Ask the Experts
June 20, 2011 - Updated
June 20, 2011 - Originally Posted

Stagnant DI Water Usage

We have a tap water filter and a pair of mixed beds for our DI water system. If we have not run our cleaning system for some time, is it advisable run the system to flush the stagnant DI from the cleaner and supply lines? Or, does it make no difference, since the DI treated water remained deionized until exposed to the atmosphere?

M. R.

Expert Panel Responses

You didn't mention whether your cleaning system is open or closed loop which will make a difference on system charge capacity and thus time and cost. Also, no mention was made of your process requirements for cleanliness. Most systems will have an indication of some sort to give the operator an idea of water quality -- resistivity or conductivity in-line meters, red light/green light system etc. If the system indicates proper water quality for your operation, then there should be no need to flush the lines. If there is no indication system, then in my opinion, I would flush adequate volume to turn over the system just to maintain the cleanliness requirements. In the area of cleaning, there's no reason to take chances that may result in product failure. Our set-up is fairly small for our laboratory testing, however it may be unused for a week or so. We have an indication system in-line and occasionally we do flush through a side stream until the required output is met prior to cleaning/testing. This takes a very small volume to bleed and return to the required quality. I would suggest you contact your water vendor and together you can set the system requirements and maintenance procedures.

Pierce Pillon
Laboratory Mgr.
Pierce Pillon is the Laboratory Manager and lead formulations chemist at Techspray, a division of Illinois Tool Works (ITW) and a leading manufacturer of chemical products for the electronics industry.

To be on the safe side I would exchange the columns for fresh ones, the whole idea of Ionic exchange columns for DI is to remove any ionic material it may not remove bacteria and if the water has become stagnant (smells) it may have bacteria in it. You could use UV light tubes to try to kill the bacteria but really the quickest and safest way would be to install fresh and get the supplier the check the water source as well. Alternatively the fact that the system may have become stagnant would imply that you do not use it on a regular basis. if this is the case then it might be worth buying the DI water in, you could get this supplied in drums or bottles and this could be a more cost effective way to get a known good supply.

Richard Boyle
Global Product Champion
Henkel Electronics
Richard Boyle is a Global Product Champion at Henkel Electronics. He has over 25 years experience in the electronics assembly industry and is responsible for the global technical service of all of Henkel's solder materials.

Actually, water left in ion exchange resin tanks will maintain a high level of resistivity. It is common for water which has become stagnant in a resin tank to exit the tank with very high resistivity levels. The resistivity will normally spike up as the old water exits the tanks then will come back down as new water enters and exits the tanks.

Mike Konrad
Aqueous Technologies
Mr. Konrad has been in the electronic assembly equipment industry since 1985. He is founder and CEO of Aqueous Technologies Corporation, a manufacturer of automatic de-fluxing equipment, chemicals, and cleanliness testing systems.
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