Preparation of Ultrapure Water with Mixed Bed Resin

  • 2022-10-26

Ultra pure water, conductivity should be less than 0.1 μ S/cm (sometimes 0.06 μ S/cm), silica shall be less than 5 μ G/L, the amount of various impurity ions is μ G/L level and strict requirements on the number of bacteria.

Conductivity is the conductivity of water. It is usually used to express the purity of water. It is reciprocal with resistivity. The limit resistivity of pure water is 18.3 M Ω· cm, and the minimum conductivity is 0.055 μ S/cm。

In the electronic industry, from the cleaning of various electronic components to the preparation of a series of process solutions, high-quality pure water is required, especially in the production of semiconductor devices and large-scale integrated circuits. Almost every process needs to be cleaned with ultrapure water. Ultra pure water plays an increasingly important role in the electronic industry and has become one of the important factors affecting the quality and production cost of electronic components.

When the integration degree of integrated circuit products reaches 1M, the resistivity of pure water is required to reach above 18 M Ω· cm. When the integration degree of integrated circuit products reaches 16M, the resistivity of pure water is required to reach above 18.2 M Ω· cm, which has reached the theoretical value of ultrapure water.

Specifically, the best standards for ultrapure water for electronic industry are: (1) dissolved inorganic matter: none (ppb level), (2) dissolved organic matter: none (control bacterial growth); (3) Solid organic matter: None; (4) Transparency: best (no turbidity); (5) PH=7 (neutral); (6) Resistivity: 18~18.3M Ω· cm (25 ℃); (7) Temperature: keep at 10~15 ℃ (control bacterial growth); (8) Silicic acid: completely removed; (9) Microorganism: completely removed.

Ultrapure water for electronic industry is prepared by multi-stage reverse osmosis and two-stage mixed bed treatment, as well as ultraviolet sterilization and ultrafiltration technologies. The greatest feature of reverse osmosis technology is that it can remove ions in water to a low degree, but it cannot completely remove them. At this time, ion exchange resin will play an irreplaceable role. Ion exchange resin is applicable to the treatment of water with low ion content. It can completely remove ions from water, especially in the polishing stage of ultrapure water, which is one of the reasons why ion exchange resin has strong vitality.

Conventional mixed bed resin can be used for Grade I mixed bed prepared by ultrapure water in electronic industry, while electronic grade resin is required for Grade II refined mixed bed. As the influent water of the Grade II refining mixed bed has reached the level of trace or ultra trace, its flow rate is high, and its operation cycle is long, which may lead to large differential pressure between the inlet and outlet, bacterial propagation, etc., the resin is required to have not only strong exchange capacity and high mechanical strength, but also high regeneration purity and uniform particle size distribution. Among them, the H-type rate of cation resin must be above 99.0%, and the iron content must be below 50.0ppm dry resin; The OH type rate of anion resin must be above 95.0%, and the chloride ion content must be below 0.50%. The H-type ratio of cation resin used in the mixed bed for ultrapure water polishing must be above 99.9%.

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