FPD Screen Washing

Contents

TVZ-225-03-EK-D019

Final

2004-05-25

Screen processing

LG.Philips Displays

PPD

Eindhoven

Functional Process Description

Screen washing

Contents

1Contents

11. Introduction

12. Flowchart

23. Room conditions

34. Specification incoming components/sub assemblies/Chemicals

35. Process description process steps

35.1 Screen temperature conditioning (optional)

55.2 Pre-wetting

65.3 Degreasing (optional)

75.4 Acid spraying and etching

105.5 Water spraying and draining

115.6 External screen drying

125.7 Hanger washing

136. Specification outgoing product

137. Auxiliary, tools and filter specifications

148. Cleaning procedures

159. Waste treatment

1510. Process control

1511. Miscellaneous

1712. References

Introduction

Aim of the screen wash process is to remove all contamination from the inside of the screen and create a clean and activated surface for the pre-coat, matrix and flowcoat process.

This is done by spraying water at the inside of the screen, degreasing the inside with an alkaline solution, etching with a strong acid and spraying water to remove chemicals and deposits.

Flowchart

Many different versions of screen wash lines are operational in IPCs of LG.Philips Displays.

A general overview of screen wash lines is given the flowchart below.

Room conditions

ItemLimitsReason/remark

HumidityNo requirementOrientation value 40 75 %

TemperatureNo requirementOrientation value 20 30 (C

Dust class100.000After final water rinsing. To prevent re-contamination

Special caution has to be taken for screen contamination with copper and teflon. Copper reacts at flowcoating with blue phosphor during fritting into green phosphor. Teflon is an emission killer of the tube!

See also ref. [1]

Specification incoming components/sub assemblies/Chemicals

Incoming components:

Incoming component is a fresh screen or a screen from rewash

Sub assemblies:

The screen can be part of a married couple with a mask

Chemicals used are:

De-ionized water and or

Tap water1322 505 41701

1322 506 19501

Cleaner 155 (Sodium carbonate from cone washing)

Prosol1322 512 65401

t.b.f.

Cleaner 824 (Mixed acid)

HYDROFLUORIC ACID 5%, TECHNICAL1322 530 07801

1322 507 56101

Fresh de-ionized water must be used for the last (outside) screen rinsing position. For other water spraying positions tap water can be used as an alternative.

For detailed information see the process steps where the chemicals are used and the 12 NC of the chemical.

Process description process steps

1.1 Screen temperature conditioning (optional)

Reason

Heat or cool a screen uniformly to a specified temperature.

Description of the process step

For an effective temperature conditioning, the screen is sprayed on both sides of the screen with an excessive amount of water. The screen has to be wetted extensively and completely to have an overall temperature equalizing effect and effective heat transfer.

For this reason on both sides, one or more open-ended pipes are used.

The water is continuously circulated.

The water temperature is controlled on a preset temperature.

Note:

After conditioning, the screen is sprayed with relative cold acid, fresh de-ionized water and air for external screen drying. Furthermore, the inside screen will be wet during transportation to the pre-coat/matrix line and will extract heat from the screen due to evaporation. Therefore the screen temperature will reduce between the conditioning process and arriving at precoating up to 3 (C lower as directly after conditioning.

Relevant process parameters, typical values and tolerances, essentials and reasons

Process parameterTypical value and toleranceReason

Water temperature30 33 (CTo meet precoat/matrix loading temperature

Water flow2000 + 500 l/h for each positionSufficient heat transfer

Immediate check needed at abnormal deviation from 100% screen temperature monitoring before resist spraying at matricizing

See also process control list in chapter 10.

Description of chemicals and utilities

Cold tap water (Chemical code CA) or raw demin water (Chemical code CC) [15].

Description of equipment requirements

For conditioning a circulation tank is used as described in chapter 11.

To use the water for temperature conditioning of screen glass, the water temperature has to be controlled on a specified level.

The following functions to the circulation tank are added:

Heating up the water. (Water could be cold because of evaporation, cold screens, filling with cold water)

Cooling down the water. (Water could be heated up because of too warm incoming screens and energy from the circulation pump)

Because spraying is done on both sides of the screen, spraying in a hanger system is most effective. The hangers are transported through a tunnel (see also chapter 11).

The total needed spraying time can be estimated from a calculation model [2].

Some pre-calculations are done and given below. Input conditions were:

Temperature of the conditioning water equal to target screen temperature.

Final screen temperature deviates 1 (C from target screen temperature.

Screens are sprayed on both sides.

Excessive water spraying. Energy transfer is not limited by water supply.

Calculations for conditioning time.

1.2 Pre-wetting

Reason

When aggressive agents like fluoric acid are sprayed directly into a dry inner screen, the covering by the acid can be too slow. The flow pattern can lead to etching patterns that are visible in the screen. Therefore pre-wetting is done. The inner screen must be completely covered with water, before spraying of the acid.

Note:

In some cases (e.g. 17 CDT) pre-wetting can be omitted without problem.

Screen conditioning will also result in a wet inside screen surface. In that case this process step can be omitted.

Splashes of e.g. fluoric acid on the external dry screen will lead to stains.

For this reason the external screen is also often sprayed with water.

With pre-wetting large particles can be removed.


Process sequence is:

Spraying of water, both internal and external.

Draining.

On most positions for internal spraying, tap water or recycled de-ionized water can be used. Only at the last position, fresh and filtered de-ionized water must be used to remove remaining contamination from the screen.

Note:

A temperature specification for the recycled or tap water is not needed. Large fluctuations must be avoided. Often 30 (C de-ionized water is used because it is the only de-ionized water available.

For external water spraying only de-ionized water may be used, in order to prevent drying stains or salt deposits from non de-ionized water.

Spraying is done with nozzles or open-ended pipes. Spraying time and flow is adjusted in such a way that the whole screen is covered with water.

Note:

Often it is not very effective because off bad wetting properties of the external screen.



Spraying time5 secComplete covering of screens

Water flow400 1500 l/hDepending on screen type. Complete wetting of screens

Draining time> 20 secLimit intake of water to acid or degreasing carts



External:de-ionized water (Chemical code CA or CC) [15]

Internal: cold tap water (Chemical code CA) or recycled de-ionized water.


Water sprayingScreen diagonal

< 21 (CDT)21 29> 29

Externalnozzlesnozzlesnozzles

InternalOpen ended pipePipe or nozzlePipe or nozzle

For supply of de-ionized water and/or tap water a service unit with filter, a pressure gauge and/or flow meter to control the water flow is required.

1.3 Degreasing (optional)

Reason

While etching the glass (see section Acid etching), grease, glue etc. can protect the glass. This will give local differences in etching rate and can cause etching faults.

To remove the grease, glue etc., a hot alkaline solution is sprayed against the inside of the screen.

Note:

In the past, the quality of screen glass was such that degreasing of the glass was an essential part of the screen washing process [3]. General experience from production centers today is that degreasing is not needed. Some still use it as kind of insurance, but added value for this process is hard to proof. Point of attention can be reclaim screens from tube separation process, which might contain glue residues from the rim band. New large/jumbo lines have no degreasing positions but use double acid spraying instead.


The degreasing agent is sprayed in such way that the internal screen is completely covered. To enhance dissolving grease, oil and glue, the agent is heated to approx. 50oC. Degreasing agent Prosol is more effective than soda [3,4]. Further increase of temperature might somewhat increases the degreasing efficiency [3,4].



Soda flow800 + 100 l/hComplete covering of screen

Soda concentration8 + 3 %Efficient degreasing

Soda temperature50 + 5 (CEfficient degreasing

Spraying time> 15 secEfficient degreasing



Soda or Prosol solution at 50 (C.


The degreasing position is fed from a supply cart. The liquid is circulated in the cart via a bypass and via the spraying position. The flow can be controlled by a flow meter.

Filtration is done over a mat to remove coarse dirt particles (e.g. graphite residues from rewash screens).

The liquid can be supplied either manually or by an automatic control system with automatic valves and level control system. Furthermore, the temperature is controlled with temperature measurement and heating elements.

Liquid supply system

The liquid is sprayed against the inside of the screen with 1 or 2 open pipes with a diameter of 6 8 mm. Spraying time must be > 15 sec.

1.4 Acid spraying and etching

Reason

Removing part of the glass surface, offering fresh and clean glass to subsequent processing

Removal of particles sealed in or attached to the glass surface.

Formation of silanol groups at the glass surface, essential for adhesion of the PVAl pre-coat layer


A solution of fluoric acid or a mixture of fluoric acid and nitric acid is sprayed against the inside the screen. It is essential that the screen is completely covered with acid. After stop spraying, during a specified time the acid is allowed to react with the glass (etching). After etching, the reaction products are removed by water rinsing.

Two reasons for etching can be given.

Creating a fresh (clean) glass surface and formation of silanol groups on the glass surface. For this purpose, only a minimal layer of glass (< 1 (m) has to be removed.

Due to pressing of the screens is the glass factory, some inclusions will be present in the top layer of the inside glass surface. These inclusions can cause inner screen defects during matricizing. During etching, the top layer, including the inclusions will be removed.The dimensions of the top layer are strongly supplier related. CPT glass has generally more faults than CDT glass. Different optimizations w.r.t. acid concentrations and process settings are used in different IPCs.

Cross section screen glass.

The following rules of thumb can be used:

Removal of glass, (m/s.

HF sprayingMaximum at etching[Ref.]

4% HF and 10 % HNO30.04, (m/s.0.4 (m5,6

8% HF and 20 % HNO30.07, (m/s.0.9 (m5,6

Etching rejects may occur due to non-uniform distribution of the acid.

Inclusions may remain in the screen in case of insufficient etching. This will cause hook & eye rejects at matricizing.



Acid concentrationHF: 4 - 8 % w/w

HNO3: 10 - 20 % w/wSufficient glass etching

Reduce precipitation of silicates

Acid flow350 - 1000 l/h depending on screen sizeComplete covering of screen

Spraying time5 10 sec Sufficient glass etching

Etching timeOrientation value 20 sSufficient glass etching



One of the following acids are used for glass etching:

HF (5% - 10%)

a mixture of HF (4 - 8 % w/w) and HNO3 (10 - 20 % w/w)

Concentration values are rough indications and optimized for local applications.

The main components of glass for CRTs are oxides of silicon (Si), barium (Ba), sodium (Na), potassium (K) and strontium (Sr). The only inorganic etching components with sufficient etching speed are HF and HF2-.

The overall etching reaction can be expressed as:

SiO2 + 6 HF H2SiF6 + 2 H2O

(1)

In an aqueous solution of HF the following reactions will occur:

HF H+ + F-

(2)

andHF + F- HF2-

(3)

For high etching rates, not-dissociated HF or HF2- is required. These molecules are only sufficiently present in high concentrated HF solutions.

By adding a strong acid like HNO3, more HF and HF2- molecules will be formed. This will increase the reaction rate significantly [7]. Equivalent etching results can be expected by using hydrochloric acid (HCl) instead of HNO3 [6, 8, 9]. For each screen some glass will be dissolved in the etching solution. After some production time the barium-silicon-fluorides (BaSiF) will precipitate in the acid circulation system. The (super-) saturated solution will deposit everywhere, on the wall of the tank, block piping, demolish the pump etc. Nitric acid can dissolve BaSiF and reduce or prevent precipitation.

Improvements for process or yield are not expected from alternative cleaning methods [6,10]. Organic alternatives are expensive and contain fluoride too.

HF2- if formed with HF and fluoride containing salts, formed by HF etching of glass and / or by adding e.g. ammonium fluoride (NH4F) [6].

In the past, only a solution of HF was used. The mixture of HF and HNO3 has been introduced with the introduction of black matrix in the picture tubes. Introduction of the HF/HNO3 mixture resulted in significant yield improvement (up to 10 %) [11]. An attempt to understand the mechanism is given in [3,12].

Factories that do not apply a matrix layer in their picture tubes generally use HF only for etching. From introduction of HF/HNO3 mixture, some yield improvement (< 1 % and depending on glass quality) can be expected.

To prevent etching patterns in the screen, the etching agent has to be distributed fast and fully over the internal screen. Therefore spraying is done in a pre-wetted screen.

After stop spraying, the reaction (etching) continues for 20 - 25 s. [5]. By then, all HF is consumed. A deposit of BaSiF salts is formed. At this point etching differences on small scale might occur, e.g. because of the non-uniform acid layer or near salt crystals. No negative influences were ever reported about the location and the force of acid spraying.

After pre-wetting and draining the screen, the screen is moved to the acid spray position. After acid spraying and etching, the screen is transported to a water rinse position to remove the remaining acids and deposited BaSiF salts. The etching time is determined between stop acid spraying and start water rinsing. The sprayed acid is reclaimed to the acid tank.

The process in practice is done in a screen conveyor. Acid spraying and etching has to be divided over 2 positions. To increase the removed layer of glass, longer acid spraying can be applied or the cycle can be repeated.

In the past (many factories still have) a separate etching position between acid spraying and water rinsing. This can lead to two problems.

Etching is too long, deteriorating the roughness of the glass surface.

The dripping of by BaSiF saturated acid form large stalagmites, without action even up to seal edge.

Both problems are eliminated by described process sequence.

HF is a very aggressive chemical and must be handled with utmost precaution.

When working on the process positions and/or acid supply carts use protective clothing like facemask, rubber boots, protective skirt and acid resistant gloves. Safety shower, eye shower and Ca-gluconate gel (or equivalent) for treatment of acid burns must be available in the direct neighborhood of the position and supply cart.

Handling of HF acid is only allowed by trained and authorized operators.


Acid spraying and etchingScreen diagonal

< 21 (CDT)21 29> 29

NozzlesOpen ended pipeOpen ended pipeOpen ended pipe, 2 for real flat

Pipe diameter8 mm10 mm10 mm

1.5 Water spraying and draining

Reason

Water is sprayed external to remove splashes of aggressive chemicals.

Water is sprayed internal to remove the degreasing or etching chemicals and deposits from the inner screen surface, small glass cracks, pit-holes etc.


The screens are sprayed external and internal via nozzles or open-ended pipes.

For external spraying always de-ionized water is used. Spraying is done with a nozzle. Spraying time and flow is adjusted in such way, that the whole screen surface is covered. Spraying time can be short.

Note:

Often external wetting is not very effective because off bad wetting properties of the external screen.

For internal rinsing, tap water or recycled de-ionized water can be used. Again only complete coverage of the screen surface is important. Extensive rinsing is not only required to remove degreasing or etching chemicals and reaction residues (like BaSiF), but also for removing residues out of small cracks in the glass surface [3].

To limit the water intake into circulation systems for degreasing or etching agents, some draining is needed.



Water flow internal spraying500 1500 l/h depending on screen sizeSufficient rinsing

Spraying time internal spraying30 50 secSufficient rinsing

Water flow external spraying500 1000 l/h depending on screen sizeSufficient rinsing

Spraying time external spraying5 10 secSufficient rinsing

DrainingOrientation value > 20 s.Limit intake of water to next process step



De-ionized water (Chemical code CA or CC) [15]

Cold tap water (Chemical code CA) or recycled de-ionized water,

Note:

When screen washing is used in combination with screen temperature conditioning by water spraying, de-ionized water, tap water or recycle water has to be 30-35 (C.


Water spraying Screen diagonal

< 21 (CDT)21 29> 29

Externalnozzlesnozzlesnozzles

InternalOpen ended pipePipe or nozzlePipe or nozzle

For supply of de-ionized water and/or tap water a service unit with filter, pressure gauge and/or flow meter to control the water flow is required.

When using circulation water, a circulation tank is required. See chapter 11 for more information. The last spraying position is supplied with fresh demi water.

1.6 External screen drying

Reason

Dry the outside screen surface of the panel.


Drying in done by blowing large amounts of air onto the external screen surface. The air drives the water away from the screen. To generate sufficient air, so-called air-movers are used. Air-movers generate up to 20 times the air volume of the compressed inlet air. For most types 2 air movers are sufficient.

Best results are obtained when both air-movers are positioned at the same side. External air blowing is preferably combined with internal water spraying. Air blowing has to be stopped just before stopping internal de-ionized water spraying, in order to avoid rejects caused by high air turbulence and splashes of dirty water.

Air movers.



Air flow primary air50 + 5 Nm3/hSufficient blowing power

Air blowing time15 20 sec



Filtered compressed air, dry and oil free (Chemical code AC) [18].


For supply of compressed air, a service unit with active carbon and particle filter, pressure gauge and/or flow meter to control the airflow is required.

1.7 Hanger washing

Reason

After screen washing and/or pre-coating, the hanger transport system and the seal edge from the screen can be polluted with acid. Transport of polluted hangers and screens through the factory is dangerous for operators and can give serious damage to equipment and factory floor.


A container filled with water is lifted into the hanger with the screen. The hanger and the seal edge are immerged in the water. Simultaneously the screen is lifted a few mm to enable cleaning between seal edge and hanger. Water is sprayed against the screen center (inside screen).

The spraying water gradually refreshes the water in the container.

Generally this process is one of the water rinsing positions after screen washing but before external drying.

Hanger washing



Washing time> 5 secEffective removal of acid

Water flow500 1000 l/hDepending on screen size



Raw demin water (Chemical code CC) [18]:


For supply of de-ionized water and/or tap water a service unit with filter, pressure gauge and/or flow meter to control the water flow is required.

Specification outgoing product

The outgoing product is a clean screen with dry outside surface and a wet activated inside surface.

Auxiliary, tools and filter specifications

Auxiliary materials and tools

PurposeTool

Process times.Stop watch

Temperature measurementsThermometers up to 100 (C

Portable IR meter

Acid concentration controlTitration equipment

Screen inspectionMagnifying glasses (V=10*)

Screen/mask storageScreen/mask transport carts

Small adjustments / repairsWrenches, hammer, flexible ruler, screw drivers, etc

Rinsing cleaningKitchen-sink with water / drain

Towels,

Sponges,

Buckets

SafetyShowers (for people) and eye shower bottles.

pH paper for detection of acid leakages

Ca-gluconate gel or equivalent for acid burns

Screen handlingManual vacuum chucks

ProtectionRubber gloves

Safety glasses

Rubber boots, protective skirts

Ear plugs

Sampling, measuring and adjustmentPoly propylene ware:

Beakers, 250 ml

Beakers, 100 ml

Spraying bottles 500 ml

See also auxiliary list is ref [13].

Filter specifications

For filtration of demi water a pore size of 6 (m is required. Size of the filter is depending on the required water flow.

Compressed air must be filtered over an active carbon filter to remove oil and over an absolute particle filter with a pore size of 0.2 (m.

Acid and soda solutions must be recycled over a filter mat

An example of the filters that are used in the screen wash area of large/jumbo lines:

PositionHousingSupplierCartridgeSupplier

Circulation tanksFH630-50-SGParkerPM 050-30AN-DOParker

Service racks airAG0006 A/EPallAK 03/10Pall

Service racks airn.a.TNFZ 01 H03 H03Parker

Acid cartsn.a.Filtrair R50

See also ref [14] for more information regarding process filters.

Cleaning procedures

HF is a very aggressive chemical and must be handled with utmost precaution.

For cleaning of acid spraying positions and acid supply carts use protective clothing like face mask, rubber boots, protective skirt and acid resistant gloves.

Cleaning is only allowed by trained and authorized operators.

Acid and soda supply carts

Drain the tanks completely. Dispose dirty filter mat

Flush the tanks with water

Close drain and re-fill the tanks with acid

Install new filter mats

Acid and soda spraying positions Remove course materials

Flush with water only

Water circulation tanks Drain circulation tank.

Wash inside tank. Remove deposits from the wall with cloth and commercial detergent.

Rinse the tank with de-ionised water.

Close the drain and refill with de-ionised water.

Water spraying positions

Check function of spraying nozzles. When some nozzles are blocked, open, clean and re-install the nozzles.

Clean the inside of the tunnel with water and a cloth.

Waste treatment

Mixed acid, soda and water from the first rinsing positions after soda and acid spraying must be drained to a special acid drain and must be treated according local safety and environmental regulations.

All other water can be drained directly into the normal city sewer.

Process control

This process control list gives an overview of the items that have to be controlled in the screen washing area during normal production. An advice is given about the frequency of control. The list can be used as a starting point for defining a process control list dedicated for a certain line or as help for updating existing checklists. It is important that a process control list is made specifically for a certain line and type, using the process description, this list and the local situation as input.

ProcessItemSpec*Advised control frequency

UtilitiesDemi water pressure 30 (C

Compressed air pressure

- process air

- control air6.0 + 0.5 bar

6.0 + 0.5 bar

6.0 + 0.5 bar1x / shift

1x / shift

1x / shift

Water sprayingWater flow internal / external spraying

Water temperature2000 + 100 l/h

32 + 1 (C1x / shift

1x / shift

Soda spraying

(optional)Soda flow

Soda concentration

Soda temperature1500 + 100 l/h

8 + 3 %

50 + t.b.f. (C1x / shift

1x / shift (SPC chart)

1x / shift

Acid sprayingAcid flow

Acid concentration1500 + 100 l/h

HF: 6 + 2 %,

HNO3: 15 + 5 %1x / shift

1x / shift (SPC chart)

Ext. screen dryingAir flow50 + 5 l/h1x / shift

Miscellaneous

Water supply system.To save water, each screen washing line is equipped with one or more water circulation (reclaim) tanks. This tank has a shared function with other spraying positions

The tank has the following general functions:

Upper level for automatic filling

Lower level 1; for automatic filling

Lower level 2; for pump safeguarding

Over flow and drain

Circulation pump

Filtration of the water is not essential. In case of conditioning, the tank(s) is also equipped with a temperature control system with temperature measurement and heating elements.

Automatic filling of the tank can be done by tap water or de-ionized water.

Circulation water can be used for:

Pre-wet and / or conditioning positions

Water rinsing positions after degreasing and HF/HNO3 etching.

Circulation water is reclaimed from:

Pre-wet or conditioning position

Water rinsing using fresh de-ionized water.

Note:

Water is extracted from the circulation system by

Rinsing 1st pos. after degreasing (if present)

Rinsing 1st pos. after HF/HNO3 etching

Overflow of the circulation tanks (not preferred).

Level control of the tank.

Water is added to the system by

Positions with fresh de-ionized water spraying

Level control of the tank.

Screen wash tunnel.

The washing is done by use of an overhead conveyer. The screen is placed in a hanger and moves with the hanger from one position to the other.

Screen wash tunnel.

The process liquids are sprayed against the inside and/or outside screen by means of nozzles or open-ended pipes. Shielding for spray water is needed on top of the tunnel.

Spraying of process liquids.

References

2. NIESSEN F.Room conditions for new linesTVR-217-03-FN-D006, 2003-10-07

3. DURLINGER I.Screen heating/cooling before screen wash for new large/Jumbo lines.TVB-698-00-ID-D051, 2000-03-31

4. PENNERS H.J.M, Inventory of the washing and precoating of screen panels for matrizing/flow coating. TVR-34-90-HP/D108, 1990-02-16

5. HEIJKANT J. v.d., Vervolg wasproeven 14" schermen met reiningingsmiddelen. TVM 67-90 JH/1977, 1990-01-19

6. PENNERS H.J.M. and BOUWMANS J.R.M. The etching of screen glass in the -wash and precoat process. TVB-57-96-HP-D2393, 1996-05-03

7. SOMERS M.J.M. Glass etching using different liquid compositions, TVR-298-03-MS-D001, 2003-02-13

8. HEIJKANT, J. VANThe effect on varying acid concentrations on screen glass etching, TVR 67-91-JH2070, 1991-01-14

9. TAREK SLEIMAN, MARY PHILIPHydrochloric Acid Drip Test. Report 2489 (PDC,1994-04-07)

10. SIMONS A.J.An examination of the faceplate etching process for the 14" colour monitor tube. CML 1265; 1989-12-12

11. HOOGSTEEN W., STEYVERS R., BOOGAARD A.The effect of substrate cleaning precoating and matricizing on phosphor adhesion, Nat Lab. Technical Note 053/97, 1997-01-01

12. MEERTENS S.The HF/HNO3 Screenwash process as developed for the 14" CMT, TVR - sq 88/34-0080, 1988-02-05

13. JACOBS JAN and POLS ERIC van der Pitting corrosion model for glass pits. TVB-657-97-JJ-D1927; 1997-11-21

14. H. PENNERS

Auxiliary list for mask washing, screen washing, matricizing and rewashing.TVZ-298-01-HP/D002A, 2001-01-04

15. J.A. NillissenFiltration managementTVR-657-99-JN/D0139, 199-07-15

16. PTE, Standardisation mechanical constructionsUtility and chemical standards00-04-15

AMENDMENT RECORD

RevisionReferencePagesDescription

AAllFirst issue

--0--0--0--

LG.Philips Displays

Page 1 of 19COMPANY RESTRICTED

_1123058078.vsd

FPD Screen Washing

Documents

inside screen

fresh screen

screen contamination

external screen

screen wash process

water temperature

spraying water

screen processing lg