Method of producing semiconductor device, thermoconductive sheet, and method of producing thermoconductive sheet

Abstract

A method for manufacturing a semiconductor device includes the following steps: applying pressure to a heat-generating element and a heat-dissipating element disposed therebetween, in the thickness direction of the heat-conducting sheet, thereby bonding the heat-generating element and the heat-dissipating element together via the heat-conducting sheet, wherein the heat-conducting sheet has a compressive modulus of 1.40 MPa or less at 150°C and a compressive stress of 0.10 MPa, and an adhesive strength of 5.0 N·mm or more at 25°C.

Description

[Technical Field]

[0001] This case relates to a method for manufacturing a semiconductor element, a thermally conductive sheet, and a method for manufacturing a thermally conductive sheet. [Previous Technology]

[0002] In recent years, with the increasing density of circuits in multilayer circuit boards, the increasing density of circuits in semiconductor packages, the increasing density of electronic components, and the increasing heat generation per unit area due to the high integration of semiconductor components, there is a growing expectation to improve the heat dissipation of semiconductor packages.

[0003] Among them, semiconductor components such as CPUs (Central Processing Units) and power components, which generate a lot of heat, require excellent heat dissipation. These semiconductor components have a mechanism for heat dissipation by sandwiching a thermally conductive material such as thermal paste or thermally conductive sheet between the heat-generating element and a heat sink such as aluminum or copper, and ensuring a tight seal (see, for example, Patent Documents 1-4). [Prior Art Documents] (Patent Documents)

[0004] Patent Document 1: Japanese Patent Application Publication No. 05-247268; Patent Document 2: Japanese Patent Application Publication No. 10-298433; Patent Document 3: Japanese Patent No. 4743344; Patent Document 4: Japanese Patent No. 5316254 [Summary of the Invention]

[0005] [Problem to be Solved by the Invention] In recent years, with the increasing performance of semiconductor packages, the size of semiconductor wafers and semiconductor packages has continued to grow. Due to this increase in size, when thermal paste is used as a thermal conductive material, pump-out is prone to occur during thermal cycling, making it increasingly difficult to ensure adequate heat dissipation. On the other hand, when thermal conductive sheets are used as thermal conductive materials, the following problem arises: because the warpage of semiconductor wafers or semiconductor packages increases due to the increase in the size of the heat-generating element, the thermal conductive sheets are prone to peeling off from the heat-generating element and heat sink, making it difficult to ensure heat dissipation.

[0006] In view of this situation, the problem to be solved in this case is to provide: a method for manufacturing a semiconductor device with excellent heat dissipation; a thermally conductive sheet capable of manufacturing a semiconductor device with excellent heat dissipation; and a method for manufacturing the thermally conductive sheet. [Technical Means for Solving the Problem]

[0007] The technical means to solve the above problems include the following aspects. <1> A method for manufacturing a semiconductor element, comprising the steps of: applying pressure to a heat-generating element and a heat-dissipating element disposed therebetween, in the thickness direction of the heat-conducting sheet, and bonding the heat-generating element and the heat-dissipating element together via the heat-conducting sheet, wherein the compressive modulus of the heat-conducting sheet is 1.40 MPa or less at 150°C and a compressive stress of 0.10 MPa, and the adhesive force is 5.0 N·mm or more at 25°C. <2> The method for manufacturing a semiconductor element as described in <1>, wherein the thermal conductivity of the heat-conducting sheet, determined by the thermal resistance measured by the steady-state method, is 7 W / (m·K) or more. <3> The method for manufacturing a semiconductor element as described in <1> or <2>, wherein the aforementioned pressure is 0.05 MPa to 10.00 MPa. <4> A method for manufacturing a semiconductor element as described in <3>, wherein the aforementioned pressure is 0.10 MPa to 0.50 MPa. <5> A method for manufacturing a semiconductor element as described in any one of <1> to <4>, wherein the aforementioned heating element is a semiconductor wafer and the aforementioned heat sink is a heat sink. <6> A method for manufacturing a semiconductor element as described in any one of <1> to <5>, wherein the area of ​​the surface of the aforementioned heating element facing the aforementioned thermally conductive sheet is 25 mm² or more. <7> A method for manufacturing a semiconductor element as described in any one of <1> to <4>, wherein the aforementioned heating element is a semiconductor package equipped with a heat sink and the aforementioned heat sink is a heat sink plate. <8> A method for manufacturing a semiconductor element as described in any one of <1> to <4>, wherein the aforementioned heating element is a semiconductor module. <9> A method for manufacturing a semiconductor element as described in any one of <1> to <8>, wherein the area of ​​the surface of the aforementioned heating element facing the aforementioned thermally conductive sheet is 100 mm² or more. <10> A thermally conductive sheet having a compressive modulus of elasticity of 1.40 MPa or less at 150°C and a compressive stress of 0.10 MPa, and an adhesive strength of 5.0 N·mm or more at 25°C, and the thermally conductive sheet is used to bond the heat-generating element and the heat sink of a semiconductor device. <11> The thermally conductive sheet as described in <10> has a thermal conductivity of 7 W / (m·K) or more, determined by the thermal resistance measured by a steady-state method. <12> The thermally conductive sheet as described in <10> or <11>, wherein the heat-generating element is a semiconductor wafer and the heat sink is a heat sink. <13> The thermally conductive sheet as described in <10> or <11>, wherein the heat-generating element is a semiconductor package equipped with a heat sink and the heat sink is a heat sink sheet. <14> The thermally conductive sheet as described in <10> or <11>, wherein the aforementioned heating element is a semiconductor module.<15> A method for manufacturing a heat-conducting sheet, wherein the heat-conducting sheet is used to bond the heat-generating element and the heat-dissipating element together via the heat-conducting sheet when pressure is applied to a heat-generating element and a heat-dissipating element disposed therebetween in the thickness direction of the heat-conducting sheet. The method for manufacturing the heat-conducting sheet includes the following steps: selecting the compression ratio and thickness of the heat-conducting sheet such that the compression amount of the heat-conducting sheet satisfies the following formula: Formula: C > L2 - L1; where L1 is the predicted warpage amount (μm) of the heat-generating element under heating and pressurization, L2 is the predicted warpage amount (μm) of the heat-generating element when cooled to 25°C after the heating and pressurization ends, and C is the predicted compression amount (μm) of the heat-conducting sheet under heating and pressurization conditions and C = thickness of the heat-conducting sheet before pressurization (μm) × compression ratio (%) under heating and pressurization conditions. [Effectiveness].

[0008] According to this case, it is possible to provide: a method for manufacturing a semiconductor device with excellent heat dissipation; a thermally conductive sheet capable of manufacturing a semiconductor device with excellent heat dissipation; and a method for manufacturing the thermally conductive sheet.

Implementation Method

[0010] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps, etc.) are not essential unless specifically specified. The numerical values ​​and ranges are also the same and are not intended to limit the present invention.

[0011] In this case, the term "step" includes steps that are independent of other steps, even if they cannot be clearly distinguished from other steps, as long as the purpose of the step can be achieved. In this case, the numerical range indicated by "~" includes the values ​​recorded before and after "~" as the minimum and maximum values, respectively. In the numerical ranges recorded in stages in this case, the upper or lower limit value recorded in one numerical range can be replaced by the upper or lower limit value of other numerical ranges recorded in stages. Furthermore, in the numerical ranges recorded in this case, the upper or lower limit value of the numerical range can be replaced by the value disclosed in the embodiments. In this case, each component may contain a plurality of substances equivalent to each component. When a plurality of substances equivalent to each component are present in the composition, the content or percentage of each component, unless otherwise specified, means the total content or percentage of the plurality of substances present in the composition. In this case, the particles equivalent to each component may contain a plurality of types. When a composition contains a plurality of particles corresponding to each component, the particle size of each component, unless otherwise specified, refers to the value of the mixture of the plurality of particles present in the composition. In this case, the term "layer" includes not only the case where the layer is formed entirely within the region where it exists, but also the case where it is formed only within a portion of the region. In this case, the term "layering" indicates the stacking of layers, which can be two or more layers combined together, or two or more layers that can be separated. In this case, when describing an embodiment with reference to the drawings, the composition of that embodiment is not limited to the composition shown in the drawings. Furthermore, the sizes of the components in the drawings are merely conceptual, and the relative sizes of the components are not limited thereto.

[0012] Manufacturing Method of Semiconductor Element The manufacturing method of the semiconductor element of this invention includes the following steps: applying pressure in the thickness direction of a heat-generating element and a heat-dissipating element with a thermally conductive sheet disposed therebetween, thereby bonding the heat-generating element and the heat-dissipating element through the thermally conductive sheet. The thermally conductive sheet has a compressive modulus of elasticity of 1.40 MPa or less at 150°C and a compressive stress of 0.10 MPa, and an adhesive strength of 5.0 N·mm or more at 25°C. By using the manufacturing method of the semiconductor element of this invention, peeling of the thermally conductive sheet can be suppressed, thereby manufacturing a semiconductor element with excellent heat dissipation.

[0013] [Heat-generating element] In this case, the heat-generating element is an object that dissipates heat by bonding a heat sink together with a thermally conductive sheet. Examples of heat-generating elements include: semiconductor wafers, semiconductor packages, automotive power modules, and industrial power modules. Furthermore, a heat-generating element does not necessarily mean that the component in contact with the thermally conductive sheet itself can generate heat. For example, when the thermally conductive sheet is used for the application of the thermally conductive material (thermal interface material 2, TIM2) described later, although the heat sink of the semiconductor package is in contact with the thermally conductive sheet, the semiconductor package with the heat sink is considered a "heat-generating element".

[0014] There is no particular limitation on the size of the heating element. For example, when the thermally conductive sheet is used in the application of the thermally conductive material (thermal interface material 1, TIM1) described later, the area of ​​the surface of the heating element facing the thermally conductive sheet can be 25 mm2 or more, or 100 mm2 or more, or 200 mm2 or more, or 400 mm2 or more. The area of ​​the surface of the heating element facing the thermally conductive sheet can, for example, be 15000 mm2 or less, or 5000 mm2 or less, or 2000 mm2 or less. When the thermally conductive sheet is used in the application of TIM2 described later, the area of ​​the surface of the heating element facing the thermally conductive sheet can be 100 mm2 or more, or 400 mm2 or more, or 1000 mm2 or more. The area of ​​the surface of the heating element facing the heat-conducting sheet can be, for example, 40,000 mm² or less, 20,000 mm² or less, or 5,000 mm² or less. When the heat-conducting sheet is used for electrical component applications described later, the area of ​​the surface of the heating element facing the heat-conducting sheet can be 100 mm² or more, 400 mm² or more, or 1,000 mm² or more. The area of ​​the surface of the heating element facing the heat-conducting sheet can be, for example, 40,000 mm² or less, 20,000 mm² or less, or 5,000 mm² or less.

[0015] [Heat Dissipator] The heat dissipator in this case is a component used to dissipate heat from a heat-generating body via a heat-conducting fin. Examples of heat dissipators include: radiators, heat sinks, cooling pipes, etc.

[0016] [Thermal Conductive Sheet] The thermal conductive sheet of this invention is a sheet used to bond the heat-generating element and the heat-dissipating element of a semiconductor device. In this invention, "sheet" refers to a non-liquid sheet-like product, distinguishing it from liquid thermal pastes, etc. Here, "liquid" means a substance with a viscosity of 1000 Pa·s or less at 25°C. Viscosity is defined as the value measured at 25°C using a rheometer at a shear rate of 5.0 s⁻¹. The viscosity is measured as shear viscosity at 25°C using a rotary shear viscometer equipped with a cone plate (40 mm in diameter, cone angle 0°).

[0017] When thermal paste is used as the thermally conductive material between the heat source and the heat sink, there is a possibility that the thermal resistance may increase due to leakage of the thermal paste during thermal cycling. However, since a thermally conductive sheet is used in the manufacturing method of this invention, leakage does not occur. Furthermore, when a sheet is used as the thermally conductive material, sometimes the sheet may peel off as the warp of the heat source increases, thus failing to achieve the desired heat dissipation. However, the thermally conductive sheet used in this invention can maintain sufficient adhesion area between the heat source and the heat sink even in semiconductor packages with increased warp. This ensures excellent heat dissipation characteristics. Although the reason may not be clear, we believe that if a thermally conductive sheet with the aforementioned specific compressive modulus and adhesive strength is placed between the heat source and the heat sink and pressure is applied, the thermally conductive sheet will deform sufficiently and adhere sufficiently to the heat source and the heat sink. Therefore, even if the warp changes after pressure is applied, the adhesion area can still be maintained by following the warp.

[0018] If the bonding area can be maintained without the thermally conductive sheet peeling off from the heat-generating element and the heat sink, the increase in contact thermal resistance can be suppressed, thereby suppressing the decrease in the heat dissipation characteristics of the semiconductor device. Therefore, even if the heat-generating element warps, the bonding area between the thermally conductive sheet and the heat-generating element and the heat sink is maintained.

[0019] The thermally conductive sheet used in this case can be used to bond the heat-generating element and the heat sink of a semiconductor, and its application is not particularly limited. The thermally conductive sheet can be, for example, a thermally conductive material (TIM1: Thermal Interface Material 1) disposed between the heat-generating element, i.e., the semiconductor wafer, and the heat sink, i.e., the heat radiator. Alternatively, it can be a thermally conductive material (TIM2: Thermal Interface Material 2) disposed between the heat-generating element, i.e., the semiconductor package with a heat sink, and the heat sink, i.e., the heat fin. Furthermore, it can also be a thermally conductive material (such as thermally conductive materials for power components) disposed between the heat-generating element, i.e., the semiconductor module, and the heat sink.

[0020] In the past, thermal paste has been used for TIM1. In the field of TIM1, with the increasing size of the heat-generating element, it is difficult to ensure sufficient heat dissipation by thermal paste. Therefore, the thermally conductive sheet used in this case is particularly useful.

[0021] Figure 1 illustrates a specific example of the application of a thermally conductive sheet as TIM1. The thermally conductive sheet 1 is used in such a way that one side is tightly bonded to the semiconductor wafer 2 (heat source) and the other side is tightly bonded to the heat sink 3 (heat sink). In Figure 1, the semiconductor wafer 2 (heat source) is fixed to the substrate 4 using a bottom filler material 5, and the heat sink 3 (heat sink) is fixed to the substrate 4 using a sealing material 6, and the tightness between the thermally conductive sheet 1 and the semiconductor wafer 2 and the heat sink 3 is improved by pressing. The heat source and the heat sink are stacked together via the thermally conductive sheet, which allows for efficient heat conduction from the heat source to the heat sink. If heat conduction is efficient, a semiconductor device can be provided that has an increased lifespan during use and functions stably even after long-term use.

[0022] The thermally conductive sheet used in this case has a compressive modulus of elasticity of 1.40 MPa or less at 150°C and a compressive stress of 0.10 MPa, and an adhesive strength of 5.0 N·mm or more at 25°C. We believe that since the compressive modulus of elasticity and adhesive strength meet the above ranges, the thermally conductive sheet can maintain a tight seal between the heat-generating element and the heat sink, and thus maintain the adhesive area, even in semiconductor devices where the warpage of the heat-generating element increases. We believe that this ensures heat dissipation.

[0023] We believe that if the compressive modulus of elasticity is below 1.40 MPa at 150℃ and a compressive stress of 0.10 MPa, the thermally conductive sheet exhibits excellent flexibility. When pressure is applied, the thermally conductive sheet easily deforms and adheres more readily to the heating and cooling elements. Furthermore, we believe that even if the warpage of the heating element increases after pressure is applied, the thermally conductive sheet will still adhere stably to the heating and cooling elements, thus suppressing the reduction of the bonding area.

[0024] The thermally conductive sheet has a compressive modulus of elasticity of 1.40 MPa or less, preferably 1.30 MPa or less, and more preferably 1.20 MPa or less, at 150°C and a compressive stress of 0.10 MPa. If the compressive modulus of elasticity is 1.20 MPa or less, the sealing performance will be further improved, and it will be easier to follow warpage. There is no particular limitation on the lower limit of the compressive modulus of elasticity at 150°C and a compressive stress of 0.10 MPa. The compressive modulus of elasticity can be 0.50 MPa or more, or 0.70 MPa or more.

[0025] The compressive modulus of elasticity of the thermally conductive sheet can be measured using a compression testing device (e.g., INSTRON 5948 Micro Tester (INSTRON Corporation)). A load is applied to the thermally conductive sheet in the thickness direction at a displacement rate of 0.1 mm / min, and the displacement (mm) and load (N) are measured. The strain (dimensionless) obtained from displacement (mm) / thickness (mm) is displayed on the horizontal axis, and the stress (MPa) obtained from load (N) / area (mm2) is displayed on the vertical axis. The slope at a specified stress is set as the compressive modulus of elasticity (MPa). Specifically, the measurement can be performed using, for example, the method described in the embodiments.

[0026] The adhesion of the thermally conductive sheet at 25°C is 5.0 N·mm or more, preferably 6.0 N·mm or more, and more preferably 7.0 N·mm or more. If the adhesion is 5.0 N·mm or more, there is a tendency to suppress the thermally conductive sheet from the heat-generating element and the heat-dissipating element when warping occurs and the distance between them increases. There is no particular limitation on the upper limit of the adhesion. The adhesion can be 20.0 N·mm or less, or 15.0 N·mm or less.

[0027] The adhesive force of the thermally conductive sheet at 25°C can be measured using a universal physical property testing machine (e.g., a texture analyzer (Eng Hong Precision Machinery Co., Ltd.)). At 25°C (room temperature), a probe with a diameter of 7 mm is pressed onto the thermally conductive sheet with a load of 40 N and held for 10 seconds. The area obtained by integrating the load-displacement curve when the probe is lifted is then set as the adhesive force (N·mm) at 25°C. Specifically, the measurement can be performed using, for example, the method described in the examples.

[0028] The thermally conductive sheet has a compressive modulus of 1.40 MPa or less at 150°C and a compressive stress of 0.10 MPa, and an adhesion of 5.0 N·mm or more at 25°C. There are no particular limitations on the method of obtaining the thermally conductive sheet, and it can be obtained by adjusting the types and proportions of the various components such as the thermally conductive filler and resin used in the thermally conductive sheet.

[0029] There is no particular limitation on the thermal conductivity of the thermally conductive sheet; the higher the better. The thermal conductivity of the thermally conductive sheet, determined by the thermal resistance measured by the steady-state method, is preferably 7 W / (m·K) or higher, preferably 10 W / (m·K) or higher, and even better 15 W / (m·K) or higher. If the thermal conductivity is 7 W / (m·K) or higher, there is a tendency that even if the thickness of the thermally conductive sheet is increased to improve the warp following of the heating element, it is still easy to suppress the increase of thermal resistance.

[0030] In this case, the thermal conductivity of the thermally conductive sheet is specifically determined as follows: The thermally conductive sheet is cut into 10 mm squares and sandwiched between the heating element, i.e., the transistor (2SC2233), and the heat sink, i.e., the copper block. While pressing the transistor at 80°C with a pressure of 0.14 MPa, the temperature T1 (°C) of the transistor and the temperature T2 (°C) of the copper block when an electric current is applied are measured. Based on the measured values ​​and the applied electric current W1 (W), the thermal resistance value X (K・cm2 / W) per unit area (1 cm2) is calculated as follows: X=(T1-T2)×1 / W1. The thermal conductivity λ (W / (m・K)) is further calculated using the thickness t (μm) as follows: λ=(t×10- 6) / (X×10- 4)

[0031] The thickness of the thermally conductive sheet is not particularly limited and can be appropriately selected according to the specifications of the semiconductor package, etc. used. There is a tendency for a smaller thickness to result in lower thermal resistance, and a tendency for a larger thickness to result in better warp follow-through. The average thickness of the thermally conductive sheet can be from 50 μm to 3000 μm; from the viewpoint of thermal conductivity and sealing, 100 μm to 500 μm is preferred, and 150 μm to 300 μm is even better. The average thickness of the thermally conductive sheet is obtained by measuring the thickness at three points using a micrometer and taking its arithmetic mean. The thickness of the thermally conductive sheet can also be selected based on the warp of the heat-generating element, as described later.

[0032] There is no particular limitation on the compression amount of the thermally conductive sheet. For example, the compression amount at 150°C and a compressive stress of 0.10 MPa can be 20 μm to 1000 μm, 30 μm to 200 μm, or 40 μm to 100 μm. The compression amount at 150°C and a compressive stress of 0.15 MPa can also be the above values. The so-called "compression amount" of the thermally conductive sheet refers to the compression amount of the thermally conductive sheet when pressure is applied in the thickness direction of the thermally conductive sheet, and is the value obtained by subtracting the thickness of the thermally conductive sheet under pressure from the thickness of the thermally conductive sheet before pressure is applied.

[0033] There are no particular limitations on the compressibility of the thermally conductive sheet. For example, the compressibility at 150°C and a compressive stress of 0.10 MPa can be 10% to 60%, 15% to 50%, or 15% to 40%. The compressibility at 150°C and a compressive stress of 0.15 MPa can also be the above values. The "compression ratio" of the thermally conductive sheet refers to the ratio (%) of the above compression amount (μm) to the thickness (μm) of the thermally conductive sheet before pressure is applied.

[0034] To protect the adhesive surface, the thermally conductive sheet can be prepared as follows: at least one side has a protective film. In this case, the thermally conductive sheet after peeling off the protective film is used to bond the heat-generating element to the heat-dissipating element. As the protective film, resin films, coated papers, and coated fabrics such as polyethylene, polyester, polypropylene, polyethylene terephthalate, polyimide, polyetherimide, polyether naphthalene, methylpentene, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, and perfluoroalkoxyalkylene can be used; as well as metal foils such as aluminum. These protective films can be used alone or in combination of two or more to form a multilayer film. Preferably, the protective film is surface-treated with a silicone-based or silica-based release agent.

[0035] As long as the thermally conductive sheet meets the above-mentioned specific compressive modulus and viscosity, the composition of the thermally conductive sheet is not particularly limited. For example, a thermally conductive sheet may contain resin and thermally conductive filler.

[0036] Examples of thermally conductive fillers include: aluminum nitride, alumina, boron nitride, titanium oxide, zinc oxide, silicon carbide, silicon, silicon oxide, silica, glass, metal particles, carbon fiber, graphite, graphene, carbon nanotubes, etc. The thermally conductive filler may undergo surface treatment. One type of thermally conductive filler may be used alone or in combination of two or more types.

[0037] The shape of the thermally conductive filler is not particularly limited, and examples include: spherical, ellipsoidal, scaly, granular, rod-shaped, needle-shaped, fibrous, etc.

[0038] There is no particular limitation on the average particle size of the thermally conductive filler, but it is preferable to set it according to the material of the thermally conductive filler.

[0039] The aspect ratio (major diameter / minor diameter) of the thermally conductive filler is not particularly limited and can be in the range of 1 to 100, 5 to 50, or 10 to 40. The aspect ratio of the thermally conductive filler is set as the arithmetic mean of the following measured values, which are obtained by measuring the ratio of the major diameter to the minor diameter (major diameter / minor diameter) of 20 representative particles using a scanning electron microscope (SEM).

[0040] From the viewpoint of thermal conductivity, it is preferable that the thermally conductive filler is oriented in the thickness direction of the thermally conductive sheet. In this case, "oriented in the thickness direction" means that in a thermally conductive filler having a major axis and a minor axis (i.e., an aspect ratio greater than 1), the angle (also called the "orientation angle") between the major axis of the thermally conductive filler and the surface (main surface) of the thermally conductive sheet is 60° or more. An orientation angle of 80° or more is preferred, 85° or more is preferable, and 88° or more is even more preferable.

[0041] The content of thermally conductive filler in the thermally conductive sheet is preferably selected appropriately from the viewpoint of balancing thermal conductivity and sealing performance, depending on the material of the thermally conductive filler. For example, the content of thermally conductive filler relative to the total volume of the thermally conductive sheet can be 25% to 75% by volume, 30% to 60% by volume, or 35% to 50% by volume.

[0042] There are no particular limitations on the resin contained in the thermally conductive sheet, and it can be, for example, a curable resin or a non-curable resin. Examples of resins include: epoxy resin, silicone resin, acrylic resin, polyimide resin, bismaleimide resin, benzocyclobutene resin, phenolic resin, unsaturated polyester, diallyl phthalate resin, polyurethane, polyimide silicone resin, thermosetting polyphenylene ether, thermosetting modified polyphenylene ether, polybutene, polyisoprene, polysulfide, acrylonitrile rubber, silicone rubber, hydrocarbon resin, terpene resin, terpene phenol resin, hydrogenated terpene phenol, etc. One type of resin may be used alone or in combination with two or more types.

[0043] The resin content in the thermally conductive sheet is preferably selected based on the type of resin and the desired flexibility, adhesion, sealing properties, sheet strength, and hydrolysis resistance. For example, the resin content relative to the total volume of the thermally conductive sheet is preferably 25% to 75% by volume, more preferably 40% to 70% by volume, and even more preferably 50% to 65% by volume.

[0044] In addition to thermally conductive fillers and resins, thermally conductive sheets may also contain various additives such as flame retardants and antioxidants. There are no particular limitations on the flame retardants; they can be appropriately selected from commonly used flame retardants. Examples include red phosphorus-based flame retardants and phosphate ester-based flame retardants. From the viewpoint of excellent stability and improved adhesion due to plasticizing effect, phosphate ester-based flame retardants are preferred.

[0045] The method for manufacturing the thermally conductive sheet is not particularly limited as long as it is a method that can obtain a thermally conductive sheet having the specific compressive modulus and viscosity described above. For example, a composition containing the components of the thermally conductive sheet can be prepared, and the sheet can be made by calendering, pressing, extrusion, coating, etc. Alternatively, the sheet can be made by forming a molded body using the composition containing the components of the thermally conductive sheet, and then slicing the molded body. In this case, it is preferable to slice the molded body in a manner that orients the thermally conductive filler toward the thickness direction.

[0046] In one embodiment, the thermally conductive sheet can be manufactured by: preparing a composition containing the components of the thermally conductive sheet, thinning the composition to obtain a sheet, stacking the aforementioned sheet to form a laminate, and slicing the side end face of the laminate. Manufacturing the thermally conductive sheet in this way tends to form an efficient heat conduction path and obtain a thermally conductive sheet with excellent thermal conductivity and adhesion. Furthermore, the obtained thermally conductive sheet can be laminated after being adhered to a protective film.

[0047] [Method for bonding heating element and heat sink] In the semiconductor device manufacturing method of this invention, pressure is applied in the thickness direction of the heat-conducting sheet to a heat-conducting element and a heat sink with a heat-conducting sheet disposed therebetween, thereby bonding the heat-conducting element and the heat sink together via the heat-conducting sheet. In this invention, bonding refers to a state in which multiple surfaces are joined together by chemical or physical forces or both. By the semiconductor device manufacturing method of this invention, there is a tendency to maintain a good bonding area between the heat-conducting element and the heat-conducting sheet, the heat sink and the heat-conducting sheet, or both. When a heat-generating element and a heat-dissipating element are bonded together and assembled into a semiconductor device via a thermally conductive sheet, the bonding area is preferably more than 80% of the area of ​​the surface of the heat-generating element or heat-dissipating element facing the thermally conductive sheet, more preferably more than 85% of the area of ​​the surface of the heat-generating element or heat-dissipating element facing the thermally conductive sheet, even more preferably more than 90% of the area of ​​the surface of the heat-generating element or heat-dissipating element facing the thermally conductive sheet, and most preferably more than 95% of the area of ​​the surface of the heat-generating element or heat-dissipating element facing the thermally conductive sheet.

[0048] As a method for placing a heat-conducting sheet between a heat-generating element and a heat-dissipating element, the heat-conducting sheet may be placed on the heat-generating element first, and then the heat-dissipating element may be placed via the heat-conducting sheet; alternatively, the heat-conducting sheet may be placed on the heat-dissipating element first, and then the heat-generating element may be placed via the heat-conducting sheet. For one heat-conducting sheet, there may be one heat-generating element and one heat-dissipating element, or there may be multiple heat-generating elements and heat-dissipating elements.

[0049] Pressure is applied in the thickness direction of the heat-conducting sheet to the heat-generating element and the heat-dissipating element, which are disposed therebetween, so that the heat-generating element and the heat-dissipating element are bonded together through the heat-conducting sheet. At this time, pressure can be applied from the heat-generating element side or from the heat-dissipating element side.

[0050] From the viewpoint of ensuring the tightness of the thermally conductive sheet and reducing the load on electronic components, the pressure applied to the thickness direction of the thermally conductive sheet is preferably 0.05 MPa to 10.00 MPa, more preferably 0.10 MPa to 5.00 MPa, and even more preferably 0.10 MPa to 1.00 MPa. From the viewpoint of reducing the load on electronic components, 0.10 MPa to 0.50 MPa is particularly good. From the viewpoint of ensuring the tightness of the thermally conductive sheet, the pressure can be adjusted according to the thermally conductive sheet. For example, when the thickness of the thermally conductive sheet is 200 μm or more, the pressure is set to 0.20 MPa or less; when the thickness of the thermally conductive sheet is less than 200 μm, the pressure is set to more than 0.20 MPa.

[0051] There are no particular restrictions on the temperature at which pressure is applied, but it is preferable to select a suitable temperature range depending on the type of heat-conducting sheet. The temperature at which pressure is applied can be room temperature, but from the viewpoint of improving the compression ratio, a heated temperature is preferable. For example, the heated temperature can be 80°C to 200°C, 100°C to 190°C, or 120°C to 180°C.

[0052] Preferably, a pressure of 0.10 MPa to 1.00 MPa is applied within a temperature range of 120°C to 180°C. Setting the pressure to 0.10 MPa or higher, or the heating temperature to 120°C or higher, tends to result in excellent sealing performance. Furthermore, setting the pressure to 1.00 MPa or lower, or the heating temperature to 180°C or lower, tends to further improve the reliability of the seal. We believe this is because it can suppress the following: excessive compression of the thermally conductive sheet leading to thinning, or excessive strain or residual stress in the surrounding components.

[0053] When pressure is applied, for example, when a pressure of 0.10 MPa is applied at 150°C, the warpage of the heating element can be, for example, 10 μm or more, 20 μm or more, or 25 μm or more. Furthermore, when pressure is applied, for example, when a pressure of 0.10 MPa is applied at 150°C, the warpage of the heating element can be 80 μm or less, 70 μm or less, or 60 μm or less. The warpage of the heating element when a pressure of 0.15 MPa is applied at 150°C can also be within the above range.

[0054] The warpage of the heating element after pressure release may be, for example, 40 μm or more, 50 μm or more, or 60 μm or more. Furthermore, the warpage of the heating element after pressure release may be 150 μm or less, 140 μm or less, or 130 μm or less. When the warpage after pressure release changes with temperature, the aforementioned "warpage of the heating element after pressure release" is set to the warpage at 25°C.

[0055] In the step of bonding the heating element and the heat sink, the difference between the warpage of the heating element when pressure is applied and the warpage of the heating element after the pressure is released can be 30 μm or more, or 40 μm or more, or 45 μm or more. Furthermore, the upper limit of the above difference can be, for example, 120 μm or less.

[0056] The so-called "warpage amount" of the heating element refers to the maximum deformation (μm) in the thickness direction of the heating element when it warps. Figure 2 illustrates an example of a method for measuring the warpage amount when the thermally conductive sheet is used in the TIM1 application. As described below, the warpage amount can be measured based on the deformation of the substrate on which the heating element is mounted. The analysis range of the warpage amount is defined as the portion on which the heating element is mounted when viewed from the substrate side (heating element portion a). The following is defined as the warpage amount b: the displacement difference between the portion of the substrate with the largest deformation in the thickness direction and the end of the heating element in heating element portion a. The larger the warpage amount, the easier it is for the thermally conductive sheet to peel off from the heating element and the heat sink when warpage occurs. The thermally conductive sheet used in this case tends to not peel off from the heating element and the heat sink even if the warpage amount of the heating element increases, and the bonding area can be maintained well.

[0057] The specific method for bonding the heating element and the heat sink via the aforementioned heat-conducting sheet is not particularly limited as long as it can fix each heat sink and the heating element in a sufficiently tight state. Examples include: placing the heat-conducting sheet between the heating element and the heat sink, fixing it with a fixture capable of applying pressure to approximately 0.05 MPa to 1.00 MPa, and then heating the heating element in this state, or using an oven or similar device to heat it to approximately 80 to 180°C. Furthermore, examples include: using a press capable of heating and pressurizing at 80 to 180°C and 0.05 MPa to 1.00 MPa.

[0058] In addition to clamps, screws, springs and other fixtures can be used for fixing. From the point of view that it can maintain a tight fit, it is preferable to further fix it by commonly used means such as adhesives.

[0059] Semiconductor devices can be manufactured in the following manner: as described above, using a heat-generating element and a heat-dissipating element that have been bonded together by a thermally conductive sheet. There are no particular limitations on the type of semiconductor device; examples include electronic materials incorporating integrated circuits (ICs) such as CPUs and memory chips. Other examples include power devices such as bipolar transistors, power MOSFETs, and insulated-gate bipolar transistors (IGBTs).

[0060] Manufacturing Method of Thermally Conductive Sheet In one embodiment of this invention, a manufacturing method of a thermally conductive sheet is provided. The thermally conductive sheet is used to heat a heat-generating element and a heat-dissipating element disposed therebetween. When the heat-generating element is heated and pressure is applied in the thickness direction of the thermally conductive sheet, the heat-generating element and the heat-dissipating element are bonded together via the thermally conductive sheet. The manufacturing method of the thermally conductive sheet includes the following steps: selecting the compression ratio and thickness of the thermally conductive sheet such that the compression amount of the thermally conductive sheet satisfies the following formula: Formula: C > L2 - L1 Wherein, L1 is the predicted warpage amount (μm) of the heat-generating element under heating and pressurization, L2 is the predicted warpage amount (μm) of the heat-generating element when cooled to 25°C after the heating and pressurization ends, C is the predicted compression amount (μm) of the thermally conductive sheet under heating and pressurization conditions, and C = thickness (μm) of the thermally conductive sheet before pressurization × compression ratio (%) under heating and pressurization conditions.

[0061] The predicted warpage (L1) of the heating element under heating and pressurization refers to the predicted warpage of the heating element under predicted pressure and temperature conditions. For example, when it is predicted that the heating element and the heat sink will be bonded together by applying pressure of 0.10 MPa at 150°C through a thermally conductive sheet, it refers to the predicted warpage under the condition of applying pressure of 0.10 MPa at 150°C. Similarly, when it is predicted that the heating element and the heat sink will be bonded together by applying pressure of 0.15 MPa at 150°C through a thermally conductive sheet, it refers to the predicted warpage under the condition of applying pressure of 0.15 MPa at 150°C. The predicted warpage (L1) of the heating element under heating and pressurization can be, for example, 10 μm or more, 20 μm or more, or 25 μm or more. Furthermore, the predicted warpage (L1) of the heating element under heating and pressurization can be 80 μm or less, 70 μm or less, or 60 μm or less.

[0062] The predicted warpage (L2) of the heating element when cooled to 25°C after the heating and pressurization are completed can be, for example, 40 μm or more, 50 μm or more, or 60 μm or more. Furthermore, the predicted warpage (L2) of the heating element when cooled to 25°C after the heating and pressurization are completed can be 150 μm or less, 140 μm or less, or 130 μm or less.

[0063] The difference (L2-L1) between L1 and L2 can be 30 μm or more, or 40 μm or more, or 45 μm or more. In addition, the upper limit of the difference can be, for example, 120 μm or less.

[0064] The predicted compression (C) of the heat-conducting sheet under heating and pressurization conditions refers to the compression of the heat-conducting sheet under predicted pressure and temperature conditions. For example, when it is predicted that the heat-generating element and the heat-dissipating element will adhere to each other through the heat-conducting sheet under a pressure of 0.10 MPa at 150°C, it refers to the compression under the conditions of 0.10 MPa at 150°C. Furthermore, when it is predicted that the heat-generating element and the heat-dissipating element will adhere to each other through the heat-conducting sheet under a pressure of 0.15 MPa at 150°C, it refers to the compression under the conditions of 0.15 MPa at 150°C. The predicted compression (C) of the heat-conducting sheet under heating and pressurization conditions can be, for example, 20 μm to 1000 μm, 30 μm to 200 μm, or 40 μm to 100 μm.

[0065] The thickness of the heat-conducting sheet before pressurization refers to the average thickness of the heat-conducting sheet before pressurization. The preferred range of the thickness of the heat-conducting sheet is as described above.

[0066] The preferred range of the compression ratio of the thermally conductive sheet is as described above.

[0067] We believe that the thermally conductive sheet prepared by selecting the compression ratio and thickness in the above manner has sufficient compression because it follows the warpage change of the heating element during the bonding step of the heating element and the heat sink, thus appropriately suppressing the peeling of the thermally conductive sheet. [Example]

[0068] Hereinafter, the present invention will be described in detail by way of embodiments, but the present invention is not limited to these embodiments. Furthermore, in each embodiment, the evaluation of compressive modulus, compression amount, viscosity, thermal conductivity, warpage, and adhesive area is performed by the following methods.

[0069] (Determination of compressive modulus and compression amount) The compression test apparatus (INSTRON 5948 Micron Tester (INSTRON Corporation)) equipped with a thermostatic bath was used for the measurement. A thermally conductive sheet was cut into a circle with a diameter of 14 mm for testing. The thermally conductive sheet was sandwiched between 0.1 mm thick paper (release paper), and a load was applied to the thickness direction of the thermally conductive sheet at a displacement speed of 0.1 mm / min at a thermostatic bath temperature of 150°C. The displacement (mm) and load (N) were measured. The strain (dimensionless) obtained from displacement (mm) / thickness (mm) was displayed on the horizontal axis, and the stress (MPa) obtained from load (N) / area (mm2) was displayed on the vertical axis. The slope when the stress was 0.10 MPa was set as the compressive modulus (MPa). In addition, the maximum displacement when compressed to any pressure was set as the compression amount (μm).

[0070] (Determination of viscosity) Using a universal physical property tester (texture analyzer (Yinghong Precision Machinery Co., Ltd.)), at 25°C (room temperature), a probe with a diameter of 7 mm was pressed onto a thermally conductive sheet with a load of 40 N and held for 10 seconds. The area obtained by integrating the load and displacement curve when the probe was lifted was then set as the viscosity (N·mm).

[0071] (Determination of thermal conductivity) A thermally conductive sheet was cut into 10 mm squares and sandwiched between the heating element (transistor 2SC2233) and the heat sink (copper block). While pressing the transistor at 80°C with a pressure of 0.14 MPa, the temperatures of the transistor (T1, °C) and the copper block (T2, °C) when an electric current was applied were measured. Based on the measured values ​​and the applied electric current (W1, W), the thermal resistance per unit area (1 cm2) X (K·cm2 / W) was calculated as follows: X = (T1 - T2) × 1 / W1. The thermal conductivity λ (W / (m·K)) was further calculated using the thermal resistance (K·cm2 / W) and the thickness t (μm) as follows: λ = (t × 10⁻⁶) / (X × 10⁻⁴).

[0072] (Measurement of Warpage Amount) The warpage amount was measured using a 3D heated surface shape measuring device (TherMoiré PS200, AKROMETRIX). The warpage amount of the substrate corresponding to the wafer area (20 mm × 20 mm) was measured. The warpage amount of the substrate of the wafer area at 150°C, the condition for assembling the package, was 29 μm. Furthermore, the warpage amount of the substrate of the wafer area at 25°C after assembly was 75 μm. Therefore, the difference between the above warpage amounts is 46 μm.

[0073] (Adhesion Area Evaluation Test) The adhesion area was evaluated as follows. Using an ultrasound imaging diagnostic device (Insight-300, Insight Corporation), the adhesion status was observed at 35 MHz using the reflectance method. Furthermore, the image was binarized using image analysis software (Image J), ​​and the proportion of the adhered area in each 20 mm square wafer portion was calculated and set as the adhesion area (%).

[0074] The adhesive area evaluation test was conducted using a simplified package manufactured as follows: The substrate was MCL-E-700G(R) (0.81 mm thick, Hitachi Chemical Co., Ltd.), the underfill material was CEL-C-3730N-2 (Hitachi Chemical Co., Ltd.), and the sealing material was a silicone-based adhesive (SE4450, Dow Corning Toray Co., Ltd.). Furthermore, the heat sink was made of a 1 mm thick copper plate plated with nickel. The substrate and heat sink were 45 mm square, and the semiconductor wafer was 20 mm square. At this time, the warpage of the heat sink was 29 μm when a pressure of 0.15 MPa was applied at 150°C, and 75 μm when the pressure was released and the temperature was cooled to 25°C.

[0075] The assembly of the package is performed as follows: A thermally conductive sheet of any thickness is cut into 23 mm squares and adhered to a heat sink. The semiconductor wafer is positioned on the heat sink via the thermally conductive sheet. A high-precision pressure heating bonding device (HTB-MM, ALPHA DESIGN Inc.) is used to apply pressure at any temperature and pressure in the thickness direction of the thermally conductive sheet for 3 minutes. Then, it is treated in a constant temperature bath at 150°C for 2 hours to allow the sealing material to fully harden.

[0076] <Example 1> A 0.3 mm thick thermally conductive sheet manufactured by Hitachi Chemical Co., Ltd. was selected. The package was assembled using the method described above at 150°C and 0.15 MPa, and the thermally conductive sheet was bonded to the heat source (i.e., the semiconductor wafer) and the heat sink (i.e., the radiator). The thermally conductive sheet had a compressive modulus of 1.16 MPa at 150°C and a compressive stress of 0.10 MPa, an adhesive strength of 7.6 N·mm at 25°C, and a thermal conductivity of 21 W / (m·K). At this point, the bonding area was 99%. The warp follower index, i.e., the bonding area, showed over 90%, indicating excellent warp follower performance. The compression ratio of the thermally conductive sheet at 150°C and 0.15 MPa compression was 19%, and the compression amount of the thermally conductive sheet was 57 μm.

[0077] <Example 2> A 0.2 mm thick thermally conductive sheet manufactured by Hitachi Chemical Co., Ltd. was selected. The package was assembled using the method described above at 150°C and 0.15 MPa, and the thermally conductive sheet was bonded to the heat source (i.e., the semiconductor wafer) and the heat sink (i.e., the radiator). The thermally conductive sheet had a compressive modulus of 1.16 MPa at 150°C and a compressive stress of 0.10 MPa, an adhesive strength of 7.6 N·mm at 25°C, and a thermal conductivity of 18 W / (m·K). At this point, the bonding area was 95%. The warp follower index, i.e., the bonding area, showed over 90%, indicating excellent warp follower performance. The compression ratio of the thermally conductive sheet at 150°C and 0.15 MPa compression was 21%, and the compression amount of the thermally conductive sheet was 47 μm.

[0078] <Example 3> A 0.15 mm thick thermally conductive sheet manufactured by Hitachi Chemical Co., Ltd. was selected. The package was assembled using the method described above under conditions of 150°C and 0.31 MPa, and the thermally conductive sheet was bonded to the heat-generating element (i.e., the semiconductor wafer) and the heat-generating element (i.e., the heat sink). The thermally conductive sheet had a compressive modulus of 1.16 MPa at 150°C and a compressive stress of 0.10 MPa, an adhesive strength of 7.6 N·mm at 25°C, and a thermal conductivity of 16 W / (m·K). At this time, the bonding area was 90%. The compression ratio of the thermally conductive sheet under compression at 150°C and 0.31 MPa was 35%, and the compression amount of the thermally conductive sheet was 52 μm.

[0079] <Comparative Example 1> A liquid silicone paste (thermal grease, manufactured by SANWA SUPPLY, TK-93K (trade name)) with a thermal conductivity of 2 W / (m・K) was selected as the thermal conductive material. The package was assembled using the method described above at 150°C and 0.03 MPa, and then bonded to the heat-generating element (i.e., the semiconductor wafer) and the heat-generating element (i.e., the heat sink). Furthermore, since it was liquid, the compressive modulus of elasticity and adhesive force could not be measured. The assembled silicone paste had a thickness of 40 μm and an adhesion area of ​​63%.

[0080] <Comparative Example 2> A 0.3 mm thick thermally conductive sheet manufactured by Hitachi Chemical Co., Ltd. was selected. Under conditions of 150°C and 0.15 MPa, a package was assembled using the method described above, and the thermally conductive sheet was bonded to the heat-generating element (i.e., the semiconductor wafer) and the heat-generating element (i.e., the heat sink). The thermally conductive sheet had a compressive modulus of 1.44 MPa at 150°C and a compressive stress of 0.10 MPa, an adhesive strength of 7.2 N·mm at 25°C, and a thermal conductivity of 20 W / (m·K). At this time, the bonding area was 72%. The compression ratio of the thermally conductive sheet under compression at 150°C and 0.15 MPa was 13%, and the compression amount of the thermally conductive sheet was 40 μm.

[0081] <Comparative Example 3> A 0.3 mm thick thermally conductive sheet manufactured by Hitachi Chemical Co., Ltd. was selected. Under conditions of 150°C and 0.15 MPa, a package was assembled using the method described above, and the thermally conductive sheet was bonded to the heat-generating element (i.e., the semiconductor wafer) and the heat-generating element (i.e., the heat sink). The thermally conductive sheet had a compressive modulus of 1.73 MPa at 150°C and a compressive stress of 0.10 MPa, an adhesive strength of 1.8 N·mm at 25°C, and a thermal conductivity of 23 W / (m·K). At this time, the bonding area was 74%. The compression ratio of the thermally conductive sheet under compression at 150°C and 0.15 MPa was 13%, and the compression amount of the thermally conductive sheet was 44 μm. <Comparative Example 4> A 0.3 mm thick thermally conductive sheet manufactured by Hitachi Chemical Co., Ltd. was selected. Under conditions of 150°C and 0.15 MPa, a package was assembled using the method described above, and the thermally conductive sheet was bonded to the heat-generating element (i.e., the semiconductor wafer) and the heat-generating element (i.e., the heat sink). The thermally conductive sheet had a compressive modulus of 1.35 MPa at 150°C and a compressive stress of 0.10 MPa, an adhesive strength of 3.8 N·mm at 25°C, and a thermal conductivity of 18 W / (m·K). The bonding area was 78%. The compression ratio of the thermally conductive sheet under compression at 150°C and 0.15 MPa was 16%, and the compression amount was 48 μm.

[0082] As described above, when the method of the embodiment is used to bond the heat-generating element and the heat-dissipating element, a good bonding area can be maintained. We believe that this allows for the acquisition of a semiconductor device with excellent heat dissipation.

[0083] All documents, patent applications and technical specifications described in this specification are referenced hereto in such a specific and to the same extent as those described herein. [Simplified Explanation of the Diagram]

[0009] Figure 1 shows a schematic cross-sectional view of a semiconductor device when a thermally conductive sheet is used as the thermally conductive material (thermal interface material 1). Figure 2 is a diagram showing the amount of warpage for a semiconductor device using a thermally conductive sheet as the thermally conductive material (thermal interface material 1).

Claims

1. A thermally conductive sheet having a compressive modulus of 0.50 MPa to 1.40 MPa at 150°C and a compressive stress of 0.10 MPa, an adhesive strength of 5.0 N·mm or more at 25°C, and a thickness of 100 μm to 500 μm, the thermally conductive sheet having a protective film surface-treated with a release agent, the thermally conductive sheet containing a thermally conductive filler at a content of 25% to 75% by volume relative to the total volume of the thermally conductive sheet, and the thermally conductive sheet being disposed between a heat-generating element and a heat-dissipating element of a semiconductor device to bond the heat-generating element and the heat-dissipating element together.

2. The thermally conductive sheet as described in claim 1 has a thermal conductivity of 7 W / (m・K) or higher, determined by the thermal resistance measured by the steady-state method.

3. The thermally conductive sheet as described in claim 1 or 2, wherein, The aforementioned heat-generating element is a semiconductor chip, and the aforementioned heat-dissipating element is a heat sink.

4. The thermally conductive sheet as described in claim 1 or 2, wherein, The aforementioned heat-generating element is a semiconductor package with a heat sink, and the aforementioned heat sink is a heat sink.

5. The thermally conductive sheet as described in claim 1 or 2, wherein, The aforementioned heating element is a semiconductor module.

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