JP3298110B2 - Anisotropic conductive adhesive and bonding method thereof - Google Patents

Abstract

PURPOSE:To obtain the subject adhesive, homogeneously containing particles of a light absorber for black to brown color having a smaller outside diameter than that of electrically conductive particles in the interior of the adhesive and capable of preventing junction quality of OLB junctions and COG junctions from deteriorating by heat. CONSTITUTION:The objective adhesive homogeneously containing particles of a light absorber for black to brown color, composed of carbon powder particles, black plastic balls, etc., and having a smaller outside diameter (the smaller the diameter, the better) than that of electrically conductive particles in the interior of the adhesive. Furthermore, a curing accelerator, colored to black to brown and contained in microcapsules is preferably contained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION OUTER-L of liquid crystal display panel
Bonding of glass panel and flexible tape in EAD-BONDING mounting, and CHIP-ON-GL
The present invention relates to an anisotropic conductive adhesive and a bonding method using the same in bonding a glass panel and an IC chip in ASS mounting.

[0002]

2. Description of the Related Art An electrode for driving a liquid crystal is formed on a glass panel of a liquid crystal display panel. The glass electrode is formed of a flexible tape on which an IC for driving a liquid crystal is mounted and the shape and pitch of a lead wire. Thermocompression bonding is performed by an anisotropic conductive adhesive which is not restricted by the above and can be connected to a target bonding. Alternatively, the liquid crystal driving IC may be replaced with a flexible tape.
Thermo-compression bonding is directly performed with an electrode of a glass panel using an anisotropic conductive adhesive without using a loop. The former is OUTER-LE
AD-BONDING implementation (hereinafter referred to as OLB implementation),
The latter is called CHIP-ON-GLASS implementation (hereinafter referred to as COG implementation). As the anisotropic conductive adhesive, conductive particles for securing conductivity, for example, particles obtained by plating nickel gold on a plastic ball of about 10 μm to 30 μm or a solder ball are used. For example, a thermoplastic adhesive that exhibits plasticity by applying heat or a thermosetting adhesive that exhibits curability by applying heat is used. Since the conductive particles are evenly and appropriately dispersed in the adhesive and do not come into contact with each other, when the particles are sandwiched between the conductors and compressed, they are conductive in the compression direction (z direction) of the particles and perpendicular to the direction (x , Y-direction). FIG. 2 shows a sectional view of a conventional anisotropic conductive adhesive. The conductive particles 1 are evenly dispersed in the adhesive 2 so as not to contact each other. The thickness of the adhesive 2 is 2 to 5 times the thickness of the conductive particles 1.

The OLB mounting method or the COG mounting method using an anisotropic conductive adhesive secures the conductivity of a glass electrode and a conductive electrode of a flexible tape or a glass electrode and a conductive electrode of an IC chip through conductive particles. Therefore, a force for compressing the anisotropic conductive adhesive below the diameter of the conductive particles is evenly applied. Further, since heat is applied to the adhesive to secure the adhesion between the glass and the flexible tape or the glass and the IC chip, the heating head is applied to a flexible tape or an IC chip having a small heat capacity and a high thermal conductivity. A method is known in which heat is applied to the adhesive and heat energy is transmitted to the adhesive by heat transfer.

[0004]

However, in the conventional method,
Since the method does not directly supply heat to the adhesive but uses heat transfer from a flexible tape or an IC chip, it has the following problems.

[0005] OLB mounting: Since the temperature of the flexible tape is higher than the temperature required by the adhesive for bonding, a flexible tape having a high heat-resistant temperature is required. Further, in the joining process, since the flexible tape expands due to thermal expansion, a positional shift due to the expansion is remarkably exhibited. Further, in order to suppress these, a flexible tape having high heat resistance and low thermal expansion is required, resulting in an expensive flexible tape. FIG. 5 is a cross-sectional view showing an OLB failure caused by expansion of the flexible tape due to thermal expansion. In some cases, the relative positions of the electrode 5 of the flexible tape and the electrode 7 of the glass panel do not match, causing the electrodes that should be conductive to be conductive and the electrodes that should not be conductive to be conductive. Has occurred.

[0006] COG mounting: Since the temperature of the IC chip is higher than the temperature required for bonding, the IC chip is warped due to heat, and the periphery of the IC chip or the center of the IC chip. In this case, a gap is formed between the electrode of the glass panel and the electrode of the IC chip, and poor conduction tends to appear. FIG. 6 is a sectional view showing this state. Since the flatness of the IC chip is deteriorated, the distance between the glass panel 6 and the IC is larger than the distance determined by the conductive particles in the center of the figure.
The conductive particles 1 on both sides of the figure
Then, a gap occurs between the electrode 9 of the IC chip or the conductive particles 1 and the electrode 7 of the glass panel, or a short contact area due to a small contact area results in poor conduction. In both methods, since the pressure bonding head is heated, it is difficult to control the flatness of the head in a heated state, resulting in uneven pressure bonding depending on the location.

Accordingly, the present invention has been made to solve the above problems, and provides an anisotropic conductive adhesive which is easily heated directly and a method for directly heating the anisotropic conductive adhesive. And to prevent a decrease in bonding quality of COG pressure bonding.

[0008]

The anisotropic conductive adhesive according to the present invention is an anisotropic conductive adhesive in which conductive particles are uniformly dispersed therein, and has an outer diameter smaller than that of the conductive particles. Light absorbing particles made of a body are uniformly dispersed therein, and the light absorbing particles have a characteristic of converting irradiated light energy into heat energy. Further, the bonding method of the present invention is a method of electrically bonding a target A and a target B with an anisotropic conductive adhesive in which conductive particles are uniformly dispersed. Light absorbing particles made of an insulator having a small outer diameter are uniformly dispersed therein, and the light absorbing particles have a characteristic of converting irradiated light energy into heat energy.

Further, in the bonding of the glass panel to the flexible tape or the bonding of the glass panel and the IC chip using the above-mentioned anisotropic conductive adhesive, the transparent pedestal is placed with the anisotropic conductive adhesive interposed therebetween. A glass head and a flexible tape or a glass panel and an IC chip are sandwiched by a pressurizing head to apply a constant pressure, and light is applied to the anisotropic conductive adhesive from below the transparent receiving base by heat energy.
In this case, the glass panel and the flexible tape or the glass panel and the IC chip are joined. .

[0010] Alternatively, in bonding a glass panel to a flexible tape or bonding a glass panel to an IC chip using the anisotropic conductive adhesive described above, a transparent pedestal is placed with the anisotropic conductive adhesive interposed therebetween. Glass panel and flexible tape or glass panel and IC with pressure head
In order to improve the temperature rise of the anisotropic conductive adhesive by irradiating the anisotropic conductive adhesive with light as heat energy from below the transparent pedestal while applying a constant pressure while sandwiching the chip. By heating the pressurizing head, the glass panel and the flexible tape or the glass panel and the IC chip are joined.

[0011]

In the joining using the anisotropic conductive adhesive, the method of supplying the heat energy necessary for securing the adhesiveness to the anisotropic conductive adhesive is based on the anisotropic conductive heating by contact heating symmetrical to the bonding. A direct heating method by non-contact heating of the anisotropic conductive adhesive becomes possible instead of a method of conducting heat to the adhesive. Thereby, the mechanism separation and independent control of the pressurizing mechanism and the heating mechanism, which are the apparatus conditions for bonding, can be performed.

[0012]

FIG. 1 is a sectional view of an anisotropic conductive adhesive according to the present invention. The fact that the conductive particles 1 for securing the conductivity are uniformly dispersed in the adhesive 2 for securing the adhesion to the extent that the conductive particles 1 can exhibit anisotropy in conductivity when compressed is different from the conventional case. Absent. The present invention is further characterized in that the adhesive 2 uniformly contains particles that easily absorb light energy, that is, light absorbing particles 3. The diameter of the light absorbing particles 3 needs to be smaller than the diameter of the conductive particles 1. This is because when the anisotropic conductive adhesive is compressed, it must be compressed to a thickness determined by the diameter of the conductive particles 1, and the smaller the diameter of the light absorbing particles 3, the better.
Regarding the conductivity, it may be a conductor or an insulator. Further, in order to improve light energy absorption, black or brown coloring is performed. This includes carbon powder particles and black plastic balls. Further, the thermosetting adhesive contains a curing accelerator for accelerating the curing of the adhesive. The curing accelerator is protected as a microcapsule at normal temperature, and the microcapsules are destroyed by heating, thereby exhibiting a role as a curing accelerator. Therefore, the effect of the present invention can be directly exhibited by coloring the curing accelerator itself with a black or brown color. As described above, the light absorbing particles 3 are substances capable of maximizing the absorption of light energy without impairing the role of the adhesive 2 and the anisotropic conductivity of the conductive particles 1.

Next, FIG. 7 is a sectional view showing the principle of heating when the bonding method using the anisotropic conductive adhesive according to the present invention is applied to OLB mounting and COG mounting. The flexible tape or IC chip 20 to be bonded and the glass panel 6 are pressed and compressed by the pressure receiving table 19 and the pressure head 14 with an anisotropic conductive adhesive therebetween. Due to the compression, the electrode 21 of the flexible tape or the electrode 21 of the IC chip and the electrode 7 of the glass panel become conductive through the conductive particles 1. Now, the method for heating the anisotropic conductive film, which is a feature of the present invention, is as follows. A glass capable of transmitting light is selected for the pressure receiving pedestal 19, and light is irradiated from the pressure receiving pedestal 19 side. Quartz glass may be used for the glass panel 6, but in general, soda glass or Pyrex glass is used, so that light having a wavelength range of 300 nm or more, for example, light from a halogen lamp or a xenon lamp close to natural light is used. The light beam 10 passes through the pressure receiving table 19 and the glass panel 6, reaches the light absorbing particles 3, and converts light energy into heat energy. The heat energy received by the light absorbing particles 3 is given to the adhesive 2 as heat transfer 11 from the light absorbing particles 3.
Since the light beam 10 is also applied to a portion other than the light absorbing particles 3 such as the flexible tape or the IC chip 20 or the conductive particles 1, the same effects as those found in the light absorbing particles 3 such as the conversion of light energy into heat energy are also obtained. can get.

FIG. 8 is a cross-sectional view of the heating principle when the method of improving the temperature rise characteristic of the method shown in FIG. 7 is applied, that is, the bonding method according to claim 3 is applied to OLB mounting and COG mounting. . By heating the pressure bonding head 14 in addition to the method shown in FIG.
The heat energy of the flexible tape or the IC chip 20 is given to the flexible tape or the IC chip 20 as the heat transfer 12 and the heat energy of the flexible tape or the IC chip 20 is further transferred to the heat transfer 1.
3 is given to the adhesive 2. Here, it should be noted that the reason why the pressure bonding head 14 is heated is to prevent the heat energy given to the adhesive 2 in the method of FIG. 7 from being taken by the flexible tape or the IC chip 20 as heat transfer. The point is that it is aimed at. That is, it is to prevent heat energy to the adhesive 2 obtained by the light beam from being taken away by peripheral substances other than the adhesive 2.

FIG. 9 is a temperature rise characteristic diagram for explaining the effect of FIG. The horizontal axis indicates time, and the vertical axis indicates temperature. The temperature 23 of the adhesive in the case of FIG. 8 is the same as the temperature of the adhesive 22 in the case of FIG. 7, but the temperature rise is substantially improved. However, although the ultimate temperature of the flexible tape or IC chip also increases by ΔT, the head temperature may be set so that the temperature does not become as high as the problem described in the problem. Improvement of the rise property of the adhesive temperature is indispensable for shortening the time of the thermocompression bonding step.

FIG. 10 shows the conventional method and FIGS. 7 and 8 described above.
FIG. 5 is an explanatory diagram comparing differences of the present method shown in FIG. At each point of the pressure bonding head 14, the flexible tape or the IC chip 20, the adhesive 2, and the glass panel 6, a temperature distribution 26 according to the conventional method, a temperature distribution 27 according to FIG. 7, and a temperature distribution 28 according to FIG. Note that the adhesive temperature is the same in both methods, but there is a significant difference in the flexible tape or IC chip temperature. In the conventional method, the temperature of the flexible tape or the IC chip naturally becomes higher than the temperature of the adhesive because the contact heating is performed from the pressure bonding head. On the other hand, in the method according to the present invention, the adhesive can be directly heated because of non-contact heating using light, and the temperature of the flexible tape or the IC chip can be kept lower than the adhesive temperature. Specifically, when the adhesive temperature is set to 200 degrees, the flexible tape temperature is about 250 in the conventional method.
Degrees in the method according to the invention, approximately 100-150 degrees. That is, at a flexible tape temperature of 150 to
This is a temperature decrease of 100 degrees, and the rate of change between normal temperature and heating is also 1/3 to 1/2 as compared with the conventional method. That is, this is equivalent to suppressing the thermal effect on the flexible tape to 1/3 to 1/2. This means that I
The same applies to the case of the C chip.

Next, concrete examples of the method described above will be described for each of the OLB mounting and the COG mounting. FIG. 3 is an OLB bonding diagram according to the present method. Flexible tape 4 at the joint position of glass panel 6
Are aligned and then thermocompression-bonded. In FIG.
The left side is the temporary pressure bonding step, and the right side is the main pressure bonding step according to the present invention. The pressure bonding head 14 is pressed against the portion where the anisotropic conductive adhesive is present, and a light beam is irradiated from the glass panel 6 side through the transparent pressure bonding support 19. Crimping head 1
4, the flexible tape 4 is pressed in units of one unit because the number of light beam sources is one and the movable stroke is limited. It is also possible to press them together. The light beam is guided from an optical fiber source by an optical fiber 16 and condensed into a spot by a spot condensing lens 17. Since the anisotropic conductive adhesive to be condensed is not a spot but an elongated line, the light beam needs to be developed from the spot to a line, and the optical fiber 16 is moved in the line direction. The moving speed is determined by satisfying the heat energy required by the adhesive, and the number of times may be one movement or several reciprocations.

FIG. 4 is a COG bonding diagram according to the present invention. As in the case of the OLB bonding, a plurality of IC chips 8 are aligned with the bonding position of the glass panel 6, and then thermocompression-bonded. However, the steps may not be divided as in the temporary pressure bonding step and the main pressure bonding step. However, the thermocompression bonding process can be considered independently. The shape of the IC chip 8 is generally rectangular, and the arrangement of the electrodes 9 of the IC chip is also rectangular accordingly. Therefore, IC
An external dimension similar to or larger than the external dimension of the chip 8 is required. Since the anisotropic conductive adhesive to be irradiated with light is also arranged on a rectangular line, it is necessary to adjust the light beam irradiation method accordingly. As in the case of the OLB junction, the spot light can be moved in a rectangular line shape. However, a case where the spot light is not moved is described here.
The light beam is guided from the light source by the optical fiber 16 and is condensed in a four-sided line shape by the four-sided line condenser lens 18. The optical fiber emits a light beam for a certain time without moving. As described above, there are two cases: the case where the light beam is spot-shaped for scanning and the case where the irradiation is performed collectively according to the shape of the irradiation target.The former is flexible in that the irradiation target can be arbitrarily selected and the latter is the irradiation. Although the target is limited, there is an advantage in that it has no moving mechanism and irradiation unevenness due to uneven moving speed is hardly generated, and can be used properly depending on the purpose.

Crimping head 14 in FIGS. 3 and 4
Can be satisfied by using a crimping head with a built-in heater such as a conventional crimping head in order to satisfy claim 3. However, as described above, the purpose is to improve the temperature rise of the anisotropic conductive adhesive, and the heating of the pressure bonding head, which causes the problem described in the problem, is not performed.

Finally, the embodiment described so far is claim 1
Although the conventional anisotropic conductive film has been premised, the effect of directly heating the adhesive is weakened even with the conventional anisotropic conductive film, but it is an effective means for solving the problem. 3 and 4 are also applied to the embodiment.

[0021]

In the process of joining a glass panel and a flexible tape or a glass panel and an IC chip using an anisotropic conductive adhesive, the adverse effect of heat applied to the joining object can be minimized. It is possible to stabilize the uniform thermal energy distribution for securing the joining quality, that is, the positional accuracy and gap accuracy for ensuring the conductivity, and the adhesiveness.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of the anisotropic conductive adhesive of the present invention.

FIG. 2 is a cross-sectional view of a conventional anisotropic conductive adhesive.

FIG. 3 is an OLB bonding diagram according to the present invention.

FIG. 4 is a COG bonding diagram according to the present invention.

FIG. 5 is a cross-sectional view of an OLB defect in the conventional bonding.

FIG. 6 is a cross-sectional view of a COG junction in a conventional junction.

FIG. 7 is a sectional view of a heating principle according to the present invention.

FIG. 8 is a sectional view of the principle of heating according to the present invention.

FIG. 9 is a temperature rise characteristic diagram according to the present invention.

FIG. 10 is a comparison diagram of heat distribution between the present invention and the related art.

[Explanation of symbols]

1: Conductive particle 2: Adhesive 3: Light absorbing particle 4: Flexible tape 5: Flexible tape electrode 6: Glass panel 7: Glass panel electrode 8: IC chip 9: IC chip electrode 10: Light Beam 11: Heat transfer from light absorbing particles 12: Heat transfer from pressure bonding head 13: Heat transfer from flexible tape 14: Pressure bonding head 15: Anisotropic conductive adhesive 16: Optical fiber 17: Spot Light-collecting lens 18: Four-sided line light-collecting lens 19: Crimping cradle 20: Flexible tape or glass panel 21: Flexible tape or glass panel electrode 22: Adhesive temperature in FIG. 7 23: FIG. 24: Flexible tape or IC chip temperature of FIG. 7 25: Flexible tape or IC chip temperature of FIG.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI H01B 5/00 H01B 5/00 Z 5/16 5/16 H01R 4/04 H01R 4/04 // H01L 21/52 H01L 21 / 52 E H05K 1/14 H05K 1/14 J 3/32 3/32 B (56) References JP-A-62-18793 (JP, A) JP-A-4-237903 (JP, A) JP-A Sho 62- 135579 (JP, A) JP-A-52-53941 (JP, A) JP-A-57-111366 (JP, A) JP-A-62-79281 (JP, A) JP-A-49-28630 (JP, A) JP-A-59-75968 (JP, A) JP-A-61-152777 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09J 201/00-201/10 C09J 5/00 -5/10 C09J 9/02 C09J 11/00-11/08 H01B 1/20-1/24 H01B 5/00 H01B 5/16 H01R 4/04 H01L 21/52 H05K 1/14 H05K 3/32

Claims (2)

(57) [Claims] 1. An anisotropic conductive adhesive in which conductive particles are uniformly dispersed therein, wherein light-absorbing particles comprising an insulator having a smaller outer diameter than said conductive particles are uniformly dispersed therein. Wherein the light-absorbing particles have a property of converting irradiated light energy into heat energy. 2. A method of electrically joining an object to be joined A and an object to be joined B with an anisotropic conductive adhesive in which conductive particles are uniformly dispersed, wherein the outer diameter of the object is smaller than that of the conductive particles. A bonding method, wherein light-absorbing particles made of an insulator are uniformly dispersed therein, and the light-absorbing particles have a property of converting irradiated light energy into heat energy.