Water is the fluid most often used in cleaning, whether it is for personal, household, industrial, or the manufacture of high-value product. Water is the most abundant cleaning chemical. With appropriate additives, water-based cleaning has proven successful. However, particularly in critical manufacturing, the wrong water quality can derail the process and undermine product quality.
No single water treatment process meets all manufacturing requirements. Water softening replaces one ionic material with another. DI processes do not remove non-ionic materials, either dissolved or particulate. One industrial facility in the Northwest U.S. found fragments of salmon eggs in the effluent of a DI system. Distillation will not eliminate impurities such as organic solvents with substantial vapor pressure. RO processes separate most, but not all, dissolved material. Ultra-violet (UV) light may kill bacteria and other life forms but does not separate the dead bacteria from the water.
Getting water to be purer and keeping it pure are two separate issues. Because water is such an aggressive solvent, ultra-pure “18 Mega-ohm” water generally does not remain pure for long. Ions can leach into pure water from containers and pipes. Even small amounts of atmospheric gases, including carbon dioxide or laboratory acid fumes, can rapidly degrade the purity (and resistivity) of water.
What process is best for my application?
The answer depends on knowing what you need. For cleaning of gross amounts of contaminants at an early stage of assembly, tap water may be adequate, provided that the seasonal consistency is acceptable. Keep in mind that if the process is moved to another location, the tap water may be different. Also, because dried-on contaminants tend to be more adherent, any impurities in the tap water that remain when the part is dry may be more difficult to remove at a later stage of operation. For general cleaning, perhaps a single stage DI or RO system will provide the purity and consistency needed. Many high performance applications employ systems that incorporate more than one treatment process, or have a multi-pass system to increase the purity. Any system must be properly monitored and maintained.
This cleanroom tip was taken from “Perfect Water,” which appeared in the May 2013 issue of Controlled Environments.
