Achieving and maintaining ultrapure water (UPW) is extremely important in light of its widespread presence throughout the manufacture of semiconductor integrated circuits. The technology of the industry has advanced so rapidly over the past few years that it has redefined cleanliness requirements, specifically with regard to the need for quantitatively removing colloidal silica, particles, total organic carbon (TOC), bacteria, pyrogens (bacterial fragments) and metal ions.
A well-designed UPW system with strategically placed filters, will ensure achievement of this goal, since the type of filter selected in each of the key areas will make a measurable difference in ultimate quality.
To meet the demands of a high-purity deionized (DI) water system, filters must:
– Not contribute organic, particulate or metal ion contamination to the effluent stream.
– Not unload trapped contaminants or shed filter material
– Be integrity testable to verify removal ratings
– Perform identically from lot to lot
– Have a low-pressure drop for long life and maximum economy.
DI Water :
A well-maintained UPW system will have a number of carefully selected filters and purifiers placed in strategic positions.
Deionized water which is also known as demineralized water (DI water or de-ionized water; can also be spelled deionised water, see spelling differences) is water that has had its mineral ions removed, such as cations from sodium, calcium, iron, copper and anions such as chloride and bromide. Deionization is a physical process which uses specially-manufactured ion exchange resins which bind to and filter out the mineral salts from water. Because the majority of water impurities are dissolved salts, deionization produces a high purity water that is generally similar to distilled water, and this process is quick and without scale buildup. However, deionization does not significantly remove uncharged organic molecules, viruses or bacteria, except by incidental trapping in the resin. Specially made strong base anion resins can remove Gram-negative bacteria. Deionization can be done continuously and inexpensively using electrodeionization.
Electro deionization (EDI) :
Electro deionization is a water treatment process that removes ionizable species from liquids using electrically active media and an electrical potential to effect ion transport. It differs from other water purification technologies such as conventional ion exchange in that it is does not require the use of chemicals such as acid and caustic. EDI is commonly used as a polishing process to further deionize Reverse Osmosis (RO) permeate to multi-megohm-cm quality water.
The continuous electrodeionization (EDI) process, is distinguished from other electrochemical collection/discharge processes such as electrochemical ion exchange (EIX) or capacitive deionization (CapDI), in that EDI performance is determined by the ionic transport properties of the active media, not the ionic capacity of the media. EDI devices typically contain semi-permeable ion-exchange membranes and permanently charged media such as ion-exchange resin. The EDI process is essentially a hybrid of two well-known separation processes – ion exchange deionization and electrodialysis, and is sometimes referred to as filled-cell electrodialysis.