ESD Systems - Questions And Answers

I need to explain, in laymen terms, how an electrostatic charge can be induced. The area is a wafer fab. Maybe; How can a electrostatic charge be induced into a wafer from a CRT? Your help would be greatly appreciated in explaining this to our associates on the line. –Anonymous, Chandler, Arizona

Charge induction is a means of charging (bringing into imbalance) a materials’ surface valence electrons. Typically, when an object is “charged”, it has a large enough imbalance of charges on its surface to cause local disturbances, e.g., an electric field. This electric field imposes its field onto the surfaces of nearby materials and will try to put its surface into imbalance to compensate the field. That is if the charged object has a surface charge of negative 5 kV/inch, then the electric field will try to impose an equal but opposite charge on the nearby surface (say at 1 inch away) of positive 5 kV. This causes the free electrons to move away from the field causing a deficit of them equal to the field strength and when the initial field is removed, then the nearby object is still left in a charged state.This is analogous to a computer monitor’s surface being charged and bringing an ESD Sensitive (ESDS) device nearby its electric field and inadvertently inducing a charge onto the ESDS device.

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