CN1557585A - A kind of preparation method of spray deposition forming Si-Al alloy - Google Patents

Abstract

The invention provides a method for preparing Si-Al alloys formed by spray deposition, which is characterized in that: firstly prepare 25-50 wt% Si-Al master alloy ingots. Then the Si-Al alloy with 50-70 weight percent is prepared by spray deposition forming method. The spray forming process parameters are selected as follows: atomizing gas: nitrogen; atomizing pressure: 0.6-0.8 MPa; deposition distance: 400-600 mm; diameter of the draft tube: 3.2-4.0 mm. The invention has the advantages that the coefficient of thermal expansion of the Si-Al alloy is adjustable in the range of 6-13×10 ^-6 /K, the thermal conductivity is 110-150W/mK, and the density is 2.4-2.5g/cm ³ . It can be widely used in new packaging or heat dissipation materials required by telecommunications, aviation, aerospace, national defense and other related industrial electronic components.

Description

A kind of preparation method of spray deposition forming Si-Al alloy

technical field

The invention belongs to the field of silicon-aluminum alloy preparation technology and electronic packaging materials, and in particular provides a method for preparing a spray-formed high-silicon aluminum alloy with low thermal expansion coefficient, high thermal conductivity, low density and machinability, which is widely used in telecommunications, aviation , Aerospace, national defense and other related industrial electronic components required for new packaging or heat dissipation materials.

Background technique

In recent years, with the development of the electronic packaging industry towards high density and high speed, it is imperative to develop materials with good thermal conductivity to meet the heat dissipation requirements brought about by the increase in integration.

Ideal advanced electronic packaging materials should match typical semiconductor materials such as gallium arsenide and silicon, or have a slightly higher coefficient of thermal expansion (CTE), high thermal conductivity (>100W/m K) and Low density (<3 g/cm ³ ). In addition, encapsulation materials are expected to have reasonable stiffness (>100GPa) that can provide sufficient mechanical support for components and substrates that are sensitive to mechanical action. It also needs to be easily machined into shape and be painted using economical industry standard methods such as electroplating. Because the metal package can be integrated with some components (such as hybrid integrated A/D or D/A converter), the shape of the package is diversified, the heat dissipation is fast, the volume is small, the cost is low, and it is also conducive to reducing The inductance, capacitance and crosstalk between signals have become an important class of packaging materials.

The traditional metal electronic packaging materials (excluding particle-reinforced metal matrix composites) and their key properties are shown in Table 1. Among them, pure aluminum and copper are usually used as heat-dissipating electronic packaging materials because their thermal conductivity is as high as 200-390W/m·K. However, these materials have large thermal expansion coefficients and poor thermal matching performance with the ceramic substrate, which is not conducive to improving the overall reliability of the device. In order to reduce the thermal expansion coefficient of the material, Cu is mixed with Mo and W with a small thermal expansion coefficient (powder metallurgy or cold rolling) to form a composite material, which can obtain a high thermal conductivity effect, but the weight of the packaging structure is significantly increased, which is very important for aerospace. Packaged applications are an Achilles' heel. Moreover, the wettability between Cu-Mo and Cu-W is poor, the airtightness of the composite material is not good, the degree of densification is low, and the packaging performance is affected. Materials containing Be are toxic, which limits the application of this material. Other materials, such as Kovar (Fe-29Ni-17Co) and Invar (Ni-Fe) alloys, have low thermal expansion coefficients, but have high resistance and poor thermal conductivity, so they can only be used as heat dissipation and connection materials for low-power rectifiers. W and Mo have a linear expansion coefficient similar to Si, and have better thermal conductivity than Kovar and Invar alloys, so they are often used as supporting materials for semiconductor Si sheets. However, due to the poor wettability and poor solderability of W, Mo and Si, it is often necessary to plate or coat a special Ag-based alloy or Ni on the surface, which makes the process complicated and poor in reliability. Moreover, W and Mo are relatively expensive and dense, so they are not suitable for mass use. It can be seen that the current traditional metal electronic packaging materials cannot meet the comprehensive performance requirements of modern electronic packaging.

Table 1 Key performance data of typical metal electronic packaging materials Material Coefficient of thermal expansion (20℃)×10 ^-6 /K Thermal conductivity(k)W/m·K Density (ρ) g/cm ³ al 23.6 230 2.7 Cu 17.6 391 8.9 Cu-75%W 8.8 190 14.6 Cu-85%W 7.2 180 16.1 Cu-85%Mo 6.7 160 10 be 7.2 260 2.9 Kovar alloy 5.8 17 8.2 Invar alloy 0.4 11 8.1 W 4.45 168 19.3 Mo 5.1 140 10.2

Si-Al alloy has been proved to be a material system whose comprehensive properties meet the requirements of advanced electronic packaging (M.Jacobson and SPSSangha, Future trends in materials for lightweightmicrowave packaging, Microelectronics Int., 1998, 15, No3:47. SPSSangha, NovelAluminum Silicon Alloys for Electronics packaging, Journal of Engineering Science and Education, 1997, No 11:195). In the present invention, as one of the basic components of the alloy, silicon has a low thermal expansion coefficient (CTE of 4.1×10 ^-6 /K), high thermal conductivity (150W/m·K), low density (2.34g/cm ³ ), It has the advantages of stable chemical properties, low cost and abundant sources. Its main disadvantages are high melting point (1414°C) and high brittleness of the material. By adding an appropriate amount of low-melting-point Al to Si, the melting point of the alloy can be effectively reduced, the fracture toughness of the material can be improved, and the machinability of the material can be improved.

Si-Al alloys with a low silicon content can be formed by casting methods. However, in the range of 50-70 wt% Si composition, the as-cast microstructure of Si-Al alloy is mainly composed of large and isolated, polyhedral and high-aspect-ratio primary Si crystals, which obviously affects the mechanical properties and processing of the material. Bad performance. Usually, the size of the acicular primary silicon phase particles is on the order of millimeters, which easily leads to extreme anisotropy of the material structure and is not suitable for electronic packaging applications. For example, the thickness of the plate used for electronic packaging is generally 1-5mm. If casting materials are used, a single Si crystal may penetrate the entire plate thickness. This would make the material extremely difficult to process to the high-precision quality required for surface coating, since Si particles are prone to unidirectional cracking along preferred crystallographic planes. In addition, due to the existence of large-sized Si particles, the local CTE and thermal conductivity of the material will change greatly. It is generally considered that alloys with such a microstructure have no engineering application value.

A fine, isotropic microstructure is facilitated by the use of powder metallurgy techniques. However, powder metallurgy technology often involves complex procedures, resulting in increased costs, so it has not been popularized and applied in the preparation of Si-Al alloys. Another industrial technology that can achieve the above purpose is spray deposition forming technology. During spray forming, molten metal is atomized with a high velocity inert gas through an atomizer to produce fine droplets (typically ~40 μm in diameter). These droplets are deposited on a cold rotating substrate, undergoing rapid solidification to form a blank with a fine isotropic structure. The atomized Si-Al alloy droplets start to form Si crystals during the flight process, and the solidification phase on the surface of the deposition body is broken to produce a large number of Si phase nucleation sites, and these nuclei grow up and collide with each other to limit the Si phase. The growth process makes it impossible to form isolated, highly oriented Si particles as in the cast structure, and the formed Si crystals are randomly oriented, which solves the problem of anisotropy in microstructure and properties. As a result, the coherence of the deposited blank structure is achieved, the isotropic alloy structure and properties are produced, and it is beneficial to the fine processing of the surface. After appropriate subsequent treatment to eliminate the small amount of porosity formed during the deposition process, these deposited blanks can be used to manufacture various high-performance packaging components. Obviously, Si-Al alloys with low density, low thermal expansion, high thermal conductivity and machinability are controllable thermal expansion materials (the thermal expansion coefficient of the alloy can be controlled by adjusting the composition according to needs), and have good comprehensive packaging process performance advantages.

Contents of the invention

The object of the present invention is to provide a method for preparing a low thermal expansion coefficient, high thermal conductivity, low density and machinable high-silicon aluminum alloy, which is widely used in telecommunications, aviation, aerospace, national defense and other related industrial electronic components. New packaging or heat dissipation materials.

The composition of the present invention: Prefabrication of 25-50% by weight Si-Al master alloy by medium frequency induction furnace, and then according to the final target composition, the final 50-70% by weight Si-Al is obtained by spray deposition forming method by adding Si to the master alloy. Al alloy; the specific method is as follows:

1. Preparation of master alloy:

Putting 25-50% by weight of pure Si and the rest being industrial pure Al are put into an intermediate frequency induction furnace to heat up and melt, and cast into an intermediate alloy ingot for future use. Both pure Si and industrial pure Al are lumps.

2. Preparation of 50-70% by weight Si-Al alloy by spray deposition: put the above-mentioned master alloy ingot into the crucible of an intermediate frequency induction furnace. According to the composition requirements of 50-70% by weight Si-Al alloy, if necessary, add 0-45% by weight of pure Si to heat up and melt (the master alloy is 50% by weight of Si-Al, and when preparing spray deposition and forming 50% by weight of Si-Al alloy at the same time , without adding pure Si). Then the 50-70 wt% Si-Al alloy is prepared by spray deposition forming method. The spray forming process parameters are selected as follows: atomizing gas: nitrogen; atomizing pressure: 0.6-0.8 MPa; deposition distance: 400-600 mm; diameter of the draft tube: 3.2-4.0 mm.

The advantages of the present invention are:

(1) Uniform and isotropic excellent physical properties: low thermal expansion coefficient (can be adjusted according to requirements, range: 6～13×10 ^-6 /K). According to different packaging matching materials, the required Si-Al alloy materials can be designed to match the thermal expansion coefficients of the two as much as possible; low density (2.4-2.5g/cm ³ ), especially suitable for packaging applications of aerospace electronic components; High thermal conductivity (110 ~ 150W/mK), meeting the heat dissipation requirements brought about by increased integration; low electrical conductivity (<10 ^-6 Wm); high stiffness (specific stiffness > 44GPa cm ³ /g); good thermomechanical stability (The operating temperature can reach 500°C);

(2) Good machinability and packaging process performance: high machining accuracy can be easily obtained by using carbide or polycrystalline diamond tools; it is easy to process into different shapes (including various grooves, narrow grooves and corners, etc. ); environmentally friendly, free of elements harmful to health, easy to recycle; easy to carry out surface coating treatments such as gold plating, silver and nickel; good welding performance.

Description of drawings

Fig. 1 is the microstructure of (a) spray-formed 60 wt% Si-Al alloy and (b) spray-formed 70 wt% Si-Al alloy in the present invention.

Fig. 2 is an experimental data diagram of the linear expansion coefficient and silicon content of the spray-formed Si-Al alloy in the present invention. The abscissa is the Si content and weight percentage; the ordinate is the linear expansion coefficient, and the unit is 10 ^-6 /K.

Fig. 3 is an experimental data diagram of thermal conductivity and temperature of the spray-formed Si-Al alloy in the present invention. The abscissa is the temperature, ℃; the ordinate is the thermal conductivity, the unit is W/mK.

Fig. 4 is an experimental data diagram of the resistivity and silicon content of the spray-formed Si-Al alloy in the present invention. The abscissa is Si content and weight percentage; the ordinate is resistivity, and the unit is 10 ^-6 /Ωm.

Fig. 5 is an example diagram of a spray-formed 50% by weight Si-Al alloy machined part (25×15×5 mm) in the present invention. Part surface roughness R _a ≤1.6μm.

Detailed ways

Example 1

A 50% by weight Si-Al alloy was prepared. A 50% by weight Si-Al master alloy ingot was melted in a 150 kg medium frequency induction furnace. Put pure Si with a block size of 4-6 mm and a weight of 15 kg and industrial pure Al with a weight of 15 kg into an intermediate frequency induction furnace crucible, heat up to melt, and cast into an intermediate alloy ingot for later use. The above-mentioned master alloy ingot was remelted, and a 50% by weight Si-Al alloy was prepared by a spray deposition forming method. The process parameters are selected as follows: atomization gas: nitrogen; atomization pressure: 0.7MPa; deposition distance: 550mm; diameter of draft tube: 3.6mm. The coefficient of thermal expansion of the material is 10.6×10 ^-6 /K. The thermal conductivity is 121W/mK (150°C). The resistivity is 0.4×10 ^-6 Ωm.

Example 2

A 60% by weight Si-Al alloy was prepared. A 30% by weight Si-Al master alloy ingot was melted in a 150 kg medium frequency induction furnace. Put pure Si with a block size of 4-6 mm and a weight of 3 kg and industrial pure Al with a weight of 7 kg into an intermediate frequency induction furnace crucible, heat up to melt, and cast into an intermediate alloy ingot for later use. The above-mentioned master alloy ingot was remelted, 4.3 kg of pure Si was added, and a 60% by weight Si-Al alloy was prepared by spray deposition forming method. The process parameters are selected as follows: atomization gas: nitrogen; atomization pressure: 0.8MPa; deposition distance: 600mm; diameter of draft tube: 3.8mm. The coefficient of thermal expansion of the material is 9.1×10 ^-6 /K. The thermal conductivity is 113W/mK (150°C). The resistivity is 0.9×10 ^-6 Ωm. The density of the as-deposited 60wt% Si-Al alloy is 2.3164g/cm ³ , and the density after hot isostatic pressing is 2.4486g/cm ³ , which is close to the theoretical density of the alloy.

Example 3

A 70% by weight Si-Al alloy was prepared. A 30% by weight Si-Al master alloy ingot was melted in a 150 kg medium frequency induction furnace. Put pure Si with a block size of 4-6 mm and a weight of 6 kg and industrial pure Al with a weight of 14 kg into an intermediate frequency induction furnace crucible, heat up to melt, and cast into an intermediate alloy ingot for later use. The above-mentioned master alloy ingot was remelted, 13.3 kg of pure Si was added, and a 70% by weight Si-Al alloy was prepared by spray deposition forming method. The process parameters are selected as follows: atomization gas: nitrogen; atomization pressure: 0.75MPa; deposition distance: 590mm; diameter of draft tube: 4.0mm. The coefficient of thermal expansion of the material is 8.1×10 ^-6 /K. The resistivity is 1.6×10 ^-6 Ωm.

Claims (1)

1, a kind of preparation method of jet deposition formation Si-Al alloy, it is characterized in that: adopt prefabricated 25～50 weight %Si-Al master alloys of medium-frequency induction furnace, obtain final 50～70 weight %Si-Al alloys by the mode of in master alloy, adding Si with the jet deposition formation method according to the ultimate aim composition then; Concrete grammar is as follows:

The preparation of a, master alloy: will account for the pure Si of 25 ~ 50 weight %, all the other put into the medium-frequency induction furnace fusing that heats up for the starting material of industrial pure Al, and it is standby to be cast into intermediate alloy ingot, and pure Si and industrial pure Al are block;

The preparation of b, jet deposition formation 50～70 weight %Si-Al alloys: above-mentioned intermediate alloy ingot is put into the medium-frequency induction furnace crucible, according to 50～70 weight %Si-Al alloying constituent requirements, the pure Si that optionally adds 0～45 weight % heats up and melts, and adopts jet deposition formation method preparation 50 ~ 70 weight %Si-Al alloys then; The spray deposition processing parameter is selected as follows: atomizing gas: nitrogen; Atomizing pressure: 0.6～0.8MPa; Deposition distance: 400～600mm; Draft-tube diameter: 3.2～4.0mm.

Images