Call it parts cleaning, surface prep, precision cleaning, residue removal, or critical product cleaning – manufacturers think about three steps for most cleaning processes—wash, rinse and dry. That’s not enough! Cleaning means removing unwanted material and achieving the correct surface attributes for your application. As soon as the cleaning process is complete, product surfaces interact with the environment; the product becomes contaminated. Therefore, after wash, rinse, and dry, there is a fourth step. Let’s term this fourth step: keep it clean.
Keeping the product clean involves protection during storage, handling, and shipping. What environment does the part need to be in? It depends on the materials of construction, on the product, on what it will be used for, and on what contaminants might interfere with production, coating, and functionality.
The most effective approach is to do surface finishing immediately after cleaning.
Extreme measures
Plasma vapor deposition is conducted in a sealed deposition chamber. Often, final plasma cleaning is conducted in that chamber immediately prior to deposition. We have to emphasize that the freshly-cleaned part is kept in this highly-controlled environment. An important “gotcha” is that the part better be pretty darn clean before it is placed in that deposition chamber. Plasma cleaning will not remove heavy contamination by organic and inorganic materials. Unwanted “stuff” that is trapped in blind holds and tight spaces can move around in the deposition chamber. This means that processes for upstream cleaning, upstream storage, and upstream shipping must be scrupulously designed, monitored, and controlled. In vapor deposition, problems may be manifested by poor adhesion and unusual, unwanted bright colors on the coated part. While this may be aesthetically pleasing, this typically elicits colorful language by those involved, product reject and extensive, time-consuming decontamination of the deposition chamber. Chamber deposition is not the answer for all surface finishing.
Cleanrooms
So, you might think, let’s just toss the product into the cleanroom. For high-value applications in areas like optics, microelectronics, implantable medical devices, and microelectronics, cleanrooms or other controlled environments are essential.
However, a cleanroom alone is not a magic bullet; a cleanroom does not prevent contamination. If there is soil on the part, moving the part into the cleanroom does not confer dispensation from contamination. Our colleague, cleanroom expert Scott Mackler reminds us that a cleanroom doesn’t prevent recontamination; it simply slows down the rate of recontamination. How is the product stored in the cleanroom? Moving the product into the cleanroom for storage does not prevent recontamination. Product can become recontaminated by other activities within the controlled environment. The infamous “product recontamination station” comes to mind. This was a case where the freshy-cleaned product was stored on a bench in the cleanroom next to the output of the drier for the cleaning system. Product can be contaminated with oils and particles if unfiltered shop air comes in contact with cleaned product. Product may become contaminated by moisture in the air and by evanescent volatiles like ammonia. A more effective approach is to transfer the product to an appropriate storage container or a dedicated cabinet.
Storage rooms, product access
Cleaned parts are often stored in a warehouse. We’ve observed ostensibly clean parts stored without packaging on open shelving. Is open storage good enough to avoid recontamination? often not. Open shelving can allow exposure to the outdoors and to all of the suspended particles, oil droplets, and assorted flora and fauna that make their way into the manufacturing facility. How long are parts stored? What steps need to be taken to protect the parts?
Even short-term storage can be problematic. The third shift may complete a cleaning process, only to leave the product sitting out in the shop waiting for someone to continue the fabrication or coating process it in the morning. In the interim, the product becomes recontaminated.
Product Handling; storage containers
On plant tours our host sometimes invites us to pick up the product and inspect it without offering gloves. Should we wear gloves? No need, they tell us. But we should be wearing gloves. Even with lots of handwashing, handling the parts without gloves means depositing fingerprints. Do you know how hard it is to remove fingerprints? Real hard! Fingerprints are among the more difficult soils to remove! Manually handling the product adds to cleaning costs and to potential contamination.
The correct storage container, as we always say, depends on the application. Additives for corrosion inhibition can be considered part of keeping it clean. We will discuss storage and shipping in a future article.
We will share one pertinent anecdote. Long, long ago, during the last millenium, Barbara was asked to do failure analysis on a high value component that was manufactured in a cleanroom. She arranged for the component to be shipped to the lab in a container that was not likely to contaminate the part. After a few frustrating days of extensive analytical testing that yielded confusing information, she noticed that some of the results were consistent with contamination by food and with contamination by people. She discovered that the engineer requesting the tests had stored the component on their desk and showed it to colleagues during lunch meetings. After this learning experience, she became much more definitive about asking how the parts were stored.
What level of product protection do you need?
Product surfaces change after cleaning. Contaminants, both particulate and thin film, inevitably accumulate on surfaces. Keeping parts, components, and product clean means managing contamination during handling, storage, and shipping.
It may not be necessary to protect your product with the same stringent policies and procedures as our local pharmacy uses to protect deodorant from exposure to customers. However, an informal risk/benefit analysis is likely to uncover ways to save money and produce a more reliable product, by keeping the product clean.
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