High-thermal-conductivity aluminum-silicon / diamond composite material for electronic packaging and preparation method thereof

Abstract

This invention discloses a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging and its preparation method, comprising: diamond surface modification; mixing silicon powder and modified diamond micropowder with a binder, followed by molding, debinding, and sintering, and then CNC machining and laser cutting to obtain a silicon preform and a diamond preform; assembling the diamond preform into a confined preform by embedding it into a groove in the silicon preform and cold pressing it for shaping; pressure impregnation of high-silicon aluminum melt in a mold, followed by pressure holding and cooling demolding. The composite material has an aluminum-silicon coating-aluminum / diamond interlayer-aluminum-silicon coating sandwich structure, with a thermal conductivity ≥525W / (m·K) and a coefficient of thermal expansion ≤5.0×10⁻⁶. ‑6 / K, interfacial bonding strength ≥280MPa, airtightness ≤5×10 ‑10 Pa·m 3 / s, dimensional tolerance ≤±0.01mm. This invention enables one-time precision molding of complex-shaped electronic packaging materials, which can be used for ultra-high power electronic packaging substrates and heat sinks.

Description

Technical Field

[0001] This invention relates to the field of electronic packaging materials technology, and in particular to a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging and its preparation method. Background Technology

[0002] The electronics and information industry is one of the leading and pillar industries of the world's economic development. With the rapid development of electronic devices towards high power, high integration, and lightweight design, the heat flux density of power devices is increasing dramatically, placing stringent demands on the heat dissipation performance, shape adaptability, and structural stability of electronic packaging materials. Traditional electronic packaging materials, such as pure aluminum, copper alloys, and ceramics, struggle to balance high thermal conductivity, low coefficient of thermal expansion, and good processability, failing to meet the heat dissipation and packaging requirements of ultra-high power devices. Metal matrix composites organically combine the excellent thermal conductivity and plastic deformation properties of the metal matrix with the low coefficient of thermal expansion and high strength of the reinforcement, resulting in electronic packaging materials with controllable thermal conductivity and coefficient of thermal expansion over a wide range. This has become a core direction for solving high-end heat dissipation challenges. Among them, high-silicon aluminum / diamond composites stand out due to their unique advantages: high-silicon aluminum alloys possess both a low coefficient of thermal expansion and excellent processability, while diamond, as the natural material with the highest thermal conductivity, achieves a synergistic performance of "high thermal conductivity - low thermal expansion - easy sealing" when combined, showing broad application prospects in high-end fields such as aerospace, high-power electronic devices, and IGBT modules.

[0003] However, high-silicon aluminum / diamond composites still face many technical bottlenecks in practical applications. First, interfacial bonding is a significant problem. The physicochemical properties of aluminum and diamond differ greatly, resulting in extremely poor wettability (wetting angle as high as 148°), weak interfacial bonding, and a tendency for stress concentration and failure. Furthermore, the high-temperature preparation process easily generates brittle interfacial products, Al4C3, which are prone to deliquescence and hydrolysis, leading to interfacial debonding, increased thermal resistance, and severely deteriorating the thermal properties and mechanical stability of the composite material. Second, existing preparation methods, such as hot-pressing sintering and pressureless impregnation, are insufficient for precise molding of specific structures such as plates, grooves, and embedded structures. Complex shapes require multiple processing and splicing steps, which is not only inefficient but also prone to interfacial cracking, making it difficult to guarantee airtightness (traditional processes typically only achieve an airtightness of 1×10⁻⁶). -8 Pa·m 3 The shape controllability is poor (at the / s level). Furthermore, the low packing density of single-size diamond particles results in insufficient volume fraction of the reinforcing phase, easily leading to defects such as porosity and shrinkage within the composite material. Simultaneously, the silicon phase in high-silicon aluminum alloys tends to agglomerate, further reducing material density and limiting improvements in thermal conductivity and mechanical properties. Existing processes or equipment are costly (e.g., vacuum hot pressing) or inefficient (e.g., pressureless infiltration), and it is difficult to achieve integrated fabrication of gradient structure composites, thus hindering the industrial application of the material.

[0004] Therefore, how to achieve synergistic breakthroughs in improving interface bonding, enhancing shape control precision, and improving material density and thermophysical properties through innovative process design, in order to overcome the adverse effects of weak interface bonding, poor shape controllability, and insufficient density in existing technologies, and to realize the controllable preparation of composite materials for electronic packaging with high thermal conductivity, low expansion, high precision, and high reliability, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention provides a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging and its preparation method, which solves the defects of weak interfacial bonding, poor shape controllability, insufficient thermal conductivity and poor density in the preparation process of high silicon aluminum / diamond composite materials in the prior art.

[0006] On one hand, the present invention provides a method for preparing a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging, comprising the following steps: (1) Surface modification treatment of diamond micro powder to obtain surface modified diamond micro powder; (2) The silicon powder is mixed with the composite binder, molded, degreased, sintered and densified, and then CNC precision machined to obtain a silicon preform with a preset shape; the surface modified diamond micro powder is mixed with the composite binder, molded, degreased, sintered and densified, and then laser-cut to obtain a diamond preform. (3) The diamond preform is embedded in the groove of the silicon preform, and then assembled by a precision jig and cold-pressed to obtain the confined preform. (4) Place the confined preform in a mold, and impregnate the refined high-silicon aluminum melt into the confined preform under pressure. Hold the pressure and cool, then demold to obtain a high thermal conductivity aluminum-silicon / diamond composite material.

[0007] According to the present invention, a method for preparing a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging is provided, wherein the surface modification treatment in step (1) includes: (1-1) The diamond micro powder is kept at 400-500℃ for 20-40 minutes in air to form an oxide layer; (1-2) The micro-oxidized diamond powder was immersed in an ethanol solution containing tetraethyl orthosilicate, ultrasonically dispersed, and then vacuum dried at 100-130℃ for 1-3 hours to grow a silicon-based transition layer in situ on the surface of the oxide layer. (1-3) Keep at 180-220℃ for 0.5-1.5h to allow the silicon-based transition layer to crosslink and solidify.

[0008] According to the present invention, a method for preparing a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging is provided. In step (2), the CNC precision machining uses a carbide end mill with a spindle speed of 8000-12000 r / min, a feed rate of 150-250 mm / min, and a cutting depth of 0.1-0.3 mm / cut. The laser cutting process uses a pulsed fiber laser with a laser power of 300-500 W, a pulse frequency of 20-50 kHz, a spot diameter of 50-80 μm, and a cutting speed of 20-40 mm / s.

[0009] According to the present invention, a method for preparing a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging is provided, wherein the diamond micro powder is composed of one or more particle size distributions, the particle size being selected from at least one of 45μm, 180μm, and 270μm, and the distribution mass ratio is 3:1 or 9:3:1; the silicon powder is composed of two or more particle size distributions, the particle size being selected from at least two of 3μm, 5μm, 12μm, and 45μm, and the distribution mass ratio is 3:1.

[0010] According to the present invention, a method for preparing a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging is provided. In step (3), the precision fixture is a vacuum adsorption platform. The vacuum adsorption platform has a partitioned vacuum cavity, and the adsorption force of each adsorption region is independently adjustable. The bonding and assembly process is supplemented by ultrasonic vibration with a vibration frequency of 20-30kHz and an amplitude ≤5μm.

[0011] According to the present invention, a method for preparing a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging is provided, wherein the silicon content of the high silicon aluminum melt in step (4) is 30-70 wt.%; the impregnation pressure is 70-85 MPa, the impregnation temperature is 830-900 °C, and the holding time is 30-50 min.

[0012] According to the present invention, a method for preparing a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging is provided, wherein the composite binder is prepared by mixing silicone resin and paraffin wax in a mass ratio of 3:1 and dissolving them in solvent gasoline.

[0013] On the other hand, the present invention provides a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging, which is prepared by a method for preparing high thermal conductivity aluminum-silicon / diamond composite materials for electronic packaging. The composite material has a sandwich structure of aluminum-silicon coating - aluminum / diamond composite intermediate layer - aluminum-silicon coating. The interfacial bonding strength between the aluminum-silicon coating and the aluminum / diamond composite intermediate layer is ≥280MPa, and the airtightness is ≤5×10⁻⁶. -10 Pa·m 3 / s.

[0014] According to the present invention, a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging is provided, wherein the composite material has a plate-like structure, a groove-like structure, or an embedded structure.

[0015] According to the present invention, a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging is provided, wherein the dimensional tolerance of the composite material is ≤ ±0.01 mm.

[0016] The high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging and its preparation method provided by this invention have the following advantages compared with the prior art: (1) The high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging and its preparation method provided by the present invention, through diamond surface modification treatment (surface micro-oxidation + in-situ growth of silicon-based transition layer), forms a silicon-based composite film layer with good wettability with aluminum liquid on the diamond surface, which solves the technical problems of poor wettability between diamond and aluminum liquid and easy formation of brittle Al4C3 phase, and achieves the beneficial effects of reducing the wetting angle from more than 145° to less than 65°, effectively suppressing the formation of brittle phase at the interface, and achieving an interface bonding strength ≥280MPa.

[0017] (2) The high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging and its preparation method provided by the present invention solves the technical problems of low packing density of single-size particles, insufficient volume fraction of reinforcing phase, and easy formation of pores and shrinkage by multi-size particle gradation design (diamond particle size 45 / 180 / 270μm gradation, silicon powder particle size 3 / 5 / 12 / 45μm gradation). It achieves the beneficial effects of controlling the diamond volume fraction at 50-75 vol.%, composite material density ≥99.5%, and thermal conductivity up to 560 W / (m·K).

[0018] (3) The high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging and its preparation method provided by the present invention, through the precise confinement process of "preform preparation - cutting and assembly - integrated pressure impregnation", combined with CNC precision machining and laser cutting technology, solves the technical problems of complex shape products being difficult to form in one step, poor dimensional accuracy, and easy delamination between the coating and the substrate. It achieves the beneficial effects of dimensional tolerance ≤ ±0.01mm, being able to be directly formed into sandwich structures such as plate-shaped / grooved / embedded, and not requiring secondary shaping processing.

[0019] (4) The high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging and its preparation method provided by the present invention solves the technical problems of insufficient bonding and micro gaps between the diamond preform and the silicon preform groove by using gradient vacuum adsorption, elastic buffer composite structure and ultrasonic vibration assisted bonding. It achieves the beneficial effects of bonding gap ≤0.02mm, bonding degree compliance rate ≥99.5%, and ensuring the integrity of the interface after impregnation.

[0020] (5) The high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging and its preparation method provided by the present invention, through optimization of aluminum alloy refining process (argon removal + refining agent + modifier) ​​and synergistic control of pressure impregnation parameters (70-85MPa, 830-900℃), solves the technical problems of high hydrogen content, many impurities, coarse grains and insufficient impregnation in aluminum liquid, achieving an aluminum liquid density ≥2.49g / cm³. 3 Hydrogen content ≤ 6.0%, composite material air tightness ≤ 5×10 -10 Pa·m 3 The beneficial effects include a bending strength of up to 320 MPa. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a process flow diagram of the preparation method of the high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging provided by the present invention; Figure 2 This is a schematic diagram of the structure of the high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging provided by the present invention; Figure 3 This is a front view of the high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging provided by the present invention; Figure 4 This is a back view of the high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging provided by the present invention.

[0023] Figure label: 1. Aluminum-silicon coating; 2. Aluminum / diamond composite intermediate layer. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] The following is combined Figures 1-4 The present invention describes a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging and its preparation method.

[0026] Figure 1This is a process flow diagram of the preparation method of the high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging provided by the present invention.

[0027] like Figure 1 As shown, the preparation method of the high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging provided by the present invention includes the following steps: surface modification treatment of diamond micro powder to obtain surface-modified diamond micro powder; mixing silicon powder with a composite binder, molding, degreasing, sintering and densifying, and then precision machining by CNC to obtain a silicon preform with a preset shape; mixing the surface-modified diamond micro powder with a composite binder, molding, degreasing, sintering and densifying, and then laser cutting to obtain a diamond preform; embedding the diamond preform into the groove of the silicon preform, bonding and assembling it by a precision jig, cold pressing and shaping to obtain a confined preform; placing the confined preform in a mold, impregnating the confined preform with refined high-silicon aluminum melt under pressure, holding pressure and cooling, demolding, and obtaining the high thermal conductivity aluminum-silicon / diamond composite material.

[0028] In step (1) of the present invention, the surface modification treatment includes: keeping diamond micro powder at 400-500℃ for 20-40 min in an air atmosphere to form an oxide layer; immersing the micro-oxidized diamond micro powder in an ethanol solution containing tetraethyl orthosilicate, dispersing it ultrasonically, and then vacuum drying it at 100-130℃ for 1-3 h to grow a silicon-based transition layer in situ on the surface of the oxide layer; and keeping it at 180-220℃ for 0.5-1.5 h to crosslink and solidify the silicon-based transition layer.

[0029] In this invention, the oxide layer has a thickness of 5-10 nm, the silicon-based transition layer has a thickness of 20-30 nm, and the total thickness of the silicon-based composite film covering the diamond surface after the silicon-based transition layer is cross-linked and cured is 25-40 nm.

[0030] In a preferred embodiment of the present invention, the mass fraction of the tetraethyl orthosilicate is 5 wt.%, the ultrasonic dispersion time is 20 min, the vacuum drying temperature is 120 °C, the heat preservation time is 2 h, the low-temperature curing temperature is 200 °C, and the heat preservation time is 1 h.

[0031] In this invention, after the surface modification treatment, the wetting angle between diamond and molten aluminum is reduced from more than 145° to less than 65°, and the continuous formation of the brittle interfacial phase Al4C3 can be effectively suppressed.

[0032] In some embodiments of the present invention, a pretreatment of cleaning diamond micro powder is included before step (1): ultrasonic cleaning with ethanol for 15 min, rinsing with deionized water 3 times, and drying at 60°C.

[0033] In step (2) of this invention, the CNC precision machining uses a carbide end mill with a spindle speed of 8000-12000 r / min, a feed rate of 150-250 mm / min, and a cutting depth of 0.1-0.3 mm / cut; the laser cutting process uses a pulsed fiber laser with a laser power of 300-500 W, a pulse frequency of 20-50 kHz, a spot diameter of 50-80 μm, and a cutting speed of 20-40 mm / s.

[0034] In a preferred embodiment of the present invention, the CNC precision machining employs a helical cutting method when machining the groove, with a helix angle of 30°; during the machining process, emulsion cooling is used, with a coolant flow rate of 10-15 L / min.

[0035] In this invention, for parts with high surface precision requirements, the CNC precision machining process further includes a grinding finishing process: the grinding wheel grit size is W14, the grinding speed is 20-30m / s, and the feed rate is 0.01mm / cycle.

[0036] In a preferred embodiment of the present invention, nitrogen is used as a protective gas in the laser cutting process, with a gas flow rate of 15-25 L / min; a Z-axis dynamic focusing system is used during the cutting process, and the focal length deviation is controlled within ±2 μm.

[0037] In this invention, after laser cutting and finishing, the surface roughness Ra of the diamond preform is ≤0.8μm.

[0038] In this invention, the diamond micro powder is composed of one or more particle size distributions, with the particle size selected from at least one of 45μm, 180μm, and 270μm, and the distribution mass ratio is 3:1 or 9:3:1; the silicon powder is composed of two or more particle size distributions, with the particle size selected from at least two of 3μm, 5μm, 12μm, and 45μm, and the distribution mass ratio is 3:1.

[0039] In this invention, through the aforementioned gradation design, the diamond volume fraction of the diamond preform is controlled within the range of 50-75 vol.%, preferably 55-70 vol.%, more preferably 60-65 vol.%, and the silicon volume fraction of the silicon preform is controlled within the range of 30-50 vol.%.

[0040] In a preferred embodiment of the present invention, when a high thermal conductivity of the aluminum-silicon coating is desired, the silicon powder is selected with a larger particle size of 12-45 μm and a lower volume fraction of 30 vol.% for gradation; when a low coefficient of thermal expansion is desired, the silicon powder is selected with a smaller particle size of 3-5 μm and a higher volume fraction of 50 vol.% for gradation.

[0041] In step (3) of the present invention, the precision fixture is a vacuum adsorption platform, which has a partitioned vacuum cavity and the adsorption force of each adsorption area is independently adjustable; the bonding assembly process is supplemented by ultrasonic vibration with a vibration frequency of 20-30kHz and an amplitude of ≤5μm.

[0042] In this invention, the vacuum adsorption platform is divided into multiple adsorption areas according to the contour of the silicon preform groove, and the adsorption force of each area is adjusted by an independent vacuum valve, wherein the adsorption force of the edge area is 10-15% higher than that of the center area.

[0043] In a preferred embodiment of the present invention, the adsorption surface of the diamond preform adsorption fixture is an elastic silicone pad, and the silicone pad is embedded with micro-air channels to achieve uniform adsorption; during the bonding process, the elastic silicone pad adapts to the surface micromorphology of the diamond preform.

[0044] In this invention, through the synergistic effect of the vacuum adsorption platform and ultrasonic vibration, the contact gap between the diamond preform and the silicon preform groove is ≤0.02mm, preferably ≤0.01mm, and the adhesion compliance rate is ≥99.5%.

[0045] In this invention, the cold pressing and shaping pressure is 15-25 MPa, preferably 18 MPa.

[0046] In step (4) of the present invention, the silicon content of the high-silicon aluminum melt is 30-70 wt.%; the impregnation pressure is 70-85 MPa, the impregnation temperature is 830-900℃, and the holding time is 30-50 min.

[0047] In a preferred embodiment of the present invention, for embedded sandwich structure products, the impregnation pressure is increased to 80-85 MPa and the pressure holding time is extended to 40-50 min.

[0048] In this invention, the high-silicon aluminum melt is made by melting and refining ZL104 aluminum alloy or a customized high-silicon aluminum alloy. The composition of the ZL104 aluminum alloy is Si 7.97wt.%, Mg 0.716wt.%, Fe 0.725wt.%, with the balance being Al.

[0049] In this invention, the smelting and refining process includes: smelting at 700-750℃, continuously introducing argon gas into the molten aluminum and mechanically stirring to remove hydrogen, adding 0.3% of the total mass of the molten aluminum as a refining agent to remove impurities, wherein the refining agent is a mixture of sodium salt, potassium salt and fluoride in a mass ratio of 2:1:1; then adding 0.3 wt.% each of the modifiers aluminum-titanium-boron (Al-Ti5-B) and aluminum-strontium (Al-10Sr) to refine the grains; and refining for 120 minutes from the time the aluminum ingot is completely melted.

[0050] In a preferred embodiment of the present invention, the density of the refined aluminum liquid is ≥2.49 g / cm³. 3 The corresponding hydrogen content is ≤6.0%.

[0051] In this invention, the mold in step (4) is preheated to 200-250°C, the inner wall is uniformly sprayed with release agent, and a layer of graphite felt is laid on the top of the mold. The graphite felt is used to reduce the heat loss of the preform and maintain temperature stability.

[0052] In this invention, the pressure-holding cooling is cooling to below 200°C, preferably 150-180°C, while maintaining pressure.

[0053] In this invention, the composite adhesive is a mixture of silicone resin and paraffin wax in a mass ratio of 3:1, dissolved in solvent gasoline.

[0054] Figure 2 This is a schematic diagram of the structure of the high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging provided by the present invention; Figure 3 This is a front view of the high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging provided by the present invention; Figure 4 This is a back view of the high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging provided by the present invention.

[0055] like Figure 2 , Figure 3 and Figure 4 As shown, the high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging provided by this invention is prepared using a method for preparing high thermal conductivity aluminum-silicon / diamond composite materials for electronic packaging. The composite material has a sandwich structure of aluminum-silicon coating - aluminum / diamond composite intermediate layer - aluminum-silicon coating. The interfacial bonding strength between the aluminum-silicon coating and the aluminum / diamond composite intermediate layer is ≥280MPa, and the airtightness is ≤5×10⁻⁶. -10 Pa·m 3 / s.

[0056] In this invention, the composite material has a density of ≥99.5% and no internal through-holes or shrinkage.

[0057] In this invention, the thermal conductivity of the composite material is 450-600 W / (m·K), and the coefficient of thermal expansion is 4.5-7.5 × 10⁻⁶. -6 / K, with a bending strength of 250-350MPa.

[0058] In some embodiments of the present invention, the thermal conductivity of the composite material can reach 550 W / (m·K) or higher, and the coefficient of thermal expansion is as low as 4.5 × 10⁻⁶. -6 / K, with a bending strength of up to 320MPa.

[0059] In this invention, the composite material is a plate-like structure, a groove-like structure, or an embedded structure. In some embodiments of this invention, the composite material may also be a stepped structure or a structure with heat dissipation teeth.

[0060] In this invention, the dimensional tolerance of the composite material is ≤ ±0.01 mm.

[0061] In this invention, the surface of the composite material can be directly milled and welded.

[0062] Example 1 Synthetic diamond powder with a particle size of 180 μm and a nitrogen content of 170 ppm was selected. It was ultrasonically cleaned with ethanol for 15 min, rinsed three times with deionized water, and dried at 60 °C. The cleaned diamond powder was placed in a tube furnace and kept at 450 °C for 30 min in an air atmosphere to form a uniform oxide layer with a thickness of 5-10 nm. An ethanol solution containing 5 wt.% tetraethyl orthosilicate was prepared, and the micro-oxidized diamond powder was immersed in the solution and ultrasonically dispersed for 20 min. Then, it was placed in a vacuum drying oven at 120 °C for 2 h to grow a silicon-based transition layer with a thickness of 20-30 nm in situ on the surface of the oxide layer. The treated diamond powder was placed in an oven at 200 °C for 1 h to allow the silicon-based transition layer to crosslink and solidify, resulting in modified diamond powder with a silicon-based composite film layer covering the surface of 25-40 nm.

[0063] 12μm and 45μm silicon powders were graded at a mass ratio of 3:1, with a silicon volume fraction of 30 vol.%. The graded silicon powder was mixed evenly with a silicone resin-paraffin composite binder (mass ratio 3:1, dissolved in solvent gasoline), and molded into a block blank under a pressure of 15 MPa. The blank was placed in a heating furnace, and after holding at 250℃ for 0.5 h to remove paraffin, holding at 400℃ for 1 h to crosslink the silicone resin, and holding at 750℃ for 1 h to sinter and densify, a silicon preform was obtained after cooling. A CNC vertical milling machine was used. A carbide end mill was used to mill a silicon preform at a spindle speed of 10000 r / min, a feed rate of 200 mm / min, and a depth of cut of 0.2 mm / cut. The grooves were machined using a helical cutter (helix angle 30°). The process was cooled with emulsion (flow rate 12 L / min). After machining, the preform was finished by grinding with a grinding wheel (grit size W14, grinding speed 25 m / s, feed rate 0.01 mm / cut) to obtain an aluminum-silicon coated sheet with a dimensional tolerance of ±0.01 mm.

[0064] Modified diamond micro powder was mixed evenly with a composite binder and molded into a block blank under a pressure of 20 MPa. After undergoing the same degreasing, cross-linking, and sintering densification process as the silicon preform, a diamond preform was obtained. The preform was then cut using a pulsed fiber laser with a laser power of 400 W, a pulse frequency of 30 kHz, a spot diameter of 60 μm, and a cutting speed of 30 mm / s. Nitrogen was used as the protective gas (flow rate of 20 L / min), and a Z-axis dynamic focusing system was employed (focal length deviation ≤ 2 μm). After cutting, the edges were finished by grinding with a grinding wheel to obtain a diamond intermediate block with a surface roughness Ra ≤ 0.8 μm.

[0065] ZL104 aluminum alloy (Si 7.97wt.%, Mg 0.716wt.%, Fe 0.725wt.%, balance Al) was selected as the base material and blended at a mass ratio of 40:60 to obtain a high-silicon aluminum alloy with a Si content of 60wt.%, which was then melted at 880℃. High-purity argon gas was continuously introduced into the aluminum melt while mechanically stirring to remove hydrogen. 0.3% of the total mass of the aluminum melt was added as a refining agent (sodium salt:potassium salt:fluoride = 2:1:1) to remove impurities. Then, 0.3wt.% each of the modifiers aluminum-titanium-boron (Al-Ti5-B) and aluminum-strontium (Al-10Sr) were added to refine the grains. After 120 minutes of refining from the complete melting of the aluminum ingot, a sample was taken for testing, and the density of the aluminum melt was 2.51 g / cm³. 3 (Corresponding to a hydrogen content of 5.2%), keep warm and ready for use.

[0066] The mold was preheated to 220℃, and a release agent was evenly sprayed onto the inner wall. A layer of graphite felt was laid on top. The mold was stacked and assembled in the order of "aluminum-silicon coated sheet - diamond intermediate block - aluminum-silicon coated sheet". A gradient vacuum adsorption platform was used for bonding. The adsorption force in the edge area was 12% higher than that in the center area. The bonding process was supplemented with ultrasonic vibration (frequency 25kHz, amplitude 3μm) to make the gap between the contact surfaces ≤0.01mm. Then, it was cold-pressed and shaped under 18MPa pressure to obtain a confined preform (diamond volume fraction 62 vol.%). The confined preform was placed in a pressure impregnation device, and high-silicon aluminum melt at 880℃ was slowly poured in. After complete coverage, an impregnation pressure of 80MPa was applied and held for 35min. The pressure was kept stable during the holding process. The mold was cooled to 180℃ under the pressure and demolded to obtain a high thermal conductivity aluminum-silicon / diamond composite material.

[0067] The composite material prepared in this embodiment was subjected to performance tests: the thermal conductivity was 552 W / (m·K), and the coefficient of thermal expansion (25-200℃) was 5.0 × 10⁻⁶. -6 / K, with a flexural strength of 315MPa, an interfacial bond strength between the aluminum-silicon cladding and the aluminum / diamond composite interlayer of 295MPa, and an airtightness of 3.2×10. -10 Pa·m 3 / s.

[0068] Example 2 Artificially synthesized diamond micropowder with a particle size of 270 μm and a nitrogen content of 165 ppm was selected. It was cleaned, micro-oxidized, grown in situ with a silicon-based transition layer, and cured at low temperature according to the method in Example 1 to obtain modified diamond micropowder with a silicon-based composite film covering the surface.

[0069] 5μm and 12μm silicon powders were selected and graded at a mass ratio of 3:1, with a silicon volume fraction of 50 vol.%. After molding, degreasing, crosslinking, and sintering densification according to the method of Example 1, silicon preforms with embedded grooves were machined by CNC milling with a dimensional tolerance of ±0.01 mm.

[0070] Modified diamond micro powder was mixed with a composite binder, and then molded, densified, laser-cut and finished according to the method in Example 1 to obtain a diamond intermediate block with a surface roughness Ra≤0.8μm.

[0071] Using ZL104 aluminum alloy as the base material, a high-silicon aluminum alloy with a Si content of 70 wt.% was prepared and smelted at 900℃. Following the method in Example 1, argon was used to remove hydrogen, and refining agents and modifiers were added. After refining for 120 minutes, the density of the molten aluminum was 2.49 g / cm³. 3 (Corresponding to a hydrogen content of 5.8%), keep warm and ready for use.

[0072] The mold is preheated to 250℃, and the inner wall is sprayed with a release agent. The diamond intermediate block is inserted into the groove of the silicon preform and bonded using a gradient vacuum adsorption platform. The edge adsorption force is 15% higher than that of the center area. The ultrasonic vibration frequency is 20kHz and the amplitude is 5μm. The contact surface gap is ≤0.02mm. The mold is cold-pressed at 20MPa for shaping. The outer layer is covered with high-silicon aluminum powder with a Si content of 50wt.%. The mold is assembled into a confined preform according to the structure of "aluminum-silicon cladding sheet - embedded diamond intermediate block - aluminum-silicon cladding sheet". The confined preform is placed in a pressure impregnation device, and 900℃ high-silicon aluminum melt is poured in. An impregnation pressure of 85MPa is applied and the pressure is held for 40 minutes. The mold is then cooled and demolded to obtain a high thermal conductivity aluminum-silicon / diamond composite material.

[0073] The composite material prepared in this embodiment was subjected to performance tests: the thermal conductivity was 560 W / (m·K), and the coefficient of thermal expansion was 4.5 × 10⁻⁶. -6 / K, flexural strength is 310MPa, interfacial bond strength is 290MPa, and air tightness is 4.5×10 -10 Pa·m 3 / s.

[0074] Example 3 Artificial synthetic diamond powder with a particle size of 45 μm and a nitrogen content of 175 ppm was selected and cleaned and surface modified according to the method of step (1) in Example 1 to obtain modified diamond powder.

[0075] 2.6μm and 5μm silicon powders were selected and graded at a mass ratio of 3:1, with a silicon volume fraction of 40 vol.%; after molding and densification according to the method of Example 1, the aluminum-silicon cladding sheet was CNC milled to fit the grooved mold, with a dimensional tolerance of ±0.01 mm.

[0076] Modified diamond micro powder is mixed with a composite binder, molded, densified, and then laser-cut into grooved diamond intermediate blocks with a surface roughness Ra≤0.8μm.

[0077] A high-silicon aluminum alloy with a Si content of 65 wt.% was prepared, melted at 890°C, and refined for 120 min according to the method in Example 1. The density of the molten aluminum was 2.50 g / cm³. 3 (Corresponding to a hydrogen content of 5.5%), keep warm and ready for use.

[0078] The mold is preheated to 240℃ and the inner wall is sprayed with a release agent. The diamond intermediate block is assembled with the aluminum-silicon cladding sheet and cold-pressed at 15MPa to obtain a confined preform with a volume fraction of 60 vol.%. The confined preform is placed in a pressure impregnation device, and high-silicon aluminum melt at 890℃ is poured in. An impregnation pressure of 75MPa is applied, and the pressure is held for 32 minutes. After holding the pressure and cooling, the mold is demolded to obtain a high thermal conductivity aluminum-silicon / diamond composite material.

[0079] The composite material prepared in this embodiment was subjected to performance tests: the thermal conductivity was 525 W / (m·K), and the coefficient of thermal expansion was 4.9 × 10⁻⁶. -6 / K, flexural strength 320MPa, interfacial bond strength 300MPa, air tightness 3.8×10 -10 Pa·m 3 / s.

[0080] Comparative Example 1 Artificially synthesized diamond micropowder with a particle size of 180μm and a nitrogen content of 170ppm was selected. It was ultrasonically cleaned with ethanol for 15 minutes, rinsed with deionized water 3 times, and dried at 60℃ without any surface modification treatment, and was ready for use directly.

[0081] Silicon powder with a single particle size of 45μm (without multi-particle size gradation) and a silicon volume fraction of 30 vol.% was selected, mixed with a composite binder, and molded at 15 MPa. After degreasing at 250℃ for 0.5 h, crosslinking at 400℃ for 1 h, and sintering at 750℃ for 1 h to densify, the aluminum-silicon coated sheet was obtained by direct crushing and screening after cooling. No CNC precision machining was performed, and the dimensional tolerance was ±0.1 mm.

[0082] Unmodified diamond micro powder was mixed with a composite binder, molded at 20 MPa, and then subjected to the same densification process before being directly mechanically ground to obtain a diamond intermediate block with a surface roughness Ra≥2.0 μm and obvious edge chipping.

[0083] Using ZL104 aluminum alloy as the base material, a high-silicon aluminum alloy with a Si content of 60wt.% was prepared and smelted at 880℃. Only argon gas was passed through for mechanical stirring for 10 minutes to remove hydrogen. 0.3% refining agent (sodium salt:potassium salt:fluoride = 2:1:1) was added and refined for 60 minutes. The mixture was then directly kept at the temperature for later use. The density and hydrogen content of the molten aluminum were not tested.

[0084] Preheat the mold to 220℃, spray the inner wall with release agent, and lay 10mm graphite felt on the top of the preform; directly stack the aluminum-silicon coated sheet and diamond intermediate block into the mold, cold press at 18MPa to shape, with a contact surface gap ≥0.1mm; place the mold into a pressure impregnation device, pour in 880℃ high-silicon aluminum melt under normal pressure, apply 80MPa impregnation pressure, maintain for 35min, and allow to cool naturally to room temperature before demolding.

[0085] The composite material prepared in this comparative example was tested for performance: its thermal conductivity was 386 W / (m·K), and its coefficient of thermal expansion was 9.8 × 10⁻⁶. -6 / K, flexural strength 156MPa, interfacial bond strength 122MPa, air tightness >100×10 -10 Pa·m 3 / s (The hermeticity requirements of electronic packaging are not met).

[0086] The properties of the composite materials obtained in Examples 1-3 and Comparative Example 1 are summarized in Table 1.

[0087] Table 1. Comparison of the properties of composite materials obtained in each embodiment and comparative example

[0088] As shown in Table 1, the composite materials prepared by Examples 1-3 using the technical solution of the present invention are significantly better than those of Comparative Example 1 in terms of thermal conductivity, coefficient of thermal expansion, mechanical strength, interfacial bonding strength and air tightness. This indicates that the present invention has successfully achieved high performance and high precision molding of high thermal conductivity aluminum-silicon / diamond composite materials through the synergistic effect of multiple technical features such as diamond surface modification, particle size distribution, precision machining, precise confined assembly and pressure infiltration.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging, characterized in that, Includes the following steps: (1) Surface modification treatment of diamond micro powder to obtain surface modified diamond micro powder; (2) The silicon powder is mixed with the composite binder, molded, degreased, sintered and densified, and then CNC precision machined to obtain a silicon preform with a preset shape; the surface modified diamond micro powder is mixed with the composite binder, molded, degreased, sintered and densified, and then laser-cut to obtain a diamond preform. (3) The diamond preform is embedded in the groove of the silicon preform, and then assembled by a precision jig and cold-pressed to obtain the confined preform. (4) Place the confined preform in a mold, and impregnate the refined high-silicon aluminum melt into the confined preform under pressure. Hold the pressure and cool, then demold to obtain a high thermal conductivity aluminum-silicon / diamond composite material.

2. The preparation method according to claim 1, characterized in that, The surface modification treatment described in step (1) includes: (1-1) The diamond micro powder is kept at 400-500℃ for 20-40 minutes in air to form an oxide layer; (1-2) The micro-oxidized diamond powder was immersed in an ethanol solution containing tetraethyl orthosilicate, ultrasonically dispersed, and then vacuum dried at 100-130℃ for 1-3 hours to grow a silicon-based transition layer in situ on the surface of the oxide layer. (1-3) Keep at 180-220℃ for 0.5-1.5h to allow the silicon-based transition layer to crosslink and solidify.

3. The preparation method according to claim 1, characterized in that, In step (2), the CNC precision machining uses a carbide end mill with a spindle speed of 8000-12000 r / min, a feed rate of 150-250 mm / min, and a cutting depth of 0.1-0.3 mm / cut. The laser cutting process uses a pulsed fiber laser with a laser power of 300-500 W, a pulse frequency of 20-50 kHz, a spot diameter of 50-80 μm, and a cutting speed of 20-40 mm / s.

4. The preparation method according to claim 1, characterized in that, The diamond micro powder is composed of one or more particle size distributions, with the particle size selected from at least one of 45μm, 180μm, and 270μm, and the distribution mass ratio is 3:1 or 9:3:1; the silicon powder is composed of two or more particle size distributions, with the particle size selected from at least two of 3μm, 5μm, 12μm, and 45μm, and the distribution mass ratio is 3:

1.

5. The preparation method according to claim 1, characterized in that, The precision fixture mentioned in step (3) is a vacuum adsorption platform. The vacuum adsorption platform has a partitioned vacuum cavity, and the adsorption force of each adsorption area is independently adjustable. The bonding and assembly process is supplemented by ultrasonic vibration with a vibration frequency of 20-30kHz and an amplitude of ≤5μm.

6. The preparation method according to claim 1, characterized in that, The silicon content of the high-silicon aluminum melt in step (4) is 30-70 wt.%; the impregnation pressure is 70-85 MPa, the impregnation temperature is 830-900℃, and the holding time is 30-50 min.

7. The preparation method according to claim 1, characterized in that, The composite adhesive is made by mixing silicone resin and paraffin wax in a mass ratio of 3:1 and dissolving them in solvent gasoline.

8. A high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging, characterized in that, The composite material is prepared by the method according to any one of claims 1 to 7, wherein the composite material has a sandwich structure of aluminum-silicon cladding, aluminum / diamond composite interlayer, and aluminum-silicon cladding, wherein the interfacial bonding strength between the aluminum-silicon cladding and the aluminum / diamond composite interlayer is ≥280MPa, and the airtightness is ≤5×10⁻⁶. -10 Pa·m 3 / s.

9. The high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging according to claim 8, characterized in that, The composite material is a plate-like structure, a groove-like structure, or an embedded structure.

10. The high thermal conductivity aluminum-silicon / diamond composite material for electronic packaging according to claim 8, characterized in that, The dimensional tolerance of the composite material is ≤ ±0.01 mm.

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