static electricity buildup

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Hi, 1) Was reading the links provided by Dave F, under th... - Apr 23, 2002 by ianchan

PROPER GROUNDING OF THE "OBJECT" PCBA BOARD: You cannot gro... - Apr 24, 2002 by davef

ianchan

#19641

static electricity buildup | 23 April, 2002

Hi,

1) Was reading the links provided by Dave F, under the thread "waste" which was about the ESD grounding of drums.

2) thanks to Dave F, now have "back-bone" refer sources to explain ESD terms to those who ask and seek to better understand this natural phenomeon of our physical world.

3) Have a pondering question after reading all that material on ESD, as follows:

If proper grounding of the "object" PCBA board in a factory floor, means to balance the potential difference(p.d) between two points, thus eliminating the excess buildup of static electricity; does this mean we actually do not need to have ion blowers all over the work bench top? and that operator individual wriststrap grounding is of secondary importance?

Coz, from my understanding of ESD now (and this understanding could be warp) it seems as long as we properly "bond/ground" the static electricity between the PCBA board to the earth grounding source, then external introduction from operator hands/body is negligible? Its like saying an external 3rd party source of "zap" onto the PCBA board will not have static discharge to "kill" the board, as the proper "bond/ground" is continual draining away any introduced "zap" between the "object" board and earth grounding (ie. the grounding rod several feet into the factory floor)?

Of course, the fact we still factor "prevention is best" ideals; we still ask the operator to wear static electricity conductive wriststraps to help balance the p.d between the operator hands/body and the PCBA board.

Is this thinking correct (at least to some physics law extent?) or else can someone help correct any misconceptions displayed herein thread share?

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davef

#19676

static electricity buildup | 24 April, 2002

PROPER GROUNDING OF THE "OBJECT" PCBA BOARD: You cannot ground an insulator. Insulators accumulate a charge, but the charge must be neutralized, usually by ionization. We only use ionizers at tape stations and bins where travelers and other paper are collected.

Bottom line: Use a field meter to determine where you need to use ionizers.

PROPER GROUNDING OF PEOPLE: The moisture on the surface of people makes people conductors. They accumulate charge because they move and are insulated from ground. So, a wrist strap properly connected to ground is the proper way to dissipate charges on people. People generate huge charges by fidgeting in their chair and other common movements. For instance:

||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

Comments are: * How do you currently �properly �bond/ground� the static electricity between the PCBA board to the earth grounding source�? * So continuing with your line of thought, if someone is not grounded and generates 6kv while sitting at their bench, and picks-up a board and touches the trace leading to a component that is sensitive to

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