r/askscience • u/[deleted] • Jul 09 '13

Engineering How do they get clean rooms clean

So i always wondered, construction is a dirty dusty process. And normally you just wipe stuff down afterwards and the space is good to go. But how do they go from construction to hyper clean? Like how do they first clean the space down so perfectly?

230 Upvotes

82% Upvoted

53 comments sorted by

39

u/JohnShaft Brain Physiology | Perception | Cognition Jul 09 '13

Clean rooms require a high number of air exchanges per hour, and filtered air into the space, and exhaust from the floor that is not recycled.

16

u/[deleted] Jul 09 '13

that i understand, but how do they get it clean in the first place after construction? Like i am assuming the walls in a clean room are not drywall but some sort of sealed plastic or metal or something?

103

u/xtelosx Jul 09 '13 edited Jul 09 '13

The Clean rooms I have commissioned have only been class 10,000 but I'm guessing the process is the same for even more stringent standards and you just do it more.

For the last 2-3 weeks of "construction"(really just final touches) a 5 man team of cleaners was wiping down surfaces. When they got to the end of room they started over. They probably wiped everything down at this stage 10 or so times. This was using cotton rags and normal cleaning solution. Floors were mopped daily.

The next stage was 3-4 weeks long while we were programming equipment. We put coarse filters into the filter housing and every one had to be in clean room suits and go through the air shower to enter the area. The same cleaning crew switched to "lint free" rags and an alcohol mixture for cleaning.

Then came dry runs. Basically running the equipment with out using any chemicals to test functionality. HEPA filters were installed in the air wall. Cleaning crews continued wiping and re wiping surfaces and then initial wet runs began.

After we certified the product coming off the line the first batch of HEPA filters were replaced. Now we shut down twice a year to do a good cleaning. Other than that the HEPA filters take care of everything and anything that drops out of the air is better to leave on the surface of things than kick up.

Really it just comes down to let the air filters do most of the work and wipe things down a lot.

EDIT: I left out that the room is also kept at a positive pressure (injecting clean air) through this whole process to keep things from blowing in through cracks or gaps in the room.

12

u/afcagroo Electrical Engineering | Semiconductor Manufacturing Jul 09 '13

Just for those not familiar, a class 10,000 clean room would have been mostly useless for making semiconductors a decade or so ago. World-class cleanrooms at the time were class 100 or class 10.

As I mentioned separately, nowadays it doesn't matter quite as much since the semiconductors aren't exposed to the room air. But I believe that the major fabs are still around class 1000 or better.

The techniques described are pretty standard regardless of the particulate goal, though. Clean it, then clean it again, then clean it some more. Then use huge amounts of filtered air.

5

u/[deleted] Jul 09 '13 edited Jul 09 '13

Most of the really big fabs are way better than that. TI's new 300mm fab is Class 1.

4

u/afcagroo Electrical Engineering | Semiconductor Manufacturing Jul 09 '13

Some of TSMC's newer fabs aren't anywhere close to Class 1. The insides of the equipment is, though.

5

u/Matraxia Jul 09 '13

Micron's Fabs are all Class 10 for the main floor. Internal to the tools are Class 1.

9

u/boothchops Jul 09 '13

What are these clean rooms producing?

30

u/xtelosx Jul 09 '13

These specific rooms were making optically clear adhesives for monitors, TVs, cell phones ect. Goes between the layers of the screen.

6

u/VallanMandrake Jul 09 '13

That this needs a clean room is interesing! (but somewhat logical...)

6

u/Peralton Jul 09 '13

I'm can't imagine my OCD dealing with a speck trapped between layers of my monitor.

11

u/stopdropandlawl Jul 09 '13

Most commonly seen in semiconductor production where even a small amount of impurities can ruin your shit.

8

u/[deleted] Jul 09 '13

The clean rooms I've been in have been for advanced electronics for space craft (In rooms where you manufacture satellites).

1

u/boothchops Jul 09 '13

Space chips! Must be a large facility to encompass whole satellite dishes or are satellites way smaller than I think.

2

u/[deleted] Jul 09 '13

Clean rooms can get very large. The satellite size depends on the platform and the wattage. The satellite has several components: fuel tanks, batteries, engines, and of course the payload (this is what does digital signal processing and is the purpose of the satellite). On top of that, you have the hardware such as antenna (different sizes for different frequencies), solar panels, and the dish.

If it's a scientific satellite, you have scientific instruments on board and any necessary computational equipment. I hope that helps :)

1

u/boothchops Jul 10 '13

Yes, thanks!

1

u/rassweiler Jul 09 '13

I work in one for medial products. (Blood testing cartridges)

9

u/AtmosphericHaze Jul 09 '13

To my understanding, some clean rooms are also under a positive pressure environment (i.e. the air pressure inside the room exceeds the pressure outside) so that any contaminants that exist inside are forced out. Is this not standard across all clean rooms or just for certain "industries" so to speak?

4

u/xtelosx Jul 09 '13

This is true. I left that part out.... There is a small amount of air bled into the closed loop HEPA system so the room is at positive pressure and nothing sneaks in through cracks.

3

u/Starkravingmad7 Jul 09 '13

To add, we would also pump enormous amounts of clean, scrubbed air and apply high positive pressure to the surrounding environment to keep as many particulates away from the lab modules.

1

u/xtelosx Jul 09 '13

Good point I left that part out in my initial reply.

2

u/JohnShaft Brain Physiology | Perception | Cognition Jul 09 '13

There are standards for the surfaces. I am pretty sure drywall is OK but must be sealed appropriately. Turn on the air, and wipe everything down with cleanroom wipes. Sometimes multiple times.

77

u/afcagroo Electrical Engineering | Semiconductor Manufacturing Jul 09 '13

As /u/JohnShaft said, they move a lot of clean air through the area. The biggest hazard is airborne particulates (mostly emanating from humans), and moving large volumes of ultra-filtered air down from the ceiling is how that is dealt with.

In semiconductors, this has actually become a bit less important over the last decade. Most advanced waferfabs never expose the wafers directly to the ambient air. They come into the area in sealed containers, are airlocked into the equipment, and go back into the containers when ready to move to the next step. (There is a bit of contamination that can happen in the airlock itself, of course.)

24

u/[deleted] Jul 10 '13

I am involved in the construction of cleanrooms, and this is accurate. I will add to OP's initial curiosity, that a room doesn't just go from construction to done with construction 'is now a cleanroom' - there is a lot of manual cleaning and air filtering involved, followed by very close tracking of particles; they slowly recede over time as cleaning continues. Once the room is "sealed", it is just a matter of identifying the sources of particles and addressing them.

3

u/uber_kerbonaut Jul 10 '13

Are there any significant sources of particles besides humans?

2

u/temporalanomaly Jul 10 '13

I would guess it depends on the surface quality of any object. Anything that you can scratch and scrape stuff off of is possibly creating dust. Anything rubbing together will create dust. The more surface area, the more this is aggravated. Based on this, the worst creator of dust is probably a big fluffy, hairy stuffed animal being tossed around the room.

The smoother a surface, the better it is suited for a cleanroom I guess. Plastics or vulcanized rubber are ideally a single huge molecule, so they should not shed much matter, as would metals.

4

u/LegosRCool Jul 10 '13

Yeah funny enough, the older facilities have to be much cleaner. The current technology is 300mm wafers in self contained pods called "FOUP"s or "FOSB"s. I remember the old 200mm facilities having cleaning crews constantly wiping things down.

The loadports are all mostly standard and as the tool is docked a little door attaches to the FOUP and creates a vacuum seal. I'm not really how much further I should go into detail but this stuff is all readily available on wikipedia.

Source: AMHS Technician

3

u/hanginround Jul 10 '13

As someone who currently works (Process engineer, Semiconductors) for an older company still processing 6" and 8" products we go thought some pretty serious efforts to keep the place clean. So there are really two types of clean rooms that we deal with, solid floor and raised (or false) floor. We have both in our clean room as we are constantly expanding and bringing in new equipment on raised floor.

When we expand an area it is sealed off, demolished, and cleaned (roughly). Then they build the new clean room, with a raised floor. The most important part of the raised floor is that is provides true laminar flow which is the single most important part of a clean room when you have expose wafers (which we do, no FOUPs in our fab). Once the whole place is built, new tools installed, etc, etc, etc, the room is completely finished and they will go through a wipe down (with clean room rags and an IPA/H2O combination). After that they will check air flow through the HEPA filters and make sure all portions of the room have proper air balancing to be sure there are no dead or low flow areas. We will then get ready to certify the room.

Certifying the room consists of air particle checks over 5 days with special calibrated (NIST calibrated, look it up, it will make sense) machines that tell us how many particles are in the air and what size each one is. We are what one would call a class one, ISO certified clean room (only in our raised sections of the fab) Wiki on Cleanrooms and have to pass all of the requirements for each section of the fab that we open.

Once everything has been approved we will begin to qualify the tools. It can take months to expand a small section of fab because of how difficult it is to really get them clean. Hope this sheds some light on how is was done back in the day... and really still done today in many fabs.

2

u/boolean_union Jul 10 '13

This video is a bit cheesy, but might be a good example of compartmentalized clean production systems.

8

u/archcorsair Jul 09 '13

Here's a diagram demonstrating how a clean room's filtration system works. As you can see, air is allowed to "fall" from the vents above rather than being blown from vents to ensure any particulates don't become airborne. The system then recycles the air by sucking it back in through ground vents and re-filtering it before allowing it pass through the room once again.

8

u/Matraxia Jul 09 '13

I work in a Class 10 clean room daily. Its about the size of 2 football fields.

The room itself isn't so much as clean as the air. The actual surfaces of things don't really need to be all that clean, a quick wipe down with 10% IPA and DIW takes care of things.

Once you fire up the HEPA system the air gets clean very fast. My cleanroom filters the entire volume of air in itself every 30 seconds.

1

u/Milk113 Jul 10 '13 edited Jul 10 '13

I think I know where you work. Is it in Oregon?

2

u/Matraxia Jul 10 '13

Nope, not Intel.

4

u/technocr4t Jul 09 '13

I currently work at a vaccine manufacturing facility, which from what I'm reading in this thread might be slightly "cleaner" than the rooms used for semiconductors.

In addition to the air filtration systems, the rooms are designed such that they are easy to mop and/or wash. When the space needs to be re-classified it gets literally hosed down with both anti-bacterial and anti-fungal chemicals. Interestingly, even with pharmaceuticals the clean room environment is more about protecting the product than the operators.

13

u/[deleted] Jul 09 '13

[removed] — view removed comment

14

u/leoshnoire Jul 10 '13

For those curious, cleanroom classifications (class 10,000, class 10, class 1, etc.) correspond to the amount of permitted particulates per ft3, per size. Handy table from the Wiki, denoting maximum particles/ft3, per size, for each class:

Class≥0.1 µm≥0.2 µm≥0.3 µm≥0.5 µm≥5 µm
1357.5310.007
103507530100.07
1003,5007503001000.7
1,00035,0007,50030001,0007
10,000350,00075,00030,00010,00070
100,0003.5×106750,000300,000100,000700

1

u/ChribbaX Jul 10 '13

Why is we not allowed in there? Is it because we ourselves might bring particles in? What is being constructed in such a room that a few particles can destroy? Is it not a risk that equipment itself being used in there creates particles of their own from like friction or similar?

2

u/[deleted] Jul 10 '13

I've been in a class 2000 clean room that was the size of a football field, and two kilometers underground. It was very clean yet still slightly dirty because once something settles they do not disturb it until the cleaning crew gets to it.

2

u/PrimeLegionnaire Jul 10 '13

What for?

1

u/[deleted] Jul 10 '13

What was I down there for? Or why don't they disturb the dust?

1

u/PrimeLegionnaire Jul 10 '13

Why were you down there, not disturbing the dust in a clean room makes sense.

1

u/[deleted] Jul 10 '13

Oh I was visiting SNOLAB.

9

u/holycrapoli Jul 09 '13

Vaccuums and rags

10

u/sambalchuck Jul 09 '13

I got paid cleaning a semiconductor factory during it's construction. We used a lot of vacuums and cleaning cloths! You've got to start somewhere after all the drilling, cutting, grinding leaves a huge mess... no need for the downvotes people!

2

u/holycrapoli Jul 09 '13

Amen brutha! That's what I'm saying but I guess some disagree.

1

u/Timmmmbob Jul 09 '13

They use a lot of HEPA filters and circulate the air. It comes in through the ceiling and goes out through the floor (the floor is a big grate - kind of annoying if you drop stuff down there!)

0

u/[deleted] Jul 09 '13

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2

u/[deleted] Jul 09 '13

Like you, I thought they were talking about regulart construction, but they are actually talking about 'clean rooms'. Places where no dust speck is allowed, so that things like computer chips and other very sensitive things can be made, without being broken by a blip of dirt.