Liquid Crystal Display (LCD)
Production of LED starts with cutting of flat glass into a square of 10 by 10 cm
dimension which is then cleaned in ammonium hydroxide solution. It is later
immersed in a stripping solution of alkaline and then rinsed in deionized water,
spun dried, and sent for photolithographic process where it is masked with liquid,
exposed, and developed. Thereafter, it is thoroughly rinsed with deionized water,
dried before being chemically etched with acid, re-rinsed in deionized water, and
then solvent dry. After this, the square is stripped in alkaline solution, rinsed with
deionized, and spun dried. As in the production of silicon-based semiconductor, the
square is subjected to passivation process. Liquid silicon dioxide is further deposited
on the glass layer; however, silicon and oxygen gas may be used with phosphine gas
as a dopant. Sodium ions on the glass surface are removed from spots to improve the
electronic characteristic of the LED. The glass is dipped in an ammonium fluoride
bath, rinsed with deionized water, and dry spinned. The glass is then reprocessed
through the passivation procedures and screen printed with devitrified liquid glass in
matrix. The glass is further vitrified through baking and sawed into patterns indicated
by the vitrified glass boundaries. This is followed by cleaning the glass in alkaline
solution, rinsing in deionized water and a layer of silicon oxide is evaporated onto its
surface. Two mirror-image pieces of vitrified glass are bonded with a space between
the two pieces of glass by heating them in a furnace. The glass is transferred into a
vacuum chamber, where air in between the two glass pieces is removed and liquid
crystal of biphenyl compound is injected, sealed with epoxy, and finished by vapor
degreasing using solvent and finally shaped for assessment and assemblage. This
device is widely used in machines that need to display responses.
2.5.2 Water Use
Water is significantly employed in virtually all steps involved in the manufacturing
of all the components identified under this subcategory as contact water. Large
volume of deionized water is consumed in the semiconductor subcategory, essentially, to rinse the body of the wafer after each production step, which includes
cutting, etching, sputtering, electroplating, etc. Water is further employed for cooling
and lubrication of some machines like the diamond saws and grinding machines
used for slicing, lapping, and dicing wafer. An estimate of 628 million L/day of
water is consumed in the entire semiconductor industry and very small amount is
recycled for reuse.
2.5.3 Wastewater Characterization
Water is used to wash off deposited materials, chemical solvent, and grease in the
production steps of semiconductor manufacturing plants, which invariably result to
generation of wastewater in the plant. The large volume of the wastewater is
4 Electrical and Electronic Wastes Treatment
157
Production of LED starts with cutting of flat glass into a square of 10 by 10 cm
dimension which is then cleaned in ammonium hydroxide solution. It is later
immersed in a stripping solution of alkaline and then rinsed in deionized water,
spun dried, and sent for photolithographic process where it is masked with liquid,
exposed, and developed. Thereafter, it is thoroughly rinsed with deionized water,
dried before being chemically etched with acid, re-rinsed in deionized water, and
then solvent dry. After this, the square is stripped in alkaline solution, rinsed with
deionized, and spun dried. As in the production of silicon-based semiconductor, the
square is subjected to passivation process. Liquid silicon dioxide is further deposited
on the glass layer; however, silicon and oxygen gas may be used with phosphine gas
as a dopant. Sodium ions on the glass surface are removed from spots to improve the
electronic characteristic of the LED. The glass is dipped in an ammonium fluoride
bath, rinsed with deionized water, and dry spinned. The glass is then reprocessed
through the passivation procedures and screen printed with devitrified liquid glass in
matrix. The glass is further vitrified through baking and sawed into patterns indicated
by the vitrified glass boundaries. This is followed by cleaning the glass in alkaline
solution, rinsing in deionized water and a layer of silicon oxide is evaporated onto its
surface. Two mirror-image pieces of vitrified glass are bonded with a space between
the two pieces of glass by heating them in a furnace. The glass is transferred into a
vacuum chamber, where air in between the two glass pieces is removed and liquid
crystal of biphenyl compound is injected, sealed with epoxy, and finished by vapor
degreasing using solvent and finally shaped for assessment and assemblage. This
device is widely used in machines that need to display responses.
2.5.2 Water Use
Water is significantly employed in virtually all steps involved in the manufacturing
of all the components identified under this subcategory as contact water. Large
volume of deionized water is consumed in the semiconductor subcategory, essentially, to rinse the body of the wafer after each production step, which includes
cutting, etching, sputtering, electroplating, etc. Water is further employed for cooling
and lubrication of some machines like the diamond saws and grinding machines
used for slicing, lapping, and dicing wafer. An estimate of 628 million L/day of
water is consumed in the entire semiconductor industry and very small amount is
recycled for reuse.
2.5.3 Wastewater Characterization
Water is used to wash off deposited materials, chemical solvent, and grease in the
production steps of semiconductor manufacturing plants, which invariably result to
generation of wastewater in the plant. The large volume of the wastewater is
4 Electrical and Electronic Wastes Treatment
157