KR100370406B1 - Method for laser vacuum packaging of flat-panel display - Google Patents

Abstract

Disclosed is a vacuum packaging method for sealing an upper substrate and a lower substrate by using a laser such that the inside of the flat panel display is in a vacuum state. The disclosed laser vacuum packaging method comprises the steps of forming a first frit layer along an upper edge of a lower substrate, drying and prefiring the first frit layer to remove moisture and binder components in the first frit layer; Forming a second frit layer on the first frit layer and prefiring the same; heating the substrate at a predetermined temperature in a vacuum firing furnace with the upper substrate aligned on the lower substrate; and forming the first and second frit layers. Sealing the upper substrate and the lower substrate by irradiating a laser beam only on the portion to melt at least the second frit layer. Here, the thickness of the first frit layer is thicker than the thickness of the second frit layer, preferably 90% or more of the gap between the upper substrate and the lower substrate. According to the present invention, it is possible to minimize the generation of bubbles in the frit layer to increase the adhesive strength of the upper substrate and the lower substrate and maintain a high vacuum state therein.

Description

Vacuum packaging method for a flat panel display using a laser {Method for laser vacuum packaging of flat-panel display}

The present invention relates to a vacuum packaging method of a flat panel display device, and more particularly, to a vacuum packaging method of a flat panel display device such as a field emission display device using a laser.

BACKGROUND ART Display devices, which are widely used as an important part of information transmission media, are mainly applied to monitors and television receivers of personal computers, and recently, new application fields have been widely created. Such display devices may be broadly classified into display devices using a cathode ray tube, that is, a cathode ray tube (CRT) display device and a flat panel display (FPD). In particular, the flat panel display device is showing rapid technological development in recent years, such as a liquid crystal display (LCD), a plasma display panel (PDP), a fluorescent display and an electric field Field emission displays (FEDs) and the like are currently being actively researched and developed in their respective fields.

In order to manufacture a flat panel display device that requires a vacuum therein among the flat panel display devices as described above, the upper substrate and the lower substrate facing each other are sealed at a predetermined interval and packaging to make the interior into a vacuum state. Going through the process.

1 is a view illustrating a conventional packaging method of a flat panel display device. Referring to this, in the related art, such a packaging process includes a process of sealing an upper substrate 11 and a lower substrate 12 and an upper substrate 11. And the evacuation process of vacuuming the space formed between the lower substrate 12 and is carried out in two processes. Referring to the sealing process, first, a low melting glass powder called frit 13 is formed into a paste and applied to a portion to be sealed on the lower substrate 12 with a predetermined thickness. Subsequently, the frit 13 coated on the lower substrate 12 is prebaked to remove moisture, binder components, and the like in the frit 13. Thereafter, the upper substrate 11 is aligned on the lower substrate 12, and then heated to the predetermined temperature in the firing furnace 14 to melt the frit 13 to seal the upper substrate 11 and the lower substrate 12. do. In addition, referring to the exhaust process, the upper substrate 11 and the lower substrate 12 are formed through the exhaust port 15 provided in the lower substrate 12 after the upper substrate 11 and the lower substrate 12 are sealed as described above. The space is made into a predetermined vacuum state by discharging gases in the space formed between the spaces. Thereafter, the exhaust port 15 is sealed by a predetermined method for maintaining the vacuum state, thereby completing the packaging process of the flat panel display device.

However, according to the conventional method, although the heating temperature of the kiln 14 is slightly different depending on the material of the frit 13, it usually reaches 400 ° C., and the electrodes formed on the surfaces of the substrates 11 and 12 may be Oxidation or contamination of light emitting elements, etc. may occur, resulting in deterioration of light emission performance. In addition, there is a problem in that the productivity is lowered because it has to go through two processes, a sealing step and an exhaust step.

Accordingly, a vacuum packaging method that can solve the problems of the conventional method as described above has been proposed and used. Since vacuum packaging is a method of firing a frit in a vacuum, oxidation and contamination of an electrode, a light emitting element, and the like formed on a substrate surface can be prevented, and an exhaust process is omitted, and thus productivity is improved. In addition, it is not necessary to make the exhaust port, thereby eliminating the need to seal the exhaust port. The vacuum packaging method having this advantage is basically calcined in a vacuum, but may be divided into a method of heating the entire substrate and a method of locally heating only the portion to which the frit is applied, according to the firing method. The method of heating the entire substrate has the disadvantage of deteriorating the characteristics of the display device due to the high temperature since the entire substrate must be heated to the melting point of the frit, while the local heating method heats the substrate to an appropriate temperature below the melting point of the frit and then frits. Since only the coated portion is heated to a temperature higher than the melting point of the frit, there is an advantage of shortening the process time and protecting the display device from deterioration of its characteristics.

Although there exist various local heating methods mentioned above, the local heating method using a laser has attracted attention in recent years. The laser vacuum packaging method will be described in more detail. After the frit is applied to a predetermined thickness along the edge of the lower substrate, the binder component in the frit is removed by heating and prefiring the frit. Thereafter, the upper substrate is aligned on the lower substrate and charged into a vacuum firing furnace and heated to an appropriate temperature below the melting point of the frit, whereby the frit is melted by locally heating only the portion where the frit is applied with a laser beam. The substrate and the lower substrate are sealed.

However, in the vacuum packaging method using the laser as described above, a large number of bubbles are generated when the frit is melted by the irradiated laser beam, there is a problem that the adhesive strength decreases, such as vacuum leakage occurs. This is because the area where the bubble generating source such as moisture or binder component is sufficiently removed in the prefiring step is about 30 μm to 40 μm from the surface of the frit, and the bubble generating source is not sufficiently removed therein. In other words, a trace amount of binder components that were retained without melting due to the pressure difference in the pin-hole trapped therein while melting the frit by the laser beam due to the pressure difference in the vacuum kiln. Bubbles are generated by the gas generated while burning. Figure 3a is a micrograph of the cross section taken by cutting the frit after the actual firing process by the vacuum packaging method using the conventional laser, it can be seen that large and small bubbles are generated inside the frit. In addition, as a result of thermogravimetric analysis (TGA) with a sample, a trace amount of binder component remained.

The present invention has been made to solve the above problems of the prior art, in particular, to minimize the occurrence of bubbles in the frit to improve the adhesive strength of the upper substrate and the lower substrate and to maintain a high vacuum state of the flat panel display device It is an object of the present invention to provide a vacuum packaging method.

1 is a view for explaining a packaging method of a conventional flat panel display device;

2a to 2e is a view for explaining a vacuum packaging method of a flat panel display using a laser according to the present invention step by step,

3A and 3B are micrographs of a cross section of the frit, FIG. 3A is a cross-sectional photograph of a frit by a conventional laser vacuum packaging method, and FIG. 3B is a cross-sectional photograph of a frit by a laser vacuum packaging method according to the present invention. ,

4A and 4B illustrate a temperature distribution on a substrate during a vacuum packaging method of a flat panel display using a laser according to the present invention. FIG. 4A is a view illustrating a temperature measurement position, and FIG. 4B is a unit of a frit. A graph showing the temperature change at each location with absorbed energy per length,

5 is a photograph of a scanner device of a laser beam.

<Explanation of symbols for the main parts of the drawings>

11,21 ... top board 12,22 ... bottom board

13 ... Frit 14,24 ... Fire Furnace

23a ... first frit layer 23b ... second frit layer

25.Heater 27.Laser

28 ... laser beam 29 ... scanner

In order to achieve the above technical problem, the present invention provides a vacuum packaging method for sealing an upper substrate and a lower substrate by using a laser so that the inside of the flat panel display device is in a vacuum state:

(A) forming a first frit layer along the upper edge of the lower substrate;

(B) drying and prefiring the first frit layer in an air kiln to remove moisture and binder components in the first frit layer;

(C) forming a second frit layer on the first frit layer and prefiring it in an atmospheric kiln;

(D) heating to a predetermined temperature lower than the melting point of the frit, which is a constituent material of the first and second frit layers, in a firing furnace in a vacuum state with the upper substrate aligned on the lower substrate; And

(E) sealing the upper substrate and the lower substrate by irradiating a laser beam only on a portion where the first and second frit layers are formed to melt at least the second frit layer.

Here, the thickness of the second frit layer formed in the step (c) is preferably 30㎛ ~ 40㎛.

The alignment of the lower substrate and the upper substrate in the step (d) may be performed both before and after charging the kiln, and this order may vary depending on the shape of the kiln. In addition, the heating temperature of the charged lower substrate and the upper substrate is lower than the melting point of the frit, which is a constituent material of the first and second frit layers, for example, 250 ° C to 300 ° C, preferably substantially 300 ° C. This is to prevent the upper substrate and the lower substrate from being damaged by the temperature difference due to the local melting of the frit layer by local heating.

The prebaking in the steps (b) and (c) is preferably carried out in a kiln, and the step (e) is preferably performed after the temperature of each part is in equilibrium in the step (d).

As the laser beam, it is preferable to use an infrared laser beam, for example, a CW Nd: YAG laser beam having a wavelength of 1,064 nm.

According to the present invention, it is possible to minimize the generation of bubbles in the frit layer to increase the adhesive strength of the upper substrate and the lower substrate and maintain a high vacuum state therein.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of a vacuum packaging method of a flat panel display using a laser according to the present invention in detail.

2A to 2E are diagrams for explaining step by step a vacuum packaging method of a flat panel display using a laser according to the present invention.

First, referring to FIG. 2A, the first frit layer 23a is formed by applying a frit to a predetermined thickness T ₁ along an upper edge of a lower substrate 22 of a flat panel display such as a field emission display. Frit is a paste made of low melting glass powder. The application of the frit may be by a variety of methods, but generally by a screen-printing method. The thickness T ₁ of the first frit layer 23a is appropriately determined according to the final spacing between the lower substrate 22 and the upper substrate and the thickness of the second frit layer described later. For example, in the case of vacuum packaging a field emission display device in which the gap between the upper substrate and the lower substrate 22 is set to 500 µm, the thickness T ₁ of the first frit layer 23a is approximately 480 µm. Be sure to

Subsequently, as shown in FIG. 2B, a first firing layer 23a formed on the lower substrate 22 is dried, and a prefiring step of charging and heating the first frit layer 23a into an atmospheric firing furnace 24 is performed. At this time, the lower substrate 22 and the first frit layer 23a are heated by a flat plate heater 25 provided in the firing furnace 24, for example, a graphite plate heated by a halogen lamp. In this step, moisture, binder components, and the like inside the first frit layer 23a are removed. In particular, as described above, the bubble generation source such as water or a binder component is sufficiently removed from the surface of the first frit layer 23a to approximately 40 µm.

Next, referring to FIG. 2C, the second frit layer 23b is formed by applying the frit again to a predetermined thickness T ₂ by the screen printing method on the first frit layer 23a formed on the lower substrate 22. Let's do it. In this case, the thickness T ₂ of the second frit layer 23b is preferably 30 μm to 40 μm. The formed second frit layer 23b is subjected to a prefiring step in the same manner as the prefiring of the first frit layer 23a described above. At this time, since the thickness T ₂ of the second frit layer 23b is 30 μm to 40 μm, bubble generation sources such as moisture or a binder component may be sufficiently removed as described above. In the above example, the thickness T ₁ of the first frit layer 23a is approximately 480 μm while the thickness T ₂ of the second frit layer 23b is approximately 40 μm. Therefore, the total thickness of the first frit layer 23a and the second frit layer 23b is approximately 520 μm.

Subsequently, the upper substrate 21 is aligned on the lower substrate 22 as shown in FIG. 2D. Therefore, an internal space is formed between the lower substrate 22 and the upper substrate 21 by the first frit layer 23a and the second frit layer 23b. In this state, they are charged into a vacuum firing furnace 24 and heated to a predetermined temperature. The heating is performed by a flat plate heater 25 provided in the firing furnace 24, for example, a graphite plate heated by a halogen lamp. The heating temperature in this step is a temperature lower than the melting point of the frit, which is a constituent material of the first and second frit layers 23a and 23b, for example, 250 ° C to 300 ° C, preferably approximately 300 ° C. Since this step is performed in the firing furnace 24 in a vacuum state, gases between the lower substrate 22 and the upper substrate 21 are exhausted, and the interior space thereof becomes a vacuum state.

When the temperatures of the respective portions of the flat panel display apparatus are in an equilibrium state as shown in FIG. 2E, the first substrate 21 and the lower substrate 22 are loaded in the vacuum furnace 24 in a vacuum state as shown in FIG. 2E. And the laser beam 28 is irradiated only to the portion where the second frit layers 23a and 23b are formed. When the laser beam 28 is irradiated, at least the second frit layer 23b is melted, and the surface portion of the first frit layer 23a may also be melted. As a result, the upper substrate 21 and the lower substrate 22 are sealed. At this time, the thicknesses of the first and second frit layers 23a and 23b melted by the laser beam 28 are controlled to be 80 μm or less. This thickness is sufficient to seal the upper substrate 21 and the lower substrate 22.

As such, the thickness of the melted portions of the first and second frit layers 23a and 23b by the laser beam 28 is 80 µm or less, and the portions are sufficiently removed from the bubble generation source in the two pre-firing steps described above. Area. Therefore, even when the first and second frit layers 23a and 23b are melted by the laser beam 28, bubbles are hardly generated. Figure 3b is a micrograph of the cross section taken by cutting the frit layer after the actual firing process by the method according to the present invention, it can be seen that little bubbles are generated inside the frit layer. Therefore, the adhesive strength between the upper substrate 21 and the lower substrate 22 is improved, and vacuum leakage can be prevented.

On the other hand, as the laser beam 28 used in this step, an infrared laser beam, preferably a CW Nd: YAG laser beam having a wavelength of 1,064 nm is used. The maximum power of the laser beam 28 is 50 W, which can be adjusted according to the nature and thickness of the frit layers 23a and 23b to be melted. The laser beam 28 emitted from the laser 27 is irradiated at a predetermined speed along the edge of the upper substrate 21 via the scanner 29. The galvanometer shown in FIG. 5 is used as the scanner 29, and the device is a device that mounts a mirror on two axes rotating at high speed to enable beam scanning of the X and Y axes, respectively. . High speed scanning of the laser beam has the advantage of being able to simultaneously and uniformly melt the entire surfaces of the frit layers 23a and 23b. If the laser beam cannot be scanned at high speed, the local melting and solidification of the frit layers 23a and 23b are repeated to generate thermal stress, and the alignment of the upper substrate 21 and the lower substrate 22 is during melting. Can be wrong. In addition, the beam scanning method has an advantage that the beam scanning from small to large area is possible only by adjusting the position and rotation angle of the scanner without additional equipment investment.

At this stage, the temperature change on the substrate can be seen in the graph of FIG. 4B. 4A shows the temperature measurement position, and FIG. 4B shows the temperature change at each position according to the absorbed energy per unit length of the frit layer. As shown in FIG. 4A, a temperature sensor is disposed at an upper portion A of the frit layer 23 of the upper substrate 21, a central portion B of the upper substrate 21, and a central portion C of the lower substrate 22, respectively. Was installed to measure the temperature change of each site. As a result, as shown in the graph of FIG. 4B, the temperature of the A site heated by the laser beam continuously rises to 400 ° C. in proportion to the energy absorbed by the frit layer, but the temperature of the B and C sites is 300 ° C. It can be seen that there is almost no change in the degree. As described above, when the upper substrate and the lower substrate are sealed using the laser beam, packaging can be performed while maintaining the upper substrate and the lower substrate at a temperature lower than the melting point of the frit, and the characteristics of the flat panel display are degraded due to the high temperature. Can be prevented.

As described above, according to the vacuum packaging method of the flat panel display using the laser according to the present invention, the frit layer is formed into two layers and subjected to two pre-firing steps to melt bubbles in the frit layer by the laser beam. The occurrence of can be minimized. Accordingly, the adhesive strength between the upper substrate and the lower substrate is increased and vacuum leakage is prevented, thereby maintaining a high vacuum state inside the flat panel display device. In addition, the use of a galvanometer for scanning the laser beam enables high-speed beam scanning, and the high-speed scanning of the beam has the advantage of simultaneously melting the entire surface of the frit layer uniformly. Therefore, the occurrence of thermal stress due to local melting and solidification of the frit layer is prevented, and the problem that the alignment of the upper substrate and the lower substrate is distorted during melting is solved. In addition, this beam scanning method has the advantage that it is possible to scan the beam from small to large area only by adjusting the position and rotation angle of the scanner without additional equipment investment.

Claims (10)

In the vacuum packaging method of sealing the upper substrate and the lower substrate using a laser so that the inside of the flat panel display is in a vacuum state: (A) forming a first frit layer along the upper edge of the lower substrate; (B) drying and prefiring the first frit layer in an air kiln to remove moisture and binder components in the first frit layer; (C) forming a second frit layer on the first frit layer and prefiring it in an atmospheric kiln; (D) heating to a predetermined temperature lower than the melting point of the frit, which is a constituent material of the first and second frit layers, in a firing furnace in a vacuum state with the upper substrate aligned on the lower substrate; And (E) sealing the upper substrate and the lower substrate by irradiating a laser beam only on a portion where the first and second frit layers are formed to melt at least the second frit layer. Vacuum packaging method of using a flat panel display device. The method of claim 1, The thickness of the second frit layer formed in the step (c) is 30㎛ ~ 40㎛ vacuum packaging method of a flat panel display using a laser, characterized in that. The method of claim 1, And the first and second frit layers are formed by applying the frit by screen printing. delete The method of claim 1, The heating temperature in the step (d) is a vacuum packaging method of a flat panel display using a laser, characterized in that 250 ℃ ~ 300 ℃. The method of claim 1, The vacuum packaging method of a flat panel display using a laser, characterized in that the heating in the steps (b), (c) and (d) is performed by a heater. The method of claim 1, The vacuum packaging method of the flat panel display using a laser, characterized in that the step (e) is performed after the temperature of each part is in equilibrium in the step (d). The method of claim 1, The laser beam is a vacuum packaging method of a flat panel display using a laser, characterized in that the infrared laser beam. The method of claim 8, The laser beam is a vacuum packaging method of a flat panel display using a laser, characterized in that the CW Nd: YAG laser beam having a wavelength of 1,064nm. The method of claim 8, The laser beam irradiation is a vacuum packaging method of a flat panel display using a laser, characterized in that using a galvanometer.