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I know manufacturers often keep components sensitive to ESD problems in climate controlled rooms and I'm just wondering what the ideal temperature and relative humidity is to prevent ESD problems?

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Ideal for ESD is as humid as possible. That's not ideal overall when other factors are considered though. –  Olin Lathrop Jan 17 '13 at 19:11
@OlinLathrop - So what's the "sweet spot" when all factors (such as a comfortable working environment) are taken into account? –  Nate Jan 17 '13 at 19:14
That's a longer discussion not relevant to the question. –  Olin Lathrop Jan 17 '13 at 20:25
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3 Answers

up vote 3 down vote accepted

From Henry Ott re: static discharge (ch 15.3) in "Electromagnetic Compatibility Engineering"

Charge accumulated on an object leaves the object by one of two ways, leakage or arcing. Because it is better to avoid arcing, leakage is the preferred way to discharge an object. Charge can leak off an object through the air, because of humidity. The higher humidity, the faster the charge will leak off the object.

Temperature affects humidity, so that is where the temperature sensitivity arises. Temperature per se does not directly affect ESD conditions.

One techniques that is used , aside from ground straps etc. is the use of ionizers on benches when there is extreme ESD sensitivity.

MIL-STD-1695 addresses relative humidity levels between 30 - 70 percent in areas where electronic parts and hybrid microcircuits are handled or processed.

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Nobody relies on temperature and humidity to prevent ESD. Some people might use it to minimize ESD, but they don't rely on it to eliminate the problem.

If you want to eliminate ESD as a potential problem then there is no replacement for proper equipment and proper handling of parts. Ground straps, conductive/dissapative tools, floor, and furniture. All the usual stuff.

Temperature does not matter much, but humidity does. Temperature matters only in that it can effect humidity. Ideally, the whole factory would be under water. Clearly that is not practical, as it prevents the soldering irons from heating up. So anything less than "underwater" is a compromise of ESD safety.

Ironically, it is becoming common to store sensitive electronics in low-humidity environments. Some chip packages, like BGAs, are humidity sensitive. When stored in a humid environment they absorb water from the air. Before soldering, the parts have to be baked to get that water out. After soldering water absorption from the air isn't a factor (for reasons I don't completely understand).

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point of argument: I would think ideally the factory should be filled with liquid solder or some other highly conductive material (water can be a very good insulator if pure enough, Wire EDM is one example where this property is taken advantage of). This of course has it's own problems (really hot, quite toxic, shorting out all the wiring, etc.) –  helloworld922 Jan 17 '13 at 19:57
The reason the humidity isn't a problem after soldering is because a little humidity absorbed by the packaging doesn't hurt the device if everything else is designed right. The problem with water in the package is that it can cause the package to explode when heated, like during soldering. Baking heats it to lower temperature and more gently, so the water can diffuse out instead of insisting on being let out all at once. Packages need to be dry during soldering. –  Olin Lathrop Jan 17 '13 at 20:28
@OlinLathrop Good to know. Thanks! –  user3624 Jan 17 '13 at 20:35
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Actually, ionizing the air — rather than humidifying it — is much more effective at encouraging the leakage of static charges, and it doesn't incur all the other problems associated with high humidity.

However, ionization systems need to be carefully designed so that they don't end up depositing charges where you don't want them.

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