A ltcc substrate assembly and a eutectic sintering process method thereof

Abstract

The application provides a LTCC substrate assembly and a eutectic sintering process method thereof, and belongs to the technical field of electronic packaging. The LTCC substrate assembly comprises a LTCC substrate main layer, a eutectic sintering layer, an embedded circuit structure and a surface passivation layer. The application fills a vertical through hole with Ni@Ag core-shell particles, stacks an Ag-Cu nanowire alternately in a horizontal wiring layer, and cooperatively designs an Au-Sn-In eutectic sintering layer and a SiO2-Al2O3 composite passivation layer with a biomimetic micro-nano structure, so that the conductivity, mechanical strength, high-frequency performance and environmental stability of the substrate are significantly improved. Compared with the traditional LTCC technology, the application solves the problems of insufficient interlayer bonding force, low circuit density, poor thermal cycle reliability and weak surface protection.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic packaging, and in particular relates to an LTCC substrate assembly and a eutectic sintering process method thereof. Background Art

[0002] Low-temperature co-fired ceramic (LTCC) technology has been widely used in electronic packaging due to its excellent high-frequency characteristics, thermal stability, and integration capabilities. However, as electronic devices evolve towards miniaturization, higher density, and greater multifunctionality, traditional LTCC substrates are gradually exposing numerous performance limitations. First, traditional LTCC substrates rely primarily on conventional metal pastes for interlayer bonding, resulting in low interfacial bonding strength after sintering. This makes them susceptible to cracking or delamination under thermal cycling or mechanical stress, compromising device reliability. Second, embedded circuit vias and wiring layers are typically constructed from a single metal material, whose thermal expansion coefficient is mismatched with that of the ceramic substrate. This leads to interfacial stress concentration, potentially causing short circuits or performance degradation over long-term use. Furthermore, the surface protective layers of traditional LTCC substrates are typically simple SiO2 or polymer coatings, which lack effective protection against environmental pollutants and cannot meet the long-term stability requirements required in harsh environments. Furthermore, existing LTCC eutectic sintering technologies lack precise control over slurry composition and sintering conditions, which can easily lead to uneven metal diffusion or void defects, compromising circuit performance.

[0003] Therefore, developing an LTCC substrate assembly and its preparation method that have high bonding strength, high circuit density, excellent environmental stability and process controllability has become a key technical problem that needs to be solved urgently in the current electronic packaging field.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The first object of the present invention is to provide an LTCC substrate assembly that solves the problems of insufficient interlayer bonding, low circuit density, and poor environmental stability of traditional LTCC substrates by combining a core-shell structure composite material, a three-dimensional interconnection design, a bionic surface protection, and a low-temperature eutectic sintering process, thereby providing a reliable solution for high-performance electronic packaging.

[0006] The second object of the present invention is to provide a eutectic sintering process method for the above-mentioned LTCC substrate assembly. This method, through systematic optimization of material selection, structural design and parameter control, simultaneously achieves high bonding strength, excellent high-frequency performance and long-term environmental stability under low-temperature conditions, solving the core problem of the difficulty in balancing conductivity, reliability and protection in traditional LTCC technology.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0008] The application discloses an LTCC substrate assembly, which comprises an LTCC substrate main layer, a eutectic sintering layer, an embedded circuit structure and a surface passivation layer.

[0009] The LTCC substrate main layer is stacked by multiple LTCC substrate sub-layers, and the eutectic sintering layer is arranged between adjacent LTCC substrate sub-layers.

[0010] The embedded circuit structure comprises vertical vias and horizontal wiring layers, multiple vertical vias are uniformly arranged on the LTCC substrate sub-layers, the vertical vias penetrate through the LTCC substrate sub-layers and realize interlayer interconnection through the eutectic sintering layer, and the interval of the vertical vias is 100-200 mu m; the horizontal wiring layers are arranged on the surfaces of the LTCC substrate sub-layers and are in contact with the end portions of the vertical vias to form three-dimensional orthogonal interconnection.

[0011] The surface passivation layer covers the upper surface and the lower surface of the outermost LTCC substrate sub-layer, and the outer surface of the surface passivation layer is further provided with a biomimetic lotus leaf micro-nano structure.

[0012] The application provides an LTCC substrate assembly, wherein the core structure of the LTCC substrate assembly comprises an LTCC substrate main layer, a eutectic sintering layer, an embedded circuit structure and a surface passivation layer, the LTCC substrate main layer is stacked by multiple LTCC substrate sub-layers, the layered design not only improves the mechanical strength of the substrate, but also provides the possibility of realizing high-density circuit integration, and the eutectic sintering layer is arranged between adjacent LTCC substrate sub-layers, which realizes firm connection between layers through the low-melting-point characteristic of the eutectic alloy and ensures the reliability of electrical interconnection, and the design avoids the problems of material deformation or performance degradation that may occur in the traditional high-temperature sintering process, and is particularly suitable for application scenarios with high requirements for thermal sensitivity.

[0013] The embedded circuit structure is a key part of the LTCC substrate assembly, which comprises vertical vias and horizontal wiring layers, the vertical vias penetrate through the LTCC substrate sub-layers and realize interlayer interconnection through the eutectic sintering layer, the vertical interconnection technology significantly improves the three-dimensional integration capability of the circuit, so that the signal transmission path is shorter, thereby reducing transmission loss and delay; the interval of the vertical vias is controlled to be 100-200 mu m, which not only guarantees sufficient wiring density, but also avoids the signal crosstalk problem caused by too small interval, and the horizontal wiring layers are arranged on the surfaces of the LTCC substrate sub-layers and are in contact with the end portions of the vertical vias to form three-dimensional orthogonal interconnection, and the orthogonal design further optimizes the layout of the circuit and improves the signal transmission efficiency; and the horizontal wiring layers are composed of alternating Ag nanowires and Cu nanowires, the Ag nanowires have excellent electrical conductivity, and the Cu nanowires provide good mechanical support and cost advantage, and the combination of the two achieves a balance between electrical performance and structural stability.

[0014] The surface passivation layer covers the upper and lower surfaces of the outermost LTCC substrate sublayer. Its main function is to protect the internal circuit from environmental factors. The surface passivation layer adopts SiO2-Al2O3 composite film material with a thickness of 5-15μm. This material combination not only has excellent insulation and chemical stability, but also can effectively block the invasion of harmful substances from the outside world. In addition, the outer surface of the passivation layer is also provided with a bionic lotus leaf micro-nano structure. This structure consists of SiO2 micron columns and Al2O3 nano-hairs, which imitates the hydrophobic properties of the lotus leaf surface. At the same time, the height of the micron columns is 2-5μm, and the length of the nano-hairs is 100-300nm. This multi-scale structure can significantly improve the surface hydrophobicity and self-cleaning ability, thereby further enhancing the environmental adaptability and long-term reliability of the substrate assembly.

[0015] From a material perspective, the sub-layer of the LTCC substrate uses a low-temperature co-fired ceramic composite material, which consists of Al2O3, SiO2, a glass phase and a sintering aid. The glass phase is borosilicate glass and the sintering aid is MgO or CaO. The selection of these components ensures the densification and good mechanical properties of the material during low-temperature sintering. The eutectic sintering layer uses a Au-Sn-In ternary eutectic alloy, in which Au accounts for 50-60%, Sn accounts for 30-40%, and In accounts for 5-10%. This alloy has a low melting point and good wettability, and can achieve reliable interlayer connections in the temperature range of 250-300°C, while avoiding the adverse effects of high temperature on material properties.

[0016] In summary, the LTCC substrate assembly of the present invention achieves high-density integration, excellent electrical performance, and exceptional environmental stability through innovative structural design, material selection, and processing methods. Its multilayer stacking design, three-dimensional interconnect technology, and biomimetic surface treatment not only meet the miniaturization and high-performance demands of modern electronic devices but also provide new insights for the future development of electronic packaging technology.

[0017] Preferably, as a further specific embodiment, the vertical via is filled with a core-shell structure composite material, and the core-shell structure composite material is Ni@Ag core-shell particles, wherein the particle size of the Ni core is 20-50 nm and the thickness of the Ag shell is 5-15 nm.

[0018] In an LTCC substrate assembly of the present invention, the vertical vias are further filled with a core-shell structure composite material, specifically Ni@Ag core-shell particles, wherein the particle size of the Ni core is 20-50nm and the thickness of the Ag shell is 5-15nm. The unique design of the core-shell structure significantly improves the conductivity, mechanical strength and thermal stability of the vertical vias, while solving the problems of easy oxidation and decreased conductivity of traditional filling materials during high-temperature sintering. The Ni core in the Ni@Ag core-shell particles has excellent mechanical strength and thermal stability, and its high melting point and good creep resistance can ensure that the vertical vias maintain structural integrity during high-temperature sintering, avoiding hole deformation or fracture caused by thermal stress, while the Ag shell, with its extremely high High electrical and thermal conductivity provide excellent electrical and thermal conductivity for vertical vias. In addition, the chemical properties of Ag are relatively stable, especially under the protection of inert gas, it is not easy to oxidize, which can effectively avoid the increase in contact resistance caused by the surface oxide layer. This combination of core-shell structure not only fully utilizes the respective advantages of the two metals, but also achieves further performance improvement through interface synergistic effects. For example, the rigid support of the Ni core can inhibit the diffusion and agglomeration of the Ag shell at high temperature, while the wrapping of the Ag shell avoids the potential corrosion problem of the Ni core in a humid environment. Secondly, the nanoscale Ni core can provide a sufficiently large specific surface area, which is conducive to forming a close interface bonding with the Ag shell, thereby enhancing the overall mechanical strength of the composite particles. At the same time, the thickness of the Ag shell within this size range can ensure a continuous conductive path without increasing costs or affecting filling density due to excessive thickness; when the Ag shell thickness is less than 5nm, its coverage may be incomplete, resulting in local exposure of the Ni core, inducing oxidation or electrochemical corrosion; when it exceeds 15nm, the amount of Ag used increases significantly, the economic efficiency decreases, and stress concentration may occur during the sintering process due to the excessive thickness of the shell; and if the particle size in the Ni core is too small, it is easy to cause particle agglomeration, making it difficult to fill evenly; if the particle size is too large, it may reduce the density of the filling in the conductive hole and affect the conductive performance.

[0019] Preferably, as a further specific embodiment, the horizontal wiring layer is composed of alternately stacked Ag nanowires and Cu nanowires, the diameter of the Ag nanowires is 50-150 nm, the diameter of the Cu nanowires is 30-100 nm, and the spacing between the two is 10-30 nm.

[0020] The present invention also defines the structure of the horizontal wiring layer, clearly stating that the wiring layer is composed of alternately stacked Ag nanowires and Cu nanowires, and specifically stipulates that the diameter of the Ag nanowires is 50-150nm, the diameter of the Cu nanowires is 30-100nm, and the spacing between the two is 10-30nm. The present invention achieves a perfect balance of conductivity, electromigration resistance and cost-effectiveness at the nanoscale by constructing a composite structure of alternating Ag-Cu nanowires. This alternating stacking structure creatively utilizes the complementary properties of Ag and Cu metals, where Ag has Ag nanowires have the lowest bulk resistivity of all metals, but their resistance to electromigration is poor. Although Cu has a slightly higher resistivity, it has excellent resistance to electromigration. Therefore, the present invention precisely controls the diameter ratio and spacing of the two nanowires, allowing electrons to automatically select the optimal path according to the local current density during transmission. When the current density is low, the electrons mainly flow through the low-resistance Ag nanowires, while in high-current density areas, the electrons are shunted through the adjacent Cu nanowires. This adaptive conductive mechanism allows the overall wiring to maintain ultra-low resistance while increasing the electromigration life to more than five times that of pure Ag wiring. The diameter of the Ag nanowire is controlled within the range of 50-150nm. This size not only ensures a sufficient current-carrying cross-section (when the diameter is less than 50nm, the surface scattering effect will cause the resistivity to rise sharply), but also avoids the stress concentration problem caused by volume shrinkage of overly thick nanowires during sintering. When the diameter of the Cu nanowire is less than 30nm, its surface oxide layer accounts for more than 15%, which will significantly increase the contact resistance. When the diameter is greater than 100nm, the synergistic effect with the Ag nanowire is weakened. The design of a spacing of 10-30nm allows electrons to tunnel efficiently between the two metals, while being close enough to produce a significant proximity effect.

[0021] Preferably, as a further specific embodiment, the surface passivation layer is a SiO2-Al2O3 composite film with a thickness of 5-15 μm; the bionic lotus leaf micro-nano structure is composed of SiO2 micron columns and Al2O3 nano-hairs, the micron columns are 2-5 μm high and the hairs are 100-300 nm long.

[0022] The surface passivation layer of the present invention includes a basic passivation layer and a bionic lotus leaf micro-nano structure as a surface functional layer, wherein the composite film has a thickness of 5-15 μm, and the bionic structure is composed of SiO2 micron columns and Al2O3 nano-hairs. SiO2 provides excellent electrical insulation, but its relatively low hardness and thermal expansion coefficient easily lead to compatibility problems with the LTCC substrate. Therefore, the present invention introduces Al2O3, which not only adjusts the thermal expansion coefficient of the composite film to an appropriate range to achieve thermal matching with the substrate, but also improves the hardness of the film layer and its scratch resistance. The design of the bionic lotus leaf micro-nano structure is inspired by the super-hydrophobic phenomenon in nature. The secondary structure of its SiO2 micron columns and Al2O3 nano-hairs has unique surface functional characteristics, which makes the surface self-cleaning. In a humid environment, the rapid rolling of water droplets on the surface reduces the probability of electrolytic corrosion; in a dusty environment, the electrostatic repulsion effect generated by the nano-hairs reduces the amount of particle adsorption.

[0023] Preferably, as a further specific embodiment, the material of the LTCC substrate sub-layer is a low-temperature co-fired ceramic composite material, and the composition of the low-temperature co-fired ceramic composite material is, by mass percentage, 40-50% Al2O3, 20-30% SiO2, 20-30% glass phase, and 5-10% sintering aid; and the glass phase is borosilicate glass, and the sintering aid is one or both of MgO and CaO.

[0024] The present invention also defines the material composition of the LTCC substrate sublayer, specifically a low-temperature co-fired ceramic composite material, whose formula includes, by mass percentage, 40-50% Al2O3, 20-30% SiO2, 20-30% glass phase, and 5-10% sintering aid. The glass phase is borosilicate glass, and the sintering aid is one or both of MgO and CaO. This material formula, through the precise proportioning and synergistic effect of the multi-component system, perfectly balances the conflicting requirements between low-temperature sintering characteristics, mechanical strength, thermal stability, and dielectric properties, providing an ideal substrate material solution for modern high-density electronic packaging.

[0025] Preferably, as a further specific embodiment, the eutectic sintered layer is a Au-Sn-In ternary eutectic alloy layer, the composition of which is Au 50-60%, Sn 30-40%, and In 5-10% by mass percentage.

[0026] The present invention also provides a eutectic sintering process for the above-mentioned LTCC substrate assembly, comprising the following steps:

[0027] The low-temperature co-fired ceramic composite material is tape-casted into multiple LTCC substrate sub-layers, and vertical conductive holes are formed on each LTCC substrate sub-layer by laser drilling, and the composite material is filled in the hole;

[0028] A horizontal wiring layer is formed by alternately stacking nanowires on the surface of each LTCC substrate sublayer using nanowire printing technology;

[0029] Lay a eutectic sintered layer between adjacent LTCC substrate sub-layers, and achieve interlayer interconnection through hot pressing sintering. The sintering temperature is 250-300℃, the pressure is 5-10MPa, and the holding time is 30-60 minutes.

[0030] A surface passivation layer is deposited on the surface of the outermost LTCC substrate sublayer, and a bionic lotus leaf micro-nano structure is formed through photolithography and etching processes.

[0031] Preferably, as a further specific embodiment, the composite material is filled by vacuum pressure impregnation, and is cured by low-temperature heat treatment after filling, with the heat treatment temperature being 150-200° C. and the time being 10-20 minutes.

[0032] Preferably, as a further specific embodiment, the heating rate of the hot pressing sintering is 5-10° C. / min, the cooling rate is 2-5° C. / min, and the sintering atmosphere is a nitrogen protective atmosphere.

[0033] Preferably, as a further specific embodiment, the preparation method of the bionic lotus leaf micro-nano structure is: first forming SiO2 micron columns by reactive ion etching, and then growing Al2O3 nano-hairs by atomic layer deposition.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention provides an LTCC substrate assembly, which solves the problems of insufficient interlayer bonding strength, low circuit density, and poor environmental stability of traditional LTCC substrates by combining core-shell structure composite materials, three-dimensional interconnection design, bionic surface protection and low-temperature eutectic sintering process, and provides a reliable solution for high-performance electronic packaging.

[0036] (2) The present invention provides a eutectic sintering process method for the above-mentioned LTCC substrate assembly. This method achieves high bonding strength, excellent high-frequency performance and long-term environmental stability at low temperature conditions through systematic optimization of material selection, structural design and parameter control, solving the core problem of the difficulty in balancing conductivity, reliability and protection in traditional LTCC technology. DETAILED DESCRIPTION

[0037] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, those skilled in the art will understand that the embodiments described below are part of the embodiments of the present invention, not all of them, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] In order to more clearly illustrate the technical solutions of the present invention, specific embodiments are provided below for illustration.

[0039] Example 1

[0040] The preparation process of the LTCC substrate assembly of the present invention is as follows:

[0041] 1. Preparation of LTCC substrate sublayer

[0042] Material ratio:

[0043] The low-temperature co-fired ceramic composite material is composed of the following proportions by mass: Al2O3: 40%, SiO2: 30%, borosilicate glass: 20%, and MgO 10%;

[0044] The low-temperature co-fired ceramic composite material was mixed by ball milling with a ball-to-material ratio of 5:1 and a ball milling time of 8 hours to ensure that the materials were evenly mixed to obtain a mixed slurry;

[0045] Tape casting:

[0046] The mixed slurry was coated on the PET base film by a tape casting machine, with the scraper gap set to 200 μm, the drying temperature to 80 ° C, and the drying time to 30 minutes to form an LTCC substrate sublayer with a thickness of about 100 μm;

[0047] Laser drilling:

[0048] Ultraviolet laser (wavelength 355nm) is used to evenly drill multiple vertical vias on the LTCC substrate sublayer, with a hole diameter of 50μm and a hole spacing of 100μm, ensuring that the hole wall is smooth and burr-free;

[0049] 2. Fill vertical vias

[0050] Composite material preparation:

[0051] Ni@Ag core-shell particles (Ni core particle size 20 nm, Ag shell thickness 5 nm) were dispersed in an organic solvent and sonicated for 30 min to ensure uniform dispersion;

[0052] Vacuum pressure impregnation:

[0053] Place the LTCC substrate sublayer in a vacuum impregnation device, evacuate the vacuum, and inject the composite material slurry. Pressurize to 5 MPa and hold for 10 minutes to ensure that the holes are completely filled.

[0054] Low temperature heat treatment:

[0055] Heat treatment at 150°C for 10 minutes to solidify the composite material while preventing deformation of the LTCC substrate sublayer;

[0056] 3. Forming a horizontal wiring layer

[0057] Nanowire printing:

[0058] Ag nanowires (50 nm in diameter) and Cu nanowires (30 nm in diameter) were dispersed in ethanol at a concentration of 1 mg / mL;

[0059] Using inkjet printing technology, Ag and Cu nanowires were alternately printed on the surface of the LTCC substrate sublayer with a spacing of 10nm. After printing, the nanowires were dried at 80℃ for 5 minutes.

[0060] 4. Laying the eutectic sintering layer

[0061] Eutectic alloy preparation:

[0062] Au-Sn-In alloy (Au 50%, Sn 40%, In 10%) was prepared by vacuum melting at 600°C for 30 min and cast into foil with a thickness of 20 μm.

[0063] Layered laying:

[0064] Place eutectic alloy foil between adjacent LTCC substrate sub-layers, align the hole positions, and ensure interlayer conductivity to form a pre-processed substrate;

[0065] 5. Hot pressing sintering

[0066] Sintering parameters:

[0067] The pretreated substrate was sintered in a nitrogen atmosphere, heated to 250°C at a rate of 5°C / min, and subjected to a pressure of 5 MPa, and kept at this temperature for 30 minutes to obtain a crude substrate assembly.

[0068] 6. Deposition of surface passivation layer

[0069] SiO2-Al2O3 composite film deposition:

[0070] A surface passivation layer was deposited on the rough substrate assembly using magnetron sputtering, first depositing SiO2 (thickness 3 μm) and then Al2O3 (thickness 2 μm), with a total thickness of 5 μm.

[0071] Bionic structure preparation:

[0072] Reactive Ion Etching (RIE):

[0073] Use CF4 / O2 mixed gas (flow ratio 4:1), power 100W, etching for 5 minutes to form SiO2 micron columns (height 2μm);

[0074] Atomic Layer Deposition (ALD):

[0075] Using trimethylaluminum (TMA) and water as precursors, Al2O3 nanohairs (length 100 nm) were deposited for 100 cycles.

[0076] Example 2

[0077] The preparation process of the LTCC substrate assembly of the present invention is as follows:

[0078] 1. Preparation of LTCC substrate sublayer

[0079] Material ratio:

[0080] The low-temperature co-fired ceramic composite material is composed of the following proportions by mass: Al2O3: 50%, SiO2: 20%, borosilicate glass: 25%, and CaO 5%;

[0081] The low-temperature co-fired ceramic composite material was mixed by ball milling with a ball-to-material ratio of 5:1 and a ball milling time of 8 hours to ensure that the materials were evenly mixed to obtain a mixed slurry;

[0082] Tape casting:

[0083] The mixed slurry was coated on the PET base film by a tape casting machine, with the scraper gap set to 300 μm, the drying temperature to 100 ° C, and the drying time to 30 minutes to form an LTCC substrate sublayer with a thickness of about 200 μm;

[0084] Laser drilling:

[0085] Use ultraviolet laser (wavelength 355nm) to evenly drill multiple vertical vias on the LTCC substrate sublayer, with a hole diameter of 100μm and a hole spacing of 200μm, ensuring that the hole wall is smooth and burr-free;

[0086] 2. Fill vertical vias

[0087] Composite material preparation:

[0088] Ni@Ag core-shell particles (Ni core particle size 50 nm, Ag shell thickness 15 nm) were dispersed in an organic solvent and sonicated for 30 min to ensure uniform dispersion;

[0089] Vacuum pressure impregnation:

[0090] Place the LTCC substrate sublayer in a vacuum impregnation device, evacuate the vacuum, and inject the composite material slurry. Pressurize to 10 MPa and hold for 10 minutes to ensure that the holes are completely filled.

[0091] Low temperature heat treatment:

[0092] Heat treatment at 200°C for 20 minutes to solidify the composite material while preventing deformation of the LTCC substrate sublayer;

[0093] 3. Forming a horizontal wiring layer

[0094] Nanowire printing:

[0095] Ag nanowires (150 nm in diameter) and Cu nanowires (100 nm in diameter) were dispersed in ethanol at a concentration of 1 mg / mL;

[0096] Using inkjet printing technology, Ag and Cu nanowires were alternately printed on the surface of the LTCC substrate sublayer with a spacing of 30nm. After printing, the nanowires were dried at 80℃ for 5 minutes.

[0097] 4. Laying the eutectic sintering layer

[0098] Eutectic alloy preparation:

[0099] Au-Sn-In alloy (Au 60%, Sn 30%, In 10%) was prepared by vacuum melting at 600°C for 30 min and cast into foil with a thickness of 30 μm.

[0100] Layered laying:

[0101] Place eutectic alloy foil between adjacent LTCC substrate sub-layers, align the hole positions, and ensure interlayer conductivity to form a pre-processed substrate;

[0102] 5. Hot pressing sintering

[0103] Sintering parameters:

[0104] The pretreated substrate was sintered in a nitrogen atmosphere, heated to 300°C at a rate of 10°C / min, under a pressure of 10 MPa, and kept at this temperature for 60 minutes to obtain a crude substrate assembly.

[0105] 6. Deposition of surface passivation layer

[0106] SiO2-Al2O3 composite film deposition:

[0107] A surface passivation layer was deposited on the rough substrate assembly using magnetron sputtering, first depositing SiO2 (thickness 10 μm) and then Al2O3 (thickness 5 μm), with a total thickness of 15 μm.

[0108] Bionic structure preparation:

[0109] Reactive Ion Etching (RIE):

[0110] Use CF4 / O2 mixed gas (flow ratio 4:1), power 100W, etching for 5 minutes to form SiO2 micron columns (height 5μm);

[0111] Atomic Layer Deposition (ALD):

[0112] Using trimethylaluminum (TMA) and water as precursors, Al2O3 nanohairs (length 300nm) were deposited for 300 cycles.

[0113] Example 3

[0114] The preparation process of the LTCC substrate assembly of the present invention is as follows:

[0115] 1. Preparation of LTCC substrate sublayer

[0116] Material ratio:

[0117] The low-temperature co-fired ceramic composite material is composed of the following proportions by mass: Al2O3: 45%, SiO2: 25%, borosilicate glass: 25%, CaO 2.5%, and MgO 2.5%;

[0118] The low-temperature co-fired ceramic composite material was mixed by ball milling with a ball-to-material ratio of 5:1 and a ball milling time of 5 hours to ensure that the materials were evenly mixed to obtain a mixed slurry;

[0119] Tape casting:

[0120] The mixed slurry was coated on the PET base film by a tape casting machine, with the scraper gap set to 250 μm, the drying temperature to 90 ° C, and the drying time to 40 minutes to form an LTCC substrate sublayer with a thickness of about 150 μm;

[0121] Laser drilling:

[0122] Ultraviolet laser (wavelength 355nm) is used to evenly drill multiple vertical vias on the LTCC substrate sublayer, with a hole diameter of 75μm and a hole spacing of 150μm, ensuring that the hole walls are smooth and burr-free;

[0123] 2. Fill vertical vias

[0124] Composite material preparation:

[0125] Ni@Ag core-shell particles (Ni core particle size 35 nm, Ag shell thickness 10 nm) were dispersed in an organic solvent and sonicated for 30 min to ensure uniform dispersion;

[0126] Vacuum pressure impregnation:

[0127] Place the LTCC substrate sublayer in a vacuum impregnation device, evacuate the vacuum, and inject the composite material slurry. Pressurize to 7.5 MPa and hold for 15 minutes to ensure that the holes are completely filled.

[0128] Low temperature heat treatment:

[0129] Heat treatment at 175°C for 15 minutes to solidify the composite material while preventing deformation of the LTCC substrate sublayer;

[0130] 3. Forming a horizontal wiring layer

[0131] Nanowire printing:

[0132] Ag nanowires (100 nm in diameter) and Cu nanowires (65 nm in diameter) were dispersed in ethanol at a concentration of 1 mg / mL;

[0133] Using inkjet printing technology, Ag and Cu nanowires were alternately printed on the surface of the secondary layer of the LTCC substrate with a spacing of 20nm. After printing, the nanowires were dried at 80℃ for 5 minutes.

[0134] 4. Laying the eutectic sintering layer

[0135] Eutectic alloy preparation:

[0136] Au-Sn-In alloy (Au 55%, Sn 32%, In 13%) was prepared by vacuum melting at 600°C for 30 min and cast into foil with a thickness of 25 μm.

[0137] Layered laying:

[0138] Place eutectic alloy foil between adjacent LTCC substrate sub-layers, align the hole positions, and ensure interlayer conductivity to form a pre-processed substrate;

[0139] 5. Hot pressing sintering

[0140] Sintering parameters:

[0141] The pretreated substrate was sintered in a nitrogen atmosphere, heated to 275°C at a rate of 7.5°C / min, under a pressure of 7.5 MPa, and kept at this temperature for 45 minutes to obtain a crude substrate assembly.

[0142] 6. Deposition of surface passivation layer

[0143] SiO2-Al2O3 composite film deposition:

[0144] A surface passivation layer was deposited on the rough substrate assembly using magnetron sputtering, first depositing SiO2 (thickness 5 μm) and then depositing Al2O3 (thickness 5 μm), with a total thickness of 10 μm.

[0145] Bionic structure preparation:

[0146] Reactive Ion Etching (RIE):

[0147] Use CF4 / O2 mixed gas (flow ratio 4:1), power 150W, etching for 5 minutes to form SiO2 micron columns (height 3.5μm);

[0148] Atomic Layer Deposition (ALD):

[0149] Using trimethylaluminum (TMA) and water as precursors, Al2O3 nanohairs (length 200nm) were deposited for 200 cycles.

[0150] Comparative Example 1

[0151] The specific implementation steps are the same as those in Example 3, except that traditional Ag paste is used to fill the vertical via holes.

[0152] Comparative Example 2

[0153] The specific implementation steps are consistent with those of Example 3, except that the horizontal wiring layer is a single Ag wiring layer without a Cu nanowire alternating structure.

[0154] Comparative Example 3

[0155] The specific implementation steps are consistent with those of Example 3, except that there is no Ag shell layer in the vertical via hole, and the via hole is filled with pure Ni.

[0156] Comparative Example 4

[0157] The specific implementation steps are consistent with those of Example 3, except that the surface passivation layer adopts a planar SiO2 passivation layer without the bionic lotus leaf micro-nano structure.

[0158] Experimental Example 1 LTCC Substrate Performance Test

[0159] 1. Experimental Design

[0160] The purpose of this experiment is to systematically evaluate the differences between Examples 1-3 and Comparative Examples 1-4 in key performance indicators such as electrical, mechanical, thermal and environmental reliability.

[0161] 2. Experimental methods and test conditions

[0162] Sample: The LTCC substrates finally prepared in Examples 1-3 and Comparative Examples 1-4 are samples;

[0163] Test equipment:

[0164] Conductivity: four-probe tester (Keithley 2450), current 1A, room temperature 25°C;

[0165] Mechanical properties: universal material testing machine (Instron 5967);

[0166] Thermal cycling: thermal shock chamber (ESPEC TSE-11);

[0167] High-frequency performance: Vector network analyzer (Keysight N5227A);

[0168] Environmental test: salt spray test (5% NaCl, 35°C, 96h);

[0169] Contact angle meter (KRÜSS DSA100);

[0170] 3. Experimental Procedure

[0171] Conductivity test:

[0172] The vertical via resistance (mΩ) and horizontal wiring layer resistivity (×10 -8 Ω·m), current 1A, room temperature 25℃;

[0173] Mechanical properties test:

[0174] The flexural strength (MPa) and fracture toughness (MPa·m¹ / ²) were measured by the three-point bending method with a loading rate of 0.5 mm / min;

[0175] Thermal Cycling Reliability:

[0176] -65℃↔150℃ cycle (30min / cycle), record the resistance change rate (%) after 1000 cycles;

[0177] High frequency performance test:

[0178] Insertion loss (dB / mm) measured at 40GHz;

[0179] Environmental stability:

[0180] After the salt spray test (5% NaCl, 35°C, 96h), the surface insulation resistance (×10 12 Ω);

[0181] Water contact angle (°) and sliding angle (°) were used to evaluate hydrophobicity;

[0182] The final test results are shown in Table 1 below.

[0183] Table 1 Test results

[0184] Test items Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Via resistance (mΩ) 3.2 2.8 2.6 8.3 6.7 12.5 7.1 <![CDATA[布线层电阻率 (10 -8 Ohm)]]> 1.9 1.8 1.7 2.4 3.2 2.8 2.1 Flexural strength (MPa) 412 428 435 320 380 350 350 <![CDATA[断裂韧性 (MPa·m 1 / 2 )]]> 4.3 4.6 4.8 3.1 3.8 2.7 3.5 Thermal cycle resistance change rate (%) 2.4 2.1 1.9 8.7 5.2 7.3 4.6 40GHz insertion loss (dB / mm) 0.18 0.16 0.15 0.35 0.28 0.32 0.24 <![CDATA[盐雾后绝缘电阻 (10 12 Oh)]]> 3.8 4.1 4.3 3.2 3.5 3.1 1.5 Water contact angle (°) 152 154 156 138 135 130 105 Roll angle (°) 6.2 5.8 5.5 6.4 6.6 7.3 25.0

[0185] The above experimental results show that Examples 1-3 demonstrate the comprehensive performance advantages of the LTCC substrate assembly and the eutectic sintering process method thereof of the present invention, among which Example 3 is the optimal solution. Through systematic testing of Examples 1-3 and Comparative Examples 1-4, the LTCC substrate assembly and the eutectic sintering process method thereof of the present invention show significant advantages in electrical performance, mechanical strength, thermal reliability and environmental stability.

[0186] In terms of electrical performance, the via resistance of Example 3 is only 2.6 mΩ, which is significantly lower than 8.3 mΩ of Comparative Example 1 and 12.5 mΩ of Comparative Example 3. This result illustrates the key role of the Ni@Ag core-shell structure composite material in the vertical via, where the high mechanical strength and thermal stability of the Ni core ensure the structural integrity of the via during high-temperature sintering, while the excellent conductivity of the Ag shell significantly reduces the interfacial contact resistance. In addition, the horizontal wiring layer design of alternating stacked Ag-Cu nanowires reduces the resistivity of the wiring layer of Example 3, which is much lower than the single Ag wiring layer of Comparative Example 2. This alternating stacking structure not only utilizes the low resistivity of Ag and the anti-electromigration properties of Cu, but also optimizes the current distribution through a synergistic effect at the nanoscale, thereby exhibiting lower insertion loss in high-frequency signal transmission.

[0187] The mechanical properties test results show that the bending strength of Example 3 reaches 435 MPa and the fracture toughness is 4.8 MPa·m 1 / 2 , which are both better than Comparative Example 1. This improvement is mainly attributed to the optimized ratio of the composite materials in the LTCC substrate sublayer and the thermal expansion matching between the eutectic sintered layer and the substrate. The metallurgical bonding formed by the eutectic sintered layer at low temperature effectively reduces the interfacial residual stress, thereby avoiding the common cracking and delamination problems in traditional slurry sintering. In addition, the filling of Ni@Ag core-shell particles in the vertical vias further enhances the overall mechanical properties of the substrate. Especially under thermal cycling conditions, its stability is significantly better than that of Comparative Examples 1 and 3.

[0188] In terms of high-frequency performance, the insertion loss of Example 3 is 0.15 dB / mm, which is much lower than that of Comparative Example 1. This advantage stems from the coordinated design of vertical vias and horizontal wiring layers in the three-dimensional interconnect structure. The uniform distribution of vertical vias and the low dielectric loss of the core-shell filling material reduce electromagnetic scattering in signal transmission, while the alternating arrangement of Ag-Cu nanowires suppresses the skin effect, thereby maintaining excellent signal integrity in high-frequency environments. In contrast, Comparative Examples 1 and 3 significantly increase high-frequency signal losses due to the unevenness and interface defects of the via filling materials.

[0189] In the environmental stability test, the insulation resistance of Example 3 after salt spray was as high as 4.3, the water contact angle was 156°, and the rolling angle was only 5.5°, which fully demonstrated the dual protective effect of the surface passivation layer and the bionic lotus leaf micro-nanostructure. The SiO2-Al2O3 composite film blocked the penetration of moisture and corrosive ions through its chemical inertness and high density, while the bionic micro-nanostructure achieved self-cleaning function through its superhydrophobic properties; in comparison, the insulation resistance of Comparative Example 4 after salt spray was only 1.5, and the rolling angle was 25°, indicating that the protection capability of the planar passivation layer in complex environments is limited.

[0190] In summary, the present invention successfully solves the technical bottlenecks of traditional LTCC substrates in terms of interlayer bonding strength, circuit density, high-frequency performance, and environmental stability through the triple breakthroughs of material composite, structural design, and process innovation. Example 3, as the optimal solution, has significantly improved its comprehensive performance, which not only verifies the technical feasibility of the present invention but also provides reliable technical support for the application of high-performance electronic packaging.

[0191] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An LTCC substrate assembly, characterized in that: It includes LTCC substrate main layer, eutectic sintering layer, embedded circuit structure and surface passivation layer; The LTCC substrate main layer is formed by stacking multiple LTCC substrate sub-layers, and the eutectic sintered layer is arranged between adjacent LTCC substrate sub-layers, and the eutectic sintered layer is arranged at its hole position; The embedded circuit structure includes vertical vias and a horizontal wiring layer. The LTCC substrate sub-layer is evenly provided with a plurality of vertical vias, and the vertical vias penetrate the LTCC substrate sub-layer and achieve inter-layer interconnection through the eutectic sintered layer. The vertical vias are spaced 100-200 μm apart. The horizontal wiring layer is provided on the surface of the LTCC substrate sub-layer and contacts the ends of the vertical vias to form a three-dimensional orthogonal interconnection. The surface passivation layer covers the upper surface and the lower surface of the outermost LTCC substrate sub-layer, and the outer surface of the surface passivation layer is also provided with a bionic lotus leaf micro-nano structure; The vertical vias are filled with a core-shell structure composite material, wherein the core-shell structure composite material is Ni@Ag core-shell particles, wherein the particle size of the Ni core is 20-50 nm and the thickness of the Ag shell is 5-15 nm; The horizontal wiring layer is composed of alternately stacked Ag nanowires and Cu nanowires, the Ag nanowires have a diameter of 50-150 nm, the Cu nanowires have a diameter of 30-100 nm, and the spacing between the two is 10-30 nm; The surface passivation layer is a SiO2-Al2O3 composite film with a thickness of 5-15 μm; the bionic lotus leaf micro-nano structure is composed of SiO2 micron columns and Al2O3 nano-hairs, the micron columns are 2-5 μm high and the hairs are 100-300 nm long.

2. The LTCC substrate assembly according to claim 1, wherein: The material of the LTCC substrate sub-layer is a low-temperature co-fired ceramic composite material, and the composition of the low-temperature co-fired ceramic composite material is 40-50% Al2O3, 20-30% SiO2, 20-30% glass phase, and 5-10% sintering aid in mass percentage; the glass phase is borosilicate glass, and the sintering aid is one or both of MgO and CaO.

3. The LTCC substrate assembly according to claim 1, wherein: The eutectic sintered layer is a Au-Sn-In ternary eutectic alloy layer, and its composition by mass percentage is Au 50-60%, Sn 30-40%, and In 5-10%.

4. A eutectic sintering process for an LTCC substrate assembly according to any one of claims 1 to 3, characterized in that: The following steps are involved: The low-temperature co-fired ceramic composite material is tape-casted into multiple LTCC substrate sub-layers, and vertical conductive holes are formed on each LTCC substrate sub-layer by laser drilling, and the composite material is filled in the hole; A horizontal wiring layer is formed by alternately stacking nanowires on the surface of each LTCC substrate sublayer using nanowire printing technology; Lay a eutectic sintered layer between adjacent LTCC substrate sub-layers, and achieve interlayer interconnection through hot pressing sintering. The sintering temperature is 250-300℃, the pressure is 5-10MPa, and the holding time is 30-60 minutes. A surface passivation layer is deposited on the surface of the outermost LTCC substrate sublayer, and a bionic lotus leaf micro-nano structure is formed through photolithography and etching processes.

5. The eutectic sintering process according to claim 4, characterized in that: The composite material is filled by vacuum pressure impregnation, and is cured by low-temperature heat treatment after filling, wherein the heat treatment temperature is 150-200° C. and the time is 10-20 minutes.

6. The eutectic sintering process according to claim 4, characterized in that: The heating rate of the hot pressing sintering is 5-10°C / min, the cooling rate is 2-5°C / min, and the sintering atmosphere is a nitrogen protective atmosphere.

7. The eutectic sintering process according to claim 4, characterized in that: The preparation method of the bionic lotus leaf micro-nano structure is: firstly forming SiO2 micron columns by reactive ion etching, and then growing Al2O3 nano-hairs by atomic layer deposition.