ESD Systems - Questions And Answers

1. "Static electricity is NOT a build up of electrons". As I see it protons & electrons are in balanced numbers in an atom. When charge separation tales place it is usually the electron that is moved from one surface (atom) to another. Using the example of a person walking across a carpeted floor - as they collect electrons they leave behind an equal and opposite charge on the atom that lost the electron but don't the electrons that are collected build up in the recipient? Otherwise how can varying levels of static charges be generated? 2. "Electrons in metals move around and between the mass of atoms.." Does this mean that on the surfaces the electrons are whizzing round in orbit but underneath the surface they are held in check by the protons? Or does it mean that throughout the metal the electrons are whizzing about but that they are not connected to any particular atom, so they move from end to end at random but always maintaining the balance with protons within any one atom? 3. (In describing antistatic bags) "A conductive (in the dissipative range) ...."What does this mean? Is it that dissipative is a conductor of such an area that any charge will be conducted and spread across the whole width to the point where it does not pose a threat AND THAT THE CONDUCTOR IS NOT GROUNDED? 4. How does a static discharge damage a device? Is it because the voltage discharged can burn out a track in the same way as trying to pass too much current through a fuse will burn it out. The fuse wire is essentially a resistor capable of carrying a certain amount of current (amps x volts) and if it's exceeded the wire heats up and very quickly burns out. Tracks in Integrated Circuits are now as thin as one micron (remember 1 micron is roughly one hundredth the thickness of a piece of copying paper) and so are similarly vulnerable to burn out if the current is too high? - Bernard McTernan, Woolhope, UK

"Static electricity is NOT a build up of electrons". Refer to: http://www.eskimo.com/~billb/redgreen.html This article may clear a few things up. It is an imbalance of electrons….just semantics. 2. "Electrons in metals move around and between the mass of atoms.." In general, metal atoms have what’s called a fair amount of valence electrons (an electron that belongs to the outermost shell of an atom) and they tend to be ‘free electrons’ (an electron that is not constrained to remain in a particular atom, and is therefore able to move in matter or in a vacuum when acted on by external electric or magnetic fields) hence making them good conductors. All molecules (groupings of atoms) want to be in a neutral state (electrically balanced). Metal molecules usually share their free electrons to obtain a balanced state. 3. (In describing anti-static bags) "A conductive (in the dissipative range) ...." there are two definitions for conductive. In ESD control, conductive refers to the resistance of a material that is less than 1x10^4 ohms and dissipative being greater than 1x10^4 ohms. Conductive also has another definition, the ability to conduct free charges. By this definition, anything that is less than 1x10^11 ohms is considered conductive. 4. How does a static discharge damage a device? It is not really a static discharge but an ESD event (an arc or large current pulse between two conductors). It is this large current that does the ESD damage.

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