Demonstrating CDM Discharge using Common Hand Tools
What is the significance of the time to the charge generation in tribocharging?
Why is it that in tribocharging, there is a big charge produce in short period of time while small charge will be generated at long time? ( at the same force)
(I took the liberty here to respond to the question and go a bit further and look at CDM Testing as described in a recent issue of Conformity.)
A: First a little background about charge as it relates to ESD (ElectroStatic Discharge).
Triboelectric charge is merely the contact and separation of materials. “It involves the transfer of electrons between materials.” Which materials lose electrons and which gain them depends on the materials.
Static electricity can be measured in coulombs, and related to voltage potential via the equation: q=CV. q = charge in coulombs, C = Capacitance, V = Voltage
The industry typically uses electrostatic potential and thus uses voltage to look at this energy form. Voltage is merely charge potential with respect to a ground point or reference and measured in volts (v).
Insulators or materials with high resistance restricts or prevents flow of electrons across (surface) or through (volume) it’s material.
Conductors or materials with low resistance easily allows the flow of electrons across it (surface) or through (volume) it’s material.
Insulators and isolated conductors can tribocharge to high voltages and will remain for a long time… so long as energy is not transferred via induction (isolated conductors) by bringing other objects into it’s vicinity and grounding the other object, by grounding the isolated conductor, or by balanced ionization (isolated conductors or insulators).
When isolated conductors are grounded, they (becoming grounded conductors) will enable electrons to flow easily to ground and the charge upon it will become neutralized and reduced to near zero.
Insulators cannot be grounded. They can induce charge to isolated conductors and can cause electrical overstress/ESD events to isolated conductors at the time they are grounded via the charge field and do not need to contact the isolated conductors in order to do so.
Here’s another way to say that; “CDM (Charged Device Model) charging can produce two separate discharge events. Here’s how it works. If you ground a conductor (the conductive blade of a screwdriver for example) while it is in the presence of any item carrying an electrostatic field ( a charged piece of plastic or clothing), the conductor will acquire an electrostatic charge that may be sufficient to cause damage when discharged.”
Human Body Model, as is described in ANSI/ESD S20.20-2007… and the ESD control thereof, is concerned with limiting the voltage in the EPA for the protection of ESDS devices (ESD sensitive devices) to 100 volts and a discharge to within that level in less than 0.3 seconds for ESD Technical Elements (some quicker) at minimum.
I need to know what specifically are you interested in; the HBM, MM (Machine Model), or CDM (Charged Device Model)? Keep in mind, that “volt per volt, MM discharge is an order magnitude more powerful than HBM discharge because the resistance of human body has been removed from the equation.”
In the article in Conformity, “Demonstrating CDM Discharge Using Common Hand Tools” provided by the ESDA, they state; “The damage threat from hand tools is CDM charging of the hand tool, accompanied by MM discharge to the component or device.”
Source: Conformity : ESD Open Forum April 2009 pg 20.
The following pics depict the testing I did in my lab in accordance with what I’d learned from a recent Conformity article from the ESD Open Forum entitled Demonstrating CDM Discharge using Common Hand Tools. It involves charge, not by contact, but by induction;