Flat panel displays (FPDs), which include liquid crystal display (LCD), plasma display panel (PDP), field emission display (FED) and vacuum fluorescence display (VFD), are expected to become major means for communicating information in the 21st century due to their low noise and low power consumption. In the prior art method for sealing two glasses, as will be described in detail, seal material or frit is pre-baked in the air with oxygen present under atmospheric pressure, and then glasses and pre-baked seal material are heated and sealed under inert gas environment at atmospheric pressure, and then vacuum is generated to form hermetic sealing.

Now prior art method for sealing two glasses using frit will be described. To one side of backplate, which is one of the two glasses to be sealed, frit is deposited with predetermined width and thickness. Dispensing or screen printing is generally used as a depositing method. Glass with frit deposited thereon undergoes drying process to remove water and solvent in the frit. The time required is 10 minutes and the temperature is about 100 degrees centigrade. After drying process, pre-baking process starts to remove binder material in the frit. In the pre-baking process, binder (kind of acryl) material is burnt out in the air with oxygen present so that oxidation is possible.

The temperature is 370 to 450 degrees centigrade and required time is 30 to 60 minutes.

After pre-baking process, frit and glass are attached together and sealing process to seal another glass (faceplate) starts. In sealing process, two glasses, backplate and faceplate, which are aligned and fixed with clip to maintain alignment are inserted into furnace and heat is applied. The temperature is maintained at 400 to 450 degrees centigrade for 10 to 30 minutes. The gases for sealing process are gases like nitrogen or carbon dioxide, which do not degrade the device characteristics.

In some cases pre-baking process can be skipped after drying process and two glasses which are aligned and fixed using clip are inserted into furnace for sealing process.

By performing above processes of depositing frit, drying, pre-baking and sealing at the predetermined temperature and gas environment, the process for sealing panels or glasses using frit under atmospheric pressure completes. When it is necessary to maintain

predetermined distance between two glasses, frit is deposited on both sides of glass with thickness corresponding to the predetermined distance using said method, and above process of drying and pre-baking are performed separately. The glass with frit deposited on both sides, is cut with predetermined width and placed on the predetermined position of glass to be sealed, aligned with another glass to be sealed, fixed with clip and then inserted into the furnace for sealing process.

The method for sealing glasses using frit has been used in the manufacturing process of FED, PDP and VFD. After sealing, in the prior art method, the sealed area is evacuated to predetermined degree of vacuum using evacuation tube provided on one side of the glass. The time required for evacuation is generally more than 10 hours. After evacuation, tube of FED or VFD is sealed by heating and tube of PDP is sealed by heating after discharge gas is inserted through evacuation tube. In this way, prior art method of sealing FED, PDP or VFD completes.

Prior art method of sealing glasses and evacuating after sealing, however, suffer many problems. Electrode material formed on the glass during sealing process is degraded by the gases like oxygen and productivity is lowered because of long evacuation time.

Also, there are additional process such as attachment of evacuation tube and sealing of tube by melting after evacuation.

Much effort has been made on the sealing method of glasses using frit under a vacuum to solve these problems of degradation of device and addition of evacuation process. But there still are problems in the sealing method of glasses using frit under a vacuum. Especially, there remain binder material which is not completely removed before sealing temperature from the frit which is inserted into a vacuum after preprocessing step, and other materials which are not evacuated from the frit after binder is oxidized, which generate as air bubbles on the surface and inside of frit degrading vacuum sealing and weakening the sealing strength such that seal portion is easily broken away even by hand.

Disclosure of the Invention One object of the invention is to provide a method for sealing two panels using frit under a vacuum.

Another object of the invention is to provide a method for sealing at low temperature under a vacuum.

To achieve these objects, one embodiment of the present invention comprises preprocessing step wherein frit is heated under a vacuum to remove binder and gas and then frit is attached to a glass using gas, and sealing step wherein another glass is aligned to the preprocessed glass and sealed under a vacuum.

According to one embodiment of the present invention, the present invention includes maintaining the temperature of vacuum chamber at not less than 300 degrees centigrade for at least 10 minutes in the preprocessing step.

According to one embodiment of the present invention, the present invention also includes attaching frit to the glass by introducing gas into the vacuum chamber after removing binder and gas in the frit.

According to another embodiment of the present invention, the present invention includes heating the frit under a vacuum to remove binder and gas in the preprocessing step and sealing preprocessed glass and another glass which is aligned with preprocessed glass by applying mechanical pressure on top and bottom sides of two glasses while applying heat under a vacuum.

Brief Description of the Drawings Fig. 1 is a perspective view illustrating glass with frit deposited thereon, Fig. 2a through Fig. 2d illustrate the process of one embodiment of the present invention, Fig. 3a and Fig. 3b are graphs illustrating the relation of pressure versus time and temperature versus time, Fig. 4a through Fig. 4e illustrate the process of another embodiment of the present invention, Fig. 5a through Fig. 5f illustrate the process of yet another embodiment of the present invention, and Fig. 6 is a graph illustrating the relation of pressure versus time and temperature versus time according to another embodiment of the invention.

Best Mode for Carrying out the Invention Now a method for sealing a panel under a vacuum according to the present invention will be described in detail with reference to accompanying drawings. The method for sealing a panel according to one embodiment of the present invention comprises

preprocessing step wherein the first glass or backplate with frit painted thereon is heated under the first condition in a vacuum chamber and then gas is introduced into said vacuum chamber; and sealing step wherein the first glass preprocessed by said preprocessing step and corresponding second glass or faceplate are sealed by heating said faceplate and backplate under the second condition in a vacuum chamber.

Preprocessing step will now be described. The surface of the backplate to be sealed is cleaned by alcohol to remove organic materials. When there are patterns to form display element, appropriate cleaning method is used such as plasma cleaning or thermal cleaning according to the pattern forming material.

Then, as shown in Fig. 1, frit 20 is deposited on the predetermined portion of backplate 10 using the method of dispensing or screen printing with predetermined width and thickness. In general, thickness is 100 micrometer and width is 4 mm. Deposited frit undergoes drying process for about 10 minutes at temperature of 100 degrees centigrade. When frit bars are used, frit bars are placed on the predetermined position of the surface of glass.

Binder 21 and gas 22 are included in the frit 20 as shown in Fig. 2a. In the preprocessing step, binder material and gas in the frit are completely removed. A glass with frit deposited on it is placed in the preprocessing chamber (hereinafter referred to as evacuation chamber). Evacuation chamber can be evacuated to high degree of vacuum and equipped with heater which can heat the chamber to the temperature of 500 degrees centigrade and gas inlet valve which can destroy vacuum promptly. The glass placed in the evacuation chamber is heated under a vacuum. The heating temperature depends on the frit but generally between 370 and 450 degrees centigrade under atmospheric environment and the time is about 10 minutes. The glass and frit, or the glass and frit bar maintained under this condition are completely outgassed and outbindered. But even under this condition, air bubble can be formed on the surface or inside the frit as in Fig.

2b or, in the case of glass and frit bar, there may be space between glass and frit bar and glass are not completely attached.

At this time, by introducing gas into the evacuation chamber, frit bar and glass are attached due to the pressure of the introduced gas as shown in Fig. 2c, and air bubbles inside and on the surface of the frit are removed by pressing using the pressure of gas while frit has fluidity. Preferably, the speed of introducing gas should be fast. In general, according to the present invention, the time required to reach atmospheric pressure from the vacuum of preprocessing step (l0E-5 l0E-6) is 10 seconds. After vacuum is destroyed by introducing gas, the pressure inside the chamber is not less than atmospheric pressure (760torr).

Then, by lowering temperature with predetermined speed, preprocessing step

completes. The gas for destroying vacuum may be chosen depending on the characteristics of device but generally argon or nitrogen. The joining surface of preprocessed frit and glass is in a complete state for sealing without air bubble.

Preprocessed glass and frit, or glass and frit bar are attached and together with another glass undergoes sealing step for vacuum sealing.

As shown in Fig. 2d, two glasses 10 and 30 are inserted into the sealing chamber which is maintained under a vacuum and are fixed by fixing device which fixes upper and lower plate facing each other. After aligning, two glasses are heated by heater to the predetermined temperature and when the predetermined temperature is reached, pressure is applied for predetermined time to attach two glasses, and then by lowering the temperature, sealing step under a vacuum completes. The predetermined temperature depends on the characteristics of the frit, but is generally between 270 and 350 degrees centigrade. The time is generally 10 minutes but shorter time is possible. In the present invention the time is 1 minute but, as readily can be seen, shorter time is required at high temperature and longer time is required at low temperature.

Fig. 3a is a graph showing the change of pressure and temperature versus time in the vacuum chamber. As shown in the figure, vacuum is generated and pressure is lowered.

Then after predetermined temperature is maintained for certain time (10 minutes), vacuum is destroyed by introducing gas for 10 seconds to make frit attached to the glass.

After frit is attached to the glass, sealing step is carried out as shown in Fig. 3b. The procedure is the same as shown in Fig. 3a, and predetermined temperature is maintained for certain time (about 1 minute) after vacuum is made.

According to another embodiment of the present invention, pressure is applied during sealing step without step of destroying vacuum by introducing gas during preprocessing step.

First, as shown in Fig 4a, frit 20 is deposited on the glass 10 and the glass with frit deposited on it is placed in the vacuum chamber. Then, the glass placed in the vacuum chamber is heated under a vacuum. The heating temperature of the frit depends on the frit material but generally between 370 and 450 degrees centigrade under atmospheric environment and the time for heating is 10 minutes. As illustrated in Fig. 4b, binder 21 and gas 22 evaporate and when this condition is maintained for predetermined time, the gas and binder of the glass and frit, or glass and frit bar are completely removed. But even in this state, depending on the characteristics of the frit material, air bubble can be formed inside the frit and on the surface of frit, and in the case of glass and frit bar, there can be space between glass and frit bar.

Then, sealing step starts. As shown in Fig. 4d, preprocessed frit from which gas and binder are removed is deposited on the glass and this glass is placed on the other glass and while maintaining aligned state, mechanical pressure is applied to the upper and lower surface of two glasses while applying heat under a vacuum as shown in Fig. 4e.

In this way, two glasses 10,30 are sealed without generating bubble from the frit 20.

According to another embodiment of the present invention, frit bar in the shape of square frame as shown in Fig. 5a is used in the above preprocessing step. Heat is applied to the frit containing binder 21 and gas 22 as shown in Fig 5b, then binder 21 and gas 22 evaporate as shown in Fig. 5c, and as gas is introduced into the vacuum chamber the projected portion shown in Fig. 5d is removed by the pressure of gas as shown in Fig.

5e. Then, preprocessed frit is placed between two glasses 10,30 and by applying heat under a vacuum sealing step is carried out without generating air bubble.

The sealing of glasses using frit under a vacuum can be carried out at lower temperature than is needed in sealing under atmospheric pressure (270 degrees centigrade). The same temperature as the temperature needed in sealing under atmospheric pressure or higher temperature is also possible. Heating can be performed using a laser.

Sealing can be performed locally so as not to destroy the alignment after aligning step and sealing is performed by heating in other vacuum chamber.

In an alternative embodiment of the present invention preprocessing step can be carried out as follows. When predetermined temperature is reached in lowering the temperature after vacuum is destroyed by the introducing gas, the temperature is no more lowered and, as shown in Fig. 6, the chamber is evacuated again and the sealing process is carried out in the sealing chamber.

. As described above, the present invention provides the method for sealing glasses using frit under a vacuum. By sealing glasses under a vacuum, there is no need of pre- glazing and glazing step in the atmosphere in attaching evacuation tube, and of evacuation step after glazing step in the production of flat panel display such as FED, PDP and VFD, and only preprocessing step and sealing step under a vacuum are needed.

Thus the present invention reduces manufacturing processes and the number of defects and since sealing can be carried out at low temperature, production costs are reduced. In addition, since there is no need of exposing the electrode pattern to the atmosphere for sealing process after plasma cleaning step, the quality of display device is greatly enhanced.