KR100717132B1 - Hollow diamond shells filled composite materials - Google Patents

Abstract

The present invention relates to a composite material in which a hollow diamond shell is filled in a base material such as a polymer resin. As a filler of thermal interface material (TIM), one of the core materials of semiconductor devices, hollow diamond shell particles of several tens to several tens of micrometers are used to overcome high-performance thermal interface composites that exceed the limitations of conventional materials. to provide. This composite can be used as an underfill or encapsulation filler material, such as flip chip, and can be used as a lightweight, high strength material such as spacecraft.

Semiconductor, Thermal Interface Material, Composites, Fillers, Diamond Shell, CVD Diamond, Porous, Micro, Nano, Heat Dissipation

Description

Composite filled with hollow diamond shells {HOLLOW DIAMOND SHELLS FILLED COMPOSITE MATERIALS}

Figure 1 shows a cross-sectional schematic diagram of the diamond shell filled thermointerface layer of the present invention.

*** Explanation of symbols on main parts of drawing ***

1: Thermal interface layer (composite) 1-1: Diamond shell

1-2: epoxy 2: heat source

3: heat sink 4: heat flow

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to composites for thermal interface materials (TIM) and lightweight high strength structural materials, such as high performance semiconductor devices and multi chip modules (MCM).

Like Moore's law, the density of microchips in the semiconductor industry is doubling in 12-18 months. To improve the performance of these devices, the development of integrated device fabrication technologies such as the production of fine line widths, the development of low resistance conductors, and the development of low dielectric thin films, along with the development of integrated device fabrication technologies, requires the use of low dielectric constant fillers. do.

Heat generated in the semiconductor element (heat source) is generally removed via a thermal spreader in thermal contact with the upper surface of the element. This thermal contact is a thermal interface material. The thermal interface material layer is filled with 40-60% of ceramic particles (filler) in a polymer resin such as epoxy, and serves to facilitate heat transfer from the device to the heat sink. Therefore, the thermal interface material should have good heat transfer characteristics.

The heat transfer characteristics of the thermal interface material layer are expressed as the thermal resistance (mm ² K / W) of this layer (the sum of the bulk thermal resistance of the resin and the charge and the contact thermal resistance at the top and bottom interfaces). Good heat transfer characteristics The thermal resistance R is expressed by the following equation.

R = L / kA ---------------- (Equation 1)

L: thermal interface layer thickness

k: thermal conductivity of the thermal interface layer

A: area of thermal interface material

As can be seen from this equation, in the specification of a constant thermal interface material layer, the thermal resistance increases in inverse proportion to the thermal conductivity of the thermal interface material layer. The thermal conductivity of the thermal interface material layer depends on the thermal conductivity of the constituent filler and epoxy base material. Since the thermal conductivity of epoxy generally used is very low, below 0.5 W / mK, in order to increase the thermal conductivity of the thermal interface material layer, a high thermal conductivity filler should be used.

Common fillers used in semiconductors, such as flip chips, are spherical silica (SiO ₂ ). However, when silica is low in thermal conductivity and high heat transfer is required, relatively good thermal fillers such as boron nitride (BN), aluminum nitride (AlN) and alumina (Al ₂ O ₃ ) are used. Besides these thermal conductivity, the required properties of the filler are high electrical resistance, low dielectric constant, low dielectric loss, small coefficient of linear thermal expansion, low density and high hardness. Physical properties of the main fillers are shown in Table 1.

[Table] Comparison of characteristics of main fillers

Diamond BN AlN Al ₂ O ₃ Molten SiO ₂ Thermal Conductivity (W / mK) @ 25 ℃ 2,000 300 260 30 1.4 Electrical resistance (ohm-cm) 10 ¹⁵ 10 ¹⁵ 10 ¹⁴ 10 ¹⁴ 10 ¹⁴ Dielectric constant 5.7 3.9 8.8 9.7 3.8 Dielectric loss (x10 ^-3 ) @ 1 Mhz 0.1 0.2 0.4 0.1 0.2 Coefficient of thermal expansion (x10 ^-6 / ℃) One <1 4.4 6.7 0.5 Density (g / cc) 3.52 2.25 3.26 3.98 2.20 Knoop Hardness (kg / mm ² ) 10,000 11 1,200 1,500 500

As can be seen from Table 1, conventionally used heat transfer fillers (boron nitride, aluminum nitride and alumina) have better thermal conductivity than silica, but have high dielectric constant and thermal expansion coefficient, which are important characteristics of the filler. there is a problem. This problem may cause excessive energy loss or thermal breakdown of the thermal interface layer. In addition, there is a limit to heat transfer that can be achieved with these conventional fillers.

Accordingly, an object of the present invention is to provide a new composite material for thermal interface materials having low dielectric constant and excellent physical properties.

In order to achieve such an object, this invention provides the composite material for thermal interface materials which mixed the hollow hollow micro size diamond shell with the polymeric resin base material, such as an epoxy.

The size of the diamond shell can be formed in the range of 1 to 5,000 ㎛, for example, the base material may be any one selected from epoxy, silicon, glassy bond.

Composite according to the present invention can change the physical properties of the composite due to the micro air space (micro air space) inside the diamond shell of the geometric shape mixed in the polymer resin.

Figure 1 schematically shows the cross-sectional structure of the composite of the present invention used as a thermal interface material. In the composite material 1 of the present invention, a diamond shell 1-1, which is a filler, and a polymer resin 1-2 are mixed, and are formed between the heat source 2 and the heat sink 3. The heat source may be a semiconductor element or the like, and the heat flow 4 takes place from the heat source to the heat sink.

As shown in Table 1, diamond has superior properties to other materials except for dielectric constant and density. In addition, the dielectric constant and density can be reduced by using the hollow diamond shell of the present invention.

Since the dielectric constant of air is 1, the dielectric constant of the diamond shell which is empty inside the shell decreases. The degree of reduction will be smaller as the shell wall thickness decreases at a constant shell size, the larger the shell size at the constant shell wall thickness (ie, the larger the volume of air), and the range of possible dielectric constants is diamond. It will be between the dielectric constant of 5.7 and the dielectric constant of air 1. Here, it is impossible to measure the dielectric constant of each diamond shell, and the dielectric constant of the entire diamond shell filled in the composite can be obtained. Also, assuming that the shell wall thickness is 5% and 10% of the shell size (100 μm in diameter), the diamond shell has a very low density of 0.51-1.84 g / cc, which changes the shell wall thickness. Can be controlled by

A diamond shell is prepared by combining a CVD diamond synthesis and a base material etching technique. That is, in the manufacture of a diamond shell, a diamond film is deposited on the surface of spherical porous silica particles having a predetermined size by CVD to form a diamond film having fine pores. In the prepared diamond film / silica composite, an porous hollow diamond shell is obtained by etching and removing porous silica particles inside the composite. Control of the formation and size of the voids in the diamond film can be made during pretreatment and synthesis for diamond film deposition. Etching is performed by acid-processing the base material of a composite_body | complex, for example in boiling Murakami solution. Here, the etching solution may reach the silica base material through the minute gap formed in the diamond film, and then, due to the capillary phenomenon of the porous base material, the base material sucks the solution and melts away. Through this process, the hollow porous diamond shell can be manufactured. The method for producing the diamond shell is not limited to the above method.

The prepared diamond shell is mixed with an epoxy base material to constitute a composite for thermal interface material. The volume of diamond shell in the composite is 40-60%, the thickness of the composite is about 50-200 μm, and the size of the diamond shell as a filler ranges from several μm to 1/2 of the thickness of the composite (ie, several μm to 100 μm). Μm), but is not limited to these ranges. In addition, the filler may be used by mixing a diamond shell and boron nitride, alumina, aluminum nitride, silica and the like together.

Such hollow diamond shell filled composites may also be used as underfill or encapsulation materials such as flip chips and lightweight high strength materials such as spacecraft.

Example 1.

Diamond shells having a diameter of 30-40 μm, a wall thickness of 3-5 μm and having one or several nanosize (1-1,000 nm) pores were prepared. This diamond shell was prepared by depositing a diamond film on porous silica matrix particles having a diameter of 20-30 µm using a next pole DC power plasma plasma synthesizer, and removing the substrate from a boiling Murakami solution. The synthesis conditions of diamond were 15 kW input power, 10% methane composition in hydrogen gas, 100 Torr pressure, and 200 sccm gas flow rate. Synthesis time was 1 hour. Since the dielectric constant of each diamond shell cannot be measured, the dielectric constant of the diamond in the free film form obtained under the same conditions as the diamond shell synthesis conditions is measured to predict the dielectric constant of the diamond shell. The dielectric constant of the free-film diamond (size 1 cm ² ) having a thickness of 500 μm obtained under these diamond synthesis conditions is 5.9, and the dielectric loss is 0.0067. Therefore, the dielectric properties of the diamond film forming the diamond shell can be expected to be similar.

Example 2.

The diamond shell prepared in Example 1 was mixed with an epoxy base material (density 1.5 g / cm ² , thermal conductivity 0.2 W / mK) having dielectric properties to make a composite material (thermal interface material). The size was 10 mm x 10 mm and the height was 5 mm. The bulk density of the diamond shell was 50%. For comparison, composites were prepared using silica (particle size: 3-20 μm), alumina (1-40 μm) and boron nitride (particle size: 50 μm) particles of the same volume and specification. The properties of these composites are shown in Table 2. Diamond shell composites have the highest thermal conductivity and the lowest dielectric constant and density. This shows that diamond shell composites are much better than other composites.

[Table 2] Comparison of properties of thermal interface materials

Epoxy Silica composites Alumina Composite Boron Nitride Composites Diamond shell composite Thermal Conductivity (W / mK) 0.2 1.2 1.6 2.0 2.9 Dielectric constant 3.5 3.7 8.1 3.9 3.5 Density (g / cc) 1.5 1.9 3.1 2.0 1.1

As can be seen from the above, the present invention uses a composite material filled with a micro diamond shell in a polymer resin as a thermal interface material of a semiconductor device, thereby providing a thermal interface material having excellent thermal dielectric properties that exceed the limits of existing materials. Could provide. The present invention can be used as a thermal interface material of a device that can cause thermal problems such as next-generation high-performance CPU and MCM. The composite can also be used as an underfill or sealing filler material, such as flip chips, or as a lightweight, high strength material such as spacecraft.

Claims (4)

Composite for thermointerface materials filled with a hollow diamond shell in a polymer resin matrix. The composite material of claim 1, wherein an outer diameter of the diamond shell is 1 to 5,000 μm. The composite of claim 1, wherein the base material is any one selected from epoxy, silicone, and glassy bonds. The composite of claim 1, further comprising silica, alumina, boron nitride, aluminum nitride particles together with a diamond shell.

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