Efforts to preserve clean water resources
Complete washing of wafer is indispensable for IC production. Complicated ICs are produced through as many as 500 processes, which means wafer washing is required about 100 times before completion since washing is needed every 5 to 6 processes.
Various chemicals, such as hydrofluoric or sulfuric acid, are used for wafer washing according to the materials which need to be removed. Hyperpure water is used for washing off the chemicals and final wafer washing. As much as 400 tons of water is consumed per day !
Seiko NPC aims to save precious water resources by recycling 240 tons of drained water, which includes comparatively less chemicals, out of 400 tons of water consumed through the whole processes. Hyperpure water is reproduced from the recycled water by removing impurities through ion exchange resin and filters. By water recycling, Seiko NPC not only prevents exhaustion of ground water but also reduces service water expense.
Rest of the drained water (160 tons) and daily life drainage (90 tons), which is not suitable for recycling, is discharged from the factory after neutralization, purification and chlorination in the wastewater treatment facility in the factory site. Seiko NPC has its own standard for the level of residue in the discharged water, which is stricter than laws and regulations. Actually, the level of residue in the discharged water is much lower than its own standard.
Through wastewater treatment, as much as 450kgs of residue is collected every day in a sedimentation tank. The residue, after dehydration, is recycled as submaterial for concrete.