clean room cleanliness requirement on drawing

[KENAT]

Gents,

This may not be the most appropriate forum but I’ll start here.

I’m working in the Semi Industry. Most of our equipment ends up in a clean room.

We’re trying to find an easy way to specify on the drawing that the stuff needs to be cleaned before it goes in there.

We looked at raising a generic cleaning & packing procedure that could be referenced but this got blocked by manufacturing as it was difficult to come up with a simple set of wording/techniques that covered both really small things and larger assemblies. Our manufacturing Engineers are meant to be looking into a suitable spec but we’ve been waiting months.

We can’t really just say something like ‘Part to be clean to the Requirements of Fed Std **** Class 1000 clean room’ (yes I know the Fed std is obsolete but I can’t remember the ISO spec right now) since the way the standards define cleanliness applies to the amount of particles in the air as I recall.

We don’t want to have a spec saying something like ‘no more than X particles of Y size per square inch of surface area’ as the inspection would be problematic and none of us are expert enough to define the values of X & Y.

Has anyone seen any good ways of doing it?

Ken

 

[wes616]

Do you know what a suitable cleanliness is? How do YOU define a part to be clean?

Wes C.
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[wes616]

Why not have one definition for small things, and another for large things.

Wes C.
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[KENAT]

We have a spec for one specific small sub assy that I initially wanted to make generic.

Basically it says on drawings that the parts from the machine shop are to be free of grease etc. The spec itself then washes them in de-ionized vibro bath, drys them with CDA, wraps them in non contaminating clean room wraps and puts them in zip seal bags.

While we haven't been able to quantify the level of cleanliness this provides we've been told it is adequate.

However, as well as the size issue, if the assemblies have electronics, actuators etc you may not want to immerse them in water. Also they'd rather we don't refer to any chemicals in our spec so they don't have to worry about Safety in it.

So our first attempt at turning it into a generic spec had a lot of 'or equivalents' etc which weren't very satisfactory.

Hence I'm seeing if anyone has any ideas.

 

[KENAT]

Just realised I was somewhat sexist in my question starting with Gents. I would of course appreciate the input of any engineers of the female persuasion and did not mean to imply otherwise.

Appologies,

Ken

 

[ctopher]

You should have a separate spec written up to suit your company for cleaning. Reference this spec on the dwg. The details of the cleaning should not be spelled out on a dwg.

Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)

 

[KENAT]

Ctopher

That's what I was aiming for and what we did for that one specific sub assy. Previously if the designer happended to think of it there would be half assed cleaning instructions on the drawing.

Trouble is there are so many factors affecting the different cleaning techniques and then packaging techniques to keep it clean that it's more difficult than it originally sounded.

I was wondering if I was re-inventing the wheel and someone already knew to make it round!

 

[ctopher]

There are a lot of cleaning specs around. You can search for some here.

http://assist.daps.dla.mil/quicksearch/

It's OK to have several different cleaning specs for different types of materials/parts/processes.

Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)

 

[wes616]

Ken,

I think that you have stumbled into something that probablly can not be adressed within a simple spec. The idea of cleanliness of parts (for your application) is an entire career for some enigneers.

http://curator.jsc.nasa.gov/genesis/cleaning.cfm

Here are a couple of specs to look at (even though they won't directly apply).

http://pbma.hq.nasa.gov/docs/public/pbma/bestpractices/bp_gsfc_07.doc

(this one is pretty good)

http://misspiggy.gsfc.nasa.gov/tva/meldoc/photonicsdocs/LRRP/Johncanham4.pdf

http://mscweb.gsfc.nasa.gov/545web/Groups/P4/545p4.html

Wes C.
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No trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.

 

[KENAT]

Thanks guys.

I pretty much figured from the digging I've previously done that I may have to prepare one, or wait for manufacturing to prepare one but wondered if anyone had come up with something smart.

Ctopher, I know it's OK to have a number of specs but from a doc control & simplicity point of view I think 1 is better if possible. My concern is if it's too much effort they won't do it, don't get me started. Thanks for the link I don't think any of it looked like applying but it added some more to think about.

Wes

Thanks for the links, you are apparantly better at searching than I. I'm adding them to the sources I already found.

You may be right about the career, I just don't want it to be my career

 

[ewh]

If you want to limit it to one spec, I would break that spec down into subsections which cover differing requirements, depending on the part. Without subsections, too many variations leave much room for mistakes.

 

[KENAT]

Thanks ewh, the same thought occured to me especially after looking as what little information I found on the net and the links wes gave me and seeing how it was handled.

Ken

 

[ctopher]

I agree with ewh.
But, I don't know if you do any designs for military. If you do, you may want to separate the specs. If they audit, they will require separate revs.

Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)

 

[KENAT]

No real military, I think another part of our company sells a few things to the government so we have a cage code but not what I'm working on.

Plus being commercial we aren't getting paid to create the paperwork so while I try to keep to the high standards the government requires we also try and do the minimum necessary.

Thx

 

[wes616]

...the high standards the government requires...

Ken, you are joking right?

Wes C.
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No trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.

 

[KENAT]

Compared to what this place has historically done government standards are high!;-)

I've worked mainly UK government systems which may bias my viewpoint some but I've also seen a bit of US.

 

[KENAT]

Well,

Having looked at the sources I found, the sources Wes gave and getting some input from Manufacturing I have discovered.

There was a MIL-STD-1246C which covered this.

This has been replaced by IEST-STD-CC1246D Product Cleanliness Levels and Contamination Control Program.

Essentially for my purposes they have defined classes of surface contamination, i.e. X particles of size Y per square foot.

Thanks for the help.

Ken