KR20220085116A - Free-standing copper-silver foil and preparation method thereof - Google Patents

Abstract

The present invention relates to a freestanding copper-silver sheet and a method for manufacturing the same. More particularly, the present invention relates to a copper-silver thin plate in a freestanding state in which the copper-silver of nano grains is supersaturated with improved mechanical properties and electrical properties at the same time, and a method for manufacturing the same.

Description

Free-standing copper-silver foil and preparation method thereof

The present invention relates to a freestanding copper-silver (Cu-Ag) foil and a method for manufacturing the same. More particularly, the present invention relates to a copper-silver thin plate in a freestanding state in which the copper-silver of nano grains is supersaturated with improved mechanical properties and electrical properties at the same time, and a method for manufacturing the same.

Copper foil can be manufactured through rolling and electroplating. All of the pure copper foils made by rolling or electroplating have low mechanical strength, and thus there are difficulties in thinning and application to flexible electronic devices.

On the other hand, copper-silver alloy has high strength (>1 GPa) and high conductivity (> 70% IACS), so it is attracting attention as a next-generation probe pin material. In the case of Cu-Ag thin plate, it can be generally manufactured through methods such as cold drawing, cold rolling, and dynamic plastic deformation. The mechanical and electrical properties of Cu-Ag thin plates are affected by the size, distribution, crystal size, and fraction of nano-twins of the Ag-rich phase, and the main strengthening mechanism is caused by the precipitated Ag-rich phase. These include precipitation hardening, nano-twinning, and work hardening. When heat treatment is performed on the dissolved Cu-Ag or the resulting plate, additional property improvement due to precipitation is also observed. Although there is a difference according to the crystal structure characteristics, when the Ag content is 6% to 24%, the tensile strength is about 900 to 1100 MPa, and the conductivity is reported to be about 80 to 87 % IACS based on the IACS %.

In the case of the existing Cu-Ag thin plate, most of it is manufactured through the rolling method, but it is difficult to implement a thickness of 100 μm or less due to mechanical strength, making it difficult to make a thin plate and apply it to a flexible electronic device.

The Cu-Ag plating layer may be prepared by electroplating in a cyanide, ammonia, methanesulfonic acid, or pyrophosphate-based bath. Cu-Ag made through electroplating is generally formed as a metastable solid solution in the range of 3% to 4.4% of Ag content, and a mixture of a metastable Cu-rich solid solution and Ag-rich phase at a concentration higher than that is formed. Depending on the process conditions, they are composed of fine grains, and the Vickers hardness is reported to be 450-600HV and the specific resistance is 2.2uΩ*cm. When the Ag content is 10%, the solid solution strengthening effect is not large, and it is considered that the high strength of the 0-10 wt% Cu-Ag plating layer is caused by grain-boundary strengthening based on the Hall-Petch relationship. When the resulting Cu-Ag plating film is exposed to high temperature (>200 °C), precipitation of dissolved Ag and growth of crystals are observed. Unlike the general Cu-Ag supersaturated solid solution in which additional strength improvement is reported, in most cases, a large decrease in strength is accompanied. This decrease in strength means that, in the case of the plated Cu-Ag layer, grain-boundary strengthening effect is superior to precipitation hardening by Ag.

In addition to grain-solid-solid strengthening, a strengthening effect through nanometer-scale Cu/Ag multilayer repeat formation has also been reported. D. M. Tench et al. and Ebrahimi et al. prepared a Cu/Ag multilayer of 20-60 um through repetition of electroplating and Ag displacement reaction, in which case a high UTS of 871 MPa and 1.0% A plastic strain of In addition, it was confirmed that the Hall-Petch relationship was established according to the thickness of each Cu and Ag layer. After heat treatment of the produced Cu/Ag, the tensile properties were tested, and it was confirmed that the tensile strength was significantly reduced (880 MPa to 450 MPa) after heat treatment. This means that, as in the case of Cu-Ag supersaturated solid solution, the strengthening effect due to the Hall-Petch relationship is greater than that of precipitation hardening.

Although the Cu-Ag plating layer is known to provide high strength according to the Hall-Petch relationship, Cu and Ag grains having a nano-scale size are thermodynamically unstable. In the case of a Cu plating layer having a nano-scale grain size, several groups have reported a room temperature recrystallization phenomenon called self-annealing, and thus crystal growth, increase in conductivity, and decrease in strength are also reported. For the application of the prepared Cu-Ag plated thin plate, it is necessary to discuss the structural stability of the crystal structure, but there are few reports on this.

As described above, although CuAg alloy plating technology has been proposed, most crystal growth is not dense, so it is difficult to use it for purposes other than simple coating layer formation. That is, it was difficult to form a freestanding CuAg thin plate with a dense structure that can be used as a secondary battery current collector, a flexible electronic board, and the like.

As a background art of the present invention, a method of manufacturing a copper alloy foil is described in Japanese Patent Application Laid-Open No. 2015-078436.

It is an object of the present invention to provide a copper-silver alloy sheet having excellent mechanical strength and conductivity of 100 μm or less, which cannot be provided by conventional copper-silver rolled sheet material technology.

Another object of the present invention is to provide a freestanding copper-silver alloy sheet having a dense texture layer that cannot be provided by conventional copper-silver plating technology.

Another object of the present invention is to provide a method for efficiently manufacturing a freestanding copper-silver alloy sheet having excellent mechanical strength and conductivity.

Other objects and advantages of the present invention will become more apparent from the following detailed description of the invention, claims and drawings.

The present applicant introduced a specific additive during electroplating and manufactured a dense CuAg plated thin plate (m-CuAg) in a metastable form and a multi-layer of CuAg/Ag through a process of supplementing the consumed Ag concentration. As a result of observing the mechanical/electrical properties of the produced thin plate according to the process conditions and examining the properties of the crystal structure and thermal stability, 5 to 100 μm thick freestanding copper-silver alloy thin plate with excellent mechanical strength and conductivity could provide

According to one aspect, a free-standing copper-silver sheet having a thickness of 5 to 100 μm is provided as a free-standing copper-silver sheet.

According to an embodiment, the average size of the grains may be 50 nm or less.

According to an embodiment, the content of Ag may be 1 to 8 wt%.

According to an embodiment, the copper-silver sheet may have a gradient in the Ag content of 0 to 8 wt%.

According to an embodiment, the difference in Ag content between the upper end and the lower end of the copper-silver sheet may be 3 wt% or less.

According to an embodiment, a supersaturated nanocrystal structure of copper-silver may be formed.

According to an embodiment, Ag may be in the form of a solid solution in the copper crystal lattice.

According to an embodiment, Ag may be in the form of segregation at a grain boundary of Cu.

According to one embodiment, it may be formed by electroplating.

According to another aspect, in the method for producing a free-standing copper-silver sheet described herein, polyethyleneimine (Polyethylenimine, PEI) and antimony ion (antimony (III))) are added to a cyanide-based plating solution There is provided a method for manufacturing a free-standing copper-silver sheet, comprising the step of adding an additive to be added.

According to an embodiment, in the method of manufacturing a free-standing copper-silver sheet, Triton-X may be additionally added in the step of adding the additive.

According to an embodiment, in the method of manufacturing a free-standing copper-silver sheet, in the case of direct current, plating may be performed with a current density of 1 to 3 A/dm ² .

According to an embodiment, the method of manufacturing a free-standing copper-silver sheet may include an Ag ion replenishment step of replenishing Ag ions into the plating bath during electroplating.

According to an embodiment, the Ag ion supplementation step may supplement Ag ions such that the Ag content in the plating layer is 3 wt% or less, such that the Ag content difference between the upper end and the lower end of the copper-silver sheet is 3 wt% or less.

According to an embodiment, the method of manufacturing a free-standing copper-silver sheet may further include a heat treatment step of 100° C. or less.

According to one embodiment, it is possible to provide a copper-silver alloy thin plate having excellent mechanical strength and conductivity of 100 μm or less, which cannot be provided by conventional copper-silver rolled plate material technology. Therefore, it can be usefully applied to a secondary battery current collector, a flexible electronic board, and the like.

According to an embodiment, it is possible to manufacture a supersaturated CuAg thin plate of nanocrystal grains, which is difficult to implement through the conventional rolling method.

According to one embodiment, it is possible to provide a nano-grained copper-silver supersaturated alloy thin plate to solve the problem of poor thermal stability when the grain size of the existing pure copper foil becomes nano-scale.

According to one embodiment, it is possible to provide a freestanding copper-silver alloy thin plate having a dense texture layer such as a dense surface that cannot be provided by conventional copper-silver plating technology.

According to an embodiment, a freestanding copper-silver alloy thin plate having excellent mechanical strength and conductivity may be efficiently manufactured by introducing a specific additive during plating.

According to an embodiment, by introducing a step of supplementing the consumed Ag concentration, the distribution of the copper-silver alloy thin plate can be controlled, and the problem of the Ag concentration distribution in the thickness direction in the existing copper-silver plating layer being different can be solved. have.

1 is a diagram illustrating the microstructure of a Cu-Ag thin plate according to an embodiment of the present invention and comparing it with that of a conventional Cu-Ag thin plate.
Figure 2 is a view schematically showing a Cu-Ag alloy thin plate manufacturing apparatus and process according to an embodiment of the present invention.
3 is a photograph showing a jig for plating for a cathode according to an embodiment of the present invention.
4 is an image showing the surface shape of a Cu-Ag thin plate according to the presence and type of additives for plating when manufacturing a Cu-Ag thin plate by electroplating according to an embodiment of the present invention.
FIG. 5 is an image showing the Cu-Ag surface structure according to the addition of plating additives and process techniques when manufacturing a Cu-Ag thin plate by electroplating according to an embodiment of the present invention.
6 is a view showing the results of EDS analysis after the introduction of a continuous Ag supply process in manufacturing a Cu-Ag thin plate by electroplating according to an embodiment of the present invention.
7 is a graph showing the analysis results of tensile strength and conductivity after introduction of an additive for plating and a continuous Ag supply process in manufacturing a Cu-Ag thin plate by electroplating according to an embodiment of the present invention.
8 is a graph showing changes in tensile strength and conductivity of a copper-silver thin plate according to an average Ag content when a Cu-Ag thin plate is manufactured by electroplating according to an embodiment of the present invention.
9 is a graph showing the results of X-ray diffraction analysis of the Cu-Ag thin plate according to the difference in Ag concentration of the Cu-Ag thin plate by electroplating according to an embodiment of the present invention.
10 is a TEM image showing a result of analyzing the microstructure before and after heat treatment of a Cu-Ag thin plate manufactured through electroplating according to an embodiment of the present invention.
11 is a graph showing the analysis result of the grain size measured through the image J according to an embodiment of the present invention.
12A and 12B are graphs showing changes in tensile strength and conductivity before and after heat treatment of a Cu-Ag thin plate manufactured through electroplating according to an embodiment of the present invention.
13 is a view showing X-ray diffraction analysis results after heat treatment of a Cu-Ag thin plate manufactured through electroplating according to an embodiment of the present invention.
14 is a graph comparing the characteristics of the Cu-Ag thin plate according to an embodiment of the present invention with a low content (<10 wt% Ag) CuAg rolled structure.

Objects, specific advantages and novel features of the present disclosure will become more apparent from the following detailed description and embodiments taken in conjunction with the accompanying drawings.

Prior to this, the terms or words used in the present specification and claims should not be construed in a conventional and dictionary meaning, and the inventor may properly define the concept of a term to describe his invention in the best way. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present disclosure.

In this specification, when an element, such as a layer, portion, or substrate, is described as being "on," "connected to," or "coupled with" another element, it is directly "on", "on" the other element. It may be "connected" or "coupled", and one or more other elements may be interposed between both elements. In contrast, when an element is described as being "directly on," "directly connected to," or "directly coupled to," another element, the other element cannot be interposed between the two elements. .

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present disclosure. The singular expression includes the plural expression unless the context clearly dictates otherwise.

In this specification, terms such as 'comprising' or 'having' are intended to designate that the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification exist, and one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

In the present specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated. In addition, throughout the specification, "on" means to be located above or below the target part, and does not necessarily mean to be located above the direction of gravity.

Since the present disclosure can apply various transformations and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present disclosure to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present disclosure. In describing the present disclosure, if it is determined that a detailed description of a related known technology may obscure the gist of the present disclosure, the detailed description thereof will be omitted.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, and in the description with reference to the accompanying drawings, the same or corresponding components are given the same reference numerals, and the overlapping description thereof will be omitted. do.

According to one aspect, a free-standing copper-silver sheet having a thickness of 5 to 100 μm is provided as a free-standing copper-silver sheet.

As used herein, the free-standing thin plate refers to a thin plate that is not attached to the substrate. The thin plate of the present application maintains the form of a free-standing thin plate even at a thickness of 100 μm or less, which cannot be provided by conventional copper-silver rolled plate technology, thereby providing a copper-silver alloy thin plate with excellent mechanical strength and conductivity. .

Although not limited thereto, the thickness of the copper-silver thin plate in a free-standing state according to the present application is 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, 30 It may be less than or equal to μm, less than or equal to 20 μm, or less than or equal to 10 μm, and may be suitable for application to flexible electronic devices.

Although not limited thereto, the average size of the crystal grains of the free-standing copper-silver thin plate of the present application may be 50 nm or less. With the above configuration, Ag solubility may increase due to a grain boundary segregation effect. That is, Ag may exist in a solid solution form inside the copper crystal lattice. Accordingly, the formation of a supersaturated nanocrystal structure of Cu-Ag may be possible, and the occurrence of Ag precipitation may be suppressed. Due to the Ag segregation effect, the thermal stability of the nanostructure may be improved, and thus recrystallization may be suppressed at room temperature, unlike the existing Cu nanocrystal structure.

1 is a diagram illustrating the microstructure of a Cu-Ag thin plate according to an embodiment of the present invention and comparing it with that of a conventional Cu-Ag thin plate. As shown in FIG. 1 , Cu crystals are present in the core and Ag is segregated at grain boundaries, which increases the solid solubility of grain boundaries. Thereby, thermal stability is improved and mechanical properties are improved. Therefore, it may be possible to form a supersaturated nanocrystal structure of Cu-Ag. In addition, it is possible to provide a free-standing copper-silver alloy thin plate having a dense texture layer that cannot be provided by conventional copper-silver plating technology.

In contrast, the conventional Cu-Ag thin plate structures 1 and 2 of FIG. 1 have a large crystal size, and precipitates are present in the tissue or have a lamellar structure.

Although not limited thereto, the Ag content of the copper-silver thin plate of the present application of 1 to 8 wt% may be suitable in terms of improving the mechanical strength and conductivity of the copper-silver thin plate.

Although not limited thereto, the copper-silver thin plate of the present application may have a gradient within the Ag content of 0 to 8 wt%, and the difference in Ag content between the upper end and the lower end of the copper-silver thin plate may be 3 wt% or less. With the above configuration, the Ag content between the upper end and the lower end of the copper-silver thin plate has a uniform characteristic. The copper-silver thin plate manufactured through the conventional electroplating has a problem in that the Ag content deviation according to the thickness direction is large.

Although not limited thereto, the copper-silver thin plate of the present application may be formed by electroplating, and may be formed by electroplating including a step of continuously supplying Ag or a step of introducing an additive in the electroplating process. . With the above configuration, unlike the conventional copper-silver thin plate manufactured through electroplating, the copper-silver thin plate of the present application may have a dense structure and/or uniform Ag content. Therefore, it is possible to increase the tensile strength and conductivity of the copper-silver sheet. In addition, it is possible to reduce the process cost while realizing the tensile strength and conductivity comparable to that of the rolled copper-silver thin plate.

According to another aspect, in the method for manufacturing a free-standing copper-silver thin plate of the present application, polyethyleneimine (Polyethylenimine, PEI) and antimony ion (antimony (III)) are added to the cyanide-based plating solution. A method for making a free-standing copper-silver sheet comprising an addition step is provided. According to the above configuration, it is possible to increase the tensile strength by precisely controlling the structure of the copper-silver thin plate. That is, when PAT is used alone, the electrodeposited film layer is brittle and it may be difficult to obtain a thin plate. When PEI is used alone, there may not be much difference from the case of non-additive. However, when the two are combined, dendrite growth can be suppressed and surface roughness can be reduced.

Although not limited thereto, in the method for manufacturing a free-standing copper-silver thin plate of the present application, Triton-X, a surfactant, may be additionally added in the additive addition step. According to the above configuration, the microstructure becomes uniform and pores between particles are reduced, so that the copper-silver thin plate structure can be more precisely controlled.

Although not limited thereto, in the method of manufacturing a free-standing copper-silver sheet of the present application, in the case of direct current, plating may be performed at a current density of 1 to 3 A/dm ² . According to the above configuration, the tensile strength can be increased by controlling the copper-silver thin plate more precisely.

Although not limited thereto, the method for manufacturing a free-standing copper-silver sheet according to the present disclosure may include an Ag ion replenishment step of replenishing Ag ions into the plating bath during electroplating. In addition, it may be appropriate to reduce the initial Ag ion concentration and supplement the Ag ion in order to uniform the distribution of silver in the plating layer. According to the above configuration, the copper-silver thin plate can have a uniform configuration by minimizing the variation in the Ag content along the thickness direction, thereby increasing the tensile strength and the conductivity at the same time.

Although not limited thereto, the Ag ion replenishment step may replenish Ag ions such that the Ag content in the plating layer has a difference in Ag content between the upper end and the lower end of the copper-silver sheet of 3 wt% or less. According to the above configuration, the copper-silver thin plate can have a uniform configuration by minimizing the variation in the Ag content along the thickness direction, thereby increasing the tensile strength and the conductivity at the same time. Those skilled in the art to which the present application pertains can easily implement the above configuration by controlling known conditions during electroplating.

Although not limited thereto, the method of manufacturing a free-standing copper-silver sheet may further include a heat treatment step of 100° C. or less. According to the above configuration, stability can be further improved, and the tensile strength of the copper-silver thin plate can be increased.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are only for illustrating the present invention, and the scope of the present invention is not to be construed as being limited by these examples.

[Example]

1. Cu- Ag Plating sheet manufacturing

2 schematically shows a plating apparatus and a process for manufacturing a Cu-Ag alloy. First, SUS304 was cut into 13 cm × 13 cm, and then alkaline degreasing was performed for 3 minutes. After degreasing, washing with distilled water was performed, and pickling was performed for 3 minutes in 10% H ₂ SO ₄ (purity, Samjeon Pure Chemical Industry) to remove organic-inorganic substances on the surface.

Ni strike and chromate processes were performed to control the adhesion between the substrate and the plating layer. The Ni strike process was carried out in a solution of 1.85 M NiCl ₂ (purity, Samchun Pure Chemical Industry), 0.0018 M HCl (35.0~37.0 %, Samchun Pure Chemical Industry) for 30 seconds at 57.85 mA/cm2, and after washing, 0.5 M CrO ₃ The chromate layer was raised by immersing the substrate in the solution for 2 minutes.

For Cu and Cu-Ag plating solution, 0.78 M CuCN (Copper(i)cyanide, 98 %, TCL), 3.73×10 ^-4 M AgCN (Sliver cyanide, 99 %, SIGMA-ALDRICH), 2.08 M KCN (Potassium cyanide) , 98%, Samchun Pure Chemical Industry), 0.079 M Rochelle salt(Potassium sodium tartrate tetrahydrate, 99 %, Samchun Pure Chemical Industry), 0.27 M KOH(Potassium hydroxide, 95 %, Samchun Pure Chemical Industry), 0.36 MK ₂ CO ₃ (Potassium carbonate) , anhydrous, 99 %, AlfaAesar) was used.

As plating additives for improving properties, 5.45 × 10 ^-4 M saccharin (98 %, SIGMA-ALDRICH), 7.48 × 10 ^-5 M potassium antimonyl tartrate hydrate (PAT, 99 %, SIGMA) -ALDRICH), 0.0029 M polyethyleneimine (Polyethylenimine, PEI, branched), and 0.0049 M Triton-X 100 (SIGMA-ALDRICH) were used.

A home-made jig (FIG. 3) having an exposed area of 121 cm ² was used for electroplating. Plating was performed in a two-electrode system, the volume of the plating bath was 3L, and an IrO ₂ based metal-metal oxide (MMO) electrode was used for the anode. Stirring was performed to suppress the generation of hydrogen gas on the substrate during plating, and the temperature of the plating bath was kept constant at 60 °C during the process.

Plating was carried out in two waveforms, DC and pulse, using an AC rectifier (System DC Power Supply, KEYSIGHT). The current density when performed with direct current is 7.5 mA/cm ² , and the application time is 142 min. In the case of a pulse, the peak current density is 15 mA/cm ² , the on-time is 12 seconds, and the rest period is 12 seconds, the total application time was fixed at 142 min.

The thickness of the plating layer is measured using a 0-25 mm micrometer (Mitutoyo), an eddy current plating thickness gauge (FISCHER), a field emission secondary electron microscopy (FESEM, JSM-7900F, JEOL), and an electronic balance (METTLER TOLEDO). verified. For thickness measurement using an electronic scale, the following assumption formula was used.

In Equations 1 and 2 (Eq. 1 and 2), t is the thickness, m is the mass, w is the width of the specimen, l is the length of the specimen, d _m is the average density, d _Cu is the density of copper, d _Ag is the amount of silver Density, x _Cu is the mass fraction of copper, x _Ag is the mass fraction of silver.

In order to equalize the distribution of Ag in the plating layer, the experiment was conducted while reducing the initial Ag ion concentration and supplementing the Ag ion. Table 1 shows the Ag ion concentration and replenishment rate of the initial plating solution and the replenishment solution during the experiment, and the Ag concentration of the plating layer under the corresponding conditions. Ag ion replenishment proceeded through a liquid pump from immediately after application of current until the end of the experiment.

After plating, the Cu-Ag plating layer deposited on the substrate was separated from the substrate, washed with distilled water, and stored in a vacuum chamber until post-processing.

After the heat treatment, a heat treatment process was performed through a gas atmosphere heat treatment furnace (TS Technics) to observe the change in the characteristics of the plating layer. The heat treatment was carried out at a temperature of 100 to 300 ℃ in an N ₂ atmosphere for 1 hour, and the change and characteristics of the microstructure were observed, and thermal stability was secured.

2. Experimental example : Characterization of copper-silver alloy sheet

2.1 Cu- according to additive conditions Ag Microstructure analysis

The structure and characteristics of the prepared Cu-Ag thin plate were analyzed. Surface shape and thickness were analyzed by FE-SEM, and Energy-Dispersive X-ray Spectroscopy (EDS) was used to observe Ag content and distribution. In order to observe the microcrystalline structure, a cross section was cut with a focused ion beam (FIB), and then, a transmission electron microscope (HR-TEM, High-Resolution Transmission Electron Microscopy) analysis was performed.

An X-ray diffraction analyzer (X-ray diffraction, D/Max 2500, Softdisk) was used to observe trends on crystal orientation and grain size. Analysis was performed by scanning the range of 2theta from 20 to 80 at room temperature at a rate of 3°/min.

The results are shown in FIG. 4 . 4 is an image showing the surface shape of a 40 ㎛ Cu-Ag thin plate according to the presence and type of additives for plating when manufacturing a Cu-Ag thin plate by electroplating according to an embodiment of the present invention. When no additive was administered, when the Ag concentration was increased from 0 mM to 0.37 mM, it was confirmed that the electrodeposited shape was changed to a dendrite. When the Ag concentration was increased to 2.24 mM, dendritic growth caused the sample to break in the middle of plating.

Since it was not observed when the Ag concentration was 0 mM, it is thought that this dendritic growth was caused by the non-uniform electrodeposition of Ag. Since the concentration of Ag ions is very low and the standard reduction potential of Ag+ is higher than that of Cu+, it is thought that the growth of Ag proceeded in the mass transfer region when the current density was applied. In many cases, the growth in the mass transfer region causes dendritic formation because it does Since such dendritic growth is a factor of lowering mechanical strength and conductivity by increasing the porosity of the formed thin plate, a leveler-type additive was selected to suppress dendritic growth and administered to the plating solution.

The effect was tested by selecting as additives PEI and PAT, which are materials used in alkaline-based Cu or Ag plating. As a result, when PAT was used alone, the electrodeposited film layer was brittle, making it difficult to obtain a thin plate. When PEI was used alone, there was no significant difference from the case of non-additive. However, when the two were combined, it was confirmed that dendritic growth was suppressed and the surface roughness was reduced.

2.1.1 Microstructure Analysis by Triton-X Addition

In order to improve the surface roughness increase due to mass transfer and hydrogen gas generation during electroplating, the current density was lowered (1.5 ASD), the Pulse (PC) process technique was introduced, and Triton-X (surfactant) was added.

5 is an image showing the Cu-Ag surface structure according to the PEI-PAT-Triton-X addition and process technique when manufacturing a Cu-Ag thin plate by electroplating according to an embodiment of the present invention. With the addition of Triton-X, the microstructure became uniform and the pores between particles were reduced.

In FIG. 4, in the PEI-PAT microstructure, crystal grains exist in the form of irregular Ag dendrites. The causes of such dendrite formation include a factor in which Cu or Ag deposition proceeds in the mass transfer region, and a factor in which the hydrogen generation rate increases. There is this.

On the other hand, when the current density is lowered to 1.5 ASD in FIG. 5 , it has the effect of reducing the consumption of Cu and Ag ions on the surface and alleviating the generation of hydrogen gas, thereby improving the compact structure. When the PC process technique was also introduced, the consumption of ions on the surface was further reduced, and a more compact structure was formed.

As a result of EDS analysis of the electroplated Cu-Ag thin plate, it was possible to confirm the imbalance of Ag content on the front and back sides. Ag+ ions in the diffusion layer are reduced from ions close to the electrode during plating, and Ag+ concentration decreases over time. As the concentration of Ag+ in the diffusion layer, which can participate in the electrochemical reaction, gradually decreased, it was confirmed that the difference in Ag content between the initial Cu-Ag plating and the surface of the thin plate occurred.

2.1.2 Electroplated Cu- Ag Thin plate microstructure and cross-section EDS analysis

In order to solve the non-uniformity of Ag content along the thickness direction, plating was performed by lowering the initial Ag concentration (1.49mM → 0.37mM) inside the plating solution and adding Ag supplement solution. The results are shown in FIG. 6 . 6 is a view showing the results of EDS analysis after the introduction of a continuous Ag supply process in manufacturing a Cu-Ag thin plate by electroplating according to an embodiment of the present invention.

As shown in the EDS results of Figs. 6 (b) and (d), it was confirmed that the Ag content deviation along the Cu-Ag thin plate thickness direction was significantly reduced. In addition, when compared with (b) and (d) of Fig. 5, a film-like growth with a dense surface microstructure was observed. This may cause an effect of reducing internal porosity and surface roughness, thereby enhancing mechanical properties and electrical conductivity.

2.1.3 Analysis of Tensile Strength and Conductivity by Additives and Process Techniques

Tensile strength and conductivity analysis according to additives and process techniques was performed according to the following method, and the same was applied to other experimental examples.

First, UTM (3542-0125M-050HT2, EPSILON TECHNOLOGY CORP) was used for the analysis of tensile properties. A thin plated plate was cut in a rectangular shape of 12.7 mm X 12.7 mm through a self-made cutter, and the average value was obtained by measuring 4 or more times on the same specimen. The interval between the jigs was 3 cm, the strain rate was 2 mm/min, and it was performed at room temperature.

To analyze the electrical conductivity of the thin plate, the sheet resistance was measured using a 4-point probe (SR-4-6L). The analysis was performed at least 5 times on the same specimen at room temperature.

The results of Ag content, tensile strength, and electrical conductivity according to the presence or absence of additives (AgCN, PEI-PAT-Triton X) and differences in process techniques are shown in FIG. 7 .

That is, FIG. 7 is a graph showing the analysis results of tensile strength and conductivity after introduction of an additive for plating and a continuous Ag supply process in manufacturing a Cu-Ag thin plate by electroplating according to an embodiment of the present invention. The upper part (a) of FIG. 7 is by the DC process technology, and the lower part (b) is by the PC process technology.

As shown in (a) of FIG. 7 , in the case of pure Cu made of DC, the electrical conductivity was excellent at 85% IACS, but showed a low tensile strength of 273 MPa. When a Cu-Ag thin plate was formed with the additive combination of PEI-PAT, the tensile strength was improved from 273 MPa to 407 MPa, but the conductivity decreased from 85 % IACS to 38 % IACS. On the other hand, the Cu-Ag thin plate to which PEI-PAT-TritonX was added showed improved tensile strength of 637 MPa and electrical conductivity of 48% IACS compared to the case in which PEI-PAT was added. This is thought to be due to the effect of reducing the current density and adding Triton-X (surfactant) to alleviate the surface roughness caused by mass transfer and hydrogen gas generation. In addition, when the Ag supply process technique was introduced, it was confirmed that the tensile strength of 993 MPa and the conductivity of 66% IACS were increased due to the additional porosity reduction effect.

As shown in (b) of FIG. 7 , in the case of plating with PC, a tendency similar to that of DC was shown, but overall tensile strength and conductivity were low. This means that in the case of DC, a dense Cu-Ag thin plate was formed overall compared to PC.

2.1.4 Analysis of tensile strength and conductivity according to Ag content

According to the method described in 2.1.3 above, according to the Ag content Tensile strength and conductivity were analyzed and the results are shown in FIG. 8 .

That is, FIG. 8 is a graph showing changes in tensile strength and conductivity of a copper-silver thin plate according to an average Ag content when a Cu-Ag thin plate is manufactured by electroplating according to an embodiment of the present invention. As shown in FIG. 8 , as the Ag concentration increased in both DC and PC, the tensile strength increased and the electrical conductivity decreased. For example, the tensile strength/conductivity of 645 MPa/59 %IACS at 0.35 wt% for DC, 811 MPa/66%IACS for 2.16 wt% Ag, and 976 MPa/60%IACS for 3.62 wt% Ag seemed In the case of PC, the Ag content was somewhat higher than that of DC under the same conditions due to the displacement response of the off-time phase, and in the case of Ag 1.49 wt%, 649 MPa/67% IACS, and in the case of 3.18 wt% of Ag, 757 MPa/66 % IACS, Ag 4.86 wt % showed tensile strength/conductivity of 867 MPa/67 % IACS. Characteristically, it can be seen that DC provides higher tensile strength than PC at the same Ag content.

2.1.5 Electroplated Cu- Ag laminar Ag according to the content XRD analysis

After electroplating through DC and PC, microstructure analysis was performed. The results are shown in FIG. 9 .

That is, FIG. 9 is a graph showing the results of X-ray diffraction analysis of the Cu-Ag thin plate according to the difference in Ag concentration of the Cu-Ag thin plate by electroplating according to an embodiment of the present invention. As shown in FIG. 9 , in the case of pure Cu, a peak was observed at 43.4°50.5°74.3°, indicating Cu(111), Cu(200), and Cu(220) direction crystallinity, respectively. In the case of Cu-Ag thin plate, no additional Ag peak was observed, and the Cu-related peak position shifted in the negative direction. For example, when the Ag content in the film increased from 0 wt% to 3.62 wt%, the Cu(311) peak position shifted from 74.2° to 73.91°. At this time, the corresponding lattice parameter values are 3.610 Å (Cu(111)) and 3.622 Å (Cu(200)), respectively. This peak change indicates that Cu-Ag is formed as a metastable solid solution in the form of FCC. In addition, the growth of Cu (220) and the decrease of Cu (111) according to the increase in the Ag content were also observed. In the case of pure Cu, the intensity ratio between Cu(111), Cu(200), and Cu(220) was 5508: 3306: 2933, whereas when the Ag content was 3.62 wt%, the intensity ratio was 4525: 1983: 9425. This change means that the stress on the plating layer increases as the Ag content increases. When the plating layer grows, the crystal orientation is determined by surface energy and stress energy, and when the thickness is thin, the Cu(111) direction, which can minimize the surface energy, is In this case, the Cu(200) and Cu(220) directions in which the stress term is minimized are the main growth directions. It is believed that the addition of Ag increases the internal stress of the plating layer, which leads to Cu (220) direction growth.

In the case of Cu-Ag made using PC, peaks of Cu(111), Cu(200), and Cu(220) were observed like DC, and no additional Ag peaks were observed. As with DC, when the Ag content was changed from 0 wt% to 4.86 wt%, the lattice parameter changed from 3.607 Å to 3.614 Å, indicating metastable Cu-Ag solid solution formation. However, there was no further change in the lattice parameters when the Ag content was further increased from 1.49 wt% to 3.18 wt%. As in the case of DC, the value of FWHM, which is proportional to the grain size, increased as the Ag content increased. For example, in the case of the Cu(111) peak, it can be seen that the FWHM value increases from 0.24 to 0.47 when the Ag content is from 0 wt% to 4.86 wt%.

In the case of Cu-Ag formed using PC, unlike DC, the Cu(111) direction growth rather increased as the Ag content increased. This is thought to be because the influence of surface energy rather increased as the Ag content in the plating solution increased. Unlike DC, the Cu-Ag plating layer using PC is formed in a multilayer structure in which CuAg and Ag layers appear repeatedly, and the thickness and density of the Ag layer increase as the Ag concentration in the plating solution increases. Since the middle Ag layer has a high lattice parameter mismatch of 12% with Cu, the main electrodeposition, a high surface energy is expected between the two layers. Accordingly, it is considered that the growth proceeded in the direction of Cu (111) that can minimize the surface energy.

Table 2 shows the XRD analysis results of DC according to the Ag content, and Table 3 shows the XRD analysis results of PC according to the Ag content.

2.3 Analysis of physical properties according to Cu-Ag thin plate heat treatment

2.3.1 TEM analysis before and after Cu-Ag thin plate heat treatment

DC and PC microstructure analysis was performed after electroplating and heat treatment. The results are shown in FIGS. 10 and 11 .

That is, FIG. 10 is a TEM image showing the results of analyzing the microstructure before and after heat treatment of a Cu-Ag thin plate manufactured through electroplating according to an embodiment of the present invention, and FIG. 11 is a TEM image according to an embodiment of the present invention. It is a graph showing the analysis result of the measured grain size. 10 and 11, (a) to (d) are related to DC processing technology, (e) to (h) are related to PC processing technology. During the heat treatment process, it was carried out in a vacuum condition to avoid surface oxidation reaction.

Figure 10 (a) shows a representative image of CuAg (DC) by HR-TEM before heat treatment. The derived average grain size is 13.45 nm, and each crystal is composed of a solid solution containing both Cu and Ag. On the other hand, after the heat treatment of the thin plate, crystal growth inside the thin plate and the movement of dissolved Ag were observed. Specifically, the crystal size grew from 13.45 nm to 255.34 nm (after 300 °C heat treatment) before heat treatment, and at the same time, dissolved Ag segregated near GB (after 100 °C heat treatment) and precipitated (200 °C, 300 °C heat treatment after heat treatment) became

In (e) of FIG. 10, it can be seen that the thin plate made of PC is also composed of 12.79 nm nanocrystal grains similar to DC. However, it was composed of a multi-layered CuAg/Ag type by the substitution plating reaction in the manufacturing process, and the thickness of each layer was about 100 nm. Crystal growth, Ag segregation, and precipitation were observed after heat treatment, similar to thin plates made of DC.

2.3.2 Analysis of tensile strength and conductivity before and after Cu-Ag thin plate heat treatment

The Cu-Ag alloy thin plate fabricated here has a supersaturated Cu-Ag nanocrystal structure, and high strength is realized by the Hall-Petch relationship and the solid solution strengthening effect. However, according to the results of previous papers, the nanocrystal structure has weak thermal stability, and recrystallization and crystal growth can be observed after heat treatment. Such crystal growth may improve conductivity, but may cause a decrease in tensile strength. On the other hand, when the supersaturated Cu-Ag alloy is heat-treated, precipitation hardening by Ag is also expected, which can be a factor in improving the tensile strength on the contrary. Accordingly, in the present application, changes in strength, conductivity, and microstructure after heat treatment were observed.

12A and 12B are graphs showing changes in tensile strength and conductivity before and after heat treatment of a Cu-Ag thin plate manufactured through electroplating according to an embodiment of the present invention.

As shown in FIGS. 12A and 12B , when heat treatment was performed at 100° C. for 1 hour, a tendency to increase the tensile strength of both DC and PC thin plates was observed. In the case of thin plate made of DC, the tensile strength increased from 993 MPa to 1043 MPa, and in the case of thin plate made of PC, it increased from 900 MPa to 1008 MPa.

Heat treatment usually results in crystal growth and lowering of dislocation density, leading to softening of the metal, but some strength enhancement is reported. Huang et al, reported the strength strengthening of roll-bounding Al by dislocation source strengthening after heat treatment. Ebrahimi et al. fabricated a multilayer Cu/Ag through plating, and reported on strength enhancement after heat treatment at 100 °C. Zhang et al. made a Cu-Ag plate with mixed nanocrystal grains, nanotwins, and dislocation structures through dynamic plastic deformation (DPD), and reported that the strength was rather strengthened at an annealing temperature of up to 300 °C. did. They explained that the structural change of Ag precipitation in the crystal resulted in an additional increase in strength. Strengthening in the present application is also considered to be strength improvement by Ag precipitation.

When the heat treatment temperature was increased to 200 °C and 300 °C, a decrease in tensile strength and an increase in conductivity were observed in both DC and PC conditions. Specifically, in the case of DC at 300 °C, tensile strength of 614 MPa and conductivity of 84 % IACS, and in case of PC, tensile strength of 581 MPa and conductivity of 92 % IACS were obtained.

12 is an S-S curve obtained by performing a tensile test at room temperature.

2.3.3 XRD analysis after heat treatment

13 is a view showing X-ray diffraction analysis results after heat treatment of a Cu-Ag thin plate manufactured through electroplating according to an embodiment of the present invention.

In all cases after the heat treatment, crystal growth occurred and the value of FWHM was reduced, and in the case of DC, Cu(220) growth was dominant, and in the case of PC, Cu(111) direction growth was dominant. In the case of DC, an additional peak was still not observed, but in the case of PC, it was confirmed that Ag(111) peaks were developed at 200 °C and Ag(311) peaks at 300 °C.

In the case of DC, after the heat treatment, the development of (220) peaks along with the decrease of (111) and (200) peaks was observed. At a temperature of 100 °C or higher, the position of the Cu(220) peak decreased from 74.33° to 74.3° due to the precipitation of dissolved Ag, and the FWHM value of the peak decreased as the crystal size increased. At a heat treatment temperature of 300 °C, a peak for Ag 220 was also observed at 65.06 °, which means crystal growth of Ag precipitates.

In the case of PC, unlike DC, growth in the Cu(111) direction was observed even after heat treatment. Even after the heat treatment, there was no change in the lattice constant, and like DC, the value of FWHM decreased as the heat treatment temperature increased. Ag(111) peak was observed at 38.12° after 200 °C heat treatment, and Ag(200) peak at 44.21 ° after 300 °C heat treatment. and phase separation of Cu-Ag at the grain boundary.

Table 4 shows the XRD analysis of DC through annealing, and Table 5 shows the XRD analysis of PC through annealing.

14 is a graph comparing the characteristics of the Cu-Ag thin plate according to an embodiment of the present invention with a low content (<10 wt% Ag) CuAg rolled structure.

As shown in Figure 14, the Cu-Ag thin plate of the present application has a tensile strength of up to 104. MPa and a conductivity of about 64% IACS, prepared by conventional rolling It has tensile strength and conductivity comparable to that of CuAg, while realizing a thin thickness of less than 100 μm. possible, and the process cost can be reduced. Table 6 below is a table exemplarily showing the properties of the Cu-Ag thin plate of the present application.

In this application, a Cu-Ag thin plate was manufactured by changing the additive, current density, and Ag content through the electroplating process. In addition, the following conclusions were obtained through microstructure analysis and XRD analysis through heat treatment.

[One]. When the Ag concentration is increased from 0 mM to 0.37 mM during CuAg electroplating, it can be seen that the electrodeposited shape changes to a dendritic form. When increasing to 2.24 mM, it was confirmed that the sample was damaged in the middle of plating due to dendritic growth. To inhibit dendritic growth, leveler-type additives were selected and administered. When PAT, which is a material used on a basic basis, is used alone, it becomes brittle and it is difficult to obtain a homogeneous thin plate. When PEI was used alone, there was no significant difference from the case of non-additive. When these two were combined, dendrites were suppressed and surface roughness was reduced.

[2]. In order to improve the surface roughness increase due to hydrogen gas generation, the current density was lowered (1.5 ASD), the pulse process technique was introduced, and Triton-X was added. The microstructure became uniform and the pores between the particles were reduced. In addition, when the PC process technique was introduced, the amount of ions consumed on the surface was further reduced, and a more compact structure was formed. However, as a result of cross-sectional EDS analysis, it was confirmed that there was a difference in the Ag content between the initial plating and the surface of the thin plate.

[3]. In order to reduce the variation in the Ag content, the Ag supply process was introduced, resulting in high tensile strength (993 MPa) and electrical conductivity (66 %IACS). In addition, it was confirmed that the tensile strength increased with the increase of the Ag content. DC provides higher tensile strength than PC at the same Ag content (DC: 976 MPa. PC: 867 MPa).

[4]. A thin CuAg plate of nanocrystals was formed through electroplating, and changes in crystal properties were observed through heat treatment from 100°C to 300°C. The crystal size grew from ~15 nm before heat treatment to ~250 nm (after heat treatment at 300 °C), and at the same time, dissolved Ag segregated near GB (after heat treatment at 100 °C) and precipitated (after heat treatment at 200 °C, 300 °C) confirmed to be.

Although the present disclosure has been described in detail through specific examples, this is for the purpose of describing the present disclosure in detail, and the present disclosure is not limited thereto, and by those of ordinary skill in the art within the technical spirit of the present disclosure It is clear that the modification or improvement is possible. All simple modifications or changes of the present disclosure fall within the scope of the present disclosure, and the specific protection scope of the present disclosure will be made clear by the appended claims.

Claims (15)

As a copper-silver thin plate in a free-standing state,
A free-standing copper-silver sheet having a thickness of 5-100 μm.
According to claim 1,
A free-standing copper-silver sheet having an average grain size of 50 nm or less.
According to claim 1,
A free-standing copper-silver sheet having an Ag content of 1 to 8 wt%.
According to claim 1,
A free-standing copper-silver sheet, wherein the copper-silver sheet has an Ag content gradient within 0 to 8 wt %.
According to claim 1,
A free-standing copper-silver sheet, wherein the difference in Ag content between the upper end and the lower end of the copper-silver sheet is 3 wt% or less.
According to claim 1,
A free-standing copper-silver sheet formed with a supersaturated copper-silver nanocrystal structure.
According to claim 1,
A free-standing copper-silver sheet in which Ag is dissolved in a copper crystal lattice.
According to claim 1,
A free-standing copper-silver sheet in which Ag is segregated at the grain boundaries of Cu.
According to claim 1,
A free-standing copper-silver sheet formed by electroplating.
10. A method for producing a free-standing copper-silver sheet according to any one of claims 1 to 9, comprising:
Including an additive addition step in which polyethyleneimine (Polyethylenimine, PEI) and antimony ions (antimony (III)) are added to the cyanide-based plating solution,
A method for manufacturing a free-standing copper-silver sheet.
11. The method of claim 10,
A method for producing a free-standing copper-silver sheet, further adding Triton-X in the step of adding the additive.
11. The method of claim 10,
In the case of direct current, the plating is carried out with a current density of 0.5 to 3 A/dm ² , a free-standing copper-a method of manufacturing a silver thin plate.
11. The method of claim 10,
A method for manufacturing a free-standing copper-silver sheet, comprising the step of replenishing Ag ions into the plating bath during electroplating.
14. The method of claim 13,
The Ag ion replenishment step replenishes Ag ions so that the Ag content in the plating layer has a difference in Ag content between the upper end and the lower end of the copper-silver sheet of 3 wt% or less, a method for producing a free-standing copper-silver sheet .
11. The method of claim 10,
A method of manufacturing a free-standing copper-silver sheet, further comprising a heat treatment step of 100° C. or less.

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