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DI vs Distilled Water for Passivation Immersion Test


We do passivation to AMS AMSQQP35 [canceled, affil. link], with a 24-hour water immersion test per MIL-STD-753 [affil link or DLA / cancelled] [replaced by AMSSTD753 [affil link]], Method 100, as called out. Mil-Std-753 says to use "distilled water". Given that Nadcap auditing sometimes comes down to a matter of semantics, is DI water an acceptable alternative? My researches on the web seem to indicate there's no practical difference. Any thoughts?

David Morgan
Plating job shop - Inglewood, California



I hate to present technicalities but in the case of Distilled or Deionized water, they are made by two completely different processes and are technically not the same. For practical purposes they are the same entity.

If the cleanliness of the water is specified correctly you should be able to use either. The best way to avoid problems with you auditor is to measure important attributes of the Distilled water and use DI water that meets those attributes. Keep the data to show your auditor that they are, in fact the same material. If your auditor objects, get him/her to call his/her engineering department to rule on your data.

Some things I have found important in water purity:
1) resistivity (the best, and most expensive, water is around 18 megohms),
2) clarity,
3) silicon/dissolved solids content
4) biological content.

There are others but that's all my simple brain can remember right now.

Ernie James
- Vista, California

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