The terms critical cleaning and precision cleaning are often used interchangeably.1 We have developed a strong preference for the term critical cleaning. Precision cleaning conjures up a vision of cleaning in a highly-restricted cleanroom. Perhaps each individual component is cleaned separately by a highly-trained technician; perhaps there are wet benches with automated product handling; maybe there is a multi-chamber automated spray system that feeds directly into the cleanroom. Precision cleaning often involves employing a carefully-defined set of washing, rinsing, and drying steps, including the chemical nature and/or concentration of cleaning agent or rinsing agent, the forces involved, the temperature, and the time. Precision cleaning may involve establishing that the product meets acceptable levels of residual soil using sophisticated, costly analysis of particles, leachable residue, or of specific contaminants. This is a limited view of cleaning. While it is crucial to define the cleaning step and to use controlled environments where appropriate, depending on precision cleaning may be wrong, may result in a contaminated product, or may lead to a false sense of security.
TIPPING POINT CLEANING
It is more important to determine the critical cleaning steps. Critical cleaning steps are lynchpin cleaning process steps that, if conducted properly and at the appropriate point in the process flow, have a positive impact on the overall product performance. In our experience, the important cleaning step, the critical cleaning step, may occur early in the process, in a machine shop or in a job shop (eg. a coating facility), in what looks at first glance like a repair facility. Critical cleaning may or may not require precision cleaning processes. Defining and optimizing critical cleaning steps is akin to the concepts aptly communicated by Malcolm Gladwell in “The Tipping Point.”2 In one example, Gladwell recounts the relationship of prompt removal of graffiti from subway cars to the reduction in crime in the New York City subways. Graffiti would not seem to be the critical issue, and concern with graffiti “at a time when the entire system was close to collapse seems as pointless as scrubbing the decks of the Titanic as it headed toward the icebergs.”3
One way to define a critical step is to consider the negative consequences of not performing that step or not performing it adequately. In the Gladwell example, graffiti was either removed immediately, or the car was taken out of service; the motivation was to send a clear message to vandals that their “artwork” would not be observed by others. In the case of critical cleaning, the motivation is to minimize product failure. If the soil (matter out of place) is not adequately removed at that critical cleaning step, at that “tipping point” step, subsequent cleaning may not resolve the problem. Subsequent processing and cleaning steps may actually exacerbate contamination by inadvertent chemical reaction of the soil, drying of the soil, or by embedding the soil in the surface of product.
Contamination happens long before the product enters the cleanroom; critical cleaning often happens long before the product enters the cleanroom. Critical cleaning may involve aqueous, solvent, or non-chemical cleaning agents. A cleanroom can minimize re-contamination, but the most sophisticated cleanroom or controlled environment may not correct a contaminated product.4
Clearly defining the cleaning steps is important, but they have to be the correct steps, at the correct point in the build process. Identify, then qualify/validate and monitor the critical cleaning steps; you will achieve a quality product.
- This topic is adapted from the preface to the second edition, “Handbook for Critical Cleaning,” B. Kanegsberg and E. Kanegsberg, ed., CRC Press, scheduled for publication imminently.
- M. Gladwell, “The Tipping Point: How Little Things Can Make a Big Difference,” Little Brown and Company, 2000 & 2002.
- “The Power of Context,” Ibid, p. 142.
- Kanegsberg, B. and E. Kanegsberg, “Contamination Detection Basics,” Controlled Environments Magazine, June, 2010.