TW202237781A - Anisotropic conductive adhesive and bonding method - Google Patents

Abstract

Embodiments of the present disclosure provide an anisotropic conductive adhesive and a bonding method. The anisotropic conductive adhesive includes a liquid optical transparent adhesive and a plurality of conductive particles mixed in the liquid optical transparent adhesive. Each of the conductive particles includes a conductive ball and an insulating layer wrapping the conductive ball.

Description

Anisotropic conductive adhesive and bonding method

The invention relates to the technical field of bonding, in particular to an anisotropic conductive adhesive and a bonding method.

Anisotropic conductive adhesives are often used in the hot-press bonding process of touch panels to bond an object to be bonded (such as a touch panel) with a flexible circuit board, and use its anisotropic conductive properties to realize The electrical connection between the object to be bonded and the flexible circuit board.

However, the known anisotropic conductive adhesive is an adhesive tape with uniform thickness. When the anisotropic conductive adhesive is placed on the flexible circuit board, since the gold finger on the flexible circuit board and the surface of the substrate of the flexible circuit board have a certain Due to the difference in height, the surface of the anisotropic conductive adhesive covering the gold finger protrudes compared with the surface directly covering the substrate, so that the surface away from the substrate is uneven. This results in that during the hot pressing process, due to the effect of high pressure, the base material of the flexible circuit board is sunken in the direction of the object to be bonded relative to the area where the gold finger is not provided with the area where the gold finger is provided, thereby causing the entire base material to appear Water ripples affect the yield rate in the back-end process of the product. In addition, if the bonding area of the object to be bonded has irregular-shaped edges (that is, the bonding area has non-linear distribution edges), it may be difficult to achieve special-shaped attachment with traditional anisotropic conductive adhesives, or it is necessary to Additional border cropping is a waste of cost.

The first aspect of the present invention provides an anisotropic conductive adhesive, which includes: a liquid optically transparent adhesive and a plurality of conductive particles mixed in the liquid optically transparent adhesive, each of the conductive particles includes a conductive ball and an insulating layer surrounding the conductive ball , the diameter of the conductive particles is less than 10 μm, and the density of the conductive particles is 2×10 ⁶ to 3×10 ⁶ particles/mL.

The anisotropic conductive adhesive uses liquid optically transparent adhesive as its adhesive, so that the shape of the anisotropic conductive adhesive can be controlled. Different dispensing volumes are set for the gaps between the gold fingers, so that the area with gold fingers has a smaller dispensing volume, and the area between the gold fingers has a larger dispensing volume, so as to effectively improve the adhesion. The thickness of the colloid in the joint area can reduce the risk of deformation of the flexible circuit board during the hot pressing process. Moreover, if the bonding area of the object to be bonded (such as a touch panel) has irregular edges (that is, the bonding area has non-linear distribution edges), it can be achieved by controlling the dispensing of the anisotropic conductive adhesive. Shape and dispensing amount Dispensing glue of any shape can realize the special-shaped attachment of the object to be laminated and the flexible circuit board, and at the same time, there is no need for additional border cutting, which saves costs.

The second aspect of the present invention also provides a bonding method, which includes:

Coating the above-mentioned anisotropic conductive adhesive on a flexible circuit board, wherein the flexible circuit board includes a flexible substrate and a plurality of golden fingers arranged at intervals on the substrate, the anisotropic conductive adhesive coating In the surface of the gold finger away from the substrate and in the gap between two adjacent gold fingers; Pre-curing the anisotropic conductive adhesive; The object to be bonded and the flexible circuit board are bonded by heat and pressure through the anisotropic conductive adhesive, wherein the object to be bonded has connection pads corresponding to the gold fingers on the flexible circuit board one by one. After pressing and bonding, the connection pad and the gold finger are electrically connected by the anisotropic conductive adhesive, and the surface of the base material away from the gold finger is flat.

In this pasting method, the above-mentioned anisotropic conductive adhesive is used to heat-press the object to be pasted and the flexible circuit board. Since the anisotropic conductive adhesive uses liquid optically transparent adhesive as its adhesive, the anisotropic The shape of the conductive adhesive is controllable. When it is applied in the panel bonding process, different dispensing volumes are set for the area of the gold finger and the gap between the gold fingers of the flexible circuit board, so that the area with the gold finger There is a small dispensing amount, and the area between the gold fingers has a larger dispensing amount to effectively improve the thickness of the glue in the bonding area, thereby reducing the risk of deformation of the flexible circuit board during the hot pressing process. Moreover, if the bonding area of the object to be bonded (such as a touch panel) is irregular (that is, the bonding area has non-linear distribution edges), it can be controlled by controlling the dispensing shape and point of the anisotropic conductive adhesive. The amount of glue can be dispensed in any shape, so that while realizing the special-shaped attachment of the object to be attached and the flexible circuit board, there is no need for additional border cutting, which saves costs.

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some of the embodiments of the present invention, but not all of them.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field of the invention. The terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention.

In order to further explain the technical means and effects adopted by the present invention to achieve the intended purpose, the present invention will be described in detail below in conjunction with the accompanying drawings and preferred embodiments.

An embodiment of the present invention provides an anisotropic conductive adhesive. Figure 1 is a schematic diagram of the anisotropic conductive adhesive observed under a 50X microscope. As shown in FIG. 1 , the anisotropic conductive adhesive 10 includes a liquid optical clear adhesive (Liquid Optical Clear Adhesive, LOCA) 12 and a plurality of conductive particles 14 mixed in the liquid optical clear adhesive 12 . Wherein, each of the conductive particles 14 includes a conductive ball (not shown in the figure) and an insulating layer (not shown in the figure) surrounding the conductive ball. The conductive ball is made of copper, gold, silver and other metals. The material of the conductive ball can also be metal alloy or other conductive materials. The material of the insulating layer may be insulating resin.

The anisotropic conductive adhesive 10 uses liquid optically transparent adhesive 12 as its adhesive, so that the shape of the anisotropic conductive adhesive 10 can be controlled. During the manufacturing process, different dispensing volumes can be set for the area of the gold finger and the gap between the gold fingers of the flexible circuit board, so that the area with the gold finger has a smaller dispensing volume, and the area between the gold fingers has a smaller dispensing volume. The area of the gap has a larger dispensing amount to effectively improve the thickness of the glue in the bonding area, thereby reducing the risk of deformation of the flexible circuit board during the hot pressing process. Moreover, if the bonding area of the object to be bonded (such as a touch panel) is irregular (that is, the bonding area has non-linear distribution edges), it can be controlled by controlling the dispensing shape and point of the anisotropic conductive adhesive. The amount of glue can be dispensed in any shape, so that the special-shaped attachment of the object to be attached (such as a touch panel) and the flexible circuit board can be achieved without additional border cutting (Die-cut), which simplifies the manufacturing process. save costs.

In one embodiment, the viscosity of the liquid optically transparent adhesive 12 is less than 50 cps, and the liquid optically transparent adhesive 12 is an ultraviolet-heat (UV/Heat) dual-curing adhesive. The liquid optically transparent adhesive 12 with a lower viscosity (less than 50 cps) is selected to facilitate the uniform dispersion of the conductive particles 14 inside the colloid, and is also suitable for the water-based glue spraying process. In addition, the liquid optically transparent adhesive 12 is selected as an ultraviolet-heat dual-curing adhesive, so that in the bonding process, the anisotropic conductive adhesive 10 can be coated first, and pre-cured by ultraviolet light, and then borrowed The anisotropic conductive adhesive 10 is further cured by heating in a hot pressing process.

In one embodiment, the diameter of the conductive particles 14 is less than 10 μm, and the density of the conductive particles 14 is 2×10 ⁶ -3×10 ⁶ particles/mL. By mixing the conductive particles 14 and the liquid optically transparent adhesive 12 according to the mass or volume ratio, and fully stirring, the conductive particles 14 are uniformly dispersed in the liquid optically transparent adhesive 12 . After the conductive particles 14 are mixed with the liquid optically transparent adhesive 12 , the conductive particles 14 can be uniformly dispersed in the liquid optically transparent adhesive 12 by using ultrasonic vibration. In FIG. 1 , the diameter of the conductive particles 14 is 5 μm-10 μm, and the viscosity of the liquid optically transparent adhesive 12 is about 30 cps. In other embodiments, the diameter and density of the conductive particles 14 are not limited thereto. For example, the diameter of the conductive particles 14 is less than 5 μm.

The embodiment of the present invention also provides a bonding method. As shown in Figure 2, the bonding method includes:

Step S1: coating the anisotropic conductive adhesive on a flexible circuit board.

Step S2: pre-curing the anisotropic conductive adhesive.

Step S3: hot-press bonding a product to be bonded to the flexible circuit board through the anisotropic conductive adhesive.

In this pasting method, the above-mentioned anisotropic conductive adhesive is used to heat-press the object to be pasted and the flexible circuit board. Since the anisotropic conductive adhesive uses liquid optically transparent adhesive as its adhesive, the anisotropic The shape of the conductive adhesive is controllable. When it is applied in the panel hot-pressing lamination process, different dispensing volumes are set for the area of the gold finger of the flexible circuit board and the area between the gold fingers, so that the area with the gold finger The area between the gold fingers has a small dispensing amount, while the area between the gold fingers has a larger dispensing amount to effectively improve the thickness of the glue in the bonding area, thereby reducing the risk of deformation of the flexible circuit board during the hot pressing process . Moreover, if the bonding area of the object to be bonded (such as a touch panel) is irregular (that is, the bonding area has non-linear distribution edges), it can be controlled by controlling the dispensing shape and point of the anisotropic conductive adhesive. The amount of glue can be dispensed in any shape, so that the special-shaped attachment of the object to be attached (such as a touch panel) and the flexible circuit board can be achieved without additional border cutting, which simplifies the manufacturing process and saves costs.

The above lamination method will be described below with reference to FIG. 3 to FIG. 5 .

Step S1: coating the anisotropic conductive adhesive on a flexible circuit board.

In step S1, the anisotropic conductive adhesive 10 is coated by a glue dispenser, and the spray head of the glue dispenser is controlled by a program to adjust the shape and amount of glue dispensed in a local area.

As shown in FIG. 3 , the flexible circuit board 20 includes a flexible substrate 22 and a plurality of gold fingers 24 disposed on the substrate 22 at intervals. The anisotropic conductive adhesive 10 is coated on the surface of the gold finger 24 away from the substrate 22 and in the gap between two adjacent gold fingers 24 . Regarding the distribution of gold fingers 24 on the flexible circuit board 20 , the area on the flexible circuit board 20 to be glued is divided into three areas. Wherein, the dispensing amount in the gap between two adjacent gold fingers 24 (the area marked as B in FIG. 3 ) is larger than the surface of the gold finger 24 away from the substrate 22 (the area marked as A in FIG. 3 ). area). The amount of glue dispensing near the edge of the substrate 22 (the area labeled C in FIG. 3 ) is smaller than that in the gap between two adjacent gold fingers 24 (the area labeled B in FIG. 3 ). quantity.

In Fig. 3, the coating of the anisotropic conductive adhesive 10 can be carried out by adopting different dispensing amounts according to different areas, so that the dispensing amount of the area A with the gold fingers 24 is smaller than the gap between the gold fingers 24, that is, the area B The amount of dispensing. For example, corresponding to the dispensing amount of area A is 70%, and the dispensing amount of area B is 100%. In this way, since the anisotropic conductive adhesive 10 adopts the liquid optically transparent adhesive 12 as the adhesive, the anisotropic conductive adhesive 10 is in a liquid state, and can be dispensed for different regions of the flexible circuit board 20, and the flexible circuit board 20 Different areas of the machine have different dispensing volumes.

In one embodiment, the diameter of the conductive particles 14 is 5 μm to 10 μm, and the diameter of the nozzle of the dispenser is 50 μm to 80 μm. Before the anisotropic conductive adhesive 10 enters the dispenser, it is fully stirred to ensure the conductivity The particles 14 are uniformly dispersed in the liquid optically transparent adhesive 12 .

In one embodiment, the substrate 22 is made of organic material, such as polyimide (PI) or polyethylene terephthalate (PET). The material of the gold finger 24 is, for example, copper or copper alloy. The height of the gold finger 24 along the thickness direction of the substrate 22 is approximately 10 μm˜20 μm. The flexible circuit board 20 may also include traces on the surface of the base material 22 connected to the gold fingers 24 , and the thickness of the gold fingers 24 is not limited thereto.

Step S2: pre-curing the anisotropic conductive adhesive.

In one embodiment, in the anisotropic conductive adhesive 10 , the liquid optically transparent adhesive 12 is an ultraviolet-heat (UV/Heat) dual-curing adhesive. In step S2, the step of pre-curing is ultraviolet curing.

As shown in FIG. 3 , in step S1 , by controlling the amount of glue dispensed in different regions, the surface of the anisotropic conductive adhesive 10 away from the substrate 22 is flat after pre-curing.

Step S3: hot-press bonding a product to be bonded to the flexible circuit board through the anisotropic conductive adhesive.

As shown in FIG. 4 , the object 30 to be bonded is a touch panel. The touch panel has a touch area 301 and a non-touch area 302 surrounding the touch area 301 . The touch area 301 is roughly rectangular. The flexible circuit board 20 and the touch panel are bonded in the non-touch area 302 . In other embodiments, the object 30 to be bonded is not limited to a touch panel, and it can also be another flexible circuit board, a rigid circuit board, or a display panel.

The touch panel includes a plurality of touch electrodes (not shown) located in the touch area 301 . The plurality of touch electrodes are, for example, single-layer self-capacitive touch electrodes. When a touch occurs, there is a difference in the capacitive sensing signal corresponding to the vicinity of the touch point. The capacitive sensing signal is received and processed, and then converted to obtain the relative position of the touch point. A plurality of touch electrodes can also form a mutual capacitance touch sensing structure. When a touch occurs, the capacitive coupling between the driving electrodes and the sensing electrodes corresponding to the touch point will be affected, resulting in a mutual capacitance-related induction. The signal (such as voltage value) changes, and then the coordinates of each touch point can be calculated.

As shown in FIG. 5 , the touch panel further includes a substrate 32 and a plurality of connection pads 34 disposed on the surface of the substrate 32 at intervals. The connection pad 34 is located in the non-touch area 302 and is electrically connected to the touch electrodes. The connection pads 34 correspond to the gold fingers 24 on the flexible circuit board 20 one by one.

In step S3 , the anisotropic conductive adhesive 10 is further cured after hot pressing, and the connection pad 34 and the golden finger 24 are electrically connected by the anisotropic conductive adhesive 10 . Specifically, the conductive particles 14 between the golden fingers 24 and the connection pads 34 are deformed by being squeezed in a direction perpendicular to the substrate 22, so that the insulating layer in the conductive particles 14 is broken to expose the conductive balls therein, Furthermore, the connection pad 34 and the golden finger 24 are electrically connected by the conductive ball in the direction perpendicular to the substrate 22 , while other positions are electrically insulated laterally because the conductive particles 14 are not broken.

In addition, since step S1 has different dispensing volumes for different areas, the area with golden fingers 24 has a smaller dispensing volume, and after pre-curing (ultraviolet light curing), the obtained colloid is far away from the surface of the substrate 22. The surface has better flatness; after the hot-pressing process, the anisotropic conductive adhesive 10 is further cured (heat-cured), which can effectively improve the thickness of the adhesive in the bonding area, thereby reducing the deformation of the flexible circuit board during the hot-pressing process risk.

In some embodiments, in the step of coating the anisotropic conductive adhesive 10 , the dispenser dispenses glue along a straight line. In the thermocompression bonding step, the object to be bonded 30 is bonded to the flexible circuit board 20 in a linear manner. As shown in FIG. 4 , the bonding area between the touch panel and the flexible circuit board 20 is roughly rectangular, which is non-shaped. In the glue dispensing step, the glue dispenser dispenses glue along the direction parallel to the long side of the rectangle. In the thermocompression bonding step, the touch panel and the flexible circuit board 20 are bonded in a rectangular area.

In some embodiments, in the step of coating the anisotropic conductive adhesive 10, the dispenser performs glue dispensing along a curve; For a curved fit. Curves are, for example, arcs or polylines. For example, the object 30 to be bonded is a touch panel, which has a special-shaped bonding area (that is, a bonding area whose edges are not distributed along a single straight line). Since the anisotropic conductive adhesive 10 uses liquid optically transparent adhesive 12 as the adhesive, in the dispensing step, the dispensing machine of any shape (such as straight lines and curves) can be controlled by the program, and then bonded by hot pressing In the step, while the special-shaped attachment of the touch panel and the flexible circuit board 20 is realized, additional boundary cutting is not required, the manufacturing process is simplified, the cost is saved, and the production efficiency is improved.

The above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced. Without departing from the spirit and scope of the technical solutions of the present invention.

10: Anisotropic conductive adhesive 12: Liquid optical transparent glue 14: Conductive particles 20: Flexible printed circuit board 22: Substrate 24: Goldfinger 30: to be attached 301: touch area 302: Non-touch area 32: Substrate 34: connection pad

FIG. 1 is a schematic plan view of an anisotropic conductive adhesive according to an embodiment of the present invention.

FIG. 2 is a schematic flow chart of a bonding method according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of the structure of coating anisotropic conductive adhesive in step S1 of FIG. 2 .

FIG. 4 is a schematic plan view of thermocompression bonding a product to be bonded to the flexible circuit board in step S3 of FIG. 2 .

FIG. 5 is a schematic cross-sectional view of FIG. 4 along the section line V-V.

10: Anisotropic conductive adhesive

20: Flexible printed circuit board

22: Substrate

24: Goldfinger

Claims (10)

An anisotropic conductive adhesive, the improvement of which includes: a liquid optically transparent adhesive and a plurality of conductive particles mixed in the liquid optically transparent adhesive, each of the conductive particles includes a conductive ball and an insulating layer surrounding the conductive ball layer, the diameter of the conductive particles is less than 10 μm, and the density of the conductive particles is 2×10 ⁶ to 3×10 ⁶ particles/mL. The anisotropic conductive adhesive according to claim 1, wherein the liquid optically transparent adhesive has a viscosity less than 50 cps, and the liquid optically transparent adhesive is an ultraviolet-heat dual-curing adhesive. A bonding method, comprising: Coating the anisotropic conductive adhesive as described in claim 1 or 2 on a flexible circuit board, wherein the flexible circuit board includes a flexible substrate and a plurality of gold fingers arranged at intervals on the substrate, the isotropic A directional conductive adhesive is coated on a surface of the gold fingers away from the base material and in a gap between two adjacent gold fingers; Pre-curing the anisotropic conductive adhesive; Bonding a product to be bonded with the flexible circuit board by means of the anisotropic conductive adhesive, wherein the product to be bonded has a plurality of connection pads corresponding to the golden fingers on the flexible circuit board After heat-compression lamination, the connection pads and the gold fingers are electrically connected by the anisotropic conductive adhesive, and a surface of the base material away from the gold fingers is flat. The bonding method according to claim 3, wherein the pre-curing step is ultraviolet curing. The bonding method according to claim 3, wherein the object to be bonded is a touch panel, and the touch panel includes a plurality of touch electrodes and the connection pads electrically connected to the touch electrodes. The laminating method as described in claim 3, wherein the anisotropic conductive adhesive is coated by a dispenser, and the spray head of the dispenser is controlled by a program, so that the dispensing shape and dispensing of the local area can be adjusted quantity. The bonding method as described in claim 6, wherein, in the step of coating the anisotropic conductive adhesive, the dispenser dispenses glue along a straight line; In the step of thermal compression bonding, the object to be bonded is linearly bonded to the flexible circuit board. The bonding method as described in claim 6, wherein, in the step of coating the anisotropic conductive adhesive, the dispenser performs dispensing along a curve; In the heat-compression bonding step, the object to be bonded is bonded to the flexible circuit board in a curved manner. The bonding method according to claim 6, wherein the amount of glue dispensed in the gap between two adjacent gold fingers is greater than the amount of glue dispensed on a surface of the gold fingers away from the substrate. The bonding method as described in claim 3, wherein, after thermal compression bonding, the insulating layer of the conductive particles between the connection pads and the golden fingers is broken to expose the conductive balls therein , and then the connection pads and the gold fingers are electrically connected through the conductive balls in a direction perpendicular to the substrate.

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