KR20090102865A - Method of forming a cold cathode fluorescent lamp, thick film electrode compositions used therein and lamps and lcd devices formed thereof - Google Patents

Abstract

The present invention relates to method(s) of fabricating a cold cathode fluorescence lamp (CCFL) utilizing thick film compositions. The CCFL of the present invention may be used in thin film transistor-liquid crystal display (TFT-LCD) applications and for providing a structure of the electrodes of used in TFT-LCD backlight units.

Description

TECHNICAL FIELD OF FORMING A COLD CATHODE FLUORESCENT LAMP, THICK FILM ELECTRODE COMPOSITIONS USED THEREIN AND LAMPS AND LCD DEVICES FORMED THEREOF

The present invention claims the priority of US Provisional Application No. 60 / 802,912, filed May 24, 2006.

The present invention relates to a method (s) for producing a cold cathode fluorescence lamp (CCFL) using a thick film composition. The CCFL of the present invention can be used for thin film transistor-liquid crystal display (TFT-LCD) applications, and can be used to provide the structure of the electrode of the CCFL used in the TFT-LCD backlight unit.

The liquid crystal display device includes two polarizing glass pieces having a polarizing film side and a glass side. Specific polymers that produce microscopic grooves (oriented in the same direction as the polarizing film) on the surface are rubbed onto the non-polarizing film side of the glass. A coating of nematic liquid crystal is added to one of the filters. The groove causes the first layer of liquid crystal molecules to align with the filter orientation. A second glass piece is added with the polarizing film at right angles to the first glass piece. Each successive layer of liquid crystal molecules is gradually twisted until the top layer is at an angle of 90 degrees to the bottom, consistent with the orientation of the second polarizing glass filter.

If light shines on the first filter, the light is polarized. If the final layer of liquid crystal molecules coincides with the second polarizing glass filter, light will pass through. The light passing through is controlled through the use of electric charges to the liquid crystal molecules.

Active matrix LCDs depend on thin film transistors (TFTs). Basically, TFTs are small switching transistors and capacitors arranged in a specific matrix on a glass substrate. These TFTs control which regions receive charges, and thus the image that the viewer sees.

Light to the LCD device can be supplied through the use of a backlight unit (BLU). Two possible backlight unit types include a cold cathode fluorescent lamp (CCFL) and an external electrode fluorescent lamp (EEFL). In some embodiments, compared to EEFLs, CCFLs have been used as TFT-LCD BLU light sources because of improved lifetime / reliability performance and ready mass production lines.

Fluorescent lamps are used to provide illumination in typical electrical devices for general lighting purposes because they are more efficient than incandescent lamps in generating light. Fluorescent lamps are low pressure gas discharge sources, where light is mainly produced by fluorescent powders activated by ultraviolet energy generated by mercury plasma forming arcs. Lamps, typically in the form of tubular bulbs with electrodes sealed into each end, contain low pressure mercury vapor with a small amount of inert gas for lighting. The inner wall of the bulb is coated with fluorescent powder, commonly called phosphor. When an appropriate voltage is applied, a plasma-forming arc is created by the current flowing between the electrodes through the mercury vapor. This discharge generates some visible radiation. Ultraviolet light then excites the phosphor to emit light.

In some fluorescent lamps, two electrodes are hermetically sealed into the bulb, one at each end. These electrodes are designed to act as "cold" or "hot" cathodes or electrodes. The electrode for cold cathode (or glow) operation may consist of a closed-end metal cylinder coated internally with a luminescent material.

1A shows a prior art cold cathode fluorescent lamp (CCFL). The lamp is in the form of a tubular bulb, typically a glass tube 1, in which two electrodes 4 extend from each end. The lamp holds the fluorescent powder 3 and the discharge gas 2. Typical prior art CCFL electrodes achieve electrical connection between the inverter and the CCFL by soldering the connections 5 from each electrode to an inverter. In this prior art CCFL structure, the electrical connection is made by soldering the wires to the electrodes of the CCFL lamp before assembling the lamps into the BLU module. When assembling the CCFL lamps, these lamps with wires suspended at both ends are placed on the BLU panel. The electrical connection from the lamp to the BLU module is then made by further soldering the wires to the inverter on the BLU module. This is very time and labor intensive. 1B shows a connection by soldering a prior art CCFL. 1C shows a typical CCFL with multiple 1-to-2 inverters 6.

In another CCFL example, a metal cap is attached to the internal electrode and connected from the CCFL to the inverter. The metal cap is attached to the lamp by soldering. The lamp is then placed and clamped in a holder on the BLU module to form an electrical connection. This method still requires soldering to attach the metal cap to the lamp. Despite the improvement of the metal cap, there is still a need to improve CCFL treatment with regard to ease of handling, ease of assembly and replacement of lamp (s).

2A illustrates a conventional external electrode fluorescent lamp (EEFL) in which a metal capsule 10 is coupled to the end of a glass tube 1 and a ferrodielectric is applied inside the metal capsule. Electrodes of this type are disclosed in US Pat. No. 2,624,858 to Greenlee. However, the bonded portion of the electrode can be easily damaged because the coefficient of thermal expansion of the glass tube is different from that of the metal capsule.

2B illustrates another type of electrode disclosed in US Pat. No. 6,674,250 to Cho et al. An electrode such as a bath is a metal cap 13 attached to a sealing glass tube using a conductive adhesive 16. In the same document, as shown in Figure 2C, the electrode can also be a conductive tape 14 with an adhesive, where the tape is attached to a glass tube.

2D illustrates another type of electrode disclosed in US Pat. No. 6,914,391 to Takeda et al. The electrode disclosed in Toda et al. Is an aluminum foil 15 attached to a sealed glass tube using an electrically conductive silicone adhesive layer.

As with the EEFL described above, the use of adhesives has the disadvantage of creating a weak bond between the glass tube and the electrode of the EEFL device. The adhesive provides only mechanical bonding and weak bonding of the electrodes can result in poor reliability performance. For example, a mismatch in the coefficient of thermal expansion between the metal cap (electrode) and the glass tube can cause a gap between the electrode and the glass tube during the thermal cycle. In addition, gaps may occur when the adhesive degrades in harsh environments. Since the high operating voltage of the EEFL will not be applied uniformly to the glass tube, the gap between the electrode and the glass tube can lead to EEFL failure. Higher electrical resistance around the gap leads to breakage damage of the glass tube. In addition, higher stresses around the gap can increase separation, which can accelerate device failure during reliability testing.

The present invention solves the above problems by providing a novel method for forming a CCFL and a method for forming an LCD device.

Summary of the Invention

The present invention provides a method of forming a cold cathode fluorescent lamp comprising the steps of: providing a conductive layer thick film composition comprising electrically functional particles and an organic medium; Cylindrical glass tube having a first end, a second end, a first inner electrode, a second inner electrode, and an inner circumferential wall, wherein a fluorescent material is provided along the inner circumferential wall, discharge gas is injected into the glass tube, and the first An inner electrode extends from inside the glass tube through the first end to form inner and outer portions of the first electrode, and the second inner electrode extends from inside the glass tube through the second end to extend the second electrode. Forming inner and outer portions of the glass tube, the first electrode and the second electrode being sealed to form a glass tube structure in which the fluorescent material and the discharge gas are contained therein; Applying a conductive layer thick film composition on the first and second ends of the glass tube structure to form a first conductive layer and a second conductive layer; And firing the glass tube and conductive layer thick film composition to form a cold cathode fluorescent lamp.

In one embodiment of the present invention, the applying step is selected from dip coating, screen printing, roll coating and spray coating. In another embodiment, the method further comprises drying the conductive layer thick film composition before the firing step. In yet another embodiment, the method further comprises providing a protective layer composition over one or both of the first conductive layer and the second conductive layer. In yet another embodiment, the conductive layer thick film composition of the present invention further comprises glass frit.

In another embodiment of the present invention, a cold cathode fluorescent lamp is formed by the method (s) of the present invention described above and described in detail below. In yet another embodiment, a liquid crystal display device is formed comprising the cold cathode fluorescent lamp described above.

1A is an illustration of a conventional cold cathode fluorescent lamp.

1B is an illustration of a conventional single cold cathode fluorescent lamp with soldered connections.

1C is an illustration of conventional cold cathode fluorescent lamps with multiple 1-to-2 inverters and soldered connections.

2A-2D illustrate exemplary external electrode fluorescent lamps.

2E-2G illustrate exemplary external electrode fluorescent lamps disclosed in US Provisional Patent Application No. 60/802912.

3A to 3E are illustrations of a cold cathode fluorescent lamp of the present invention.

Drawing-reference sign

1-tubular bulb (glass tube)

2-discharge gas

3-fluorescent layer (typically phosphor)

4-internal electrode

5-solder connection

6-inverter

10-combined metal capsule

13-metal cap

14-conductive tape with adhesive

15-aluminum foil

16-adhesive material

17-thick film conductive paste

18-protective layer

19-EEFL holder with mechanical contact to the electrode

20-CCFL holder with mechanical contact to the electrode

FIG. 2E shows an external electrode fluorescent lamp (EEFL) disclosed in U.S. Provisional Patent Application 60 / 802,912 (Agent No. EL-0663), which is incorporated herein by reference. 2F and 2G show various embodiments of solder-free connections using EEFLs as described in Lynn et al . Although U.S. Provisional Patent Application 60 / 802,912 relates to EEFL applications, the present invention relates to CCFL applications.

One advantage of the present invention is the excellent bonding strength of the thick film conductive layer to the inner electrode and the glass tube 3 of the fluorescent lamp, so that better reliability performance of the inner electrode can be achieved. During the firing process, the glass frit in the electrode paste provides strong chemical and mechanical bonding of the conductive layer to the glass tube. Compared with the prior art examples, the strong, uniform and tight coupling of the electrodes provides excellent performance in reliability and electrical properties.

Other advantages of good bonding of the electrodes are electrical performance and increased reliability. Strong and uniform bonding of the electrodes provides very close contact of the electrodes to the glass tubes of the lamp, thereby lowering the electrical resistance and increasing the efficiency of converting the power applied to the lamp into power to excite the fluorescent material inside the glass tube. AC power for operating the CCFL is usually in the range of 20 kHz to 100 kHz, and the coupling at the interface of the electrode and the glass tube will likely have more substantial impact on reliability performance at high electrical frequency conditions such as in CCFLs.

A further advantage of the present invention is the ease of adaptation to mass production. Processes in the present invention, such as rolling, spraying, dipping and the like, are typically processes that are easy to implement in the industry. Low equipment investment costs are required, and CCFL devices with high performance reproducibility can be manufactured. When the conductive material is in the form of a paste as mentioned in the present invention than in the form of a tape, metal cap or foil as mentioned in the prior art, the physical and performance uniformity of the electrode is easier to be achieved. Thus, high quality CCFL devices can be manufactured in large quantities. The present invention also eliminates the need for soldered connections through the use of thick film pastes. The paste is applied to the lamp and fired to form a solderless electrode. The lamp is then placed and clamped in a holder on the BLU module to form a complete backlight unit.

Description of the process

The fluorescent lamp manufacturing processes and the structure of the internal electrode of the fluorescent lamp in one embodiment of the present invention are described in detail. Those skilled in the art will appreciate that the present description is merely an example of a manufacturing process and other manufacturing processes are known to those skilled in the art.

3A-3E illustrate fluorescent lamps in accordance with exemplary embodiments of the present invention. 3A to 3E, the fluorescent lamp includes a cylindrical glass tube 1. The fluorescent substance 3 is provided along the inner circumferential wall of the glass tube 1. After the fluorescent material is applied inside the glass tube 1, the discharge gas 2 including the inert gas, mercury (Hg), and the like mixed with each other is injected into the glass tube 1, and then both ends of the glass tube 1 are sealed. do.

The electrodes of the fluorescent lamp are each formed at opposite ends of the glass tube 1. The structure of the electrode 4 is coated with a thick film conductive layer 17 and an optional protective layer 18 which partially or completely covers the conductive layer 17. The portion of the electrode 4 extending out of the glass tube 1 may be completely covered by the conductive layer 17 or may extend beyond the conductive layer 17.

Conductive layer 17 is a thick film paste comprising a metal and binder material selected from the group comprising Al, Ag, Cu, Pd, Pt and mixtures thereof. The metal selected in the present invention provides very low electrical resistance to the conductive layer 17. Electrical sheet resistance of less than 100 m ohm / sq at 25 μm can be achieved. In one embodiment, the electrical surface resistance ranges from 1 to 10 m ohms / sq at 25 μm. In another embodiment, the surface resistance is 3 m ohm / sq at 25 μm. The binder composition provides strong adhesion to the glass tube 1 and the electrode material to the conductive layer 17. Typically, the method of application of thick film paste is screen printing or dip coating. However, other methods are well known to those skilled in the art. Applicable thick film film paste compositions useful in the present invention are described in detail below.

I. Thick Film Paste Conductive Layer

A. Electrically Functional Particles

In conductor applications, the functional phase consists of electrically functional conductor powder (s). The electrically functional powder in certain thick film compositions may comprise a single type of powder, a mixture of powders, an alloy or compound of several elements. Electrically functional conductive powders that may be used in the present invention include gold, silver, nickel, aluminum, palladium, molybdenum, tungsten, tantalum, tin, indium, ruthenium, cobalt, tantalum, gallium, zinc, magnesium, lead, antimony, conductive carbon, Platinum, copper, and mixtures thereof.

Metal particles may or may not be coated with an organic material. In particular, the metal particles may be coated with a surfactant. In one embodiment, the surfactant is selected from stearic acid, palmitic acid, salts of stearate, salts of palmitate and mixtures thereof. Counter-ion may be, but is not limited to, hydrogen, ammonium, sodium, potassium and mixtures thereof.

Virtually any shape metal powder (s), including spherical particles and flakes (rods, cones, and plates) can be used to practice the present invention. In one embodiment, the metal powder is gold, silver, palladium, platinum, copper and combinations thereof. In further embodiments, the particles may be spherical.

In a further embodiment, the present invention relates to a dispersion. Dispersions may include compositions, particles, flakes or combinations thereof. The metal powder (s) may be nanoscale powders. In addition, the electrically functional particles may be coated with a surfactant. Surfactants can help to produce desirable dispersion properties. Typical particle sizes of electrically functional particles are less than approximately 10 micrometers. It is understood that the particle size will vary depending upon the application of the thick film composition and the desired properties. In one embodiment, an average particle size (D ₅₀ ) of 2.0 to 3.5 micrometers is used. In further embodiments, D ₉₀ is approximately 9 micrometers. In addition, in one embodiment, the surface area to weight ratio is in the range of 0.7 to 1.4 m 2 / g.

B. Organic Medium

Inorganic components are typically mixed with organic media by mechanical mixing to " pastes, " with consistency and rheology suitable for applicable coating methods, including but not limited to screen printing and dip coating. It forms a viscous composition called. A wide variety of inert viscous materials can be used as the organic medium. The organic medium should be one in which the inorganic components can be dispersed with appropriate stability. The rheological properties of the media give them good application properties, including stable dispersion of solids, adequate viscosity and thixotropy for screen printing, adequate wettability of substrate and paste solids, good drying rate and good plasticity properties. It should be. The organic vehicle used in the thick film composition of the present invention is preferably a non-aqueous inert liquid. Any of a variety of organic vehicles, which may or may not contain thickeners, stabilizers and / or other conventional additives, may be used. The organic medium is typically a solution of the polymer (s) in solvent (s). In addition, small amounts of additives such as surfactants may be part of the organic medium. The most frequently used polymer for this purpose is ethyl cellulose. Other examples of polymers useful in the present invention include ethyl hydroxyethyl cellulose, wood rosin, varnish resins, mixtures of phenol resins and ethyl cellulose, and polymethacrylates of lower alcohols may also be used. The most widely used solvents found in thick film compositions are terpenes such as ester alcohols and alpha- or beta-terpinols or these and pine oils, kerosene, dibutylphthalate, butyl carbitol, butyl carbitol acetate, hex Mixtures with other solvents such as styrene glycol and high boiling alcohols and alcohol esters. In addition, volatile liquids may be included in the vehicle to facilitate rapid curing after application on the substrate. Various combinations of these and other solvents are formulated to achieve the desired viscosity and volatility requirements.

The polymer present in the organic medium is in the range of 0.2% to 8.0% by weight of the total composition and any range contained therein. The thick film conductive composition of the present invention can be adjusted to a desired screen printable viscosity using an organic medium. In one embodiment, the thick film conductive composition comprises silver.

The ratio of the organic medium in the thick film composition to the inorganic component in the dispersion depends on the method of applying the paste and the type of organic medium used, which can vary. Typically, the dispersion will contain 40 to 90% by weight of inorganic components and 10 to 60% by weight of organic medium (vehicle) in order to obtain good wettability.

C. Optional Glass Frit

Typical glass frit compositions (glass compositions) of the present invention are listed in Table 1 below. The glass frit of the present invention is optional. It is important to note that the compositions listed in Table 1 below are not limiting, as it is expected that one of ordinary skill in the art of glass chemistry may subsidize additional ingredients and substantially not change the desired properties of the glass compositions of the present invention. Do. For example, those skilled in the art understand that useful glass frit compositions can be modified to optimize wear resistance, solderability, plating as well as other properties.

The glass compositions in weight percent of the total glass composition are shown in Table 1. Preferred glass compositions found in the examples include the following oxide components in the following composition ranges in weight percent of the total glass composition: SiO ₂ 4 to 8, Al ₂ O ₃ 2 to 3, B ₂ O ₃ 8 to 25, CaO 0 to 1, ZnO 10 to 40, Bi ₂ O ₃ 30 to 70, SnO ₂ 0 to 3. A more preferred composition of the glass is SiO ₂ 7, Al ₂ O ₃ 2, B ₂ O ₃ in weight percent of the total glass composition. 8, CaO 1, ZnO 12, Bi ₂ O ₃ 70. Some embodiments of the present invention include Pb-free glass compositions. When glass is used in the thick film compositions of the present invention, this can lead to more common thermal expansion coefficient (TCE) agreement between the substrate and the composition upon treatment. Particularly advantageous embodiments are those wherein the thick film composition comprises a Pb-free glass.

Glass frits useful in the present invention include ASF1100 and ASF1100B, commercially available from Asahi Glass Company.

The average particle size of the glass frit (glass composition) of the present invention is in the range of 0.5 to 5.0 μm in practical applications, but an average particle size in the range of 2.5 to 3.5 μm is preferred. The softening point (Ts: second transition point of DTA) of the glass frit should be in the range from 300 to 600 ° C. When present in the conductive layer thick film composition, the amount of glass frit in the total composition ranges from 0.5 to 10 weight percent of the total composition. In one embodiment, the glass composition is present in an amount of 1 to 3 weight percent of the total composition. In further embodiments, the glass composition is present in the range of 4-5% by weight of the total composition.

The glasses described herein are produced by conventional glass making techniques. Glass was prepared in an amount of 500-1000 g. Typically, the components are weighed, then mixed in the desired proportions and heated in a bottom-loading furnace to form a melt in a platinum alloy crucible. As is well known in the art, heating is carried out to a peak temperature (1000-1200 ° C.) for a time that allows the melt to become completely liquid and uniform. The molten glass is quenched between counter rotating stainless steel rollers to form a glass plate of 10 to 20 mils thick. The resulting glass plates were then milled to achieve a 50% volume distribution at 1 to 3 micrometers. The set powder was formed.

II. Selective of electrode Protective layer

As detailed above in various embodiments of the invention detailed in FIGS. 3B-3E, a protective layer 18 is shown that at least partially covers the conductive layer 17. Protective layer 18 may cover the entire conductive layer or only a portion thereof. Additionally, in some embodiments, the electrode extends into the protective layer, and the protective layer covers the electrode. The protective layer 18 of the electrode is made of a low reactive metal such as Sn to protect the conductive layer 17 from reaction with environmental elements such as moisture and reactive gases. The protective layer is entirely optional.

Various methods of applying the conductive layer 17 onto the glass tube 1 can be used. The portion of the electrode 4 extending out of the glass tube 1 may be completely covered by the conductive layer 17 or may extend beyond the conductive layer 17. In some embodiments, as long as the electrode is connected to the conductive layer, the electrode may extend beyond the conductive layer even if the protective layer is not over the conductive layer.

In some embodiments, the electrode extends past the conductive layer and into the protective layer. The protective layer may partially or completely cover the electrode and the conductive layer. The electrode materials, including the metal powder and the binder (as detailed above), mix well together to form the electrode paste. The conductive layer 17 is made of thick film conductive paste. Thick film conductive pastes of different viscosities can be applied on glass tubes and electrodes by various coating processes such as rolling, spraying, dipping processes and the like.

In one embodiment, the thick film conductive paste approaches the glass tube to a paste container or tank, transfers the paste to the glass tube, and then the glass tube leaves the thick film conductive paste tank, leaving a coating of the thick film conductive paste at the desired location of the glass tube. Both are applied by a roll coating process. Throughout the rolling process, the glass tube rotates about an axis passing through both ends, and the glass tube is aligned at a small angle with respect to the surface of the thick film conductive paste in the tank.

In another embodiment, the CCFL is formed by applying a conductive paste through a spraying process whereby the thick film paste is released into the air through a nozzle to form droplets and the droplets of the paste accumulate on the ends of the glass tubes. It is desirable that the glass tube rotates during the process for better coating uniformity.

Immersion processes can be used for conductive layer thick film applications by immersing the glass tube in conductive paste and moving away from the surface of the paste in the tank. The alignment of the glass tubes is not limited to being perpendicular to the surface of the paste, and rotation of the glass tubes may be employed during the dipping process.

Subsequent processes typically include drying, firing and cooling the glass tube. In some embodiments, no specific drying step is necessary depending on the conditions of the process. The processes of drying, firing and cooling can be carried out in a batch or continuous process manner.

In one embodiment, the drying process is defined and performed by heating the glass tube and conductive layer to 50 to 180 ° C. for a predetermined amount of time. The heating of the glass tube can be done in a drying oven by radiation, circulation of the heated atmosphere or a combination of both. The low boiling organic solvent in the electrode paste on the glass tube is removed during the drying process and the glass tube is then ready to be subjected to the firing process because the conductive layer is less sensitive to physical deformation after drying.

In one embodiment, the firing process is defined by and is thereby performed by heating the glass tube and conductive layer to a temperature in the range of approximately 300 to 600 ° C. The glass tubes can be heated in the firing furnace by radiation, circulation of the heated atmosphere or a combination of both. During the firing step, a heat resistant carrier, for example a quartz tube, is typically used for uniform heating and mechanical support of the glass tube 1. The composition of the atmosphere to be heated can be varied and controlled for various types of conductive pastes and various target performances of the electrodes. In a continuous firing process, the glass tubes can be aligned perpendicular to the direction of movement of the carrier to uniformly heat the glass tubes. The purpose of the firing process is to achieve low electrical resistance of the conductive layer (low surface resistance of less than 100 m ohm / sq at 25 μm can be achieved) and high bonding strength of the conductive layer to the glass tube. During the firing process, all the organic material in the conductive layer thick film is burned out. Typically, the firing step takes place in the temperature range of 300 to 600 ° C. After firing, only the metal and glass frit (if added to the thick film composition) remain in the conductive layer.

After the firing process, the glass tube is cooled slowly. The cooling process gives the glass tube a controlled reduced temperature gradient. Normal cooling rates are typical to slowly release the thermal stress at the interface between the glass tube and the conductive layer during the cooling process. In some embodiments, the glass tube may be suitably cooled at ambient conditions.

In one embodiment of the invention, the glass frit is not included in the thick film paste conductive layer. The electrode paste in this alternative embodiment will include functional metals such as Al, Cu, Ag, Au and mixtures thereof as described above, and organic media such as solvents and resins. In one embodiment of this glass-free embodiment, the firing temperature ranges from 80 to 300 ° C. In further glass-free embodiments, the firing temperature ranges from 300 to 600 ° C. In one embodiment, the electrically functional particles are nano sized particles. In some embodiments, the thick film composition comprises a polymer and is therefore a polymeric thick film composition. Such polymeric thick film compositions can be cured. Such curing typically enables lower firing temperatures and lower energy usage.

Advantages of this alternative glass-free embodiment include lower machinery costs, lower material costs, and higher process throughput. Disadvantages of alternative embodiments will be lower bond strength and slightly worse electrical performance. Both glass- and glass-free embodiments share the advantage of easy adoption for mass production.

An optional protective layer 18 is applied to the conductive layer 17 after the cooling process. Coating the conductive layer with a less reactive metal layer, such as Sn, Ni, and Zn, can provide a protective layer 18. Various coating processes, such as soldering, electroplating, chemical plating, can be employed for the protective layer 18.

The length of the thick film paste layer (ie the coverage of the glass tube) needs to be optimized. The thick film coverage of the CCFL has a significant impact on the electrical performance of the lamp. Longer coverage lamps have a larger contact area with the glass tube, resulting in lower electrical resistance. For example, to obtain a typical tube current of 4 mA in a lamp with a reduced length lamp of 10 mm length, a voltage as high as 1.7 times the voltage required in a lamp with a 20 mm length electrode must be applied. Higher operating voltages of lamps with shorter electrodes lead to problems such as ozone production around the electrodes, the need for specially prepared insulating materials in the backlight module, and reaching the inverter output voltage limit. Higher brightness of the lamp requires higher operating currents. In order to operate the lamp at high current without high operating voltage, a solution of increasing the electrode length has been widely adopted. The disadvantage of this solution is that the longer the electrode, the smaller the actual illumination area of the lamp will be. Therefore, optimization of electrode length and lamp brightness should be considered.

Claims (13)

As a method of forming a cold cathode fluorescent lamp, Providing a conductive layer thick film composition comprising electrically functional particles and an organic medium; Cylindrical glass tube having a first end, a second end, a first inner electrode, a second inner electrode, and an inner circumferential wall, wherein a fluorescent material is provided along the inner circumferential wall, discharge gas is injected into the glass tube, and the first An inner electrode extends from inside the glass tube through the first end to form inner and outer portions of the first electrode, and the second inner electrode extends from inside the glass tube through the second end to extend the second electrode. Forming inner and outer portions of the glass tube, the first electrode and the second electrode being sealed to form a glass tube structure in which the fluorescent material and the discharge gas are contained therein; Applying a conductive layer thick film composition on the first and second ends of the glass tube structure to form a first conductive layer and a second conductive layer; And Firing the glass tube and conductive layer thick film composition to form a cold cathode fluorescent lamp How to include. The method of claim 1, wherein the first conductive layer completely covers the outer portion of the first electrode. The method of claim 1, wherein a protective layer is applied over one or more of the first and second conductive layers. The method of claim 3, wherein the protective layer is a lead-free layer. The method of claim 1 wherein said applying step is selected from the group comprising dip coating, screen printing, roll coating and spray coating. The method of claim 1, further comprising drying the conductive layer thick film composition before the firing step. The method of claim 1, wherein the conductive layer thick film composition further comprises glass frit. The method of claim 1, wherein the firing occurs in a temperature range of 300 to 600 ° C. 3. The method of claim 1 wherein said firing occurs in a temperature range of 80 to 300 ° C. 8. The method of claim 7, wherein the glass frit composition is a lead free glass frit composition. The method according to claim 7, wherein the glass frit composition is SiO ₂ 4 to 8, Al ₂ O ₃ 2 to 3, B ₂ O ₃ 8 to 25, CaO 0 to 1, ZnO 10 to 40 by weight percent of the total glass frit composition , Bi ₂ O ₃ 30 to 70, SnO ₂ 0 to 3 method. A cold cathode fluorescent lamp formed by the method of claim 1. A liquid crystal display device comprising the cold cathode fluorescent lamp of claim 12.