Practical Electronics by John M. Hughes

Author:John M. Hughes
Language: eng
Format: epub
Publisher: O'Reilly Media
Published: 2015-03-25T00:00:00+00:00

Electrostatic Discharge Control

Static charges are the mortal enemy of solid-state components. Devices based on CMOS technology are particularly susceptible, but any solid-state device can be damaged under the right conditions. ESD control includes safe practices for component storage and handling.

The first step is to obtain and wear a grounded wrist strap when working with static-sensitive parts. You can pick up a decent production-line-grade wrist strap from most electronics suppliers, or you can order one (or several) online. Even one of the cheap things sometimes found at computer supply outlets will work in a pinch, but don’t expect it to last very long. Read and follow the instructions for connecting the strap to ground. Some straps have a built-in resistor to limit current, but some don’t. Some have an alligator clip to connect to a metal ground, while others use a banana-type plug.

The second item is a grounded mat for the workbench. These mats are made of a conductive, high-resistance material that is intended to dissipate stray static charges. Like a wrist strap, a mat will have a lead that must be connected to a solid earth ground.

Lastly, if you plan to stock logic ICs, you really should have a supply of high-density anti-static foam sheets on hand. These are made of a black or dark gray material, usually about 1/4-inch thick. The idea is to push the leads of an IC into the foam. The foam contains carbon or some other high-resistance conductive material and prevents a potential difference between the pins of an IC. For this reason, you should pick up a piece of foam containing ICs with your wrist strap securely in place before removing any of the parts. This discharges the foam and any parts on it. Plucking a part from the foam without first making sure that there is no overall charge on it can put an IC in a position where some leads are grounded by your fingers while some are still in contact with the foam. The part is in grave peril at that moment, and it could get damaged by a static discharge through it from the foam to you.

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