Method for forming a heat dissipation path and heat dissipation path

Abstract

The present invention provides a method for forming a heat dissipation path between gaps that cannot be directly subjected to external pressure, such as air or a vacuum, and also provides a heat dissipation path. [Solution] The method for forming the heat dissipation path is such that the thickness Ta is 0.5 μm or more and 25 μm or less, wrinkles are formed, the thermal conductivity in the direction of the film surface is 800 W / m·K or more, and the density is 1.8 g / cm³ 3 The above-mentioned thermal interface material (TIM) made of a graphite film is inserted into a gap where no external pressure is directly applied, and the conditions are 1.2Ta ≤ Tb ≤ 100Ta, 0.4Gd ≤ Tb ≤ 15Gd, 1.3Ta ≤ Gd, and the pressure applied in the direction of the graphite film thickness is 10 N / cm². 2 It is less than [value missing]. (Ta: Net graphite film thickness without considering wrinkles. Tb: Apparent graphite film thickness considering wrinkles (4 times the arithmetic mean roughness Ra of the graphite film). Gd: Spacing of the gap into which the graphite film is inserted.)

Description

[Technical Field]

[0001] This invention relates to forming a heat dissipation path between gaps separated by air, vacuum, or the like, where external pressure is not directly acting. It also relates to a heat dissipation path formed by the above method. [Background technology]

[0002] Gaps, separated by air, vacuum, or inert gas, often exist between the surfaces of various electronic devices and semiconductor devices. These gaps are created for a variety of reasons, including preventing interference, damage, and stress due to thermal expansion of the components, and their size also varies. While gaps between components are necessary, it is often desirable to allow as much heat transfer as possible between these gaps.

[0003] For example, consider semiconductor packaging. In semiconductor packaging, semiconductor elements are covered with a cover to protect them and dissipate heat, and a gap is provided between the semiconductor elements and the cover. On the other hand, there is a requirement to quickly dissipate the heat generated by the semiconductor elements to the outside, so it is necessary to quickly transfer the heat to the cover.

[0004] Thermal interface materials (TIMs) are materials that facilitate the smooth transfer of heat between surfaces of components, and many types have already been commercialized. TIMs are inserted into the gap between a heat source device (e.g., a semiconductor element) and a heat dissipation component (e.g., a semiconductor element cover or heat sink), and are often tightened with screws or springs and used under external pressure. The pressure applied to the TIM in this case is typically 10, 20, 30, 40, or 50 N / cm². 2 And so on.

[0005] The degree of heat dissipation is measured by the thermal resistance value (unit: K·cm). 2The thermal resistance (TIM) is expressed as (W), and its value is the sum of the bulk thermal resistance of the TIM material itself and the thermal resistance at the TIM's contact interface (interfacial thermal resistance). Typical TIMs include flexible TIMs such as grease, or composite TIMs in which fine, highly thermally conductive fillers such as carbon, metal, or ceramics are added to a flexible polymer to improve thermal conductivity. The reason why flexibility is required in TIMs is to reduce the interfacial thermal resistance.

[0006] However, greases and polymers have drawbacks such as insufficient heat resistance and leakage (pump-out). Furthermore, in composite TIMs, increasing the amount of filler to achieve high thermal conductivity leads to a loss of flexibility and an increase in interfacial thermal resistance, thus limiting the improvement in thermal conductivity. For this reason, the thermal conductivity of typical composite TIMs is around 0.2 to 10 W / m·K.

[0007] On the other hand, in solid-to-solid contact, it is known that the interfacial thermal resistance increases because gaps are created at the contact interface due to the irregularities of the solid surface. For this reason, there are few examples of TIMs made of a completely solid material, but problems such as insufficient heat resistance and leakage are relatively easy to solve.

[0008] Graphite films have been proposed as one of the few solid-state thermal insulators (TIMs) (Patent Document 1). Graphite films are unique thermal conductors that possess high heat resistance and extremely high thermal conductivity in the direction of the film plane. The thermal conductivity of highly crystalline graphite films is approximately 1500-2000 W / m·K in the direction of the basal plane of the carbon atoms, while the thermal conductivity in the direction of film thickness (C-axis direction, perpendicular to the basal plane) is approximately 5-10 W / m·K.

[0009] The reason why graphite films are used as TIMs is that their interfacial thermal resistance can be reduced to a certain extent by applying strong pressure. In other words, pressure is considered essential for a graphite film to function as a TIM, for example, 10 N / cm². 2The above pressure is said to be necessary. For this reason, such a conventional TIM of a graphite film may have voids (air layers) inside the film as shown in Fig. 1 to provide flexibility and compressibility for reducing the interfacial thermal resistance, and may have a relatively low density. For example, the density of a conventional TIM of a graphite film may be less than 1.8 g / cm 3 and may be less than.

[0010] Also, a proposal has been made to use a graphite sheet between a semiconductor element (electronic circuit) and its cover to perform heat dissipation of the electronic circuit (Patent Document 2). However, there is no disclosure regarding effectively forming a heat dissipation path between gaps under a small pressure, or the relationship between the shape and physical property values such as the thickness and wrinkles of graphite and the size of the gap.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0012] The problem to be solved by the present invention is to form a solid heat dissipation path with low thermal resistance while solving durability problems such as insufficient heat resistance and leakage between gaps where external direct pressure cannot be applied, and between gaps where large pressure is not desired for protecting fragile elements and members. That is, the present invention forms a heat dissipation path using a solid TIM between gaps separated by air, vacuum, etc., and reduces the thermal resistance value between the gaps. For example, in a semiconductor package, the thermal resistance between the semiconductor element and the inner surface of the semiconductor element cover is effectively reduced.

Means for Solving the Problems

[0013] In this invention, by inserting a graphite film having specific physical properties and structure, the thermal resistance between gaps that are not subject to pressure from substantially external sources can be significantly reduced. A significant effect can be obtained by using the graphite film alone, but multiple films may also be used in layers. Furthermore, by thinly coating the surface of the graphite film or the surface in contact with the solid graphite film forming the gap with a flexible layer such as silicone oil, silicone grease, or silicone gel, the thermal resistance between the gaps can be further reduced.

[0014] The present invention (1) The thickness Ta is 0.5 μm or more and 25 μm or less, wrinkles are formed, the thermal conductivity in the direction of the film surface is 800 W / m·K or more, and the density is 1.8 g / cm³. 3 A method for forming a heat dissipation path by inserting a graphite film, as described above, into a gap where no external pressure is directly applied, wherein the values ​​are 1.2Ta ≤ Tb ≤ 100Ta, 0.4Gd ≤ Tb ≤ 15Gd, 1.3Ta ≤ Gd, and the pressure applied in the direction of the graphite film thickness is 10 N / cm². 2 A method for forming a heat dissipation path, characterized in that it is less than (Ta: Net thickness of the graphite film without considering wrinkles, Tb: Apparent thickness of the graphite film considering wrinkles (4 times the arithmetic mean roughness Ra of the graphite film), Gd: Spacing of the gap into which the graphite film is inserted) (2) A method for forming a heat dissipation path as described in (1), characterized in that 1.0Gd ≤ Tb. (3) The pressure applied to the graphite film in the direction of film thickness is 5 N / cm 2 A method for forming a heat dissipation path according to (1) or (2), characterized in that it is as follows: (4) The method for forming a heat dissipation path according to (1) or (2), wherein the electrical conductivity of the graphite film in the direction of the film surface is 10,000 S / cm or more. (5) A method for forming a heat dissipation path according to (1) or (2), wherein the graphite film surface or the surface of the member forming the gap is covered with a flexible layer. (6). The graphite film is obtained by heat-treating an aromatic polymer film at 2400 °C or higher in an inert gas atmosphere. The method for forming a heat dissipation path according to (1) or (2), (7). An aromatic polymer film is inserted between graphites with a gap and heat-treated to produce the graphite film having wrinkles. The method for forming a heat dissipation path according to (1) or (2), (8). The size of the wrinkles of the graphite film is controlled by the size of the gap between the graphites. The method for forming a heat dissipation path according to (7), (9). A method for manufacturing a semiconductor package in which the method for forming a heat dissipation path according to (1) or (2) is applied to the gap between a semiconductor element and the inner surface of a semiconductor element cover, (10). The thickness Ta is 0.5 μm or more and 25 μm or less, wrinkles are formed, the thermal conductivity in the film surface direction is 800 W / m·K or more, and the density is 1.8 g / cm 3 The graphite film above is inserted into the gap where no external direct pressure is acting. It is a heat dissipation path where 1.2Ta ≦ Tb ≦ 100Ta, 0.4Gd ≦ Tb ≦ 15Gd, 1.3Ta ≦ Gd, and the pressure applied in the film thickness direction of the graphite film is less than 10 N / cm 2 It is characterized by being less than. Heat dissipation path, (Ta: The thickness of the net graphite film without considering wrinkles. Tb: The apparent thickness of the graphite film considering wrinkles before insertion into the gap (4 times the arithmetic mean roughness Ra of the graphite film). Gd: The interval of the gap into which the graphite film is inserted) (11). A semiconductor package in which the heat dissipation path according to (10) is applied to the gap between a semiconductor element and the inner surface of a semiconductor element cover, relates to.

Effect of the Invention

[0015] In gaps where direct external pressure cannot be applied, or where high pressure should not be applied to protect fragile elements or components, a solid heat dissipation path with low thermal resistance can be formed while solving durability problems such as insufficient heat resistance and heat leakage. In other words, a heat dissipation path can be formed using solid TIM in gaps separated by air or vacuum, thereby reducing the thermal resistance value between the gaps. For example, in semiconductor packages, the thermal resistance between the semiconductor element and the inner surface of the semiconductor element cover can be effectively reduced. [Brief explanation of the drawing]

[0016] [Figure 1] Cross-sectional view of a conventional graphite film TIM. [Figure 2] Schematic diagram of a semiconductor package [Figure 3] Schematic cross-sectional view of the graphite film TIM of the present invention [Figure 4] Thermal conduction paths in the graphite film-based TIM of the present invention [Figure 5] Surface of the graphite film-based TIM of the present invention [Figure 6] Cross-section of the graphite film TIM of the present invention [Figure 7] Schematic cross-sectional view when the graphite film TIM of the present invention is inserted into a gap. [Figure 8] Example of semiconductor package structure using graphite film TIM of the present invention [Figure 9] Examples of application to semiconductor packages containing multiple semiconductor elements [Figure 10] Examples of application to 3D packaging [Figure 11] Example of a heating method for forming wrinkles in a graphite film [Modes for carrying out the invention]

[0017] The present invention consists of the following:

[0018] The film has a thickness of 0.5 μm to 25 μm, exhibits wrinkle formation, has a thermal conductivity of 800 W / m·K or higher in the film plane direction, and has a density of 1.8 g / cm³. 3 A method for forming a heat dissipation path by inserting a graphite film, as described above, into a gap where no external pressure is directly applied, wherein the values ​​are 1.2Ta ≤ Tb ≤ 100Ta, 0.4Gd ≤ Tb ≤ 15Gd, 1.3Ta ≤ Gd, and the pressure applied in the direction of the graphite film thickness is 10 N / cm². 2 A method for forming a heat dissipation path, characterized in that it is less than [a certain value]. Here, Ta: the net thickness of the graphite film without considering wrinkles, Tb: the apparent thickness of the graphite film considering wrinkles (four times the arithmetic mean roughness Ra of the graphite film), and Gd: the spacing of the gap into which the graphite film is inserted.

[0019] Figure 2 schematically represents the structure of a semiconductor package. In Figure 2, two types of TIMs are shown: TIM1, located between the semiconductor element and the semiconductor element cover, and TIM2, located between the semiconductor element cover and the heat sink. High pressure can be applied to TIM2 by tightening a screw. Other methods of applying pressure, such as tightening with a spring, may also be used. Furthermore, since both the semiconductor element cover and the heat sink have excellent physical strength, they can withstand strong pressure without problems.

[0020] On the other hand, it is undesirable to apply large pressure to semiconductor elements. Also, since the gap between the semiconductor element and the semiconductor element cover is of fixed dimensions, there is some pressure due to the repulsive force caused by the elasticity of TIM1 itself, but it is not subjected to the large external pressure that TIM2 is subjected to. Therefore, TIM1 needs to be able to form a sufficient heat dissipation path even under low pressure. Consequently, conventional graphite film TIMs that require high pressure can be used for TIM2 in Figure 2, but are not suitable for TIM1.

[0021] The present invention provides a method for effectively forming a heat dissipation passage in a gap where direct external pressure cannot be applied, and only pressure corresponding to the elastic force of the TIM itself is applied, by using a graphite thin film as the TIM, which has a thinner net thickness than conventional graphite film TIMs and possesses appropriate physical properties and wrinkle structure according to the size of the gap into which it is inserted.

[0022] The wrinkles in the graphite film used in this invention are defined below. Figure 3(a) shows a schematic cross-section of the graphite film. As shown in Figure 3(a), the net thickness of the graphite film without considering wrinkles is Ta. On the other hand, the thickness considering wrinkles is Tb. Here, in this invention, Tb is defined as four times the surface roughness Ra of the graphite film. Also, as shown in Figure 3(b), the size of the gap between the solids into which the graphite film is inserted is Gd.

[0023] The net thickness Ta of the graphite film used in this invention, excluding wrinkles, is 0.5 μm to 25 μm. Figure 4 shows a schematic diagram of the heat conduction routes between the graphite film and the solids forming the gaps. The graphite film is a solid, and as shown in Figure 4, the interface with another solid surface is in contact via point-like contacts. Therefore, when heat is transferred from a solid surface on one side of the graphite film to a solid surface on the opposite side of the graphite, heat conduction in the direction of the graphite film plane contributes significantly.

[0024] To increase heat conduction in the direction of the film plane, a larger cross-sectional area of ​​the heat conduction path in that direction is advantageous. In other words, a thicker graphite film is advantageous. Therefore, if the graphite film is too thin, sufficient heat conduction in the direction of the film plane will not occur, resulting in a large thermal resistance between the gaps. On the other hand, the fabricated graphite films with a net film thickness Ta exceeding 25 μm tended to have many irregularities and air layers in the graphite layer, resulting in hard and brittle films. If the film is hard, the contact area at the interface with the solid is small, resulting in a large contact thermal resistance, which is unfavorable for reducing thermal resistance between the gaps. Also, if the film is brittle, there is a possibility of undesirable effects such as fragments of the chipped graphite film contaminating the surroundings. For these reasons, it was determined that it is difficult to fabricate a graphite film with a film thickness Ta exceeding 25 μm that is suitable for the present invention.

[0025] Conversely, a thin graphite film is advantageous because the peaks and valleys of the wrinkles are flexible, making it easier to secure a contact area at the junction and thus reducing the contact thermal resistance. The net thickness Ta of the graphite film is preferably 1 μm or more and 20 μm or less, and more preferably 2 μm or more and 15 μm or less. It is even more preferably 3 μm or more and 10 μm or less.

[0026] The thickness Tb of the graphite film used in the present invention, considering wrinkles, is 1.2 times or more and within 100 times the thickness Ta without considering wrinkles. That is, 1.2Ta ≤ Tb ≤ 100Ta. Since Ta is a maximum of 25 μm, the maximum Tb is 2.5 mm. In order to allow the wrinkles in the graphite film to deform flexibly and easily increase the contact area with the solid surface, the ratio of Tb to Ta is 1.2 times or more, preferably 1.5 times or more, and more preferably 2.0 times or more. Furthermore, it is even more preferable that it is 5 times or more, or 10 times or more.

[0027] On the other hand, if Tb is too large relative to Ta, the heat conduction distance along the surface of the graphite film tends to increase, as shown in Figure 4. Also, the cross-sectional area of ​​the heat conduction path is proportional to the net thickness Ta of the graphite film, but this becomes relatively small compared to the heat conduction distance in the direction of the film surface. For these reasons, it is disadvantageous from the viewpoint of reducing the thermal resistance between gaps. For this reason, Tb should be 100 times or less than Ta, preferably 80 times or less, and even more preferably 50 times or less. Furthermore, it may even be 20 times or less.

[0028] The thickness Tb of the graphite film used in this invention, taking wrinkles into account, is between 0.4 and 15 times the gap Gd into which the graphite film is inserted. That is, 0.4Gd ≤ Tb ≤ 15Gd. If Tb is 0.4 times or more Gd, the ridges and valleys of wrinkles larger than the average of the graphite film can come into contact with the solid surface forming the gap to some extent, and heat conduction through the graphite film can be effectively utilized.

[0029] From the viewpoint of increasing the contact points between the graphite film and the solid forming the gap, it is preferable that 0.8Gd≦Tb is preferred, more preferable that 1.0Gd≦Tb is preferred, even preferable that 1.1Gd≦Tb is preferred, even preferable that 1.2Gd≦Tb is preferred, even preferable that 1.3Gd≦Tb is preferred, and even preferable that 1.4Gd≦Tb is preferred.

[0030] On the other hand, from the viewpoint of reducing the pressure on the gap-forming member (solid), it is preferable that Tb ≤ 10Gd, more preferable that Tb ≤ 5Gd, and even more preferable that Tb ≤ 3Gd.

[0031] Figure 5 shows a photograph of the surface of a graphite film used in the present invention. As you can see, uniform wrinkles are formed across the entire surface of the film. The average distance between the peaks of the wrinkles in a single graphite film can be, for example, 2 μm, 5 μm, 10 μm, 20 μm, 50 μm, 100 μm, 200 μm, 500 μm, 1000 μm, or 2000 μm, and such a graphite film can be used in the present invention.

[0032] In order to increase the areas that are in contact with the solid, such as the peaks and valleys of wrinkles, that is, the apex of the unevenness and the gaps, it is preferable that the spacing between the peaks of the wrinkles and between the valleys of the wrinkles be small. From this viewpoint, the spacing between the peaks of the wrinkles and between the valleys of the graphite film is preferably 1000 μm or less, more preferably 500 μm or less, more preferably 200 μm or less, and more preferably 100 μm or less.

[0033] On the other hand, if the spacing between the peaks of the wrinkles is small relative to the thickness of the graphite film, the pressure required to deform the peaks of the wrinkles tends to be large, and therefore the pressure between the graphite film and the solid surface forming the gap tends to be large. For this reason, it tends to be difficult to use in gaps where large pressure cannot or should not be applied. From this viewpoint, the average value of the spacing between the peaks of the wrinkles in the graphite film is preferably 5 μm or more, more preferably 10 μm or more, more preferably 20 μm or more, and more preferably 50 μm or more.

[0034] The density of the graphite film used in this invention is 1.8 g / cm³. 3 That concludes the explanation. As shown in Figure 4, it is also important that the thermal conductivity of the graphite film is high in the direction of film thickness. If there are voids (air layers) in the graphite film as shown in Figure 1, the thermal conductivity of the graphite film in the direction of film thickness will be low, so it is preferable that the graphite film does not contain air layers. The extent of the air layer can be estimated by measuring the density of the graphite film, and the density is one of the criteria for determining whether the graphite film is suitable for the present invention. The density of the graphite film used in the present invention is 1.8 g / cm³.3 The above is 1.9 g / cm³. 3 It is more preferable that it be greater than or equal to 2.0 g / cm³. 3 It is even more preferable that the amount be greater than or equal to 2.1 g / cm³. 3 The above is most preferable. The density of the graphite film is 2.26 g / cm³, which is the theoretical density of graphite crystals. 3 The results are as follows:

[0035] Figure 6 shows examples of cross-sections of the graphite film used in the present invention observed using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). As can be seen, unlike Figure 1, it is a graphite film composed of layered graphite crystals without voids (air layers). Although the graphite film of the present invention has wrinkles throughout the entire film surface as shown in Figure 5, these SEM and TEM images observe only very small areas, so the curvature of the graphite film cross-section, which corresponds to the wrinkles seen with the naked eye, is not visible in Figure 6, and the film surface and graphite layer appear linear.

[0036] The thermal conductivity of the graphite film used in this invention is 800 W / m·K or higher in the direction of the film plane. As shown in Figure 4, thermal conductivity in the direction of the film plane of the graphite film plays a major role in heat conduction between gaps. That is, since the contact points between the graphite film and the solid forming the gap are not necessarily directly above or directly below, smooth heat conduction in the direction of the graphite film is necessary to form an effective heat dissipation path between the gaps. In other words, the thermal conductivity of the graphite film in the direction of the film plane needs to be high. High thermal conductivity in the direction of the film plane also means that the density of the graphite film is high and the air layer tends to be small.

[0037] A high thermal conductivity in the direction of the graphite film plane is desirable, preferably 1000 W / m·K or higher. 1200 W / m·K or higher is even more desirable, 1500 W / m·K or higher is even more desirable, 1700 W / m·K or higher is still desirable, and 1800 W / m·K or higher is even more desirable. Furthermore, 1900 W / m·K or higher, and 2000 W / m·K or higher are preferred.

[0038] On the other hand, achieving high thermal conductivity in the plane of the film requires firing the graphite film at high temperatures for a long period of time, which is costly. Therefore, from a productivity standpoint, it is realistic to limit the thermal conductivity of the graphite film in the plane of the film to 2100 W / m·K or less.

[0039] The electrical conductivity of the graphite film used in this invention is 10,000 S / cm or higher in the direction of the film surface. The thermal conductivity that the graphite film of this invention should possess is as described above, but measuring the thermal conductivity of a graphite film is relatively time-consuming. Therefore, electrical conductivity in the direction of the film surface is used as a means to easily estimate the thermal conductivity of a graphite film. It is known that the higher the electrical conductivity, the higher the thermal conductivity, and an electrical conductivity of 10,000 S / cm in the direction of the film surface of a graphite film is roughly equivalent to a thermal conductivity of 800 W / m·K in the direction of the film surface.

[0040] The electrical conductivity of the graphite film in the direction of the film plane is preferably 12,000 S / cm, more preferably 14,000 S / cm, more preferably 16,000 S / cm, more preferably 18,000 S / cm, more preferably 20,000 S / cm, more preferably 22,000 S / cm, more preferably 24,000 S / cm, and more preferably 25,000 S / cm. On the other hand, achieving high electrical conductivity in the direction of the film plane requires firing the graphite film at high temperatures for a long period of time, which is costly. For this reason, an electrical conductivity of 26,000 S / cm or less in the direction of the film plane of the graphite film is realistic.

[0041] In this invention, the graphite film is subjected only to pressure caused by the deformation of wrinkles in the graphite film, which occurs when it is sandwiched between solids forming a gap. This pressure is calculated by dividing the force acting on the entire surface of the graphite film in the direction of film thickness by the projected area when the graphite film is viewed from directly above the film surface, and is 10 N / cm². 2 It is less than, for example, 8 N / cm². 2 , 6 N / cm 2 , 5 N / cm 2 , 4N / cm 2 , 3N / cm 2 , 2N / cm 2 , 1 N / cm 2 , 0.5 N / cm 2 , 0.2 N / cm 2 , 0.1 N / cm 2 , 0.05 N / cm 2 , 0.02 N / cm 2 , 0.01 N / cm 2 , 0.005 N / cm 2 , 0.002 N / cm 2 , 0.001 N / cm 2 Therefore, it is effectively 0 N / cm 2 That's fine.

[0042] Figure 7(a) shows one embodiment of the present invention in which a graphite film is inserted into the gap. Since the thickness Ta of the graphite is thin, the pressure between the gaps generated by the elasticity of the wrinkles in the graphite film is very small. Furthermore, if the apparent thickness Tb of the graphite film due to the wrinkles formed in the film is 0.4 times or more the gap gap Gd, at least a portion of the convex parts such as the peaks and valleys of the wrinkles in the graphite film will be in direct contact with the solid surface forming the gap, and an effective heat dissipation path will be formed between the gaps.

[0043] Figure 7(b) shows the situation when the gap gap Gd narrows due to reasons such as expansion of the solid forming the gap due to temperature rise. The graphite film of the present invention is characterized by its toughness and elasticity, so in response to changes in the gap gap, it can reversibly deform like a spring by changing the shape of the wrinkles, and can maintain contact with the solid forming the gap without being destroyed. At this time, the pressure on the solid forming the gap increases slightly, but it does not become a large pressure as long as the gap gap Gd does not narrow to the same as or less than the net thickness Ta of the graphite film.

[0044] From the viewpoint of reducing the pressure on the gap, the ratio of Gd to Ta, Gd / Ta, is preferably 1.3 or higher, more preferably 1.5 or higher, more preferably 2.0 or higher, even more preferably 4.0 or higher, and most preferably 6.0 or higher. On the other hand, from the viewpoint of improving heat conduction between the gaps, Gd / Ta is preferably 15 or lower, more preferably 12 or lower, even more preferably 10 or lower, and most preferably 8 or lower.

[0045] As shown in Figure 7(c), the thermal resistance between gaps can be further reduced by covering the surface of the solid forming the gap with a layer of flexible material, i.e., a flexible layer, and inserting a graphite film. This is because, generally, contact between solids is point-like contact between the protrusions of their surfaces, and the contact area is limited, whereas by providing a flexible layer, a large planar contact area can be obtained through the flexible layer.

[0046] The flexible layer may cover both sides of the graphite film, or it may be effective even if only one side is covered. Furthermore, the flexible layer may cover only the surface of the solid forming the gap, or it may cover both the graphite film and the surface of the solid forming the gap. Alternatively, the graphite film may be inserted into the gap by bonding the graphite film and the solid forming the gap via the coated flexible layer.

[0047] The flexible layer used for coating is preferably made of a material with excellent heat resistance and is an insulator. Suitable materials for the flexible layer that satisfy these conditions include, for example, silicone oil, ester oil, hydrocarbon oil, mineral oil, fluorine oil, polyglycol oil, and greases and gels based on these.

[0048] The flexibility layer can be effective even at thin thicknesses, such as 1 μm, 2 μm, 5 μm, 10 μm, 20 μm, or 50 μm. Unlike cases where the entire gap is filled solely with the flexibility layer, the risk of the flexibility layer leaking out is significantly reduced. Furthermore, the thermal diffusion effect of the graphite film prevents localized heat concentration in the flexibility layer and reduces the thermal load, effectively improving the durability of the flexibility layer.

[0049] Figure 7(d) is a schematic diagram showing a case where a stopper structure is provided in the solid forming the gap to prevent the graphite film from protruding from the gap. Shifting of the graphite film can be prevented by such a simple stopper structure.

[0050] Figure 7(e) is a schematic diagram showing the case where two graphite films are inserted into the gap. Multiple graphite films may be inserted into the gap in this manner, taking into account the balance of the gap distance Gd, the pressure between the gaps, the required heat conduction between the gaps, and the retention of the flexible layer. Furthermore, the number of graphite films inserted may be three, four, five, or more.

[0051] Figure 8(a) shows one embodiment of the present invention in which a graphite film is inserted into the gap between the semiconductor element and the semiconductor element cover. Since the net thickness Ta of the graphite film is smaller than the gap distance Gd between the semiconductor element and the semiconductor element cover, there is almost no pressure between the semiconductor element and the semiconductor element cover even when the graphite film is inserted. Due to the wrinkles in the graphite film, a portion of the graphite film is in direct contact with the surface of the semiconductor element and the inner surface of the semiconductor element cover.

[0052] Figure 8(b) is a schematic diagram of Figure 8(a) in which the inner surface of the semiconductor element cover is further coated with a flexible layer. When inserting the graphite film into the gap between the semiconductor element and the semiconductor element cover, it is preferable to include a process of attaching the graphite film to the semiconductor element cover or the semiconductor element using a flexible layer, as this makes it easier to prevent the graphite film from shifting.

[0053] The method of the present invention is also effective for semiconductor packages filled with resin. Figure 8(c) is a schematic diagram of a case in which a graphite film is inserted inside a semiconductor element cover filled with resin. By creating a structure in which a graphite film is inserted into the resin, the thermal resistance between the semiconductor element and the semiconductor element cover can be further reduced. As a result, the temperature of the semiconductor element can be lowered, and the thermal load and stress load on the package can be reduced.

[0054] For example, silicone gel or heat-resistant epoxy resin can be preferably used as the filler resin. In addition, in such a structure, the graphite film can also mitigate the concentration of heat generated in the filler resin and prevent the deterioration of the filler resin due to thermal load. Therefore, it becomes possible to use filler resins that are difficult to use on their own within semiconductor device covers.

[0055] The present invention can also be used in semiconductor packages containing multiple semiconductor elements. Figure 9 shows how the graphite film of the present invention is attached to the inner surface of a semiconductor element cover containing multiple semiconductor elements via a flexible layer, and is individually connected to each semiconductor element. Each semiconductor element and the graphite film may be in contact via the flexible layer, or they may be in direct contact. By using a structure in which contact is made via a flexible resin layer and a structure in which contact is not, heat can be dissipated more effectively in semiconductor packages containing multiple semiconductor elements.

[0056] In Figure 9, the semiconductor element labeled 8A (semiconductor element 2) refers to, for example, a memory chip, while the semiconductor element labeled 8B (semiconductor element 3) refers to, for example, a microprocessor or a system-on-a-chip (SoC). Since these semiconductor elements each generate different amounts of heat, selecting a contact method in this way allows for efficient heat dissipation and cooling.

[0057] The method of the present invention is also preferably used in 3D and 2.5D semiconductor packages. Heat generation is a serious problem in 3D and 2.5D packaging, and thermal countermeasures are particularly important in the stacking of central processing units (CPUs) and dynamic random-access memory (DRAMs). The formation of heat dissipation channels using the graphite film of the present invention is extremely effective in 3D semiconductor packages. As an example, Figure 10 shows an example in which the graphite film of the present invention is used in a 3D-packaged high-bandwidth memory system (HBM). The graphite film is inserted into the gap between the CPU / graphics processing unit (GPU) and the stacked DRAMs and the copper block (heat sink), forming a heat dissipation channel.

[0058] The method of the present invention can be widely used to form heat dissipation paths between gaps separated by vacuum, air, inert gas, etc. The method of the present invention is not limited to the material of the solid forming the gap, such as between metals, between metals and inorganic materials, between metals and organic materials, between inorganic materials, or between organic materials. Furthermore, since graphite films have particularly high heat resistance and are chemically stable, they can be effectively used to form heat dissipation paths between gaps that become particularly hot, such as in electric vehicles (EVs), power semiconductors, and semiconductor packages.

[0059] The graphite film used in the present invention can be produced by heat treatment of a heat-resistant aromatic polymer film. Among these, aromatic polyimide films are preferably used for the purposes of the present invention. For example, polyimide films abbreviated as PMDA-ODA type (pyromellitic dianhydride-4,4'-oxydianiline type) can be suitably used. The graphite film of the present invention is produced by the following process. First, a PMDA-ODA type polyimide film is inserted into a gap formed by graphite blocks, heated in nitrogen gas to cause thermal decomposition, and then heated to approximately 1000°C to carbonize it. The resulting carbonized film is then heated in argon gas to a maximum temperature of 2400 to 3100°C to graphite it.

[0060] The net thickness Ta of the graphite film, excluding wrinkles, is controlled by the thickness of the heat-resistant aromatic polymer film used as the starting material. Furthermore, physical properties such as thermal conductivity and electrical conductivity of the graphite film are primarily controlled by the maximum heating temperature. For example, in the case of a PMDA-ODA type polyimide film, the Ta value of the graphite film obtained by graphitization at 2800°C is approximately half the thickness of the starting polyimide film.

[0061] Furthermore, if the thickness of the graphite film is 25 μm or less, that is, if the thickness of the PMDA-ODA type polyimide film is approximately 50 μm or less, it is tough, elastic, and has a density of 1.8 g / cm³. 3 A graphite film can be obtained. The thermal conductivity in the direction of the film plane of a graphite film with a thickness of 25 μm or less, obtained by graphitization at a temperature of 2400°C or higher, is 800 W / m·K or higher. In addition, the electrical conductivity in the direction of the film plane is 10000 S / cm or higher.

[0062] In order to easily increase the thermal conductivity and electrical conductivity in the direction of the film surface, the graphitization temperature is preferably 2600°C or higher, more preferably 2700°C or higher, and most preferably 2800°C or higher. Above 3300°C, the sublimation of graphite makes it difficult to obtain the graphite film, and the consumption of the heater and insulation material of the electric furnace used for graphitization also increases rapidly, so the graphitization temperature is preferably 3300°C or lower.

[0063] The resulting graphite film exhibits high heat resistance of over 2000°C in a vacuum or inert gas, and heat resistance of 500-600°C in air. Therefore, the graphite film of the present invention has sufficient heat resistance for use in high-temperature gaps, such as inside semiconductor packages. Furthermore, the resulting graphite film is highly pure and highly crystalline, and contains virtually no impurities that cause gas generation during heating.

[0064] Wrinkles in graphite films are caused by the expansion and contraction of the film during the heat treatment processes of carbonization and graphitization. The size of the resulting wrinkles is controlled by conditions such as the heating rate during carbonization and graphitization. For example, a PMDA-ODA type polyimide film will shrink to about 68% of its original area and 96% of its thickness after heating to 800°C unless special techniques are used, such as firing it under tension in the direction of the film surface. If heated further to 2800°C, the thickness will decrease even more to about 50% of the original polyimide film, but the area will expand to 85-88% of the original polyimide film. Wrinkles inevitably occur in the film during this expansion and contraction process during heating.

[0065] Figure 11 shows an example of a carbonization and graphitization method for controlled wrinkle formation. Figure 11(a) shows a state in which a raw material polyimide film is set in a gap formed by graphite blocks, allowing it to stretch and contract freely in the direction of the film surface. The size of the gap is determined according to the value of Tb (thickness of the graphite film considering wrinkles) to be produced. Figure 11(b) shows a schematic diagram of the wrinkled graphite film of the present invention produced by this method. The range of wrinkle size in the graphite film is controlled by the size of the gap in the graphite block. Although it varies depending on the composition and thickness of the polyimide film, and the conditions during carbonization and graphitization, Tb is generally 0.5 to 1.2 times the size of the gap formed by the graphite block.

[0066] The present invention allows for the fabrication of films in which Tb is 1.2 times or more and 100 times or less than Ta. In a graphite film with a thickness Ta of 25 μm, if Tb / Ta is set to 100, Tb becomes 2.5 mm. Therefore, the maximum gap Gd that can be formed to create a heat dissipation path using a single graphite film is 2.5 mm / 0.4 times = 6.25 mm, and preferably 4.0 mm or less.

[0067] The method of the present invention can be more preferably used when the gap size Gd is 5 μm to 1 mm, and most preferably when it is 10 μm to 500 μm. On the other hand, there is no theoretical lower limit to the gap size, but considering the limit of the flatness of the solid surface forming the gap, it is practically considered that Gd should be 1 μm or more in order to prevent large pressure from being applied between the gaps. [Examples]

[0068] (Thermal resistance between gaps) Thermal resistance was measured using a thermal resistance measuring device manufactured by Hitachi Technology & Services, Ltd. The measurement was performed by placing the object to be measured, such as a graphite film or air, between two copper rods with parallel faces facing each other, heating one end of one copper rod, and cooling the other end of the other copper rod.

[0069] The temperature gradient obtained from thermocouples embedded at regular intervals in each copper rod was extrapolated to determine the temperatures of the surfaces of one copper rod in contact with the object being measured and the surfaces of the other copper rod in contact with the object being measured. The temperature difference ΔT between the copper rods was then calculated from the difference between these temperatures. The thermal resistance between the copper rods with the object being measured on either side was determined by dividing the obtained ΔT by the heat flux passing through the copper rods.

[0070] The contact area of ​​the copper rods with the object being measured is 10 mm x 10 mm. The temperature between the two copper rods, i.e., the average of the temperature of the contact surface of one copper rod with the object and the temperature of the contact surface of the other copper rod with the object, was considered as the temperature of the object being measured, and this was controlled to be 60°C. The contact surfaces of the two copper rods with the object were pre-polished to a mirror finish. When measuring thermal resistance, the gap size Gd (μm) between the copper rods and the pressure (N / cm) applied between the copper rods were measured. 2 ) is also measured using a thermal resistance measuring device.

[0071] The thermal resistance was measured when the gap between the copper rods of the measuring device, Gd, was kept at a predetermined distance, no graphite film was placed between the copper rods, and the gap was filled with air. The thermal resistance of air at each gap Gd was 4.0 K·cm for a gap of 10 μm. 2 For a wattage of 20 μm and a gap of 20 μm, the value is 8.4 K·cm. 2 For a wattage of 25 μm and a gap of 25 μm, the value is 10.2 K·cm. 2 For a wattage of 30 μm and a gap of 30 μm, the value is 12.0 K·cm. 2 For a wattage of 15.1 K·cm with a gap of 40 μm, the value is 15.1 K·cm. 2 For a wattage of 50 μm and a gap of 18.0 K·cm, the value is 1.0 K·cm. 2 For a wattage of 100 μm and a gap of 100 μm, the value is 34.7 K·cm. 2 For a wattage of 125 μm and a gap of 125 μm, the value is 42.2 K·cm. 2 It was / W.

[0072] (Net thickness of graphite film Ta) The net thickness Ta of the graphite film was measured using a contact-type thickness gauge, the CT2501, manufactured by Heidenhain Co., Ltd.

[0073] (Surface roughness Ra of graphite film) The surface roughness (arithmetic mean roughness) Ra of the graphite film was measured using a Surfcom DX surface roughness measuring instrument (manufactured by Tokyo Seimitsu Co., Ltd.) in accordance with JIS B 0601. For example, when Ra was greater than 10 μm and 80 μm or less, the evaluation length was set to 40 mm and the reference length L (cutoff value) to 8 mm. For other Ra values, the reference length was determined according to JIS B 0633. The thickness Tb, taking into account wrinkles in the graphite film, was set to four times the value of Ra.

[0074] (Density of graphite film) The density of the graphite film was measured using a dry-type automatic densimeter, Accupic II 1340 (manufactured by Shimadzu Corporation).

[0075] (Electrical conductivity of graphite film) The electrical conductivity of the graphite film was measured by cutting a 5mm x 5mm square sample from the graphite film, contacting electrodes with silver paste at the four corners (edges), and measuring the sheet resistance using the Van der Pauw method with a ResiTest 8300 resistivity / DC & AC Hall measurement system manufactured by Toyo Technica Corporation.

[0076] (Electrical conductivity of graphite film) The thermal diffusivity of the graphite film was measured at 23°C under vacuum and at 10Hz using a thermal diffusivity measurement device (LaserPit, manufactured by ULVAC, Inc.) based on the optical AC method. The thermal conductivity was calculated from the measured thermal diffusivity using the density and specific heat values ​​of the graphite film.

[0077] (Examples 1-17) In Examples 1 and 17, a PMDA-ODA type polyimide film was inserted into the gaps of a graphite block as shown in Figure 11, heated at 1000°C for 30 minutes in a nitrogen gas atmosphere to carbonize it, and then heated at 2700°C for 10 minutes in an argon gas atmosphere to graphitize it, thereby obtaining a graphite film. In Examples 2 to 16, the heating in the graphitization process was 2800°C for 20 minutes, while the other procedures were the same.

[0078] Next, after inserting a graphite film between sufficiently spaced copper rods, the gap distance Gd was set to a predetermined value, and the thermal resistance was measured. Furthermore, the fraction of the thermal resistance when the gap was filled with air was calculated. The results are shown in Table 1. Note that in Examples 1 to 17, the pressure applied to the gap was 5 N / cm² in all cases. 2 The results were as follows:

[0079] [Table 1] The thermal resistance obtained when a graphite film is inserted into a gap varies depending on the net thickness Ta of the graphite film, the thickness Tb considering wrinkles, and the thermal conductivity, but when the gap Gd is 10 μm (Examples 1-5), it is 0.46-1.48 K·cm. 2 The result was / W. The thermal resistance of air with a gap of 10 μm is 4.0 K·cm, as shown above. 2 Since the value was / W, the thermal resistance could be reduced to 1 / 2.7 to 1 / 8.7 by inserting a graphite film.

[0080] Similar effects were observed even with different Gd values. When a graphite film was used between the gaps, the thermal resistance could be reduced to as low as 1 / 27, demonstrating a significant reduction in thermal resistance. In other words, the formation of a heat dissipation path was confirmed.

[0081] Since air has high thermal resistance, even if the thermal resistance is reduced to, for example, 1 / 1.5 of that of air, it is considered that this is not sufficient to form a heat dissipation path between the gaps. For this reason, in this invention, a heat dissipation path is considered to have been formed when the thermal resistance between the gaps can be reduced to 1 / 2 or less compared to the case where there is air.

[0082] As shown in Examples 2-5, when Gd is the same value, a greater reduction in thermal resistance tended to be observed when the net thickness Ta of the film was greater and Tb / Ta was smaller, compared to when the gap was filled with air. This is thought to be because a larger Ta results in a larger cross-sectional area of ​​the heat conduction path in the direction of the graphite film, which is advantageous for heat conduction as shown in Figure 4. Also, a smaller Tb / Ta results in a larger Ta, and a shorter heat conduction distance in the direction of the graphite film between the contact points of the graphite film and the solid (copper rod) forming the gap, which is also considered advantageous for reducing the thermal resistance between the gaps.

[0083] Furthermore, as shown in Examples 16 and 17, even if Ta is the same, if the thermal conductivity or electrical conductivity in the plane direction of the graphite film is relatively low, the effect of reducing thermal resistance is also relatively small.

[0084] Furthermore, as shown in Examples 14 and 15, when the net thickness Ta of the film is the same, a larger Tb / Ta ratio tended to result in a greater reduction in thermal resistance compared to the case where the gap is filled with air. This is thought to be because a larger Tb / Ta ratio means that the size of the peaks and valleys of the wrinkles is larger than that of the net film thickness Ta, allowing the wrinkles to deform more flexibly through contact with the solid forming the gap, and consequently increasing the total contact area of ​​all contact points.

[0085] If Tb / Gd is 1.0 or higher, the thermal resistance is less than 1 / 6.3 of that when the gap is filled with air, indicating that the thermal resistance has been effectively reduced. Thus, it can be seen that sufficient heat dissipation passages can be formed if the peaks and valleys of the wrinkles in the graphite film of the present invention make minimal contact with the solid forming the gap. In other words, it can be seen that even without applying a large external pressure between the gaps, it is sufficient for the graphite film to make minimal contact with the solid forming the gap due to the elasticity of the wrinkles.

[0086] On the other hand, as in Examples 1 and 2, when Ta is the same but Tb / Gd is small at 0.5, the reduction in thermal resistance was not that significant, at 1 / 2.7 compared to when the gap was filled with air. This is thought to be because only a limited portion of the peaks and valleys of the graphite film's wrinkles are in contact with the solid forming the gap, and therefore the number of contact points, i.e., the total contact area, is not that large. Furthermore, as in Example 10, even if multiple graphite films are stacked and inserted between gaps, a heat dissipation path can be effectively formed between the gaps.

[0087] (Examples 18-23) Silicone grease was applied to both sides of the graphite films in Examples 5, 7, 8, 9, 13, and 16, and thermal resistance measurements were performed in the same manner as in Examples 5, 7, 8, 9, 13, and 16. The results are shown in Table 2. In Examples 18-23, the pressure applied across the gap was 5 N / cm² in all cases. 2 The results were as follows:

[0088] [Table 2] Compared to the thermal resistance when only air is present in the gap, applying 20 mg / cm² of silicone grease to both sides... 2 The thermal resistance when the coated graphite film was inserted could be reduced to 1 / 15 to 1 / 41. Furthermore, as can be seen from the comparison of Examples 5 and 18, Examples 7 and 19, Examples 8 and 20, Examples 9 and 21, Examples 13 and 22, and Examples 16 and 23, using a graphite film coated with grease can further reduce thermal resistance compared to using a graphite film without grease.

[0089] (Examples 24-26, Comparative Example 1) Using the graphite film from Example 13, the size of the gap spacing Gd was varied, and thermal resistance measurements were performed in the same manner as in Examples 1 to 17. The results are shown in Table 3. In Examples 24 to 26, the pressure applied across the gap was 5 N / cm² in all cases. 2 The results were as follows:

[0090] [Table 3] As the gap spacing Gd decreases, the thermal resistance decreases. When Gd is set to 1.26 times the net film thickness Ta (Comparative Example 1), the thermal resistance is 0.18 K·cm. 2 The result was / W (1 / 57 of the thermal resistance of the air gap). This result indicates that when the gap distance decreases due to reasons such as the expansion of the solid forming the gap as the temperature rises, the thermal resistance decreases, improving the heat dissipation and cooling efficiency, which is one of the advantages of the present invention.

[0091] On the other hand, in Comparative Example 1, the pressure across the gap was 10 N / cm². 2 The values ​​were as large as shown above. This is thought to be because the Gd / Ta ratio was less than 1.3 times, and the gap spacing Gd was small, not much different from the net thickness Ta of the graphite film, so the pressure generated by the compression of wrinkles in the graphite film increased rapidly.

[0092] When Tb / Gd is 0.56 (Example 26), the thermal resistance is 6.82 K·cm. 2 The result was / W, which is 1 / 5.1 of the thermal resistance of the air gap, indicating that the effect of reducing thermal resistance was not very significant. When Tb / Gd is 1.1 (Example 13), the effect of reducing thermal resistance is relatively large, so it can be seen that Tb / Gd is preferably 1.0 or higher. On the other hand, even when Tb / Gd is 0.56, the thermal resistance is significantly reduced compared to when there is air between the gaps, indicating that an effective heat dissipation path can be formed.

[0093] (Examples 27-30) Thermal resistance measurements were performed in the same manner as in Examples 1 to 17 using graphite films with approximately the same net thickness Ta and Tb / Ta as in Example 13, but with different thermal and electrical conductivity in the film plane direction. The thermal and electrical conductivity in the film plane direction of the graphite films were adjusted by changing the maximum heating temperature and heating time during graphitization.

[0094] In Example 27, a PMDA-ODA type polyimide film was inserted into the gap of a graphite block as shown in Figure 11, heated at 1000°C for 30 minutes in a nitrogen gas atmosphere to carbonize it, and then heated at 2950°C for 40 minutes in an argon gas atmosphere to graphitize it, thereby obtaining a graphite film. In Example 28, the heating for graphitization was 2750°C for 20 minutes, and the rest was the same as in Example 27. In Example 29, the heating for graphitization was 2700°C for 10 minutes, and the rest was the same as in Example 27. In Example 30, the heating for graphitization was 2600°C for 10 minutes, and the rest was the same as in Example 27. The results of the thermal resistance measurement are shown in Table 4. Note that the pressure applied across the gap in all Examples 27 to 30 was 5 N / cm 2 The results were as follows:

[0095] [Table 4] These results show that the greater the thermal and electrical conductivity of the graphite film inserted between the gaps in the direction of the film plane, the greater the reduction in thermal resistance compared to when the gap is filled with air. If the thermal conductivity of the graphite film in the direction of the film plane is 820 W / m·K, the thermal resistance is 1 / 3.4 compared to when the gap is filled with air. Although the reduction in thermal resistance is relatively small compared to other graphite films, it is effective in forming a heat dissipation path.

[0096] (Comparative Examples 2-6) In Comparative Examples 2-4, a PMDA-ODA type polyimide film was inserted into the gaps of a graphite block as shown in Figure 11, heated at 1000°C for 30 minutes in a nitrogen gas atmosphere to carbonize it, and then heated at 2800°C for 20 minutes in an argon gas atmosphere to graphitize it, thereby obtaining a graphite film. In Comparative Example 5, the heating for graphitization was 2700°C for 10 minutes, and the rest was the same as in Comparative Examples 2-4. In Comparative Example 6, the heating for graphitization was 2750°C for 20 minutes, and the rest was the same as in Comparative Examples 2-4. Thermal resistance measurements were performed on the obtained graphite films in the same manner as in Examples 1-17. The results are shown in Table 5. In Comparative Examples 2-6, the pressure applied across the gaps was 5 N / cm² in all cases. 2 The results were as follows:

[0097] [Table 5] Comparative Example 2 has a net thickness Ta of 0.4 μm for the graphite film, and its thermal resistance is 1 / 1.9 compared to the case where the gap is filled with air, indicating that the effect of reducing thermal resistance is insufficient. This is thought to be because the cross-sectional area (thickness) of the heat conduction path in the direction of the graphite film surface is small, which is unfavorable for heat conduction as shown in Figure 4.

[0098] Comparative Example 3 has a Tb / Gd ratio of 0.28, and its thermal resistance is 1 / 1.2 compared to the case where the gap is filled with air, indicating that the thermal resistance reduction effect is insufficient. This is likely because the gap spacing Gd is more than three times larger than the graphite film thickness Tb considering wrinkles, meaning that many of the peaks and valleys of the wrinkles in the graphite film are not in contact with the solid forming the gap.

[0099] In Comparative Examples 4-6, the net thickness Ta of the graphite film was greater than 25 μm, and the thermal resistance was more than 1 / 1.9 compared to the case where the gap was filled with air, indicating that the effect of reducing thermal resistance was insufficient. As mentioned above, this is thought to be because the toughness and elasticity of the graphite film were insufficient, and the total contact area between the graphite film and the solid forming the gap was small. Furthermore, the density of the graphite film was low, and there were many voids (air layers) between the graphite layers, which is also unfavorable for heat conduction in the direction of the graphite film thickness. [Explanation of Symbols]

[0100] 1. Conventional graphite film TIM 2. Layer structure of graphite 3. Interlayer voids (air layers) in graphite 4. Heatsink 5. Tightening screws 6. Semiconductor element cover 7. Package substrate 8. Semiconductor devices 9. Bonding layer 10. TIM1 11. TIM2 12. Graphite film TIM of the present invention Ta. Net thickness of the film without considering wrinkles. Tb. Film thickness considering wrinkles (4 times the arithmetic mean roughness Ra of the film) 13. Solids that form gaps Gd. Gap interval 12A. Cross-section of the graphite film TIM of the present invention 14. Thermal conduction in the film thickness direction within a graphite film 15. Thermal conduction in the plane of the graphite film 16. Gap (air) 17. Contact Point 18. Flexible layer 18A. Filling resin 8A. Semiconductor device 2 8B. Semiconductor device 3 4A. Copper block (heat sink) 19. Memory 20. Bump 20A. Bump 2 21. Logic Semiconductors 22. Interposer 23. Solder ball 24. CPU / GPU 25. Polyimide film 26. Graphite Block 27. Gap in the graphite block

Claims

1. The thickness Ta is 0.5 μm or more and 25 μm or less, wrinkles are formed, the thermal conductivity in the direction of the film surface is 800 W / m·K or more, and the density is 1.8 g / cm³. ３ The present invention relates to a method for forming a heat dissipation path by inserting a graphite film, as described above, into a gap where no external pressure is directly applied, wherein the dimensions are 1.2Ta ≤ Tb ≤ 100Ta, 0.4Gd ≤ Tb ≤ 15Gd, 1.3Ta ≤ Gd, and the pressure applied in the direction of the graphite film thickness is 10 N / cm². ２ A method for forming a heat dissipation path, characterized in that it is less than [a certain value]. (Ta: Net graphite film thickness without considering wrinkles. Tb: Apparent graphite film thickness considering wrinkles (4 times the arithmetic mean roughness Ra of the graphite film). Gd: Gap spacing for inserting the graphite film)

2. A method for forming a heat dissipation path according to claim 1, characterized in that 1.0Gd ≤ Tb.

3. The pressure applied in the direction of the graphite film thickness is 5 N / cm ２ A method for forming a heat dissipation path according to claim 1 or 2, characterized in that it is as follows:

4. A method for forming a heat dissipation path according to claim 1 or 2, wherein the electrical conductivity of the graphite film in the direction of the film surface is 10,000 S / cm or more.

5. A method for forming a heat dissipation path according to claim 1 or 2, wherein the graphite film surface or the surface of the member forming the gap is covered with a flexible layer.

6. The method for forming a heat dissipation channel according to claim 1 or 2, wherein the graphite film is obtained by heat-treating an aromatic polymer film at 2400°C or higher in an inert gas atmosphere.

7. A method for forming a heat dissipation passage according to claim 1 or 2, wherein an aromatic polymer film is inserted between gaps in graphite and heat-treated to produce a graphite film having wrinkles.

8. The method for forming a heat dissipation path according to claim 7, wherein the size of the wrinkles in the graphite film is controlled by the size of the gaps between the graphite particles.

9. A method for manufacturing a semiconductor package, wherein the method for forming a heat dissipation path described in claim 1 or 2 is applied to the gap between the semiconductor element and the inner surface of the semiconductor element cover.

10. The thickness Ta is 0.5 μm or more and 25 μm or less, wrinkles are formed, the thermal conductivity in the direction of the film surface is 800 W / m·K or more, and the density is 1.8 g / cm³. ３ The graphite film described above is a heat dissipation path inserted between gaps where no external pressure is directly applied, with the following conditions: 1.2Ta ≤ Tb ≤ 100Ta, 0.4Gd ≤ Tb ≤ 15Gd, 1.3Ta ≤ Gd, and the pressure applied in the direction of the graphite film thickness is 10 N / cm². ２ A heat dissipation path characterized by being less than [amount]. (Ta: Net thickness of the graphite film without considering wrinkles. Tb: Apparent thickness of the graphite film considering wrinkles before insertion into the gap (4 times the arithmetic mean roughness Ra of the graphite film). Gd: Gap spacing for inserting the graphite film)

11. A semiconductor package in which the heat dissipation path described in claim 10 is applied to the gap between the semiconductor element and the inner surface of the semiconductor element cover.

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