KR102177853B1 - Method for Soldering on Flexible Substrate - Google Patents

Abstract

According to the present invention, a method for soldering on a flexible substrate includes the steps of: forming a circuit on a flexible substrate; patterning a support portion in which a through hole for accommodating a conductive liquid solder is formed on the flexible substrate; injecting the conductive liquid solder into the through hole formed in the support portion; and placing an electronic device chip on the support portion so that the electrode of the electronic device chip is electrically connected to the flexible substrate by the conductive fluid solder, and then curing the support portion. According to the present invention, even when an external force is applied, physical stress applied to an element or a wiring can be reduced.

Description

Soldering on Flexible Substrate {Method for Soldering on Flexible Substrate}

The present invention relates to a technology for electrically stably bonding a surface mount device (SMD chip) to a flexible substrate.

Recently, flexible electronic devices have been in the spotlight. These electronic devices are free to bend or bend compared to conventional electronic devices, and thus are receiving great attention in the fields of display and bioengineering. Since the flexible electronic device according to the prior art is formed on a substrate having elasticity, when the substrate is stretched or compressed, it is stretched or compressed accordingly. This is because when a general elastic body receives physical forces such as tension, bending, and warping from the outside, the degree of deformation of the elastic body is uniform and isotropic throughout the entire section.

When an external force is applied to the stretchable substrate, it is elongated in the direction in which the external force is applied. In general, an electronic circuit or wiring formed on a substrate differs from the substrate in a Young's Modulus, and the degree to which it is deformed against an applied external force is different from that of the substrate.

For example, when electrical wiring with low stretchability is formed on a substrate having high tensile properties compared to wiring, and a tensile force is applied to the substrate, electrical wiring having low stretchability compared to the stretchability of the substrate is As this increases, it cannot be stretched to the same level, and stress is applied to the electrical wiring, resulting in physical damage such as cracks in the electrical wiring. Therefore, electronic or electric devices electrically connected by electrical wiring do not operate stably. Such a case may occur when an electronic device having a different stretchability than the substrate is formed on a stretchable substrate and an external force is applied to the substrate, as well as electrical wiring, and stable operation of the electronic device formed on the stretchable substrate cannot be guaranteed. .

However, since conventional solders for soldering are made of hard materials such as metal or epoxy with a low melting point, when the substrate is deformed, a large mechanical stress can be applied between the circuit manufactured on the soft substrate and the hard solder.

The present invention is to solve the problems of the prior art, and one of the objects of the present invention is to provide a soldering method on a flexible substrate capable of reducing physical stress applied to an element or wiring even when an external force is applied. Is to do.

The present invention is a method of soldering on a flexible substrate, comprising: forming a circuit on a flexible substrate, patterning a support portion having a through hole formed on the flexible substrate for receiving conductive fluid solder, and supporting a conductive fluid solder And injecting the electronic device chip into the through hole formed in the electronic device chip, placing the electronic device chip on the support part so that the electrode of the electronic device chip is electrically bonded to the flexible substrate by conductive fluid solder, and then curing the support part.

The circuit can be made of an elastic material.

After forming the circuit on the flexible basis, the step of forming a circuit damage prevention layer may be further included.

The circuit damage prevention film is made of either a carbon-based material or a metal thin film resistant to liquid metal, and the carbon-based material is either carbon nanotube or graphene, and the metal of the metal thin film is It is either tantalum or tungsten.

The flowing solder can be a conductive flowing material of any one of liquid metal, ionic gel, and stretchable epoxy.

The support may be a curable material including epoxy.

The soldering method proposed in the present invention has the following advantages in soldering a chip on a flexible substrate.

First, one of the roles of soldering is to firmly fix the chip on the substrate, and it is difficult to perform this when using a soft fluid solder as in the present invention. Accordingly, in the present invention, a support part, which is a curable structure, is provided to secure a space for accommodating a liquid solder, and to perform a role of firmly bonding a chip on a substrate.

In addition, since the conductive fluid solder material has the property of a liquid, it cannot transmit the force on the substrate even if an external force is applied to the mounted chip.Therefore, the circuit or the substrate is not damaged, so that reliable electrical bonding can be achieved even on a smooth and deformable substrate. I can.

1 is a diagram illustrating a process flow of a soldering method in a flexible electronic substrate according to an embodiment of the present invention.
2 is an exploded perspective view of a flexible electronic board manufactured by a soldering method according to an embodiment of the present invention.
3A and 3B are cross-sectional views of a flexible electronic board manufactured by a soldering method according to an embodiment of the present invention.
4 is a diagram illustrating an example of a 7 segment flexible circuit manufactured by a soldering method on a flexible electronic board according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to embodiments of the present invention and drawings. These examples are only illustratively presented to illustrate the present invention in more detail, and it will be apparent to those of ordinary skill in the art that the scope of the present invention is not limited by these examples. .

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.

Although methods and materials similar or equivalent to those described herein may be used in the practice or testing of the present invention, suitable methods and materials are described herein.

1 is a diagram showing a process flow of a soldering method in a flexible electronic board according to an embodiment of the present invention, and FIG. 2 is an exploded perspective view of a flexible electronic board manufactured by a soldering method according to an embodiment of the present invention And FIG. 3 is a cross-sectional view of a flexible electronic board manufactured by a soldering method according to an embodiment of the present invention.

A circuit 110 is printed on the flexible substrate 100 as shown in FIG. 1A. According to an aspect, the flexible substrate 100 is made of a material having elasticity. For example, the flexible substrate may be made of any one of polydimethylsiloxane (PDMS), epoxy resin polyurethane, and ecoflex. However, this is only an example of materials capable of forming a flexible substrate, and the flexible substrate may be formed using a material having other elastic properties.

In addition, the circuit 110 may be a connection pattern connecting the seating portion and the seating portion in which at least one electronic device chip is to be positioned. According to an aspect, the circuit 110 may be made of a material having elasticity as a metal thin film. According to an aspect, the circuit 110 may be a conductive composite in which nano/micro-sized conductive fillers such as silver nanowires are embedded in a stretchable polymer as a metal thin film having elasticity. According to another aspect, the circuit 110 may be designed to be stretchable by introducing a structure such as a corrugated structure into a metal thin film.

In addition, although not shown in FIG. 1, as shown in FIG. 2, according to another embodiment, a circuit damage prevention layer 150 may be deposited on the flexible solder contact portion of the flexible substrate 100. The circuit damage prevention layer 150 may be a layer capable of preventing damage to the circuit 110 by the conductive fluid solder 130 and having conductivity. According to an aspect, the circuit damage prevention film is made of either a carbon-based material or a metal thin film resistant to liquid metal, and the carbon-based material is any one of carbon nanotubes or graphene, and metal The metal of the thin film is either tantalum or tungsten.

As shown in (b) of FIG. 1, the support part 120 in which the through hole 121 for receiving the conductive liquid solder 130 is formed on the flexible substrate 100 is patterned.

One of the roles of soldering is to firmly bond the electronic device chip on the substrate. When using the conductive fluid solder 130 as in the present invention, the conductive fluid solder 130 moves, so that the electronic device chip is It becomes difficult to bond firmly on the substrate. In the present invention, in order to solve this problem, the support 120 is disposed between the flexible substrate 100 and the electronic device chip 140.

That is, the support 120 is a material that becomes hard when hardened, such as a curable epoxy, and not only stably bonds the electronic device chip to the flexible substrate 100, but also a through hole having a predetermined height from the flexible substrate 100 Since it is patterned so that 121 is formed, the floating solder 130 can be confined and accommodated in the through hole 121 as shown in FIG. 3A.

Thereafter, as shown in (c) of FIG. 1, the liquid solder 130 is injected into the through hole 121 formed in the support part 120. Here, the fluid solder 130 is a conductive fluid material of any one of a liquid metal, an ionic gel, and a stretchable epoxy. That is, the floating solder 130 is patterned in advance, such as a liquid metal or a conductive gel, which is conductive and prevents mechanical bonding between the electronic device chip 140 and the flexible substrate 100. As a result, even if an external force is applied to the mounted electronic substrate chip 140, since the force cannot be transmitted on the flexible substrate 100, the circuit 110 or the flexible substrate 100 is not damaged, so it is reliable even on a smooth and deformable substrate. Electrical junction can be achieved.

Thereafter, as shown in (d) of FIG. 1, the electronic device chip is electrically bonded to the circuit 110 of the flexible substrate 100 by the liquid solder 130 so that the electrode of the electronic device chip 140 is electrically connected to the circuit 110 of the flexible substrate 100. 140) is disposed on the upper part of the support part 120, and then the support part 120 is cured. Here, the electronic device chip may be a surface mount device (SMD) type chip.

Accordingly, as shown in FIG. 3A, while the electronic device chip 140 and the flexible substrate 100 are fixed by the support part 120, the electrode 141 of the electronic device chip 140 is applied by the floating solder 130. ) Is an electrical junction.

However, since the floating solder 130 is not hardened and fixed, but can be moved, the floating solder 130 located at the edge shown in FIG. 3A may move and be separated from the through hole of the support part 130. However, when the edge is formed on the support part 130 to prevent this, the hard epoxy for the edge may break the circuit underneath again.

Accordingly, according to another embodiment of the present invention, a portion of the flexible substrate 100 to which the electronic device chip 140 is bonded may be encapsulated. That is, as illustrated in FIG. 3A, a capsule unit 160 may be additionally formed to surround the electronic device chip 140 bonded on the flexible substrate 100. According to one aspect, the capsule unit 160 may be made of a soft material, for example, PDMS used as a material of the flexible substrate 100.

In addition, the capsule unit 160 may be formed to cover the entire electronic device chip 140, as shown in FIG. 3B, but according to another aspect, from the side surface of the electronic device chip 140 other than the upper surface It may be formed in a shape that surrounds the upper part of (100). 4 is a diagram illustrating an example of a 7 segment flexible circuit manufactured by a soldering method on a flexible electronic board according to an embodiment of the present invention.

4A and 4B show an optical image of a 7 segment flexible circuit, (c) shows an operation of a 7 segment flexible circuit after it is manufactured, and ( d) shows a state in which a 7 segment flexible circuit is tensioned, and (e) shows the IV characteristics of a three-color LED chip with four contact pads. have.

As shown in (a) and (b) of Figure 4, the soldering method in the flexible electronic board according to the present invention is a complex and sophisticated circuit composed of microscale chips and conductive elements (conducting elements). Shows that it is suitable for That is, the SMD-type LED chips are tightly integrated on the flexible PDMS substrate, and as shown in FIG. Is showing the sound.

In addition, as shown in (d) of FIG. 4, it is shown that the flexible circuit is actually operated normally even in a tensioned state.

In addition, as shown in (e) of FIG. 4, the present invention shows that it can be applied to an LED chip having four pad terminals.

In the present specification, only a few examples of various embodiments performed by the present inventors will be described, but the technical idea of the present invention is not limited or limited thereto, and may be modified and variously implemented by a person skilled in the art.

100: flexible substrate 110: circuit
120: support 130: fluid solder
140: electronic element chip 150: circuit damage prevention film
160: capsule part

Claims (7)

Forming a circuit on the flexible substrate,
Forming a circuit damage prevention film,
Patterning a support portion in which a through hole for accommodating a conductive liquid solder is formed on the flexible substrate; and
Injecting conductive fluid solder into the through hole formed in the support,
Arranging the electronic device chip on the support part so that the electrode of the electronic device chip is electrically connected to the flexible substrate by conductive fluid solder, and then curing the support part,
The circuit damage prevention film is made of either a carbon-based material or a metal thin film resistant to liquid metal,
The carbon-based material is any one of carbon nanotubes or graphene,
A method of soldering a flexible substrate in which the metal of the metal thin film is either tantalum or tungsten.
The method of claim 1, wherein the circuit is
A method of soldering on a flexible substrate made of an elastic material.
delete delete The method of claim 1, wherein the flow solder is
A method of soldering on a flexible substrate that is a conductive flowing material of any one of liquid metal, ionic gel and stretchable epoxy.
The method of claim 1, wherein the support
A method of soldering on a flexible substrate, which is a curable material containing epoxy.
The method of claim 1,
After the step of curing, the method of soldering on a flexible substrate further comprising the step of encapsulating around an electronic device chip.

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