Operating a cleanroom with a stable particle count is hard work, and when contamination enters your critical environment it can make for a very difficult time. The most common offenders that will cause your particle counts to climb might surprise you, but they are easily identifiable, and in some cases easy to fix.
Operators are typically the largest source of contamination in a cleanroom. This is because humans have "free will" and sometimes either deliberately, and sometimes accidently, fail to follow protocols and procedures for gowning, entry, and operating procedures.
A classic example is the operator not properly wearing their facemask, and allowing unfiltered breathing air to "blow-by" the filter media in the face mask. In the event of an operator, who has recently smoked a cigarette prior to entering the cleanroom, who has not rinsed their mouth, the residual smoke will be directly introduced into your critical environment.
Because of the inherent unpredictability of human behavior, the operator can be a real "wild card" in keeping your cleanroom particle counts consistent.
2. PROCESS CONTROL
Process Control can also contribute to unwanted particles being released into your critical environment. The development of an "Equipment Chase Area" helps reduce particle generation by process equipment.
Only the clean process area of the tool faces into the clean area. The dirty process area of the tool is the chase area. Most process tool maintenance can be completed by maintenance technicians through the chase area. Numerous other variables can impact contamination generation by process equipment including ambient temperature, equipment speed relative to maximum capacity, etc.
3. MECHANICAL MATINENCE
If your mechanical maintenance is not given imporatance in the overall scope of work, the operating platform of your controlled environment will deliver neither predicatble, nor acceptable outcomes. Your HVAC system needs regular maintenance to ensure that the proper air velocity and volume is operating per your cleanrooms' design criteria. If proper air pressure differentials are not maintained, certain areas in your cleanroom can actually suck in airborne particles from adjacent non-critical areas. HEPA filters need to have scheduled inspections to determine when they need to be replaced. HEPA pre-filters need to be replaced a minimum of 2 times annually. Any gross contaminates (visible to the human eye) in the pre-filters require your immediate attention to determine the source.
If your operators use the improper consumables, no amount of best practice training can overcome this error. Focus on the consumables that make potential direct product/process contact, which is typically you gloves and wipers. The incorrect wiper substrate can actually increase your particle counts. The wrong glove material can represent ESD and contamination risk to your product. Operator preference for a specific cleanroom consumable needs to be balanced with product performance. For example, when some facilities convert from a flat packaged wiper to a bulk packaged, the operators abandon the proper 1/4 fold techinque with the bulk packaging.
Housekeeping is the most obvious, and is somethings overlooked as a top contamination contributer.
How do you make a determination for the intensity, and frequency of your cleaning? A key cleanroom technician needs to be tasked to schedule airborne particle counts of your area. A "white glove" inspection should be conducted on all work surfaces, and critical areas. For sterile facilities, the need is even more acute for bacterial counts to be monitored in addition to particle counts. Scheduled daily and weekly cleaning cycles, your facility should preform a deep "super" clean in conjunction with major preventative maintenance on your process equipment.