Basically, if an operation doesn’t need to be performed in the cleanroom, keep it out! Too often, we observe processes performed in cleanrooms that either could or should be performed elsewhere.

All processes involving critical cleaning and surface preparation should not automatically be relegated to the cleanroom. Cleaning equipment, especially aqueous cleaning, takes valuable space and consumes energy. Heating process baths and drying components are energy- intensive steps. Unless heat exhaust paths are thoughtfully built into the design, heat is released into the cleanroom space and adds to the energy burden. These processes may also generate particle and thin film contaminants, resulting in more energy usage, more rework, and lower yields.

From: Cleanrooms and Energy