Liquid metal rigid-flexible interconnection method based on patterned indium in-situ doping

Abstract

The invention discloses a liquid metal rigid-flexible interconnection method based on patterned indium in-situ doping, and belongs to the technical field of rigid-flexible interconnection. The method comprises the following steps: step 1, preparing a patterned indium metal conductive material; step 2, mixing the patterned indium metal conductive material with liquid metal, and carrying out in-situ doping, so that the patterned indium metal conductive material is dissolved in the liquid metal in situ to form indium-based liquid metal; 3, along with diffusion of the indium metal, an indium metal high-doping-concentration area and a low-doping-concentration area are formed in the indium-based liquid metal, the rigid pins are immersed in the high-doping-concentration area and the low-doping-concentration area to be interconnected with the liquid metal wire, and a rigid-flexible interconnection structure is formed. The Young modulus mismatching problem of the rigid chip and the flexible circuit system at the joint interface is well solved, the interconnection reliability is improved, the conductivity is high, and the processing technology is simple.

Description

Technical Field

[0001] The present invention belongs to the technical field of rigid-flexible interconnection, and in particular relates to a liquid metal rigid-flexible interconnection method based on patterned indium in-situ doping. Background Art

[0002] Soft and stretchable electronics are being widely used in next-generation electronic devices in emerging fields, including soft robotics, wearable electronics, 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] At present, the key components that give electronic products flexibility are stretchable electrodes and interconnects, and two main manufacturing methods are used. The first method is to achieve flexibility by selecting stretchable materials, and to use the conductivity and stretchability of the material itself to build a flexible system. Although flexible electronic devices can be prepared relatively simply in this way, the electrical conductivity of the flexible materials currently prepared is low, and there is still a gap with traditional metal materials, especially in high-performance applications such as fine circuits, which face great limitations. The second method is to achieve structural flexibility through standard metal materials, and to achieve bendable and stretchable effects by using the connection method and special structure of flexible and rigid materials. However, the preparation of these flexible materials with special structures requires special equipment and processes, and the cost is high and the process conditions are harsh. For example, the existing authorized 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 complicated, and there are problems such as unreliable interconnection and low conductivity due to excessive gradient differences. Summary of the Invention

[0004] To address these technical issues, the present invention proposes a liquid metal rigid-flexible interconnect method based on patterned indium in-situ doping. This method uses patterned indium metal for in-situ doping, creating a multi-contact concentration gradient that exhibits a state between solid and liquid, significantly improving interconnect reliability.

[0005] The technical solution adopted by the present invention is: A liquid metal rigid-flexible interconnection method based on patterned indium in-situ doping comprises the following steps: Step 1. preparing a patterned indium metal conductive material; Step 2. Mixing the patterned indium metal conductive material with the liquid metal and performing in-situ doping to dissolve the patterned indium metal conductive material in the liquid metal in-situ to form an indium-based liquid metal; Step 3. As indium metal diffuses, high-doping concentration areas and low-doping concentration areas of indium metal are formed in the indium-based liquid metal. The rigid pins are immersed in the high-doping concentration areas, and the low-doping concentration areas are interconnected with the liquid metal wires to form a rigid-flexible interconnection structure.

[0006] Preferably, in step 1: indium metal is used as raw material and 3D printing technology is used to prepare a patterned indium metal conductive material; the patterned indium metal conductive material is a tree-like structure or a coral-like structure, etc., 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.

[0007] The electrical conductivity of the above indium metal is 2.0×10 6 S / m to 1.8×10 7 S / m.

[0008] Preferably, the liquid metal is gallium-indium liquid metal, gallium-indium-tin alloy, bismuth-indium alloy or bismuth-tin alloy.

[0009] Preferably, the ratio of gallium-indium alloy in the gallium-indium liquid metal is 7:3, and the conductivity range of the gallium-indium liquid metal is 2.0×10 6 S / m-1.2×10 7 S / m. Gallium-indium liquid metal is more preferred, mainly because the high-purity indium metal and the gallium metal in the liquid metal are homogeneous metals, the two have similar chemical properties, and are easier to combine.

[0010] Preferably, step 2 further includes a low-temperature heating step, wherein the mixture formed by in-situ doping of the liquid metal and the patterned indium metal conductive material is placed in an oven at 20-100° C. and heated for 2 to 10 minutes.

[0011] 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.

[0012] Preferably, step 2 further includes the following steps: Step 2.1. Select a flexible substrate and machine grooves on it; Step 2.2. Fill the trench with liquid metal and place a patterned indium metal conductive material at the end of the trench, which is the designated rigid-flexible interconnection point. At this end, the patterned indium metal conductive material is doped with the liquid metal. Step 2.3. Place in an oven and heat at 20-100°C for 2 to 10 minutes. During the heating process, the indium metal diffuses in the liquid metal.

[0013] In step 2.1 above, the steps for processing the groove on the flexible substrate are as follows: The flexible substrate is laser etched with a laser scanning speed of 20-200 mm / s and a laser power of 10-25 W. The flexible substrate is cleaned and dried with alcohol to remove carbonized residue.

[0014] Preferably, step 3 further includes the following steps: Step 3.1. An indium metal concentration gradient starting from the endpoint is formed at the rigid-flexible interconnection point, and transitions from a high-doping concentration area to a low-doping concentration area; and the undoped liquid metal in the groove forms a liquid metal wire, which is interconnected with the low-doping concentration area as a whole; then the pins of the rigid chip are immersed in the high-doping concentration area, so that the flexible liquid metal wire and the rigid chip are electrically interconnected through the rigid-flexible interconnection point.

[0015] Preferably, step 3 further includes the following steps: Step 3.2. Encapsulate the resulting rigid-flexible electronic system after electrical interconnection. Both the encapsulation material and the flexible substrate are made of elastic materials such as Ecoflex or PDMS. Encapsulation methods include blade coating or spin coating.

[0016] The beneficial technical effects of the present invention are as follows: (1) The present invention provides a liquid metal rigid-flexible interconnection method based on in-situ doping of patterned indium metal. This method effectively solves the Young's modulus mismatch problem at the joint interface between rigid chips and flexible circuit systems, and increases the reliability of the interconnection, has high electrical conductivity, and is simple in processing technology.

[0017] (2) The present invention performs in-situ doping through patterned indium metal. As the indium metal dissolves and diffuses in the liquid metal, a multi-contact concentration gradient is formed, which increases the contact area and can show a state between solid and liquid, alleviating the Young's modulus mismatch phenomenon. The rigid-flexible interconnection interface based on liquid metal can effectively overcome the detachment and fracture phenomenon during the stretching process, significantly improve the stability and reliability of the interconnection, and enhance the service life and performance of the product after repeated stretching.

[0018] (3) The present invention adopts the method of dissolving and diffusing indium metal in liquid metal, which significantly enhances the adhesion of chip pins, thereby achieving reliable and stretchable electrical connections; and the use of rigid-flexible interconnection can manufacture a system with improved stretchability while maintaining stable mechanical properties, which can achieve arbitrary bending and extrusion.

[0019] (4) The present invention uses liquid metal doped with conductive materials, which has high conductivity and good repeatability. Moreover, the method has good wettability for different metals and has a wide range of applications. In addition, the method provided by the present invention has readily available materials, low cost, and is simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of an embodiment of the liquid metal rigid-flexible interconnection method based on patterned indium in-situ doping of the present invention; Figure 2 This is a flow chart for preparing rigid-flexible interconnection by in-situ doping of indium with liquid metal in the present invention; Figure 3 This is an enlarged schematic diagram of the rigid-flexible interconnection after the indium in-situ doping of liquid metal is completed in the present invention; Figure 4 Schematic diagram of the diffusion of indium in-situ doped liquid metal in the present invention; Figure 5 This is a graph showing the tensile performance test results of a simple flexible digital tube prepared in Example 1 of the present invention; Figure 6 This is a tensile test diagram of different doping concentrations in a simple flexible resistor test circuit prepared in Example 2 of the present invention; Figure 7 This is a tensile test diagram of a 20% doped rigid-flexible interconnect in Example 2 of the present invention; Figure 8 This is a cyclic tensile test diagram of a 20% doped rigid-flexible interconnect in Example 2 of the present invention; Figure 9 This is a graph showing the specific cyclic tensile test results of the 20% doped rigid-flexible interconnect in Example 2 of the present invention.

[0021] In the figure: 1-flexible substrate, 2-laser emitting device, 3-gallium indium liquid metal, 4-indium metal, 5-rigid electronic chip. DETAILED DESCRIPTION

[0022] The present invention discloses a liquid metal rigid-flexible interconnection method based on in-situ doping of patterned indium, which aims to solve the problem of degradation of interfacial bonding force between liquid metal flexible circuits and rigid chips due to Young's modulus mismatch. Under severe and repetitive conditions, this mismatch will cause the mechanical properties of the rigid-flexible system to drop sharply. To this end, the present invention proposes an innovative interconnection method, which forms a multi-contact concentration gradient by in-situ doping patterned indium metal at the interconnection points of the rigid-flexible system, such as tree-like, coral-like and other structures, thereby increasing the contact area and showing a state between solid and liquid, thereby effectively improving the Young's modulus mismatch phenomenon. In addition, it can enhance conductivity, improve repeatability and adhesion, and ensure the stability of the rigid-flexible interconnection interface. This method can not only ensure reliable mechanical properties between the liquid metal-based flexible circuit and the rigid chip, but also maintain the excellent electrical performance of the rigid-flexible hybrid electronic system.

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] like Figure 1As shown in FIG, a method for liquid metal rigid-flexible interconnection based on patterned indium in-situ doping includes the following steps: preparing a flexible substrate with patterns such as grooves based on laser etching, patterning liquid metal in-situ doping interconnect points, and assembling a rigid-flexible hybrid electronic system and flexible packaging. The detailed process is shown in FIG. Figure 2 shown.

[0025] First, the patterning of the flexible substrate based on laser etching includes the following steps: Step 1: Prepare a flexible substrate and select Ecoflex as the elastic substrate.

[0026] Step 2: Draw the pattern using software and import it into a laser engraving machine. Use the laser to scan and etch the entire area. The scanning speed is 100 mm / s, the laser power is 18 W, and the scanned area is carbonized.

[0027] Step 3: After laser etching is complete, the substrate is cleaned with alcohol and dried to remove carbonized residue. A 1mm deep groove is formed, and the patterned flexible substrate is complete.

[0028] Next, the process for preparing patterned liquid metal in-situ doped interconnects includes the following steps: 3D printing technology is used to prepare indium metal conductive materials with certain morphologies, such as tree-like structures and coral-like 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.

[0029] The liquid metal is filled into the patterned flexible substrate grooves, and this step is repeated several times until they are fully filled.

[0030] Conductive materials are placed at the rigid-flexible interconnection points of the liquid metal in different proportions for doping, thereby obtaining indium-based liquid metals containing different in-situ doping proportions.

[0031] In this embodiment, patterned high-purity indium metal is used as the conductive material, which is soft and has a conductivity of 2.0×10 6 S / m to 1.8×10 7 S / m.

[0032] The liquid metal used in the present invention is preferably an amorphous, flowable liquid metal, such as gallium-indium liquid metal, wherein 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.

[0033] Of course, liquid metal is not limited to gallium-indium liquid metal, but also includes gallium-indium-tin alloy, bismuth-indium alloy, bismuth-tin alloy, etc.

[0034] The entire doping process is carried out at a low temperature of 20-100°C, which accelerates the doping process.

[0035] Figure 4 Microscopic diagram of liquid metal doped with conductive materials.

[0036] Finally, the assembly of the rigid-flexible hybrid electronic system and the flexible packaging are carried out, which includes the following steps: Flexible liquid metal circuits and rigid chips are electrically interconnected through interconnection points, and local amplification structures such as Figure 3 shown.

[0037] In the present invention, the packaging material of the rigid-flexible hybrid electronic system is preferably the flexible material Ecoflex, and the rigid chip used is a chip required for the rigid-flexible hybrid electronic system to achieve a certain function.

[0038] Of course, PDMS can also be used as the packaging material, which has low cost and excellent stretchability.

[0039] The rigid-flexible interconnection method of the present invention will be described in more detail below with reference to specific embodiments.

[0040] Example 1 The present invention is based on a method for forming a gradient rigid-flexible interconnection by in-situ doping of patterned indium with liquid metal, and comprises the following steps: (1) Obtaining a patterned flexible substrate; (1-1) Prepare Ecoflex flexible substrate. Mix Ecoflex A solution and Ecoflex B solution in a mass ratio of 1:1, then spin-coat the mixture on the mold at a speed of 50 rad / min for 30 seconds and heat in an oven for 30 minutes.

[0041] (1-2) The flexible substrate is laser etched. A pattern is drawn using software and imported into a laser engraving machine. The entire area is scanned and etched using a laser at a scanning speed of 200 mm / s and a laser power of 20 W.

[0042] (1-3) After laser etching, the substrate is cleaned with alcohol and dried to remove carbonized residue. A 1.5 mm deep groove is formed, and the patterned flexible substrate is complete.

[0043] (2) Preparation process of rigid-flexible interconnection points: (2-1) Gallium-indium liquid metal with a gallium-indium alloy ratio of 7:3 is filled into the laser-etched grooves until they are completely filled.

[0044] (2-2) 3D printing technology is used to prepare patterned indium metal conductive materials, such as tree-like structures and coral-like structures.

[0045] (2-3) Place the sample in a 70°C oven and heat it at low temperature for 4 min to form a gradient concentration diffusion starting from the endpoint.

[0046] (3) Assembling rigid LED digital tubes with flexible electronic circuits and performing flexible packaging; (3-1) Bonding the rigid LED digital tube to the prepared liquid metal interconnection points to obtain a rigid-flexible electronic system.

[0047] (3-2) The rigid-flexible electronic system is encapsulated using Ecoflex high-elasticity material. The encapsulation method can be either blade coating or spin coating. After encapsulation, the entire liquid metal elastic electrode or circuit is prepared by maskless printing. Through these steps, a simple flexible digital tube is obtained.

[0048] Example 2 The present invention is based on a liquid metal rigid-flexible interconnection method using patterned indium in-situ doping, comprising the following steps: (1) Obtaining a patterned flexible substrate; (1-1) A flexible substrate is prepared, wherein the flexible substrate is PDMS. The substrate and curing agent are mixed in a mass ratio of 10:1, and then spin-coated on a mold at a speed of 50 rad / min for 30 seconds, and then heated in an oven at 65°C for 90 minutes.

[0049] (1-2) Laser etching the flexible substrate: The pattern is drawn using software and imported into a laser engraving machine. The laser is used to scan and etch the entire area. The scanning speed is 50 mm / s and the laser power is 15W.

[0050] (1-3) After laser etching, the substrate is cleaned with alcohol and dried to remove carbonized residue. A 1 mm deep groove is formed, and the patterned flexible substrate is complete.

[0051] (2) Preparation process of rigid-flexible interconnection points: (2-1) Fill the laser-etched grooves with liquid metal containing a gallium-indium alloy ratio of 7:3 until they are completely filled.

[0052] (2-2) Patterned indium metal conductive materials, such as tree-like structures and coral-like structures, were prepared using 3D printing technology. The doping ratios were 0% (i.e., undoped), 10%, 20%, 30%, and 40%, respectively.

[0053] (2-3) Place the sample on a 40°C heating platform and perform low-temperature heating for 7 min to form a gradient concentration diffusion with multiple contact points.

[0054] (3) Assembling rigid resistor chips and flexible electronic circuits and performing flexible packaging; (3-1) 50Ω, 460Ω, and 1.5kΩ rigid resistor chips are bonded to the prepared liquid metal interconnects to obtain a rigid-flexible electronic system.

[0055] (3-2) The rigid-flexible electronic system is encapsulated using the same highly elastic PDMS material. The encapsulation method can be either blade coating or spin coating. After encapsulation, the entire liquid metal circuit is fabricated using maskless printing.

[0056] Through the above steps, a simple flexible resistor test circuit is obtained.

[0057] The performance test of the rigid-flexible interconnect structure obtained in the above embodiment is as follows: The tensile performance test of the simple flexible digital tube test circuit prepared in Example 1 was carried out. Figure 5 shown. Figure 5 0% liquid metal means pure liquid metal with a stretching amount of 0%, 100% indium-based liquid metal means 10% indium-doped liquid metal with a stretching amount of 100%, and so on. Figure 5 As can be seen in the figure, within a wide strain range of 0%-500%, the resistance change of the sample using the interconnection method of the present invention is significantly smaller than that of the conventional method, and the LED brightness remains stable. In contrast, as can be seen in the invention patent CN 115175449 A, the maximum stretching capacity is only 200%, demonstrating that the method of the present invention has superior mechanical stability and electrical reliability.

[0058] The flexible resistor test circuits with different doping concentrations in Example 2 were tested. Figure 6 shown. Figure 6 In the figure, 0%, 10%, 20%, 30%, and 40% doping represent liquid metals doped with different amounts of indium metal. Figure 6 The data showed that while the undoped device fractured at 150% strain, the indium in-situ doped circuit exhibited minimal resistance fluctuations over a strain range of 0% to 400%. In particular, samples with 20% and 30% doping ratios exhibited the best electromechanical coupling performance.

[0059] Further extreme tests on 20% doped flexible resistor circuits revealed that Figure 7As shown in the figure, under tensile strain of up to 600%, the three types of different resistance circuits can still maintain stable electrical connections. To verify the long-term performance, a 100% strain cycle test was performed on a 2cm long sample. Figure 8 and Figure 9 As shown, the device maintains good durability after 1500 stretching cycles.

[0060] The above experimental results fully demonstrate that the method proposed in this invention has significant advantages and application potential in constructing highly stretchable rigid-flexible hybrid electronic systems. It should be noted that this technical solution is not limited to the examples listed above; any equivalent replacement or improvement based on this technical concept falls within the scope of protection of this invention.

Claims

1. A liquid metal rigid-flexible interconnection method based on patterned indium in-situ doping, characterized in that The following steps are involved: Step 1. preparing a patterned indium metal conductive material; Step 2. Mixing the patterned indium metal conductive material with the liquid metal and performing in-situ doping to dissolve the patterned indium metal conductive material in the liquid metal in-situ to form an indium-based liquid metal; Step 3. As indium metal diffuses, high-doping concentration areas and low-doping concentration areas of indium metal are formed in the indium-based liquid metal. The rigid pins are immersed in the high-doping concentration areas, and the low-doping concentration areas are interconnected with the liquid metal wires to form a rigid-flexible interconnection structure.

2. The method for liquid metal rigid-flexible interconnection based on patterned indium in-situ doping according to claim 1, characterized in that: In step 1: using indium metal as a raw material, a patterned indium metal conductive material is prepared by using 3D printing technology; the patterned indium metal conductive material has a tree-like structure or a coral-like structure.

3. The method for liquid metal rigid-flexible interconnection based on patterned indium in-situ doping according to claim 2, characterized in that: The electrical conductivity of the indium metal is 2.0×10 6 S / m to 1.8×10 7 S / m.

4. The method for liquid metal rigid-flexible interconnection based on patterned indium in-situ doping according to claim 1, characterized in that: In step 2: the liquid metal is gallium-indium liquid metal, gallium-indium-tin alloy, bismuth-indium alloy or bismuth-tin alloy.

5. The method for liquid metal rigid-flexible interconnection based on patterned indium in-situ doping according to claim 4, characterized in that: The ratio of gallium-indium alloy in the gallium-indium liquid metal is 7:3, and the conductivity range of the gallium-indium liquid metal is 2.0×10 6 S / m-1.2×10 7 S / m.

6. The method for liquid metal rigid-flexible interconnection based on patterned indium in-situ doping according to claim 1, characterized in that: Step 2 also includes a low-temperature heating step, in which the mixture formed by in-situ doping of the liquid metal and the patterned indium metal conductive material is placed in an oven at 20-100° C. and heated for 2 to 10 minutes.

7. The method for liquid metal rigid-flexible interconnection based on patterned indium in-situ doping according to claim 1, characterized in that: In step 2, 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.

8. The method for liquid metal rigid-flexible interconnection based on patterned indium in-situ doping according to claim 1, characterized in that: Step 2 also includes the following steps: Step 2.

1. Select a flexible substrate and machine grooves on it; Step 2.

2. Fill the trench with liquid metal and place a patterned indium metal conductive material at the end of the trench, which is the designated rigid-flexible interconnection point. At this end, the patterned indium metal conductive material is doped with the liquid metal. Step 2.

3. Place in an oven and heat at 20-100°C for 2 to 10 minutes. During the heating process, the indium metal diffuses in the liquid metal.

9. The method for liquid metal rigid-flexible interconnection based on patterned indium in-situ doping according to claim 8, characterized in that: Step 3 also includes the following steps: Step 3.

1. An indium metal concentration gradient starting from the endpoint is formed at the rigid-flexible interconnection point, and transitions from a high-doping concentration area to a low-doping concentration area; and the undoped liquid metal in the groove forms a liquid metal wire, which is interconnected with the low-doping concentration area as a whole; then the pins of the rigid chip are immersed in the high-doping concentration area, so that the flexible liquid metal wire and the rigid chip are electrically interconnected through the rigid-flexible interconnection point.

10. The method for liquid metal rigid-flexible interconnection based on patterned indium in-situ doping according to claim 9, characterized in that: Step 3 also includes the following steps: Step 3.

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

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