Statguard Flooring - Questions And Answers

The one mega ohm resistor. The one mega ohm resistor in a wrist strap, is there for safety. But is it also there so as to give at slow discharge of a charged object, like a memory module? Can you zap something when you are grounded, meaning will a charged object be zap if it is connected directly to hard ground? Will it make at difference if there is a 1 mega ohm resistance between the charge object and ground?Mads Gorm Larsen

What you are describing is a very serious problem in ESD control, that a charged item will discharge even when handled by a properly grounded operator. This is true whether a 1 Megohm resistor is incorporated in the Wrist Strap coiled cord or not.

This is one of the ESD Association’s models for ESD sensitive device damage. Per ESD ADV1.0-2003 Glossary “Charged Device Model (CDM) is a specified circuit characterizing an electrostatic discharge, which results when a device isolated from ground is first charged and then subsequently grounded.”

See Evaluation Engineering magazine article “The Most Common Causes of ESD Damage by Roger J. Peirce, ESD Technical Services”. He begins his article with “Over the last eight years of investigating and eventually understanding the root causes of ESD, we have found that less than 0.10% of all the documented damage actually came from ungrounded personnel touching ESD-sensitive (ESDS) products, known as human body model (HBM) damage. That, of course, means that 99.9% of the damage originates from the charged-device model (CDM) failure mode.

In the CDM failure mode, the ESDS item, such as a wafer, chip, component, or printed circuit board (PCB), somehow becomes charged, most often by contact and separation. Subsequently, it is discharged by a large conductor, like a person or machine.”

If the process cannot be changed to eliminate charging the ESD sensitive item, then ionization should be used to neutralize the electrostatic charges that are on the item.

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