Picture a cleanroom. What comes to mind is perhaps a sanctuary, a safe haven, a place of refuge from the rough and tumble world of manufacturing. The space is carefully designed, certified, and monitored. The furnishings, the consumables are controlled and have specified attributes. The room is inhabited by white-garbed technicians gliding serenely through the space. They have been trained; there is “cleanroom discipline. ” Clothing, hygiene, and behavior are defined. At intervals, more gowned, specially-trained people clean the walls, floors, and benches.
What’s missing from this picture? The product we are manufacturing. It sometimes seems that we are more obsessed with the contamination level of the cleanroom than with the cleaning and surface quality of the product. The cleanroom does not in and of itself guarantee clean product; and components do not achieve any sort of “diplomatic immunity” simply because they are assembled in a cleanroom. A cleanroom cannot correct a contaminated product.
The correct cleanroom protocol is important, but it not the same as a product cleaning process. Product cleaning consists of washing, rinsing, and drying. Most product cleaning processes use a combination of chemical and physical forces. Moving a product into the cleanroom does not cause a product to become clean.
In fact, the bulk of components cleaning – the critical cleaning processes – ought to occur prior to final assembly in the cleanroom. There are several reasons. One is that cleanroom real estate is valuable. If a process does not have to be in the cleanroom – do it elsewhere. In addition, cleaning processes have the potential to produce contaminants such as vapors, mists, and even particles that, if not carefully directed away from the product and out of the cleanroom, can result in recontamination and cross-contamination.
Another reason why cleaning should not be deferred until the product enters the cleanroom is that the longer soil is in contact with a surface, the more likely it is to become adherent. Soils that are exposed to high temperature become more adherent; soils may become caramelized or otherwise modified. The longer the soil is in contact with the surface and the higher the temperature the components are exposed to, the more challenging cleaning becomes.
Which brings us to the issue of suppliers. Supply chains are complex and may be global. Too often, suppliers – and this includes fabricators and coaters – assume that you, as the final assembler, will “take care of cleaning.” In an attempt to take care of cleaning, some manufacturers subject all incoming parts and components to a standard cleaning process. This approach has at best mixed success given the issues of time the soil dwells on the surface and temperature excursions during handling and shipment.
A cleanroom is not a substitute for intelligent, well-monitored suppliers. We see too many instances where the supply chain is commoditized, where the price is the primary factor in supplier selection. Engineers and purchasing agents may specify the materials of construction, design, and dimensions to the supplier. However, processes for fabrication and cleaning may not be specified in sufficient detail to result in a consistent product with the appropriate surface characteristics. The problem is magnified if many different suppliers are used.
For high-value product, the ideal approach to working with suppliers is to have required specifications for both the cleaning process and the desired level of cleanliness. The pathway makes a difference. Let’s say you specify cleaning to a certain level of particles and of non-volatile residue (thin film, molecular residue, filmic). The product may “pass” the required levels. However, changes in the cleaning process may result in in an increase in certain species of undesirable residue; such changes would show up only with specialized analytical tests. So, the cleaning process matters, not just the end result. The supplier may, in fact, be unable to use an imposed cleaning process and may be reluctant to disclose exact cleaning methods. However, as the final assembler, you can contractually require them to use a consistent process and to disclose any planned process changes. The ideal arrangement involves a combination of supply chain monitoring/auditing, communication, and partnership.
While a cleanroom is valuable tool in in minimizing product contamination and is a necessary part of achieving the appropriate surface quality, it does not have mystical powers to ensure clean product. Actually, you have that power. Understand the product cleanliness requirements. Understand the manufacturing processes. Understand cleaning. Then, you can take full advantage of the power of the cleanroom.