KR101647023B1 - Stretchable circuit board and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a stretchable circuit board and a manufacturing method thereof, and more specifically, to a stretchable circuit board and a manufacturing method thereof having stretchability which can be extendable beyond flexibility that a flexible substrate has, and maintaining mechanical and electrical characteristics despite a big deformation such as bending and twisting. According to the present invention, the stretchability to the degree, that a polymer substrate has, can be secured by a liquid metal pattern by virtue of a wetting phenomenon of a liquid metal plated on a metal pattern of a substrate surface. Thus, the present invention can provide a stretchable circuit substrate capable of simultaneously achieving mechanical and electrical performances despite a physical deformation such as bending, stretching and twisting. Accordingly, there is an effect of realizing a wearable haptic interface, a stretchable solar cell array, a stretchable display and a wearable electronic device.

Description

TECHNICAL FIELD [0001] The present invention relates to a stretchable circuit board and a method of manufacturing the same.

The present invention relates to a flexible circuit board and a method of manufacturing the flexible circuit board. More particularly, the present invention relates to a flexible circuit board and a method of manufacturing the same. More particularly, the present invention relates to a flexible circuit board and a method of manufacturing the same. The present invention relates to a flexible circuit board and a method of manufacturing the same.

Printed circuit board (PCB) is a thin printed copper wiring board, which is used to connect various components such as semiconductor, condenser, and resistor. It is an electronic component that interconnects components. do.

BACKGROUND OF THE INVENTION As a carrier of integrated circuits (ICs), printed circuit boards (PCBs) have been used extensively in flat, electronic devices. However, since the human body and nature are formed in a smooth curved shape, a flexible printed circuit board (PCB) is limited in its application.

As a result, development of a flexible substrate having flexibility capable of flexing in order to put the wearable device into practical use as a next-generation smart device that overcomes the inconsistency between the non-skewed plane and the smooth curve has been actively developed.

As a conventional method of manufacturing a flexible substrate, a method of depositing a metal on the surface of a substrate having flexibility is used. That is, conventionally, a metal such as gold (Au), platinum (Pt), silver (Ag) or the like is vapor-deposited on the surface of a substrate such as PDMS, silicone rubber or acrylic rubber to form a pattern on the surface of the deposited metal thin film Thereby producing a flexible circuit board.

However, the circuit board thus fabricated has a stable electrical property under bending deformation, but under the tensile strain of 10% or more, the metal pattern layer is peeled off from the surface of the flexible substrate, and the electrical conductivity is deteriorated.

Conventionally, a carbon nanotube (CNT), carbon black (CB), graphite and the like are mixed with a polymer and a circuit pattern is formed by using a conductive material, whereby the peeling problem between the metal layer and the elastic substrate Respectively. However, the flexible circuit board thus manufactured has the advantage of showing stable electrical properties even under tensile strain of 100% or more, but has a problem of low electrical conductivity.

Recently, Wagner et al. And Rogers et al. Have reported a variety of flexible electronic devices based on a wavy pattern of wavy shapes. The flexible electronic device embodying the flexible electronic device has a problem in that it requires a complex process in manufacturing because it needs to make a wavy pattern.

Related prior arts include Korean Patent Laid-Open No. 10-2010-0123755 (an electronic device that can be folded and folded), Korean Patent Laid-Open No. 10-2014-0121325 (an elastic electronic circuit and a manufacturing method thereof), and the like.

The present invention seeks to provide a flexible circuit board in which mechanical and electrical characteristics are maintained even under bending and tensile strain, and a method of manufacturing the same.

The present invention also provides a flexible circuit board which is easy to manufacture and a method of manufacturing the same.

It is another object of the present invention to provide a flexible circuit board capable of facilitating patterning and a manufacturing method thereof.

According to an aspect of the present invention, there is provided a method of manufacturing a flexible circuit board, comprising: (a) forming a first polymer layer on a surface of a wafer; (B) coating the surface of the first polymer layer with a metal film to form a pattern; (C) plating a liquid metal on the pattern; And (d) removing the wafer. In this case, the step (c) according to the present invention is performed by using the property of the liquid metal having different wettability depending on the material of the surface to be adsorbed.

Preferably, (a) according to the present invention can form a first polymer layer by applying polydimethylsiloxane (PDMS) to the surface of the wafer.

Preferably, step (b) according to the present invention further comprises the step of forming a first polymer layer on the surface of the first polymer layer by depositing gold, chromium, silver, aluminum, copper, platinum, A metal selected from the group consisting of zinc (Zn), nickel (Ni), tin (Sn), iron (Fe), and combinations thereof.

Preferably, the liquid metal used in step (c) according to the present invention may be gallstones of gallium, indium and tin.

Preferably, the step (c) according to the present invention further comprises: an oxide film removing step of reducing the liquid metal by the vapor of the acid solution; And plating the reduced liquid metal to a pattern after the oxide film removing step. In this case, the reduced liquid metal has a characteristic of being more wettable on the surface of the metal material than the polymer material.

Preferably, the oxide film removing step according to the present invention may reduce the liquid metal by the vapor of any one of hydrochloric acid (HCl), hydrofluoric acid (HF), nitric acid (HNO ₃ ) and sulfuric acid (H ₂ SO ₄ ).

Preferably, the oxide layer removal step according to the present invention may reduce the liquid metal using a vapor of an acid solution having a concentration range of 15 wt.% To 40 wt.%.

Preferably, the step (c) according to the present invention is a step of selectively rolling a liquid metal in a droplet form on a surface of a patterned metal film and a non-patterned polymer to a desired region .

Preferably, step (c) according to the present invention may roll the liquid metal for 5 to 30 seconds.

Preferably, the step (b) according to the present invention comprises: a coating step of coating a metal film on the surface of the first polymer layer; And a pattern forming step of forming a pattern of a relief by etching the metal film after the coating step.

Preferably, the coating step according to the present invention comprises the steps of: coating chromium (Cr) on the surface of the first polymer layer to form a chromium layer; And coating gold (Au) over the chromium layer.

Preferably, after step (c) according to the present invention, optionally further comprises forming a second polymer layer on the surface of the plated liquid metal.

The present invention also provides a method of manufacturing a semiconductor device, comprising: (a) coating a surface of a wafer with a metal film to form a pattern; And (b) plating the liquid metal having different wettability depending on the material of the surface adsorbed on the pattern.

The present invention also relates to a substrate made of a polymer material; A metal film coated on the surface of the substrate in a pattern of a circuit diagram; And a liquid metal plated on the surface of the metal film so that an externally applied signal is energized along the pattern. In this case, the liquid metal may be provided as Galinstan.

According to the present invention, it is possible to ensure the elasticity of the metal substrate having the metal substrate plated with the liquid metal to a degree that the mechanical and electrical performance can be achieved at the same time even if physical deformation such as bending, stretching or twisting is applied.

The present invention also provides a method of manufacturing a flexible circuit board comprising a step of plating a metal pattern with a liquid metal having different wettability depending on the material of the surface to be adsorbed, thereby making it possible to manufacture a circuit board having elasticity by a simple process There is an advantage.

The present invention also provides a wearable touch interface, a stretchable solar cell array, a stretchable display, and a wearable display, since the pattern of the circuit diagram formed on the surface of the substrate as well as the substrate made of the polymer has elasticity without being peeled and broken by physical deformation. Electronic devices, and the like.

Further, the present invention has an advantage that a circuit pattern having a uniform edge can be formed by utilizing the wettability of the liquid metal even in a fine pattern of millimeter / microscale.

1A shows a flexible circuit board according to an embodiment of the present invention.
1B shows a stretchable circuit board according to an embodiment of the present invention.
2 is a block diagram showing a method of manufacturing a flexible circuit board according to an embodiment of the present invention.
3 is a conceptual view showing a manufacturing process of a flexible circuit board according to an embodiment of the present invention.
Figure 4 shows the wettability difference between oxidized liquid metal and reduced liquid metal on metal and non-metal surfaces.
5 is a scanning electron microscope (SEM) photograph of a liquid metal pattern formed in accordance with an embodiment of the present invention.
6 is a scanning electron microscope (SEM) photograph showing the uniformity of the edge of the liquid metal pattern according to the concentration of the acid solution used for removing the oxide film of the liquid metal.
FIG. 7 is a scanning electron microscope (SEM) photograph showing the uniformity of the liquid metal pattern according to the rolling time of the liquid metal reduced on the surface of the substrate on which the metal pattern is formed.
8 shows that the mechanical characteristics of the circuit board and the circuit pattern are maintained even when the liquid metal pattern manufactured according to the embodiment of the present invention and the flexible circuit board including the flexible circuit board are deformed by bending, stretching or the like.
FIG. 9 shows that a flexible circuit board including liquid metal wires manufactured according to an embodiment of the present invention maintains its electrical characteristics even if it is deformed by bending, stretching, or the like.
Figure 10 shows that a flexible circuit board comprising liquid metal wire made according to an embodiment of the present invention has electrical self-recovery properties.
FIG. 11 shows that the electrical characteristics are maintained even when the flexible circuit board of the present invention including the resistor, the inductor, the capacitor, and the light emitting diode is deformed by bending, twisting, and stretching.
12 shows mechanical and electrical properties are maintained even when bending, twisting, stretching deformation are applied to a flexible circuit board including a liquid metal wire connected to a low-pass filter.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to or limited by the exemplary embodiments. Like reference numerals in the drawings denote members performing substantially the same function.

The objects and effects of the present invention can be understood or clarified naturally by the following description, and the purpose and effect of the present invention are not limited by the following description.

The objects, features and advantages of the present invention will become more apparent from the following detailed description. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

1 is a view showing a flexible circuit board 10 according to an embodiment of the present invention. 1 (a) shows a flexible circuit board to which an input power and an output device are connected, and Fig. 1 (b) shows a stretched state due to a tensile force acting on the flexible circuit board.

Referring to FIG. 1, a flexible circuit board 10 is energized by a current supplied from an input unit 30, which is a power source, and outputs a signal. In the present embodiment, a light emitting diode (LED) 50 may be provided on the flexible circuit board 10 as an element for confirming an output. In addition, electronic components such as a capacitor 60, a resistor 70, and an inductor 80 may be provided as an additional component for driving the circuit in the flexible circuit board 10 .

In the present embodiment, the flexible circuit board 10 includes a substrate 101 made of a polymer, a metal film 105, a liquid metal 107, and a polymer layer 103 applied on the surface of the liquid metal 107 .

In this embodiment, the substrate 101 may be provided of a polymer material. The metal film 105 may be coated with a circuit pattern on the surface of the substrate 101 made of a polymer. The liquid metal 107 is plated on the surface of the metal film 105 so that a signal applied from the outside through the input unit 30 is conducted along the pattern.

The liquid metal 107 may be an alloy of gallium, indium, and tin, and may be Galinstan. Galindan is an alloy consisting of 68.5 wt.% Of gallium (Ga), 21.5 wt.% Of indium (In) and 10 wt.% Of tin (Sn) and has a low melting point (-19 DEG C) ° C), high electrical conductivity (3.46 × 10 ⁶ S m ^-1 ), high thermal conductivity (16.5 W m ^-1 K ^-1 ) and very low vapor pressure.

In addition, galindan is characterized in that an oxide film in the form of a gel having a viscosity which is easily oxidized in air is formed on the surface. The oxide film of the liquid metal 107 can be removed by the vapor of an acid solution.

The liquid metal 107 may be gallstones from which an oxide film formed on the surface by the vapor of an acid solution has been removed. The oxidized GALINSTAN shows higher wettability on the surface of the metal material than the polymer material.

It is possible to ensure the degree of stretchability of the polymeric substrate 101 by the pattern of the circuit diagram shape coated on the surface of the substrate 101 of the polymer material due to the liquid metal 107 plated on the surface of the metal film 105 As a result, the mechanical and electrical performance of the flexible circuit board of the present invention can be maintained even in the case of bending, twisting, and stretching as shown in FIG. 1B.

2 is a block diagram showing a method of manufacturing a flexible circuit board 10 according to an embodiment of the present invention. 2, the manufacturing method of the flexible circuit board 10 includes a first polymer layer forming step S10, a pattern forming step S30, a liquid metal plating step S50, and a wafer removing step S70 .

In the first polymer layer forming step (S10), polydimethylsiloxane (PDMS) may be applied to the surface of a wafer (not shown) to form a first polymer layer 101 made of a polymer material. Specifically, in the first polymer layer formation step (S10), a spin coater is rotated at a rotation speed of 800 rpm for 30 seconds to coat PDMS on a silicon wafer having a silicon oxide layer of 500 nm thickness have. The wafer coated with PDMS can then be cured on a hot plate at 80 ° C for 90 minutes.

The pattern forming step S30 may include a metal film coating step S301 and an embossing pattern forming step S303.

In the metal film coating step (S301), a metal film is coated on the surface of the first polymer layer (101). In the metal film coating step (S301), chromium (Cr) is coated on the surface of the first polymer layer to form a chromium layer; And coating gold (Au) over the chromium layer.

The metal film coating step S301 is preferably coated with a metal which is not etched by acid contained in the liquid metal 107 used in the liquid metal plating step S50 described later. The metal that is not etched by the acid contained in the liquid metal 107 is advantageous for producing a metal pattern having a uniform edge. In this embodiment, metals used in the metal film coating step S301 include gold (Au), chromium (Cr), silver (Ag), aluminum (Al), copper (Cu), platinum (Pt) Zn), nickel (Ni), tin (Sn), iron (Fe) and combinations thereof, and more preferably gold (Au) or a combination of gold and chromium (Au / Cr).

The step of forming the chromium layer may include coating the PDMS coated on the surface of the wafer in the first polymer layer forming step S10 with an electron beam evaporator have.

Thereafter, the step of coating gold may sequentially coat 100 nm of gold (Au) on the surface coated with chromium (Cr). The thus coated gold and chromium (Au / Cr) layer then serves as a seed layer for plating the liquid metal 107.

The pattern formation step S303 of the embossing pattern in the pattern forming step S30 may be realized by a conventional lithography process. That is, the metal film 105 coated on the surface of the first polymer layer is etched by the metal film coating step S301 to form a pattern of a relief.

The liquid metal plating step S50 may include an oxide film removing step S501 of a liquid metal and a reduced liquid metal plating step S503.

Liquid metals are metal ions, such as mercury and molten metal, and liquids derived from free electrons, which have good electrical properties due to the activity of free electrons. This liquid metal is known to induce a wetting phenomenon with a contact angle of less than 20 ° on the solid metal according to Robertson's dissolution-diffusion model.

However, in the case of some liquid metals, it is possible to maintain a large contact angle of 90 DEG or more when adsorbed onto the solid metal. In this embodiment, the liquid metal 107 exhibiting this behavior can be Geratherm Medical AG, Germany, which is a commercially available alloy of gallium, indium and tin (68.5% Ga, 21.5% In, 10 % Sn).

Maintaining a large contact angle of 90 DEG or more when adsorbed onto the solid metal is due to the oxide film on the surface produced by oxidizing gallin starter 107. The galenstane 107 does not induce a wetting phenomenon on the surface of the solid metal by the oxide film, and exhibits a viscous gel-like behavior. The oxide film formed on the surface of the oxidized liquid metal 107 may be removed through the oxide film removal step (S501) of the liquid metal.

Oxide film removal step (S501) is hydrochloric acid (HCl), hydrofluoric acid (HF), nitric acid (HNO ₃₎ and sulfuric acid (H ₂ SO ₄₎ Can be reduced by the vapor of the acid solution of any one of the above.

The concentration of the acid solution to remove the oxide film on the surface of the liquid metal 107 is very important. When the concentration of the acid solution is low, the oxide film formed on the surface of the liquid metal is not completely removed and wetting phenomena such that the metal pattern serving as the seed pattern layer is completely wetted are hardly generated, acid solution is high, it is difficult to form a circuit pattern having a uniform edge by etching the metal pattern.

Accordingly, in this embodiment, hydrochloric acid solutions of 37 wt.%, 25 wt.% And 16 wt.% Were prepared to find the optimum concentration of hydrochloric acid solution for efficiently removing the oxide film of gallstones used as the liquid metal. And the galenstans from which the oxide film was removed were each rolled on the first polymer layer having the metal pattern formed thereon for 5 seconds, and then the pattern of the formed liquid metal was observed with a scanning electron microscope (SEM).

As a result, as shown in FIGS. 6 (a) and 6 (b), the liquid metal pattern formed by rolling the galindan having the oxide film removed by the hydrochloric acid solution of 37 wt.% And 25 wt.%, Is generated to damage the edge portion of the liquid metal pattern. On the other hand, it was confirmed that the liquid metal pattern formed by rolling the gallinestane with the oxide film removed using the 16 wt.% Hydrochloric acid solution can have a uniform edge. Therefore, in this embodiment, the oxide film formed on the surface of gallin stain was removed using a 16 wt.% Hydrochloric acid solution, and the reduced gallindan was used for forming the liquid metal pattern through the above process.

In the reduced liquid metal plating step (S503), the reduced liquid metal (107) can be plated on the pattern after the oxide film removing step (S501). In the reduced liquid metal plating step S503 of this embodiment, galindan reduced by the vapor of the acid solution is covered on the surface of the first polymer layer formed with the metal pattern of the embossed pattern in the pattern forming step S30 covering, and then rolling the liquid metal 107 into the pattern.

Reduced gallstones have different wettability depending on the material of the adsorbed surface as shown in FIG. That is, referring to FIG. 4, when GALINSTAN is oxidized, the PDMS layer, which is the substrate 101 of the polymer, and the metal layer of Cu, Au, and Zn are not wetted at all, (Fig. 4 (a1), (b1), (c1), (d1)).

On the other hand, in the case of reduced gallstones, the PDMS layer exhibits water repellency with a contact angle of 90 DEG or more (Fig. 4 (a2)), but wetting occurs in the metal layer of Cu, Au and Zn (B2), (c2), (d2)).

In the present embodiment, when a droplet-shaped reduced galindan is rolled and plated on the surface of the metal film 105 on which the pattern is formed and the substrate 101 of the polymer material on which no pattern is formed, (Au) is completely wetted. Thereafter, the remaining glandane droplets remaining on the surface of the polymer in which the pattern is not formed in the first polymer layer are removed, whereby a liquid metal pattern can be formed.

The process of the present invention as described above in which a liquid metal is plated using the properties of a reduced liquid metal having different wettability depending on the material of the surface to be adsorbed is referred to as a " selective liquid-metal plating "(SLIM) process. The liquid metal pattern formed by the SLIM process of the present invention has a uniform edge even at a resolution of 10 mu m as shown in Fig.

In addition, the rolling time of the reduced galindan in this embodiment influences the formation of a uniform edge pattern. Therefore, an experiment for understanding the rolling time of the Galindran droplet for forming a pattern having a uniform edge is as follows. A substrate with a metal pattern having different widths of 40 탆, 10 탆 and 5 탆 was formed on the surface of the substrate by using a 16 wt% hydrochloric acid solution and then reduced by various rolling times of 5 seconds, 30 seconds, and 2 minutes Gt;

As a result, as shown in FIG. 7, in the case of a metal pattern having a width of 10 μm or more, it is understood that the rolling time of the reduced galindan is 5 seconds. That is, a wetting phenomenon in which the galenstans reduced on the metal pattern are completely wetted with a rolling time of 5 seconds may occur, and a liquid metal pattern having a uniform edge may be formed.

According to (c1) to (c3) of FIG. 7, when the width of the metal pattern is 5 占 퐉, in order to completely wet the metal pattern by the reduced galindan, the rolling time of the reduced galindan may be required for 30 seconds or more .

Although it is technically difficult to form a pattern having a width of 5 탆 or less for a conductive pattern to have a uniform edge, the present embodiment fully satisfies the application requirements of a flexible circuit board if the pattern has a width of 10 탆, A method of forming a liquid metal pattern by a liquid metal plating process can be widely used.

Thereafter, the surface of the first polymer layer containing the plated pattern of liquid metal 107 was washed with acetone solution, cured at 60 DEG C for 10 minutes on a hot plate, and the acetone solution was completely vaporized.

The method of manufacturing a flexible circuit board according to the present embodiment may further include the step of forming a second polymer layer 103 on the surface of the plated liquid metal 107 after the step (S50) of plating the liquid metal have. The step of forming the second polymer layer 103 may be understood as forming an insulating layer for shielding a current flowing along a pattern formed on the surface of the substrate 101. [

The step of forming the second polymer layer 103 may be performed by applying a polymer solution to the surface of the substrate 101 on which the liquid metal pattern is formed and curing the substrate 101 on a hot plate at 80 DEG C for 90 minutes, The second polymer layer 103 may be formed. In this embodiment, polydimethylsiloxane (PDMS) may be used as the polymer solution for forming the second polymer layer 103. [

In the method of manufacturing a flexible circuit board according to the present embodiment, after the step of forming the second polymer layer 103, a step S70 of removing the wafer used in the first polymer layer forming step S10 may be performed have. If the wafer under the substrate 103 is removed through the step of removing the wafer S70, the substrate portion in the flexible circuit board 10 is made of only a polymer material, thereby enhancing the stretchability of the circuit board.

According to another embodiment of the present invention, there is provided a method of manufacturing a flexible circuit board, comprising: forming a pattern by coating a metal film on a surface of a wafer; And plating a liquid metal having different wettability depending on the material of the surface to be adsorbed on the pattern.

In this case, unlike the embodiment shown in FIG. 2, the metal film 105 is directly coated on the surface of the silicon wafer to form a pattern without forming the first polymer layer, and the liquid metal 107 is plated on the formed pattern, A circuit board can be manufactured.

According to this method, a chromium (Cr) layer is first coated in the form of a thin film before the gold (Au) layer is coated on the surface of the silicon wafer, Layer acts to enhance the ability to deposit between gold (Au) and the silicon oxide of the wafer.

Except for the above difference, the process of fabricating the flexible circuit board by plating the liquid metal is as described above with reference to FIG.

Hereinafter, with reference to FIGS. 8 to 12, a performance example of the liquid metal pattern manufactured according to the present embodiment and the performance of the flexible circuit board including the liquid metal pattern will be described in detail.

Experimental Example 1. Analysis of Mechanical Properties of Flexible Circuit Board

8 (a) to 8 (e), according to the embodiment of the present invention, a liquid metal pattern formed by plating a liquid metal 107 having a resolution of millimetry / microscale is referred to as a square, And the like. [0052] The substrate 101 is made of a polymer material.

In Figs. 8 (f) and 8 (g), a flexible circuit board including a fine liquid metal pattern having a line and a square shape was prepared and subjected to physical deformation by bending. As a result, it was confirmed that the liquid metal pattern was not peeled off or broken on the substrate and the mechanical properties were maintained.

8 (h) to 8 (g), off-axis stretching of the flexible circuit board including the liquid metal pattern in the diagonal direction (liquid metal pattern) does not peel off or break on the substrate, .

Experimental Example 2. Electrical Characteristic Analysis of Flexible Circuit Board

2-1. Electrical Characteristic Analysis of Flexible Circuit Board Containing Liquid Metal Wire

In order to confirm whether electrical characteristics can be maintained even when the stretchable circuit board according to the embodiment of the present invention is stretched, twisted, bent, or the like, a liquid metal wire having a width of 10 mu m, a length of 20 mm and a width of 50 mu m and a length of 20 mm , And the resistance (R) was measured when the manufactured flexible circuit board was pulled by 100% length in its original length.

As a result, as shown in Fig. 9, the flexible circuit board 10 including the liquid metal wires of 10 mu m ((a1) to (a3)) and 50 mu m (b1 to b3) When extended by 100% in length, the resistance was increased by 130? And 4?, Respectively.

Moreover, it can be confirmed that restoration of the extensions again restores the initial resistance of the liquid metal wire.

On the other hand, as can be seen from (a3) and (b3) in FIG. 9, it can be confirmed that some cracks are generated on the surface of the liquid metal. These cracks have no influence on the electrical characteristics of the flexible circuit board 10. Because the cracked oxide layer is relatively thin relative to the diameter of the liquid metal wire, the liquid metal beneath the oxide layer still meets electrical and mechanical properties.

On the other hand, as shown in (c1) to (c3) of FIG. 9, in the case of a conventional flexible circuit board including a metal wire, it is confirmed that it is disconnection when extended by 100% And if it is restored to its original length again, it can be confirmed that it is still in an insulated state.

Accordingly, it can be seen that the electrical characteristics are maintained even by stretching and stretching due to stretching and stretching of the flexible circuit board including the liquid metal wire manufactured according to the embodiment of the present invention.

2-2. Electrical Characterization of Flexible Circuit Boards Containing Liquid Metal Wire Connected to Output Device (LED)

After connecting a liquid metal wire and an LED device according to an embodiment of the present invention, a flexible circuit board including the flexible circuit board was manufactured and various electrical characteristics were maintained even after various physical modifications were made.

As a result, as shown in (d1) to (d4) of Fig. 9, a physical deformation (a 3V external voltage supply), a 180 DEG bend, a 180 DEG twist, It can be seen that the electrical characteristics are stably maintained by confirming that the light of the LED element is emitted even when the voltage is applied to the light emitting element and the voltage-current characteristic can be confirmed through the graph of FIG. 9 (e).

FIG. 9 (f) shows the normalized resistance (R = R _a / R ₀ ) when the stretchable circuit board 10 including the liquid metal wire connected to the LED element is stretched by 180 ° in a twisted state.

Where R _a represents the resistance in the stretched state and R ₀ represents the resistance before stretching. As a result, as can be seen from the graph of FIG. 9 (f), it can be seen that a substantially constant resistance value is maintained even when the length is increased by 100% of the original length in the state of being twisted by 180 °.

FIG. 9 (g) shows current-voltage characteristics when a stretchable circuit board including a liquid metal wire connected to an LED element is stretched by a length of 60% of its original length in a state where the stretched circuit board is twisted by 180 ° for 6,000 repetitions.

As a result, as shown in the graph, it was confirmed that the current-voltage characteristics were maintained in the same manner as when 100, 2000, and 4000 repetitions were applied to 6000 repetitive applications, It can be understood that the electrical characteristics are maintained as they were before the deformation even in the repeated expansion and contraction of the physically large deformation and restoration.

Experimental Example 3. Confirmation of Self-Healing Properties of Flexible Circuit Board Containing Liquid Metal Wire Connected to LED Element

In Fig. 10, the self-recovery characteristics of the flexible circuit board 10 including the liquid metal wire of the present invention were confirmed. That is, after connecting the liquid metal wire and the LED element, a flexible circuit board including them was manufactured according to the embodiment of the present invention. The wire portion was cut by scissors to insulate it. However, And the light emitted from the LED device was emitted.

Experimental Example 4. Analysis of Practicality and Efficiency of Flexible Circuit Board

In order to put the flexible circuit board including the liquid metal pattern (or the wire) into practical use in accordance with the embodiment of the present invention, even if it is manufactured as an integrated electronic device package with conventional electronic parts which are not flexible and stretchable, Should be maintained.

Accordingly, the flexible circuit board manufactured in accordance with the embodiment of the present invention can be connected to the LED 50, the capacitor 60, the resistor 70, the inductor 80, A flexible circuit board including a low-pass filter was fabricated and their mechanical and electrical properties were analyzed.

4-1. Flexible circuit board integrated with light emitting diodes, capacitors, resistors and inductors

After connecting the liquid metal wires with the LEDs, capacitors, resistors and inductors, a flexible circuit board containing them was fabricated, and it was confirmed that the electrical characteristics were retained when physical deformations such as bending, twisting, and diagonal stretching were applied.

As a result, as shown in FIG. 11, by confirming that the light of the LED element is emitted even when the bending, twisting, and diagonal stretching are applied, the flexible circuit board according to the embodiment of the present invention, And can be widely used as an electronic device having elasticity.

4-2. Flexible circuit board integrated with low-pass filter

As shown in FIG. 12, a liquid metal wire according to an embodiment of the present invention is connected to a low-pass filter, and then a flexible circuit board including the liquid metal wires is manufactured and analyzed for mechanical and electrical characteristics. Fig. 12 (a) shows a state of a flexible circuit board including a liquid metal wire connected to a low-pass filter, and Fig. 12 (b) shows a circuit diagram of Fig.

(90 °), torsion (90 °), and torsion (90 °) to the substrate, as shown in Figures 12 (c) to (f), to confirm the mechanical properties of the flexible circuit board comprising the liquid metal wire connected to the low- And a physical deformation that extends the original length by 30%, but it can be confirmed that the optical transparency is maintained even with such a large deformation.

In order to analyze electrical characteristics of a flexible circuit board including a liquid metal wire connected to a low-pass filter, a waveform is generated using a function generator, and an output signal V _out is generated using an oscilloscope In this process, the voltage of the filter was measured and compared at 10 kHz, 0.1 MHz, and 1 MHz according to the scaling and stretching conditions by applying a stretching (30%) physical strain.

As a result, as can be seen from (g1) to (g3) in FIG. 12, the output waveform at the low frequency (10 kHz) is almost similar to the input waveform, but shows a slight difference due to the charging of the capacitor. At a higher frequency (1 MHz), the output voltage is converted to a triangular waveform for the input quadrature waveform signal. This form of waveform in the low-pass filter can be attributed to the frequency-dependent reactance of the capacitor.

It can be seen from FIG. 12 (g1) to (g3) that the output waveform under the condition of stretching without stretching coincides with that of the stretching condition (30%). It can be seen that a flexible circuit board including a connected liquid metal wire stably maintains its electrical performance even when subjected to physical deformation such as stretching.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. will be. Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be determined by all changes or modifications derived from the scope of the appended claims and equivalents of the following claims.

10: Elastic circuit board
30: Input unit
50: Light emitting diode (LED)
60: Capacitor
70:
80: inductor
101: substrate made of a polymer material
103: second polymer layer
105: metal film
107: liquid metal

Claims (16)

A method of manufacturing a flexible circuit board,
(a) forming a first polymer layer on a surface of a wafer;
(b) coating a surface of the first polymer layer with a metal film to form a pattern;
(c) plating the pattern with a liquid metal; And
(d) removing the wafer,
Wherein the step (c) is performed by using a property of a liquid metal having different wettability depending on the material of the surface to be adsorbed.
The method according to claim 1,
The step (a)
Wherein the first polymer layer is formed by applying polydimethylsiloxane (PDMS) to the surface of the wafer.
The method according to claim 1,
The step (b)
(Au), chromium (Cr), silver (Ag), aluminum (Al), copper (Cu), platinum (Pt), zinc (Zn), nickel (Ni) Sn), iron (Fe), and a combination thereof.
The method according to claim 1,
The step (c)
Wherein the pattern is plated with a liquid metal consisting of gallium, indium and tin.
The method according to claim 1,
The step (c)
An oxide film removing step of reducing the liquid metal by vapor of an acid solution; And
Plating the reduced liquid metal onto the pattern after the oxide film removing step,
Wherein the reduced liquid metal has higher wettability on the surface of the metal material than the polymer material.
6. The method of claim 5,
The oxide film removing step may include:
Wherein said liquid metal is reduced by the vapor of any one of hydrochloric acid (HCl), hydrofluoric acid (HF), nitric acid (HNO ₃ ) and sulfuric acid (H ₂ SO ₄ ).
The method according to claim 6,
The oxide film removing step may include:
Wherein the liquid metal is reduced using a vapor of an acid solution having a concentration range of 15 wt.% To 40 wt.%.
The method according to claim 1,
The step (c)
Wherein the droplet-shaped liquid metal is rolled and plated on a surface of a patterned metal film and a non-patterned polymer.
9. The method of claim 8,
The step (c)
Wherein said liquid metal is rolled for 5 to 30 seconds.
The method according to claim 1,
The step (b)
A coating step of coating a metal film on a surface of the first polymer layer; And
And a pattern forming step of forming a pattern of a relief by etching the metal film after the coating step.
11. The method of claim 10,
Wherein the coating step comprises:
Forming a chromium layer by coating chromium (Cr) on the surface of the first polymer layer; And
And coating gold (Au) on the chromium layer.
The method according to claim 1,
After the step (c)
Further comprising forming a second polymer layer on the surface of the plated liquid metal.
(a) forming a pattern by coating a surface of a wafer with a metal film; And
(b) plating liquid metal having different wettability depending on the material of the surface adsorbed on the pattern.
A substrate made of a polymer material;
A metal film coated on the surface of the substrate in a pattern of a circuit diagram; And
And a liquid metal plated on the surface of the metal film so that an externally applied signal is conducted along the pattern.
15. The method of claim 14,
Wherein said liquid metal is Galinstan. ≪ RTI ID = 0.0 > 11. < / RTI >
16. The method of claim 15,
Wherein the liquid metal is gallstones from which an oxide film formed on the surface is removed,
Wherein the galenustane from which the oxide film is removed has higher wettability on the surface of the metal material than the polymer material.

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