JPH0411797A - Connecting structure for circuit board - Google Patents

Abstract

PURPOSE:To improve reliability by employing ultraviolet ray curable resin as the component of a base material of an anisotropically conductive film to be used as a connecting structure of a circuit board. CONSTITUTION:For example, an anisotropically conductive film 3 for connecting the electrode 11 of a liquid crystal display element to the electrode 7 of a flexible board 6 is composed by mixing or dispersing conductive particles in light curable resin. It has thixotropy before curing. The resin is used solely or in combination with other light curable resin or thermally curable resin so as to obtain suitable connection conditions such as adhesive strength, moisture resistance, etc. The dispersed particles may have conductivity on the outer surface. The electrode 11 of an element 12 is connected to the electrode of the board 6 by pressure contact of a rubber sheet 8, an aluminum retainer 15, a quartz glass 9 through an anisotropically conductive film 3. An ultraviolet ray is emitted from an upper surface through a hot-wire shut-off filter in the pressurized state to cure the film 3. That is, an electric connection is conducted by aggregating and securing the particles and a mechanical connection is executed by curing the resin.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a connection structure for a circuit board using an anisotropic conductive film, and is suitably used, for example, to connect a liquid crystal display element to an external circuit that drives it. be able to.

2. Description of the Related Art In recent years, the degree of integration of pixels in liquid crystal display devices, typified by liquid crystal television receivers, has increased. Along with this, the electrode extraction pitch from the liquid crystal display element is also 100 to 200 μm.
The extent of this is becoming extremely small. For this reason, the conductive rubber connector method conventionally used for electrical connection of modules such as LCD watches cannot be used, and the mainstream is a connection method using an anisotropic conductive film that can support fine-pitch connections. It is becoming.

A connection method using this anisotropic conductive film is used in the IT○ (Indifum Oxide Edition) for liquid crystal display elements! ! Taking as an example a case in which a pole is connected to a Cu electrode of a flexible substrate, this will be explained using FIGS. 3 and 4. In Figure 3, conductive particles 1 such as metal particles such as Ni or solder or carbon fiber are dispersed in a base material 2 made of a thermosetting resin such as epoxy resin or a thermoplastic resin such as SBS (styrene butadiene styrene). The anisotropic conductive film 3 thus prepared is sandwiched between the ITOtJ pole 5 on the glass substrate 4 of the liquid crystal display element and the CU electrode 7 on the flexible substrate 6. Further, the entire structure is sandwiched between a rubber sheet 8 and a quartz glass 9, and infrared rays are irradiated from the surface of the quartz glass 9 under pressure to heat the anisotropic conductive film 3. By pressurizing and heating the anisotropic conductive film 3 in this way,
As shown in FIG. 4, the conductive particles 1 in the portion sandwiched between the ITO electrode 5 and the cut electrode 7 aggregate and stick together, causing a short circuit between the upper and lower electrodes. The other portions remain in a non-conductive state, and as a result, conduction between the electrodes is selectively established by the conductive particles 1. Further, the base material 2 provides a mechanical connection between the glass substrate 4 and the flexible substrate 6 of the liquid crystal display device.

Problems to be Solved by the Invention As mentioned above, in connection using an anisotropic conductive film in which conductive particles are dispersed in a thermosetting resin or thermoplastic resin, the resin is cured by irradiation with an infrared lamp, and the connection part The temperature rises to about 200°C. At this time, the coefficient of linear expansion α of each material constituting the connection part differs greatly, as shown in Table 1 below, so this may cause the electrode to shift after cooling to room temperature, or may occur during heating. This is the cause of residual thermal stress.

(Leaving space below) Table 1 In Table 1 above, the length of the flexible substrate and the anisotropic conductive film is 50 mm, and the deviation between the flexible substrate and the liquid crystal display element substrate is 50 mmX (1.4X10-5. ;7℃3.2〆10-
',,/℃)><200℃-25℃)#94.5
It becomes μm.

This amount corresponds to the electrode pitch. Of course, during heating, the displacement is suppressed by applying pressure.
It is difficult to completely prevent the occurrence of misalignment and residual stress due to differences in thermal expansion coefficients.

Furthermore, since the difference in thermal expansion coefficient between the anisotropic conductive film and the liquid crystal display element substrate is larger, the influence on residual stress becomes even larger. When residual stress is present, the force impedes electrical contact between the conductive particles, possibly causing disconnection.

As described above, connection of anisotropic conductive films by heating may cause poor electrode facing precision and disconnection defects, and some countermeasures are desired. Therefore, an object of the present invention is to provide a circuit board connection structure that solves the above technical problems.

Means for Solving the Problems The present invention provides a first terminal formed on a first circuit board and a second terminal formed on a first circuit board.
In a circuit board connection structure in which a second terminal formed on a circuit board is connected via an anisotropic conductive film made of a base resin mixed with conductive particles, the resin includes a photocurable resin. This is a circuit board connection structure characterized by comprising:

Function: According to the circuit board connection structure of the present invention, no heat is applied during connection, so that displacement of electrodes and generation of residual stress due to differences in thermal expansion coefficients are suppressed.

Embodiment FIG. 1 is a schematic sectional view showing an embodiment to which the circuit board connection structure of the present invention is applied, and FIG. 2 is an enlarged sectional view of a section 14 thereof. Referring to FIG. 1 and FIG. 2, a liquid crystal display element 12 is constructed by interposing a liquid crystal 13 between a pair of glass substrates 12 having electrodes 11 formed on opposing surfaces.

The electrodes 11, which are the first terminals formed on the glass substrate, which is the first circuit board, are ITO electrodes selectively formed at a pitch of 100 to 200 Jim by, for example, photolithography. In addition, Ni-Mo, Ti, Ta
Electrodes may be formed from various metal thin films such as. The pair of glass substrates described above have regions that do not overlap with each other, and a flexible substrate 6, which is a second circuit board on which an integrated circuit for driving a liquid crystal, etc. is mounted, is connected to this region. The second terminal formed on the flexible board 6 is the electrical terminal 4F! 7 is Cu or tin-plated Cu 1]
etc., they are arranged corresponding to the electrodes 11 on the glass substrate using thin film pattern processing technology. The electric conductor WA3 that connects the electric fill of the liquid crystal display element and the electrode 7 of the flexible substrate 6 is composed of a photocurable resin mixed or dispersed with conductive particles, and has thixotropic properties before curing. ing. As photocurable resins, those that have photoreactive groups introduced into synthetic resins such as epoxy, acrylic, and polyester are preferably used, and those that are mixed with a photocuring agent. etc. may also be used. These photocurable resins can be used alone or with adhesive strength,
In order to obtain suitable connection conditions such as moisture resistance, it is used in combination with other photocurable resins or thermosetting resins. The conductive particles to be mixed or dispersed only need to have conductivity at least on the outer surface. For example, a metal layer may be formed on the surface of the elastic member.
These particles have a particle size of about 5 μm to 20 μm and are coated with two or more layers for the purpose of determining adhesion with a layer or an elastic member. As the elastic member, particles made of elastic polymer materials such as rubbers such as silicone rubber and urethane rubber and synthetic resins are used, and as the metal layer, Ni, A, etc. are used.
u, Ag, C1Cu, Pd, Pb, Sn, or In
metals such as or alloys of these metals are used.

The electrodes 11 of the liquid crystal display element 12 and the electrodes 7 of the flexible substrate 6 are connected via the above-described anisotropic conductive film 3 to the rubber sheet 8, aluminum holding plate 15, and quartz glass 9.
It is done by pressing between.

In this pressurized state, ultraviolet rays are irradiated from the upper surface through a heat ray blocking filter, etc., and the ultraviolet rays are introduced through the quartz glass 9 and the liquid crystal panel 4. This irradiation causes the anisotropic conductive film 3 to harden. That is, as already explained using FIGS. 3 and 4, the electrical connection is established by the agglomeration and fixation of the conductive particles, and the mechanical connection is established by the hardening of the resin. A connection is made.

In this embodiment, a transparent ITO electrode is formed on the glass substrate on the ultraviolet irradiation side (upper side in FIG. 1) of the liquid crystal display element 4, so that ultraviolet rays are not blocked and curing is performed smoothly. In addition, since heating is not required in this way, it becomes possible to move the polarizing plate, which has poor heat resistance and has been pasted apart from the connection part, closer to the connection part, thereby promoting an expansion of the image display area. Furthermore, when the electrode is formed using a material that blocks ultraviolet rays, such as a metal, a photocurable resin and a thermosetting resin may be used together as the base material of the anisotropic conductive film 3. That is, first, the liquid crystal display element 12 and the flexible substrate 6 are fixed by irradiating ultraviolet rays to harden the photocurable resin, and then heated to harden the thermosetting resin at the portion where the electrodes face each other. Since the liquid crystal display element 12 and the flexible substrate 6 are already firmly attached, displacement due to thermal expansion can be suppressed.

Although the case where the present invention is implemented in a liquid crystal display device has been described above, the present invention can also be implemented in other display devices such as a plasma display device, an electroluminescent display device, and an electrochromic display device.

Effects of the Invention As described above, according to the present invention, since an ultraviolet curable resin is used as a component of the base material of the anisotropic conductive film, the deviation of the electrode pitch due to thermal expansion caused by heating during connection is effectively prevented. A highly reliable circuit board connection structure with low residual stress and low residual stress can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the present invention, FIG. 2 is an enlarged sectional view of section 14 thereof, FIGS. 3 and 4 [2I
FIG. 2 is a cross-sectional view illustrating a connection method using an anisotropic conductive film. DESCRIPTION OF SYMBOLS 1... Conductive particle, 2... Base material, 3... Anisotropic conductive film, 4... Glass substrate, 5... ITO electrode, 6... Flexible substrate, 7... Cu electrode, 8・-Rubber sheet,
9. Quartz glass, 10. Polarizing plate, 11. Electrode, 12. Liquid crystal display element, 13. Liquid crystal agent Patent attorney Number of strokes Keiichi Figure

Claims (1)

[Scope of Claims] A first terminal formed on a first circuit board and a second terminal formed on a second circuit board are formed by an anisotropic conductive film made by mixing conductive particles into a resin serving as a base material. A circuit board connection structure in which the circuit board is connected through a circuit board, wherein the resin includes a photocurable resin.