A method for manufacturing a thermal conductive layer.

Abstract

A thermal conductive layer for semiconductor chip heating elements is manufactured by increasing the proportion of thermal conductive particles or fibers with high thermal conductivity (W / m·k). [Solution] The target object is selected from semiconductor chips that act as heat sources, heat dissipation means, and substrates for thermal interface materials (TIM) sheets. One or more thermal conductive materials are selected from thermal conductive particles or fibers with high thermal conductivity, dispersed in a solvent or dispersant to form a dispersion or slurry, and then directly, or if necessary, made into a liquid binder with an inorganic or organic binder and solvent. Each is then made into liquid particles using a particle generator and sprayed out, and coated or impacted onto the heated target object by external collision mixing, thereby forming a thermal conductive layer with a high proportion of thermal conductive material. Alternatively, the liquid binder is applied to the target object as a liquid film, and the selected thermal conductive material is sprayed onto the liquid film and penetrated into the liquid film to produce a thermal conductive layer with a high proportion of thermal conductive particles or fibers.

Description

Technical Field

[0006] ,

[0001] The present invention relates to the formation of a heat conduction layer for conducting the heat of a heating element such as a semiconductor chip.

Background Art

[0002] As the integration of semiconductor chips increases in size and sophistication, such as in CPUs and GPUs, the amount of heat generated is increasing, and heat dissipation means have become a major problem.

[0003] For example, Patent Document 1 proposes a method of detecting the temperature of a semiconductor element and cooling a heat radiation fin with a heat radiation fan. Patent Document 2 also discloses a method of disposing a heat conduction grease between a semiconductor module and a heat sink.

[0004] Patent Document 1 detects an increase in the temperature of a heat radiation fin connected to a substrate on which a semiconductor element is fixed and cools it with a cooling fan. Therefore, the heat conduction grease fills the uneven portions of the contact surface between the temperature detection element and the heat radiation fin, and has the function of making the contact area between the heat radiation fin and the temperature detection element uniform and large, and it is said that the detection accuracy can be improved. Patent Document 2 also discloses a method of interposing a flexible material such as a heat radiation sheet or a carbon sheet with a thermal conductivity of several W / m·K to several tens of W / m·K or less in addition to a heat conduction grease containing a filler such as aluminum oxide. The heat conduction grease is also said to absorb the warping of the semiconductor module due to heat.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] With the increasing integration of CPUs and GPUs, the temperature rise of chips is accelerating. Consequently, a fundamental solution is needed. The heat-generating surface of a chip typically forms a thermal conductive layer containing thermally conductive particles between it and heat-dissipating objects such as heat spreaders or heat sinks. Since gases have poor thermal conductivity, the interface between the heat-generating surface, the heat-dissipating object surface, and the thermal conductive layer should ideally be at the nanometer level. Furthermore, materials with high thermal conductivity, such as diamond particles, nanodiamond particles, silicon carbide, and aluminum nitride, are considered suitable for the thermal conductive layer. While not insulators, carbon nanotubes, carbon nanofibers, and graphene are expected to have high thermal conductivity potential and flexibility in the thermal conductive layer. Graphite is also soft, has good thermal conductivity, and is low-cost, so its use, either alone or in combination, is important to utilize its unique characteristics. On the other hand, from the perspective of complete insulation and thermal conductivity, insulating diamond particles obtained by removing the carbon surface layer from nanodiamonds, or crushed artificial diamonds, are good. Considering insulation, thermal conductivity, and cost, aluminum nitride particles are a good choice. Because crushed natural or synthetic diamonds, which have the best thermal conductivity, are expensive, nanodiamonds, which can be manufactured relatively cheaply using the detonation method, are attracting attention. Nanodiamonds are used in many fields, including semiconductor manufacturing processes such as polishing.

[0007] Thermal conductive layers need to be able to follow the warping and compression caused by the heat of semiconductor chips, heat dissipation methods, heat spreaders, heat sinks, and other heat dissipation devices. Therefore, there is a need for a flexible thermal conductive layer that can follow these changes. There has been a tendency to increase the content of gel-like polymers or polymers with rubber elasticity and adhesiveness, but this has conversely led to a decrease in thermal conductivity. Due to the high thermal conductivity of diamond, nanodiamonds are mixed into fluid gel-like materials such as grease and are commercially available as nanodiamond grease. However, it is well known that when solid fine particles are mixed and dispersed in a high proportion in grease-like fluids, solutions, or emulsions, the viscosity becomes high, for example, several hundred thousand mPa·s, or even several million mPa·s or more, making handling difficult and posing a challenge to uniform coating on thin films. [Means for solving the problem]

[0008] To solve the above problems, the thermal conductive layer at the interface between the heating element and the heat dissipation means is made of a material with high thermal conductivity in order to quickly transfer heat without heat accumulation and reduce warping, etc. In particular, in this invention, solid particles and fibers with good thermal conductivity exceeding 250 W / m·k, such as diamond, silicon carbide, gallium nitride, aluminum nitride, silver, copper, graphite, carbon nanotubes, carbon nanofibers, and graphene, were selected. Furthermore, the ratio of these materials was increased and they were mixed with solvents and dispersants to form dispersions and slurries. This slurry was generated as a liquid particle group or pulsed particle group using a particle generator and sprayed onto heated TIM substrates, heat dissipation objects such as heat sinks and heat spreaders, and heat-generating objects such as semiconductor chips and packages including CPUs and GPUs, causing them to collide with the target object. The solvent, which has become a thin film, is instantly evaporated and multiple layers are stacked, thus creating a thermal conductive layer with a high ratio of thermal conductivity, high density, and high adhesion. By laminating multiple layers of thin films, the thermal conductive layer can be made to the desired thickness, and the proportion of thermally conductive solid particles and fibrous materials such as CNTs can be increased. Polymeric dispersants and surfactant dispersants can be used as dispersants. In particular, at the interface between the heat-generating element and heat-dissipating object of the target, a high-density thermal conductive layer can be formed by impacting the heated object with liquid particles and causing the solvent to volatilize instantly. Furthermore, adhesive polymers such as silicone-based and acrylic-based liquid polymers can be applied or dispersed in small amounts as liquid particles for the purpose of fixing the desired parts of the thermal conductive layer. Therefore, even the amount of polymer at the interface can be kept to a minimum according to the method of the present invention, and a highly thermal conductive layer can be formed. Then, by laminating the desired heat-generating element thermal conductive layer, TIM, and heat-dissipating object thermal conductive layer, a thermal conductive layer with high thermal conductivity can be formed. According to the present invention, by directly impacting the target object with liquid particles, a nano-level thin film layer can be formed, especially at the interface, so a layer that follows even fine uneven surfaces at the nano-level can be formed. Therefore, in this invention, the surface area can be increased by creating an uneven surface on the semiconductor chip surface or the surface of the heat dissipation object facing it via the heat conduction layer. In addition, by mixing materials such as CNTs, which have a high potential for thermal conductivity, into the heat dissipation objects of heat sinks and heat spreaders made of copper or aluminum, the thermal conductivity can be increased several times, creating an overall heat conduction system.

[0009] On the other hand, when using adhesive or soft TIM sheets such as gels for the interface of heating elements or heat dissipation objects, the present invention allows for the formation of a liquid film by applying a liquid polymer solution or emulsion with a low solid content of 10 wt% or less, or a liquid polymer mixed with thermally conductive particles or fibers, to the target object or substrate. Thermally conductive solid particles or fibers are then ejected into the liquid film, penetrating it, and a polymer layer can be formed on the top layer as needed. Liquid film formation can be achieved using particle generation methods such as spraying, die coating, roll coating, inkjet printing, or airless spray nozzles, forming a liquid film at a low liquid pressure, for example, around 0.2 to 0.5 MPa, and then applying a film coating with the liquid film. Similarly, spray particles, a type of particle generation device, can be used for application by ejection or pulsed jet stream. Furthermore, by impacting a dried, heated polymer film of a desired thickness, for example, several micrometers, with thermally conductive particles or fibers in the form of a dispersion or slurry, for example, using a pulsed jet stream, some of the particles can be embedded into the polymer layer, resulting in a dense and tightly adhering film.

[0010] The heat dissipation effect of semiconductor chip surfaces and heat-dissipating objects, which are heat-generating elements in contact with the heat conduction layer, is better the larger the surface area. Therefore, creating uneven surfaces, especially fine unevenness, is effective. To make the unevenness even more effective, it is good to use shapes such as sawtooth, cone, pyramid, or even pyramidal shapes. When the pulsed jet stream from the particle generator of the present invention is subjected to impact, even if the object has an uneven shape, the liquid particles that collide with it are compressed into a solvent layer at the micrometer or even nanometer level. As a result, the solvent evaporates instantly, and a highly adhesive, thermally conductive thin film layer that conforms to the uneven interface can be formed. Furthermore, by laminating multiple layers, a desired thermally conductive layer can be formed.

[0011] Particle generation can be achieved using spray methods such as two-fluid sprays. The generated fine particles can be transferred by carrier gas and applied to the target object by methods such as bubblers, ultrasonic atomization, centrifugal atomization, or by colliding the spray flow with an object to atomize it. By increasing heating or contact with gas between the microparticle creation process and coating, the solvent can be effectively detached from the microparticles, resulting in particles with a higher solid content that can then be attached. Therefore, this method can be applied not only to the dry coating of thermally conductive materials onto a binder liquid film, but also to other methods.

[0012] In addition to the above, dispersions of thermoelectric particles or fibers can be made into liquid particles and directly attached to heating elements or heat-dissipating objects by jet stream. When the dispersant is polymer-based, the adhesion strength increases, so a heat-conducting layer of heat-conducting material can be formed without the need for a binder. On the other hand, since the desired amount of liquid binder can be applied separately as liquid particles, the polymer non-volatile content in the heat-conducting layer can be reduced to zero or less than 10% by weight. In particular, by heating the target object and impacting it with a pulsed jet stream, the solvent is instantly evaporated, improving the adhesion at the interface of the object and the density of the heat-conducting layer.

[0013] The thermally conductive material of this invention is not particularly limited, but the higher the thermal conductivity, the better, and the greater the bonding and contact between materials, the better. Furthermore, the interface between the heat-generating element and the heat-dissipating object is required to be free of gas layers or bubbles that would form an insulating layer, and nano-level conformability is required. For this reason, the surface of the TIM sheet in particular needs to be flexible and soft, and be able to conform even if the surface of the object is rough. In this invention, carbon nanotubes (CNTs), carbon nanofibers, graphene, and even 3D graphene, which have high thermal conductivity potential, can be effectively used in a structure that facilitates contact between thermally conductive materials, thereby providing flexibility and improving thermal conductivity. In this invention, these CNTs, etc., are expressed as thermally conductive fibers. These fibers can be combined to form a desired thermally conductive network, and when combined with thermally conductive particles, a good thermally conductive layer can be formed. Furthermore, to improve the conformability of the interface and thermal conductivity, it can be mixed with a small amount of gel or polymer. On the other hand, in this invention, cellulose nanofibers (CNF), which have a high thermal conductivity of 2 W / m·k, are selected from polymers such as silicone that have adhesiveness and rubber elasticity, and can be used as a network or composite material with polymers.

[0014] Since CNF is an insulating material, it can be used as a dispersion with solvents such as water or organic solvents. A dispersion of aluminum nitride particles or nanodiamond particles, which have high thermal conductivity, can be added to the CNF dispersion, and an organic binder such as a resin solution can be added as needed to form a composite dispersion for application. To further increase the proportion of thermally conductive materials, separate dispersions can be alternately applied as thin films to an object or substrate to form an insulating film with good thermal conductivity. It is particularly suitable for use as a heat conduction layer for heat-generating elements such as semiconductor chips. On the other hand, for heat dissipation objects or TIM sheets on the opposite side, to provide flexibility and adhesiveness, a solution or emulsion of adhesive, rubber-elastic polymer or gel with a low solid content concentration (for example, 10 wt% or less, or even 3 wt% or less) can be applied by alternately layering a dispersion of thermally conductive particles or fibers in liquid form. In this case, thermally conductive particles such as nanodiamonds or fibers such as CNTs may be mixed into the liquid polymer.

[0015] Furthermore, when applying a thermal conductive layer as a TIM sheet or film to an object, a solution or emulsion is first applied to the surface of a transfer film substrate to form a liquid film. Then, thermally conductive particles or fibers are directly applied, or converted into liquid particles using a particle generator as a dispersion or slurry, and ejected and collided with the liquid film, allowing the particles to penetrate the liquid film and form a thermal conductive layer, thus increasing the proportion of thermally conductive particles. The inventors of this invention possess a patented technology that allows for application of thermally conductive particles as solid particles when they are submicron or larger. Therefore, solid particles can be applied on thin liquid films or dried liquid films, and by increasing the particle speed, solid particles can be applied while penetrating into the undried liquid film.

[0016] Furthermore, the aforementioned solutions and emulsions can be selected from materials with high elasticity, such as silicone-based polymers or acrylic adhesives. If heat resistance is required, the adhesive can be modified by cross-linking, for example, UV curing. Heat-resistant silicones and fluorine-based rubber solutions and emulsions can also be selected. Furthermore, cellulose nanofibers can be used alone or in combination with the aforementioned polymers. If non-insulating thermal conductivity is acceptable, high thermal conductivity CNTs, particularly single-walled carbon nanotubes (SWCNTs), carbon nanofibers, and graphene can be selected, and by dispersing cellulose nanofibers, which have a higher thermal conductivity of 2 W / m·k and higher heat resistance than the resin group, a highly flexible thermal conductive layer structure can be formed. If interfacial adhesion is desired, at least the interface can be a polymer solution or emulsion with soft, low-solid content and non-volatile components, or a mixture of these with trace amounts of nano-sized particles or fibers.

[0017] For heating elements and heat dissipation objects using TIM sheets, the interface should preferably consist of a soft adhesive layer or rubber-elastic layer with as high a proportion as possible of thermally conductive particles, especially fine particles of a few nanometers to submicrons, and fibers such as CNTs and graphene. On the other hand, when a dispersion of thermally conductive particles is sprayed directly onto a heating element or heat dissipation object as dispersed particles, heating the object causes rapid evaporation of the solvent through collision of the dispersed particles with the object, allowing for the formation of a dense, dry thermal conductive layer through thin film lamination. For substrates such as heat dissipation objects and transfer films, which are relatively easy to heat, a dense thermal conductive layer can be formed by repeatedly heating the object, spraying a thermally conductive dispersion as particles, and allowing the solvent to evaporate the moment the substrate becomes wet. In this invention, for devices where the temperature does not exceed 150°C, an adhesive can be used on the TIM sheet to bond the interface using adhesive force. The internal thermal conductive layer outside the interface can have a higher proportion of selected thermally conductive particles and fibers such as CNTs. Furthermore, some particles and fibers can penetrate the polymer layer of the thermal conductive layer to form a thermal conductive layer structure that directly contacts the surface of the heating element or heat sink. In addition, to give the thermal conductive layer flexibility and improve thermal conductivity through inter-particle contact of thermal conductive particles, CNTs, graphene, and especially three-dimensional (3D) graphene which is easy to arrange in the thickness direction of the thermal conductive layer can be incorporated. If non-insulating properties are acceptable, from the perspective of cost and bonding strength, particles with good thermal conductivity such as diamond, silicon carbide, and aluminum nitride can be bonded to graphite with a low Mohs hardness by collision. Alternatively, a network with good thermal conductivity can be made by bonding CNTs, carbon nanofibers, and graphene with graphite particles by collision. Furthermore, in this invention, a thermal conductive layer with strong bonding strength can be formed by combining nanodiamond particles or aluminum nitride with a Mohs hardness of 9 or higher with graphite, silver, and copper with a Mohs hardness of 4 or lower. For this reason, the thermal conductive layer of this invention is as follows.

[0018] The present invention provides a method for manufacturing a thermal conductive layer that dissipates heat from a semiconductor chip, which is a heat-generating element, through a thermal conductive layer to a heat dissipation means, comprising the steps of: selecting an object from the heat-generating element, the heat dissipation means, and a substrate for a thermal interface material sheet; selecting at least one thermal conductive material, such as thermal conductive particles or thermal conductive fibers with high thermal conductivity, and forming one or more thermal conductive material dispersions or slurries with a solvent and a dispersant; adding a liquid binder consisting of an inorganic binder or an organic binder and a solvent to the thermal conductive material dispersion or slurry, or to the dispersion or slurry, and converting it into liquid particles using an independent particle generator to form a jet stream or pulsed jet stream; mixing the jet stream in the air or impacting the object, which has been heated sequentially or in no particular order, to form a thin film of solvent which is instantly evaporated and laminated multiple times; and contacting or bonding at least a portion of the thermal conductive materials together to form a thermal conductive layer with high thermal conductivity.

[0019] The present invention provides a method for forming a thermal conductive layer, characterized in that the thermal conductive material is selected from thermal conductive particles or fibers of diamond, nanodiamond, silicon carbide, gallium nitride, aluminum nitride, silver, copper, graphite, carbon nanotubes, carbon nanofibers, and graphene, and the contact or bonding of the thermal conductive particles or fibers is such that, when the Mohs hardness of diamond particles is 10, the thermal conductive particles have a Mohs hardness of 4 or less and the thermal conductive particles or fibers have a Mohs hardness of 9 or more, and the method is characterized in that the material is prepared as an assemblage or as a separate dispersion or slurry, and at least a portion of the thermal conductive particles with a Mohs hardness of 9 or more and the thermal conductive particles or fibers with a Mohs hardness of 4 or less come into contact or bond with each other when the dispersion or slurry is ejected from a particle generator or as a pulsed ejection flow onto the heated object.

[0020] The present invention provides a method for forming a heat conductive layer, characterized in that the heat conductive layer is fixed by adhering heat conductive particles or fibers of the heat conductive layer to at least a portion of the heat conductive layer by applying liquid particles using a particle generator of the liquid binder by ejection flow or pulsed ejection flow.

[0021] In forming an insulating layer as the heat conduction layer on the semiconductor chip, the present invention selects at least one from diamond, nanodiamond, and aluminum nitride heat-conductive particles, and forms one or more dispersion liquids or slurries with a solvent and a dispersant; and the semiconductor chip is made into liquid particles by a particle generator with the dispersion liquid or slurry, and ejected as an ejection flow or a pulsed ejection flow and collided with the semiconductor chip heated to 80° C. or lower to form a thin film of the solvent and instantaneously evaporate the solvent, and a dense insulating heat conduction layer is formed by a step of laminating a plurality of times in order or in any order. A method for forming a heat conduction layer is provided, which is characterized by the above.

[0022] The non-volatile content of the liquid binder of the present invention is 10% by weight or less. A method for forming a heat conduction layer is provided, which is characterized in that a step of applying the liquid binder to the object to form a liquid film and a step of ejecting the selected heat conductive material into the liquid film by a dry method are performed to increase the weight ratio of the heat conductive material.

[0023] In the heat generating body and the heat radiating means of the present invention, a heat conduction layer having a higher ratio of the heat conductive material than the solid content of the binder by weight ratio is formed, and a heat conduction layer is formed with a heat interface material sheet having a lower ratio of the heat conductive material than the heat generating body and the heat radiating means interposed therebetween. A method for forming a heat conduction layer is provided, which is characterized by the above.

[0024] As described above, in the present invention, a heat conduction layer containing more solid particles and fibers having high heat conductivity, for example, 250 W / m·k (meter kelvin) or more, can be formed. The material of the heat conduction layer is desirably selected from insulating materials such as diamond, aluminum nitride, cellulose nanofiber, and polymer in order to make the mixing of electrically conductive foreign substances into the circuit of the semiconductor element zero.

[0025] On the other hand, in this invention, in order to improve cost and the formation of a network that improves contact and bonding of thermally conductive materials and thus improves thermal conductivity, soft graphite particles with a Mohs hardness of 1 or less can be bonded with other thermally conductive particles. The other particles can be relatively soft metals such as copper and silver with a Mohs hardness of 4 or less, or nanodiamonds or aluminum nitride with a Mohs hardness of 9 or more. By combining graphite with fibers selected from CNTs, carbon nanofibers, and graphene, which have high Mohs hardness and high thermal conductivity potential, a thermally conductive layer with high thermal conductivity can be formed.

[0026] Furthermore, as described above, the present invention allows for the effective use of fibrous CNTs, which have a high theoretical potential value for thermal conductivity. In this invention, CNTs, carbon nanofibers, thin and planar graphene, and three-dimensional graphene are defined as fibers. By combining these fibers with the aforementioned thermally conductive particles, an ideal thermal conduction network can be constructed that takes into account the thickness direction of the thermal conduction layer. Therefore, a highly thermally conductive layer can be constructed in a composite structure that combines nanodiamond particles and other particles or fibers with excellent thermal conductivity. In this invention, by adding inorganic binders such as water glass or organic cellulose nanofibers, which have higher thermal conductivity than polymers, a network with good thermal conductivity can be formed in combination with CNTs, etc. Furthermore, by attaching and solidifying liquid fine particles of adhesives or polymers to desired parts of the thermal conduction layer, the thermal conduction function of the thermally conductive particles and fibers of the thermal conduction layer can be maintained over time. Moreover, a low-solids polymer solution or emulsion can be impregnated into the thermal conduction layer in which a high-density thermal conduction structure has been maintained by the above method. Therefore, a thermal conduction layer with a soft surface corresponding to the interface of the target object can be formed. Furthermore, this invention enables the industrial production of TIM thermal conductive sheets with a high proportion of thermal conductive particles near the interface of the object.

[0027] The application of the liquid to a substrate such as a liquid polymer according to the present invention can be carried out by a single method or a combination of liquid film coating methods such as inkjet, liquid particle ejection using a particle generator including a spray, roll coater, screen printing, or die coating, and the means are not limited.

[0028] Furthermore, the means of applying thermally conductive particles or fibers are not limited. For example, solid particles may be sprayed dry onto a pre-applied liquid film, such as a polymer solution. These can be applied with precision by applying the methods described in Patent Publication No. 2015-512536 or Patent Publication No. 2016-077982, invented by the present inventors. Liquid particles can also be made to collide with the liquid film using high-speed pulses of, for example, 5 cycles / second or more, causing them to penetrate the liquid film with speed. On the other hand, in coating methods that do not require a liquid film such as polymer, thermally conductive solid particles or fibers can be dispersed with a solvent, such as ion-exchanged water or a dispersant, and sprayed using a spray means, one of the means of particle generation devices, in a pulsed flow that also impacts the spray particles. By laminating a thin film onto a heated object, the solvent can be instantly evaporated, forming a dense dry layer. Alternatively, thermally conductive particles can be mixed with a polymer solution, etc., while colliding with the liquid film and penetrating it. The solvent for the liquid film and the thermally conductive particles should be the same or compatible. Water is a suitable solvent. The solvent or dispersion for spraying should be an organic solvent with a low boiling point, such as alcohol, as this promotes solvent evaporation before the particles collide with the liquid film. The dispersion, slurry, or solution may be preheated before spraying, and the spray atmosphere can also be heated. Alternatively, a method of collision mixing of different dispersions, slurries, or solutions downstream of the particle generator can be employed.

[0029] In this invention, by the method described above, a dense heat-conducting layer can be formed by dispersing fine powder, preferably heat-conducting particles or fibers with an average particle diameter of 2 to several thousand nanometers, in a polymer-based dispersant or solvent, and spraying it onto a directly heated object or substrate to create a thin film layer. Furthermore, if a thick film thickness of the heat-conducting layer is required, the particle diameter can be made to a size of several to several tens of micrometers, for example, like graphite. [Effects of the Invention]

[0030] As mentioned above, it is well known that when fine particles, especially nano-sized to submicron-sized fine particles, are mixed and dispersed in liquids such as solutions and emulsions that contain non-volatile components, the viscosity becomes abnormally high, ranging from tens to hundreds of mPa·s. Therefore, there have been limitations to increasing the nanoparticle ratio by mixing nano-sized particles with good thermal conductivity with polymer solutions, etc. However, in the present invention, liquids such as polymer solutions and emulsions with low non-volatile components, for example, 10% by weight or less, more preferably 2% by weight or less, and thermally conductive particles can be handled separately and applied separately without mixing the solutions and particles in or upstream of the coating apparatus. Therefore, the ratio of resin, etc. to thermally conductive particles can be set to desired conditions. Fine particles or fibers can be prepared in advance as a stable dispersion and mixed with low-solids solutions or emulsions immediately before or immediately after coating. Also, for example, by using a polymer-based dispersant, solvent, and thermally conductive particles or fibers, the ratio of thermally conductive particles or fibers can be increased to 75% by weight or more. Alternatively, a similar effect can be achieved by applying a polymer solid content of, for example, 1 percent, and then directly applying thermally conductive particles on top of it, either by dispersing them with a solvent or dispersant, forming them into particles using a particle generator, and then launching them at high speed.

[0031] Furthermore, the present invention allows for the lamination of multiple layers, such as 2 to 200 layers or more, under the same conditions or with varying conditions. To achieve greater uniformity, the number of layers can be increased while automatically offsetting the phase of the spray pattern for each layer. For example, when applying 30 layers with a pitch feed of 6 mm, the offset (correction) can be set to 200 micrometers for each layer, resulting in a uniform coating distribution. Additionally, by changing the spraying conditions, such as by changing the size of the thermally conductive particles and thus their ratio, or by changing the ratio of different material particles or fibers during lamination, the present invention allows for the ratio distribution of thermally conductive particles and fibers to be arranged in a desired gradient distribution structure, for example, in the film thickness direction.

[0032] Furthermore, the surface area of ​​the heat conduction layer in contact with the heating element or heat dissipation object can be increased by creating an uneven structure. In particular, by using liquid microparticles and pulsed ejection of impactful microparticles to cause collisions, it is possible to form an interface consisting of a heat conduction layer that can follow uneven surfaces of a few micrometers or less and ignore voids at the nanoscale. By selecting the desired fine particle size and particle size distribution and the desired number of particles, a denser heat conduction particle layer can be formed. In addition, in this invention, by increasing the number of particle generators, the mixing ratio and distribution of different types of particles or particles of different shapes can also be changed. Therefore, by selecting materials with particularly excellent thermal conductivity and facilitating contact and bonding between particles or through fibers, a highly heat conduction layer can be formed. If necessary, a highly insulating heat conduction layer can be formed by selecting a heat conduction material.

[0033] In particular, by efficiently distributing diamond particles or nanodiamond particles and bringing them into contact with other thermally conductive materials, an ideal thermal conductive layer can be formed. By ejecting a dispersion of nanodiamond dispersion liquid from a particle generator, either sequentially or in any order, a thermally conductive film with high thermal conductivity and flexibility can be created by contacting or entangling the dispersion of carbon nanotubes (CNTs), especially single-walled carbon nanotubes (SWCNTs), with a solvent or dispersant, using a particle generator. By heating the target object or substrate and preventing a temperature drop due to the heat of vaporization of the solvent that evaporates instantaneously, a dense thermal conductive layer containing almost no solvent can be instantly formed by heating and vacuum adsorption of the substrate. Furthermore, to reduce costs, the thermal conductivity can be increased by contacting or bonding a desired amount of soft graphite particles with diamond or other particles with excellent thermal conductivity, such as aluminum nitride, silver, or copper powder. Moreover, a thermally conductive layer with high thermal conductivity can be formed by combining it with CNTs or graphene, which have high thermal conductivity potential. [Brief explanation of the drawing]

[0034] [Figure 1] Figure 1 is a schematic cross-sectional view of the semiconductor heating element, heat conduction layer, and heat dissipation means (object). [Figure 2] Figure 2 is a schematic cross-sectional view of the heating layer formed on the substrate. [Figure 3] Figure 3 is a schematic cross-sectional view of a heat conductive layer formed on a heat dissipation object facing the semiconductor heat-generating element. [Figure 4] Figure 4 is a schematic cross-sectional view showing thermally conductive particles being ejected onto a liquid film on a substrate by a particle generator. [Modes for carrying out the invention]

[0035] Preferred embodiments of the present invention will be described below with reference to the drawings. Note that the following embodiments are merely examples to facilitate understanding of the invention and do not preclude additions, substitutions, modifications, etc., that can be implemented by those skilled in the art without departing from the technical spirit of the present invention.

[0036] The drawings schematically illustrate preferred embodiments of the present invention.

[0037] In Figure 1, a thermal conductive layer 2 and a heat dissipation means (heat dissipation object) 3 are laminated on a semiconductor heat-generating section 1. The area of ​​the heat dissipation means 3 may be larger than the area of ​​the semiconductor heat-generating section 1. If insulation is required for even a part of the heat-generating section, attention must be paid to the shape of the thermal conductive layer if it is a conductive layer. Alternatively, the thermal conductive layer may need to be an insulating layer. The thermal conductive layer can be formed by coating one or both surfaces of the heat-generating layer 1 or the heat dissipation object 3 facing the heat-generating layer 1. Alternatively, a thermal conductive layer such as a TIM sheet can be placed between them.

[0038] Figure 2 shows a thermal conductive layer 22 formed on a substrate 29 such as TIM. The substrate is preferably a peelable film or the like, and the thermal conductive layer 22 can be transferred to a heat-generating part or heat-dissipating object (not shown). It is desirable that the interface with the heat-generating part and the interface with the heat-dissipating object be filled with a flexible polymer or a fluid material such as grease. On the other hand, from the perspective of thermal conductivity, the problem of thermal conductivity at the interface can be solved by including more particles or fibers with high thermal conductivity, such as nanodiamonds or CNTs.

[0039] Figure 3 shows a heat dissipation object 33 with three layers of thermal conductive layers 33a, 33b, and 33c stacked on top of it. The number of layers can be five or fifteen, and there is no limit to the number of layers. The target object can be a heat-generating part of a semiconductor chip or a substrate for a TIM sheet. Therefore, it is crucial to create a structure that distributes highly thermally conductive materials such as nanodiamonds and CNTs at the heat-generating layer interface and heat-dissipating object interface, where polymers with low thermal conductivity are abundant. In this invention, CNTs such as single-walled carbon nanotubes can be efficiently arranged within a range that does not impair insulation resistance, thereby increasing the flexibility of the entire or partial heat-conducting layer. Furthermore, considering the overall effect and cost of the heat-generating layer, graphite, and especially highly thermally conductive graphite and CNTs, can be mainly distributed on the heat-dissipating object side, while the heat-generating layer side can be made into an insulating layer with insulating thermal conductor particles, cellulose nanofibers, or polymers. [Examples]

[0040] Creation of a thermally conductive layer The thermal conductive layer was formed using the following procedure.

[0041] Experimental Example 1: A 1 wt% aqueous dispersion of nanodiamonds (UDD, manufactured by Vision Development Co., Ltd.) was diluted to 0.5 wt% with pure water manufactured by Wako Co., Ltd. and applied in 15 layers over a 5 cm x 5 cm area using the impact pulse method, obtaining a nanodiamond layer with a dry weight of 1.4 mg / 25 cm². Other test conditions are as follows: Dispersion pressure: 10kPa, Atomization pressure: 0.25MPa, Pitch: 6mm, Offset per layer: 400μm, Pulse: 10Hz, Coating time: 12ms, Travel speed: 66mm / s The ND adhered strongly to the instantly dried coated surface, and there was no detachment during the peel test using gauze. Example 2: An aluminum plate heated to 60°C and vacuum-adsorbed was coated with AINEX Nanodia Grease JP-DX-1 using a spatula. After the volatile components evaporated at 60°C, 75 layers of 0.5 wt% nanodia aqueous dispersion were applied on top to obtain a dense synthetic film. The nanodia coating weight was 7 mg / 25 cm². The conditions were the same as in Experiment Example 1, except for the number of layers. The ND coating adhered strongly to the coated surface, and there was no detachment during the peel test using gauze. Example 3: An aluminum plate heated to 60°C and vacuum-adsorbed was coated with 150 layers of the UD nanodiamond aqueous dispersion film (0.5 wt%) over a 5 cm x 5 cm area using the impact pulse method. The coating weight of nanodiamonds was 14.4 mg / 25 cm². A dense nanodiamond deposition layer with a density of 0.58 mg / cm² was formed. The ND coating adhered strongly to the coated surface, and there was no detachment during the peel test using gauze.

[0042] The results from Example 3 showed that even without adding a polymer binder, the impact pulse method strongly implants nanodiamond particles into the aluminum plate at the nanoscale, resulting in strong adhesion that prevents them from falling off even when rubbed with gauze or similar material. Experimental Examples 1 and 2 further supported this finding.

[0043] On the other hand, the present invention allows for the handling and application of submicron-sized powders, such as thermally conductive solid particles, without the need to disperse the particles in a solvent. As mentioned above, the present inventors can utilize methods that have been invented and licensed by the present inventors. Since the bulk density of powders changes, it is important to manage them by weight. A method for precisely applying powder by sucking up a constant weight of powder per unit area, moving it through a flow path, and ejecting it is disclosed in Japanese Patent Publication No. 2014-171535 and Japanese Patent Publication No. 2016-077982, so a detailed explanation will be omitted.

[0044] When the nanodiamond aqueous dispersion is applied directly to a heating layer or heat dissipation means and fixed by other means such as a heat spreader, only a minute amount of polymer is needed. When the dispersion particles are pulsed and sprayed directly onto a heated heat dissipation object to form a film, the amount of polymer can be reduced to almost zero. Heat dissipation means include not only heat dissipation objects such as heat sinks, but also means of releasing heat by suction with a vacuum pump or blowing cold air. As described in Example 3, the impact pulse method allows the nanodiamond aqueous dispersion particles to adhere firmly to heat spreaders and heat sinks made of copper or pure aluminum. Furthermore, it has been confirmed that commercially available CNT dispersions also adhere strongly to metal plates such as aluminum using the impact pulse method.

[0045] Furthermore, a common problem with heat spreaders and heat sinks is that the heat conduction layer surface of the heat dissipation object warps due to thermal deformation caused by heat transfer from the heat source. As a result, gaps are created in the heat conduction layer at the warped areas, requiring a heat conduction layer with adhesive properties or rubber elasticity. On the other hand, the thermal warping of heat sinks and other heat dissipation objects can be solved by polishing the deformed areas at the operating temperature of the heat sink or heat spreader facing the heat-generating elements such as semiconductor chips and packages. Therefore, it is not necessary to restrain the heat spreader and semiconductor chip with a large restraining pressure. As a result, the polymer ratio can be reduced, making it possible to create a heat conductive layer with a high thermal conductivity due to the high proportion of heat conductive particles. Furthermore, in this invention, single-walled carbon nanotubes, graphene, etc., can be efficiently distributed in areas that do not impair the insulation resistance of the semiconductor chip, thereby providing flexibility to the desired thermal conductivity layer. Moreover, considering the overall effect and cost of the heat-generating layer, graphite or graphite mixed with carbon nanotubes or graphene can be mainly distributed on the heat dissipation means (object) side, and the area around the heat-generating layer, especially the part connected to the electrical circuit, can be insulated and sealed with insulating thermal conductive particles and heat-resistant polymers, while other areas can be made into an insulating layer with the desired thermal conductivity. [Industrial applicability]

[0046] The present invention, particularly the method of dispersing nanoparticles, submicron particles, and fibers such as SWCNTs in a dispersion solution and laminating them onto an object as a thin film, can be applied not only to the formation of thermal conductive layers in the semiconductor field, but also to increasing the density of electrode formation using electrode slurries in secondary batteries and reducing the resistance of interfaces. It can be applied to laminating thin films such as LLZO onto separators in semi-solid-state batteries. It can be applied to increasing the particle density at the interface between the solid electrolyte layer and electrodes in all-solid-state batteries. Furthermore, it can form thin films that conform to the fine unevenness of the object. Moreover, it can be suitably applied to processes for handling and coating nanoparticles in pharmaceuticals, biotechnology, chemicals, and perovskite solar cells. In perovskite solar cells, it can be applied to the formation of electron transport layers and hole transport layers of 20 nanometers or less. In particular, it can be suitably applied to the formation of thin films that conform to the fine unevenness of the silicon surface of perovskite-on-silicon tandem batteries. [Explanation of symbols]

[0047] 1. Semiconductor heating element 2, 22 Thermal conductive layer 3.33 Heat dissipation means (heat sink) 29, 49 Base material 32a Thermal conductive layer a 32b Thermal conductive layer b 33c thermal conductive layer c 42 Liquid film 45 Jet stream 46 Thermally conductive particles 47. Thermal Conductivity Layer Rich Layer

Claims

1. A method for manufacturing a thermal conductive layer that dissipates heat from a semiconductor chip, which is a heat-generating element, through a thermal conductive layer to a heat dissipation means, comprising the steps of: selecting an object from the heat-generating element, the heat dissipation means, and a substrate for a thermal interface material sheet; selecting an object from thermal conductive materials such as thermal conductive particles or thermal conductive fibers with high thermal conductivity and forming one or more thermal conductive material dispersions or slurries with a solvent and a dispersant; adding a liquid binder consisting of an inorganic binder or an organic binder and a solvent to the thermal conductive material dispersion or slurry, or to the dispersion or slurry, and turning it into liquid particles using an independent particle generator to form a jet stream or pulsed jet stream; mixing the jet stream in the air or impacting the object which has been heated sequentially or in no particular order to instantly evaporate the solvent, which has been formed into a thin film, and stacking it multiple times; and contacting or bonding at least a portion of the thermal conductive materials together to form a thermal conductive layer with high thermal conductivity.

2. The thermal conductive material is selected from thermal conductive particles or fibers of diamond, nanodiamond, silicon carbide, gallium nitride, aluminum nitride, silver, copper, graphite, carbon nanotubes, carbon nanofibers, and graphene, and the contact or bonding of the thermal conductive particles or fibers is such that, when the Mohs hardness of diamond particles is 10, the thermal conductive particles have a Mohs hardness of 4 or less and the thermal conductive particles or fibers have a Mohs hardness of 9 or more, and the method for forming a thermal conductive layer according to claim 1 is characterized by the steps of forming an assemblage or independent dispersion or slurry, and the collision of the dispersion or slurry with the heated object by a jet stream or pulsed jet stream from a particle generator, causing at least a portion of the thermal conductive particles with a Mohs hardness of 9 or more and the thermal conductive particles or fibers with a Mohs hardness of 4 or less to come into contact or bond.

3. The method for forming a heat conductive layer according to claim 2, characterized in that the heat conductive layer is fixed by adhering the heat conductive particles or fibers of the heat conductive layer to at least a portion of the heat conductive layer by applying liquid particles by ejection flow or pulsed ejection flow from a particle generator of the liquid binder.

4. A method for forming a thermal conductive layer according to claim 1, characterized by the steps of: selecting at least one of the thermal conductive particles of diamond, nanodiamond, and aluminum nitride, and forming one or more dispersions or slurries with a solvent and a dispersant, forming the thermal conductive layer on the semiconductor chip as an insulating layer; forming the dispersion or slurry into liquid particles using a particle generator, ejecting it as a jet stream or pulsed jet stream, and impacting the semiconductor chip heated to 80°C or below to form a thin film of solvent and instantly evaporating the solvent; and stacking multiple times in sequence or in no particular order to form a dense insulating thermal conductive layer.

5. The method for forming a thermal conductive layer according to claim 1, characterized in that the non-volatile content of the liquid binder is 10 weight percent or less, and the thermal conductive layer is formed by the steps of applying it to the target object to form a liquid film and spraying the selected thermal conductive material into the liquid film using a dry method to allow it to penetrate the liquid film.

6. A method for forming a heat conductive layer according to claim 1, characterized in that a heat conductive layer is formed on the heating element and the heat dissipation means, with a heat conductive layer having a heat conductive material ratio higher than the binder solid content by weight, and a heat interface material sheet having a lower ratio of heat conductive material than the heating element and the heat dissipation means interposed between them.

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