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Water quality for rinse water

James Lalicker

#13152

Water quality for rinse water | 29 December, 1998

We use a inline water wash system to clean our PWA's. How low should i be able to let my DI water resistivity get before replacing the DI tanks. Is there a standard i can get on this subject.

Thanks JL

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Mike Konrad

#13153

Re: Water quality for rinse water | 29 December, 1998

James,

Most rental DI systems are as follows:

Option #1: 2 mixed bed resin tanks: In this case, a 1 M-Ohm light should be installed on the output of tank #1, before tank #2. When the 1 M-Ohm light indicates that the output of the #1 tank is below 1 M-Ohm, the #2 tank should be put into the #1 position, and a new tank put into the #2 position.

Option #2: 4 mixed bed resin tanks: In this case, a 1 M-Ohm light should be installed on the output of tank #2, before tank #3 & #4. When the 1 M-Ohm light indicates that the output of the #1 and #2 tanks is below 1 M-Ohm, the #3 and #4 tanks should be put into the #1 and #2 positions, and a new tanks put into the #3 & #4 positions.

Rinsing is one of the most important cleaning functions. The quality of the rinse water, in most cases, determines the final cleanliness of the boards.

One more bit of advise... Don't purchase a DI system. All you will be purchasing is a box and some empty tanks. These are no real value! Rent the DI system. Companies like Culligan, US Filter (they own Culligan), and others are by far your best value. Average monthly rental cost for a 4 tank system is $ 80.00 per month with about $ 50.00 tank exchange costs.

Good Luck and Happy New Year!

Mike

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Scott McKee

#13154

Re: Water quality for rinse water | 30 December, 1998

| We use a inline water wash system to clean our PWA's. How | low should i be able to let my DI water resistivity get before replacing the DI tanks. Is there a standard i can get on this subject. | | Thanks | JL | You'll want to look at IPC-AC-62A for your standard which is 1 megohm/cm for pre-conformal coating applications. Though some people will say 500K is good enough, it isn't if you're building high impedance assemblies.

I rent from US Filters but I'd recommend a Carbon/Resin combination -- Carbon for the organics, Resin for the inonics. I have a 4 tank combination (2 Carbon & 2 Resin) that is just great! I got rid of my own tanks that I use to fill and spliced in the US Filters' system. Being a closed loop system, I still need the water purification system to keep the water flowing 24 hours a day to prevent organics from growing. Works very well and my resistivity typically hoovers around 17megohms before it starts needing replaced.

Good luck...

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Christopher Lampron

#13155

Re: Water quality for rinse water | 1 January, 1999

| We use a inline water wash system to clean our PWA's. How | low should i be able to let my DI water resistivity get before replacing the DI tanks. Is there a standard i can get on this subject. | | Thanks | JL | JL, I too have been looking for a written standard on water quality. I use an inline water cleaner with a rented US filters DI cabinet. We have found that the golden number is 10 Mohm. Until the resistivity drops to that point we have no cosmetic or SIR testing problems. I prefer to change tanks at about 12 Megohm. Once the resistivity drops below 16 Megohm, it continues to drop quickly so I use this as my alarm. Please let me know if you do find a written standard.

Thanks

Chris

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