Deionized water refers to pure water after removal of impurities in the form of ions. The “deionization” defined by the International Organization for Standardization ISO/TC 147 is defined as: “Deionized water completely or incompletely removes ionic substances, mainly refers to the treatment method using ion exchange resin.” The deionized water process mainly adopts the method of RO reverse osmosis.
Ion exchange resin is used to remove anions and cations from water, but there are still soluble organic substances in the water, which can contaminate the ion exchange column and reduce its efficiency. It can also cause bacterial growth after deionized water storage. In the semiconductor industry, deionized water is referred to as “ultra-pure water” or “18 megohm water.”
The processing from tap water to deionized water:
- First to filter coarse particles by quartz sand
- Then high pressure through the reverse osmosis membrane
- In the end, it is generally necessary to go through a step of ultraviolet sterilization to remove micro-organisms from the water.
- If the resistivity is not as high as required, the maximum resistivity of the ion exchange process can be up to 18 megabytes.
Relatively speaking, distilled water is only vaporized and then condensed. and its purity, such as conductivity, is not as high as that of deionized water with high purity. Most of the semiconductor industry uses high purity deionized water.