Vertical interconnection structure for assisting liquid metal to fill soft substrate through hole and preparation method of vertical interconnection structure

Abstract

The invention belongs to the technical field of flexible electronics, and particularly relates to a vertical interconnection structure for assisting liquid metal in filling a soft substrate through hole and a preparation method of the vertical interconnection structure. The structure comprises a soft substrate with a through hole, a metal intermediate layer deposited on the side wall of the through hole, and a liquid metal layer filled in the through hole through an electroplating process. By introducing the metal intermediate layer as an electroplating substrate and an infiltration transition layer and utilizing electric field driving and alloying effects, efficient, complete and site-controllable filling of the liquid metal in micropores can be effectively realized, and the problems of non-infiltration and difficult filling of the liquid metal caused by high surface tension are solved. The vertical interconnection structure has good process compatibility, has good process compatibility with a flexible polymer substrate, is suitable for realizing liquid metal filling at normal temperature, and is especially suitable for three-dimensional flexible electronic integration. The structure can be widely applied to a high-density and multifunctional flexible electronic system, and supports vertical integration of a multi-layer flexible circuit or a heterogeneous device.

Description

Technical Field

[0001] This invention belongs to the field of flexible electronics technology, and particularly relates to a vertical interconnect structure for filling through-holes in a soft substrate with auxiliary liquid metal and its fabrication method. Background Technology

[0002] With the development of stretchable electronics and heterogeneous integrated systems, three-dimensional flexible integration has become an important path to achieve high-density interconnection and functional heterogeneous integration of devices. In three-dimensional integrated architecture, conductive vias that vertically penetrate the flexible substrate are key structures for achieving efficient electrical interconnection between different functional layers, shortening transmission distances, and improving integration density and signal integrity.

[0003] Currently, materials used to construct stretchable vertical interconnects mainly include rigid metal solders, conductive hydrogels, and cured silver pastes. However, rigid solders are prone to fatigue fracture under repeated stretching; while hydrogels possess good biocompatibility and stretchability, their electrical conductivity is typically low, making it difficult to meet the requirements of high-frequency or high-current transmission; and fillers such as silver paste tend to form stress concentration points after curing, which may lead to interface delamination or breakage of conductive pathways during dynamic deformation. In contrast, liquid metals (such as gallium-based alloys) are considered ideal conductive materials for achieving reliable flexible three-dimensional interconnects due to their room-temperature fluidity, high electrical conductivity, natural stretchability, and self-healing capabilities.

[0004] Nevertheless, the extremely high surface tension of liquid metals causes them to be non-wetting on most polymer substrates. This makes it difficult for them to stably adhere to the hole walls and they exhibit a tendency to shrink without external constraint, resulting in uncontrollable filling shape and path within the micropores. Consequently, liquid metals cannot spontaneously enter and completely fill through-holes, severely limiting their application in vertical interconnect structures. Therefore, there is an urgent need for a controllable external driving force or field effect to guide the liquid metal to fill the through-holes in a directional and complete manner, thereby achieving stable and reliable vertical interconnects.

[0005] To address this issue, this invention proposes a liquid metal filling method based on metal interlayer-assisted electroplating. This method first chemically deposits a metal interlayer on the sidewalls of vias as both the electroplating substrate and the wetting layer. Then, through an electroplating process, utilizing an electric field and the liquid-solid interface alloying effect, liquid metal is rapidly and uniformly filled into the vias. This method effectively solves the filling problem caused by the non-wetting of liquid metal with soft substrates, providing a practical and feasible process for achieving highly reliable and stretchable three-dimensional vertical interconnect structures. Summary of the Invention

[0006] In view of the above-mentioned technical defects in the prior art, the technical problem to be solved by this application is to provide a vertical interconnect structure and its preparation method for assisting liquid metal to fill soft substrate vias, so as to enable liquid metal to enter and fill the vias quickly and continuously, thereby forming a stable vertical interconnect path.

[0007] Specifically, the present invention is achieved through the following scheme:

[0008] This invention discloses a vertical interconnect structure for filling vias in a soft substrate with assisted liquid metal, comprising:

[0009] (1) A soft substrate with through holes: the soft substrate is a flexible or stretchable material, preferably, the soft substrate is one of PDMS, SEBS, PET, PI and EcoFlex;

[0010] The depth of the through hole is 50-500μm, and the radius of the through hole is 10-500μm. Preferably, the radius of the through hole is 50-250μm.

[0011] (2) Metal intermediate layer deposited on the sidewall of the through hole:

[0012] The metal interlayer is an intermetallic compound that wets with liquid metal, specifically at least one of copper, nickel, gold, silver, tin, or zinc.

[0013] The thickness of the metal interlayer is 1nm-50μm and is smaller than the radius of the via.

[0014] (3) A liquid metal layer filled into the through-hole by electroplating:

[0015] The liquid metal layer is at least one of Ga, GaIn, EGaIn, and GaInSn.

[0016] This invention also discloses a method for fabricating a vertical interconnect structure with assisted liquid metal filling of vias in a soft substrate, comprising the following steps:

[0017] (1) Preparation of through holes: Prepare through holes with specified dimensions and depths on a soft substrate;

[0018] (2) Deposited metal intermediate layer:

[0019] a. Immerse the soft substrate in a Tris-HCl buffer solution containing dopamine;

[0020] b. Immerse the soft substrate in an aqueous solution containing a catalytic metal salt;

[0021] c. Immerse the soft substrate in a chemical deposition solution containing metal salt, reducing agent and auxiliary reagent, and reduce the metal ions through a chemical reduction reaction and deposit them on the surface of the soft substrate to form a metal intermediate layer;

[0022] d. Alternatively, the metal raw material can be directly deposited on the surface of a soft substrate using methods such as thermal evaporation, magnetron sputtering, or physical vapor deposition to form a metal interlayer;

[0023] More preferably,

[0024] The catalytic metal salt mentioned in step b is at least one of the following: palladium chloride, chloroauric acid, and silver nitrate;

[0025] The chemical deposition solution described in step c comprises at least the following components: metal salt, reducing agent, complexing agent, and pH adjuster.

[0026] The chemical deposition solution described in step c comprises at least the following components: metal salt, reducing agent, complexing agent, and pH adjuster.

[0027] The metal salt is at least one of the following: copper sulfate pentahydrate, copper nitrate, copper chloride, nickel nitrate, nickel chloride, gold nitrate, gold chloride, silver nitrate, silver sulfate, zinc chloride, zinc nitrate, zinc sulfate, indium nitrate, indium chloride, tin nitrate, and tin chloride;

[0028] When depositing copper layers:

[0029] The main metal salt is at least one of the following: copper sulfate pentahydrate, copper nitrate, copper chloride, and basic copper carbonate;

[0030] The reducing agent is formaldehyde, paraformaldehyde, or glyoxal;

[0031] The complexing agent is at least one of the following: potassium sodium tartrate, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, sodium citrate, triethanolamine, glycine, and tris(hydroxymethyl)aminomethane;

[0032] The pH adjuster is at least one of the following: sodium hydroxide, potassium hydroxide, and sodium carbonate;

[0033] When depositing a nickel layer:

[0034] The main metal salt is at least one of the following: nickel sulfate hexahydrate, nickel chloride, nickel aminosulfonate, and nickel acetate;

[0035] The reducing agent is sodium hypophosphite or potassium hypophosphite;

[0036] The complexing agent is at least one of the following: sodium citrate, potassium citrate, lactic acid, malic acid, glycine, and succinic acid;

[0037] The pH adjuster is at least one of the following: ammonia, sodium hydroxide, potassium hydroxide, and sodium carbonate;

[0038] When depositing a silver layer:

[0039] The main metal salt is at least one of the following: silver nitrate, potassium silver cyanide, and silver carbonate;

[0040] The reducing agent is at least one of the following: formaldehyde, glucose, potassium sodium tartrate, ascorbic acid, and dimethylamine borane;

[0041] The complexing agent and pH adjuster are ammonia water;

[0042] When depositing a tin layer:

[0043] The main metal salt is at least one of the following: stannous chloride, stannous sulfate, stannous fluoroborate, and stannous methanesulfonate;

[0044] The reducing agent is at least one of the following: sodium borohydride, dimethylamineborane, trimethylamineborane, and sodium hypophosphite;

[0045] The complexing agent is at least one of the following: ethylenediaminetetraacetic acid, citric acid, tartaric acid, and triethanolamine;

[0046] The pH adjuster is at least one of the following: an organic base buffer system, an ammonia-ammonium chloride buffer, and a citrate-sodium hydroxide buffer;

[0047] When depositing a zinc layer:

[0048] The main metal salt is at least one of the following: zinc sulfate, zinc chloride, zinc acetate, and zinc nitrate;

[0049] The reducing agent is at least one of the following: sodium borohydride, potassium borohydride, and dimethylamineborane;

[0050] The complexing agent is at least one of the following: triethanolamine, ethylenediamine, sodium citrate, and sodium cyanide;

[0051] The pH adjuster is at least one of the following: sodium hydroxide, potassium hydroxide, or an ammonia-ammonium salt buffer system.

[0052] (3) Electroplating process to fill liquid metal: The soft substrate is immersed in an aqueous solution of sodium hydroxide containing liquid metal and a voltage of 1-8V is applied. The liquid metal is connected to the anode and the metal intermediate layer is connected to the cathode. The liquid metal is deposited into the through holes of the soft substrate through the electroplating process.

[0053] More preferably, the liquid metal is at least one of Ga, GaIn, EGaIn, and GaInSn.

[0054] More preferably, a method for fabricating a vertical interconnect structure with assisted liquid metal filling of vias in a soft substrate includes the following steps:

[0055] (1) Preparation of vias: Prepare vias with specified dimensions and depths on a soft substrate, and control the via radius to be 10-500 μm;

[0056] (2) Deposited metal intermediate layer:

[0057] a. Immerse the soft substrate in a 1-5 g / L dopamine Tris-HCl buffer solution;

[0058] b. Immerse the soft substrate in a 0.1-0.9 mol / L silver nitrate aqueous solution;

[0059] c. Immerse the soft substrate in a chemical deposition solution to form a metal interlayer; the chemical deposition solution is composed of the following raw materials: 5-10 g / L sodium hydroxide, 5-10 g / L potassium sodium tartrate, 5-10 g / L copper sulfate pentahydrate, 5-15 g / L disodium ethylenediaminetetraacetate, 2-8 g / L formaldehyde, and the balance is water.

[0060] (3) Electroplating process to fill liquid metal: The soft substrate is immersed in a 0.5-2 mol / L sodium hydroxide aqueous solution containing liquid metal, and a voltage is applied to deposit the liquid metal into the through holes of the soft substrate through an electroplating process; the liquid metal is at least one of Ga, GaIn, EGaIn and GaInSn.

[0061] Optimally, the following step is added between step a and step b: immersing the soft substrate in an ethanol solution of 1-3 wt% aminopropyltriethoxysilane.

[0062] The vertical interconnect structure and its fabrication method for assisted liquid metal-filled soft substrate vias proposed in this invention achieve the following advantages compared with existing technologies:

[0063] (1) Solving the problem of liquid metal filling: This invention introduces a metal intermediate layer as an electroplating substrate and a wetting transition layer, and utilizes electric field driving and alloying effects to successfully overcome the non-wetting and difficult-to-fill problems caused by the high surface tension of liquid metal. Liquid metal can achieve efficient, complete and site-controllable filling in microporous structures, ensuring the reliability and stability of the structure.

[0064] (2) Applicable to flexible electronic integration: Unlike the high-temperature welding or conductive adhesive technology in the prior art, the preparation process of the present invention does not rely on high temperature or solder sintering, and can achieve liquid metal filling at room temperature. This characteristic makes the method of the present invention compatible with common flexible polymer substrate processes and suitable for the process of three-dimensional flexible electronic integration, with good process scalability and wide applicability.

[0065] (3) Reliable conduction of high aspect ratio microvias: The present invention can effectively achieve reliable conduction of high aspect ratio microvias. In particular, during the liquid metal filling process, the filling accuracy is significantly improved through the electroplating process and the metal intermediate layer, ensuring the complete conductivity of the via, thereby providing strong support for the vertical integration of multilayer flexible circuits or heterogeneous devices.

[0066] The fabrication method of this invention provides a new solution for the development of high-density, multifunctional flexible electronic systems. Utilizing the self-healing properties and excellent conductivity of liquid metal, it can meet the future demands of flexible electronic devices for high frequency, high current transmission, and high integration. Attached Figure Description

[0067] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0068] Figure 1 A schematic diagram of the fabrication process for a vertical interconnect structure that uses liquid metal to fill vias in a soft substrate;

[0069] Figure 2 A cross-sectional schematic diagram of a vertical interconnect structure for filling vias in a soft substrate with auxiliary liquid metal;

[0070] Figure 3 This is a top-view photograph of the vertical interconnect structure of the through-hole in the soft substrate filled with auxiliary liquid metal prepared in Example 1. Detailed Implementation

[0071] A method for fabricating a vertical interconnect structure with assisted liquid metal filling of vias in a soft substrate includes the following steps:

[0072] (1) Preparation of vias: A via with a specified size and depth is prepared on a soft substrate, wherein the soft substrate is a flexible or stretchable material, and the soft substrate is one of PDMS, SEBS, PET, PI and EcoFlex; the radius of the via is 10-500μm, preferably 50-250μm, and the depth of the via is 50-500μm.

[0073] (2) Deposited metal intermediate layer:

[0074] a. The soft substrate is immersed in a Tris-HCl buffer solution containing 1-5 g / L dopamine for surface treatment, so that functional groups that can promote metal deposition are formed on the surface of the soft substrate.

[0075] b. Immerse the soft substrate in an aqueous solution of silver nitrate containing 0.1-0.9 mol / L; the silver ions in the silver nitrate solution are reduced to silver atoms, forming a silver seed layer on the surface of the soft substrate. This silver seed layer acts as a catalyst, which can reduce the activation energy of the oxidation reaction of the reducing agent and the reduction reaction of copper ions, thereby promoting the metal deposition process.

[0076] c. Immerse the soft substrate in a chemical deposition solution, and reduce and deposit metal ions onto the surface of the soft substrate through a chemical reduction reaction to form a metal interlayer; the chemical deposition solution is composed of the following raw materials:

[0077] 5-10 g / L sodium hydroxide,

[0078] 5-10 g / L potassium sodium tartrate,

[0079] 5-10 g / L copper sulfate pentahydrate

[0080] 5-15 g / L disodium ethylenediaminetetraacetate,

[0081] 2-8g / L formaldehyde,

[0082] The remainder is water.

[0083] In the chemical precipitation solution, sodium hydroxide provides an alkaline environment so that formaldehyde has sufficient reducing power under strongly alkaline conditions; potassium sodium tartrate and disodium ethylenediaminetetraacetate act as complexing agents to prevent copper hydroxide precipitation and control the release rate of copper ions; formaldehyde, as a reducing agent, provides electrons to complexed Cu 2+ It is reduced to metallic copper.

[0084] (3) Electroplating process to fill liquid metal: The soft substrate is immersed in a 0.5-2 mol / L sodium hydroxide aqueous solution containing liquid metal, and a voltage is applied to deposit and fill the through holes of the soft substrate by electroplating process; wherein, sodium hydroxide provides an alkaline environment, adjusts the pH of the solution, enhances the conductivity of the solution, and promotes the electroplating deposition of liquid metal; the liquid metal is at least one of Ga, GaIn, EGaIn and GaInSn.

[0085] To further improve performance, an additional step is added between steps a and b: the soft substrate is immersed in an ethanol solution of 1-3 wt% aminopropyltriethoxysilane. Aminopropyltriethoxysilane, acting as a silane coupling agent, binds to the dopamine layer via Si-O-Si or Si-O covalent bonds, with its terminal amino groups exposed on the surface. This allows for strong adsorption of metal cations from the solution in the next step, aiding in the adsorption of Ag. + It is reduced to silver atoms. By forming high-density catalytic seed sites, copper nucleation is promoted, and the deposited copper grains can be rapidly connected to form sheets, ultimately forming a copper film with low porosity and high density.

[0086] Partial list of raw materials: Sodium hydroxide (S580606, Aladdin), potassium sodium tartrate (P112611, Aladdin), copper sulfate pentahydrate (C141239, Aladdin), disodium ethylenediaminetetraacetate (D684233, Aladdin), formaldehyde (F754240, Aladdin), silver nitrate (S116264, Aladdin), aminopropyltriethoxysilane (A107147, Aladdin), EGaIn liquid metal (G380237, Aladdin), PDMS film (Dongguan Jiening), dopamine (D103111, Aladdin), Tris-HCl buffer (T301503, dopamine)

[0087] Example 1:

[0088] Figure 1 A schematic diagram of the fabrication process of a vertical interconnect structure with auxiliary liquid metal filling of through-holes in a soft substrate. Step (1) is performed on a to prepare through-holes to obtain b, then step (2) is performed to deposit a metal intermediate layer to obtain c, and then step (3) is performed as shown in d to fill liquid metal, finally obtaining the vertical interconnect structure e of the auxiliary liquid metal filling through-holes in the soft substrate of the present invention. Figure 2 This is a cross-sectional schematic diagram of the vertical interconnect structure of the soft substrate via filled with auxiliary liquid metal according to the present invention, wherein 1 is the soft substrate, 2 is the metal intermediate layer, and 3 is the liquid metal layer.

[0089] Specifically, a method for fabricating a vertical interconnect structure with assisted liquid metal filling of vias in a soft substrate includes the following steps:

[0090] Step A: A 200μm thick PDMS film of 5cm×1cm is processed by femtosecond laser with a pulse duration of 50fs, a center wavelength of 800nm, and a repetition frequency of 1kHz. The laser is vertically focused on the surface of the PDMS film through an objective lens in air, and the drilling radius is set to 250μm to obtain a PDMS substrate with a 250μm radius through hole.

[0091] Step B: Expose a 5mm×5mm area centered on the center of the via in the PDMS substrate, and cover the remaining area with transparent tape.

[0092] Step C: At room temperature, place the PDMS substrate into 100 mL of dopamine Tris-HCl buffer, with a dopamine concentration of 2 g / L and a pH of 8.5. Stir on a magnetic stirrer in the dark for 24 h. Wash with water and then with ethanol. Place in a vacuum drying oven at 40 °C for 20 min and peel off the transparent tape.

[0093] At room temperature, the PDMS substrate was immersed in 100 ml of ethanol solution containing 2 wt% aminopropyltriethoxysilane for 30 minutes, washed with water and then washed with ethanol, and then placed in a vacuum drying oven at 40°C for 20 minutes.

[0094] At room temperature, the PDMS substrate was immersed in 100 mL of 0.2 mol / L silver nitrate aqueous solution for 4 hours, washed with water and then washed with ethanol, and then placed in a vacuum drying oven at 40°C for 20 min.

[0095] The PDMS substrate was then immersed in 200 mL of chemical deposition solution for copper chemical deposition. The reaction conditions were stirring in a 40°C water bath for 20 minutes to finally obtain a copper-coated PDMS substrate.

[0096] The chemical deposition solution is composed of the following raw materials: 7.5 g / L sodium hydroxide, 7.5 g / L potassium sodium tartrate, 7.5 g / L copper sulfate pentahydrate, 10 g / L disodium ethylenediaminetetraacetate, 3.5 g / L formaldehyde, with the balance being water;

[0097] Step D: At room temperature, immerse the copper-clad PDMS substrate in a petri dish containing 100 mL of 1 mol / L sodium hydroxide aqueous solution. Add 1 mL of EGaIn liquid metal to the area of ​​the petri dish away from the copper-clad PDMS substrate. Use EGaIn liquid metal as the anode and the copper-clad PDMS substrate as the cathode. Apply a voltage of 5V for electroplating for 30 seconds. Finally, the vias of the copper-clad PDMS substrate are filled with EGaIn liquid metal, thus obtaining the vertical interconnect structure of the soft substrate vias filled with auxiliary liquid metal of the present invention.

[0098] Figure 3This is a top-view photograph of the vertical interconnect structure of the through-hole in the soft substrate filled with auxiliary liquid metal prepared in Example 1. As can be seen from the figure, the liquid metal is continuously filled within the through-hole structure.

[0099] Example 2:

[0100] The process is basically the same as in Example 1, except that in step A, the drilling radius is set to 50 μm to obtain a PDMS substrate with a through hole of 50 μm radius.

[0101] Example 3:

[0102] The process is basically the same as in Example 1, except that in step A, the drilling radius is set to 100 μm to obtain a PDMS substrate with a through hole of 100 μm radius.

[0103] Example 4:

[0104] The process is basically the same as in Example 1, except that in step A, the drilling radius is set to 150 μm to obtain a PDMS substrate with a through hole of 150 μm radius.

[0105] Example 5:

[0106] A method for fabricating a vertical interconnect structure with assisted liquid metal filling of vias in a soft substrate includes the following steps:

[0107] Step A: A 200μm thick PDMS film of 5cm×1cm is processed by femtosecond laser with a pulse duration of 50fs, a center wavelength of 800nm, and a repetition frequency of 1kHz. The laser is vertically focused on the surface of the PDMS film through an objective lens in air, and the drilling radius is set to 250μm to obtain a PDMS substrate with a 250μm radius through hole.

[0108] Step B: Expose a 5mm×5mm area centered on the center of the via in the PDMS substrate, and cover the remaining area with transparent tape.

[0109] Step C: At room temperature, place the PDMS substrate in 100 mL of dopamine Tris-HCl buffer, with a dopamine concentration of 2 g / L and a pH of 8.5, and stir on a magnetic stirrer in the dark for 24 h. Wash with water and then with ethanol, and place in a vacuum drying oven at 40 °C for 20 min.

[0110] At room temperature, the PDMS substrate was immersed in 100 mL of 0.2 mol / L silver nitrate aqueous solution for 4 hours, washed with water and then washed with ethanol, and then placed in a vacuum drying oven at 40°C for 20 min.

[0111] The PDMS substrate was then immersed in 200 mL of chemical deposition solution for copper chemical deposition. The reaction conditions were stirring in a 40°C water bath for 20 minutes to finally obtain a copper-coated PDMS substrate.

[0112] The chemical deposition solution is composed of the following raw materials: 7.5 g / L sodium hydroxide, 7.5 g / L potassium sodium tartrate, 7.5 g / L copper sulfate pentahydrate, 10 g / L disodium ethylenediaminetetraacetate, 3.5 g / L formaldehyde, with the balance being water;

[0113] Step D: At room temperature, immerse the copper-clad PDMS substrate in a petri dish containing 100 mL of 1 mol / L sodium hydroxide aqueous solution. Add 1 mL of EGaIn liquid metal to the area of ​​the petri dish away from the copper-clad PDMS substrate. Use EGaIn liquid metal as the anode and the copper-clad PDMS substrate as the cathode. Apply a voltage of 5V for electroplating for 30 seconds. Finally, the vias of the copper-clad PDMS substrate are filled with EGaIn liquid metal, thus obtaining the vertical interconnect structure of the soft substrate vias filled with auxiliary liquid metal of the present invention.

[0114] Comparative Example 1:

[0115] A 200μm thick PDMS film measuring 5cm×1cm was processed by femtosecond laser with a pulse duration of 50fs, a center wavelength of 800nm, and a repetition frequency of 1kHz. The laser was vertically focused onto the surface of the PDMS film through an objective lens in air. The perforation radius was set to 250μm, and the center of the perforation circle was coincident with the center point of the PDMS film, thus obtaining a PDMS substrate with a through hole of 250μm radius.

[0116] GaIn liquid metal was injected into the vias of a PDMS substrate using a micro-syringe with a tip radius of 100 μm, filling the vias with EGaIn liquid metal. Subsequently, the EGaIn liquid metal detached from the vias. Ultimately, a vertical interconnect structure with auxiliary liquid metal filling of the soft substrate vias could not be obtained.

[0117] Comparative Example 2:

[0118] A 200μm thick PDMS film measuring 5cm×1cm was processed by femtosecond laser with a pulse duration of 50fs, a center wavelength of 800nm, and a repetition frequency of 1kHz. The laser was vertically focused onto the surface of the PDMS film through an objective lens in air. The perforation radius was set to 50μm, and the center of the perforation circle was coincident with the center point of the PDMS film, thus obtaining a PDMS substrate with a 50μm radius through-hole.

[0119] GaIn liquid metal was injected into the vias of a PDMS substrate using a commercially available microsyringe with a tip radius of 100 μm. However, the vias of the PDMS substrate could not be filled with EGaIn liquid metal. Ultimately, a vertical interconnect structure with auxiliary liquid metal filling of the vias in the soft substrate could not be obtained.

[0120] Comparative Example 3:

[0121] A 200μm thick PDMS film measuring 5cm×1cm was processed by femtosecond laser with a pulse duration of 50fs, a center wavelength of 800nm, and a repetition frequency of 1kHz. The laser was vertically focused onto the surface of the PDMS film through an objective lens in air. The perforation radius was set to 100μm, and the center of the perforation circle was coincident with the center point of the PDMS film, thus obtaining a PDMS substrate with a through hole of 100μm radius.

[0122] GaIn liquid metal was injected into vias in a PDMS substrate using a commercially available microsyringe with a tip radius of 100 μm, filling the vias with EGaIn liquid metal. Subsequently, the EGaIn liquid metal detached from the vias. Ultimately, a vertical interconnect structure with auxiliary liquid metal filling of vias in the soft substrate could not be obtained.

[0123] Comparative Example 4:

[0124] A 200μm thick PDMS film measuring 5cm×1cm was processed by femtosecond laser with a pulse duration of 50fs, a center wavelength of 800nm, and a repetition frequency of 1kHz. The laser was vertically focused onto the surface of the PDMS film through an objective lens in air. The perforation radius was set to 150μm, and the center of the perforation circle was coincident with the center point of the PDMS film, thus obtaining a PDMS substrate with a through hole of 150μm radius.

[0125] GaIn liquid metal was injected into vias in a PDMS substrate using a commercially available microsyringe with a tip radius of 100 μm, filling the vias with EGaIn liquid metal. Subsequently, the EGaIn liquid metal detached from the vias. Ultimately, a vertical interconnect structure with auxiliary liquid metal filling of vias in the soft substrate could not be obtained.

[0126] Test Example 1:

[0127] The vertical interconnect structure with auxiliary liquid metal-filled soft substrate vias, prepared in the examples or comparative examples, was fixed at both ends using a tensile testing machine (MTS Systems C42). The initial spacing between the clamps at both ends was 2 cm, and the via structure was located in the center of the clamps. The liquid metal at the vias at both ends was connected to a data acquisition multimeter system (DAQ6510) via 10 cm long, 0.5 mm diameter copper wires to record resistance in real time. The uniaxial tensile rate for the electrical tensile test was 1 cm per minute, and the tensile strain rate was the percentage of the uniaxial tensile distance to the initial clamp spacing. The tensile strain rate when the resistance displayed on the data acquisition multimeter system became infinite was recorded as the electrical failure tensile strain rate. A larger electrical failure tensile strain rate indicates better stability of the vertical interconnect structure with auxiliary liquid metal-filled soft substrate vias. Test data is shown in Table 1.

[0128] Table 1: Tensile Strain Rate Test Table for Electrical Failure

[0129] Initial resistance value, Ω Electrical failure tensile strain rate, % Example 1 1.35 71.3 Example 2 1.98 95.2 Example 3 1.68 88.5 Example 4 1.54 78.5 Example 5 2.05 59.7

[0130] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A vertical interconnect structure for filling vias in a soft substrate with auxiliary liquid metal, characterized in that, include: (1) A soft substrate with through holes: the soft substrate is a flexible or stretchable material; (2) Metal intermediate layer deposited on the sidewall of the through hole: (3) A liquid metal layer filled into the through hole by electroplating process.

2. The vertical interconnect structure of the soft substrate via filled with auxiliary liquid metal as described in claim 1, characterized in that, The soft substrate is one of PDMS, SEBS, PET, PI, and EcoFlex.

3. The vertical interconnect structure of the soft substrate via filled with auxiliary liquid metal as described in claim 1, characterized in that, The depth of the through hole is 50-500μm, and the radius of the through hole is 10-500μm.

4. The vertical interconnect structure of the soft substrate via filled with auxiliary liquid metal as described in claim 1, characterized in that, The metal interlayer is at least one of copper, nickel, gold, silver, tin, or zinc.

5. The vertical interconnect structure of the soft substrate via filled with auxiliary liquid metal as described in claim 1, characterized in that, The liquid metal is at least one of Ga, GaIn, EGaIn, and GaInSn.

6. A method for fabricating a vertical interconnect structure with assisted liquid metal filling of through-holes in a soft substrate, characterized in that, Includes the following steps: (1) Fabrication of vias: Throughs are fabricated on a soft substrate; (2) Depositing a metal intermediate layer: The soft substrate is immersed in a chemical deposition solution containing metal salts, reducing agents and auxiliary reagents, and metal ions are reduced and deposited on the surface of the soft substrate through a chemical reduction reaction to form a metal intermediate layer; or metal raw materials are deposited on the surface of the soft substrate by methods such as thermal evaporation, magnetron sputtering, physical vapor deposition, etc. to form a metal intermediate layer. (3) Electroplating process to fill liquid metal: The soft substrate is immersed in a solution containing liquid metal and a voltage is applied to deposit liquid metal into the through holes of the soft substrate through an electroplating process.

7. The method for fabricating a vertical interconnect structure with assisted liquid metal filling of soft substrate vias as described in claim 6, characterized in that, The metal intermediate layer deposited in step (2) is: a. Immerse the soft substrate in a Tris-HCl buffer solution containing dopamine; b. Immerse the soft substrate in an aqueous solution containing a catalytic metal salt; c. The soft substrate is immersed in a chemical deposition solution containing metal salt, reducing agent, complexing agent and pH adjuster, and the metal ions are reduced and deposited on the surface of the soft substrate through a chemical reduction reaction to form a metal intermediate layer.

8. The method for fabricating a vertical interconnect structure with assisted liquid metal filling of soft substrate vias as described in claim 7, characterized in that, The catalytic metal salt mentioned in step b is at least one of the following: palladium chloride, chloroauric acid, and silver nitrate; The chemical deposition solution described in step c comprises at least the following components: metal salt, reducing agent, complexing agent, and pH adjuster. The metal salt is at least one of the following: copper sulfate pentahydrate, copper nitrate, copper chloride, nickel nitrate, nickel chloride, gold nitrate, gold chloride, silver nitrate, silver sulfate, zinc chloride, zinc nitrate, zinc sulfate, indium nitrate, indium chloride, tin nitrate, and tin chloride; When depositing copper layers: The main metal salt is at least one of the following: copper sulfate pentahydrate, copper nitrate, copper chloride, and basic copper carbonate; The reducing agent is formaldehyde, paraformaldehyde, or glyoxal; The complexing agent is at least one of the following: potassium sodium tartrate, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, sodium citrate, triethanolamine, glycine, and tris(hydroxymethyl)aminomethane; The pH adjuster is at least one of the following: sodium hydroxide, potassium hydroxide, and sodium carbonate; When depositing a nickel layer: The main metal salt is at least one of the following: nickel sulfate hexahydrate, nickel chloride, nickel aminosulfonate, and nickel acetate; The reducing agent is sodium hypophosphite or potassium hypophosphite; The complexing agent is at least one of the following: sodium citrate, potassium citrate, lactic acid, malic acid, glycine, and succinic acid; The pH adjuster is at least one of the following: ammonia, sodium hydroxide, potassium hydroxide, and sodium carbonate; When depositing a silver layer: The main metal salt is at least one of the following: silver nitrate, potassium silver cyanide, and silver carbonate; The reducing agent is at least one of the following: formaldehyde, glucose, potassium sodium tartrate, ascorbic acid, and dimethylamine borane; The complexing agent and pH adjuster are ammonia water; When depositing a tin layer: The main metal salt is at least one of the following: stannous chloride, stannous sulfate, stannous fluoroborate, and stannous methanesulfonate; The reducing agent is at least one of the following: sodium borohydride, dimethylamineborane, trimethylamineborane, and sodium hypophosphite; The complexing agent is at least one of the following: ethylenediaminetetraacetic acid, citric acid, tartaric acid, and triethanolamine; The pH adjuster is at least one of the following: an organic base buffer system, an ammonia-ammonium chloride buffer, and a citrate-sodium hydroxide buffer; When depositing a zinc layer: The main metal salt is at least one of the following: zinc sulfate, zinc chloride, zinc acetate, and zinc nitrate; The reducing agent is at least one of the following: sodium borohydride, potassium borohydride, and dimethylamineborane; The complexing agent is at least one of the following: triethanolamine, ethylenediamine, sodium citrate, and sodium cyanide; The pH adjuster is at least one of the following: sodium hydroxide, potassium hydroxide, or an ammonia-ammonium salt buffer system.

9. The method for fabricating a vertical interconnect structure with assisted liquid metal filling of soft substrate vias as described in claim 7, characterized in that, The liquid metal mentioned in step (3) is at least one of Ga, GaIn, EGaIn and GaInSn.

10. The method for fabricating a vertical interconnect structure with assisted liquid metal filling of soft substrate vias as described in claim 7, characterized in that, Includes the following steps: (1) Preparation of vias: Prepare vias with specified dimensions and depths on a soft substrate, and control the via radius to be 10-500 μm; (2) Deposited metal intermediate layer: a. Immerse the soft substrate in a 1-5 g / L dopamine Tris-HCl buffer solution; b. Immerse the soft substrate in a 0.1-0.9 mol / L silver nitrate aqueous solution; c. Immerse the soft substrate in a chemical deposition solution to form a metal interlayer; the chemical deposition solution is composed of the following raw materials: 5-10 g / L sodium hydroxide, 5-10 g / L potassium sodium tartrate, 5-10 g / L copper sulfate pentahydrate, 5-15 g / L disodium ethylenediaminetetraacetate, 2-8 g / L formaldehyde, and the balance is water. (3) Electroplating process to fill liquid metal: The soft substrate is immersed in a 0.5-2 mol / L sodium hydroxide aqueous solution containing liquid metal, and a voltage is applied to deposit the liquid metal into the through holes of the soft substrate through an electroplating process; the liquid metal is at least one of Ga, GaIn, EGaIn and GaInSn.

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