For many of us involved in contamination control, it may seem that building and monitoring the cleanroom is a goal in and of itself. Therefore, let us all be reminded that the goal of any cleanroom, of any controlled environment, is to support fabrication or assembly of high-value product that performs well in the short and long term. We may expend considerable effort in controlling airborne particles and airborne molecular contamination in the cleanroom. However, it is all too easy to lose track of what it takes to clean and maintain cleanliness of the product itself.
The concept of critical cleaning applies to both the product and to the cleanroom surfaces. There are many specifications, including international standards, defining levels of cleanliness on cleanroom surfaces (e.g. ISO 14644-9 and 14644-10). Specifications for approaches and techniques for cleaning of cleanroom surfaces are under development.1 While the underlying principles of critical cleaning and good process design are similar for both the product and the cleanroom, the processes and requirements may be distinctive for the cleanroom surface.
Cleanroom cleaning is generally a clean-in-place (CIP) operation. The walls, floors, bench tops, and large fixtures are not removed for the cleaning operation. On the other hand, both product and the fixtures or tooling for product processing may undergo clean-out-of-place (COP) operations that more appropriately occur out of the cleanroom. This increases the number of options in cleaning processes and cleaning equipment that could be used to enhance cleaning efficacy; but it also means that attention must be given to how a cleaned part or fixture is transferred to the cleanroom for further assembly operations.2 No matter how many air filters are in place or how often the walls and floors are scrubbed, introduction of a contaminated fixture can compromise the entire working environment and product.
Fixtures versus product
It may be more difficult to clean support equipment than it is to manage the product itself. A cleaning process that is effective for the product may not be appropriate for fixtures and tooling, and vice versa. Products or components with simple, readily-accessible surfaces may be held and spatially manipulated during cleaning or other manufacturing processes using complex tooling or fixturing. The product may require immersion cleaning. Or, for removing sub-micron particles, megasonics may be the optimal method. The line of sight acoustic streaming characteristic of megasonics makes that approach to cleaning appropriate for flat substrates that are readily damaged.
The tooling requires cleaning to avoid contamination of the product and to assure proper mechanical functioning. The cleaning process selected for the product may be ineffective for tooling or complex objects with blind holes that could entrap soils and that are used repeatedly during assembly. Ultrasonic cleaning, which involves omni-directional cleaning action, is a more promising choice.
Designing, cleaning, and maintaining the tooling seems to us to be, in many respects, akin to the challenges involved in managing re-usable medical devices.3 The tooling must be readily disassembled, cleaned, and reassembled. This means that the tooling must be designed for cleanability. We have to understand what soils and the state of matter of those soils that are generated during product fabrication and assembly.
Obviously, soils generated during use of medical devices are different than those generated during fabrication in a cleanroom; however, the thought processes behind avoiding contamination are similar. We have to understand the contaminants that are likely to be generated during manufacturing, develop techniques for removing those contaminants, selecting the appropriate analytical techniques, determining acceptable levels of residue, and monitor that tooling maintenance and critical cleaning are successfully occurring.
We have to consider materials compatibility issues. Assuring materials compatibility is at least as important for the tooling as they are for the product, in part because the product typically has limited exposure to process chemicals. In contrast, the materials of construction of tooling have to withstand repeated exposure to the forces and chemicals used in the cleaning process. The cleaning technique has to be designed, developed, and demonstrated; and it must be defendable (logical). For automated processes, design and cleaning of the tooling can be more challenging than that for the product. Therefore, consideration of the 4Ds4 and taking a life-cycle approach5 to design and critical cleaning of tooling can make the difference in success and failure of product assembly.
Certainly, in pharmaceutical production where containers, transfer lines, and other items come in contact with the product, there are well-defined protocols for CIP and monitoring. In manufacture of product, many surfaces may come into close contact with the product. It is a good idea to set up procedures to avoid inadvertent product contamination. Unfortunately, we regularly observe assembly and coating failures that could have been avoided by planning and validating cleaning and maintenance processes for tooling, fixturing, and even ovens.
Other cleanroom surfaces, such as floors, walls, and bench tops, can cause problems with the product. Contaminants can be particle, thin film, or vapor. They can be organic, inorganic, biological, or a complex mixture. Repeated cleaning and polishing can lead to biofilms.
Having a cleaning and maintenance program in place is essential. We often hear something to the effect that “we hire people” who “take care of” the floors and walls after the first and second shift leave. The vision that comes to mind is that of a cadre of earnest elves who, every night, quietly enter the cleanroom, scrub it down with toothbrushes, and then steal away before the break of dawn, leaving the cleanroom spotless and meeting all specifications. There are wonderful cleanroom cleaning services. However, the same provisos apply to using cleanroom cleaning services as to using contract cleaners for the product. That is, you are responsible for the process; you are responsible for cleaning. Find out what cleaning protocol is used; make sure it is what you need for production. Pin down the specifics, make modifications if necessary, and get the protocol in writing. Every now and then, you might consider a friendly visit to those earnest elves.
1. ISO/TC 209 WG 12: “Cleaning of surfaces to achieve defined levels of cleanliness in terms of particle and chemical classifications.”
2. B. Kanegsberg, E. Kanegsberg and K. O’Donoghue, “Keeping Product Clean In and Out of the Cleanroom,” Controlled Environments Magazine, Jan. 2009 and Feb. 2009.
3. J. Broad and B. Kanegsberg, “Putting Cleaning Protocols to the Test,” Controlled Environments Magazine, July 2012.
4. B. Kanegsberg and E. Kanegsberg, “4D Processes,” Controlled Environments Magazine, Jan. 2014.
5. B. Kanegsberg and E. Kanegsberg, “Medical Device Manufacturing Shifts to Lifecycle,” Controlled Environments Magazine, Apr. 2014.
Barbara Kanegsberg and Ed Kanegsberg (the Cleaning Lady and the Rocket Scientist) are experienced consultants and educators in critical and precision cleaning, surface preparation, and contamination control. Their diverse projects include medical device manufacturing, microelectronics, optics, and aerospace. Contact: email@example.com
This article appeared in the July/August 2014 issue of Controlled Environments.