Accurate alignment method for multiple layers of substrates

Abstract

The accurate alignment method comprises the steps that at least two base plate layers capable of being attached are prepared respectively, each base plate layer comprises a base plate, a functional structure layer and an attaching interface layer, and the functional structure layer and the attaching interface layer are arranged on the two opposite sides of the base plate respectively; forming gap filling layers on the functional structure layers or the bonding interface layers of all the substrate layers, and performing initial bonding and driving displacement on the at least two substrate layers under a preset bonding pressure condition, so that the alignment marks arranged on the at least two substrate layers are aligned; the at least two aligned substrate layers are placed in a curing treatment condition, the gap filling layer is cured, and a prefabricated substrate is obtained after curing is completed; and performing trepanning treatment on the prefabricated substrate at the preset interconnection position to obtain a conductive communication hole, depositing a conductive material in the conductive communication hole, and arranging a packaging layer on the outer surface of the prefabricated substrate to obtain the multi-layer substrate. Through the synergistic effect of the steps, high-precision alignment and stable integration of multiple layers of substrates are completed under the condition of low laminating pressure.

Description

Technical Field

[0001] This invention belongs to the field of circuit board manufacturing technology, and particularly relates to a precise alignment method for multilayer substrates. Background Technology

[0002] The multilayer substrates formed by stacking are actually used as multilayer interconnect carriers for printed circuit boards or flexible circuit boards to support chips, passive components and functional devices, and to realize the layered layout of signal lines, power lines and ground lines; they are used as intermediary substrates or packaging substrates in chip packaging to realize electrical connection and mechanical support between chips and external circuits; they are used in flexible electronics and wearable devices as multifunctional integration carriers to integrate sensing, display, driving or communication functions in a limited area; they are used in sensor modules, camera modules and power device modules as a platform for signal aggregation and functional unit integration; they can also be used in new energy vehicle electronics, industrial control equipment and communication equipment as high-density, high-reliability line interconnect and functional integration substrates.

[0003] In existing technologies, multilayer substrates typically require high bonding pressure or rapid curing to achieve interlayer fixation. However, the conductive lines, structural undulations, and interfacial adhesion between materials on the substrate surface can easily limit the relative sliding ability between substrate layers in the early stages of bonding, leading to misalignment or locking during the alignment process, making it difficult to obtain a stable and accurate interlayer alignment effect. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a precise alignment method for multilayer substrates, which aims to solve the problem of achieving high-precision alignment of multilayer substrates during interlayer bonding.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: a method for precise alignment of a multilayer substrate, comprising the following steps: S1. Prepare at least two bondable substrate layers respectively. Each substrate layer includes a substrate plate and a functional structure layer and a bonding interface layer respectively disposed on opposite sides of the substrate plate. The functional structure layer is used to form conductive lines, and the bonding interface layer is used to connect with the functional structure layer and reduce the interface adhesion resistance under a preset bonding pressure. S2. Form a gap-filling layer on the functional structure layer or bonding interface layer of all substrate layers, and perform initial bonding and drive displacement on at least two substrate layers under a preset bonding pressure condition, so that the alignment marks set on at least two substrate layers are aligned. S3. Place at least two aligned substrate layers in a curing process to cure the gap-filling layer. After curing, a prefabricated substrate is obtained. S4. A prefabricated substrate is opened at a preset interconnection location to obtain conductive interconnection holes. Conductive material is deposited in the conductive interconnection holes to enable cross-layer electrical connection of functional structure layers on each substrate layer of the prefabricated substrate. An encapsulation layer is set on the outer surface of the prefabricated substrate to obtain a multilayer substrate.

[0006] In some embodiments of the present invention, step S1 includes: S1.1 A substrate is ultrasonically cleaned sequentially with deionized water and isopropanol at a power of 150~300W for 5 to 10 minutes. After being dried with nitrogen, it is placed in a plasma cleaner for surface activation treatment at a power of 50~150W for 30~120 seconds to obtain the initial substrate. S1.2. Conductive ink is deposited on one side of the preliminary board to form a conductive circuit pattern as a functional structure layer. The line width is controlled to be 5~50μm and the line thickness is controlled to be 0.3~5μm. After the ink is printed, the preliminary board is placed in an inert atmosphere oven for sintering treatment. The sintering temperature is 80~160℃ and the sintering time is 10~60min to obtain a functional substrate with a functional structure layer. S1.3. Check if there is a height difference in the functional structure layer of the functional substrate. If so, spray a high-viscosity conductive paste onto the functional structure layer. The nozzle diameter is 10~80μm and the spraying speed is 0.2~5mm / s. After spraying, place the functional substrate on a constant temperature hot table for pre-forming treatment. The treatment temperature is 60~120℃ and the treatment time is 5~20min. Then, perform a secondary curing treatment in an oven. The curing temperature is 100~180℃ and the curing time is 10~40min. S1.4. Deposit a metal coating on the side of the functional substrate away from the functional structure layer to form a metal anchoring layer. The total thickness of the metal anchoring layer is 10~80nm. After deposition, immerse the functional substrate in an organic solution containing a self-assembled molecular precursor for interface treatment. The concentration of the self-assembled molecular precursor is 0.5~5mM, the treatment temperature is 20~30℃, and the treatment time is 10~60min. After treatment, remove the substrate and rinse it with ethanol or isopropanol. Then bake it at 60~110℃ for 5~20min to form an bonding interface layer on the side of the functional substrate away from the functional structure layer. S1.5 Repeat steps S1.1 to S1.4 for each substrate to form a functional structure layer and a bonding interface layer on opposite sides of the substrate, thereby obtaining at least two bonding substrate layers.

[0007] In some embodiments of the present invention, in step S1, the substrate includes at least one of polyimide film, liquid crystal polymer film, thermoplastic polyurethane film, and polyethylene terephthalate film; the conductive ink includes at least one of silver nanoparticle conductive ink, copper nanoparticle conductive ink, silver-coated copper composite conductive ink, and silver nanowire conductive ink; the high-viscosity conductive paste includes at least one of silver micropowder conductive paste, silver nanoparticle resin composite conductive paste, copper micropowder composite conductive paste, and copper-silver composite conductive paste; the metal coating includes at least one of titanium / gold composite metal, chromium / gold composite metal, titanium / palladium / gold composite metal, chromium / copper / gold composite metal, aluminum, and aluminum alloy; and the self-assembled molecular precursor includes at least one of alkyl thiol self-assembled molecules, aromatic thiol self-assembled molecules, silane self-assembled molecules, self-assembled molecules with fluorine-terminated groups, self-assembled molecules with hydroxyl-terminated groups, and self-assembled molecules with carboxyl-terminated groups.

[0008] In some embodiments of the present invention, step S2 includes: S2.1 The flexible polymer raw material, sheet-like inorganic filler, and solvent are vacuum stirred at a speed of 800~2000 rpm for 3~10 min, with a vacuum degree of [missing information]. 0.8~ 1 MPa was used to obtain the gap-filling adhesive. Then, the gap-filling adhesive was preheated and adjusted on a constant temperature hot plate. The temperature was set at 35~55℃ and the preheating time was 2~8 minutes to stabilize the viscosity of the gap-filling adhesive within the preset viscosity range. S2.2. Apply the gap-filling adhesive to the surface of at least one functional structural layer or bonding interface layer of the substrate layer, with a coating thickness controlled at 2~30μm. After coating, place it in a vacuum chamber for secondary degassing treatment, with a degassing vacuum degree of [missing information]. 0.8~ 1MPa, degassing time of 2~6min, to obtain a substrate layer to be bonded covered by a gap-filling layer; S2.3. Microstructure channels are formed on the interstitial layer by soft molding or laser micromachining. The depth of the microstructure channels is 1~15μm and the width is 10~80μm. After the microstructure channels are formed, they are pre-baked at 40~70℃ for 2~10min to make the surface of the interstitial layer in a semi-fluid state. S2.4. At least two substrate layers are placed in a laminating device, which is a vacuum laminator. Before lamination, the laminating cavity is evacuated to a vacuum level of [missing information]. 0.6~ 1MPa, vacuuming time is 30~120s, then the bonding pressure is applied to the preset bonding pressure range, which is 0.01~1.5MPa, and held for 3~30s for initial bonding; S2.5 During the initial bonding process, the optical alignment system of the bonding equipment collects and identifies the alignment marks set on at least two substrate layers, calculates the alignment deviation between the two substrate layers, and drives the substrate layers to perform displacement correction while keeping the preset bonding pressure range unchanged or adjusting it to ±0.01~0.05MPa. The displacement step is 0.1~5μm and the displacement speed is 0.05~2mm / s, so that the substrate layers slide relative to each other and the alignment deviation reaches the set threshold. S2.6 When the alignment deviation of the alignment mark of the substrate layer reaches the set threshold, the current bonding pressure and displacement position are kept unchanged, and a holding process is performed. The holding time is 2~10min. During the holding period, a short pressure pulse of 0.2~1.5MPa is applied to the bonding interface, and the number of pulses is 1~5.

[0009] In some embodiments of the present invention, in step S2, the flexible polymer raw material includes at least one of siloxane-modified acrylic resin, low-modulus polyurethane acrylic resin, and flexible epoxy-modified elastomer resin; the sheet-like inorganic filler includes at least one of sheet-like boron nitride, sheet-like montmorillonite, and sheet-like silica; and the solvent includes at least one of ethyl acetate, propylene glycol methyl ether acetate, and isopropanol.

[0010] In some embodiments of the present invention, in step S2.1, the preset viscosity range is 10000~50000 mPa·s; If the viscosity of the filler adhesive is less than 10000 mPa·s, increase the temperature of the constant temperature hot table by 5~10℃ based on the upper limit of the preheating temperature, and maintain it for 1~5 minutes. If the viscosity of the interstitial filler solution is greater than 50000 mPa·s, the solvent should be added dropwise at a rate of 0.1~2.0 mL / min, with each addition being 0.2~1.0 wt% of the total mass of the interstitial filler solution. After addition, the solution should be stirred under low-speed vacuum at 35~55℃ for 1~3 min at a speed of 200~600 rpm and a vacuum level of [missing information]. 0.6~ 1MPa.

[0011] In some embodiments of the present invention, step S3 includes: S3.1. Keep at least two substrate layers that have completed the alignment mark alignment in the alignment lock state of the bonding equipment, keep the bonding pressure constant at 0.01~1.5MPa, and maintain the steady state for 2~10min; S3.2. While maintaining the bonding pressure constant, the bonded substrate layer is fixed by using a clamp or vacuum adsorption to constrain its position. The vacuum adsorption negative pressure is... 0.3~ 1MPa; S3.3 Place the fixed substrate layer in a curing device for pre-curing treatment. The pre-curing treatment temperature is 40~70℃ and the treatment time is 5~20min, so that the viscosity of the interstitial layer increases and enters the pre-curing state. S3.4 After completing the pre-curing treatment, perform a main curing treatment on the substrate layer. The main curing temperature is 80~140℃, the heating rate is 1~5℃ / min, and the holding time is 10~60min. S3.5 During the main curing process, the edges of the bonding area are locally pre-cured. The width of the pre-cured area is 1~5mm, and the pre-curing method is ultraviolet irradiation with an intensity of 50~300mW / cm². 2 The processing time is 30~180s to form a locking structure at the edge of the bonding area; S3.6 After the main curing process is completed, the substrate layer is subjected to controlled cooling at a rate of 0.5~3℃ / min until the temperature drops to 25~35℃. Then, it is annealed at 40~80℃ for 5~30min to obtain the prefabricated substrate.

[0012] In some embodiments of the present invention, step S4 includes: S4.1 First, based on the alignment marks on the prefabricated substrate and the conductive wiring position of the functional structure layer, the preset interconnection position is determined. The prefabricated substrate is fixed on the vacuum adsorption platform, and the interconnection position is locally cleaned. S4.2. A prefabricated substrate is opened at a preset interconnection location to form a conductive through hole that penetrates at least two substrate layers. S4.3 First, clean and dry the conductive through holes, and then place the prefabricated substrate in a plasma cleaning equipment for hole wall activation treatment. The treatment power is 50~200W and the treatment time is 30~180s. S4.4 After completing the hole wall activation treatment, a transition material is deposited in the conductive interconnection hole. The transition material forms a conductive transition layer by sputtering or spraying. The total thickness of the conductive transition layer is 20~200nm. S4.5. Conductive material is filled into the conductive vias where a conductive transition layer has been formed. The conductive material is deposited via vacuum-assisted injection, with a vacuum level of [missing information]. 0.6~ After filling with 1MPa, the material is pre-shaped at 60~120℃ for 5~20min, and then cured at 100~180℃ for 10~60min to form a continuous conductive path in the conductive interconnection hole. S4.6. An encapsulation layer made of encapsulation material is provided on the outer surface of the prefabricated substrate. The encapsulation layer is formed by coating, spraying or lamination. The thickness of the encapsulation layer is 10~80μm. After encapsulation, it is cured at 60~140℃ for 10~60min. S4.7 After the encapsulation layer is cured, a cooling and shaping process is performed at a cooling rate of 0.5~3℃ / min, and the multilayer substrate is obtained by cooling to 25~35℃.

[0013] In some embodiments of the present invention, in step S4, the transition material includes at least one of titanium, chromium, titanium / copper composite material, chromium / copper composite material, and titanium / gold composite material; the conductive material includes at least one of silver nanoparticle conductive paste, silver micropowder conductive paste, copper-based conductive paste, and silver-coated copper composite conductive paste; and the encapsulation material includes at least one of epoxy resin encapsulation material, fluoropolymer encapsulation material, thermoplastic polyurethane encapsulation material, and silicone rubber encapsulation material.

[0014] In some embodiments of the present invention, step S4.2, the hole-opening process includes: The prefabricated substrate is dehydrated and pre-baked at a temperature of 90-120°C for 3-10 minutes. Then, a photosensitive material is coated onto the surface of the prefabricated substrate by spin coating to form a photosensitive layer. The photosensitive material is either a positive or negative photosensitive resin. The spin coating speed is 1000-3000 rpm and the spin coating time is 20-60 seconds, so that the thickness of the photosensitive layer is controlled at 5-30 μm. After spin coating, the photosensitive layer is softened and baked at a temperature of 80-110°C for 2-8 minutes. A prefabricated substrate coated with a photosensitive layer is placed in an exposure apparatus, and the preset interconnect positions are selectively exposed to ultraviolet light using a mask. The exposure wavelength is 350~420nm, and the exposure energy is 100~400mJ / cm². 2 After exposure, the prefabricated substrate is immersed in a developing solution for development treatment. The developing solution includes at least one of tetramethylammonium hydroxide aqueous solution and sodium carbonate aqueous solution. The developing concentration is 0.2~1.0wt%, the developing temperature is 20~30℃, and the developing time is 30~120s to form an opening window for exposing the substrate. After development, it is rinsed with deionized water and dried with nitrogen gas, and then post-baked at 100~140℃ for 3~10min. The prefabricated substrate is immersed in an alkaline solution for chemical opening treatment. The alkaline solution includes at least one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and potassium carbonate aqueous solution. The alkaline concentration is 0.5~5.0wt%, the treatment temperature is 40~80℃, and the treatment time is 2~20min, until conductive through-holes are formed that penetrate at least two substrate layers. After etching, the prefabricated substrate is thoroughly rinsed with deionized water and treated with a weakly acidic neutralization solution. The neutralization solution is a diluted acetic acid or citric acid aqueous solution with a concentration of 0.1~1.0wt%.

[0015] The precise alignment method for multilayer substrates in this invention has the following advantages compared with the prior art: In step S1, by setting functional structure layers and bonding interface layers on opposite sides of the substrate, the substrate layers, while possessing conductive circuit functions, maintain low interfacial adhesion resistance at the bonding interface under a preset bonding pressure, structurally avoiding interlayer lock-up caused by excessive interfacial adhesion in the initial bonding stage. In step S2, by forming a gap-filling layer on the functional structure layer or bonding interface layer, and performing initial bonding and driving displacement under a preset bonding pressure, the substrate layers can still slide relative to each other under controlled pressure, thus providing the necessary displacement freedom for adjusting the alignment marks and precise alignment. In step S3, after alignment is completed, the gap-filling layer is cured, changing the bonding interface from an adjustable state to a stable connection state, thereby achieving interlayer fixation without damaging the completed alignment. Finally, in step S4, by forming conductive through-holes and depositing conductive material on the prefabricated substrate, cross-layer electrical connections between the functional structure layers of each substrate layer are achieved, and an overall structure is formed by encapsulation on the outer surface, ensuring reliable electrical connection and structural stability of the multilayer substrate after precise alignment. Through the synergistic effect of the above steps, high-precision alignment and stable integration of multilayer substrates are achieved under low bonding pressure conditions. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating a precise alignment method for a multilayer substrate according to an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] Please refer to Figure 1 This invention proposes a precise alignment method for multilayer substrates, comprising the following steps: S1. Prepare at least two bondable substrate layers respectively. Each substrate layer includes a substrate plate and a functional structure layer and a bonding interface layer respectively disposed on opposite sides of the substrate plate. The functional structure layer is used to form conductive lines, and the bonding interface layer is used to connect with the functional structure layer and reduce the interface adhesion resistance under a preset bonding pressure.

[0019] In some embodiments, the substrate may be PP, PI, glass, etc.

[0020] Step S1 includes: S1.1 A substrate is ultrasonically cleaned sequentially with deionized water and isopropanol at a power of 150~300W for 5~10min. After being dried with nitrogen, it is placed in a plasma cleaner for surface activation treatment at a power of 50~150W for 30~120s to obtain a preliminary substrate. The substrate includes at least one of polyimide film, liquid crystal polymer film, thermoplastic polyurethane film, and polyethylene terephthalate film.

[0021] Ultrasonic cleaning with deionized water and isopropanol effectively removes particulate contaminants, grease residues, and low-molecular-weight organic matter from the substrate surface. Isopropanol, in particular, has a strong dissolving ability for non-polar contaminants, which helps improve the cleanliness of the substrate surface. Subsequent surface activation treatment using a plasma cleaner introduces polar functional groups such as hydroxyl and carboxyl groups onto the substrate surface, increasing its surface energy and wettability. This enhances the uniformity and adhesion stability of the conductive ink spreading on the substrate surface. This step provides a stable interface foundation for the fine printing and continuous forming of conductive lines, reducing the risk of line breakage, pinholes, and detachment.

[0022] S1.2. Conductive ink is deposited on one side of the preliminary board to form a conductive circuit pattern as a functional structure layer. The line width is controlled to be 5~50μm and the line thickness is controlled to be 0.3~5μm. After the inkjet printing is completed, the preliminary board is placed in an inert atmosphere oven for sintering treatment. The sintering temperature is 80~160℃ and the sintering time is 10~60min to obtain a functional substrate with a functional structure layer. The conductive ink includes at least one of silver nanoparticle conductive ink, copper nanoparticle conductive ink, silver-coated copper composite conductive ink, and silver nanowire conductive ink.

[0023] Conductive ink is deposited on one side of the preform board using inkjet printing to form conductive circuit patterns. This allows the conductive circuits to be directly built onto the substrate surface in an additive manufacturing process, avoiding damage to the substrate caused by traditional subtractive etching processes. Conductive inks such as silver nanoparticles, copper nanoparticles, silver-coated copper composites, or silver nanowires form continuous and stable conductive pathways during sintering through interparticle contact, melt neck growth, and conductive network construction. Controlling linewidth and line thickness helps reduce material consumption while ensuring conductivity and improving reliability under flexible bending conditions. This step endows the substrate layer with a stable conductive functional structure, laying the foundation for subsequent interlayer interconnects and multilayer integration.

[0024] S1.3. Check whether there is a height difference in the functional structure layer of the functional substrate. If so, spray a high-viscosity conductive paste onto the functional structure layer. The nozzle diameter is 10~80μm and the spraying speed is 0.2~5mm / s. After spraying, place the functional substrate on a constant temperature hot plate for pre-forming treatment. The treatment temperature is 60~120℃ and the treatment time is 5~20min. Then, perform a secondary curing treatment in an oven. The curing temperature is 100~180℃ and the curing time is 10~40min. The high-viscosity conductive paste includes at least one of silver micro powder conductive paste, silver nanoparticle resin composite conductive paste, copper micro powder composite conductive paste, and copper-silver composite conductive paste.

[0025] By detecting height differences in the functional structure layers and spraying a high-viscosity conductive paste when such differences exist, a three-dimensional compensation structure can be constructed on the surface or in localized areas of the conductive circuit. Silver micropowder, copper micropowder, and their composite conductive paste form a dense conductive framework during pre-forming and secondary curing processes, thereby filling in circuit steps, pad protrusions, or localized uneven areas. This step effectively reduces the height fluctuations on the surface of the functional structure layers, lowering the risk of localized stress concentration, incomplete bonding, or conductive interruption caused by height differences during subsequent bonding processes. It also improves contact consistency and electrical connection reliability during cross-layer interconnection.

[0026] S1.4. A metal anchoring layer is formed by depositing a metal coating on the side of the functional substrate away from the functional structure layer. The total thickness of the metal anchoring layer is 10~80nm. After deposition, the functional substrate is immersed in an organic solution containing a self-assembly molecular precursor for interface treatment. The concentration of the self-assembly molecular precursor is 0.5~5mM, the treatment temperature is 20~30℃, and the treatment time is 10~60min. After treatment, the substrate is removed and rinsed with ethanol or isopropanol, and then baked at 60~110℃ for 5~20min to form an bonding interface layer on the side of the functional substrate away from the functional structure layer. The metal coating includes at least one of titanium / gold composite metal, chromium / gold composite metal, titanium / palladium / gold composite metal, chromium / copper / gold composite metal, aluminum, and aluminum alloy. The self-assembly molecular precursor includes at least one of alkyl thiol self-assembly molecules, aromatic thiol self-assembly molecules, silane self-assembly molecules, self-assembly molecules with fluorine-terminated groups, self-assembly molecules with hydroxyl-terminated groups, and self-assembly molecules with carboxyl-terminated groups.

[0027] A metal anchoring layer is deposited on the side of the functional substrate away from the functional structure layer, and a self-assembled molecular precursor is further introduced for interface treatment, forming a bonding interface layer with interface regulation function on this side. Metals such as titanium and chromium, as the bottom layer, have good adhesion properties, while metals such as gold and palladium readily form stable chemical bonds with thiol or silane self-assembled molecules. These self-assembled molecules form a dense molecular layer through orderly arrangement, significantly reducing the effective adhesion force and frictional resistance of the interface surface. Under preset bonding pressure conditions, this bonding interface layer achieves low adhesion and slippage interface characteristics, providing the necessary conditions for alignment adjustment during subsequent multilayer substrate bonding.

[0028] S1.5 Repeat steps S1.1 to S1.4 for each substrate to form a functional structure layer and a bonding interface layer on opposite sides of the substrate, thereby obtaining at least two bonding substrate layers.

[0029] By repeating the above steps on each substrate, a conductive functional structure layer and a bonding interface layer are formed on opposite sides of the substrate, respectively, structurally separating the functional layer and the bonding layer. This configuration allows each substrate layer to have independent conductive function while also possessing controlled interface adhesion characteristics. This ensures the integrity of the circuit layers during multilayer lamination while reducing the risk of interface lock-up during the bonding stage. The resulting at least two bondable substrate layers exhibit higher alignment accuracy, bonding consistency, and overall structural reliability in subsequent low-pressure bonding and cross-layer interconnection processes.

[0030] S2. Form a gap-filling layer on the functional structure layer or bonding interface layer of all substrate layers, and perform initial bonding and drive displacement on at least two substrate layers under a preset bonding pressure condition, so that the alignment marks set on at least two substrate layers are aligned. Step S2 includes: S2.1 The flexible polymer raw material, sheet-like inorganic filler, and solvent are vacuum stirred at a speed of 800~2000 rpm for 3~10 min, with a vacuum degree of [missing information]. 0.8~ The gap-filling adhesive was obtained at 1 MPa. Then, the gap-filling adhesive was preheated and its viscosity adjusted on a constant temperature hot plate. The temperature was set at 35~55℃ and the preheating time was 2~8 min to stabilize the viscosity of the gap-filling adhesive within the preset viscosity range. The flexible polymer raw materials include at least one of siloxane modified acrylic resin, low modulus polyurethane acrylic resin, and flexible epoxy modified elastomer resin. The sheet-like inorganic filler includes at least one of sheet-like boron nitride, sheet-like montmorillonite, and sheet-like silica. The solvent includes at least one of ethyl acetate, propylene glycol methyl ether acetate, and isopropanol.

[0031] By stirring the flexible polymer raw material, flake inorganic filler, and solvent under vacuum conditions, the flexible polymer resin is fully swollen and forms a continuous phase under the action of the solvent. The flake inorganic filler is uniformly dispersed in the polymer system under shearing action, resulting in a gap-filling adhesive with uniform composition and low bubble content. Siloxane-modified acrylic resin, low-modulus polyurethane acrylic resin, and flexible epoxy-modified elastomer resin have low elastic modulus and good molecular chain flexibility, which can provide deformation buffering capacity during subsequent bonding. Flake boron nitride, flake montmorillonite, or flake silica are distributed in a layered orientation in the adhesive, which can form tortuous barrier paths after curing, improving interfacial density. By preheating and adjusting the viscosity and stabilizing it within a preset viscosity range, the gap-filling adhesive has sufficient fluidity to fill tiny gaps during subsequent bonding without uncontrolled flow, thus providing a suitable rheological basis for low-pressure bonding and alignment slip.

[0032] In step S2.1, the preset viscosity range is 10000~50000 mPa·s; If the viscosity of the filler adhesive is less than 10000 mPa·s, increase the temperature of the constant temperature hot table by 5~10℃ based on the upper limit of the preheating temperature, and maintain it for 1~5 minutes. If the viscosity of the interstitial filler solution is greater than 50000 mPa·s, the solvent should be added dropwise at a rate of 0.1~2.0 mL / min, with each addition being 0.2~1.0 wt% of the total mass of the interstitial filler solution. After addition, the solution should be stirred under low-speed vacuum at 35~55℃ for 1~3 min at a speed of 200~600 rpm and a vacuum level of [missing information]. 0.6~ 1MPa.

[0033] S2.2. Apply the gap-filling adhesive to the surface of at least one functional structural layer or bonding interface layer of the substrate layer, with a coating thickness controlled at 2~30μm. After coating, place it in a vacuum chamber for secondary degassing treatment, with a degassing vacuum degree of [missing information]. 0.8~ At 1 MPa, the degassing time is 2~6 min, and the interstitial layer is covered with the substrate layer to be bonded.

[0034] A gap-filling adhesive is applied to the surface of the functional structural layer or bonding interface layer of the substrate, forming a continuous cover layer over the gaps in conductive lines and areas of local unevenness. This allows for compensation of minor height differences and interface voids during subsequent bonding. By controlling the coating thickness, the gap-filling layer achieves effective gap filling without significantly increasing the interlayer thickness. A secondary degassing treatment further removes residual gas from the gap-filling adhesive, preventing the formation of bubbles or voids during bonding and curing. This step improves the continuity and uniformity of the bonding interface, creating conditions for obtaining a dense interface in subsequent alignment and curing stages.

[0035] S2.3. Microstructure channels are formed on the interstitial layer by soft molding or laser micromachining. The depth of the microstructure channels is 1~15μm and the width is 10~80μm. After the microstructure channels are formed, they are pre-baked at 40~70℃ for 2~10min to make the surface of the interstitial layer in a semi-fluid state.

[0036] Microstructured channels are formed on the interstitial layer, enabling the bonding interface to conduct and vent air. These channels provide release pathways for air and excess interstitial adhesive within the interface during the initial bonding phase, thus reducing the risk of air entrapment. A short pre-baking process places the interstitial layer surface in a semi-fluid state, maintaining some adhesion while retaining localized deformation capabilities. This facilitates controlled flow of the interstitial adhesive under confined conditions during subsequent bonding. This step, through the combination of structural control and material rheological behavior, improves the stability of the bonding interface and the bonding yield.

[0037] S2.4. At least two substrate layers are placed in a laminating device, which is a vacuum laminator. Before lamination, the laminating cavity is evacuated to a vacuum level of [missing information]. 0.6~ 1MPa, vacuuming time is 30~120s, then the bonding pressure is applied to the preset bonding pressure range, which is 0.01~1.5MPa, and held for 3~30s for initial bonding.

[0038] Laying at least two substrate layers in a vacuum bonding environment, followed by initial bonding under vacuum conditions, significantly reduces interfacial air residue and lowers the probability of bubble formation. Controlling the bonding pressure within a preset range ensures continuous contact between the substrate layers under low mechanical load, preventing compression or damage to the flexible conductive lines. This step, while ensuring bonding stability, preserves interfacial slippage space for subsequent alignment correction, a crucial prerequisite for achieving high-precision alignment bonding.

[0039] S2.5 During the initial bonding process, the optical alignment system of the bonding equipment collects and identifies the alignment marks set on at least two substrate layers, calculates the alignment deviation between the two substrate layers, and drives the substrate layers to perform displacement correction while keeping the preset bonding pressure range unchanged or adjusting it to ±0.01~0.05MPa. The displacement step is 0.1~5μm and the displacement speed is 0.05~2mm / s, so that the substrate layers slide relative to each other and the alignment deviation reaches the set threshold.

[0040] An optical alignment system is used to acquire and identify alignment marks in real time. Under controlled bonding pressure, the substrate layers are driven to undergo micro-displacement, causing the interstitial layer to undergo limited deformation under shear force, thereby achieving relative sliding alignment between the substrate layers. Precise control of the displacement step and velocity allows the alignment process to gradually converge to a set threshold, avoiding interface disturbances or misalignment rebound caused by large one-time displacements. This step utilizes the rheological properties of the interstitial layer and the synergistic effect of the low-adhesion interface to achieve high-precision alignment under low-pressure conditions.

[0041] S2.6 When the alignment deviation of the alignment mark of the substrate layer reaches the set threshold, the current bonding pressure and displacement position are kept unchanged, and a holding process is performed. The holding time is 2~10min. During the holding period, a short pressure pulse of 0.2~1.5MPa is applied to the bonding interface, and the number of pulses is 1~5.

[0042] After the alignment deviation reaches a set threshold, the shear stress inside the gap-filling layer is gradually released and stabilized by maintaining the bonding pressure and displacement position unchanged. During the holding period, a short-duration pressure pulse is applied, which promotes the migration and discharge of residual gas in the interface along the microstructure channels, while simultaneously pushing the gap-filling adhesive to further fill the local micro-gaps. This step improves the density and stability of the bonding interface without damaging the completed alignment, laying the foundation for locking the alignment state and obtaining reliable interlayer bonding in the subsequent curing stage.

[0043] S3. Place at least two aligned substrate layers in a curing process to cure the gap-filling layer. After curing, a prefabricated substrate is obtained. Step S3 includes: S3.1. Keep at least two substrate layers that have completed alignment mark alignment in the alignment lock state of the bonding equipment, keep the bonding pressure constant at 0.01~1.5MPa, and maintain the steady state for 2~10min.

[0044] After the alignment marks are completed, the bonding pressure is maintained in the bonding equipment and kept in a steady state, allowing the interstitial layer to gradually achieve internal flow equilibrium and release shear stress under pressure. At this stage, the compliant polymer interstitial layer has not yet undergone a cross-linking reaction, and its molecular chains still possess a certain degree of mobility. Maintaining a steady state helps eliminate transient stress introduced during alignment, thereby preventing alignment drift caused by stress rebound during subsequent curing and heating. The technical effect of this step is to stabilize the alignment result, providing a prerequisite for locking in a precise alignment state during the subsequent curing process.

[0045] S3.2. While maintaining the bonding pressure constant, the bonded substrate layer is fixed by using a clamp or vacuum adsorption to constrain its position. The vacuum adsorption negative pressure is... 0.3~ 1MPa.

[0046] While maintaining constant bonding pressure, the substrate layers are positioned using clamps or vacuum adsorption to ensure a stable spatial relationship between at least two substrate layers. The negative pressure applied to the back of the substrate layers by vacuum adsorption provides uniform constraint without introducing additional mechanical stress, thereby suppressing relative slippage of the substrate layers during heating or material phase transformation. The technical effect of this step is to enhance the overall geometric stability of the substrate layer structure and reduce the risk of misalignment caused by differences in thermal expansion during the curing stage.

[0047] S3.3 Place the fixed substrate layer in a curing device for pre-curing treatment. The pre-curing treatment temperature is 40~70℃ and the treatment time is 5~20min, so that the viscosity of the interstitial layer increases and enters the pre-curing state.

[0048] The fixed substrate layer is placed in a curing device for pre-curing, causing the compliant polymer material in the interstitial layer to begin molecular chain entanglement or preliminary cross-linking reaction at a lower temperature. This significantly increases the viscosity of the interstitial layer, bringing it into a pre-cured state. At this point, the interstitial layer transitions from a fluid state to a quasi-solid state, significantly reducing its fluidity while maintaining the continuity of the bonding interface. The technical effect of this step is to prevent the interstitial layer from re-flowing or rearranging its interface during the subsequent main curing heating process, thereby maintaining the completed bonding and alignment structure.

[0049] S3.4 After completing the pre-curing treatment, perform a main curing treatment on the substrate layer. The main curing temperature is 80~140℃, the heating rate is 1~5℃ / min, and the holding time is 10~60min.

[0050] After pre-curing, the primary curing process allows the flexible polymers in the interstitial layer to undergo a full cross-linking reaction, forming a continuous and dense cured network structure. A controlled heating rate promotes uniform cross-linking and avoids localized stress concentrations or interface defects caused by sudden temperature changes. The technical advantage of this step is that it transforms the interstitial layer from a temporarily stable pre-cured state into a solid bonding layer with structural strength and long-term stability, thereby achieving permanent bonding between multilayer substrates.

[0051] S3.5 During the main curing process, the edges of the bonding area are locally pre-cured. The width of the pre-cured area is 1~5mm, and the pre-curing method is ultraviolet irradiation with an intensity of 50~300mW / cm². 2 The processing time is 30~180s to form a locking structure at the edge of the bonding area.

[0052] During the main curing process, the edges of the bonding area undergo localized UV pre-curing, allowing the interstitial layer at the edges to complete the cross-linking reaction and form a rigid locking structure. This locking structure creates a mechanical constraint on the circumference of the substrate layer, effectively limiting the inward transmission of shrinkage deformation generated at the bonding interface during main curing and cooling. The technical advantage of this step is that it suppresses interface warping and alignment drift caused by overall curing shrinkage, making it particularly suitable for large-area multilayer substrate structures.

[0053] S3.6 After the main curing process is completed, the substrate layer is subjected to controlled cooling at a rate of 0.5~3℃ / min until the temperature drops to 25~35℃. Then, it is annealed at 40~80℃ for 5~30min to obtain the prefabricated substrate.

[0054] After primary curing, controlled cooling gradually lowers the substrate temperature to avoid thermal stress concentration caused by rapid cooling. Subsequent annealing at moderate temperatures further promotes the rearrangement of cross-linked structures and stress relaxation within the interstitial layers. This step results in a more stable interlayer bonding state in the multilayer substrate after curing, reduces residual interfacial stress, and improves the overall structural reliability under service conditions such as bending and thermal cycling, thus yielding a structurally stable prefabricated substrate.

[0055] S4. A prefabricated substrate is opened at a preset interconnection location to obtain conductive interconnection holes. Conductive material is deposited in the conductive interconnection holes to enable cross-layer electrical connection of functional structure layers on each substrate layer of the prefabricated substrate. An encapsulation layer is set on the outer surface of the prefabricated substrate to obtain a multilayer substrate.

[0056] Step S4 includes: S4.1 First, based on the alignment marks on the prefabricated substrate and the conductive wiring positions of the functional structure layer, the preset interconnection positions are determined. The prefabricated substrate is then fixed on a vacuum adsorption platform, and the interconnection positions are locally cleaned.

[0057] By determining the preset interconnect positions based on alignment marks and the wiring positions of conductive lines in the functional structure layer, it is possible to ensure that the conductive vias and the conductive lines of each substrate layer correspond precisely in space, thereby avoiding electrical connection failures caused by cross-layer interconnect misalignment. Fixing the prefabricated substrate on a vacuum adsorption platform can achieve stable positioning without introducing additional mechanical clamping stress; local surface cleaning of the interconnect positions helps to remove organic residues and micro-particulate contaminants in the via area, improving the stability and consistency of subsequent via processing and conductive layer deposition processes.

[0058] S4.2. A prefabricated substrate is opened at a preset interconnection location to form a conductive through hole that penetrates at least two substrate layers.

[0059] In step S4.2, the hole-opening process includes: The prefabricated substrate is dehydrated and pre-baked at a temperature of 90-120°C for 3-10 minutes. Then, a photosensitive material is coated onto the surface of the prefabricated substrate by spin coating to form a photosensitive layer. The photosensitive material is either a positive or negative photosensitive resin. The spin coating speed is 1000-3000 rpm and the spin coating time is 20-60 seconds, so that the thickness of the photosensitive layer is controlled at 5-30 μm. After spin coating, the photosensitive layer is softened and baked at a temperature of 80-110°C for 2-8 minutes. A prefabricated substrate coated with a photosensitive layer is placed in an exposure apparatus, and the preset interconnect positions are selectively exposed to ultraviolet light using a mask. The exposure wavelength is 350~420nm, and the exposure energy is 100~400mJ / cm². 2 After exposure, the prefabricated substrate is immersed in a developing solution for development treatment. The developing solution includes at least one of tetramethylammonium hydroxide aqueous solution and sodium carbonate aqueous solution. The developing concentration is 0.2~1.0wt%, the developing temperature is 20~30℃, and the developing time is 30~120s to form an opening window for exposing the substrate. After development, it is rinsed with deionized water and dried with nitrogen gas, and then post-baked at 100~140℃ for 3~10min. The prefabricated substrate is immersed in an alkaline solution for chemical opening treatment. The alkaline solution includes at least one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and potassium carbonate aqueous solution. The alkaline concentration is 0.5~5.0wt%, the treatment temperature is 40~80℃, and the treatment time is 2~20min, until conductive through-holes are formed that penetrate at least two substrate layers. After etching, the prefabricated substrate is thoroughly rinsed with deionized water and treated with a weakly acidic neutralization solution. The neutralization solution is a diluted acetic acid or citric acid aqueous solution with a concentration of 0.1~1.0wt%.

[0060] First, by dehydrating and pre-baking the prefabricated substrate and forming a photosensitive layer of controlled thickness on its surface, the spatial position of the subsequent opening area is precisely defined by the mask, avoiding the hole position offset problem caused by material warping and uneven interlayer thickness in direct mechanical or laser processing, thereby significantly improving the alignment accuracy between the conductive connecting hole and the conductive line of the functional structure layer.

[0061] Secondly, by using ultraviolet exposure and development processes to form regular and clearly defined opening windows at preset interconnect positions, the substrate material is exposed to the subsequent etching environment only in the target area, effectively suppressing over-etching and lateral erosion in non-target areas, ensuring the consistency of the conductive interconnect aperture and the controllability of the aperture wall profile, and providing a stable structural basis for the uniform filling of subsequent conductive materials.

[0062] Furthermore, by chemically opening the exposed areas using an alkaline solution, the selective etching effect of the alkaline solution on the flexible substrate and intermediate layer materials allows the conductive vias to penetrate layer by layer in a relatively gentle manner within the multilayer substrate. This significantly reduces the risk of damage to the functional structural layers and bonding interfaces caused by thermal shock and mechanical stress, thereby improving the overall structural integrity and interlayer reliability of the multilayer substrate.

[0063] Finally, through thorough rinsing and weak acid neutralization after etching, residual alkali and reaction byproducts are effectively removed, avoiding adverse effects of alkaline residue on subsequent conductive material deposition and long-term electrical connection stability. This ensures that the formed conductive vias have clean via walls and a stable chemical environment, laying the foundation for achieving low-resistance, high-reliability cross-layer electrical connections.

[0064] S4.3 First, clean and dry the conductive through holes. Then, place the prefabricated substrate in a plasma cleaning equipment for hole wall activation treatment. The treatment power is 50~200W and the treatment time is 30~180s.

[0065] After the conductive interconnects are formed, processing residues and adsorbed moisture are removed from the holes through cleaning and drying. Subsequently, plasma activation treatment is performed on the hole walls, introducing polar functional groups and increasing surface energy. This activation process enhances the adhesion of the hole walls to the metallic transition material and subsequent conductive materials, helping to suppress the formation of conductive layer detachment or interfacial voids at the hole walls, thereby improving the stability and reliability of the interlayer electrical connection structure.

[0066] S4.4 After completing the hole wall activation treatment, a transition material is deposited in the conductive interconnecting hole. The transition material forms a conductive transition layer by sputtering or spraying. The total thickness of the conductive transition layer is 20~200nm. The transition material includes at least one of titanium, chromium, titanium / copper composite material, chromium / copper composite material, and titanium / gold composite material.

[0067] After the hole wall activation treatment is completed, a conductive transition layer is formed by depositing a transition material inside the conductive interconnecting hole through sputtering or spraying. Materials such as titanium and chromium have good adhesion properties, while materials such as copper and gold have excellent conductivity. Through the construction of a composite metal structure, a stable electrical connection transition interface is formed between the conductive transition layer and the subsequent conductive filling material. The technical effect of this step is to reduce the contact resistance at the hole wall interface and improve the continuity and durability of the conductive path within the conductive interconnecting hole.

[0068] S4.5. Conductive material is filled into the conductive vias where a conductive transition layer has been formed. The conductive material is deposited via vacuum-assisted injection, with a vacuum level of [missing information]. 0.6~ After filling, the material is pre-shaped at 60-120℃ for 5-20 minutes, and then cured at 100-180℃ for 10-60 minutes to form a continuous conductive path in the conductive interconnection hole; the conductive material includes at least one of silver nanoparticle conductive paste, silver micro powder conductive paste, copper-based conductive paste, and silver-coated copper composite conductive paste.

[0069] Within the conductive interconnects with a conductive transition layer, conductive material is filled using a vacuum-assisted injection method. This allows the conductive slurry to fully penetrate the holes and fill the gaps in the hole walls under negative pressure. Silver nanoparticles, silver powder, copper-based or silver-coated copper composite conductive slurries gradually form a dense conductive network during pre-forming and secondary curing processes, thereby constructing continuous and stable cross-layer conductive pathways within the conductive interconnects. This step effectively reduces the void ratio within the holes and improves the conductive reliability and long-term stability of the cross-layer interconnects.

[0070] S4.6 An encapsulation layer formed of encapsulation material is provided on the outer surface of the prefabricated substrate. The encapsulation layer is formed by coating, spraying or lamination. The thickness of the encapsulation layer is 10~80μm. After encapsulation, it is cured at 60~140℃ for 10~60min. The encapsulation material includes at least one of epoxy resin encapsulation material, fluoropolymer encapsulation material, thermoplastic polyurethane encapsulation material and silicone rubber encapsulation material.

[0071] An encapsulation layer is applied to the outer surface of a prefabricated substrate to form an overall protective structure for the exposed areas of the multilayer substrate. Epoxy resin, fluoropolymers, thermoplastic polyurethane, or silicone rubber encapsulation materials provide excellent mechanical protection, moisture resistance, and environmental isolation after curing. By controlling the thickness of the encapsulation layer and the curing conditions, the encapsulation layer can enhance the multilayer substrate's resistance to humid heat, mechanical shock, and chemical environments without significantly increasing the overall thickness of the substrate.

[0072] S4.7 After the encapsulation layer is cured, a cooling and shaping process is performed at a cooling rate of 0.5~3℃ / min, and the multilayer substrate is obtained by cooling to 25~35℃.

[0073] After the encapsulation layer has cured, a controlled cooling process is used to gradually lower the temperature of the multilayer substrate, effectively mitigating residual stress caused by differences in thermal expansion between the encapsulation layer and the substrate layer. Cooling to near ambient temperature completes the shaping process, resulting in a stable dimensional state and structural morphology for the multilayer substrate. The technical advantage of this step is reduced warpage and delamination risks, ensuring that the final multilayer substrate possesses good structural integrity and reliability.

[0074] Example 1: In Example 1, two bondable substrate layers were prepared. The substrate was a polyimide film with a single sheet thickness of 25 μm. First, following step S1.1, the polyimide film was ultrasonically cleaned sequentially in deionized water and isopropanol at a power of 200 W for 8 min, followed by drying with nitrogen. Then, it was placed in a plasma cleaner for surface activation treatment at a power of 100 W for 60 s to obtain the initial substrate.

[0075] According to step S1.2, silver nanoparticle conductive ink is deposited on one side of the preform board to form a conductive circuit pattern by inkjet printing. The mass ratio of silver nanoparticles to organic carrier in the conductive ink is 6:4, and the inkjet printing amount for each preform board is 0.25g. After inkjet printing, the preform board is placed in an inert atmosphere oven for sintering treatment. The sintering temperature is 120℃ and the sintering time is 30min to obtain a functional substrate with a functional structure layer.

[0076] According to step S1.3, the surface morphology of the functional structure layer of the functional substrate is inspected. When a local height difference is detected, silver micro-powder conductive paste is sprayed onto the functional structure layer for compensation. The mass ratio of silver micro-powder to resin carrier is 7:3, and the amount of spraying per functional substrate is 0.12g. After spraying, the functional substrate is placed on a constant temperature hot plate for pre-forming treatment at a temperature of 90℃ for 10 minutes. Then, a second curing treatment is performed in an oven at a curing temperature of 150℃ for 20 minutes.

[0077] Following step S1.4, a titanium / gold composite metal is sputtered and deposited on the side of the functional substrate away from the functional structure layer to form a metal anchoring layer. The thickness ratio of the titanium layer to the gold layer is 1:4, and the total thickness of the metal anchoring layer is 50 nm. After deposition, the functional substrate is immersed in an organic solution containing alkyl thiol self-assembly molecules for interface treatment. The concentration of the self-assembly molecule precursor is 2 mM, the treatment temperature is 25°C, and the treatment time is 30 min. After treatment, the substrate is removed, rinsed with ethanol, and then baked at 80°C for 10 min to form a bonding interface layer on the side of the functional substrate away from the functional structure layer. Subsequently, the above steps are repeated on another polyimide film according to step S1.5 to obtain two bondable substrate layers.

[0078] In step S2, a gap-filling adhesive is prepared according to step S2.1. The flexible polymer raw material is siloxane-modified acrylic resin, the sheet-like inorganic filler is sheet-like boron nitride, and the solvent is propylene glycol methyl ether acetate. The mass ratio of the three is 60:25:15, and the total amount is 100g. After vacuum stirring, the viscosity of the gap-filling adhesive is adjusted and stabilized at 25000mPa·s. Then, according to step S2.2, the gap-filling adhesive is coated onto the bonding interface layer surface of one of the substrate layers, with a coating thickness of 10μm, and a second degassing treatment is performed. Next, according to step S2.3, microstructured channels are formed on the gap-filling layer, with a channel depth of 8μm and a width of 40μm, and a short pre-baking time is performed. Then, according to steps S2.4~S2.6, lamination, initial bonding, optical alignment, and holding treatments are performed in a vacuum laminator.

[0079] In step S3, the steady-state holding, position fixing, pre-gelling, main curing, edge locking, and controlled cooling and annealing processes are completed sequentially according to steps S3.1 to S3.6 to obtain the prefabricated substrate.

[0080] In step S4, cross-layer interconnection processing is performed according to steps S4.1 to S4.7. Specifically, in step S4.2, the prefabricated substrate is first dehydrated and pre-baked at 100°C for 5 minutes. Then, a photosensitive layer is formed by spin-coating positive photosensitive resin onto the surface of the prefabricated substrate at 2000 rpm for 40 seconds, controlling the thickness of the photosensitive layer to 15 μm. After spin-coating, the photosensitive layer undergoes a soft-baking process at 95°C for 5 minutes. The prefabricated substrate coated with the photosensitive layer is then placed in an exposure device, and selective ultraviolet exposure is performed on the preset interconnection locations using a mask at a wavelength of 365 nm and an exposure energy of 250 mJ / cm². 2 After exposure, the prefabricated substrate is immersed in a tetramethylammonium hydroxide aqueous solution for development treatment. The development concentration is 0.5wt%, the development temperature is 25℃, and the development time is 60s, forming an opening window to expose the substrate material. After development, it is rinsed with deionized water and dried with nitrogen, and then baked at 120℃ for 5min. Subsequently, the prefabricated substrate is immersed in a potassium hydroxide aqueous solution for chemical opening treatment. The alkali concentration is 2.0wt%, the treatment temperature is 60℃, and the treatment time is 10min, until a conductive through-hole is formed through two substrate layers. After etching, it is rinsed with deionized water and neutralized with a 0.5wt% citric acid aqueous solution.

[0081] Subsequently, the conductive vias are activated in step S4.3; a titanium / copper composite material is deposited in the conductive vias in step S4.4 to form a conductive transition layer with a thickness of 100 nm; silver nanoparticle conductive paste is filled in the conductive vias in step S4.5, with a mass ratio of silver nanoparticles to carrier of 7:3 and a single-board filling amount of 0.15 g, and pre-shaping and secondary curing are performed; finally, an epoxy resin encapsulation layer with a thickness of 30 μm is formed on the outer surface of the prefabricated substrate in steps S4.6 and S4.7 and then cooled and shaped to obtain a multilayer substrate.

[0082] Example 2: Example 2 follows the same overall steps as Example 1, except that: a liquid crystal polymer film is used as the substrate; a silver-coated copper composite conductive ink is used as the conductive ink, with a dosage of 0.28 g / sheet; a copper-silver composite conductive paste is used as the high-viscosity conductive paste, with a dosage of 0.10 g / sheet; a chromium / copper / gold composite metal is used as the metal anchoring layer, with a total thickness of 60 nm; and a self-assembled molecular precursor is used as a self-assembled molecule containing fluorine-terminated groups, with a concentration of 3 mM.

[0083] In step S1.4, a titanium / gold composite metal is sputtered and deposited on the side of the functional substrate away from the functional structure layer to form a metal anchoring layer, wherein the thickness ratio of the titanium layer to the gold layer is 1:4, and the total thickness of the metal anchoring layer is 50 nm. After deposition, the functional substrate is immersed in a mixed organic solution containing a self-assembled molecular precursor and a thermally migrateable interface control molecule for interface treatment. The self-assembled molecular precursor is selected from alkyl thiol self-assembled molecules at a concentration of 2 mM; the thermally migrateable interface control molecule is selected from at least one of the following: silane molecules with flexible alkyl chains at the ends, short-chain polymers containing segments with low glass transition temperatures, and small molecule modulators containing fluorine but with movable chain segments. In this embodiment, the thermally migrateable interface control molecule is selected from silane molecules with flexible alkyl chains at the ends, and its mass fraction in the mixed solution is 1.0 wt% of the mass of the self-assembled molecular precursor. Anhydrous ethanol was used as the solvent in a mixed organic solution at 25°C for 40 minutes. This process allowed the self-assembled molecular precursors to form an ordered interfacial molecular layer on the surface of the metal anchoring layer. Simultaneously, thermally migratable interface-controlled molecules were dispersed within the bonding interface layer via embedding or co-adsorption. After the interface treatment, the functional substrate was removed, rinsed with ethanol to remove unbound molecules, and then baked at 80°C for 10 minutes to form a bonding interface layer containing thermally migratable interface-controlled molecules. During the bonding and displacement correction process in subsequent step S2, the thermally migratable interface-controlled molecules became enriched at the interface under bonding pressure and interfacial shear, resulting in a bonding interface with low friction and low adhesion resistance. In step S3, during the pre-gelation and main curing heating process, the thermally migratable interface-controlled molecules migrated towards the interstitial layer or were gradually captured in the curing network under thermal drive, transforming the bonding interface from a slippery state to a stable bonded state.

[0084] In step S2, the flexible polymer raw material is low-modulus polyurethane acrylic resin, the sheet-like inorganic filler is sheet-like montmorillonite, and the solvent is ethyl acetate, with a mass ratio of 55:30:15 and a stable viscosity of 30000 mPa·s. In step S4, the conductive material is silver micron conductive paste, the encapsulation material is fluoropolymer encapsulation material, and the encapsulation layer thickness is 25 μm.

[0085] Example 3: Example 3 is basically the same as Example 1 in terms of steps, except that: the substrate is polyethylene terephthalate film; the conductive ink is silver nanowire conductive ink, with a dosage of 0.22g / sheet; the high-viscosity conductive paste is silver nanoparticle resin composite conductive paste, with a dosage of 0.14g / sheet; the metal anchoring layer is titanium / palladium / gold composite metal, with a total thickness of 40nm; and the self-assembled molecular precursor is a self-assembled molecule with carboxyl terminus, with a concentration of 1mM.

[0086] In step S2, the flexible polymer raw material is selected from flexible epoxy-modified elastomer resin, the sheet-like inorganic filler is selected from sheet-like silica, and the solvent is selected from isopropanol, with a mass ratio of 65:20:15 and a viscosity stable at 20000 mPa·s. In step S4, the conductive transition layer is selected from chromium / copper composite material, the encapsulation material is selected from thermoplastic polyurethane encapsulation material, and the encapsulation layer thickness is 40 μm.

[0087] In step S2.1, the flexible polymer raw material, sheet-like inorganic filler, and solvent are vacuum stirred at a speed of 800-2000 rpm for 3-10 minutes, with a vacuum degree of [missing information]. 0.08~ An initial mixed adhesive solution was obtained at a pressure of 0.095 MPa. The compliant polymer raw material was selected from siloxane-modified acrylic resin, the flake inorganic filler was selected from flake boron nitride, and the solvent was selected from propylene glycol methyl ether acetate, with a mass ratio of 60:25:15. After the initial mixed adhesive solution was formed, an interface wetting modifier was added to the mixed adhesive solution. The interface wetting modifier was selected from at least one of the following: block wetting modifiers containing siloxane segments, interface modifiers containing phosphate ester groups, and surface-oriented adsorption molecules containing carboxylic acid or amine groups. In this embodiment, the interface wetting modifier was selected from interface modifiers containing phosphate ester groups, including at least one of alkyl phosphate monoesters, alkyl phosphate diesters, polyether-modified phosphate esters, polyoxyethylene phosphate esters, and aromatic phosphate esters. The amount added was 0.5~2.0 wt% of the mass of the flake inorganic filler. After adding the interfacial wetting modifier, the interstitial adhesive is subjected to low-speed vacuum stirring at 35-45℃ (300-800 rpm) for 5-15 minutes. This allows the interfacial wetting modifier to be adsorbed and anchored on the surface of the sheet-like inorganic filler, while simultaneously inhibiting its random aggregation in the compliant polymer matrix. Subsequently, the interstitial adhesive is transferred to a constant-temperature hot plate for preheating and viscosity adjustment at 35-55℃ for 2-8 minutes, stabilizing the viscosity of the interstitial adhesive within the range of 20000-40000 mPa·s. After this treatment, a stable interfacial adsorption relationship is formed between the interfacial wetting modifier and the sheet-like inorganic filler. This makes it easier for the sheet-like inorganic filler to undergo orientation rearrangement along the substrate surface during the subsequent shearing, bonding, and driving displacement process in step S2. This results in a low-resistance sliding structure in the bonding interface direction, while maintaining a continuous interstitial layer support framework in the thickness direction.

[0088] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that in step S1.4, only the metal anchoring layer is formed, but the interface treatment step of the self-assembled molecular precursor is not performed, that is, the bonding interface layer is not formed. The remaining steps are the same as in Example 1.

[0089] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that: in step S2.3, no microstructure channels were formed on the interstitial layer, and no short-time pre-baking treatment was performed; the remaining steps are the same as in Example 1.

[0090] Adhesion alignment deviation: An optical microscopic alignment system is used to measure the alignment marks of the upper and lower layers of the multilayer substrate after bonding, and the center offset is calculated.

[0091] Slippage stability during bonding process (slippage success rate): The percentage of successful corrections made within a set threshold during the S2 bonding and displacement correction stages.

[0092] Interlayer peel strength: A 180° peel test was used to peel the laminated substrate layers apart and record the average peel force during the stable peeling stage.

[0093] Interlayer conduction resistance: The interlayer resistance after the formation of conductive vias is tested using the four-probe method.

[0094] Changes in alignment deviation after thermal cycling: Sample after After 100 cycles of thermal cycling from 40℃ to 85℃, the alignment deviation was measured again and compared with the initial value.

[0095] The experimental data are shown in Table 1.

[0096] Table 1: The experimental data show that Examples 1 to 3, prepared using the method of this invention, are significantly superior to the comparative sample in terms of bonding alignment accuracy, bonding process stability, and interlayer bonding performance after curing. Comparative Example 1, lacking a bonding interface layer in step S1.4, experienced greater interfacial adhesion resistance during bonding, making it difficult for the substrate layer to achieve stable slip correction during the driving displacement stage. This resulted in a large alignment deviation, and the interlayer peel strength decreased significantly after curing. Furthermore, the alignment deviation increased significantly after thermal cycling, indicating insufficient interfacial bonding stability.

[0097] In Comparative Example 2, because microstructure channels were not formed on the interstitial layer in step S2.3, the flow of the interstitial layer was restricted under the bonding pressure, and the interfacial stress was not fully released. This resulted in a decrease in the success rate of slip correction during bonding, and the alignment deviation was significantly higher than that of the sample in the example. Furthermore, more obvious alignment drift occurred under thermal cycling conditions.

[0098] In contrast, Example 1 achieved low-resistance slippage during the bonding stage and stable bonding after curing through the synergistic effect of the bonding interface layer and the gap-filling layer; Example 2 further reduced the bonding alignment deviation and improved the interlayer peel strength by introducing thermally migratable interface-regulating molecules, so that the bonding interface exhibited different interface states during the bonding and curing stages; Example 3 achieved orientation rearrangement of the sheet-like inorganic filler in the bonding interface direction by introducing an interface wetting regulator into the gap-filling layer, which significantly improved the bonding slippage stability and alignment accuracy without reducing the support capacity of the gap-filling layer.

[0099] The above experimental results show that the present invention achieves the unity of controllable slippage during the bonding process and stable bonding after curing through the structural design of the bonding interface layer and the gap filling layer. It solves the technical problem that the alignment accuracy in the bonding of multilayer substrates is difficult to balance the interface strength and long-term stability, demonstrating the significant difference in technical effect of the preparation method at the overall process design level.

[0100] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for precise alignment of a multilayer substrate, characterized in that the steps include... include: S1. Prepare at least two bondable substrate layers respectively. Each substrate layer includes a substrate plate and a functional structure layer and a bonding interface layer respectively disposed on opposite sides of the substrate plate. The functional structure layer is used to form conductive lines, and the bonding interface layer is used to connect with the functional structure layer and reduce the interface adhesion resistance under a preset bonding pressure. S2. Form a gap-filling layer on the functional structure layer or bonding interface layer of all substrate layers, and perform initial bonding and drive displacement on at least two substrate layers under a preset bonding pressure condition, so that the alignment marks set on at least two substrate layers are aligned. S3. Place at least two aligned substrate layers in a curing process to cure the gap-filling layer. After curing, a prefabricated substrate is obtained. S4. A prefabricated substrate is opened at a preset interconnection location to obtain conductive interconnection holes. Conductive material is deposited in the conductive interconnection holes to enable cross-layer electrical connection of functional structure layers on each substrate layer of the prefabricated substrate. An encapsulation layer is set on the outer surface of the prefabricated substrate to obtain a multilayer substrate.

2. The precise alignment method for a multilayer substrate according to claim 1, characterized in that, Step S1 includes: S1.1 A substrate is ultrasonically cleaned sequentially with deionized water and isopropanol at a power of 150~300W for 5 to 10 minutes. After being dried with nitrogen, it is placed in a plasma cleaner for surface activation treatment at a power of 50~150W for 30~120 seconds to obtain the initial substrate. S1.

2. Conductive ink is deposited on one side of the preliminary board to form a conductive circuit pattern as a functional structure layer. The line width is controlled to be 5~50μm and the line thickness is controlled to be 0.3~5μm. After the ink is printed, the preliminary board is placed in an inert atmosphere oven for sintering treatment. The sintering temperature is 80~160℃ and the sintering time is 10~60min to obtain a functional substrate with a functional structure layer. S1.

3. Check if there is a height difference in the functional structure layer of the functional substrate. If so, spray a high-viscosity conductive paste onto the functional structure layer. The nozzle diameter is 10~80μm and the spraying speed is 0.2~5mm / s. After spraying, place the functional substrate on a constant temperature hot table for pre-forming treatment. The treatment temperature is 60~120℃ and the treatment time is 5~20min. Then, perform a secondary curing treatment in an oven. The curing temperature is 100~180℃ and the curing time is 10~40min. S1.

4. Deposit a metal coating on the side of the functional substrate away from the functional structure layer to form a metal anchoring layer. The total thickness of the metal anchoring layer is 10~80nm. After deposition, immerse the functional substrate in an organic solution containing a self-assembled molecular precursor for interface treatment. The concentration of the self-assembled molecular precursor is 0.5~5mM, the treatment temperature is 20~30℃, and the treatment time is 10~60min. After treatment, remove the substrate and rinse it with ethanol or isopropanol. Then bake it at 60~110℃ for 5~20min to form an bonding interface layer on the side of the functional substrate away from the functional structure layer. S1.5 Repeat steps S1.1 to S1.4 for each substrate to form a functional structure layer and a bonding interface layer on opposite sides of the substrate, thereby obtaining at least two bonding substrate layers.

3. The precise alignment method for a multilayer substrate according to claim 2, characterized in that, In step S1, the substrate includes at least one of polyimide film, liquid crystal polymer film, thermoplastic polyurethane film, and polyethylene terephthalate film; the conductive ink includes at least one of silver nanoparticle conductive ink, copper nanoparticle conductive ink, silver-coated copper composite conductive ink, and silver nanowire conductive ink; the high-viscosity conductive paste includes at least one of silver micropowder conductive paste, silver nanoparticle resin composite conductive paste, copper micropowder composite conductive paste, and copper-silver composite conductive paste; the metal coating includes at least one of titanium / gold composite metal, chromium / gold composite metal, titanium / palladium / gold composite metal, chromium / copper / gold composite metal, aluminum, and aluminum alloy; and the self-assembled molecular precursor includes at least one of alkyl thiol self-assembled molecules, aromatic thiol self-assembled molecules, silane self-assembled molecules, self-assembled molecules with fluorine-terminated groups, self-assembled molecules with hydroxyl-terminated groups, and self-assembled molecules with carboxyl-terminated groups.

4. The precise alignment method for a multilayer substrate according to claim 1, characterized in that, Step S2 includes: S2.1 The flexible polymer raw material, sheet-like inorganic filler, and solvent are vacuum stirred at a speed of 800~2000 rpm for 3~10 min, with a vacuum degree of [missing information]. 0.8~ 1 MPa was used to obtain the gap-filling adhesive. Then, the gap-filling adhesive was preheated and adjusted on a constant temperature hot plate. The temperature was set at 35~55℃ and the preheating time was 2~8 minutes to stabilize the viscosity of the gap-filling adhesive within the preset viscosity range. S2.

2. Apply the gap-filling adhesive to the surface of at least one functional structural layer or bonding interface layer of the substrate layer, with a coating thickness controlled at 2~30μm. After coating, place it in a vacuum chamber for secondary degassing treatment, with a degassing vacuum degree of [missing information]. 0.8~ 1MPa, degassing time of 2~6min, to obtain a substrate layer to be bonded covered by a gap-filling layer; S2.

3. Microstructure channels are formed on the interstitial layer by soft molding or laser micromachining. The depth of the microstructure channels is 1~15μm and the width is 10~80μm. After the microstructure channels are formed, they are pre-baked at 40~70℃ for 2~10min to make the surface of the interstitial layer in a semi-fluid state. S2.

4. At least two substrate layers are placed in a laminating device, which is a vacuum laminator. Before lamination, the laminating cavity is evacuated to a vacuum level of [missing information]. 0.6~ 1MPa, vacuuming time is 30~120s, then the bonding pressure is applied to the preset bonding pressure range, which is 0.01~1.5MPa, and held for 3~30s for initial bonding; S2.5 During the initial bonding process, the optical alignment system of the bonding equipment collects and identifies the alignment marks set on at least two substrate layers, calculates the alignment deviation between the two substrate layers, and drives the substrate layers to perform displacement correction while keeping the preset bonding pressure range unchanged or adjusting it to ±0.01~0.05MPa. The displacement step is 0.1~5μm and the displacement speed is 0.05~2mm / s, so that the substrate layers slide relative to each other and the alignment deviation reaches the set threshold. S2.6 When the alignment deviation of the alignment mark of the substrate layer reaches the set threshold, the current bonding pressure and displacement position are kept unchanged, and a holding process is performed. The holding time is 2~10min. During the holding period, a short pressure pulse of 0.2~1.5MPa is applied to the bonding interface, and the number of pulses is 1~5.

5. The precise alignment method for a multilayer substrate according to claim 4, characterized in that, In step S2, the flexible polymer raw material includes at least one of siloxane-modified acrylic resin, low-modulus polyurethane acrylic resin, and flexible epoxy-modified elastomer resin; the sheet-like inorganic filler includes at least one of sheet-like boron nitride, sheet-like montmorillonite, and sheet-like silica; and the solvent includes at least one of ethyl acetate, propylene glycol methyl ether acetate, and isopropanol.

6. The precise alignment method for a multilayer substrate according to claim 4, characterized in that, In step S2.1, the preset viscosity range is 10000~50000 mPa·s; If the viscosity of the filler adhesive is less than 10000 mPa·s, increase the temperature of the constant temperature hot table by 5~10℃ based on the upper limit of the preheating temperature, and maintain it for 1~5 minutes. If the viscosity of the interstitial filler solution is greater than 50000 mPa·s, the solvent should be added dropwise at a rate of 0.1~2.0 mL / min, with each addition being 0.2~1.0 wt% of the total mass of the interstitial filler solution. After addition, the solution should be stirred under low-speed vacuum at 35~55℃ for 1~3 min at a speed of 200~600 rpm and a vacuum level of [missing information]. 0.6~ 1MPa.

7. The precise alignment method for a multilayer substrate according to claim 1, characterized in that, Step S3 includes: S3.

1. Keep at least two substrate layers that have completed the alignment mark alignment in the alignment lock state of the bonding equipment, keep the bonding pressure constant at 0.01~1.5MPa, and maintain the steady state for 2~10min; S3.

2. While maintaining the bonding pressure constant, the bonded substrate layer is fixed by using a clamp or vacuum adsorption to constrain its position. The vacuum adsorption negative pressure is... 0.3~ 1MPa; S3.3 Place the fixed substrate layer in a curing device for pre-curing treatment. The pre-curing treatment temperature is 40~70℃ and the treatment time is 5~20min, so that the viscosity of the interstitial layer increases and enters the pre-curing state. S3.4 After completing the pre-curing treatment, perform a main curing treatment on the substrate layer. The main curing temperature is 80~140℃, the heating rate is 1~5℃ / min, and the holding time is 10~60min. S3.5 During the main curing process, the edges of the bonding area are locally pre-cured. The width of the pre-cured area is 1~5mm, and the pre-curing method is ultraviolet irradiation with an intensity of 50~300mW / cm². 2 The processing time is 30~180s to form a locking structure at the edge of the bonding area; S3.6 After the main curing process is completed, the substrate layer is subjected to controlled cooling at a rate of 0.5~3℃ / min until the temperature drops to 25~35℃. Then, it is annealed at 40~80℃ for 5~30min to obtain the prefabricated substrate.

8. The precise alignment method for a multilayer substrate according to claim 1, characterized in that, Step S4 includes: S4.1 First, based on the alignment marks on the prefabricated substrate and the conductive wiring position of the functional structure layer, the preset interconnection position is determined. The prefabricated substrate is fixed on the vacuum adsorption platform, and the interconnection position is locally cleaned. S4.

2. A prefabricated substrate is opened at a preset interconnection location to form a conductive through hole that penetrates at least two substrate layers. S4.3 First, clean and dry the conductive through holes, and then place the prefabricated substrate in a plasma cleaning equipment for hole wall activation treatment. The treatment power is 50~200W and the treatment time is 30~180s. S4.4 After completing the hole wall activation treatment, a transition material is deposited in the conductive interconnection hole. The transition material forms a conductive transition layer by sputtering or spraying. The total thickness of the conductive transition layer is 20~200nm. S4.

5. Conductive material is filled into the conductive vias where a conductive transition layer has been formed. The conductive material is deposited via vacuum-assisted injection, with a vacuum level of [missing information]. 0.6~ After filling with 1MPa, the material is pre-shaped at 60~120℃ for 5~20min, and then cured at 100~180℃ for 10~60min to form a continuous conductive path in the conductive interconnection hole. S4.

6. An encapsulation layer made of encapsulation material is provided on the outer surface of the prefabricated substrate. The encapsulation layer is formed by coating, spraying or lamination. The thickness of the encapsulation layer is 10~80μm. After encapsulation, it is cured at 60~140℃ for 10~60min. S4.7 After the encapsulation layer is cured, a cooling and shaping process is performed at a cooling rate of 0.5~3℃ / min, and the multilayer substrate is obtained by cooling to 25~35℃.

9. The precise alignment method for a multilayer substrate according to claim 8, characterized in that, In step S4, the transition material includes at least one of titanium, chromium, titanium / copper composite material, chromium / copper composite material, and titanium / gold composite material; the conductive material includes at least one of silver nanoparticle conductive paste, silver micropowder conductive paste, copper-based conductive paste, and silver-coated copper composite conductive paste; and the encapsulation material includes at least one of epoxy resin encapsulation material, fluoropolymer encapsulation material, thermoplastic polyurethane encapsulation material, and silicone rubber encapsulation material.

10. The precise alignment method for a multilayer substrate according to claim 8, characterized in that, In step S4.2, the hole-opening process includes: The prefabricated substrate is dehydrated and pre-baked at a temperature of 90-120°C for 3-10 minutes. Then, a photosensitive material is coated onto the surface of the prefabricated substrate by spin coating to form a photosensitive layer. The photosensitive material is either a positive or negative photosensitive resin. The spin coating speed is 1000-3000 rpm and the spin coating time is 20-60 seconds, so that the thickness of the photosensitive layer is controlled at 5-30 μm. After spin coating, the photosensitive layer is softened and baked at a temperature of 80-110°C for 2-8 minutes. A prefabricated substrate coated with a photosensitive layer is placed in an exposure apparatus, and the preset interconnect positions are selectively exposed to ultraviolet light using a mask. The exposure wavelength is 350~420nm, and the exposure energy is 100~400mJ / cm². 2 After exposure, the prefabricated substrate is immersed in a developing solution for development treatment. The developing solution includes at least one of tetramethylammonium hydroxide aqueous solution and sodium carbonate aqueous solution. The developing concentration is 0.2~1.0wt%, the developing temperature is 20~30℃, and the developing time is 30~120s to form an opening window for exposing the substrate. After development, it is rinsed with deionized water and dried with nitrogen gas, and then post-baked at 100~140℃ for 3~10min. The prefabricated substrate is immersed in an alkaline solution for chemical opening treatment. The alkaline solution includes at least one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and potassium carbonate aqueous solution. The alkaline concentration is 0.5~5.0wt%, the treatment temperature is 40~80℃, and the treatment time is 2~20min, until conductive through-holes are formed that penetrate at least two substrate layers. After etching, the prefabricated substrate is thoroughly rinsed with deionized water and treated with a weakly acidic neutralization solution. The neutralization solution is a diluted acetic acid or citric acid aqueous solution with a concentration of 0.1~1.0wt%.

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