Manufacturing method of conductive foam and ferrite composite shielding structure

Abstract

The invention belongs to the technical field of electromagnetic shielding materials, and particularly relates to a manufacturing method of a conductive foam and ferrite composite shielding structure. The invention discloses a conductive foam-ferrite composite shielding structure and a manufacturing method thereof. The manufacturing method comprises the following steps: pre-compressing a conductive foam matrix (the compression ratio is 50-70%), dipping nickel-zinc ferrite slurry (D50 = 2-3 [mu] m), carrying out stepped curing (80-120 DEG C), carrying out magnetron sputtering on a NiCu transition layer (150-250 nm), electroplating a SnBi alloy layer (3-8 [mu] m), and carrying out laser cutting to form a grid with the aperture ratio of 28-32%. The structure realizes 10GHz frequency point shielding effectiveness of 92dB (84% higher than that of pure foam), interface shear strength of 15MPa, thermal expansion coefficient of 8 * 10 <-6 > / DEG C, resistance to 260 DEG C reflow soldering for three times and oxidation resistance time of more than 5000 hours, and is suitable for electromagnetic shielding of high-frequency electronic equipment.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic shielding materials technology, specifically relating to a method for manufacturing a composite shielding structure of conductive foam and ferrite. Background Technology

[0002] With the rapid development of 5G communication and IoT technologies, semiconductor devices are evolving towards higher frequencies (>10GHz), miniaturization (package size <1mm), and multifunctional integration, placing higher demands on electromagnetic shielding materials. It is predicted that the global electromagnetic shielding material market will exceed $12 billion by 2025, with high-frequency shielding materials accounting for over 40%. However, existing technologies face three core contradictions: 1. Material performance contradictions: While metal shielding can achieve a shielding effectiveness of ≥80dB in the DC-1GHz band, its effectiveness drops sharply to below 65dB in bands above 10GHz due to the skin effect (ASTM D4935 standard). Flexible conductive foam (such as polyurethane matrix) performs well in low-frequency bands, but lacks a magnetic loss mechanism, resulting in a shielding effectiveness of only 50dB at 10GHz, which cannot meet the requirements of 5G communication equipment.

[0003] 2. Structural Reliability Contradictions: Traditional laminated structures (such as metal foil / ferrite sheet composites) are susceptible to interfacial delamination. Related studies show that composite structures using epoxy resin adhesives experience a drop in peel strength from 15 N / cm to 5 N / cm after 100 thermal cycles (-40℃ to 85℃), resulting in a 30% decrease in shielding effectiveness. Ferrite sheets themselves are brittle (elongation at break <2%), and the probability of cracking reaches 45% when used in curved surface packaging devices.

[0004] 3. Incompatibility of processes: Existing ferrite filling processes require high-temperature sintering (>150℃), which conflicts with the thermal budget of semiconductor packaging (≤125℃). For example, polyimide substrates shrink by 2.5% after being treated at 150℃ for 30 minutes, leading to deformation and failure of the shielding structure. Although chemical copper plating can prepare conductive layers at low temperatures, the oxidation rate of copper layers in humid and hot environments reaches 0.1 μm / day (ISO 4527 standard).

[0005] The fundamental problem lies in the fact that existing solutions have not achieved synergistic optimization of materials, structure, and process: At the materials level: the lack of interfacial compatibility technology between conductive substrates and magnetic fillers leads to a single loss mechanism in composite systems.

[0006] Structural aspects: Traditional layered structures have the risk of interface peeling and cannot withstand more than 100,000 bending cycles.

[0007] At the process level: High-temperature processes conflict with the thermal budget of semiconductor packaging, limiting large-scale applications.

[0008] These shortcomings severely restrict technological breakthroughs in fields such as 5G base stations and wearable devices. For example, smartphones have a compact internal space and need to achieve a 10GHz shielding effectiveness of ≥90dB within a thickness of 0.2mm, which current solutions cannot meet. The industry urgently needs to develop new shielding materials that combine high-frequency absorption, flexible contact, and low-temperature process adaptability, achieving an SE ≥45dB, a bending life >100,000 cycles, and adaptability to 260℃ reflow soldering processes within a thickness of ≤50μm. Summary of the Invention

[0009] The purpose of this invention is to provide an ultrathin conductive cloth composite electromagnetic shielding material and its preparation method. It is particularly suitable for electromagnetic interference protection in semiconductor device packaging, specifically a highly flexible conductive cloth composite material with a thickness ≤0.1mm and its efficient preparation process.

[0010] To achieve the above objectives, the present invention provides the following technical solution: A method for manufacturing a conductive foam and ferrite composite shielding structure includes the following steps: (a) Pre-compress the conductive foam substrate with an open porosity of over 90% to 50-70% of its original thickness, thereby reducing the pore size to 40-60% of its original size; (b) Impregnate a ferrite slurry for 20-30 minutes in an environment with a vacuum degree below 0.1 Pa, wherein the slurry comprises: Nickel-zinc ferrite powder with a D50 particle size of 2-3 μm; Silane coupling agent comprising 3-8% of the powder weight; Ethanol-water mixed solvent with a volume ratio of 6:4 to 8:2; (c) First, keep warm at 80±5℃ for 25-35 minutes, then raise the temperature to 120±5℃ and keep warm for 50-70 minutes, with a heating rate of 3-8℃ / min; (d) A NiCu alloy transition layer with a thickness of 150-250 nm and a Cu content of 15-25 wt% is magnetron sputtered onto the surface of the composite. (e) Electroplating a SnBi alloy layer with a thickness of 3-8 μm on the surface of the transition layer at a current density of 1-4 A / dm 2 .

[0011] Furthermore, the viscosity of the ferrite slurry in step (b) is 800-1200 cP.

[0012] Furthermore, the general chemical formula of the nickel-zinc ferrite powder described in step (b) is Ni. （1-a） Zn a Fe2O4, where a = 0.35-0.45.

[0013] Furthermore, the nickel-zinc ferrite powder described in step (b) has a D10 ≥ 0.9 μm and a D90 ≤ 5.5 μm.

[0014] Further, the silane coupling agent in step (b) is KH-550 aminosilane or KH-560 epoxysilane.

[0015] Furthermore, step (c) uses a programmable temperature-controlled oven with a temperature fluctuation of ±3℃.

[0016] Further, after step (e), laser cutting is performed to form a mesh structure with an opening ratio of 28-32%.

[0017] A conductive foam-ferrite composite shielding structure is prepared by a method for manufacturing a conductive foam-ferrite composite shielding structure, comprising: Conductive foam matrix with a compression ratio of 50-70%, and 60-70 vol% ferrite powder filling the pores; A NiCu alloy transition layer with a thickness of 150-250 nm and a Cu content of 15-25 wt%; SnBi alloy layer with a thickness of 3-8 μm; The surface has a laser-cut mesh with an opening ratio of 28-32%.

[0018] Furthermore, the conductive foam substrate is nickel-plated graphite foam with a nickel plating thickness of 3-8 μm.

[0019] Furthermore, the ferrite powder has a real part of permeability ≥15 and a loss tangent ≤0.05 at a frequency of 1GHz.

[0020] The beneficial effects of this invention are as follows: 1. Breakthrough in wideband shielding effectiveness. Through the synergistic effect of the ferrite infiltration layer (nickel-zinc ferrite D50=2.5μm) and the conductive foam substrate, the shielding effectiveness reaches 92dB at the 10GHz frequency, an improvement of 84% compared to pure conductive foam. The shielding frequency band is extended to 40GHz, achieving both electrical shielding (conductivity 0.01Ω·cm) and magnetic loss (μm) ’ =1500) has a dual effect.

[0021] 2. Enhanced interfacial bonding. The pre-compression process (60% thickness) creates 1-3μm submicron pores, which, combined with 5wt% silane coupling agent, form -Si-O-Fe chemical bonds, resulting in an interfacial shear strength of 15MPa and a 98% peel strength retention rate after 100,000 bending cycles.

[0022] 3. Low-temperature process adaptability. Stepped curing (80℃→120℃) and the mesh structure (30% porosity) work together to eliminate internal stress, reducing the coefficient of thermal expansion to 8×10⁻⁶. -6 / ℃, which is 68% lower than that of traditional ferrite sheets, can withstand 260℃ reflow soldering 3 times, and retains 95% of the shielding effectiveness.

[0023] 4. Optimized Deformation Control. The pre-compression process (60% thickness) increases the elastic modulus of the foam to 2.0MPa. Combined with the grid structure design, the permanent compression deformation is <1%, and it can withstand bending deformation with a radius of 1mm, with a bending life of 100,000 cycles.

[0024] 5. Enhanced weldability. The NiCu transition layer (200nm) and the tin layer (5μm) form a metallurgical bond, reducing the welding contact resistance to 0.1Ω, a 99% reduction compared to traditional processes, and improving weldability by 40%, ensuring low-impedance grounding.

[0025] 6. Improved environmental stability. The SnBi alloy layer (5μm) and the coupling agent interface work together to form a physical barrier, inhibiting ferrite oxidation (Ea=120kJ / mol). After testing at 85℃ / 85%RH for 2000 hours, the shielding effectiveness decays by <5%, and the oxidation resistance time is >5000 hours, which is 10 times better than copper-based materials. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process steps in Example 1.

[0027] Figure 2 This is a schematic diagram comparing the structure of graphite foam before and after pre-compression. Figure 2 a (Comparative Example 1): Uncompressed foam structure with an open porosity of 92% and an original pore size of D0 = 50 μm. Schematic diagram of ferrite filling (filling rate of 35 vol%, with particles dispersed in the pores). Figure 2 b (Example 1): Foam structure after 60% compression, wherein the pore size is reduced to D1=25μm, schematic diagram of ferrite filling (filling rate 65vol%, particles are tightly packed).

[0028] Figure 3 This is a schematic diagram of the cross-section of a composite shielding structure made of conductive foam and ferrite. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] Example 1: 1. Pretreatment of conductive foam substrate In this embodiment, nickel-plated graphite foam conforming to GB / T26270-2022 standard is selected as the matrix material, with a nickel plating thickness of 5μm and an open porosity of 92%. A hydraulic press is used to apply a pressure of 10MPa (ISO6892-1:2019 standard for tensile testing of metallic materials) to compress the foam to 60% of its original thickness, at which point the pore size is reduced to 50% of its original value. This pre-compression process is verified by the ASTM D6242-16 porous material compression deformation test to achieve a compression rebound rate of ≥95%, ensuring that the foam matrix has an ideal pore structure for subsequent ferrite filling.

[0031] 2. Vacuum impregnation of ferrite slurry The vacuum impregnation process is carried out in a chamber with a vacuum degree of 0.08 Pa (compliant with GB / T24613-2017 Vacuum Technical Terminology Specification), and the impregnation time is set to 25 minutes. The ferrite slurry consists of the following components: the main component is Ni. 0.6 Zn 0.4 The Fe2O4 nickel-zinc ferrite powder had a lattice constant of 0.4 nm as determined by XRD analysis (according to GB / T32776-2016 microbeam analysis standard); the particle size distribution was measured by a laser particle size analyzer (ISO13320:2009), showing D50=2.5μm, D10=1.0μm, and D90=5.0μm; 5% by weight of KH-550 aminosilane was added as an interface modifier (GB / T1450.2-2006 coupling agent test standard); the solvent system was an ethanol-water mixture (volume ratio 7:3), and its density was verified by GB / T4472-2011 liquid density determination standard; the rheological properties of the slurry were measured by a rotational viscometer (ASTM D4287-17) to be 1000 cP (25℃).

[0032] 3. Stepped curing process A stepped curing process was performed using a programmable temperature-controlled oven (compliant with the technical requirements for high-temperature test chambers in GB / T11158-2019). The first stage involved holding at 80℃ for 30 minutes to complete solvent evaporation, followed by a temperature increase to 120℃ at a rate of 5℃ / min, and holding at this temperature for 60 minutes to achieve cross-linking and curing. The process was monitored using thermomechanical analysis (TMA) to ensure that the shrinkage rate of the foam matrix was controlled within 3% during curing, and that the ferrite distribution uniformity index reached 0.92 (measured by image analysis method, ISO16861:2015).

[0033] 4. Magnetron sputtering and electroplating processes A 200 nm thick NiCu alloy transition layer was deposited on the substrate surface using magnetron sputtering, with the Cu content determined to be 20 wt% by EDS energy dispersive spectroscopy (GB / T17359-2012). Subsequently, an electroplating process was performed to form a 5 μm thick SnBi alloy layer on the transition layer surface (current density 2.5 A / dm², following the GB / T13911-2020 standard for metal coatings). The coating adhesion achieved a 5B grade through cross-cut adhesion testing (GB / T9286-1998), ensuring interface reliability.

[0034] 5. The foam substrate is processed using laser cutting technology (GB / T37018-2018) to form a mesh structure with an open area ratio of 30%. The laser processing parameters are optimized as follows: wavelength 1064nm, pulse frequency 50kHz, and scanning speed 500mm / s, ensuring a processing accuracy of ±0.05mm and a heat-affected zone width of <50μm (infrared thermal imaging detection).

[0035] Example 2: 1. Adjustment of process parameters Based on Example 1, multiple parameters were optimized: the pre-compression ratio was adjusted to 55% to balance the filling rate and flexibility; orthogonal experiments confirmed that this parameter could achieve a ferrite filling rate of 62 vol% while maintaining a compression rebound rate of 97%; the ethanol-water volume ratio was adjusted to 6:4 to reduce the slurry viscosity to 850 cP (measured with a rotational viscometer); the ferrite composition was optimized to Ni. 0.65 Zn 0.3 5Fe2O4 (lattice constant 0.35nm) shows that its real permeability is increased to 18.5 according to theoretical calculations; the electroplating process parameters are adjusted to a current density of 4A / dm², which increases the deposition rate by 30% while maintaining the coating thickness of 3μm.

[0036] 2. Performance optimization results The optimized composite shielding structure achieved a shielding effectiveness of 98.3dB at the 10GHz frequency (tested with a vector network analyzer), which is 3.3% higher than Example 1. The bending life test (JEDEC JESD22-B113) showed that it can withstand 120,000 bending cycles with a radius of 1mm, and the flexibility is improved by 20%.

[0037] Example 3: 1. Comparison of ferrite Zn content is shown in Table 1. Table 1: Comparison of Zn content in ferrite value of a μ' (1GHz) tanδ (1GHz) Preferred grade 0.35 15.3 0.048 qualified 0.38 16.2 0.038 excellent 0.40 17.8 0.035 optimal 0.45 15.1 0.051 qualified 2. Selection of Coupling Agent KH-550: Bond strength 8.7MPa (FTIR shows - NH2 bonding is sufficient).

[0038] KH-560: Bonding strength 7.9MPa (epoxy group hydrolysis stability is slightly poor).

[0039] 3. Overall performance Using ferrite with a=0.40 + KH-550: Shielding effectiveness 97.2dB (10GHz).

[0040] Damp heat aging (85℃ / 85%RH, 1000h) attenuation <5% (IEC60068-2-78).

[0041] Comparative Example 1 Uncompressed foam (92% open area) was used directly for ferrite filling, with other preparation processes the same as in Example 1, resulting in a ferrite filling rate of only 35 vol%. A schematic diagram comparing the structure of the graphite foam before and after pre-compression is shown below. Figure 2 Shielding effectiveness testing showed a loss of only 42dB at 1GHz, a 41.7% decrease compared to Example 1. Failure mechanism analysis indicated that the uncompressed foam pore size was >10μm, preventing ferrite particles from forming a continuous magnetic loss path, and SEM images showed a dispersion index <0.6.

[0042] Comparative Example 2 The ferrite slurry did not contain an interface modifier, and the other preparation processes were the same as in Example 1, resulting in a ferrite shedding rate of 22% after heat treatment. Interface adhesion testing showed that the adhesion of the transition layer decreased from 5B to 2B (cross-cut test). After 100 hours of damp heat testing (85℃ / 85%RH), the shielding effectiveness decreased by 45%. XPS analysis indicated that only physical adsorption existed at the interface, lacking chemical bonding (O-Si bond content <3%).

[0043] Comparative Example 3 Using a single-temperature curing method (120℃ for 80 min), with other preparation processes the same as in Example 1, resulted in three visible cracks (width > 0.1 mm) appearing in the foam matrix, and a 58% decrease in the ferrite distribution uniformity index. Thermomechanical analysis showed a curing shrinkage rate of 8%, indicating that rapid solvent evaporation led to internal stress concentration.

[0044] Comparative Example 4 Sputtering a pure Ni layer instead of the NiCu alloy layer, with other preparation processes the same as in Example 1, resulted in a SnBi coating peel strength of only 1.2 N / cm, a 45% decrease compared to Example 1. SEM-EDS analysis showed the formation of a brittle intermetallic compound at the interface (IMC thickness > 3 μm), with a thermal expansion coefficient mismatch rate ΔCTE = 18 × 10⁻⁶. -6 / ℃, which causes stress concentration at the interface.

[0045] Product performance verification 1. Key performance indicators ( Figure 1 ) Example 1: The product was verified by multiple standards: ferrite filling rate 65 vol% (GB / T21526-2008), real part of magnetic permeability 17.3 (GB / T3655-2000), loss tangent 0.03, mesh porosity 30.2% (GB / T10796-2001), shielding effectiveness of 70-85 dB in the 1-3 GHz band (GB / T30024-2013), interfacial shear strength 15 MPa (GB / T17590-1998), and coefficient of thermal expansion 8 × 10⁻⁻⁻⁶. 6 / ℃ (GB / T4339-2008), welding contact resistance 0.1Ω (GB / T5779-2005). All indicators meet the limits specified in this application.

[0046] 2. Environmental reliability testing The shielding effectiveness decreased by less than 5% after 2000 hours of damp heat testing (85℃ / 85%RH) (GB / T2423.3-2016), and the metal layer showed no corrosion after 96 hours of salt spray testing (5% NaCl solution) (GB / T10125-2012), indicating that the product has excellent environmental adaptability.

[0047] Invention and Innovation 1. Structural Innovation The pre-compression-vacuum impregnation synergistic process achieves directional ferrite filling through pore size control, increasing the filling rate by 85.7% compared to the uncompressed process. Submicron-level pores (1-3μm) result in a ferrite dispersion uniformity index of 0.92, forming a continuous magnetic loss path. The gradient functional interface design, through a NiCu transition layer (Cu 15-25wt%), improves coating adhesion by 2.2 times, achieving an interfacial shear strength of 15MPa, meeting the requirements of MIL-DTL-83528C. A schematic diagram of the cross-section of the conductive foam and ferrite composite shielding structure is shown below. Figure 3 .

[0048] 2. Technological Innovation The dual-stage curing mechanism separates solvent evaporation from the crosslinking process, reducing the bubble defect rate from 18% to 3% (CT scan detection). The stepped heating process reduces thermal stress, lowering the coefficient of thermal expansion by 68% (DSC analysis). Laser micro-nano fabrication achieves a mesh structure with a precision of ±0.05mm, with an opening ratio control error ≤1%, and the spiral scanning mode effectively suppresses the expansion of the heat-affected zone.

[0049] 3. Performance Breakthrough The wideband shielding effectiveness averages 77.5dB in the 1-3GHz band, a 35dB improvement over traditional methods, while maintaining 68dB at the 40GHz frequency. Regarding the composite dielectric properties, the real part of the permeability to the loss tangent ratio reaches 576.7, meeting the design requirements for high magnetic efficiency and low loss. The conductive foam matrix has a volume resistivity of 0.01Ω·cm, ensuring low-impedance grounding performance.

[0050] The above description is merely a preferred embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concepts, should be covered within the scope of protection of the present invention.

Claims

1. A method for manufacturing a conductive foam and ferrite composite shielding structure, characterized in that: The steps are as follows: (a) Pre-compress the conductive foam substrate with an open porosity of over 90% to 50-70% of its original thickness, thereby reducing the pore size to 40-60% of its original size; (b) Impregnate a ferrite slurry for 20-30 minutes in an environment with a vacuum degree below 0.1 Pa, wherein the slurry comprises: Nickel-zinc ferrite powder with a D50 particle size of 2-3 μm; Silane coupling agent comprising 3-8% of the powder weight; Ethanol-water mixed solvent with a volume ratio of 6:4 to 8:2; (c) First, keep warm at 80±5℃ for 25-35 minutes, then raise the temperature to 120±5℃ and keep warm for 50-70 minutes, with a heating rate of 3-8℃ / min; (d) A NiCu alloy transition layer with a thickness of 150-250 nm and a Cu content of 15-25 wt% is magnetron sputtered onto the surface of the composite. (e) Electroplating a SnBi alloy layer with a thickness of 3-8 μm on the surface of the transition layer at a current density of 1-4 A / dm 2 .

2. The manufacturing method of the conductive foam and ferrite composite shielding structure as described in claim 1, characterized in that: The viscosity of the ferrite slurry in step (b) is 800-1200 cP.

3. The manufacturing method of the conductive foam and ferrite composite shielding structure as described in claim 1, characterized in that: The general chemical formula of the nickel-zinc ferrite powder described in step (b) is Ni （1-a） Zn a Fe2O4, where a = 0.35-0.

45.

4. The manufacturing method of the conductive foam and ferrite composite shielding structure as described in claim 1, characterized in that: The nickel-zinc ferrite powder in step (b) has a D10 ≥ 0.9 μm and a D90 ≤ 5.5 μm.

5. The manufacturing method of the conductive foam and ferrite composite shielding structure as described in claim 1, characterized in that: The silane coupling agent in step (b) is KH-550 aminosilane or KH-560 epoxysilane.

6. The manufacturing method of the conductive foam and ferrite composite shielding structure as described in claim 1, characterized in that: Step (c) uses a programmable temperature-controlled oven with a temperature fluctuation of ±3℃.

7. The manufacturing method of the conductive foam and ferrite composite shielding structure as described in claim 1, characterized in that: After step (e), laser cutting is performed to form a mesh structure with an opening ratio of 28-32%.

8. A conductive foam-ferrite composite shielding structure, characterized in that: The conductive foam and ferrite composite shielding structure is manufactured by any one of claims 1-7, comprising: Conductive foam matrix with a compression ratio of 50-70%, and 60-70 vol% ferrite powder filling the pores; A NiCu alloy transition layer with a thickness of 150-250 nm and a Cu content of 15-25 wt%; SnBi alloy layer with a thickness of 3-8 μm; The surface has a laser-cut mesh with an opening ratio of 28-32%.

9. The conductive foam-ferrite composite shielding structure as described in claim 8, characterized in that: The conductive foam substrate is nickel-plated graphite foam with a nickel plating thickness of 3-8 μm.

10. The conductive foam-ferrite composite shielding structure as described in claim 8, characterized in that: The ferrite powder has a real part of permeability ≥15 and a loss tangent ≤0.05 at a frequency of 1GHz.

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