is a graph showing the results of a thermal analysis test when copper nanoparticles are reduced. 1 and 2, the horizontal axis represents the heating temperature, and the vertical axis represents the weight change (TG) obtained by the thermogravimetry and the voltage change (DTA) obtained by the differential thermal analysis method. In Figure 1, H _o curve is oxidized thermal analysis curve obtained by differential thermal analysis. The _Wo curve is an oxidation thermal analysis curve obtained by thermogravimetry. In FIG. 2, the _Hr curve is a reduction thermal analysis curve obtained by differential thermal analysis. The _Wr curve is a reduction thermal analysis curve obtained by thermogravimetry.

  The copper nanoparticles used in this test had an average particle size of 20 nm. Thermal analysis was performed using EXSTAR 6000 TG / DTA A6200 manufactured by SSI Nanotechnology. The heating rate was 5 ° C./min. In the differential thermal analysis method, alumina powder was used as a reference sample.

In Figure 1, when observing the H _o curve, although to 0.99 ° C. from room temperature is gradually lowered, resulting a rapid rise to exothermic reaction exceeds 0.99 ° C. (temperature A _HO), the oxidation reaction of copper Indicates that it has occurred. The exothermic reaction showed a peak at 190 ° C., H _o curve when the further increasing the temperature is rapidly lowered. The first exothermic reaction is complete at 240 ° C. (temperature B _HO ). The temperature range showing this exothermic peak is related to the formation of cuprous oxide. The H _o curve shows an exothermic peak again at 280 ° C. due to the exothermic reaction as the temperature rises, then rapidly decreases to 310 ° C. as the temperature increases, and gradually decreases when it exceeds 310 ° C.

When the _Wo curve is observed, there is almost no change in weight from room temperature to 150 ° C., but when the temperature exceeds 150 ° C. (temperature A _WO ), a rapid increase in weight is shown, indicating that the copper oxidation reaction occurs. In this oxidation reaction, the _Wo curve shows an inflection point with a slightly gentler weight change gradient at 210 ° C. (temperature B _WO ). Then, the increase in weight stops at a temperature exceeding 290 ° C., and then the weight gradually decreases as the temperature increases. The inflection point relates to a reaction in which the copper nanoparticles are oxidized to change from cuprous oxide to copper oxide.

On the other hand, when observing the results of thermal analysis in the reduction process, as shown in FIG. 2, H _r curve gradually decreases from 90 ° C. (temperature A _Hr) up to 130 ° C., rapidly lowered when exceeding 130 ° C. Endothermic peak at 190 ° C (temperature B _Hr ). When the temperature is further increased, the temperature rapidly rises to 250 ° C. When the temperature exceeds 250 ° C, the value becomes almost constant and no change is observed. According to the above results, it is understood that the reduction reaction proceeds slowly in the range of 90 to 130 ° C., and rapidly proceeds above 130 ° C.

Observation of W _r curve, the W _r curve, gradually decreases from 100 ° C. before and after the temperature (temperature A _Wr) to 220 ° C., is rapidly lowered when exceeding 220 ° C. (temperature B _Wr). Then, when more than 250 ℃, W _r curve is again gradually lowered. According to the above results, the weight is only slightly decreased in the range of 100 to 220 ° C, but suddenly decreases when the temperature of the inflection point (temperature B _Wr ) _expressed at 220 ° C of the _Wr curve is exceeded. Yes. That is, the reduction reaction proceeds slowly in the range of 100 to 220 ° C, but is understood to proceed rapidly when it exceeds 220 ° C (temperature B _Wr ). In addition, when the _Hr curve and the _Wr curve are compared, it is understood that the _Hr curve can obtain more information in the reduction reaction.

In this fine wiring manufacturing method, when performing thermal analysis of such copper nanoparticles and performing thermal analysis by differential thermal analysis, the substrate is oxidized at a temperature exceeding the oxidation start temperature _AHO . Preferably, the temperature range indicating the end of the first exothermic peak related to generation of the copper oxide in the H _o curve, an oxidation process of a substrate at a temperature of B _HO ± 10 ℃. In the substrate reduction process, the substrate reduction process is performed at a temperature exceeding the reduction start temperature _AHr . Preferably, a temperature range showing a maximum endothermic, the temperature at the substrate reduction treatment of B _Hr ± 10 ° C. performed in H _r curve.

When performing thermal analysis by thermogravimetry, the substrate is oxidized at a temperature exceeding the oxidation start temperature _AWO . Preferably, W _o curve temperature range showing a bending point according to generation of the copper oxide in, an oxidation process of a substrate at a temperature of B _WO ± 10 ℃. In the substrate reduction process, the substrate reduction process is performed at a temperature exceeding the reduction start temperature A _Wr . Preferably, the substrate is reduced at a temperature of B _Wr ± 10 ° C.

  In this fine wiring manufacturing method, the thermal analysis is performed in this way to perform the oxidation treatment and reduction treatment of the substrate. For example, the substrate is oxidized at 240 ± 10 ° C. and the reduction treatment is performed at 190 ± 10 ° C. Alternatively, the substrate is oxidized at 210 ± 10 ° C. and the reduction treatment is performed at 220 ± 10 ° C. As a result, the substrate can be oxidized and reduced at a temperature of 250 ° C. or lower. Moreover, oxidation treatment and reduction treatment can be performed at an optimum temperature for the copper nanoparticles constituting the conductive paste. In addition, regarding the determination of the temperature at which the oxidation treatment and the reduction treatment are performed, the optimum method for the conductive paste to be used is selected based on whether the differential thermal analysis method or the thermogravimetry method is used.

  In this fine wiring manufacturing method, the copper nanoparticles preferably have a particle diameter of 100 nm or less. More preferable copper nanoparticles are those having a particle size of 50 nm or less.

  As the dispersant, in addition to tarpione, any dispersant may be used as long as it is generally used for the preparation of this kind of fine metal particle dispersion. For example, as a dispersant, normal hexane, cyclohexane, normal pentane, normal heptane, toluene, xylene, methyl isobutyl ketone, benzene, chloroform, carbon tetrachloride, methyl ethyl ketone, ethyl acetate, butyl acetate, isobutyl acetate, ethylbenzene, trimethylbenzene, terpineol , Decane, tridecane, tetradecane, hexadecane, methanol, ethanol, propanol, butanol and the like can be used.

  As the binder, ethyl cellulose resin or acrylic resin can be used, and it is desirable that the addition amount be as small as possible.

  As a method for drawing the conductive paste on the substrate, an inkjet printing method, a screen printing method, a transfer printing method, a dip coating method, a spray coating method, a spin coating method, or the like can be used.

  A conductive paste consisting of 100 parts by weight of copper nanoparticles (average particle size 20 nm) and 200 parts by weight of terpione (made by Wako Pure Chemical Industries, Ltd.) as a dispersant is formed on a glass substrate using an applicator, and is in an air atmosphere. An electrical resistance measurement test and a structure observation test were performed on the sample subjected to oxidation treatment and reduction treatment in an argon gas atmosphere containing 5% hydrogen. The oxidation treatment was performed at a temperature of 100 to 300 ° C. × 1 hour, and the reduction treatment was performed at a temperature of 100 to 300 ° C. × 1 hour. For the electrical resistance, the specific resistance value was measured by the four probe method. Tissue observation was performed with a scanning electron microscope (JSM-6340F manufactured by JEOL Ltd.).

  FIG. 3 shows specific resistance values when the substrate is oxidized and reduced at each temperature. In FIG. 3, the horizontal axis represents the oxidation treatment temperature, and the vertical axis represents the specific resistance value. The parameter indicates the reduction processing temperature. According to FIG. 3, the specific resistance value when oxidized at 200 to 300 ° C. and reduced at 300 ° C. is the same, and when this specific resistance value is oxidized at 250 ° C. and reduced at 200 ° C. It can be seen that the specific resistance values are almost the same. It can also be seen that the temperature dependence of the specific resistance value is very high when the oxidation temperature is between 150 and 200 or 250 ° C. Further, in the reduction treatment, it can be seen that the specific resistance value does not change much at temperatures of 100 ° C. and 200 ° C., and the temperature dependency is relatively low.

  FIG. 4 shows a structure photograph. According to FIG. 4, it can be seen that there is almost no change in the structure when both the oxidation treatment and the reduction treatment are performed at 100 ° C. and when performed at 200 ° C. However, it can be seen that when both the oxidation treatment and the reduction treatment are performed at 300 ° C., the copper nanoparticles are coarsened. The oxidation treatment and the reduction treatment are preferably performed in a temperature range that does not cause such coarsening of the copper nanoparticles.

It is a graph which shows the example of the thermal analysis which concerns on this invention, and is a graph at the time of performing the oxidation process of a copper nanoparticle. It is a graph which shows the example of the thermal analysis which concerns on this invention, and is a graph at the time of carrying out the reduction process of a copper nanoparticle. It is a graph which shows an electrical resistance measurement test result. It is a photograph which shows the structure | tissue observation result in an Example.

Claims (6)

A conductive paste made of copper nanoparticles, a dispersant and a binder drawn on a substrate according to a wiring pattern is a fine wiring manufacturing method in which a fine wiring is prepared by first oxidizing, then reducing,
A fine wiring manufacturing method in which oxidation treatment of a substrate is performed at a temperature exceeding an oxidation start temperature required by thermal analysis in the oxidation treatment and reduction treatment of the copper nanoparticles, and the substrate reduction treatment is performed at a temperature exceeding the reduction start temperature.   2. The fine wiring manufacturing method according to claim 1, wherein the thermal analysis is based on a differential thermal analysis method or a thermogravimetry method.   In the oxidation thermal analysis curve obtained by differential thermal analysis, the substrate is oxidized using the temperature in the temperature range indicating the end of the first exothermic peak of copper oxide formation as the oxidation treatment temperature, and the maximum endotherm in the reduction thermal analysis curve. The method for producing a fine wiring according to claim 2, wherein the substrate is subjected to a reduction treatment using a temperature in a temperature range indicating a reduction treatment temperature.   The oxidation treatment temperature is ± 10 ° C of the temperature indicating the end of the first exothermic peak of copper oxide formation in the oxidation thermal analysis curve, and the reduction treatment temperature is ± 10 ° C of the temperature showing the maximum endotherm in the reduction thermal analysis curve. The fine wiring manufacturing method according to claim 3.   In the thermal oxidation analysis curve obtained by thermogravimetry, the substrate is oxidized using the temperature in the temperature range indicating the inflection point for copper oxide formation as the oxidation treatment temperature, and in the reduction thermal analysis curve, rapid weight loss occurs. 3. The fine wiring manufacturing method according to claim 2, wherein the substrate is subjected to the reduction treatment using the temperature in the temperature range indicating the bending point as the reduction treatment temperature.   The oxidation treatment temperature is ± 10 ° C that shows the inflection point for copper oxide formation in the oxidation thermal analysis curve, and the reduction treatment temperature is ± 10 ° C that shows the inflection point for sudden weight loss in the reduction thermal analysis curve. The fine wiring manufacturing method according to claim 5, wherein the method is provided.

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