JP2009267304A - Heat-radiating tape and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide a heat-radiating tape that prevents warpage and separation due to the difference in the thermal coefficients of expansion, and has superior heat radiation performance. <P>SOLUTION: In the heat-radiating tape, metal foil, where one portion or entire surface of at least one surface is aluminum, is used as a substrate, an adhesive layer is formed, on at least one portion or entire surface of one side or both sides of the metal foil, and the adhesive layer has a composite layer formed by impregnating a layer, with an aluminum carbide whisker or an aluminum whisker as a main component with an adhesive resin. The layer with the whiskers as the main component is to formed with a plurality of whiskers that grow toward the outside, from the surface of the substrate as the main component. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heat dissipation tape having excellent heat dissipation performance. More specifically, the present invention relates to a heat dissipation tape having a whisker layer in an adhesive layer.

  In recent years, the problem of cooling semiconductor elements mounted on various electronic / electrical devices represented by computers and the like has attracted attention as an important issue. As a cooling method for a semiconductor element or the like that needs to be cooled, a method is provided in which a fan is attached to a device casing on which the device is mounted, and the air in the device casing is cooled. A method of cooling by attaching a (heat sink) is representative.

  When a heat sink is attached to a component such as a semiconductor element to be cooled (hereinafter referred to as a component to be cooled), sufficient cooling performance can be obtained if the thermal connectivity between the component to be cooled and the heat sink is low. Absent. Usually, if the heat sink is simply brought into contact with the component to be cooled, the contact resistance of that portion is too large, and therefore it is difficult to achieve sufficient cooling.

  If the component to be cooled and the heat sink are joined by soldering or the like, it is possible to make a connection with a much lower thermal resistance than when they are simply brought into contact with each other. However, if the difference in coefficient of thermal expansion between the component to be cooled and the heat sink is large, the problem of thermal matching occurs. Specifically, as a heat sink, an aluminum material or the like that is usually excellent in thermal conductivity is often suitably applied, but a semiconductor element that is a component to be cooled often has a much smaller coefficient of thermal expansion than that. In many cases, problems such as the occurrence of large warpage and the occurrence of peeling at the joints occur.

  In view of this, a method in which silicone grease or the like is sandwiched between the component to be cooled and the heat sink is widely used. By interposing silicone grease or the like, the resistance value of the contact portion becomes smaller than when the component to be cooled and the heat sink are simply brought into contact with each other. Also, unlike the case where the component to be cooled and the heat sink are joined by soldering, the difference in thermal expansion is absorbed by the silicone grease, and problems such as warpage are suppressed.

  However, since the thermal conductivity of a substance such as silicone grease is often much lower than that of the metal material constituting the heat sink, it is not easy to further improve the cooling performance. In recent years, there has been a further demand for cooling electronic components such as semiconductor elements, and for this reason, it is required to reduce contact resistance.

  Then, this invention makes it a subject to provide the heat dissipation tape excellent in heat dissipation performance cheaply, without the curvature and peeling by the difference in a thermal expansion coefficient arising.

  As a result of intensive studies to solve the above problems, the present inventor is effective to form a layer mainly composed of aluminum carbide whiskers or alumina whiskers on the aluminum surface and impregnate the layer with an adhesive resin. As a result, the present invention was completed. The present invention has the following features.

(1) The heat dissipation tape according to the present invention is based on a metal foil in which at least a part or the whole of the surface is aluminum, and an adhesive layer is formed on at least a part or the whole of one or both sides of the metal foil, The adhesive layer has a composite layer formed by impregnating an adhesive resin in a layer mainly composed of aluminum carbide whiskers or alumina whiskers.
(2) The heat dissipation tape according to (1) above, wherein a plurality of aluminum carbide whiskers or alumina whiskers in which the layer mainly composed of the aluminum carbide or alumina whiskers grows outward from the surface of the metal foil. It is formed as a main component.

(3) In the method of manufacturing a heat dissipation tape according to the present invention, a metal foil having aluminum at least partially or entirely on one surface is placed in a space containing a hydrocarbon-containing substance and heated to carbonize the surface of the metal foil. It is characterized by having a step of impregnating an adhesive resin into a layer containing aluminum carbide as a main component after the step of forming a layer containing aluminum whisker as a main component.
(4) In the method of manufacturing a heat dissipation tape according to the present invention, a metal foil having at least a part or the entire surface of aluminum is placed in a space containing a hydrocarbon-containing substance and heated, and carbonized on the surface of the metal foil. After forming the layer mainly composed of aluminum whiskers, the metal foil is placed in an oxidizing atmosphere and heated to convert the layer composed mainly of aluminum carbide whiskers into a layer composed mainly of alumina whiskers. After the step, there is a step of impregnating the adhesive resin into a layer mainly composed of the alumina whisker.

  According to the present invention, it is possible to provide a heat dissipation tape excellent in heat dissipation performance at low cost without warping or peeling due to a difference in thermal expansion coefficient. That is, the heat dissipation tape according to the present invention is a heat dissipation tape having a low thermal resistance and a high cooling effect when an inexpensive aluminum foil is used as the metal foil. In addition, the adhesive layer on the substrate surface absorbs the difference in thermal expansion, and the problem of warping and peeling is also eliminated. Furthermore, since the heat dissipation tape according to the present invention has a large surface area, it has high hygroscopicity / adsorption properties, and is effective as moisture, dust, and an action removing sheet during cooking.

  Hereinafter, the heat dissipation tape according to the present invention will be described in more detail. In the following description, the aluminum carbide whisker or the alumina whisker may be simply referred to as a whisker without distinction between the two. Similarly, a layer mainly composed of aluminum carbide whiskers or alumina whiskers may be simply referred to as a whisker layer without distinction between the two.

  FIG. 1 schematically shows an example of a heat dissipation tape according to the present invention. The heat dissipation tape according to the present invention has a base made of a metal foil in which at least a part of or the entire surface is aluminum, and an adhesive layer is formed on at least a part or the entire surface of one side or both sides of the base. And a composite layer formed by impregnating an adhesive resin in a layer mainly composed of aluminum carbide whisker or alumina whisker. Such a heat dissipation tape is used, for example, by being disposed between a heat sink and a component to be cooled.

  As described above, the adhesive layer is formed on one side or both sides of the metal foil as the base. In the adhesive layer, a composite layer in which a whisker layer is impregnated with an adhesive resin is combined. The whiskers are grown so as to extend directly from the surface of the substrate. That is, since innumerable whiskers grow substantially vertically from the substrate surface, a whisker layer mainly composed of whiskers is formed on the substrate surface. Since the whisker layer is not a dense layer and is porous with a gap, it can be impregnated with an adhesive resin.

  The heat dissipation tape according to the present invention has a composite layer formed by impregnating the whisker layer with an adhesive resin. Thereby, it can be set as the heat dissipation tape which has adhesiveness. Moreover, the adhesive resin layer may be formed on the composite layer by excessively impregnating the adhesive resin. In this case, the adhesive layer has a composite layer and an adhesive resin layer. Of course, it is optional to have an adhesive resin layer, but it is preferable to have an adhesive resin layer from the viewpoint of enhancing the adhesiveness with the counterpart material (heating element and / or radiator). However, it is not preferable that only the adhesive resin layer is too thick because heat conductivity is lowered. For this reason, it is preferable that the thickness of a composite layer is more than half of the thickness of the whole adhesion layer. That is, the thickness of the composite layer (whisker length) is preferably 10 μm or more.

  When the heat-radiating tape according to the present invention is attached to the heat generating member that is the counterpart material, the adhesive resin and / or whisker in the adhesive layer penetrates and adheres to the unevenness existing on the surface of the counterpart material, so that the contact heat Resistance is reduced. Heat from the heating element is transmitted to the whisker through the adhesive layer, and is transported to the substrate through the length of the whisker. At this time, since the whisker grows directly from the surface of the substrate, the thermal resistance during heat transfer to the substrate is extremely close to zero. Therefore, an extremely small thermal resistance can be obtained despite the presence of an adhesive layer having a low thermal conductivity.

The heat dissipation tape according to the present invention can be produced by a simple method.
That is, in the method for producing a heat dissipation tape according to the present invention, at least a metal foil whose surface is aluminum is placed in a space containing a hydrocarbon-containing substance and heated, and the surface of the metal foil is mainly composed of aluminum carbide whiskers. After the step of forming the layer, the method has a step of impregnating the adhesive resin into the layer mainly composed of the aluminum carbide.

  That is, a metal foil whose main component is an aluminum carbide whisker is formed on the surface of the metal foil simply by arranging and heating a metal foil whose surface is partly or entirely of aluminum in a space containing a hydrocarbon-containing substance. The At this time, an aluminum carbide phase is formed on the aluminum surface of the metal foil, and a plurality of aluminum carbide whiskers grow from the aluminum carbide phase (see FIG. 2). Aluminum carbide whiskers grow so as to extend outward from the surface of the substrate, and the length direction of many whiskers is oriented in a direction generally perpendicular to the substrate surface. Therefore, a layer mainly composed of aluminum carbide whiskers is formed on the substrate surface.

  When aluminum is provided on both sides of the substrate surface, whisker layers are formed on both sides as shown in FIG. 2, and when aluminum is provided on only one side, whiskers are formed only on one side. In the heat dissipation tape according to the present invention, a whisker layer may be formed on at least a part of or the entire surface.

Thus, since the aluminum carbide whisker is directly grown from the aluminum carbide phase on the surface of the substrate, the thermal resistance between the substrate and the whisker is substantially close to zero. Note that the layer mainly composed of aluminum carbide whiskers includes, for example, Al ₄ C ₃ crystal, but may include amorphous. Moreover, it may contain various impurities contained in the substrate or the like.

  Such whiskers are obtained at a heating temperature of 300 ° C. or higher. Considering the reaction efficiency, 450 ° C. or higher is preferable, and the upper limit is below the melting point of aluminum. There are various alloys of aluminum, and the temperature may be lower than the melting point of each.

  The kind of the hydrocarbon-containing substance used is not particularly limited. For example, paraffinic hydrocarbons such as methane, ethane, propane, n-butane, isobutane and pentane, olefinic hydrocarbons such as ethylene, propylene, butene and butadiene, acetylenic hydrocarbons such as acetylene, etc., or these hydrocarbons And derivatives thereof. Among these hydrocarbons, paraffinic hydrocarbons such as methane, ethane, and propane are preferable because they become gaseous in the process of heating the aluminum foil. More preferred is any one of methane, ethane and propane. The most preferred hydrocarbon is methane.

After forming the whisker layer on the substrate surface, the pressure-sensitive adhesive layer is formed by impregnating the pressure-sensitive adhesive resin. The kind of resin used when forming an adhesion layer is not ask | required. Acrylic and silicon adhesive resins can be widely used. Also, rubber may be used.
The heat dissipation tape according to the present invention can provide a heat dissipation tape excellent in heat dissipation performance at low cost when the aluminum foil itself is used as the substrate. However, the type of metal foil used as the substrate is not particularly limited, and at least a part or the entire surface of one surface may be aluminum. A metal foil having excellent thermal conductivity is preferred for use as a heat dissipation tape. For this reason, Cu, Au, Ag, etc. are preferable.

  Since aluminum carbide is likely to react with moisture and may have a problem with moisture resistance, in that case, it is preferable to convert aluminum carbide whiskers to alumina whiskers. For this reason, in the manufacturing method of the heat dissipation tape according to the present invention, after forming the aluminum carbide whisker layer on the surface of the metal foil as described above, the metal foil is placed in an oxidizing atmosphere and heated, and the aluminum carbide whisker is alumina. It has the process of converting into a whisker. After the step, the adhesive resin may be impregnated in a layer mainly composed of alumina whiskers.

  In the step of converting to alumina whiskers, the heating temperature is preferably 300 ° C. or higher. A more preferable temperature is 450 ° C. or higher. The upper limit of the heating temperature is the melting point of the aluminum foil used for the substrate. As the adhesive resin, the same resin as that used when the aluminum carbide whisker layer is impregnated can be used.

(1) Material <Formation of whiskers>
A pure Al foil (purity: 99.99%) having a size of 100 × 100 mm and a thickness of 30 μm was heated in an atmosphere containing various hydrocarbon gases to form a layer mainly composed of whiskers. Whiskers were formed on the surface of the Al foil after heating. The whisker phase was identified by X-ray diffraction.

<Resin impregnation>
A small amount of a polymerization initiator was added to a 20% ethyl acetate diluted product (trade name: Lipoxy VR-77-80EAC) of Showa Polymer vinyl ester resin, and then dropped onto the whisker layer. This was placed in a vacuum oven and impregnated with resin at room temperature while being evacuated with a rotary pump. Thereafter, ultraviolet rays having a wavelength of 364 nm were irradiated with a light intensity of 22 mW / cm ² to be semi-cured.

<Measurement of thermal resistance>
Each sample was set in the thermal resistance measuring apparatus shown in FIG.
An amount of heat Q was added by heating at 13.3 V and 245 mA with an AlN heater from the top. The temperature at each position of the upper and lower Cu holders was measured and held until it reached a steady state. The circumference of the Cu holder was surrounded by a heat insulating material. The upper and lower copper holders sandwiching the sample are provided with five thermocouple insertion holes each, and the temperature of the heating element surface and the fin tip of the heat sink was extrapolated from the gradient of the temperature distribution at these positions. . The surface pressure was 0.375 MPa. The surface temperature (T1) and back surface temperature (T2) of the sample were extrapolated from the temperature gradient in each Cu holder when the steady state was reached.

The thermal resistance was calculated by the following formula.
Measurement of thermal resistance (K / W) = (T1-T2) / Q

<Result>
The results are shown in Table 1.
The heat dissipation tape according to the present invention had a low thermal resistance.

It is a figure showing the outline of an example of the thermal radiation tape which concerns on this invention. It is a figure showing the outline of an example of the manufacturing method of the thermal radiation tape which concerns on this invention. It is a figure showing the outline of the apparatus which measures the thermal resistance used in the Example.

Claims (4)

At least a part or the entire surface of the surface of the metal foil is aluminum as a base,
An adhesive layer is formed on at least a part or the entire surface of one side or both sides of the metal foil,
The adhesive layer has a composite layer formed by impregnating an adhesive resin in a layer mainly composed of aluminum carbide whiskers or alumina whiskers;
Heat dissipation tape characterized by   2. The layer according to claim 1, wherein the layer mainly composed of aluminum carbide or alumina whiskers is formed based on a plurality of aluminum carbide whiskers or alumina whiskers grown outward from the surface of the metal foil. The heat dissipation tape described. After the step of disposing at least a part of or the entire surface of the surface of the metal foil made of aluminum in a space containing a hydrocarbon-containing substance and heating to form a layer mainly composed of aluminum carbide whiskers on the surface of the metal foil ,
A method for producing a heat-radiating tape, comprising a step of impregnating an adhesive resin into a layer containing aluminum carbide as a main component. A metal foil having at least a part or the entire surface of aluminum is placed in a space containing a hydrocarbon-containing substance and heated to form a layer mainly composed of aluminum carbide whiskers on the surface of the metal foil. After placing the metal foil in an oxidizing atmosphere and heating to convert the layer containing the aluminum carbide whisker as a main component into a layer containing the alumina whisker as a main component,
A method for producing a heat radiating tape, comprising a step of impregnating an adhesive resin into a layer mainly composed of the alumina whisker.

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