A method for manufacturing and application of liquid metal internal circuit

Abstract

The application belongs to the technical field of circuits, and provides a preparation method and application of a liquid metal internal circuit. The preparation method comprises the following steps: placing spherical magnetic particles coated with a low-surface-energy film in a substrate on the inner wall of which liquid metal ink is printed, and applying a magnetic field to perform moving sintering to obtain the liquid metal internal circuit. In the preparation method of the liquid metal internal circuit, the flowability of the liquid metal ink can enable the liquid metal ink to be adsorbed on an internal non-two-dimensional surface, thereby solving the problem of conformability. In addition, the method of directly creating a circuit in the interior avoids the troubles and losses in the transfer process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of circuit, in particular to a preparation method and application of liquid metal internal circuit. BACKGROUND

[0002] Circuit usually needs to be protected to maintain the stability of the entire system, so it is considered to be a generally feasible method to be placed inside the object. However, some conventional methods are complex and take up a lot of space when placing wires inside the object. The conventional method of making liquid metal circuit is difficult to perform inside the object. Mainly because the traditional mechanical sintering method is difficult to put the sintering tool into the object, and the field sintering which can penetrate is difficult to perform high-resolution selective sintering.

[0003] The current commonly used means of internal circuit includes extrusion coating process, that is, the molten plastic material is uniformly wrapped on the surface of the copper wire through the extruder, and then the wire can be stretched into the object. However, this process is not directly formed inside the object, which leads to that in some internal non-flat structures, due to the characteristics of its interlaced complexity, it is not conducive to the arrangement of multiple circuits. In addition, this method will occupy a large amount of internal space. For the currently widely used technology of printed circuit board, the circuit can be made on the PCB board and integrated in many electronic devices. However, they are usually based on rigid substrates, and with the development of technology, more and more flexible electronic demand scenarios appear, and the demand for circuit making is no longer limited to two-dimensional rigid materials but curved / flexible materials. Magnetic liquid metal can be used to make circuits on the surface of the object inside the liquid metal by adding magnetic particles, and can also be used on non-two-dimensional internal surfaces and flexible materials, but due to its inherent magnetic properties, it is not suitable for combination with other circuits / electronic components. SUMMARY

[0004] The present application aims to at least solve one of the above technical problems in the prior art. To this end, the purpose of the present application is to provide a preparation method and application of liquid metal internal circuit.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present application is:

[0006] The first aspect of the present application provides a preparation method of liquid metal internal circuit, comprising the following steps:

[0007] The spherical magnetic particles coated with a low-surface-energy film are placed in the substrate printed with liquid metal ink on the inner wall, and a magnetic field is applied for moving sintering to obtain the liquid metal internal circuit.

[0008] In the present application, the liquid metal ink is printed on the inner wall of the substrate, and then a magnetic field is applied to the magnetic iron particles to guide the orientation. Under the action of positive pressure and friction force, the oxide film between the liquid metal ink droplets is broken and crushed in a polishing-like manner, so that a conductive network is formed between the liquid metal droplets, and the circuit creation based on magnetic control sintering is realized. Furthermore, in the present application, a low surface energy film is coated on the surface of the spherical magnetic particles, which can not only reduce the surface energy of the iron particles, but also effectively prevent the spherical magnetic particles from being covered with dust or liquid metal during polishing, which can change the spherical shape and affect the formation of uniform circuits. The present application uses conductive ink as a liquid with flow properties, which can be adsorbed on the internal non-two-dimensional surface of the substrate, avoiding the difficulty of patterning the internal non-two-dimensional surface of the object, and realizing the conformalization of the circuit on the internal surface. In addition, the present application directly creates a circuit on the internal surface, avoiding the loss and trouble in the transfer process.

[0009] In some embodiments, a magnetic field is applied to guide the directional movement sintering of the spherical magnetic particles.

[0010] In some embodiments, the spherical magnetic particles include spherical magnetic metal particles; and the magnetic metal includes any one of iron, cobalt, iron-cobalt alloy, nickel, iron-nickel alloy, soft magnetic ferrite, hard magnetic ferrite, neodymium iron boron, and samarium cobalt.

[0011] In some embodiments, the average particle size of the spherical magnetic particles is 1 µm-5 mm, such as 1 µm-3 mm, 1 µm-2 mm, 100 µm, 300 µm, 500 µm, 800 µm, 1 mm, 2 mm, etc. In the present application, the spherical magnetic particles with appropriate diameter can be selected for movement sintering according to the required circuit line width.

[0012] In some embodiments, the low surface energy film includes any one of polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVDF), polytetrafluoroethylene (FEP), fluororubber, polyether ether ketone (PEEK), polyimide (PI), and ultra-high molecular weight polyethylene (UHMWPE).

[0013] In some embodiments, the strength of the magnetic field is 1.0-2.0 T, such as 1.0-1.8 T, 1.0-1.5 T, 1.1-1.3 T, 1.18-1.23 T, etc. In the present application, the appropriate magnetic field strength can be selected to guide the orientation of the magnetic particles according to the size of the magnetic particles.

[0014] In some embodiments, the liquid metal ink includes liquid metal, dispersant, and solvent.

[0015] In some embodiments, the liquid metal ink has a mass-volume concentration of the liquid metal of 1.0-5.0 g / mL, such as 1.0-4.0 g / mL, 1.0-3.0 g / mL, 2.0-3.0 g / mL, etc.

[0016] In some embodiments, the liquid metal ink has a mass percentage of the dispersant of 0.1-1.0%, such as 0.1-0.8%, 0.1-0.5%, 0.1-0.4%, 0.1-0.3%, etc.

[0017] In some embodiments, the liquid metal includes at least one of a gallium-indium alloy, a gallium-indium-tin alloy, a gallium-indium-tin-zinc alloy, a gallium-indium-zinc-tin-bismuth alloy, and a gallium-bismuth alloy. In the present application, a suitable liquid metal ink can be selected according to the actual circuit application scenario.

[0018] In some embodiments, the dispersant includes at least one of polyvinylpyrrolidone (PVP), hydroxyethyl cellulose (HEC), polyvinyl alcohol, polyethylene oxide, and polyacrylamide. In the present application, the dispersant disperses the droplets by steric hindrance.

[0019] In some embodiments, the liquid metal ink further includes a surfactant; the liquid metal ink has a mass percentage of the surfactant of 0.1-1.0%, such as 0.1-0.8%, 0.1-0.5%, 0.1-0.4%, 0.1-0.3%, etc.

[0020] In some embodiments, the surfactant includes at least one of Triton X-100, a block polyether, a sorbitan fatty acid ester, and a sorbitan fatty acid ester polyoxyethylene ether. In the present application, the surfactant can reduce the surface energy of the droplets.

[0021] In some embodiments, the solvent includes at least one of water, ethanol, ethylene glycol, and dimethylformamide (DMF).

[0022] In some embodiments, the substrate includes any one of a rigid material, a fiber, and an elastomer.

[0023] In some embodiments, the liquid metal ink is poured into the interior of the substrate to cover the target circuit creation position.

[0024] In some embodiments, the method for preparing the internal circuit of the liquid metal further includes surface protection of the internal circuit.

[0025] In some embodiments, the internal circuit is surface-protected by silica gel.

[0026] In some embodiments, the surface protection specifically includes the following steps: applying a silica gel to the interior circuit surface, and curing.

[0027] In some embodiments, the silica gel includes at least one of polydimethylsiloxane (PDMS), platinum silica gel, polyurethane resin, fiber-reinforced composite (such as the solaris series of Smooth-on).

[0028] In a second aspect of the present application, a liquid metal interior circuit is provided, which is prepared by the method for preparing the liquid metal interior circuit.

[0029] In some embodiments, the liquid metal interior circuit has a linear fitting R-square value of 0.90-0.99, such as 0.92-0.99, 0.93-0.99, 0.94-0.99, 0.95-0.99, 0.96-0.99, 0.97-0.99, 0.98-0.99, etc., for the change of resistance with the length of the circuit.

[0030] In some embodiments, the liquid metal interior circuit has an average line width of 1 µm-5 mm, such as 1 µm-3 mm, 1 µm-2 mm, 100 µm, 300 µm, 500 µm, 800 µm, 1 mm, 2 mm, etc.

[0031] In some embodiments, the liquid metal interior circuit has an average line thickness of 10-500 µm, such as 50-500 µm, 50-400 µm, 50-300 µm, 50-200 µm, 60 µm, 70 µm, 80 µm, 90 µm, 100 µm, 120 µm, 140 µm, 160 µm, 180 µm, etc.

[0032] In some embodiments, the liquid metal interior circuit surface is further covered with a silica gel protective layer.

[0033] In some embodiments, the silica gel protective layer has an average thickness of 200 µm -5 mm, such as 500 µm -3 mm, 1 mm-3 mm, etc.

[0034] In some embodiments, the silica gel includes at least one of polydimethylsiloxane (PDMS), platinum silica gel, polyurethane resin, fiber-reinforced composite (such as the solaris series of Smooth-on).

[0035] In a third aspect of the present application, a device is provided, which includes the liquid metal interior circuit.

[0036] In some embodiments, the device includes a semiconductor, a wearable electronic device, a minimally invasive electronic device, a biosensor, a pattern display.

[0037] The present application has the following advantages:

[0038] In the preparation method of the liquid metal internal circuit, small magnetic particles are used to replace macroscopic objects as sintering tools, so that the internal object can be entered without additional pre-patterning, and selective sintering can be directly performed.

[0039] In the preparation method of the liquid metal internal circuit, the fluidity of the liquid metal ink can make it adsorbed on the internal non-two-dimensional surface, solving the problem of conformability. In addition, the method of directly creating a circuit in the interior avoids the trouble and loss in the transfer process.

[0040] The preparation method of the liquid metal internal circuit only fits the internal surface, and the prepared internal circuit has small thickness, realizes ultra-high space utilization, and can enter into very small space.

[0041] The liquid metal internal circuit of the present application has very high uniformity, and the circuit can still maintain circuit conduction when subjected to extreme damage such as scratching, shearing or even hole punching, mainly because when subjected to extreme damage, the conductive percolation network of the internal liquid metal droplets will spontaneously reconfigure to maintain circuit conduction self-healing. This good self-healing will further improve the universality of the method, and has great prospects in risk areas such as space, disaster relief, unknown area exploration, etc.

[0042] The liquid metal internal circuit of the present application is inside the base body, and when observed from the external surface of the base body, it is completely "invisible", while being able to bear the functions related to the circuit and a part of the sensing functions, and has great development prospects. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The figure is a schematic diagram of the preparation principle of the liquid metal ink of the embodiment of the present application.

[0044] Figure 2 The figure is a schematic diagram of the conformability process of the liquid metal ink of the embodiment of the present application in the internal surface of the base body.

[0045] Figure 3 The figure is a schematic diagram of the magnetic control sintering mechanism of the embodiment of the present application.

[0046] Figure 4 The figure is a schematic diagram of the internal circuit prepared by different liquid metal inks of the embodiment 1 to the embodiment 3 of the present application.

[0047] Figure 5 The figure is a schematic diagram of the internal circuit creation based on magnetic control sintering in the embodiment 4 of the present application.

[0048] Figure 6 The figure is an AFM graph of the sintered region and the unsintered region of the internal circuit in the embodiment 1 of the present application.

[0049] Figure 7 This is a diagram showing the thickness of the internal circuit lines in Embodiment 1 of the present invention.

[0050] Figure 8 These are the resistance values ​​for different lengths of the internal circuit in Embodiment 1 of the present invention.

[0051] Figure 9 The results of the self-healing test of the internal circuit in Embodiment 1 of the present invention are shown, where a is the self-healing mechanism and its schematic diagram; b is the resistance change when subjected to scratches, shearing, cutting and puncture. Detailed Implementation

[0052] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments and comparative examples are all available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the test or experimental methods are conventional methods in the art.

[0053] Example 1

[0054] This embodiment fabricates a liquid metal internal circuit, the specific process of which is as follows:

[0055] a) Preparation of eutectic gallium indium ink: such as Figure 1 As shown, a PVP solution was first prepared at a ratio of 1 gram of PVP (polyvinylpyrrolidone): 10 milliliters of ethanol. A dispersant mixture was then prepared at a ratio of 10 grams of PVP: 100 milliliters of ethanol: 1 milliliter of trihexyphenidate. In centrifuge tubes, eutectic gallium-indium alloy (Ga 75.5% / In 24.5%) and the PVP solution were added at a ratio of 8 grams: 1 milliliter. After ultrasonication in a water bath for 1 minute, the dispersant mixture was added at a ratio of 8 grams: 1 milliliter, and ultrasonication continued for 4 minutes to obtain uniformly dispersed micron-sized eutectic gallium-indium ink.

[0056] b) Iron particle modification: Based on the desired circuit linewidth, select iron particles with a diameter of 1 mm, immerse them in a low-temperature curing pure PTFE solution, and stir continuously for 24 hours until the PTFE on the surface of the iron particles is cured into a film.

[0057] c) such as Figure 2 The diagram shows how to pour the obtained eutectic gallium indium ink into the bottle from the bottle opening, adjust the angle so that the ink flows over the inner wall of the bottle, pour out the excess ink, and wait for one minute until the ethanol evaporates and dries.

[0058] d) Magnetron sintering: The modified iron particles are placed into the bottle from the mouth, and the bottle is placed on a double-rail slide with a conical magnet installed (providing a magnetic field strength of 1.17 T). The double-rail slide is started, the target circuit pattern is imported, and the iron particles are moved and sintered by using the magnetic field to guide the direction.

[0059] Figure 3 A schematic diagram of the magnetic control sintering mechanism is shown. The magnetic control sintering method of the present application utilizes the concentrated magnetic field of a conical magnet to control modified iron particles of different sizes to replace traditional macroscopic objects, and to break and crush the oxide film between liquid metal droplets in a polishing-like manner through the directional guidance of the magnetic field concentration, so that an electrically conductive network is formed between the liquid metal droplets, and internal circuit creation based on magnetic control sintering is achieved.

[0060] Example 2

[0061] In this example, a liquid metal internal circuit is prepared. The specific preparation method is referred to Example 1, and the only difference is that the gallium-indium alloy Ga 75.5% / In 24.5% is replaced by the gallium-bismuth alloy Ga 99.7% / Bi 0.3%.

[0062] Example 3

[0063] In this example, a liquid metal internal circuit is prepared. The specific preparation method is referred to Example 1, and the only difference is that the gallium-indium alloy Ga 75.5% / In 24.5% is replaced by the gallium-indium-tin alloy Ga 68.5% / In 21.5% / Sn 10%.

[0064] Figure 4 The circuit physical map prepared in Examples 1 to 3 is shown. It can be seen that different liquid metal inks can achieve magnetic control sintering to prepare circuits.

[0065] Example 4

[0066] In this example, a liquid metal internal circuit is prepared. The specific preparation method is referred to Example 1, and the only difference is that the gallium-indium alloy Ga 75.5% / In 24.5% is replaced by the gallium-bismuth alloy Ga 99.7% / Bi 0.3%.

[0067] As shown in Figure 5 , the preparation method of Example 1 is referred to, and the only difference is that a transparent cup is used as the substrate, and the corresponding tool path file is input for magnetic control sintering.

[0068] Test Example

[0069] Figure 6 The sintered and unsintered regions of the liquid metal internal circuit prepared in Example 1 are shown by atomic force microscopy (AFM). It can be seen that the sintered liquid metal droplets, i.e. the dark blue part, have been crushed and broken compared to the light blue part, and this part assumes the conductive performance, and the conductive path line width is about 30 microns.

[0070] The liquid metal ink of Example 1 is coated on a 1 mm thick glass sheet, and after it solidifies, the ink thickness is tested, and the results are shown in Figure 7 . It can be seen that the liquid metal ink can be adsorbed on the glass sheet, and the thickness is about 120 microns. It can be seen that the circuit of the present application has high space utilization.

[0071] Different length sample resistance test: for the liquid metal circuit obtained in Example 1, a multimeter is used to measure the resistance, the two levels of the multimeter are respectively contacted with the two ends of the sample with a measured length, the resistance reading is obtained, the test is repeated five times to take the average to reduce the measurement error, and the resistance under the length is obtained. The above test is performed on the target length of 1-9 cm, and the data graph is as shown in Figure 8 .

[0072] The results are shown in Figure 8 , the resistance of the sample prepared in Example 1 changes with a very high linearity, and the R-square value of linear fitting reaches 0.9845.

[0073] Self-healing test: the liquid metal circuit is prepared according to the method described in Example 1, and the difference is that the substrate is replaced with a flat PDMS elastomer to facilitate the shooting to show its self-healing property.

[0074] An LED small light is placed in the middle of the circuit and the unsintered area, and the left and right ends of the circuit are connected to the power supply. It is observed that the LED small light on the sintered circuit is on and the small light in the unsintered area is not on, as shown in Figure 9 (a). Subsequently, a paper cutter, scissors, a hole puncher and the like are used to apply extreme damage to the circuit, and the resistance value is recorded, and the resistance change is as shown in Figure 9 (b). This is because when receiving extreme damage, the liquid metal droplets spontaneously reconfigure the conductive path and re-form the conductive network due to the extreme damage force, and the conductive property can still be self-healed, and the circuit is stable.

[0075] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods, and are all included in the protection scope of the present application.

Claims

1. A method of fabricating a liquid metal interconnect, the method comprising: The method comprises the following steps: ​ The spherical magnetic particles coated with low surface energy film are placed in the substrate printed with liquid metal ink on the inner wall, and a magnetic field is applied for moving sintering to obtain the liquid metal internal circuit. The liquid metal ink comprises liquid metal, dispersant and solvent. The strength of the magnetic field is 1.0-2.0T.

2. The method of claim 1, wherein: The spherical magnetic particles comprise spherical magnetic metal particles.

3. The method of claim 2, wherein: The magnetic metal comprises any one of iron, cobalt, iron-cobalt alloy, nickel, iron-nickel alloy, soft magnetic ferrite, hard magnetic ferrite, neodymium-iron-boron, samarium-cobalt.

4. The method of claim 1, wherein: The average particle size of the spherical magnetic particles is 1µm-5mm.

5. The method of claim 1, wherein: The low surface energy film comprises any one of polytetrafluoroethylene, polyvinyl fluoride, polyperfluoroethylene propylene, fluororubber, polyether ether ketone, polyimide, ultrahigh molecular weight polyethylene.

6. The method of claim 1, wherein: The liquid metal ink further comprises a surfactant; the mass fraction of the surfactant in the liquid metal ink is 0.1 1.0%.

7. The method of claim 6, wherein: The liquid metal comprises at least one of gallium-indium alloy, gallium-indium-tin alloy, gallium-indium-tin-zinc alloy, gallium-indium-zinc-tin-bismuth alloy, gallium-bismuth alloy.

8. The method of claim 1, wherein: The substrate comprises any one of hard, fiber, elastomer.

9. A method of producing a liquid metal interconnect according to any one of claims 1 to 8, characterised in that: The preparation method of the liquid metal internal circuit further comprises surface protection of the internal circuit.

10. A liquid metal interconnect, comprising: The liquid metal internal circuit is prepared by the preparation method comprising any one of claims 1-9.

11. The liquid metal interconnect of claim 10, wherein: The liquid metal internal circuit satisfies at least one of the following conditions: (I) The linear fitting R square value of the resistance of the liquid metal internal circuit changing with the length of the circuit is 0.90-0.99; (II) The average line width of the liquid metal internal circuit is 1µm-5mm; (III) The average line thickness of the liquid metal internal circuit is 10-500µm.

12. An apparatus, comprising: The liquid metal internal circuit comprises any one of claims 10 or 11.

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