METHOD FOR MANUFACTURING PHOTO-SINTERING PARTICLE, METHOD FOR MANUFACTURING PHOTO-SINTERING TARGET, AND PHOTO-SINTERING METHOD

Provided is a method for manufacturing photonic sintering particles. According to an embodiment, the method includes: preparing nano particles; and forming oxide films having different thicknesses with reference to the thermal conductivity of a substrate, on which the nano particles are to be formed, on surfaces of the nano particles.

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Description
BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method for manufacturing photonic sintering particles, a method for manufacturing a photonic sintering target, and a photonic sintering method, and more particularly to a method for manufacturing photonic sintering particles, a method for manufacturing a photonic sintering target, and a photonic sintering method, which improve photonic sintering efficiency through control of oxide films on surfaces of nano particles.

2. Description of the Prior Art

In recent years, as the electronic engineering technologies and the information technologies have developed, uses of portable electronic devices have increased gradually. Currently, almost all of electronic products are manufactured through photolithographic processes. However, because a photolithographic process has 12 or more stages, causing the process complex, the process costs are high, manufacturing time is long, and the photolithographic process uses many toxic chemicals, it may cause environmental contaminations. Accordingly, studies on printing electronics have been actively made to replace such a photolithographic process.

Printing electronics refer to electronic products in which patterns are formed through printing such as screen printing or gravure printing. This includes three stages of simple processes such as printing, drying, and sintering, and has advantages of low costs, an environmental-friendly aspect, a flexibility, a large-area mass-production, a low-temperature/simple process as compared with a conventional photolithographic process. Accordingly, the printing electronics can be applied various electronic products such as flexible electronic products and solar cells.

The core technologies of printed electronic elements include sintering, and the electrical conductivity and the quality of the patterns after sintering may depend on the sintering method and the sintering condition. The existing methods for sintering conductive ink currently includes a thermal sintering method, but because sintering is performed at a temperature of 300° C., it cannot be applied to a flexible substrate, and it requires a long process time and a chamber so it is not suitable for mass-production.

Accordingly, laser sintering, plasma sintering, microwave sintering, and the like have been suggested as a new sintering method, but they also are not suitable for mass-production, and the inventor(s) suggested a white light ultra-shortwave photonic sintering method.

SUMMARY OF THE INVENTION

A technical problem to be solved by the present invention is to provide a method for manufacturing photonic sintering particles, a method for manufacturing a photonic sintering target, and a photonic sintering method having a high efficiency.

Another technical problem to be solved by the present invention is to provide a method for manufacturing photonic sintering particles, a method for manufacturing a photonic sintering target, and a photonic sintering method, by which photonic sintering can be achieved with a high dignity even in a silicon substrate.

Another technical problem to be solved by the present invention is to provide a method for manufacturing photonic sintering particles, a method for manufacturing a photonic sintering target, and a photonic sintering method having an excellent process convenience.

Another technical problem to be solved by the present invention is to provide a method for manufacturing photonic sintering particles, a method for manufacturing a photonic sintering target, and a photonic sintering method having an excellent competitiveness in price.

Another technical problem to be solved by the present invention is to provide a method for manufacturing photonic sintering particles, a method for manufacturing a photonic sintering target, and a photonic sintering method, by which mass-production can be easily achieved.

The objectives of the present invention are not limited to the above-described ones.

According to an aspect of the present invention, a method for manufacturing photonic sintering particles may include: preparing nano particles; and forming oxide films having different thicknesses with reference to the thermal conductivity of a substrate, on which the nano particles are to be formed, on surfaces of the nano particles.

According to an embodiment, in the forming of the oxide films, oxide films of a first thickness may be formed on the surfaces of the nano particles when the thermal conductivity of the substrate is lower than a predetermined reference value, and oxide films of a second thickness may be formed on the surfaces of the nano particles when the thermal conductivity of the substrate is higher than the predetermined reference value, and the first thickness may be smaller than the second thickness.

According to an embodiment, the predetermined reference value is 1 W/mK.

According to an embodiment, the first thickness may be 1% to 3% of the diameters of the nano particles, and the second thickness may be 3% to 10% of the diameters of the nano particles.

According to another aspect of the present invention, a method for manufacturing a photonic sintering target may include 0: preparing nano particles; forming oxide films having different thicknesses with reference to the thermal conductivity of a substrate, on which the nano particles are to be formed, on surfaces of the nano particles; and manufacturing a conductive target by providing a binder resin in the nano particles, on which the oxide films are formed.

According to an embodiment, in the forming of the oxide films, oxide films of a first thickness may be formed on the surfaces of the nano particles when the thermal conductivity of the substrate is lower than a predetermined reference value, and oxide films of a second thickness may be formed on the surfaces of the nano particles when the thermal conductivity of the substrate is higher than the predetermined reference value, and the first thickness may be smaller than the second thickness.

According to an embodiment, the predetermined reference value may be 1 W/mK.

According to an embodiment, the first thickness may be 1% to 3% of the diameters of the nano particles, and the second thickness may be 3% to 10% of the diameters of the nano particles.

According to another aspect of the present invention, a photonic sintering method may include: forming oxide films having different thicknesses with reference to the thermal conductivity of a substrate, on which the nano particles are to be formed, on surfaces of the nano particles; manufacturing a conductive target by providing a binder resin in the nano particles, on which the oxide films are formed; forming the manufactured conductive target on the substrate; and photonic-sintering the conductive target formed on the substrate.

According to an embodiment, in the forming of the oxide films, oxide films of a first thickness may be formed on the surfaces of the nano particles when the thermal conductivity of the substrate is lower than a predetermined reference value, and oxide films of a second thickness may be formed on the surfaces of the nano particles when the thermal conductivity of the substrate is higher than the predetermined reference value, and the first thickness may be smaller than the second thickness, and in the photonic-sintering of the conductive target, light of a first intensity may be irradiated to the substrate when the thermal conductivity of the substrate is lower than the predetermined reference value and light of a second intensity may be irradiated to the substrate when the thermal conductivity of the substrate is higher than the predetermined reference value, and the first intensity is lower than the second intensity.

According to another aspect of the present invention, a method for manufacturing photonic sintering particles may include determining whether it is necessary to form oxide films on the surfaces of the nano particles according to the characteristics of the substrate, on which the nano particles are to be formed; and when it is necessary to form the oxide films on the surfaces of the nano particles, forming oxide films on the surfaces of the nano particles.

According to an embodiment, the characteristics of the substrate may be thermal conductivity, and when the thermal conductivity is 1 W/mK or more, it may be determined that it is necessary to form oxide films on the surfaces of the nano particles.

According to an embodiment, when the substrate includes silicon, it may be determined that it is necessary to form oxide films on the surfaces of the nano particles.

According to another aspect of the present invention, a method for manufacturing a photonic sintering target may include: determining whether it is necessary to form oxide films on the surfaces of the nano particles according to the characteristics of the substrate, on which the nano particles are to be formed; when it is necessary to form oxide films on the surfaces of the nano particles, forming oxide films on the surfaces of the nano particles; and manufacturing a conductive target by providing a binder resin in the nano particles, on which the oxide films are formed.

According to an embodiment, the characteristics of the substrate may be thermal conductivity, and when the thermal conductivity is 1 W/mK or more, it may be determined that it is necessary to form oxide films on the surfaces of the nano particles.

According to an embodiment, when the substrate includes silicon, it may be determined that it is necessary to form oxide films on the surfaces of the nano particles.

According to another aspect of the present invention, a photonic sintering method including: determining whether it is necessary to form oxide films on the surfaces of the nano particles according to the characteristics of the substrate, on which the nano particles are to be formed; when it is necessary to form oxide films on the surfaces of the nano particles, forming oxide films on the surfaces of the nano particles; manufacturing a conductive target by providing a binder resin in the nano particles, on which the oxide films are formed; forming the manufactured conductive target on the substrate; and photonic-sintering the conductive target formed on the substrate.

A photonic sintering method according to an embodiment of the present invention may include a step of forming and controlling oxide films of copper nano particles such that the copper nano particles have optimum photonic sintering characteristics according to the kind of a substrate, a step of manufacturing a conductive ink including a polymeric binder resin, a step of printing the conductive ink on the substrate and drying the substrate, and a step of photonic-sintering the printed pattern by using while light irradiated from a xenon flash lamp.

According to an embodiment of the present invention, oxide films can be reduced and sintered in a very short time of within several milliseconds (1 ms to 1000 ms) in a room temperature/atmospheric condition, and electronic elements having high electrical conductivity and reliability can be easily mass-produced.

In particular, according to an embodiment of the present invention, because a photonic sintering process may be performed on a silicon substrate, on which it is conventionally difficult to perform a photonic sintering process can become possible, the kinds of the substrates applied can be expanded.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a flowchart illustrating a photonic sintering method according to an embodiment of the present invention;

FIGS. 2A and 2B are views illustrating step S150 of the photonic sintering method according to the embodiment of the present invention;

FIG. 3 is a view illustrating a photonic sintering method according to another embodiment of the present invention;

FIG. 4 is a graph depicting resistances according to the kinds of substrates and the thicknesses of oxide films;

FIG. 5 illustrates high resolution-transmission electron microscope (HR-TEM) pictures for explaining oxide films formed according to the kinds of the substrates;

FIG. 6 illustrates graphs depicting a change in X-ray diffraction (XRD) before and after sintering according to the thickness of an oxide film of a conductive target formed in a polyimide (PI) substrate;

FIG. 7 illustrates graphs depicting a change in XRD before and after sintering according to the thickness of an oxide film of a conductive target formed in a silicon substrate;

FIG. 8 illustrates an SEM picture according the thickness of an oxide film of a conductive target formed on a PI substrate; and

FIG. 9 illustrates an SEM picture according the thickness of an oxide film of a conductive target formed on a silicon substrate.

 DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the technical spirit of the present invention is not limited to the embodiments, but may be realized in different forms. The embodiments introduced here are provided to sufficiently deliver the spirit of the present invention to those skilled in the art so that the disclosed contents may become thorough and complete.

When it is mentioned in the specification that one element is on another element, it means that the first element may be directly formed on the second element or a third element may be interposed between the first element and the second element. Further, in the drawings, the thicknesses of the films and the areas are exaggerated for efficient description of the technical contents.

Further, in the various embodiments of the present invention, the terms such as first, second, and third are used to describe various elements, but the elements are not limited to the terms. The terms are used only to distinguish one element from another element. Accordingly, an element mentioned as a first element in one embodiment may be mentioned as a second element in another embodiment. The embodiments illustrated here include their complementary embodiments. Further, the term “and/or” in the specification is used to include at least one of the elements enumerated in the specification.

In the specification, the terms of a singular form may include plural forms unless otherwise specified. Further, the terms “including” and “having” are used to designate that the features, the numbers, the steps, the elements, or combination thereof described in the specification are present, and may be understood that one or more other features, numbers, step, elements, or combinations thereof may be added. Further, in the specification, “connected to” is used to mean a plurality of elements are indirectly or directly connected to each other.

Further, in the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention unnecessarily unclear.

FIG. 1 is a flowchart illustrating a photonic sintering method according to an embodiment of the present invention. Referring to FIG. 1, a method for manufacturing photonic sintering particles and a method for manufacturing a photonic sintering target will be described together. FIG. 2 is a view illustrating step S150 of the photonic sintering method according to the embodiment of the present invention.

Referring to FIG. 1, a photonic sintering method according to an embodiment of the present invention may includes a step of providing nano particles (S110), a step of forming oxide films having different thicknesses with reference to the thermal conductivity of a substrate, on which the nano particles are to be formed, on surfaces of the nano particles (S120), a step of manufacturing a conductive target by providing a binder resin in the nano particles, on which the oxide films are formed (S130), a step of forming the manufactured conductive target on the substrate (S140), and photonic-sintering the conductive target formed on the substrate. Hereinafter, the steps will be described.

Step S110

In step S110, nano particles may be provided. The nano particles may include at least one material, among gold, silver, and copper. Hereinafter, it is assumed that the nano particles are copper nano particles unless mentioned particularly.

Step S120

In step S120, oxide films having different thicknesses with reference to the thermal conductivity of a substrate, on which the nano particles are to be formed, may be formed on surfaces of the nano particles,

The substrate, for example, may be a soft substrate or a rigid substrate. For example, the substrate may be formed of at least material among photo paper, PET, paper, polybutylene terephtalate, polyethylene terephthalate, polysulfone, polyether, polyether imide, Poly(ethylene naphthalate) (PEN), an acryl resin, heat-resistant epoxy, a BT epoxy/glass fiber, polyvinyl acetate (EVA), butyl rubber, polyarylate, and polyimide. Further, the substrate may be formed of at least one material, among glass, amorphous silicon, mono-crystaline silicon, poly-crystaline silicon, and ceramics.

Then, the thicknesses of the oxide films, which are to be formed on the surfaces of the prepared nano particles, may be controlled according to the characteristics of the substrate, for example, thermal conductivity and flexibility. For example, the substrate may have thermal conductivity and flexibility characteristics as described in Table 1 according to the kind of the substrate.

TABLE 1 Category Flexible Non-flexible Kind of substrate Amorphous Crystalline I ET aper EN BT VA silicon silicon Thermal .52 .24 .05 .15 .24 .34 1.8 149 conduc- tivity [W/mk]

According to an embodiment, oxide films of a first thickness may be formed on the surfaces of the nano particles when the conductivity is lower than the predetermined reference, and oxide films of a second thickness that is larger than the first thickness may be formed when the thermal conductivity is higher than the predetermined reference. In more detail, the oxide films of a thickness of 1% to 3% of the diameters of the nano particles may be formed on the surfaces of the nano particles when the thermal conductivity of the substrate is lower than 1 W/mK, and the oxide films of a thickness of 3% to 10% of the diameters of the nano particles may be formed on the surfaces of the nano particles when the thermal conductivity of the substrate is higher than 1 W/mK.

According to an embodiment, oxide films may be formed on the surfaces of the nano particles in various methods. For example, a method of oxidizing nano particles by heating the nano particles in air with a chamber, a hot plate, or the like may be used and also a method of oxidizing nano particles through a plasma treatment and a separate post-treatment immediately after the manufacturing of the nano particles, but the present invention is not limited thereto. Further, the thicknesses of the oxide films may be controlled by adjusting one or a combination of two or more of heating temperature, oxidation time, and oxygen partial pressure.

Through steps S110 and S120, photonic sintering particles according to an embodiment of the present invention may be manufactured. Hereinafter, step S130 will be described.

Step S130

In step S130, a conductive target may be manufactured by providing a binder resin to the nano particles on which the oxide films are formed. Then, the conductive target means a photonic sintering target, and may be understood as a concept including a photonic sintering ink and a paste.

The binder resin may be added to improve the dispersion and reduction of the manufactured photonic sintering ink. The binder resin may include at least material, among polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyvinyl butyral, polyethylene glycol, polymethyl methacrylate, dextran, azobis, and sodium dodecylbenzene sulfate. Then, the fraction of the binder may be 1 wt % to 50 wt %. Further, because the dispersion or reduction effect decreases if the weight average molecular weight of the binder is too low and the binder forms a agglomerate when it exceeds 500,000, it is preferable that the weight average molecular weight of 10,000 to 500,000 is used. The kind and the dosage of the binder may vary according to the thickness of the oxide films of the copper nano particles.

A photonic sintering target may be formed by performing step S130 on the photonic sintering particles manufactured through steps S110 and S120. Hereinafter, step S140 will be described.

Step S140

In step S140, the manufactured photonic sintering target may be formed on the substrate.

The photonic sintering target may be formed on the substrate in various methods. For example, at least one method, among screen printing, inkjet printing, micro-contact printing, imprinting, gravure printing, gravure-offset printing, flexography printing, and spin coating, may be used.

Further, the photonic sintering target formed on the substrate may be dried in a drying process. For example, the photonic sintering target formed on the substrate may be dried by a hot air blower, a heating chamber, a hot plate, an infrared ray, or a combination thereof. The drying temperature may be set such that the substrate is not damaged. If the substrate is a polymer substrate, the drying temperature may be in a range of 60° C. to 150° C.

Step S150

In step S150, the photonic sintering target formed on the substrate may be photonic-sintered. The photonic sintering target is photonic-sintered to become conductive while receiving light energy from ultra-shortwave white light emitted from a xenon lamp. In the photonic sintering process, all the oxide films are reduced and sintered only when sufficient light energy is irradiated, and it is necessary to prevent the substrate from being damaged when high energy is instantaneously irradiated. Accordingly, the white light may be irradiated through a multi-stage photonic sintering technique for gradually reducing oxide films to increase the sintering effect.

Referring to FIG. 2A for helping understanding, in a state in which the photonic sintering target 20 is formed on one surface of the substrate 10, light 50 may be provided to the photonic sintering target 20 through a xenon flash lamp 30. Then, in order to improve optical efficiency, a reflector 40 that reflects light to an object may be provided on one side of the xenon flash lamp 30.

Then, the light provided to the photonic sintering target may be combined by various factors. For example, as illustrated in FIG. 2B, the factors, such as light provision time, the intensity of light, and the pulses of light may be controlled. For example, the condition of the provided light varies according to changes in the width of the pulses (0.01 ms to 50 ms), the gap of the pulses (0.01 ms to 100 ms), the number of the pulses (one to 100 times), the intensity of light (0.1 J/cm2 to 100 J/cm2), and accordingly, a total light energy may have light energy of a maximum of 100 J/cm2.

Then, the energy range for sintering may vary according to the substrate. For example, light of a first intensity may be irradiated to the substrate when the thermal conductivity of the substrate is lower than a predetermined reference value, and light of a second intensity that is stronger than the first intensity may be irradiated to the substrate when the thermal conductivity of the substrate is height than a 7 predetermined reference value. In more detail, the intensity of light may be in a range of 0.1 J/cm2 to 20 J/cm2 when the thermal conductivity of the substrate is lower than 1 W/mK, and the intensity of light may be in a range of 20 J/cm2 to 100 J/cm2 when the thermal conductivity of the substrate is higher than 1 W/mK.

Until now, the method for manufacturing photonic sintering particles, the method for manufacturing a photonic sintering target, and a photonic sintering method according to the embodiments of the present invention have been described with reference to FIGS. 1 and 2. Hereinafter, a mechanism of an embodiment of the present invention will be described.

Photonic Sintering Mechanism Considering Characteristics of Substrate

A mechanism of a rapid photonic sintering process that uses ultra-shortwave white light is a mechanism which, if light energy of white light pulses irradiated from a xenon lamp reaches a target, converts the light energy into thermal energy to instantaneously increase the temperature of a target layer so that the target layer is sintered in a very short time. Accordingly, because not only the light absorption, the heat capacity, and the thermal conductivity of the target layer but also the photonic sintering characteristics of the target layer vary according to the physical property of the substrate, it is necessary to control the light irradiation condition and the nono particles according to the sintering atmosphere due to the variations. However, because conventionally the physical property of the substrate has not been recognized as a photonic sintering parameter, it is difficult to enhance the photonic sintering efficiency. In particular, it has been a difficulty in studying a photonic sintering measure, the target of which is a substrate of a high thermal conductivity.

The inventor(s) suggested a technical solution that considers the characteristics of a substrate.

In order to reduce and sinter a photonic sintering target, the temperatures of the photonic sintering target and/or the nano particles have to reach a specific temperature level. Because thermal energy is conducted from the photonic sintering target to the substrate more rapidly as the thermal conductivity of the substrate becomes higher in an aspect of heat transfer, the light energy that has to be irradiated to sinter the photonic sintering target increases. Accordingly, a light irradiation condition for higher energy is necessary when a material of a high thermal conductivity, such as silicon, is used than when a substrate of a low thermal conductivity, such as a polymer, is used.

Accordingly, because the photonic sintering target is deprived of thermal energy that is necessary for sintering by the substrate in the case of the silicon substrate of a high thermal conductivity, photonic sintering characteristics can be enhanced when the thickness of the oxide films are thick.

Further, in thick oxide films, light irradiation energy for sintering increases as the thermal conductivity of the substrate increases, and then, the photonic sintering target can be prevented from being burned or being delaminated from the substrate.

Unlike this, in the case of a polymer (PI, PE, or the like) substrate of a low thermal conductivity, because light energy for sintering has to be minimized to minimize damage to the substrate, and thus the photonic sintering characteristics can be enhanced when the thicknesses of the oxide films of nano particles are small.

Accordingly, according to an embodiment of the present invention, because thin oxide films and sintering light of a low intensity are provided when the thermal conductivity of the substrate is low and thick oxide films and sintering light of a high intensity are provided when the thermal conductivity of the substrate is high, the conductivity characteristics of the photonic sintering target can be enhanced and the stability of the substrate can be achieved.

FIG. 3 is a view illustrating a photonic sintering method according to another embodiment of the present invention. Referring to FIG. 3, a method for manufacturing photonic sintering particles and a method for manufacturing a photonic sintering target will be described together.

Referring to FIG. 3, a step of providing nano particles (S210), a step of determining whether it is necessary to form oxide films on the surfaces of the nano particles according to the characteristics of the substrate, on which the nano particles are to be formed (S220), a step of, when it is necessary to form oxide films on the surfaces of the nano particles, forming oxide films on the surfaces of the nano particles (S230), a step of manufacturing a conductive target by providing a binder resin in the nano particles, on which the oxide films are formed (S240), and a step of forming the manufactured conductive target on the substrate (S250), and a step of photonic-sintering the conductive target formed on the substrate (S260). Hereinafter, the steps will be described. Then, the repeated parts of the steps described above with reference to FIG. 1 will be omitted.

Step S210 will be omitted because it corresponds to step S110.

In step S220, it may be determined whether it is necessary to form oxide films on surfaces of the nano particles according to the characteristics of the substrate, on which nano particles are to be formed.

According to an embodiment, when the characteristics of the substrate, for example, the thermal conductivity of the substrate is higher than a predetermined reference, it may be determined that it is necessary to form oxide films on the surfaces of the nano particles. Then, the thermal conductivity according to the predetermined reference may be 1 W/mK.

Unlike this, according to the kind of the substrate, for example, when the substrate includes silicon, it may be determined that it is necessary to form oxide films on the surfaces of the nano particles.

In step S230, when it is determined in the determination of step S220 that it is necessary to form oxide films, oxide films may be provided to the surfaces of the nano particles.

Steps S240, S250, and S260 correspond to steps S130, S140, and S150, and a detailed description thereof will be omitted.

According to the embodiment described with reference to FIG. 3, which has been described above, photonic sintering that considers the characteristics of the substrate is possible by the step of determining whether it is necessary to form oxide films according to the characteristics of the substrate.

The effects of the consideration of the characteristics of the substrate are described already with reference to FIGS. 1 and 2, a description thereof will be omitted. Hereinafter, the characteristics of the embodiments of the present invention will be described with reference to FIGS. 4 to 9.

FIG. 4 is a graph depicting resistances according to the kinds of substrates and the thicknesses of oxide films. FIG. 5 illustrates high resolution-transmission electron microscope (HR-TEM) pictures for explaining oxide films formed according to the kinds of the substrates. FIG. 6 illustrates graphs depicting a change in XRD before and after sintering according to the thickness of an oxide film of a conductive target formed in a PI substrate. FIG. 7 illustrates graphs depicting a change in XRD before and after sintering according to the thickness of an oxide film of a conductive target formed in a silicon substrate. FIG. 8 illustrates an SEM picture according the thickness of an oxide film of a conductive target formed on a PI substrate. FIG. 9 illustrates an SEM picture according the thickness of an oxide film of a conductive target formed on a silicon substrate.

For experiments, embodiments 1 to 6 were prepared.

Embodiment 1

Copper nano particles having an average diameter of 100 nm were mixed in an oven of a temperature of 200° C. and were oxidized for 1 minute. PVP of 0.9 g was mixed with a diethylene glycol butyl ether (DGBE) solution of 4 g and was dispersed for 30 minutes by using a sonicator. After being added to the mixture solution, the oxidized copper particles of 12 g were dispersed for 40 minutes by using a 3-roll mill to manufacture a copper paste. After being printed in the form of an electrode on a silicon substrate by using a screen printer, the manufactured copper paste was dried for 15 minutes by using infrared rays of a temperature of 100° C. to finish an electrode pattern. Ultra-shortwave white light was irradiated to the electrode pattern. Then, the number of pulses of the ultra-shortwave white light was 40, the width of the pulses was 1 ms, the interval between the pulses was 20 ms, and the total irradiation energy was 60 J/cm2).

Embodiment 2

Copper nano particles having an average diameter of 100 nm were mixed in an oven of a temperature of 200° C. and were oxidized for 4 minutes. PVP of 0.9 g was mixed with a diethylene glycol (DEG) solution of 4.5 g and was dispersed for 30 minutes by using a sonicator. After being added to the mixture solution, the oxidized copper particles of 11.4 g were dispersed for 45 minutes by using a 3-roll mill to manufacture a copper paste. After being printed in the form of an electrode on a silicon substrate by using a screen printer, the manufactured copper paste was dried for 15 minutes by using infrared rays of a temperature of 100° C. to finish an electrode pattern. Ultra-shortwave white light was irradiated to the electrode pattern. Then, the number of pulses of the ultra-shortwave white light was 30, the width of the pulses was 1 ms, the interval between the pulses was 30 ms, and the total irradiation energy was 55 J/cm2).

Embodiment 3

Copper nano particles having an average diameter of 100 nm were mixed in an oven of a temperature of 200° C. and were oxidized for 7 minutes. PVP of 0.9 g was mixed with a diethylene glycol (DEG) solution of 4.5 g and was dispersed for 30 minutes by using a sonicator. After being added to the mixture solution, the oxidized copper particles of 11.4 g were dispersed for 50 minutes by using a 3-roll mill to manufacture a copper paste. After being printed in the form of an electrode on a silicon substrate by using a screen printer, the manufactured copper paste was dried for 15 minutes by using infrared rays of a temperature of 120° C. to finish an electrode pattern. Ultra-shortwave white light was irradiated to the electrode pattern. Then, the number of pulses of the ultra-shortwave white light was 25, the width of the pulses was 1.5 ms, the interval between the pulses was 25 ms, and the total irradiation energy was 50 J/cm2).

Embodiment 4

Copper nano particles of an average diameter of 40 nm were dispersed for 30 minutes by using a sonicator after PVP of 0.9 g was mixed with a diethylene glycol (DEG) solution of 4.5 g. After being added to the mixture solution, the oxidized copper particles of 11.4 g were dispersed for 45 minutes by using a 3-roll mill to manufacture a copper paste. After being printed in the form of an electrode on a polyimide (PI) substrate by using a screen printer, the manufactured copper paste was dried for 20 minutes by using infrared rays of a temperature of 100° C. to finish an electrode pattern. Ultra-shortwave white light was irradiated to the electrode pattern. The, the irradiation time was 10 ms, the number of pulses was 1, and the pulse energy was 12. 5 J/cm2.

Embodiment 5

Copper nano particles having an average diameter of 40 nm were mixed in an oven of a temperature of 100° C. and were oxidized for three hours. PVP of 0.9 g was mixed with a diethylene glycol (DEG) solution of 4.5 g and was dispersed for 30 minutes by using a sonicator. After being added to the mixture solution, the oxidized copper particles of 11.4 g were dispersed for 50 minutes by using a 3-roll mill to manufacture a copper paste. After being printed in the form of an electrode on a polyimide (PI) substrate by using a screen printer, the manufactured copper paste was dried for 1 minute by using a hot plate of a temperature of 100° C. to finish an electrode pattern. Ultra-shortwave white light was irradiated to the electrode pattern. The, the irradiation time was 10 ms, the number of pulses was 1, and the pulse energy was 15 J/cm2.

Embodiment 6

Copper nano particles having an average diameter of 40 nm were mixed in an oven of a temperature of 200° C. and were oxidized for two hours. PVP of 0.9 g was mixed with a diethylene glycol (DEG) solution of 4.5 g and was dispersed for 30 minutes by using a sonicator. After being added to the mixture solution, the oxidized copper particles of 11.4 g were dispersed for 50 minutes by using a 3-roll mill to manufacture a copper paste. After being printed in the form of an electrode on a polyimide (PI) substrate by using a screen printer, the manufactured copper paste was dried for one minute by using a hot plate of a temperature of 100° C. to finish an electrode pattern. Ultra-shortwave white light was irradiated to the electrode pattern. The, the irradiation time was 20 ms, the number of pulses was 1, and the pulse energy was 15 J/cm2.

Referring to FIG. 4, resistances of the cases in which the surface oxide films of the copper nano particles had different thicknesses could be identified according to whether the substrate is a PI substrate having a low thermal conductivity or a silicon substrate. As illustrated in FIG. 4 and Table 2, it could be identified that the conductivity becomes more excellent as the thickness of the oxide films becomes smaller in the case of a PI substrate having a low thermal conductivity. Unlike this, it could be identified that the conductivity is still excellent even though the thickness of the oxide films becomes larger in the case of a silicon substrate having a high thermal conductivity. In particular, it could be identified that the conductivity can be remarkably improved by forming oxide films on the photonic sintering target in the case of a silicon substrate.

TABLE 2 Thickness of oxide films 0.8 nm 2.1 nm 3.6 nm PI resistivity 17.339 μΩ · cm 45.818 μΩ · cm 74.213 μΩ · cm Thickness of oxide films 2.7 nm 5.8 nm 7.1 nm Silicon 15.3 μΩ · cm 10.87 μΩ · cm 16.13 μΩ · cm resistivity

Unlike this, it could be identified that both the two substrates could not be sintered by using photonic sintering when no oxide film of the copper particles was present (0 nm and 0.2 nm). This is because the copper patterns were burned out while reacting with oxygen in air when white light of strong pulses is irradiated in the case of the copper nano particles with no oxide film.

FIG. 5 is a picture illustrating that the oxide films of a predetermined thickness were formed on the surfaces of the copper nano particles, and no amorphous material (oxide film layer) was observed before the treatment process for forming oxide films, and it could be identified that optimized oxide films of 0.8 nm were formed in the PI substrate and optimized oxide films of 5.8 nm were formed in the silicon substrate after the oxidation process.

Referring to FIG. 6, a photonic sintering target was formed in the PI substrate, and an XRD graph according to variation of the thickness of the oxide films could be identified. Oxidized copper film reduction reactions by the reactions with the polymer surface modifiers coated on the outside of the copper nano particles were generated, and accordingly, it could be identified that the oxidized copper of the copper nano particles having oxide films of a thickness of 3.6 nm or less was reduced to pure copper and was sintered. Meanwhile, it was shown that many oxide films were still left after the irradiation of ultra-shortwave white light if excessive oxide films were formed and a copper oxide (II) (CuO) is excessively formed (FIG. 8), and electrical resistance is high. Accordingly, proper control of oxide films is necessarily necessary in enhancing photonic sintering characteristics of copper nano ink.

Referring to FIG. 7, a photonic sintering target was formed in the silicon substrate, and an XRD graph according to variation of the thickness of the oxide films could be identified. As illustrated in FIG. 7, it could be identified that sintering cannot be achieved by forming oxide films of a small thickness of 0.2 nm (natural oxidation), and sintering can be achieved when the thickness of the oxide films is 5.8 nm and 7.1 nm. That is, it also could be identified experimentally that the oxide films had to be thick in the case of the substrate having a high thermal conductivity.

Referring to FIGS. 8 and 9, it could be identified that the conductivity characteristics became worse because the number of pores increases as the thickness of the oxide films becomes larger in the case of the PI substrate, and there is not any big difference between the conductivity characteristics when the thicknesses of the oxide films are 2.7 nm to 7.1 nm.

According to the above-described embodiments of the present invention, optimum photonic sintering characteristics could be provided to the nano particles having oxide films according to the kind of the substrate. Accordingly, a photonic sintering process, which has been extremely difficult to realize conventionally, may be performed even to a substrate of a high thermal conductivity. Further, the photonic sintering efficiency can be enhanced by controlling the thickness of oxide films and a photonic sintering condition differently according to the characteristics of the substrate.

Although the preferred embodiments of the present invention have been described in detail until now, the scope of the present invention is not limited to the embodiments and should be construed by the attached claims. Further, it should be understood that those skilled in the art to which the present invention pertains may variously correct and modify the present invention without departing from the scope of the present invention.

Claims

1. A method for manufacturing photonic sintering particles, the method comprising:

preparing nano particles; and
forming oxide films having different thicknesses with reference to the thermal conductivity of a substrate, on which the nano particles are to be formed, on surfaces of the nano particles.

2. The method of claim 1, wherein in the forming of the oxide films, oxide films of a first thickness are formed on the surfaces of the nano particles when the thermal conductivity of the substrate is lower than a predetermined reference value, and oxide films of a second thickness are formed on the surfaces of the nano particles when the thermal conductivity of the substrate is higher than the predetermined reference value, and

wherein the first thickness is smaller than the second thickness.

3. The method of claim 2, wherein the predetermined reference value is 1 W/mK.

4. The method of claim 2, wherein the first thickness is 1% to 3% of the diameters of the nano particles, and the second thickness is 3% to 10% of the diameters of the nano particles.

5. A method for manufacturing a photonic sintering target, the method comprising:

preparing nano particles;
forming oxide films having different thicknesses with reference to the thermal conductivity of a substrate, on which the nano particles are to be formed, on surfaces of the nano particles; and
manufacturing a conductive target by providing a binder resin in the nano particles, on which the oxide films are formed.

6. The method of claim 5, wherein in the forming of the oxide films, oxide films of a first thickness are formed on the surfaces of the nano particles when the thermal conductivity of the substrate is lower than a predetermined reference value, and oxide films of a second thickness are formed on the surfaces of the nano particles when the thermal conductivity of the substrate is higher than the predetermined reference value, and

wherein the first thickness is smaller than the second thickness.

7. The method of claim 6, wherein the predetermined reference value is 1 W/mK.

8. The method of claim 6, wherein the first thickness is 1% to 3% of the diameters of the nano particles, and the second thickness is 3% to 10% of the diameters of the nano particles.

9. A photonic sintering method, comprising:

forming oxide films having different thicknesses with reference to the thermal conductivity of a substrate, on which the nano particles are to be formed, on surfaces of the nano particles;
manufacturing a conductive target by providing a binder resin in the nano particles, on which the oxide films are formed;
forming the manufactured conductive target on the substrate; and
photonic-sintering the conductive target formed on the substrate.

10. The method of claim 9, wherein in the forming of the oxide films, oxide films of a first thickness are formed on the surfaces of the nano particles when the thermal conductivity of the substrate is lower than a predetermined reference value, and oxide films of a second thickness are formed on the surfaces of the nano particles when the thermal conductivity of the substrate is higher than the predetermined reference value, and the first thickness is smaller than the second thickness, and

wherein in the photonic-sintering of the conductive target, light of a first intensity is irradiated to the substrate when the thermal conductivity of the substrate is lower than the predetermined reference value and light of a second intensity is irradiated to the substrate when the thermal conductivity of the substrate is higher than the predetermined reference value, and the first intensity is lower than the second intensity.

11. A method for manufacturing photonic sintering particles, the method comprising:

determining whether it is necessary to form oxide films on the surfaces of the nano particles according to the characteristics of the substrate, on which the nano particles are to be formed; and
when it is necessary to form the oxide films on the surfaces of the nano particles, forming oxide films on the surfaces of the nano particles.

12. The method of claim 11, wherein the characteristics of the substrate are thermal conductivity, and when the thermal conductivity is 1 W/mK or more, it is determined that it is necessary to form oxide films on the surfaces of the nano particles.

13. The method of claim 11, wherein when the substrate comprises silicon, it is determined that it is necessary to form oxide films on the surfaces of the nano particles.

14. A method for manufacturing a photonic sintering target, the method comprising:

determining whether it is necessary to form oxide films on the surfaces of the nano particles according to the characteristics of the substrate, on which the nano particles are to be formed;
when it is necessary to form oxide films on the surfaces of the nano particles, forming oxide films on the surfaces of the nano particles; and
manufacturing a conductive target by providing a binder resin in the nano particles, on which the oxide films are formed.

15. The method of claim 14, wherein the characteristics of the substrate are thermal conductivity, and when the thermal conductivity is 1 W/mK or more, it is determined that it is necessary to form oxide films on the surfaces of the nano particles.

16. The method of claim 14, wherein when the substrate comprises silicon, it is determined that it is necessary to form oxide films on the surfaces of the nano particles.

17. A photonic sintering method, comprising:

determining whether it is necessary to form oxide films on the surfaces of the nano particles according to the characteristics of the substrate, on which the nano particles are to be formed;
when it is necessary to form oxide films on the surfaces of the nano particles, forming oxide films on the surfaces of the nano particles;
manufacturing a conductive target by providing a binder resin in the nano particles, on which the oxide films are formed;
forming the manufactured conductive target on the substrate; and
photonic-sintering the conductive target formed on the substrate.
Patent History
Publication number: 20200061704
Type: Application
Filed: Oct 18, 2019
Publication Date: Feb 27, 2020
Applicant: IUCF-HYU (INDUSTRY-UNIVERSITY COOPERATION FOUNDATION HANYANG UNIVERSITY) (Seoul)
Inventors: Hak-Sung KIM (Seoul), Hyun-Jun HWANG (Seoul), Gyung Hwan OH (Uijeongbu-si), Deok Joong KIM (Seoul)
Application Number: 16/657,489
Classifications
International Classification: B22F 3/105 (20060101); B22F 7/04 (20060101); B22F 1/00 (20060101);