JP2011192947A - Manufacturing method for sintered layer, and structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a sintered layer that is dense and has excellent adhesion to a substrate, and a structure. <P>SOLUTION: The manufacturing method for a sintered layer has: a first coating step for coating a paste containing metal particles on the surface of a substrate 10 so as to form a first coating layer 20; a first sintering step for sintering the first coating layer 20 so as to form a first sintered layer 30 having a thickness of ≤1.0 μm, a second coating step for coating a paste on the surface of the first sintered layer 30 so as to form a second coating layer 22; and a second sintering step for sintering the second coating layer 22 so as to form a second sintered layer 32. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a sintered layer and a structure. In particular, the present invention relates to a method for producing a sintered layer by sintering metal fine particles and a structure.

  2. Description of the Related Art Conventionally, a method for manufacturing a circuit board by firing a conductive paste supplied on an insulating base material to form a circuit conductor, the conductive paste containing metal nanoparticles having a particle size of nanometer order with a metal material. Thus, a circuit board manufacturing method is known in which metal nanoparticles are sintered by firing a conductive paste in a low oxygen atmosphere containing alcohol (see, for example, Patent Document 1).

  According to the method for manufacturing a circuit board described in Patent Document 1, a conductive paste containing metal nanoparticles is sintered at a low temperature, and the conductive paste is baked in a low oxygen atmosphere containing alcohol. Since the alcohol of the metal functions as a reducing agent and the surface oxide film of the metal nanoparticles is removed during firing, the increase in the resistance value of the circuit conductor formed by sintering the conductive paste can be suppressed, and the bulk metal material The circuit conductor can be formed to the same extent as

JP 2007-53212 A

  However, in the method of manufacturing a circuit board described in Patent Document 1, when the thickness of the conductive paste is large, the sintering reaction may proceed only in the surface layer portion of the conductive paste. May be insufficient, and a dense sintered layer having good adhesion to the substrate may not be obtained.

  Accordingly, an object of the present invention is to provide a method and a structure for producing a sintered layer that is dense and has good adhesion to a substrate.

  (1) In order to achieve the above object, the present invention applies a paste containing metal particles to the surface of a substrate to form a first coating layer, sinters the first coating layer, A first sintering step for forming a first sintered layer having a thickness of 0.0 μm or less; a second applying step for applying a paste to the surface of the first sintered layer to form a second applied layer; There is provided a method for producing a sintered layer comprising a second sintering step of sintering two coating layers and forming a second sintered layer.

  (2) Moreover, the manufacturing method of the said sintered layer WHEREIN: While a metal particle has an average particle diameter of 20 nm or less, it is preferable to contain the particle | grains which consist of a metal selected from the group which consists of gold | metal | money, silver, and copper. .

  (3) Moreover, as for the manufacturing method of the said sintered layer, a metal particle can further contain the metal oxide.

  (4) Moreover, as for the manufacturing method of the said sintered layer, it is preferable that a 2nd sintering process forms the 2nd sintered layer which has a thickness of 1.0 micrometer or less.

  (5) Moreover, as for the manufacturing method of the said sintered layer, a 1st sintering process and a 2nd sintering process may form the 1st sintered layer and the 2nd sintered layer by which the surface was roughened, respectively. it can.

  (6) Moreover, the manufacturing method of the said sintered layer WHEREIN: A 1st sintering process and a 2nd sintering process sinter a 1st coating layer and a 2nd coating layer by irradiation of a laser beam, plasma, or a xenon lamp. can do.

  (7) Moreover, the manufacturing method of the said sintered layer can further form a sintered layer by repeating a 2nd application | coating process and a 2nd sintering process after a 2nd sintering process.

  (8) In order to achieve the above object, the present invention provides a substrate, a first sintered layer provided on the substrate and containing metal particles, and a second firing containing metal particles provided on the first sintered layer. A structure in which the first sintered layer and the second sintered layer are formed by the method for manufacturing a sintered layer according to any one of (1) to (7) above. The

  (9) Moreover, the said structure can further be provided with the sintered layer formed by repeating a 2nd application | coating process and a 2nd sintering process on a 2nd sintered layer.

  According to the method and structure for manufacturing a sintered layer according to the present invention, it is possible to provide a method and a structure for manufacturing a sintered layer that are dense and have good adhesion to a substrate.

It is a figure which shows the flow of the manufacturing process of the sintered layer which concerns on embodiment of this invention. It is a figure which shows the flow of the manufacturing process of the structure which concerns on a comparative example.

[Summary of embodiment]
In the method for producing a sintered layer in which a sintered layer is formed by sintering metal particles, a first application step of applying a paste containing metal particles to the surface of a substrate to form a first application layer; A first sintering step of sintering one coating layer to form a first sintered layer having a thickness of 1.0 μm or less; and applying the paste to the surface of the first sintered layer; There is provided a method for producing a sintered layer comprising a second coating step for forming a layer and a second sintering step for sintering the second coating layer to form a second sintered layer.

[Embodiment]

  FIG. 1 shows an example of the flow of a manufacturing process of a sintered layer according to an embodiment of the present invention.

  First, the substrate 10 is prepared (substrate preparation process). As the substrate 10, a metal substrate such as copper, or a thermoplastic resin substrate such as polyethylene or polypropylene can be used. Next, the 1st application layer 20 is formed in the surface of the board | substrate 10 by apply | coating the paste containing a metal particle on the surface of the board | substrate 10 (1st application | coating process). Here, the first coating layer 20 is formed with a thickness that allows the inside of the layer to be sufficiently sintered by the energy supplied to the first coating layer 20 in a first sintering step to be described later.

  Here, you may provide a drying process after this 1st application process and the 2nd application process mentioned later. Moreover, in order to speed up drying, you may heat-dry.

  As the metal particles according to the present embodiment, particles having an average particle diameter of 20 nm or less are used. The metal particles include particles formed from a metal selected from the group consisting of gold, silver, and copper. Further, the metal particles can include gold oxide, silver oxide, or copper oxide. In addition, as a paste, hydrocarbon type organic solvents, such as n-hexane, n-heptane, n-undecane, or aromatic type organic solvents, such as toluene, are used as a main solvent, and predetermined average particle diameter is added to this main agent. It is possible to use a paste prepared by dispersing metal particles having a predetermined viscosity.

  Subsequently, energy is locally applied to the first coating layer 20. For example, laser light 40, plasma, or a xenon lamp is irradiated from the surface of the first coating layer 20 toward the substrate 10 (FIG. 1A). Irradiation with the laser beam 40 or the like is continuous irradiation. As a result, the organic solvent in the first coating layer 20 evaporates and the first coating layer 20 is sintered to form the first sintered layer 30 (FIG. 1 (b), first sintering step). When the metal oxide is contained in the paste, oxygen of the metal oxide is supplied to the organic matter (for example, organic solvent) around the metal particles during the sintering of the paste, and the decomposition of the organic matter is promoted. .

  In the present embodiment, the thickness of the first sintered layer 30 is 1.0 μm or less. The surface of the first sintered layer 30 is roughened and has a predetermined surface roughness. Examples of the method for roughening the surface include a method of irradiating the surface with a high output energy such as a laser using pulse oscillation or Q-switch oscillation for a short time. By these methods, the surface can be roughened using an ablation effect or the like.

  Here, in the present embodiment, for example, since the laser beam 40 is used, the first coating layer 20 is locally heated, and the heated region is sintered. Therefore, in the present embodiment, the entire surface of the first coating layer 20 is sintered by scanning the surface of the first coating layer 20 with the laser light 40. It should be noted that by adjusting the condensing diameter of the laser beam 40, the size of the heating area can be adjusted. For example, the laser beam 40 can be formed into a line beam that is spread in a band shape with a predetermined optical system, or is condensed with a predetermined optical system so that the condensed diameter of the laser beam 40 is about several tens of μm. can do. Moreover, the 1st application layer 20 can also be partially sintered by irradiating the laser beam 40 only to the area | region which should be sintered. That is, the part to be sintered and the part as the first coating layer 20 can be mixed by controlling On / Off of the irradiation of the laser beam 40.

  The wavelength of the laser light is preferably 532 nm and 1064 nm, but any wavelength and wavelengths of 532 nm and 1064 nm can be irradiated simultaneously or selectively.

  Next, the 2nd application layer 22 is formed in the surface of the 1st sintered layer 30 by apply | coating the paste containing a metal particle on the surface of the 1st sintered layer 30 (2nd application | coating process). The second coating layer 22 is preferably formed immediately after the first sintered layer 30 is formed. By forming the second coating layer 22 immediately after forming the first sintered layer 30, it is possible to prevent impurities from being mixed into the second coating layer 22 from the outside, and the first sintered layer 30. Surface contamination can be suppressed. Similar to the first coating layer 20, the second coating layer 22 has a thickness that allows the inside of the layer to be sufficiently sintered by the energy supplied to the second coating layer 22 in a second sintering step described later. Formed. As the paste applied to the surface of the first sintered layer 30, the same paste as the paste applied to the surface of the substrate 10 can be used. Also, pastes with different types of metal particles can be applied.

  Subsequently, energy is locally applied to the second coating layer 22. For example, the laser beam 40, plasma, or xenon lamp is irradiated from the surface of the second coating layer 22 toward the substrate 10 (FIG. 1C). Thereby, the 2nd application layer 22 is sintered and the 2nd sintered layer 32 is formed (Drawing 1 (d) and the 2nd sintering process). Note that the second coating layer 22 is irradiated with laser light 40 or the like immediately after the second coating layer 22 is formed for the purpose of suppressing impurities from entering the second sintered layer 32 from the outside. Is preferred. In the present embodiment, the thickness of the second sintered layer 32 is 1.0 μm or less. The surface of the second sintered layer 32 is roughened and has a predetermined surface roughness. The surface of the second sintered layer 32 can be roughened by the same method as the surface of the first sintered layer 30.

  Through the above steps, the structure 1 including the substrate 10 and the sintered layer 34 including the first sintered layer 30 and the second sintered layer 32 is manufactured. That is, the structure 1 according to the present embodiment uses the laser light 40 or plasma and a xenon lamp, and the first coating layer 20 provided on the substrate 10 and the first sintered layer 30 provided on the first sintered layer 30. The first sintered layer 30 and the second sintered layer 32 made of nanometer-sized fine particles are formed in a short time by applying energy locally to the two coating layers 22.

  In addition, when forming the same sintered layer, the laser beam 40, plasma, or a xenon lamp can also be selectively irradiated on the same coating layer. As an example, the irradiation time is set to less than 1 second for one spot. Furthermore, the first sintered layer 30 and the second sintered layer 32 can be sintered with different types of light. In addition, for the purpose of improving the adhesion of the first sintered layer 30 to the substrate 10 and the adhesion of the second sintered layer 32 to the first sintered layer 30, the manufacturing process of the sintered layer is performed in a predetermined clean state. In a clean room or in a clean room.

  In the present embodiment, the first sintered layer 30 and the second sintered layer 32 are formed on the substrate 10. However, the number of the sintered layers is not limited to two, and is set to three or more layers. You can also. Moreover, the manufacturing method of the sintered layer which concerns on this Embodiment can be applied to the product using the sintered layer obtained by sintering nanometer-sized microparticles | fine-particles. For example, it can be applied to a method for manufacturing a device including a metal pad portion formed using a plating technique.

(Effect of embodiment)
In the method for manufacturing a sintered layer according to the present embodiment, the thickness of the first coating layer 20 and the second coating layer 22 is such that the inside of the layer is sufficiently sintered by the energy of the laser beam 40 or the like. Prepared and the inside of the layer is sufficiently sintered by the energy of the laser beam 40 or the like. Therefore, according to the method for manufacturing a sintered layer according to the present embodiment, it is possible to form a sintered layer 34 that is dense and has good adhesion to the substrate 10. In addition, when the board | substrate 10 is comprised using a resin material, the adhesiveness of the board | substrate 10 and the 1st sintered layer 30 can further be improved.

  In addition, according to the method for manufacturing a sintered layer according to the present embodiment, it is possible to increase the thickness of the sintered layer 34 by repeating the application and sintering of the paste containing metal particles twice or more. In addition, since the sintered layer provided closer to the substrate 10 (for example, the first sintered layer 30 in the present embodiment) is supplied with energy a plurality of times, the first sintered layer with respect to the substrate 10 is provided. The adhesion of 30 can be improved.

  Furthermore, according to the method for manufacturing a sintered layer according to the present embodiment, the first coating layer 20 and the second coating layer 22 are formed by applying a paste. The sintered layer 34 can be formed in a limited manner. Thereby, according to the manufacturing method of the sintered layer which concerns on this Embodiment, compared with the case where a sintered layer is formed by the plating method etc., the consumption of material can be reduced and manufacturing cost can be suppressed. .

(Comparative Example 1)
FIG. 2 shows the flow of the manufacturing process of the structure according to the comparative example.

In the comparative example, on the substrate 10 made of copper, silver nanoparticles (however, silver nanoparticles having an average particle diameter of 5 nm were used. The same applies to other comparative examples and examples) were also used as an organic solvent. However, it is an organic solvent containing tetradecane as a main component, and the same applies to other comparative examples and examples.) An ink-like paste (however, the silver concentration is 30 wt%) obtained by diluting A coating layer 24 was formed on the substrate 10 by spin coating. Next, the coating layer 24 was irradiated with a laser beam 40 (that is, a line beam) spread in a band shape by the optical system (FIG. 2A). By irradiating the laser beam 40, the silver nanoparticles in the coating layer 24 were sintered to form a sintered layer 36 (FIG. 2B). Thereby, the structure 2 according to the comparative example was obtained. The used laser beam 40 was a YVO ₄ laser beam having a wavelength of 1064 nm. The laser light output is 6W.

  It was 2 micrometers when the thickness of the sintered layer 36 with which the structure 2 is provided was measured. Further, the adhesion of the sintered layer 36 to the substrate 10 was evaluated by a peel test. Specifically, a tape (however, a scotch mending tape 810 manufactured by 3M Co., Ltd. was used) was applied to the surface of the sintered layer 36, and the tape was peeled off perpendicularly to the surface of the substrate 10. The peel test was carried out. As a result, the sintered layer 36 was peeled off from the substrate 10.

(Comparative Example 2)
On the substrate 10 made of copper, an ink-like paste obtained by diluting silver nanoparticles with an organic solvent (however, the silver concentration is 30 wt%) is applied by spin coating, whereby the first coating layer 20 is formed. Formed.

Next, the first coating layer 20 was irradiated with a laser beam 40 (that is, a line beam) spread in a band shape by the optical system. The silver nanoparticles in the first coating layer 20 were sintered by irradiation with the laser light 40, and the first sintered layer 30 was formed. The used laser beam 40 is a YVO ₄ laser beam having a wavelength of 1064 nm. The laser light output is 6W.

  Here, when the thickness of the 1st sintered layer 30 was measured, it was 1.1 micrometers.

  Subsequently, the paste used to form the first coating layer 20 was applied to the surface of the first sintered layer 30 by spin coating. The spin coating was performed with the rotation speed set to 2000 rpm and the rotation time set to 30 seconds. Thereby, the second coating layer 22 was formed on the surface of the first sintered layer 30. Then, the second coating layer 22 was irradiated with a laser beam 40 (that is, a line beam) spread in a band shape by the optical system. The laser beam 40 used is the same as described above. The silver nanoparticles in the second coating layer 22 were sintered by irradiation with the laser light 40, and the second sintered layer 32 was formed.

  It was 2.2 micrometers when the thickness of the sintered layer 34 which consists of the 1st sintered layer 30 and the 2nd sintered layer 32 was measured. That is, a sintered layer having a thickness of 1.1 μm is formed on the second coating layer.

  The adhesion of the sintered layer 34 to the substrate 10 was evaluated by a peel test. Specifically, a tape (however, a scotch mending tape 810 manufactured by 3M was used for the tape) was applied to the surface of the sintered layer 34, and the tape was peeled off perpendicularly to the surface of the substrate 10. The peel test was carried out. As a result, the sintered layer 34 was peeled off from the substrate 10.

(Comparative Example 3)
On the substrate 10 made of copper, an ink-like paste obtained by diluting silver nanoparticles with an organic solvent (however, the silver concentration is 30 wt%) is applied by spin coating, whereby the first coating layer 20 is formed. Formed. Thereafter, the first coating layer 20 was dried by heating. Subsequently, the second coating layer 22 was formed on the first coating layer 20 in the same manner as the first coating layer 20. Thereafter, the first coating layer and the second coating layer 22 were irradiated with a laser beam 40 to form a sintered layer.

  The adhesion of the sintered layer to the substrate 10 was evaluated by a peel test. Specifically, a tape (however, a scotch mending tape 810 manufactured by 3M was used for the tape) was applied to the surface of the sintered layer 34, and the tape was peeled off perpendicularly to the surface of the substrate 10. The peel test was carried out. As a result, the sintered layer was peeled off from the substrate 10.

  The structure 1 according to the example was manufactured using the manufacturing method described in the embodiment. Specifically, the first coating layer 20 was formed on the substrate 10 made of copper by applying an ink-like paste obtained by diluting silver nanoparticles with an organic solvent by spin coating. However, in the examples, an ink-like paste having a silver particle concentration of 30 wt% was diluted 5 times in a volume ratio using an organic solvent. That is, in the examples, a paste having a viscosity lower than that of the paste used in the comparative example was used. In any of the comparative examples and examples, the thickness of the coating layer can be adjusted by adjusting the amount of paste, the number of rotations during spin coating, the rotation time, and the like.

Next, the first coating layer 20 was irradiated with a laser beam 40 (that is, a line beam) spread in a band shape by the optical system. The silver nanoparticles in the first coating layer 20 were sintered by irradiation with the laser light 40, and the first sintered layer 30 was formed. The used laser beam 40 was a YVO ₄ laser beam having a wavelength of 1064 nm. The laser light output is 6W.

  Here, when the thickness of the 1st sintered layer 30 was measured, it was 0.5 micrometer.

  Subsequently, the paste used to form the first coating layer 20 was applied to the surface of the first sintered layer 30 by spin coating. Thereby, the second coating layer 22 was formed on the surface of the first sintered layer 30. Then, the second coating layer 22 was irradiated with a laser beam 40 (that is, a line beam) spread in a band shape by the optical system. The laser beam 40 used is the same as described above. The silver nanoparticles in the second coating layer 22 were sintered by irradiation with the laser light 40, and the second sintered layer 32 was formed.

  It was 1 micrometer when the thickness of the sintered layer 34 which consists of the 1st sintered layer 30 and the 2nd sintered layer 32 was measured. Moreover, the adhesiveness with respect to the board | substrate 10 of the sintered layer 34 was evaluated by the peel test. Specifically, a tape (however, a scotch mending tape 810 manufactured by 3M was used for the tape) was applied to the surface of the sintered layer 34, and the tape was peeled off perpendicularly to the surface of the substrate 10. The peel test was carried out. As a result, the sintered layer 34 was not peeled off from the substrate 10.

  In addition, since the coating layer is paste-like at the stage of coating, and it is difficult to accurately measure the thickness of the coating layer, the thickness of the sintered layer is described. In addition, the amount of paste applied before sintering varies depending on the amount of metal particles (wt%) and the organic solvent. Therefore, the coating amount of the paste can be appropriately adjusted depending on the solvent used, metal particles, and the like. The inventors of the present invention have confirmed that the thickness of the sintered layer is about 5 to 30% of the thickness of the coating layer depending on these conditions.

  Obtained by diluting the silver nanoparticles with an organic solvent under the same conditions as in Example 1 (that is, the paste (silver concentration is 30 wt%), the rotation speed during spin coating (2000 rpm), and the rotation time (30 seconds)). The first coating layer 20 was formed on the substrate 10 made of copper by applying an ink-like paste by spin coating.

Next, the first coating layer 20 was irradiated with a laser beam 40 (that is, a line beam) spread in a band shape by the optical system. The silver nanoparticles in the first coating layer 20 were sintered by irradiation with the laser light 40, and the first sintered layer 30 was formed. The used laser beam 40 was a YVO ₄ laser beam having a wavelength of 1064 nm. The laser light output is 6W. Here, when the thickness of the 1st sintered layer 30 was measured, it was 0.3 micrometer.

  Subsequently, the paste used for forming the first coating layer 20 was applied to the surface of the first sintered layer 30 by spin coating under the same conditions such as the rotation speed and rotation time during spin coating. Thereby, the second coating layer 22 was formed on the surface of the first sintered layer 30. Then, the second coating layer 22 was irradiated with a laser beam 40 (that is, a line beam) spread in a band shape by the optical system. The laser beam 40 used is the same as described above. By irradiating the laser beam 40, the silver nanoparticles in the second coating layer 22 were sintered to form the second sintered layer 32.

  It was 1 micrometer when the thickness of the sintered layer 34 which consists of the 1st sintered layer 30 and the 2nd sintered layer 32 was measured. That is, the thickness of the second sintered layer 32 was 0.7 μm. Moreover, the adhesiveness with respect to the board | substrate 10 of the sintered layer 34 was evaluated by the peel test. Specifically, a tape (however, a scotch mending tape 810 manufactured by 3M was used for the tape) was applied to the surface of the sintered layer 34, and the tape was peeled off perpendicularly to the surface of the substrate 10. The peel test was carried out. As a result, the sintered layer 34 was not peeled off from the substrate 10.

As in Examples 1 and 2, an ink-like paste obtained by diluting silver nanoparticles with an organic solvent by adjusting the amount of paste, the number of rotations during spin coating, the rotation time, etc. is applied by spin coating. Thus, the first coating layer 20 was formed on the substrate 10 made of copper. Next, the first coating layer 20 was irradiated with a laser beam 40 (that is, a line beam) spread in a band shape by the optical system. The silver nanoparticles in the first coating layer 20 were sintered by irradiation with the laser light 40, and the first sintered layer 30 was formed. The used laser beam 40 is a YVO ₄ laser beam having a wavelength of 1064 nm. The laser light output is 6W. Here, when the thickness of the 1st sintered layer 30 was measured, it was 0.7 micrometer.

  Subsequently, the paste used for forming the first coating layer 20 was applied to the surface of the first sintered layer 30 by spin coating under the same conditions as in Example 2, such as the number of rotations and the rotation time during spin coating. Thereby, the second coating layer 22 was formed on the surface of the first sintered layer 30. Then, the second coating layer 22 was irradiated with a laser beam 40 (that is, a line beam) spread in a band shape by the optical system. The laser beam 40 used is the same as described above. The silver nanoparticles in the second coating layer 22 were sintered by irradiation with the laser light 40, and the second sintered layer 32 was formed.

  It was 1 micrometer when the thickness of the sintered layer 34 which consists of the 1st sintered layer 30 and the 2nd sintered layer 32 was measured. That is, the thickness of the second sintered layer 32 was 0.3 μm. Moreover, the adhesiveness with respect to the board | substrate 10 of the sintered layer 34 was evaluated by the peel test. Specifically, a tape (however, a scotch mending tape 810 manufactured by 3M was used for the tape) was applied to the surface of the sintered layer 34, and the tape was peeled off perpendicularly to the surface of the substrate 10. The peel test was carried out. As a result, the sintered layer 34 was not peeled off from the substrate 10.

  In the present embodiment, sufficient energy can be supplied to each coating layer, and adhesion between the base material and the first sintered layer 30 and between the first sintered layer 30 and the second sintered layer 32. Sex can be secured. For this reason, it is not necessary to form the first coating layer 20 and the second coating layer 22 with different materials in order to improve the adhesion between the base material and the first sintered layer 30. That is, the first coating layer 20 and the second coating layer 22 can be formed of the same material, and the first sintered layer 30 and the second sintered layer 32 can be formed of the same material.

  As described above, since it is not necessary to be aware of the difference between the first sintered layer 30 and the second sintered layer 32, the entire sintered layer is formed by the first sintered layer 30 and the second sintered layer 32. Instead, a thick sintered layer can be formed from the surface of the substrate by repeating the same operation as the second coating step and the second sintering step a plurality of times.

  Further, in this example, the laser was used for sintering, but it was confirmed that the same effect could be obtained even when using a plasma or xenon lamp.

  While the embodiments and examples of the present invention have been described above, the embodiments and examples described above do not limit the invention according to the claims. It should be noted that not all combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention.

DESCRIPTION OF SYMBOLS 1, 2 Structure 10 Board | substrate 20 1st application layer 22 2nd application layer 24 Application layer 30 1st sintered layer 32 2nd sintered layer 34 Sintered layer 36 Sintered layer 40 Laser beam

Claims (9)

Applying a paste containing metal particles on the surface of the substrate to form a first application layer; and
A first sintering step of sintering the first coating layer to form a first sintered layer having a thickness of 1.0 μm or less;
A second coating step of coating the paste on the surface of the first sintered layer to form a second coating layer;
A method for producing a sintered layer, comprising: a second sintering step of sintering the second coating layer to form a second sintered layer.   2. The method for producing a sintered layer according to claim 1, wherein the metal particles include particles made of a metal selected from the group consisting of gold, silver, and copper while having an average particle diameter of 20 nm or less.   The method for producing a sintered layer according to claim 2, wherein the metal particles further include an oxide of the metal.   The method for producing a sintered layer according to claim 2 or 3, wherein the second sintering step forms the second sintered layer having a thickness of 1.0 µm or less.   5. The method according to claim 2, wherein the first sintering step and the second sintering step form the first sintered layer and the second sintered layer whose surfaces are roughened. A method for producing a sintered layer.   6. The firing according to claim 5, wherein the first sintering step and the second sintering step include sintering the first coating layer and the second coating layer by irradiation with laser light, plasma, or a xenon lamp. A method for producing a bonded layer.   The manufacturing method of Claim 1 which further forms a sintered layer by repeating the said 2nd application | coating process and the said 2nd sintering process after the said 2nd sintering process.   A substrate, a first sintered layer provided on the substrate and containing metal particles, and a second sintered layer provided on the first sintered layer and containing metal particles, the first sintered layer and The said 2nd sintered layer is a structure formed by the manufacturing method of the sintered layer of any one of Claims 1-7.   The structure according to claim 8, further comprising a sintered layer formed by repeating the second coating step and the second sintering step on the second sintered layer.

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