[MisterTea]

I have been in one. Its just a room with an air flow rating and slight positive pressure vs ambient. There's no entry control, no special clothing, no hair nets. There was visible dust on top of the equipment and no one seemed to care, not even the people who you think should. I honestly think its there for a check mark on the paperwork.

[itishappy]

Honestly that might be ok for class 10000 (ISO class 7). HEPA filters do good work! At my work we use gowns, hair nets, booties, the works. However, we also changed cleaning companies once and didn't realize they were no longer sweeping the floor for a few months until visible dust bunnies started appearing in corners. Addressed that quick but not before we ran a few tests, still in spec! We also have local controls (flow hoods) over particularly sensitive operations.

We have class 100 (ISO class 5) space that's a lot more stringent, but even that is less sensitive than you might expect. Our semicon customers have a bad habit of taking our carefully bagged product out in their uncontrolled warehouse to check the serial numbers, but I'm not aware of any issues that arose from this.

Things get a lot more interesting when you start working with DUV and EUV wavelengths, as now you care about more than dust. We're adding an advanced molecular contamination cleanroom (AMC) where we'll need to start restricting perfume, deodorant, and cigarette use.

[MPSimmons]

I've been in higher than 10,000 cleanrooms and it's not the dust on the desks they care about.

There are entry protocols around what you can take in, how you swab it, and so on. Also, specific instructions around how often to go from sitting to standing, clothing materials under your smocks, and everything else.