DI water corrosion of electronic components? 1

[jlinstrom]

We use ultrasonic humidifiers with DI water to maintain proper humidity to suppress ESD in an electronic assembly area.
We have fried 4 power supplies in 5 months on our SMT assembly machines. We have a very troublesome buildup of contamination in all pick&place machines that we think is causing the failures.
This contamination is isolated to electrical systems and looks like hoarfrost, for lack of a better name. In particular, it shows up on some wires, fuses and circuit boards but not at all on others. The contamination build-up is on a supply in use for less than 6 months. Please me if you have any ideas what could be causing it. FYI we do not see this contamination on any other equipment in the facility and the area is climate controlled and ESD safe.
I have read that DI can attack copper; we have copper-leaded components on assemblies, but also solder (lead) coated components.
The most puzzling part of this is that we see a thin white powder coating on the insulation of power supply wires.
Can any of this be explained by humidified DI water?
Thanks-
john

twodogs
SUNSPOT Svcs.

 

[Compositepro]

RO water will not be 100% pure (nothing really is). you will not see the white dust unless it is concentrated by some process. This process is electrostatic precipitation. It also requires that the area where you see the precipitation is well ventilated. It is this ventilation that brings the dust into the zone where it can be captured by the electric field on your wires. It is also likely that the ventilation air is first passing by some high voltage before passing the area where you see the precipitation.

Look-up how an electrostatic precipitator works. Installing one in your room would probably solve your problem. Changing to a steam humidifier would also probably solve your problem.

 

[bimr]

I see that typical design humidity is RH 50-60 for a clean room. And static is not possible if RH is kept above 50%.


I don't believe there should be a significant difference between RO and DI water. RO units generally remove 95% of the salts where as DI units remove 100%.

You may condsider having the "crust" analyzed. The major dissolved salt component in RO/DI water is sodium hydroxide.

Do you have a picture of the dust?

I see that the fellows over in the HVAC forum are stating that the ultrasonic units are a maintenance nightmare:

http://www.eng-tips.com/viewthread.cfm?qid=309634

 

[jlinstrom]

sample results back from the lab: sodium, calcium, magnesium and potassium carbonates, sulfates, nitrates and silicates - your basic hard well water (which we use). Humidifiers were using R.O. from day one (not DI as first supposed) and all process water is DI - except the floor mopping water! Once a week or so, all factory floors are wet-mopped.

We are going to:
1.switch all humidifiers over to D.I.
2.seal all power supplies with conformal coating or Cortec anti-corrosive spray (some pcbs inaccessible).
3.Add ESD air spray of power supplies to monthly prevent.maint. schedule.
Thanks to all who noodled along with us thru this problem; I'm impressed with all the knowledge out there.
Regards-
john


twodogs
SUNSPOT Svcs.

 

[moltenmetal]

Suggest adding a conductivity detector to your DI water line. Stop feeding it, switch over to a storage supply and fix the problem if the conductivity increases past a pre-set level.

 

[jlinstrom]

we recently purchased a TDS/EC meter and will use it for weekly water quality audits (the Culligan man is called to replenish the 'magic beads').

twodogs
SUNSPOT Svcs.