It depends on your product requirements. I have seen aluminium wire bonding operations in as high as class 100K clean rooms. These are the assembly areas for calculators. The best is class 10K clean room for wire bonding. You can go upto fine pitch wire bonding applications in a class 10K clean room. Once you establish class 10K, over time, the clean room condition will improve to about class 5K due to constant circulation of clean air. So you need to balance your product cost / profits with clean room conditions. Maintaining a class 10K or class 100 clean rooms is very expensive.