Heat exchange member and manufacturing method thereof

Abstract

A heat exchange member with excellent heat dissipation and electrical performance, and a method for manufacturing the same, are disclosed. The method includes: (1) producing a dispersion by adding a carbon material selected from carbon nanotubes, carbon nanofibers, graphene, or a mixture thereof into a solvent and subjecting it to a first ultrasonic irradiation; (2) supporting metal nanoparticles on the carbon material by adding a metal compound to the dispersion and performing a second ultrasonic irradiation to reduce the metal compound and generate the nanoparticles; and (3) forming a porous layer on a surface of a substrate by electroplating, using the nanoparticle-supported carbon dispersion as an electrolytic solution, with the substrate as a cathode and the metal as an anode. The porous layer comprises the nanoparticle-supported carbon material as a void-forming component and a metal material of the same type as the nanoparticles.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based upon and claims the benefit of priority from Japan Patent Application No. 2024-160317, filed on September 17, 2024, the entire contents of which are incorporated herein by reference.FIELD OF THE INVENTION

[0002] The present disclosure relates to a heat exchange member used in heat sinks, heat spreaders, heat transfer sheets, heat exchangers, and the like, and a manufacturing method thereof.BACKGROUND

[0003] Heat generation in electronic equipment mounted with electronic devices (such as semiconductor devices) mounted is increasing due to higher integration and higher current, etc. Insufficient heat dissipation may cause malfunction and damage in junctions and devices. Therefore, the electronic equipment is provided with heat exchange members that facilitate heat dissipation to ensure their reliability and durability. For example, the heat exchange member includes heat sinks and heat spreaders provided on one or both sides of power modules (semiconductor devices) mounted with power devices (power semiconductors). However, there are limits to the heat dissipation and thermal conductivity of the conventional heat exchange members, and higher heat dissipation characteristic is demanded in particular for electronic equipment with high heat generation.

[0004] In view of this, techniques to improve the heat dissipation characteristic by roughening a surface of the heat exchange member such as aluminum and copper using etching or other physical method has been proposed. However, such techniques had a limit for the fineness of roughening, and it was hard to obtain excellent heat dissipation characteristic.

[0005] For example, as shown in Patent Document 1, a technique to achieve finer roughening by forming a layer of fine metal particles on a surface of a substrate such as aluminum and copper has been proposed.SUMMARY OF INVENTIONPROBLEMS TO BE SOLVED BY INVENTION

[0006] However, the invention of Patent Document 1 obtains a metal foil with a rough surface by applying an alloy layer formed of nickel, and phosphorus and / or sulfur on an aggregate of adherent nickel or nickel alloy fine particles with the particle size of 0.1 to 2µm. However, even when metal fine particles with the particle size of µm level were simply used, there was still a limit for roughening, and heat exchange component with finer and larger surface and excellent heat dissipation characteristic was not obtained.

[0007] In particular, it was extremely difficult to produce metal particles with the uniform particle size of µm level or less, e.g. nano level, and to form a uniform layer of said metal particles on a surface of the heat exchange member such as aluminum and copper.

[0008] The present disclosure is proposed to address the above-described conventional problems. The objective of the present disclosure is to provide a heat exchange member with excellent heat dissipation characteristic and electrical properties, and a manufacturing method thereof.MEANS TO SOLVE THE PROBLEM

[0009] To address the above-described problems, a heat exchange member of the present disclosure includes a substrate and a porous plated layer (hereinafter referred to as 'porous plated layer') that is a mixture of a void-forming material and a metal deposit that is formed on a surface of the substrate. The void-forming material is formed from a carbon material formed of carbon nanotube, carbon nanofiber, graphene, or mixture thereof, and a metal nanoparticle supported in the carbon material, and the metal deposit is formed of a material same as the metal nanoparticle.

[0010] The heat exchange member of the present disclosure preferably has the following configuration: (1) the porous plated layer formed from the void-forming material and the metal deposit is a plating layer formed on the surface of the substrate by electroplating; (2) the metal nanoparticle and the metal deposit are any of silver, gold, copper, platinum, and palladium; (3) the carbon material is a mixture of multiple materials selected from carbon nanotube, carbon nanofiber, and graphene; (4) the substrate is a heat dissipation fin or has a rib shape; and (5) the substrate is a metal foil.

[0011] A manufacturing method of the heat exchange member of the present disclosure includes the following processes. (1) A process of producing a dispersion of a carbon material by adding the carbon material formed from any of carbon nanotube, carbon nanofiber, graphene, or a mixture thereof to a solvent, and performing a first ultrasonic cavitation. (2) A process of supporting a metal nanoparticle in the carbon material by adding a metal compound to the dispersion, and performing a second ultrasonic cavitation to reduce the metal compound and produce the metal nanoparticle in the dispersion. (3) And a process of forming a porous layer on a surface of a substrate of the heat exchange member by performing electroplating using the dispersion of the carbon material supporting the metal nanoparticle as an electrolytic solution, the substrate of the heat exchange member as a cathode, and the metal as an anode. The porous layer is a mixture of a void-forming material formed from the carbon material supporting the metal nanoparticle, and a metal deposit formed of a material same as the metal nanoparticle.

[0012] The manufacturing method of the heat exchange member according to the present disclosure preferably employs the following configuration: (1) a solvent of the dispersion is one or a mixture of two or more selected from water, ethanol, isopropanol, and ethylene glycol; (2) a process of supporting the metal nanoparticles in the carbon material includes adding metal ions to the dispersion; (3) a surfactant is added to the dispersion; (4) a reducing agent is added to the dispersion; (5) the metal nanoparticle and the metal material are any of silver, gold, copper, platinum, and palladium; and (6) the carbon material is a mixture of multiple materials selected from carbon nanotube, carbon nanofiber, and graphene. EFFECT OF INVENTION

[0013] According to the present disclosure, since the porous plated layer that is a mixture of the void-forming material formed from the carbon material supporting the metal nanoparticle and the metal deposit same as the metal nanoparticle is formed on the substrate of the heat exchange member, the heat exchange member with excellent heat dissipation and electrical properties can be obtained. Also, according to the manufacturing method of the present disclosure, the porous layer can be formed on the surface of the heat sink by electroplating by utilizing ultrasonic cavitation to produce the void-forming material formed from the carbon material supporting the metal nanoparticle. As a result, excellent heat dissipation and electrical properties can be provided to the surface of the heat exchange member.BRIEF DESCRIPTION OF DRAWINGS

[0014] Fig. 1 is a flowchart of the embodiment of the manufacturing method of the heat exchange member of the present disclosure. Fig. 2 is a photograph showing the SEM image of the surface state of the heat exchange member in Example 1. Fig. 3 is a graph showing the comparison of the heat transfer and heat dissipation properties between Example 1 and the conventional technology. Fig. 4 is a thermography showing the heat dissipation property in Example 1. Fig. 5 is a photograph showing the SEM image of the porous plating layer of Example 1 formed on the aluminum flat plate by the scanning electron microscope with analytical capabilities. Fig. 6 is a graph showing the result of the quantitative analysis of the porous plating layer of Example 1. Fig. 7 is a map image corresponding to the quantitative analysis of the porous plating layer of Example 1. Fig. 8 is a photograph showing the SEM image of the surface state of the heat exchange member in Example 2. Fig. 9 is a thermography showing the heat dissipation property in Example 2. EMBODIMENTS

[0015] Hereinafter, embodiments of the present disclosure will be described in detail. As illustrated in Fig. 1, a manufacturing method of a heat exchange member of the present embodiment is as follows:1. Process of Producing the Dispersion

[0016] A carbon material is added to an aqueous solution containing an appropriate surfactant (S1, S2), and a first ultrasonic cavitation processing is performed (S3) to obtain a stable dispersion with high concentration.2. Process of Supporting the Metal Nanoparticle in the Carbon Material

[0017] A metal compound or salt is added to the dispersion (S4), and a second ultrasonic cavitation processing is performed (S5). The metal compound or salt is reduced by the second ultrasonic cavitation to produce a metal ion. The metal ion is reduced by a reducing agent in the dispersion to form a metal nanoparticle. The produced metal nanoparticle is adsorbed and is uniformly supported on a surface of the carbon material (S6).3. Electroplating Process

[0018] A metal is arranged as an anode and a heat sink substrate formed of a material such as aluminum is arranged as a cathode (S7), and the dispersion is used as an electrolytic solution. A metal ionized water is added, if necessary (S8), the dispersion is stirred by an ultrasonic wave and a stirrer, and an electroplating process is performed with the same method as that of the normal metal plating (S9). A plating film with a porous layer formed from the metal and the carbon material supporting the metal nanoparticle is formed.

[0019] The chemical reaction formula related to the supported metal nanoparticle is as follows, in which silver oxide is used as a metal and a mixture of carbon nanotube and graphene is used as a carbon material as an example. (1) Reduction Reaction of Silver Oxide         Ag 2 O + reducing agent → ultrasonic cavitation → 2Ag + oxide product (2) Production of Silver Nanoparticle         Ag +< + e -< → Ag (nanoparticle)         CNT / graphene + Ag (nanoparticle) → CNT / graphene-Ag (3) Supporting Silver Nanoparticle in Carbon Material         CNT / graphene + Ag20 + reducing agent → ultrasonic cavitation → CNT / graphene-Ag + oxide product

[0020] Hereinafter, materials, processes, and others in each process of the present disclosure will be described in detail.[Carbon Material]

[0021] It is preferable to mix carbon nanotube powder (preferably multi-walled carbon nanotube (MWNT) with the average diameter of 1 to 100 nm and the average length of 1 to 10 µm) as a main material and a carbon material milled into nano-order size (the average particle size of 20 nm to 10 µm) at the weight ratio of 1 to 30 % (more preferably 10 to 20 %) to obtain powder of a nanocarbon material.

[0022] The carbon material mixed to the carbon nanotube powder is preferably one or more types among graphene, carbon black, and activated carbon. Furthermore, instead of or in addition to them, carbon nanofiber, fullerene, carbon nanohorn, carbon microcoil, diamond-like carbon, and carbon nanocrystal may be used.

[0023] The nanocarbon material powder is not limited to carbon nanotube and the carbon material mixed thereto, and carbon nanofiber, fullerene, carbon nanohorn, carbon microcoil, diamond-like carbon, and carbon nanocrystal may be used in single. Furthermore, multiple types of said carbon materials may be selected and mixed. When multiple carbon materials with different average particle sizes are mixed, the aggregation tendency of the carbon material in the dispersion becomes lower, so that the carbon material can be dispersed in the dispersion uniformly with high concentration.

[0024] It is considered that this excellent dispersibility is obtained because the carbon material with the nano-order size other than carbon nanotube contained in the nanocarbon material powder enters and is fixed between carbon nanotube, preventing the aggregation of carbon nanotube, and because the dispersibility of the anionic surfactant or non-ionic surfactant added to the solvent is improved by the ultrasonic cavitation .[Metal and Metal Compound]

[0025] The metal used in the present disclosure may be various metals if said metal is capable of producing a metal nanoparticle and can be electroplated. In particular, silver, gold, platinum, and palladium are preferable, and silver, gold, and copper are particularly preferable in view of thermal conductivity, etc. Furthermore, metal compounds or salt must be added to the dispersion to produce the metal nanoparticle by the ultrasonic cavitation, and said metal compound and salt are not particularly limited. In below, representative metal, and compound or salt thereof are exemplified.1. Silver (Ag)

[0026] Silver oxide (Ag 2 O) may be used for synthesizing a silver nanoparticle. Silver compounds and salt other than silver oxide (Ag 2 O) such as silver nitrate (AgNO 3 ), silver chloride (AgCl), silver acetate (AgC 2 H 3 O 2 ), and silver fluoride (AgF) may be used. If these compounds are used, the composition and preparation method of the dispersion may be different. In below, an abstract of the compound and what should be considered are described.(1) Silver Oxide (Ag 2 O)

[0027] Solvent: a polar solvent such as water and ethanol is preferable. Since silver oxide hardly dissolves in water, it is used in the form of a suspension.

[0028] Reducing Agent: it is preferable to use a reducing agent to produce the silver nanoparticle from silver oxide. Hydrazine, sodium borohydride (NaBH 4 ), ascorbic acid, and the like may be used. NaBH 4 is a strong reducing agent and tends to reduce the particle size. The particle growth can be controlled by using a mild reducing agent.

[0029] Reaction Temperature: the reaction temperature depends on the selected reducing agent and solvent and is preferably room temperature to about 60 °C. The reaction under high temperature facilitates the particle growth.

[0030] Reaction Monitoring: during the reaction, it is recommended to monitor the progress of the reaction such as by UV-Vis spectroscopy. Since the silver nanoparticle has a unique absorption peak, the production of the silver nanoparticle can be observed in real time.

[0031] Stabilization of Nanoparticles: the produced silver nanoparticle tends to aggregate. Therefore, it is preferable to stabilize the silver nanoparticle using a surfactant and a polymer (such as PVP, PEG, etc.).(2) Silver Nitrate (AgNO 3 )

[0032] Usage: Since silver nitrate has high water-solubility, the silver nanoparticle is synthesized by reducing a silver ion using the reducing agent.

[0033] Composition of Dispersion: the reducing agent (for example, glucose, hydrazine, sodium citric acid) is added to a silver nitrate solution to produce the silver nanoparticle.(3) Silver Chloride (AgCl)

[0034] Usage: Since silver chloride has low solubility, the silver nanoparticle is synthesized by light irradiation or chemical reduction.

[0035] Composition of Dispersion: A suspension of silver chloride in the solvent such as water and ethanol is used, and the reduction by light irradiation is preferable.(4) Silver Acetate (AgC 2 H 3 O 2 )

[0036] Usage: since silver acetate has solubility of middle level, silver acetate is used in an aqueous solution with the reducing agent.

[0037] Composition of Dispersion: the silver nanoparticle is synthesized by dissolving silver acetate in water or ethanol and adding the reducing agent thereto. The reducing agent is preferably ascorbic acid or sodium borate.(5) Silver Fluoride

[0038] Usage: Since silver fluoride has high water solubility and strong oxidation effect, silver fluoride must be used with care.

[0039] Composition of Dispersion: the reducing agent is added to an aqueous solution in which silver fluoride is dissolved. The reducing agent must be carefully selected because silver fluoride has strong oxidation effect. For example, the reducing agent with mild reduction effect such as ascorbic acid (vitamin C) and glucose is preferable because the size and shape of the metal nanoparticle can be easily controlled and the reaction proceeds relatively gradually even for the oxidation agent such as silver fluoride. Meanwhile, in the case of the strong reducing agent such as sodium borohydride (NaBH 4 ), the size of the nanoparticle can be kept small and uniform by carefully adding very small amount of NaBH 4 .2. Gold (Au)Tetrachloroauric acid (HAuCl 4 )

[0040] Usage: tetrachloroauric acid is preferable for the synthesis of gold nanoparticles. The reducing agent is preferably sodium borohydride and sodium citrate.3. Copper (Cu)Copper sulfate (CuSO 4 )

[0041] Usage: copper nanoparticle is produced using the reducing agent and copper sulfate together. The reducing agent is preferably hydrazine and ascorbic acid.4. Palladium (Pd)Palladium chloride (PdCl 2 )

[0042] Usage: palladium nanoparticle is produced from palladium chloride using the reducing agent. It is preferable to cause the reaction under the acidic condition.5. Platinum (Pt)Hexachloroplatinic acid (H 2 PtCl 6 )

[0043] Usage: platinum nanoparticle is synthesized using the reducing agent. The reducing agent is preferably sodium borohydride.[Dispersion]

[0044] The solvent of the dispersion may be water, and may be ethanol, isopropanol, ethylene glycol, or a mixture of these and water. For example, the solvent in which an anionic surfactant or a non-ionic surfactant of 0.1 to 10 % by weight is added to an aqueous solution containing a lower alcohol of 10 to 100 % by weight is preferably used. The lower alcohol is preferably one or more types among methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, ethylene glycol, diethylene glycol, propylene glycol, or glycerin.[Metal Nanoparticle]

[0045] Although the silver nanoparticle mainly starting from silver oxide is used as the metal nanoparticle in Example, other metals as described below may be used. 1. Gold (Au): the same method as the silver nanoparticle is used for synthesizing a gold nanoparticle. For example, the gold nanoparticle is obtained by using gold salt (such as H[AuCl 4 ]) and combining said salt with the reducing agent and the ultrasonic cavitation . 2. Palladium (Pd): a palladium nanoparticle can be synthesized by using palladium salt, and combining the ultrasonic cavitation and reduction. 3. Platinum (Pt): a platinum nanoparticle can also be synthesized by using a platinum compound, and combining the reducing agent and the ultrasonic cavitation. 4. Copper (Cu): a copper nanoparticle can be synthesized by the same method.

[0046] As used herein, the term "void-forming" refers to the capability of a carbon / metal-nanoparticle composite to generate a porous structure including interstices or cavities that increase the effective surface area of the plated layer. The term "porosity" refers to the volumetric fraction (%) of voids present in the porous plated layer, as determined by image analysis of SEM cross-sections or by BET specific surface area measurements. The term "nanoparticle size (D50)" refers to the median particle diameter of the supported metal nanoparticles, measured by electron microscopy or dynamic light scattering, such that 50% of the cumulative particle volume distribution is below this value.[Surfactant]

[0047] The surfactant may be used as appropriate according to the produced metal nanoparticle, and the anionic surfactant or the non-ionic surfactant is preferably one or more among sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, triethanolamine lauryl sulfate, or dodecyl itaconate.

[0048] In particular, it is preferable to use one or more surfactants forming a micelle structure. The surfactant forming a micelle structure has a hydrophilic portion and a hydrophobic portion and forms a micelle (the hydrophilic portion on the outer side and the hydrophobic portion in the inner side) under specific conditions due to a molecular structure thereof. For example, the surfactant forming a micelle structure is as follows: Sodium dodecyl sulfate (SDS); Sodium alkylbenzene sulfonate (SDBS); Cetyl trimethyl ammonium bromide (CTAB); Benzalkonium chloride (BAC); Lecithin; N-alkyl betaine; Polyethylene glycol alkyl ester (polysorbate); Polyethylene glycol alkyl ether Polyoxyethylene (100) stearyl ether. [Reducing agent]

[0049] The reduction agent may be added to the dispersion. In addition to the ultrasonic cavitation, the production of the metal nanoparticle is facilitated by reducing the metal ion using the reducing agent. Various reducing agents may be used such as hydrogen, alcohols, polyphenols, and citric acid. The representative reducing agent and suitable metal nanoparticle are as follows. 1. Sodium Citrate Usage: Silver (Ag), Gold (Au), Characteristic: sodium citrate is suitable for synthesizing the gold nanoparticle. The gold ion (Au 3+< ) is reduced to produce the gold nanoparticle with relatively stable size. Furthermore, citric acid also acts as a stabilizing agent and is adsorbed on the surface of the nanoparticle, preventing the aggregation of the nanoparticles. 2. Ascorbic Acid Usage: Silver (Ag), Gold (Au), Copper (Cu) Characteristic: ascorbic acid can gently reduce the gold ion and silver ion, so that the size and shape of the nanoparticle can be easily controlled. 3. Hydrazine Usage: Silver (Ag), Copper (Cu), Palladium (Pd), Platinum (Pt) Characteristic: hydrazine is a very strong reducing agent. The silver ion and copper ion are rapidly reduced to form the metal nanoparticle. The nanoparticle tends to have small size and can be synthesized in a short time by utilizing said high reduction capability. 4. Sodium Borohydride (NaBH 4 ) Usage: Silver (Ag), Gold (Au), Palladium (Pd) Characteristic: NaBH 4 is a strong reducing agent. The metal nanoparticle with very small size can be rapidly synthesized. 5. Polyol (for example, ethylene glycol) Usage: Silver (Ag), Gold (Au), Platinum (Pt) Characteristic: polyols (polyhydric alcohols), such as ethylene glycol and glycerin, are used as the reducing agent. Polyols can also control the size and shape of the nanoparticle. Since the reduction advances more under the high temperature, the production of the nanoparticle can be controlled by controlling the temperature.

[0050] The reaction rate depends on the strength of the reducing agent, which affects the size and shape of the nanoparticle. The strong reducing agent progresses the reduction rapidly and tends to produce small nanoparticle. Furthermore, since the reducing agent is adsorbed on the surface of the nanoparticle improving the stability of the produced nanoparticle, it is effective to select the reducing agent that can take part in both reduction and stabilization, such as sodium citrate and ascorbic acid. Also, the reducing agent may be selected depending on the type of the metal ion to be reduced. For example, gold and silver can be reduced easily even by using a relatively gentle reducing agent, and a strong reducing agent is required for the metal such as palladium and platinum.[Ultrasonic Cavitation]

[0051] The ultrasonic cavitation is one of the effective methods for synthesizing the metal nanoparticle. In this method, ultrasonic waves are irradiated to liquid to cause cavitation (formation and collapse of small air bubbles), and the resulting localized high-temperature and high-pressure environment help the production of the metal nanoparticle from the metal salt and metal compound. The dispersion of the nanocarbon material of the present disclosure obtained by the ultrasonic cavitation has excellent dispersibility and can maintain the dispersibility almost the same as that of immediately after the dispersion process even after several days, while a dispersion of nanocarbon material obtained by the conventional technology re-aggregates after several hours to several days.

[0052] In the ultrasonic cavitation, a solution is placed in an ultrasonic homogenizer or an ultrasonic bath, and ultrasonic waves are irradiated with appropriate frequency (generally 20 kHz to 40 kHz). This irradiation of the ultrasonic wave causes cavitation in the solution and produces air bubbles. An extremely localized high-temperature and high-pressure environment created when these air bubbles collapse reduces the metal compound or metal salt, so that the metal nanoparticle is produced.

[0053] The ultrasonic homogenizer and the ultrasonic bath may be used in the ultrasonic cavitation. The ultrasonic homogenizer is suitable for liquid with high viscosity and samples of small volumes. In particular, the ultrasonic homogenizer is effective for reaction and processes that require high energy. The ultrasonic bath is suitable for processing liquid of large volume and multiple samples at once. When the heat sink to be manufactured is large, it is preferable to use the ultrasonic bath.

[0054] The output power and frequency of the ultrasonic homogenizer and the ultrasonic bath used in the production of the metal nanoparticle largely depend on the size and shape of the metal nanoparticle and the type of the used metal. For example, the output power and frequency are selected in accordance with the size and shape of the heat sink to be manufactured, as described below.1. Output Power(1) Low Output Power (50 W to 100 W)

[0055] Low output power is suitable for the production of the nanoparticle with samples of small size or under relatively gentle conditions. For example, the low output power is used when it is desired to produce the nanoparticle with fine size and when the chemical reaction is sensitive to high temperature and high pressure. In general, for the low power output, the nanoparticle tends to have slightly large size and uniform shapes.(2) Middle Output Power (100 W to 500 W)

[0056] Middle output power is a standard power range for many nanoparticle syntheses and is suitable for the production of the metal nanoparticle and for processing multiple samples at the same time. For the middle output power, the nanoparticle has uniform and controllable size. For example, the middle output power is suitable for the synthesis of gold and silver.(3) High Output Power (500 W or more)

[0057] The high output power is used for large-scale processes (mass production of products) and for solutions with high viscosity. The cavitation with high power causes strong reaction, which is effective for producing very fine nanoparticle and particle with a special shape (for example, nanorods and nanowire).2. Frequency (kHz)(1) Low Frequency (20 kHz to 30 kHz)

[0058] The low frequency is suitable for applications that require strong cavitation. Since the cavitation with low frequency causes stronger impact force, the obtained metal nanoparticle tends to have small sizes.(2) Middle Frequency (30 kHz to 60 kHz)

[0059] The middle frequency is most suitable for the production of various metal nanoparticles in the present disclosure. The middle frequency provides balanced cavitation and can control the size and shape of the nanoparticle to be relatively uniform.(3) High Frequency (60 kHz or more)

[0060] The high frequency is suitable for applications that require more delicate processing and is used when gentle cavitation and precise control of the shape of the nanoparticles are required. The high frequency tends to provide the nanoparticle with slightly large size and uniform shape.3. Detailed Usage

[0061] (1) Silver Nanoparticle (Ag) Output Power: 100 W to 300 W Frequency: 20 kHz to 30 kHz Remarks: Since the silver nanoparticle can be produced relatively easily, excellent results can be obtained with standard output power and low frequency. (2) Gold Nanoparticle (Au) Output Power: 100 W to 400 W Frequency: 20 kHz to 40 kHz Remarks: middle output power and middle frequency are recommended when it is important to control the size and shape of gold nanoparticle. (3) Platinum Nanoparticle (Pt) Output Power: 200 W to 500 W Frequency: 20 kHz to 30 kHz Remarks: Since platinum is solid metal, relatively high output power and low frequency are required. [Metal Ion Solution]

[0062] The metal ion solution added in the electroplating process (S8) as necessary may be any from below depending on the type of metal to which electroplating is performed. Basically, it is preferable to use an aqueous solution of the metal compound or salt added in the addition process (S4) of the metal compound or salt. Examples are as follows. Silver ion: silver nitrate Gold ion: tetrachloroauric acid (HAuCl 4 ) Copper ion: Copper sulfate (CuSO 4 ) Platinum ion: Hexachloroplatinic acid (H 2 PtCl 6 ) Palladium ion: Palladium chloride (PdCl 2 ) [Other Embodiments]

[0063] The present disclosure is not limited to the above embodiment and encompasses the other embodiments as described below. (1) Although in the above embodiment, the mixture layer of the carbon material supporting the metal nanoparticle and the metal is formed on the surface of the aluminum heat sink with multiple heat dissipation fins that is the substrate, the mixture layer may be formed on the surface of the heat sink with various shapes, in addition to said heat sink. For example, the mixture layer may be directly formed on metal portions such as casings of electronic components such as CPUs. (2) The mixture layer of the carbon material supporting the metal nanoparticle and the metal may be formed on the substrate with a sheet-shape or a film-shape. Such a heat exchange member may be adhered on the surface of the electronic component to facilitate the heat dissipation, and also may be arranged between electronic components or printing boards to improve the heat dissipation and heat transfer from said components. The manufacturing method of this type of the metal foil includes attaching the aluminum foil on a cathode instead of the heat sink substrate in the fin-shape during plating. In this case, the sheet-shaped metal foil connected to the cathode is unwound and is wound while continuously immersed in a plating tank to form the mixture layer of the present disclosure on the surface of the long metal foil. Note that a drying device may be provided at the rear of the plating tank if necessary. (3) preprocessing such as etching, formation of a seed layer, and chemical plating may be performed on the surface of the plastic, and then the mixture layer of the present disclosure may be formed on the surface by electroplating. (4) Although in the above embodiment, the heat exchange member of the present disclosure is implemented in an air-cooled type heat sink, the heat exchange member of the present disclosure is not limited thereto and may be implemented in a heat exchange apparatus using liquid, such as water-cooled type. hat is, according to the present disclosure, since the surface area of the heat exchange member is large, the contact area between the heat exchange member and the cooling liquid increases, improving the thermal conductivity therebetween and obtaining excellent heat exchange efficiency.

[0064] Recent demand for more cooling performance such as in large scale GPU systems like data centers has led to the use of water-cooled systems, especially the latest immersion cooling and boiling cooling. Heat exchangers in such latest water-cooled systems are required to have efficient heat transfer between liquid coolants and heat-generating components and to remain robust even in extreme heat cycles and under high flow rates, and thus required to have new specifications with higher levels of heat exchange efficiency, durability, and reliability. The present disclosure simultaneously satisfies said new specifications and is the important components in the next generation high performance cooling systems.

[0065] In particular, the present disclosure is advantageous in that the coating will not be impaired even in extreme heat cycles and under high flow rates that require advanced liquid cooling systems due to the strong bonding by the electroplating process. Accordingly, the properties of the heat exchange member of the present disclosure are well matched with the requirement from the recent trend of the cooling industry and are ideal for the use in GPUs, data centers, and other advanced cooling solutions for large scale systems.[First Example]

[0066] First Example of the present disclosure using silver as a metal is described in below. 1. Material and Apparatus (1) aluminum substrate (pure aluminum) (2) silver anode (silver with the purity of 99.9999%) (3) electrolytic solution: a mixture of carbon nanotubes and graphene, wherein the amount of graphene is 50% by weight relative to the carbon nanotubes, silver oxide (Ag 2 O), industrial alcohol (for example, 2-propanol), surfactant, silver ion solution (6 ppm to 30 ppm) (4) ultrasonic cavitation apparatus (5) stirrer (6) power source for electroplating 2. Schemes (1) Preparation of Dispersion Carbon nanotube and graphene were dispersed in the industrial alcohol containing a surfactant. An ultrasonic cavitation was performed to the solution to produce a uniform dispersion. Silver oxide (Ag 2 O) was added to the dispersion, and the ultrasonic cavitation was performed again to the dispersion to reduce silver oxide (Ag 2 O) into silver nanoparticle. The obtained solution contained CNT / graphene uniformly supporting the silver nanoparticle. (2) Preparation of Electrolytic Solution The dispersion was mixed with the silver ion solution (6 ppm to 30 ppm). The mixture was thoroughly mixed and dispersed using the ultrasonic cavitation apparatus and the stirrer. 3. Setting Up Electroplating Apparatus The aluminum substrate was placed as a cathode in an electroplating bath. A silver anode was arranged opposite the aluminum substrate. The prepared electrolytic solution was poured into the electroplating bath. 4. Electroplating Process The aluminum cathode and the silver anode were connected to the power source. Appropriate current and voltage were applied to start the electroplating process. The process was monitored so that the composite material was uniformly deposited on the aluminum substrate. 5. Post-Processing After the electroplating process was completed, the aluminum substrate was taken out from the bath. The plated aluminum substrate was washed by distilled water to remove the residual electrolytic solution. The aluminum substrate was dried at room temperature or dried using a low-temperature drying process.

[0067] The photograph of Fig. 2 shows an observation of the electrodeposited heat exchange member (CNT / Graphene-Ag composite) after the preprocessing (preprocessing by the surfactant (alkyltrimethylammonium), and the subsequent washing by pure water) of the aluminum surface under the electrodeposition condition (electrical condition with the interelectrode voltage of 10 to 30 V and current of 1 to 3 A) of the example.[Action and Effect of Example 1]

[0068] The effect of Example 1 with the above configuration is as follows. (1) In Example 1, when silver oxide was added to the dispersion, silver oxide was transformed into a nanoscale particle in the dispersion. The ultrasonic cavitation gave energy to the particle to make the particles in the dispersion uniform and also prevented the aggregation of the particles, so that silver oxide was effectively attached to the surface of the heat exchange member. (2) During the ultrasonic cavitation , silver oxide was reduced to form the silver nanoparticle. In this process, the silver nanoparticle bonded to the surface of the heat exchange member, so that stable composite material was formed. (3) By using electroplating on the heat exchange member supporting the silver nanoparticle, said heat exchange member moved in response to an electric field and particularly tended to gather around the cathode. This is because the electric field acts effectively due to the excellent conductivity of the silver nanoparticles and their entanglement with the large surface area of the carbon material. (4) Since the heat exchange member supporting the silver nanoparticle gathered around the cathode, a new plating layer with a structure different from the conventional plating layer was formed. This plating layer with the new structure had increased electric and mechanical properties such as improved conductivity of the plating layer and increased strength and durability of the material due to the presence of the silver nanoparticle. (5) In Example 1, not only the heat exchange member supporting the silver nanoparticle, but silver was also used in the anode, so that silver in the anode dissolved in the electrolytic solution as the silver ion, and the silver ion was deposited on the surface of the substrate of the heat sink provided to the cathode with the heat exchange member supporting the silver nanoparticle alone. (6) CNT supporting the silver nanoparticle had very large specific surface area (surface area per unit mass). When this was formed on the surface area of the metal, a network structure of CNT was formed and complex nanoscale unevenness is increased, resulting in the significant increase in the total surface area of the metal. (7) Since the silver nanoparticles themselves are very small and many of them attach on the surface of CNT, further increase in the surface area can be expected. In particular, the porous structure due to CNT could be formed in the range from nanoscale to macroscale (several hundred microns or more), and therefore the effect of increasing the surface area was significant. (8) When CNT was formed on the surface of the metal, the surface area increased. In general, heat dissipation was improved as the surface area increased. In particular, since CNT supporting the silver nanoparticles formed a nanoscale complex surface structure, heat was efficiently dissipated from the metal to the air. (9) Since silver was a metal with very high thermal conductivity, CNT supporting the silver nanoparticle improved the thermal conductivity of the entire surface of the metal. Furthermore, since CNT itself also had high thermal conductivity, the efficiency of the heat dissipation from the metal was improved. (10) Since not only CNT supporting the silver nanoparticles, but also silver itself is present on the substrate in the mixture layer, the thermal conductivity is improved.

[0069] Fig. 2 shows photograph of the surface structure of the heat exchange member in which the mixture layer of Example 1 was formed on the aluminum flat plate observed by SEM with the magnification of 2000x to 20000x. It can be seen from the photograph that the CNT supporting the silver nanoparticle was appearing on the surface of the heat exchange member, forming a three-dimensional porous structure. In particular, it can be seen from the 20000x image that a nanocomposite of CNT and graphene with a very unique shape was produced.

[0070] Fig. 3 shows an example using the heat sink of Example 1 formed as described above and the observation of the heat dissipation thereof. The aluminum heat sink used in this example was L61 mm * W30 mm * H30 mm. Also, the surface of the aluminum heat sink was anodized and was formed by an aluminum oxide (Al2O3) layer. Since this layer was very hard, corrosion resistant, and highly electrically insulating, and impaired adhesion during electroplating, said layer had to be removed by preprocessing. Therefore, the aluminum heat sink was immersed in the solvent of hydrochloric acid (about 8 to 10%) and a surfactant (alkyltrimethylammonium salt) with processing time that did not cause excessive etching.

[0071] The reaction formula indicating the reaction of aluminum oxide (Al 2 O 3 ) and hydrochloric acid to form a soluble aluminum salt (aluminum chloride: AlCl 3 ) is represented as the following formula.         Reaction Formula:     Al 2 O 3 + 6HCl = 2AlCl 3 + 3H 2 O

[0072] After dissolving and removing the alumite film, the aluminum heat sink was washed by pure water, and then electrodeposition process was performed. Meanwhile, the surfactant was used to facilitate dissolution of the oxide layer on the aluminum surface, improve the effect of hydrochloric acid, remove oil and contaminated material on the surface, and improve adhesion of the plating layer during electroplating to obtain the high-quality plating layer.

[0073] Fig. 3 shows the measurement result of the temperature (value measured at the side plate) of the conventional aluminum heat sink and the new heat sink according to the present disclosure that had been processed at the interface by electrodeposition both arranged above the heater (a heater plate with temperature control: IKAC-MAGHS7) when rising and falling at the same temperature. Experiments were conducted using a PID-controlled constant-temperature hot plate (aluminum, heating surface area 200 × 200 mm) as the heating source under a laboratory environment maintained at 25 °C. A multichannel digital thermometer (THE-373 K / J THERMOMETER) equipped with K-type thermocouples and a data logger was employed to perform real-time data acquisition. Multiple synchronized measurements were carried out during both the temperature rise and temperature fall phases. The vertical axis indicates the temperature, and the horizontal axis indicated the heating time and the heat dissipation time. Note that, in Fig. 3, the left graph shows the change in seconds when the temperature rises, and the right graph shows the time in minutes when the temperature falls. The temperature difference of approximately 10 °C was observed each during the temperature rise and temperature fall, and it was observed that the heat dissipation characteristics of the new heat sink were drastically improved than that of the conventional heat sink.

[0074] Fig. 4 illustrates the thermal radiation characteristics and spatial heat distribution observed after heating, when the aluminum plate and the electroplated member according to the present disclosure were left to cool without further heating. The measurement was conducted using a thermal sensor (Seek Thermal Pro, 320 × 240 pixel resolution) . The results show not only differences in the temperature and distribution of the members themselves, but also a marked reduction in radiated heat to the surrounding space for the electroplated member, indicating improved thermal management capability.

[0075] Next, to study the composition of the porous plated layer of CNT / graphene / Ag in more detail, the porous plating layer of the example was formed on the aluminum flat plate, and SEM image observation and analysis was performed using scanning electron microscope (JSM-6390 (LA) from JEOL) with analysis function. Fig. 5 is the 20000x SEM image. Then, quantitative analysis (ZAF method) was attempted on this sample using this electron microscope.[Analysis Condition]

[0076] Accelerating Voltage: 20.0 kV Illumination Current: 1.00000 nA Energy Range: 0 to 20 KeV

[0077] The following was determined from the graph of Fig. 6 indicating the quantitative analysis result. (1) Ag and C were shown at the same time at low energy. This is consistent with the fact that the silver nanoparticle was supported in CNT or graphene, meaning that silver was physically supported in the surface of CNT or graphene, possibly because the chemical bonding was formed. (2) Silver was separately present at higher energy positions in the different X axis.

[0078] It is assumed that the peak of silver was observed by specific energy (for example, Ag Lα or Ag Kα). These peaks indicated that silver was present in a unique state (for example, the silver nanoparticles) at those places even in a very small amount.

[0079] Next, Fig. 7 shows the mapping image of each component C and Ag corresponding to the quantitative analysis of the porous plating layer formed on the aluminum flat plate. Thus, it can be seen that CNT / graphene that is the component C was uniformly present all over the material, Ag was also present all over the material, and precipitated Ag was locally present.

[0080] Note that the image with BF indicated the bright field image by SEM. The bright field image was a contrast image obtained when electrons irradiated to the sample were directly transmitted, and was used to visualize the shape and structural information of the surface of the sample (such as arrangement, size, and shape of the metal particles and other materials because the contrast was generated according to density and atomic number of the sample) .

[0081] From the same figure, if bright areas were observed in the BF image, it may indicate a portion with high density, that is, a portion where heavy elements (for example, silver) were present. It was consistent with the above result that the silver nanoparticles were supported in the wide region in the surface of CNT or graphene, while there was a place where silver was locally present.[Example 2]

[0082] In Example 2, copper was used as the metal nanoparticle instead of silver in Example 1 as follows. 1. Metal Compound or Salt: copper sulfate (CuSO 4 ) 2. Solvent of Dispersion: water of 90 wt% and ethylene glycol of 10 wt% 3. Surfactant: polyvinylpyrrolidone (PVP) of 2 wt% 4. Reducing Agent: sodium borohydride (NaBH4) of 0.5 wt% 5. Copper ions added in electroplating: aqueous solution of copper sulfate (CuSO 4 ) 6. Carbon material: a mixture of carbon nanotubes and graphene, wherein the amount of graphene is 50% by weight relative to the carbon nanotubes

[0083] Void-forming material, in which the metal nanoparticle were supported on the surface of the heat sink substrate, and a porous plated layer, in which metal deposit that is the same as said metal nanoparticles were mixed, are formed using the above material and the same method as Example 1. The heat dissipation and heat transfer characteristics in the heat sink of such a heat exchange member was observed by the same method as that for the silver nanoparticles shown in Fig. 3.

[0084] Fig. 8 is a SEM image (20000x) of the porous plating layer formed on the copper flat plate. As can be seen from this SEM image, the nanocomposite of CNT / graphene could be observed also in Example 2.

[0085] Fig. 9 is the results of thermographic observation of the heat dissipation characteristics of a heat sink of Example 2 fixed to the bottom surface of a wooden support and a copper flat plate fixed to the top surface. The experiment was conducted by heating the original copper plate and the copper plate with porous plating layer in close proximity simultaneously and uniformly with a heater, then stopping the heater heating and obtaining thermographic snapshots of the temperature drop. The positions were fixed at diagonally opposite to each other in order to minimize mutual thermal interference as much as possible. As can be seen from this observation, the contribution of the porous plating layer by Example 2 to the cooling characteristics was confirmed with respect to the heat dissipation properties.REFERENCE SIGN

[0086] S1: producing the dispersion S2: adding the carbon material S3: first ultrasonic cavitation S4: Adding the metal compound (or salt) S5: second ultrasonic cavitation S6: supporting the metal nanoparticle on the carbon material S7: setting the metal on the anode and the substrate on the cathode S8: adding the metal ion solution S9: electroplating

Claims

1. A heat exchange member comprising: a substrate; and a porous plated layer on a surface of the substrate, the porous plated layer comprising: (a) a void-forming composite including a carbon material selected from a group consisting of carbon nanotubes, carbon nanofibers, graphene, and combinations thereof, the carbon material supporting metal nanoparticles; and (b) a metal deposit comprising the same element as the metal nanoparticles.

2. The heat exchange member according to claim 1, wherein the porous layer formed from the void-forming material and the metal deposit is a plating layer formed on the surface of the substrate by electroplating.

3. The heat exchange member according to claim 1, wherein the metal of the nanoparticles in (a) and the metal deposit in (b) are each independently selected from a group consisting of Ag, Au, Cu, Pt, and Pd.

4. The heat exchange member according to claim 2, wherein the carbon material is a mixture of a plurality of materials selected from carbon nanotube, carbon nanofiber, and graphene.

5. The heat exchange member according to claim 3, wherein the substrate includes a heat dissipation fin.

6. The heat exchange member according to claim 3, wherein the substrate is a metal foil.

7. A method of manufacturing a heat exchange member, comprising: producing a dispersion by adding a carbon material selected from the group consisting of carbon nanotubes, carbon nanofibers, graphene, and combinations thereof to a solvent and subjecting the dispersion to ultrasonic cavitation; generating metal nanoparticles by introducing a metal compound providing metal ions, the compound being selected from oxides, salts, or complexes into the dispersion and reducing the metal ions under ultrasonic cavitation in the presence of a reducing agent, thereby supporting the metal nanoparticles on the carbon material; and electroplating a substrate as a cathode using the dispersion as an electrolytic bath while supplying a metal-ion solution of the same element as the nanoparticles from an anode or an external source, thereby forming on the substrate a porous plated layer comprising the carbon material supporting the metal nanoparticles and a co-deposited metal deposit comprising the same element ultrasonic cavitation8. The manufacturing method of the heat exchange member according to claim 7, wherein the solvent of the dispersion is one or more selected from water, ethanol, isopropanol, and ethylene glycol.

9. The manufacturing method of the heat exchange member according to claim 7, wherein the process of producing the metal nanoparticle includes adding a metal ion in the dispersion.

10. The manufacturing method of the heat exchange member according to claim 7, wherein a surfactant is added to the dispersion.

11. The manufacturing method of the heat exchange member according to claim 7, wherein a reducing agent is added to the dispersion.

12. The manufacturing method of the heat exchange member according to claim 7, wherein the metal nanoparticle and the metal deposit are each independently selected from a group consisting of silver, gold, copper, platinum, and palladium.

13. The manufacturing method of the heat exchange member according to claim 12, wherein the carbon material is a mixture of a plurality of materials selected from carbon nanotube, carbon nanofiber, and graphene.

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