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SMT electronics assembly manufacturing forum.


Humidity control in assembly area.

Joe

#4309

Humidity control in assembly area. | 1 May, 2000

Hi, We have a climatic controlled assembly area, with a constant temp of 22 deg C and a relative humidity of 40 - 50 %.

What I would like to ask is how should I approach a situation when the humidity starts to decrease to below 40%. The situation I'm concerned about is,that the ESD parameters will change and can cause doubt wether components have been damaged in this circumstance. Besides the controlled climate we all wear dissapative clothing and shoes. So should production continue or stop until the humidity is above 40% again.?

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#4310

Re: Humidity control in assembly area. | 3 May, 2000

Joe: Hey, just hose everyone down with water when your humidity starts to decrease to below 40%. ;-) Actually, that�s how some humidity controllers work, when added to your heating system. Well basically that�s how they work. I�m not tryin� to say they have a hozzy cow hooked-up to it or nuthin�!!!! ;-)

Anywho, questions for you (on your question): 1 What make you call your assembly area is climatic controlled, when you can�t control the climate when the humidity decreases below 40%RH? 2 What�s the point of your climatic control specification (22�C, 40-50%RH), if you don�t (can�t) follow it? And if you do follow it, you put your self out of business, because you have to shutdown operations when you reach the limit. 3 Presumably someone went to a lot of work and applied a lot of thought to determine your limits. So, here�s the part we�re struggling with � Why would someone set a factory environment spec for a plant doesn�t have the proper controls to be able to maintain the spec? (We assume they no longer work there.)

Taking a different tact on this: you�re correct that humidity levels affect turbocharging. Lookit:

Electrostatic voltage (v) Static generation process at 10 to 20% RH at 65 to 95% RH Walking on carpet 35,000 1,500 Walking on vinyl flooring 12,000 250 Worker sitting at a work bench 6,000 700 Handling a vinyl envelope used for work instructions 7,000 600 Picking-up a sandwich plastic bag from a bench 20,000 1,200 Sitting at polyurethane cushioned bench 18,000 1,500

... but I don�t find references to controlling temperature and humidity as an element of an electrostatic discharge control program in the following: * ANSI/ESD S20-20 * "ESD Program Management" by Ted Dangelmayer

Certainly plant climate should be controlled, but that�s not what we�re discussing, it�s the limits of control that�s the issue. So, what�s the point of your spec? What support do you have that these are proper limits? And what�s it going to cost you to get the proper equipment to be able to control the shop environment with the prescribed limits? Humidity is very expensive to control tightly. Certainly, you can open the humidity limit on the upper end, but we know that�s not the problem. But, it does make you wonder why it�s specified so tight. Doesn�t it?

We use J-STD-001, a widely accepted consensus document, control limits of 18-30�C, 30-70%RH. But for you, selecting these broader limits may not be as simple of a solution as it appears. The issue is designing a control program that protects components from damage by humans. And that may have been the approach that someone took in designing your limits. So, to broaden your limits, you may have to return to their analysis to determine other areas to improve as compensation for the reduced of control of humidity ( and temperature?).

We have discussed environmental control limits on SMTnet previously, but not specifically in regard to ESD control, as I recall. None the less, I�d expect some useful thoughts on the topic in the archive.

Good luck Dave F

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Joe

#4311

Re: Humidity control in assembly area. | 5 May, 2000

Thanks for the info.

Our system is capable of holding the set limits, but since breakdowns do happen I am considering what to do. So while everything is running, we have a climatic controlled area. The min. relative humidity of 40% comes from the JEDEC JESD 625-A standard, which is what our ESD policy is based on.

From your info, I can see that below 30% is a very dangreous area to be in, and between 30% and 40% is an area I can work in, until we can get above 40% again.

Have I got it right?

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#4312

Re: Humidity control in assembly area. | 6 May, 2000

Joe: That's what we do ... when the trend line is downward and below 40�C we start thinking. Apparantly, that's exactly what you do, except it's a matter of degree. Good luck. Dave F

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