JP3191432B2 - Liquid crystal device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting structure of a liquid crystal panel carried in a pocket television, a wall-mounted television, a projection television, a laptop personal computer, a game machine, and the like.

[0002]

2. Description of the Related Art Conventionally, in order to incorporate a liquid crystal panel such as a pocket television, it is necessary to construct a liquid crystal panel having a small size and a high density. As an example of the countermeasure, a method of directly mounting an IC chip on a glass substrate constituting a liquid crystal panel has been proposed.

Hereinafter, a conventional liquid crystal panel will be described with reference to the drawings. FIG. 2 shows an example of a partial cross-sectional view of a conventional liquid crystal panel mounting structure. 2 in FIG.
1 is an IC chip, 22 is a liquid crystal panel, 23 is an electrode pattern formed on a substrate of the liquid crystal panel, 24 is a flexible circuit board for supplying an input signal for driving the IC,
25 is an electrode pattern on the substrate of the liquid crystal panel for supplying the input signal, 26 is an anisotropic conductive adhesive for bonding the IC chip to the glass substrate of the liquid crystal panel, and 27 is bonding the flexible circuit substrate to the glass substrate. FIG.

In FIG. 2, an IC chip is mounted on a substrate of a liquid crystal panel by face down. IC
An electrode pad as a connection electrode is formed on the active surface of the chip. A connection circuit is formed on the substrate of the liquid crystal panel so as to face the connection electrodes of the IC chip. I above
The input signal for driving the C chip is the flexible circuit board 2
4 through the glass substrate of the liquid crystal panel.

[0005]

Generally, a large number of electrode patterns in a liquid crystal panel are arranged in parallel on a substrate.
As is apparent from FIG. 2, the electrode patterns are continuously connected from the portion where the two substrates of the liquid crystal panel are overlapped to the output electrode of the IC chip. I
The number of output electrodes of the C chip is extremely large. An input signal for driving the IC chip is transmitted from the flexible circuit board 24 to the I signal.
The liquid crystal panel 22 facing the input electrode of the C chip 21
Is supplied to the IC chip 21 through the electrode pattern 23 formed on the substrate. The bonding of the flexible circuit board 24 to the liquid crystal panel 22 is performed by an anisotropic conductive adhesive 27. Further, the IC chip 21 is bonded to a glass substrate of a liquid crystal panel by an anisotropic conductive adhesive 26. The anisotropic conductive adhesives 26 and 27 are made of a common adhesive.

Generally, in such a liquid crystal panel structure, an electrode pad of an IC chip and an electrode pattern of a liquid crystal panel glass substrate are aligned with each other so as to be opposed to each other, and between the IC chip and the glass substrate of the liquid crystal panel. The anisotropic conductive adhesive is sandwiched, and then the anisotropic conductive adhesive is heated while being pressed from above the IC chip, thereby bonding and fixing the IC chip and the glass substrate of the liquid crystal panel. Thereafter, the flexible circuit board is placed on the glass substrate of the liquid crystal panel with an anisotropic conductive adhesive interposed therebetween, and the flexible circuit board is heated and pressed by a pressure bonding tool to join and fix the flexible circuit board and the glass substrate of the liquid crystal panel.

When the IC is first crimped to the liquid crystal panel, the anisotropic conductive adhesive can be bonded and fixed under the crimping condition that reaches the maximum strength. However, after that, when the flexible circuit board is crimped to the liquid crystal panel, the crimping condition is I
When C is pressed under the same conditions as when the C is pressed onto the liquid crystal panel, the anisotropic conductive adhesive for fixing the IC which has been previously pressed is loosened at a high temperature, and the reliability of the IC bonding and fixing is reduced. Also,
If the condition for pressing the flexible circuit board to the liquid crystal panel is reduced, the curing of the anisotropic conductive adhesive is also incomplete and the connection reliability is also reduced.

Accordingly, an object of the present invention is to solve the conventional disadvantages and improve the connection reliability of a liquid crystal panel mounting structure.

[0009]

According to the present invention, there is provided a liquid crystal device comprising:
In a liquid crystal device having a liquid crystal layer sandwiched between two substrates,
Supplying an input signal to an IC chip bonded to the substrate via a first anisotropic conductive adhesive and to the IC chip bonded to the substrate via a second anisotropic conductive adhesive And the glass transition point and softening point of the first anisotropic conductive adhesive, than the glass transition point and softening point of the second anisotropic conductive adhesive, It is characterized by being higher than 10 ° C.

[0010]

FIG. 1 is a partial sectional view of an example of a liquid crystal panel mounting structure according to the present invention. In FIG. 1, 1 is an IC chip,
2 is a liquid crystal panel, 3 is an electrode pattern facing an electrode pad of an IC formed on the liquid crystal panel substrate, 4 is a flexible circuit board, and 5 is an input signal introducing section to a driver IC for bonding the flexible circuit board. 6 is an anisotropic conductive adhesive for bonding the IC to the glass substrate of the liquid crystal panel; 7 is an anisotropic conductive adhesive for bonding the flexible circuit board to the liquid crystal panel; 3 shows an electrode pad. In FIG. 1, an IC chip is mounted face down on a substrate of a liquid crystal panel. An electrode pad as a connection electrode is formed on the active surface of the IC chip. The above IC is mounted on the substrate of the liquid crystal panel.
An electrode pattern is formed facing the connection electrode of the chip. A liquid crystal layer is sandwiched between two substrates constituting a liquid crystal panel, and a large number of X lines and Y lines for driving liquid crystal are arranged in parallel on the respective opposing surfaces of each substrate. In the case of an active matrix panel, a large number of active elements such as TFTs and MIMs are connected to the line. Either one of the substrates is extended outside the overlapping portion of the two substrates, and the terminal portion of the line is disposed immediately outside the overlapping portion of the two substrates. I have. An IC chip for driving liquid crystal is mounted face-down on the extension of the substrate, and an electrode pattern is formed on the extension of the substrate in a pseudo-radial manner between the output electrode of the IC chip and the terminal of the line. ing.

On the other hand, an input signal for driving the IC chip is supplied by a flexible circuit board, and is bonded and connected to an extension of the glass substrate by an anisotropic conductive adhesive. The terminal portion of the flexible circuit board for supplying the input signal has copper foil exposed. The exposed portion of the copper foil is subjected to solder plating, Ni plating, Au plating, 9: 1 Sn plating, Sn plating or the like to prevent rust.

FIG. 3 shows the thermal expansion characteristics of the anisotropic conductive adhesive, and FIG. 4 shows the viscoelasticity of the anisotropic conductive adhesive. FIG.
4 and 11, reference numeral 11 denotes a characteristic curve of the anisotropic conductive adhesive 6 for fixing the IC to the liquid crystal panel glass, and reference numeral 12 denotes a characteristic curve of the anisotropic conductive adhesive 7 for fixing the flexible circuit board to the liquid crystal panel glass. is there. As can be seen from FIG. 3, a general adhesive has a bending point at a certain temperature T1, and this is called a glass transition point. Further, as can be seen from the viscoelasticity curve of FIG. 4, the elastic modulus of the adhesive rapidly decreases at a certain temperature T2, which is called a softening point. The softening point and the glass transition point may be very close values. However, the values may be slightly different and differ depending on the type of the adhesive. This softening point can be compared to the melting point of a metal, but the resin constituting the adhesive usually does not have a clear melting point.

Next, the meanings of the glass transition point and the softening point will be briefly described below. After joining the workpieces, when the temperature is applied, the thermal expansion coefficient below the glass transition point differs from the thermal expansion coefficient above the glass transition point. This may be a factor in deteriorating the bonding reliability. Further, since the softening point is equivalent to the melting point of a metal, if a temperature higher than the softening point is applied to the workpiece, the joining force will be loosened. This softening point also serves as a guide that determines the joining reliability of the article to be joined in a different sense from the glass transition point.

First, an IC chip is fixed to the liquid crystal panel glass with an anisotropic conductive adhesive, and then the flexible circuit board is fixed with an adhesive. The effect on the bonding adhesive must be considered.

If the position of the IC chip is close to the position of the flexible circuit board, the IC chip is pressed on the glass substrate of the liquid crystal panel, and then the flexible circuit board is heated and pressed on the glass substrate. It may loosen the anisotropic conductive adhesive that has conducted to the chip and crimped the IC. Whether or not the looseness is a problem related to the softening point of the anisotropic conductive adhesive to which the IC is pressure-bonded. Since the heat for crimping the flexible circuit board is conducted toward the IC, it is sufficient that the temperature of the anisotropic conductive adhesive under the IC is sufficiently lower than the softening point.

There is another item that poses a problem when the position of the IC chip and the flexible circuit board are close to each other. After the IC chip is pressed on the glass substrate of the liquid crystal panel, the flexible circuit board is heated and pressed on the glass substrate, and the pressure is applied. Is increased, and the reliability of bonding is reduced. The magnitude of the distortion increases as the temperature of the anisotropic conductive adhesive bonding the IC exceeds the glass transition point at which the coefficient of thermal expansion increases. Therefore, it is sufficient that the temperature reached when the flexible circuit board is crimped and reaches the IC after the crimping of the flexible circuit board is sufficiently lower than the glass transition point of the anisotropic conductive adhesive.

In general, the thermal conductivity of glass is small,
Even when the position of the IC chip and the flexible circuit board are approached to some extent, the heat generated during crimping of the flexible circuit board is rarely transmitted to the IC immediately with glass alone. However, there is generally an electrode pattern formed of a metal or the like on the glass substrate, and the amount of heat transmitted to the IC when the flexible circuit board is pressed through the electrode pattern increases.

As described above, in order to prevent the influence of heat at the time of press-fitting the flexible circuit board from reaching the IC junction, the
There is a method of increasing the distance between the flexible circuit board and the flexible circuit board or decreasing the temperature of the flexible circuit board crimping. However, if the distance between the IC and the flexible circuit board is increased, the outer size of the liquid crystal panel increases, and the commercial value of the liquid crystal panel decreases. On the other hand, when the compression temperature of the flexible circuit board is reduced, the above object can be achieved without increasing the outer size of the liquid crystal panel. However, the anisotropic conductive adhesive for crimping the flexible circuit board is the same as the anisotropic conductive adhesive for crimping the IC. As a result, the reliability of crimping the flexible circuit board is reduced.

On the other hand, in the present invention, the softening point and the glass transition point of the anisotropic conductive adhesive for crimping the flexible circuit board are lower by 10 ° C. or more than the anisotropic conductive adhesive for crimping the IC. In particular, the softening point and the glass transition point are significant as described above.

In general, the compression temperature of the anisotropic conductive adhesive is higher than the softening point or the glass transition point described above. It must be sufficiently eliminated by a protruding conductive material such as a copper foil lead. In the present invention,
Since the softening point and glass transition point of the anisotropic conductive adhesive for crimping the flexible circuit board are lower than the softening point and glass transition point for bonding the IC, the flexible circuit board can be applied to the glass substrate of the liquid crystal panel. Even if the pressure bonding temperature is set higher than the softening point of the anisotropic conductive adhesive of the flexible circuit board, since the softening point and glass transition point of the anisotropic conductive adhesive joining the IC are higher, Even if the heat of crimping is transmitted under the IC quite efficiently
The temperature under the IC does not reach the softening point and glass transition point of the anisotropic conductive adhesive for bonding the IC, and the loosening of the anisotropic conductive adhesive for bonding the IC does not occur, and the IC and the liquid crystal panel The mechanical stress during the joining of the glass substrates does not increase, and the reliability of the joining does not decrease. Further, the curing of the anisotropic conductive adhesive for joining the flexible circuit board to the glass substrate of the liquid crystal panel is completely cured, and the reliability is high.

[0021]

As described above, according to the present invention, an input signal for driving an IC chip is applied to an anisotropic conductive adhesive for mounting and mounting an IC chip directly face down on a glass substrate of a liquid crystal panel. By lowering the glass transition point and the softening point of the anisotropic conductive adhesive for bonding the flexible circuit board supplying the IC, the connection reliability of the IC mounting and the flexible circuit board mounting is improved.

[0022]

[Brief description of the drawings]

FIG. 1 is a view showing an example of a mounting structure of a liquid crystal panel in an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a mounting structure of a liquid crystal panel in a conventional example.

FIG. 3 is a graph showing a thermal expansion curve of an anisotropic conductive adhesive.

FIG. 4 is a graph showing viscoelastic properties of an anisotropic conductive adhesive.

[Explanation of symbols]

1, 21 IC chip 2, 22 Liquid crystal panel 3 Electrode pattern opposed to electrode pad of IC formed on substrate of liquid crystal panel 4 Flexible circuit board 5 Input signal introduction part to driver IC for joining flexible circuit board Electrode pattern on liquid crystal panel 6 Anisotropic conductive adhesive for bonding IC to glass substrate of liquid crystal panel 7 Anisotropic conductive adhesive for bonding flexible circuit board to liquid crystal panel 8 Electrode pad of IC 11 IC for liquid crystal panel Characteristic curve of anisotropic conductive adhesive 6 fixed to glass 12 Characteristic curve of anisotropic conductive adhesive 7 fixing flexible circuit board to liquid crystal panel glass 23 Electrode pattern formed on substrate of liquid crystal panel 24 IC Flexible circuit board for supplying an input signal for driving 25 Liquid crystal panel for supplying the input signal Electrode pattern on the glass substrate 26 Anisotropic conductive adhesive for bonding the IC chip to the glass substrate of the liquid crystal panel 27 Anisotropic conductive adhesive for bonding the flexible circuit board to the glass substrate

Claims (1)

(57) [Claims] 1. A liquid crystal device having a liquid crystal layer sandwiched between two substrates, an IC chip bonded to said substrate via a first anisotropic conductive adhesive, and a second anisotropic member. A flexible circuit board for supplying an input signal to the IC chip bonded to the board via a conductive adhesive, wherein a glass transition point and a softening point of the first anisotropic conductive adhesive are provided. Is a liquid crystal device having a temperature higher than the glass transition point and softening point of the second anisotropic conductive adhesive by 10 ° C. or more.