Alvaro: Have you been down to Brazil lately?
From our operator training program:
Problem #1 with ESD. Our day-to-day activities produce tremendous charges.
|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
� And the level of charge generated varies with the relative humidity (RH) level. This variability caused by humidity helps explain why we seem to get more "carpet shocks" in the winter, when the air is dry, than in the summer, when the air is moist.
This is because most common insulating materials such as wood, fabric, paper, or masonry contain a certain amount of moisture, which is dependent on the relative humidity of the air. To some extent, the moisture content, in turn, affects the conductivity of these materials and their ability to hold static charges.
Relative humidity|Conductivity Higher >50%|More conductive Lower <30%|More insulating
Logically, it would follow that high humidity would be an effective means of controlling static electricity, but high humidity:
� Still allows generation of unacceptable charges, even though not a large as low humidity. � Contributes to other problems including oxidation and soldering difficulties. � Is uncomfortable and expensive to generate and control.
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Our "ESD Prevention And Control" procedure says:
4.2.7 Humidification. The Company maintains relative humidity and temperature according to procedure MOP-09-05, Solder Control.
Our "Solder Control" procedure says:
3.1.4 Controlled Environment. The Company controls the environment of the soldering area to limit the entry of contamination within the limits defined as the preferred environment in the figure below.
The figure shows a graph with temperature on the y-axis and humidity on the x-axis. The "preferred environment" is bounded by the closed, four sided figure made by connecting the points (84�F, 30%RH), (78�F, 70%RH), (68�F, 70%RH), and (72�F, 30%RH) with four straight lines. (Hopefully, that�s no too obscure of a description.)
3.1.4.1 In the production area, the allowable variation within the above limits are:
Rate of temperature change|3�C (5.2�F) change per hour Desired setting|With �10%
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Good luck and stay away from the Hydrogen, bud
Dave F
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