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How clean does our water need to be?

How clean does our water need to be?

(OP)
So we are coming up the time to renew a contract for our RO system and I think we're spending way too much money for what we get. I was struck by the thought that I don't know how pure I actually need our water to be for our processes. Here's our RO system:

Incoming water is about 400 μS/cm
Tank 1 Multimedia Filter
Tank 2 Activated Carbon Filter
Tanks 3&4 Twin Softener System
Water is still about 400 μS/cm at this point
RO System
RO system gets the conductivity down to 10-20 μS/cm
DI polishing bottles
Brings the conductivity down to 0.0 (all conductivity is measured with an ECTester11+)

Which flows into a holding tank with a distribution pump and piping and includes a UV system.

Our needs are for:

PAA line (Degrease, FPL etch, PAA anodize with tap water rinse and a final DI rinse.)
Clean line (Degreaser, Alkanine cleaner (J-84), Permanganate (J-88), Acid Descaler (J-3) with tap water rinse and final DI rinse)
Alodine tank
Paint stripping tank
Waste treatment system to remove the Hexchrome from the waste water
Laboratory to perform titrations to control out tank processes

The most expensive monthly cost is in the DI polishing bottles that takes the conductivity to the limits of my test device. But do I need it that clean? How clean does my water need to be for the processes I've listed?

Thanks,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

RE: How clean does our water need to be?

KW... just took a look at related ASTM specs noted below. MOST ASTM specs that I looked at [am familiar with], clearly specify minimum [maximum?] water quality requirements such as for particulates and offending chemistries which must be carefully regulated; and some included conductivity limits [slightly higher than Your limit].

D3933 Standard Guide for Preparation of Aluminum Surfaces for Structural Adhesives Bonding (Phosphoric Acid Anodizing)

E358 Standard Test Methods for Analysis of Phosphoric Acid

USAF T.O. 42C2-1-7 PROCESS INSTRUCTIONS METAL TREATMENTS ELECTRODEPOSITION OF METALS AND METAL SURFACE TREATMENTS TO MEET AIR FORCE MAINTENANCE REQUIREMENTS has a fairly pragmatic description of water quality for plating shop processes; however I can't seem to copy/paste that block of paragraphs [something weird with PDF formating]. I'll try to figure-out how to get that section to copy and post it later.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

RE: How clean does our water need to be?

(OP)
Thanks Wil,

I've read through ASTM 1193 and am now reading a rather long diatribe on why ASTM 1193 is a terrible spec for water quality. I'll check out the specs you recommend.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

RE: How clean does our water need to be?

Caution: I know the bare minimum about electronics assembly lines.

I'd go and talk to the QA people on the two lines that use DI, and see if they have had problems in the past linked to the DI feed.

Failing that if you can afford to, run an experiment by adding somewhat ionised water back into the DI feed and see how badly it screws the process.

Is this a big cost in the scheme of things, or just a dollar conscious engineer trying to do the right thing? If the latter then perhaps conventional wisdom is that if it works, don't change it.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: How clean does our water need to be?

(OP)
One of the reasons I ask the question here is that I'm it. The most knowledgeable person concerning water quality here is me, and my knowledge is clearly lacking.

This is a cost reduction plan and $300-350 isn't huge in the grand scheme of things, but it's a big enough chunk of change to be addressed. We have had a stretch of ~8 months where we did not replace the polishing bottles and there were no consequences that we were aware of, but that was not an engineering defined test.

Hopefully by the end of October I will have a broad enough base of knowledge from which I can make an informed decision about what we need to maintain or improve our quality. Saving that, I'll stick to the belt and suspenders approach and continue with a system equivalent to what we have.

Thanks for your input.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

RE: How clean does our water need to be?

I would guess not. We used a full DI system for semiconductor processing, because ionic contamination even in the ppb range could be problematic for device performance control. I'd guess that paint is only assayed down to the 0.1% range, so I can't see how non-polished, but otherwise treated water would make much difference.

PAA line (Degrease, FPL etch, PAA anodize with tap water rinse and a final DI rinse.)
> This would require at least the pre-polish quality level of water

Clean line (Degreaser, Alkanine cleaner (J-84), Permanganate (J-88), Acid Descaler (J-3) with tap water rinse and final DI rinse)
> This would require at least the pre-polish quality level of water

Alodine tank
> This would require at least the pre-polish quality level of water

Paint stripping tank
> Can't even see why someone would use other than tap water for this

Waste treatment system to remove the Hexchrome from the waste water
> Can't even see why someone would use other than tap water for this

Laboratory to perform titrations to control out tank processes
> This would require at least the pre-polish quality level of water, and possibly the polish. Depends on the level of accuracy of the titrations, and whether the possible contaminants from the water could affect the results


One thing to note is that DI water winds up somewhat acidic, even though it's neutral immediately after polishing. Unless you're doing all your processing under pure nitrogen, you'll get carbon dioxide dissolving into the DI water, which results in a weak carbonic acid solution. This is usually not a big deal unless the water sits for a long time, or the parts sit in the water for a long time.

TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

RE: How clean does our water need to be?

(OP)
Kenat,

I don't take offense and, though I didn't calculate an ROI, I was thinking generally of cost vs. benefit myself, it's a good thing to do. But $300 per month doesn't seem like chump change to me. A few hours of work and a question (well phrased, I hope) to a forum filled with people that have the technical mastery to answer it without wasting too much (I hope) of their time, and with the added benefit of getting some of that technical mastery so I might be a benefit to my company and other engineers as well, I don't think my time is poorly spent.

IRstuff,

I was thinking along the same lines, perhaps getting a smaller DI system for the lab and just using RO water for the rest of the process lines. Just wanted to bounce the idea off others who use similar processes. That's one of the reasons I posted this here instead of in the Chemical Engineering section. My main concern was maintaining the PAA tanks within the requirements of BAC5555. The FPL etch step has a limit of 180 ppm for copper and iron and wasn't sure if these would make it past the RO system. The Phos acid tank has limits of 35 and 75 ppm for Chlorides and Fluorides respectively, though since I know the Chlorides eat up the membranes I felt confident that those would be reduced before getting that far.

Thanks for your input.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

RE: How clean does our water need to be?

If your water is coming from the potable water mains, you might want to look at your water supplier's requirements. The EPA copper limit is on the order of 1.3 ppm. Now, there's no guarantee that it will meet this requirement every second of every day, and certainly water suppliers do occasionally have massive fails of safeguards. The price that you're paying for the polishing beds is essentially insurance against the possibility that your water supplier glitches their process.

TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

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