A method for rigid-flexible interconnection of liquid metal based on patterned indium in situ doping

Abstract

This invention discloses a method for rigid-flexible interconnection using liquid metal based on patterned indium in-situ doping, belonging to the field of rigid-flexible interconnection technology. The method includes the following steps: Step 1. Preparing a patterned indium conductive material; Step 2. Mixing the patterned indium conductive material with liquid metal for in-situ doping, allowing the patterned indium conductive material to dissolve in-situ in the liquid metal to form an indium-based liquid metal; Step 3. As indium metal diffuses, high-doping concentration regions and low-doping concentration regions of indium metal are formed in the indium-based liquid metal. Rigid leads are immersed in the high-doping concentration region, and the low-doping concentration region is interconnected with the liquid metal wires to form a rigid-flexible interconnection structure. This invention effectively solves the Young's modulus mismatch problem at the interface between rigid chips and flexible circuit systems, increases interconnect reliability, provides high conductivity, and simplifies the fabrication process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of rigid-flexible interconnection, and particularly relates to a liquid metal rigid-flexible interconnection method based on patterned indium in-situ doping. BACKGROUND

[0002] Soft and stretchable electronic products are widely used in next-generation electronic devices in emerging fields, including soft robots, wearable electronic devices, biomedical devices, and human-machine interfaces. In recent years, significant progress has been made in developing new materials and architectures for stretchable sensors, displays, heaters, energy storage devices, and integrated circuits.

[0003] Currently, the key components that impart softness to electronic products are stretchable electrodes and interconnects, which are mainly manufactured using two methods. The first method is to achieve flexibility by selecting stretchable materials, which utilize the electrical conductivity and stretchability of the materials themselves to construct flexible systems. Although flexible electronic devices can be relatively simply prepared by this method, the electrical conductivity of the flexible materials prepared at present is still lower than that of traditional metal materials, and there are still gaps, especially in high-performance applications such as fine circuits, which face greater limitations. The second method is to achieve flexibility by using standard metal materials in a structural manner, which uses the connection method and special structure of flexible materials and rigid materials to achieve the effect of being bendable and stretchable. However, the preparation of these special structure flexible materials requires special equipment and processes, and the cost is high and the process conditions are harsh. For example, the existing granted invention patent CN115175449 A adopts a gradient rigid-flexible interconnection method based on doped liquid metal. Although this method solves the problem of rigid-flexible interconnection, the process is complex, and there are problems such as large gradient difference leading to unreliable interconnection and low electrical conductivity. SUMMARY

[0004] To solve the above technical problems, the application provides a liquid metal rigid-flexible interconnection method based on patterned indium in-situ doping. This method uses patterned indium metal for in-situ doping, forms a multi-contact concentration gradient, and exhibits a state between solid and liquid, which can significantly improve the reliability of the interconnection.

[0005] The technical solution adopted by the application is as follows:

[0006] A liquid metal rigid-flexible interconnection method based on patterned indium in-situ doping, comprising the following steps:

[0007] Step 1. Prepare a patterned indium metal conductive material;

[0008] Step 2. Mix the patterned indium metal conductive material with liquid metal for in-situ doping, so that the patterned indium metal conductive material is dissolved in-situ in the liquid metal to form an indium-based liquid metal;

[0009] Step 3. With the diffusion of indium metal, the indium metal high-doped concentration region and the low-doped concentration region are formed in the indium-based liquid metal, the rigid pin is immersed in the high-doped concentration region, the low-doped concentration region is connected with the liquid metal wire to form a rigid-flexible interconnection structure.

[0010] Preferably, in step 1, the indium metal is used as raw material, and a patterned indium metal conductive material is prepared by using 3D printing technology; the patterned indium metal conductive material is a dendritic structure or a coral-like structure, etc., so as to form a multi-contact concentration gradient, increase the contact area, and show a state between the solid state and the liquid state to moderate the Young's modulus mismatch.

[0011] The conductivity of the indium metal is 2.0×10 6 S / m to 1.8×10 7 S / m.

[0012] Preferably, the liquid metal is gallium-indium liquid metal, gallium-indium-tin alloy, bismuth-indium alloy or bismuth-tin alloy.

[0013] Preferably, the proportion of the gallium-indium alloy in the gallium-indium liquid metal is 7:3, and the conductivity of the gallium-indium liquid metal ranges from 2.0×10 6 S / m to 1.2×10 7 S / m. More preferably, the gallium-indium liquid metal is mainly the same metal as the high-purity indium metal and the gallium metal in the liquid metal, and the two have similar chemical properties and are easier to combine.

[0014] Preferably, in step 2, a low-temperature heating step is further included, and the mixture formed after the liquid metal and the patterned indium metal conductive material are doped in situ is heated in an oven at 20-100℃ for 2-10 minutes.

[0015] Preferably, the added mass of the patterned indium metal conductive material accounts for 5% to 40% of the mass of the formed indium-based liquid metal.

[0016] Preferably, step 2 further includes the following steps:

[0017] Step 2.1. Select a flexible substrate and process grooves thereon;

[0018] Step 2.2. Fill the liquid metal into the grooves, and place the patterned indium metal conductive material at the end of the grooves, which is the set rigid-flexible interconnection point, and the patterned indium metal conductive material is doped with the liquid metal at this end;

[0019] Step 2.3. Heat in an oven at 20-100℃ for 2-10 minutes, and during the heating process, the indium metal diffuses in the liquid metal.

[0020] The step 2.1 above, the step of processing the groove on the flexible substrate is as follows:

[0021] The laser etching is performed on the flexible substrate at a laser scanning speed of 20-200 mm / s and a laser power of 10-25 W; the flexible substrate is cleaned with alcohol and dried to remove carbonized residues.

[0022] Preferably, the step 3 further comprises the following steps:

[0023] Step 3.1. Forming an indium metal concentration gradient with the end point as the first point at the rigid-flexible interconnection point, and transitioning from the high-doped concentration area to the low-doped concentration area; and the undoped liquid metal in the groove forms a liquid metal wire which is integrated with the low-doped concentration area; then immersing the pin of the rigid chip into the high-doped concentration area, so that the flexible liquid metal wire and the rigid chip form electrical interconnection through the rigid-flexible interconnection point.

[0024] Preferably, the step 3 further comprises the following steps:

[0025] Step 3.2. Packaging the rigid-flexible electronic system obtained after electrical interconnection; the packaging material and the flexible substrate both use elastic materials such as Ecoflex or PDMS. The packaging method can be selected from the methods such as blade coating and spin coating.

[0026] The beneficial technical effects of the present application are as follows:

[0027] (1) The present application provides a liquid metal rigid-flexible interconnection method based on patterned indium metal in-situ doping, which well solves the Young's modulus mismatch problem of rigid chip and flexible circuit system at the joint interface, and increases the reliability of interconnection, has high conductivity, and simple processing technology.

[0028] (2) The present application forms a multi-contact concentration gradient by in-situ doping of patterned indium metal, increases the contact area, and can exhibit a state between solid and liquid, alleviates the Young's modulus mismatch phenomenon, so that the rigid-flexible interconnection interface based on liquid metal can effectively overcome the separation and fracture phenomenon in the stretching process, significantly improves the stability and reliability of the interconnection, and enhances the service life and performance of the product after repeated stretching.

[0029] (3) The present application uses the mode of indium metal dissolution and diffusion in liquid metal, which also significantly enhances the adhesion of chip pins, thereby realizing reliable and stretchable electrical connection; and using rigid-flexible interconnection can manufacture a system with improved stretchability while maintaining stable mechanical properties, which can realize arbitrary bending and extrusion.

[0030] (4) The liquid metal doped with conductive material has high conductivity and good repeatability, and the method has good wettability for different metals, and has wide application range. In addition, the method provided by the application is easy to obtain, low in cost and simple to operate. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 A flow chart for an embodiment of the liquid metal rigid-flexible interconnection method based on in-situ doping of indium patterning of the application;

[0032] Figure 2 A preparation flow chart for the liquid metal rigid-flexible interconnection method based on in-situ doping of indium of the application;

[0033] Figure 3 An enlarged schematic diagram of the liquid metal rigid-flexible interconnection method based on in-situ doping of indium of the application;

[0034] Figure 4 A microcosmic schematic diagram of the liquid metal rigid-flexible interconnection method based on in-situ doping of indium of the application;

[0035] Figure 5 A tensile property test result diagram of a simple flexible nixie tube prepared in Embodiment 1 of the application;

[0036] Figure 6 A tensile test diagram of different doping concentrations in a simple flexible resistance test circuit prepared in Embodiment 2 of the application;

[0037] Figure 7 A tensile test diagram of 20% doping rigid-flexible interconnection in Embodiment 2 of the application;

[0038] Figure 8 A cyclic tensile test diagram of 20% doping rigid-flexible interconnection in Embodiment 2 of the application;

[0039] Figure 9 A specific cyclic tensile test result diagram of 20% doping rigid-flexible interconnection in Embodiment 2 of the application.

[0040] In the figure: 1-flexible substrate, 2-laser emitting device, 3-gallium-indium liquid metal, 4-indium metal, 5-rigid electronic chip. DETAILED DESCRIPTION

[0041] The application discloses a liquid metal rigid-flexible interconnection method based on in-situ doping of patterned indium, and aims to solve the interface bonding force degradation problem caused by Young's modulus mismatch between a liquid metal flexible circuit and a rigid chip. Under severe and repeated conditions, the mismatch can cause a sharp drop in mechanical properties of the rigid-flexible system. Therefore, the application provides an innovative interconnection method, which in-situ dopes patterned indium metal, such as tree-shaped and coral-shaped structures, at the interconnection point of the rigid-flexible system, forms a multi-contact concentration gradient, increases the contact area, and shows a state between solid and liquid, thereby effectively improving the Young's modulus mismatch phenomenon, and in addition, can enhance the electrical conductivity, improve the repeatability and adhesion, and ensure the stability of the rigid-flexible interconnection interface. The method can not only ensure reliable mechanical properties between the liquid metal-based flexible circuit and the rigid chip, but also maintain excellent electrical properties of the rigid-flexible hybrid electronic system.

[0042] The application will be further described below in combination with the drawings and specific embodiments.

[0043] As shown in the drawings, Figure 1 A liquid metal rigid-flexible interconnection method based on in-situ doping of patterned indium includes the following steps: preparing a flexible substrate with a pattern such as a groove based on laser etching, in-situ doping of a patterned liquid metal interconnection point, and assembly and flexible packaging of a rigid-flexible hybrid electronic system. The detailed process is shown in Figure 2 .

[0044] First, the patterning of the flexible substrate based on laser etching includes the following steps:

[0045] Step 1, preparing a flexible substrate, and selecting Ecoflex as an elastic substrate.

[0046] Step 2, drawing a pattern through software and importing a laser engraving machine, and using laser to scan and etch the entire area at a scanning speed of 100 mm / s and a laser power of 18 W, and the scanned area is carbonized.

[0047] Step 3, after laser etching, the substrate is cleaned with alcohol and dried to remove the carbonized residues. At this time, a groove with a depth of 1 mm is formed, and the patterned flexible substrate is prepared.

[0048] Next, the preparation process of the in-situ doping of the patterned liquid metal interconnection point includes the following steps:

[0049] A 3D printing technology is used to prepare indium metal conductive materials with certain topography, such as tree-shaped structures and coral-shaped structures, to form a multi-contact concentration gradient, increase the contact area, and show a state between solid and liquid to alleviate the Young's modulus mismatch.

[0050] The liquid metal is filled into the patterned flexible substrate groove, and the step is repeated several times until the filling is completed.

[0051] The conductive material is placed at the rigid-flexible interconnection point of the liquid metal in different proportions respectively to dope, and indium-based liquid metals containing different in-situ doping proportions are obtained.

[0052] In this embodiment, patterned high-purity indium metal is used as the conductive material, which is soft in texture and has an electrical conductivity of 2.0*10 6 S / m to 1.8*10 7 S / m.

[0053] The liquid metal used in the present application is preferably an amorphous and flowable liquid metal, such as a gallium-indium liquid metal, and the gallium-indium alloy ratio of the gallium-indium liquid metal is 7:3, and the electrical conductivity range is 1.0*10 6 S / m to 6.0*10 6 S / m.

[0054] Of course, the liquid metal is not limited to gallium-indium liquid metal, and also includes gallium-indium-tin alloy, bismuth-indium alloy, bismuth-tin alloy, etc.

[0055] During the entire doping process, low temperature of 20-100℃ is used to accelerate the doping process.

[0056] Figure 4 Microscopic schematic diagram of the liquid metal after doping of the conductive material.

[0057] Finally, the assembly of the rigid-flexible hybrid electronic system and the flexible packaging are carried out, including the following steps:

[0058] The flexible liquid metal circuit and the rigid chip are electrically interconnected through the interconnection point, and the local enlarged structure is as shown in Figure 3 .

[0059] In the present application, the packaging material of the rigid-flexible hybrid electronic system is preferably a flexible material Ecoflex, and the rigid chip used is a chip required for the rigid-flexible hybrid electronic system to realize a certain function.

[0060] Of course, the packaging material can also be PDMS, which has lower cost and excellent stretchability.

[0061] The rigid-flexible interconnection method of the present application will be described in more detail below in conjunction with specific embodiments.

[0062] Embodiment 1

[0063] The present application is based on a gradient rigid-flexible interconnection method formed by in-situ doping of patterned indium liquid metal, including the following steps:

[0064] (1) Obtain a patterned flexible substrate;

[0065] (1-1) Prepare the Ecoflex flexible substrate, mix Ecoflex A liquid and Ecoflex B liquid in a mass ratio of 1:1, spin coat on the mold at a speed of 50 rad / min for 30S, and heat in the oven for 30 min.

[0066] (1-2) Laser etch the above flexible substrate, draw a pattern through software, and import it into a laser engraving machine. Use laser to scan and etch the entire area at a scanning speed of 200 mm / s and a laser power of 20W.

[0067] (1-3) After laser etching, clean the substrate with alcohol and dry it to remove carbonized residues. At this time, a groove with a depth of 1.5 mm is formed, and the patterned flexible substrate is prepared.

[0068] (2) Perform the preparation process of the rigid-flexible interconnection point:

[0069] (2-1) Fill the gallium-indium liquid metal with a gallium-indium ratio of 7:3 into the laser-etched recess until it is completely filled.

[0070] (2-2) Use 3D printing technology to prepare patterned indium metal conductive materials, such as tree-like structures, coral-like structures, etc.

[0071] (2-3) Place in a 70℃ oven for low-temperature heating for 4 min to form a gradient concentration diffusion starting from the end point.

[0072] (3) Assemble the rigid LED number tube with the flexible electronic circuit and perform flexible packaging;

[0073] (3-1) Bond the rigid LED number tube with the prepared liquid metal interconnection point to obtain a rigid-flexible electronic system.

[0074] (3-2) Package the rigid-flexible electronic system, and the packaging material is still Ecoflex high-elasticity material. The packaging method can be selected as blade coating or spin coating. After packaging, the entire liquid metal elastic electrode or circuit is prepared without mask printing. Through the above steps, a simple flexible number tube is obtained.

[0075] Example 2

[0076] The present application is based on a patterned indium in-situ doped liquid metal rigid-flexible interconnection method, which comprises the following steps:

[0077] (1) Obtain a patterned flexible substrate;

[0078] (1-1) Prepare a flexible substrate, which is PDMS, mix the base material and curing agent in a mass ratio of 10:1, spin coat on the mold at a speed of 50 rad / min for 30S, and heat in the oven at 65°C for 90min.

[0079] (1-2) Laser etching the above flexible substrate:

[0080] Draw the pattern by software, import it into the laser engraving machine, and use laser to scan and etch the entire area at a speed of 50mm / s and a power of 15W.

[0081] (1-3) After laser etching, clean the substrate with alcohol and dry it, remove the carbonized residue. At this time, a 1mm deep groove is formed, and the patterned flexible substrate is prepared.

[0082] (2) Perform rigid-flexible interconnection point preparation process:

[0083] (2-1) Fill the liquid metal of gallium-indium alloy with a ratio of 7:3 into the laser etched groove until it is completely filled.

[0084] (2-2) Use 3D printing technology to prepare patterned indium metal conductive material, such as tree-like structure, coral-like structure, etc. The doping ratio is 0% (i.e. no doping), 10%, 20%, 30%, and 40%, respectively.

[0085] (2-3) Place it on a 40°C heating platform for low-temperature heating for 7min to form a gradient concentration diffusion with multiple touch points.

[0086] (3) Assemble the rigid resistance chip and flexible electronic circuit and perform flexible packaging;

[0087] (3-1) Bond the rigid resistance chip with a resistance of 50Ω, 460Ω, and 1.5kΩ with the prepared liquid metal interconnection point to obtain a rigid-flexible electronic system.

[0088] (3-2) Package the rigid-flexible electronic system, and the packaging material is still PDMS high elasticity material. The packaging method can be selected as blade coating or spin coating. After packaging, the entire liquid metal circuit is prepared without mask printing.

[0089] Through the above steps, a simple flexible resistance test circuit is obtained.

[0090] Test the performance of the rigid-flexible interconnection structure obtained in the above embodiment, as follows:

[0091] Test the tensile performance of the simple flexible number tube test circuit prepared in Example 1, as shown in Figure 5 .Figure 5 "0% liquid metal" indicates pure liquid metal with a drawing weight of 0%, "100% indium-based liquid metal" indicates indium-based liquid metal with a drawing weight of 100% and a doping weight of 10%, and so on. Figure 5 As can be seen, within the large strain range of 0%-500%, the resistance change of the sample using the interconnection method of this invention is significantly smaller than that of the conventional method, and the LED brightness remains stable. In contrast, as can be seen from the invention patent CN 115175449 A, the maximum stretching shown is only 200%, proving that the method of this invention has superior mechanical stability and electrical reliability.

[0092] The flexible resistor test circuits with different doping concentrations in Example 2 were tested, such as... Figure 6 As shown. Figure 6 In this context, 0%, 10%, 20%, 30%, and 40% doping represent liquid metals doped with different amounts of indium metal. (This is achieved through...) Figure 6 Data shows that undoped devices fracture at 150% strain, while indium-doped circuits exhibit minimal resistance fluctuations within the 0%-400% strain range. Notably, samples with 20% and 30% doping ratios demonstrate the best electromechanical coupling performance.

[0093] Further extreme testing of the 20% doped flexible resistive circuit revealed that, for example... Figure 7 As shown, under tensile strains up to 600%, the three different types of resistive circuits maintained stable electrical connections. To verify long-term performance, a 2cm long sample was subjected to a 100% strain cycle test, such as... Figure 8 and Figure 9 As shown, the device maintains good durability after 1500 tensile cycles.

[0094] The above experimental results fully demonstrate that the method proposed in this invention has significant advantages and application potential in constructing highly tensile rigid-flexible hybrid electronic systems. It should be noted that this technical solution is not limited to the listed embodiments; any equivalent substitutions or improvements based on this technical concept are within the scope of protection of this invention.

Claims

1. A liquid metal flexible electronics method based on in-situ doping of patterned indium, characterized by The method comprises the following steps: Step 1. Preparing a patterned indium metal conductive material; The patterned indium metal conductive material is a dendritic structure or a coral-like structure; Step 2. Mixing the patterned indium metal conductive material with a liquid metal to perform in-situ doping, so that the patterned indium metal conductive material is dissolved in the liquid metal in-situ to form an indium-based liquid metal; Step 3. With the diffusion of the indium metal, an indium metal high-doping concentration region and a low-doping concentration region are formed in the indium-based liquid metal, a rigid pin is immersed in the high-doping concentration region, the low-doping concentration region is interconnected with a liquid metal wire to form a rigid-flexible interconnection structure.

2. The method of claim 1, wherein: The conductivity of the indium metal is 2.0 x 10 6 S / m to 1.8 x 10 7 S / m.

3. The method of claim 1, wherein the patterned in-situ doping of indium is based on liquid metal. In step 2, the liquid metal is a gallium-indium liquid metal, a gallium-indium-tin alloy, a bismuth-indium alloy or a bismuth-tin alloy.

4. The method of claim 3, wherein: The proportion of gallium and indium in the gallium-indium liquid metal is 7:3, and the conductivity of the gallium-indium liquid metal ranges from 2.0*10 6 S / m-1.2*10 7 S / m.

5. The method of claim 1, wherein the patterned in-situ doping of indium for liquid metal flexible electronics is characterized by, In step 2, a low-temperature heating step is further included, and the mixture formed after the in-situ doping of the liquid metal and the patterned indium metal conductive material is placed in an oven at 20-100℃ for heating, and the duration is 2-10 minutes.

6. The method of claim 1, wherein the patterned in-situ doping of indium for liquid metal flexible electronics is characterized by, In step 2, the added mass of the patterned indium metal conductive material accounts for 5%-40% of the mass of the formed indium-based liquid metal.

7. The method of claim 1, wherein the patterned in-situ doping of indium for liquid metal flexible electronics is characterized by, In step 2, the following steps are further included: Step 2.

1. Selecting a flexible substrate and processing a groove thereon; Step 2.

2. Filling the liquid metal into the groove, and placing the patterned indium metal conductive material at the end of the groove, which is a set rigid-flexible interconnection point, and the patterned indium metal conductive material is doped with the liquid metal at the end; Step 2.

3. Placing in an oven at 20-100℃ for heating, and the duration is 2-10 minutes, and during the heating process, the indium metal diffuses in the liquid metal.

8. The method of claim 7, wherein the patterned in-situ doping of indium is based on liquid metal. In step 3, the following steps are further included: Step 3.

1. Forming an indium metal concentration gradient starting from the end point at the rigid-flexible interconnection point, and transitioning from the high-doping concentration region to the low-doping concentration region; and the undoped liquid metal in the groove forms a liquid metal wire, which is interconnected with the low-doping concentration region as a whole; and then immersing the rigid pin into the high-doping concentration region, so that the flexible liquid metal wire and the rigid chip are electrically interconnected through the rigid-flexible interconnection point.

9. The method of claim 8, wherein the patterned in-situ doping of indium is based on liquid metal. In step 3, the following steps are further included: Step 3.

2. Packaging the rigid-flexible electronic system obtained after the electrical interconnection; and the packaging material and the flexible substrate are both made of Ecoflex or PDMS elastic material.

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