Desco Europe ESD - Questions And Answers

If a device is put into a box with the leads floating, and the leads have around several hundred Ohms lead-to-lead and lead-to-case resistance and capacitance in the 10 pF region. Given a few minutes of charging time the floating leads can easily charge up to 1kV relative to earth. (Charging can be by storing in a dry N2 box with the wrong grounding on a nozzle or by walking down a long carpeted hallway with nylon and crepe shoes during a dry winter day.) The user then being grounded, opens the ESD bag or grounded enclosure and destroys the device by discharging a lead which creates a 1 kV potential across the discharged lead and the rest of the leads. That potential across the oxide blows up the device. Do you agree that it is necessary for all leads to be shorted or clamped to provide ESD protection? - Anonymous, Milpitas, CA

For the example you site, we'll assume that the device is in a box that is a groundable enclosure (conductive) and that no ESD bag is being used. During transportation the box can become isolated from ground and charges can be induced on the outside from the carrier. On the inside, the devicecan move around and tribocharge from a few volts to tens of hundreds of volts depending on the materials in contact. It is possible then for a grounded operator, upon opening the box, to touch or come in near proximity to the floating leads of the device and cause and ESD. If the pins of the device were stored in a conductive foam material or an ESD shunt bar was used, then the susceptibility of the device to a discharge and or ESD damage is greatly reduced. The necessity of using a shunt bar or conductive foam will depend on the type of device(s) you are trying to protect, the way they are stored, and the way they are transported. Check with the manufacture of these devices for proper handling precautions.

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