Excerpts taken from an article published by Transtroncis. The full article can be viewed by clicking here.
ESD Electro Static Discharge
Everyone who works with electronics has heard about ‘static damage’. Unfortunately, there is often as much misinformation as there is hard fact. First of all 'static electricity' does no harm; it is not until there is a discharge (ESD) that we have to worry.
Often, ‘snake oil’ products are sold to make you feel like you have taken care of 'the static problem'. All that you need to keep the marketing types from preying on you whether you are a hobbyist, technician or engineer, is an understanding based in science. Once you realize that the laws of physics are not suspended for ESD (electrostatic Discharge) you will find that you already know most of the basics.
What is static electricity?
Static electricity is electricity that is static; that is electricity that doesn’t move. When you walk across a carpet on a dry winter day, you build up a static charge. As your shoes rub on the carpet there is a net wiping off of electrons that gives your body a potential that is different to ground. If the air were more humid, the charge would bleed off rapidly but on a dry winter day the charge stays on the surface of your skin for a few seconds. Static electricity is a surface phenomenon. The more surface area the greater the charge stored.
What is electrostatic discharge?
Static electricity doesn’t do any damage until it is discharged - and is then called electrostatic discharge or ESD. Quite simply, electrostatic discharge is a spark.
When you walk across the carpet on a cold winter day, the wiping motion of your feet produces a charge separation that is collected and distributed evenly about the surface of your moist and salty (thus conductive) skin. When you reach for the doorknob a spark jumps from your conductive skin to the conductive doorknob. If you felt the spark, you had a potential of at least 3500 volts. Every day, when you touch conductive items, small sparks are produced that can’t be felt yet have enough energy to damage electronics.
What to have in your work area
Use wood or an anti static work mat (not a conductive mat! - they can KILL you) for a work surface. Store parts in anti-static plastic bags (paper envelopes or cardboard boxes will work well enough for most applications just don’t use plastic containers) There are anti-static sprays that work to treat plastics that you can’t do without (treat your plastic squeeze solder suckers). The sprays need to be repeated and wear off. Carpets can be treated with this spray but be prepared to use a lot and repeat often. (Hot tip: use an anti-static floor-wax on your plastics and you shouldn’t have to ever treat them again! Just dip your plastic bins and trays in. Then let them drip drain and dry. Think of the antistatic floor wax as an almost permanent spray).
I save ground straps for last because they aren’t as important as the above items. First of all removing static generating materials reduces the need for ground straps (especially if you learn good touch habits.) The biggest reason I don’t recommend relying on ground straps, is because most engineers, hobbyist and technicians don’t and won’t wear them. When working in the field there isn’t always a ground to hook to, so understanding what a ground strap does and doesn’t do becomes even more important than wearing one.
Ground straps work by connecting your body to ground and bleeding off any charge as fast as it builds up. It supposes that every thing else you touch will also be at ground so there will be no potential difference. But, ground straps won’t stop static damage from occurring in the real world. Suppose you are sitting at a bench with a ground strap on and someone walks up and hands you a chip. If they have a charge on them from shuffling across the floor and your first contact is with a lead of the chip, you can damage an IC even while wearing a ground strap! The ground strap will even increase the potential for damage in this case because you have increased your total capacitance by connecting yourself to ground.
The Touch Rule
To avoid this kind of damage requires learning the touch rule. Whenever someone tries to hand you a chip make sure you contact their skin with your skin first, then grab the chip. Think of their skin conductor that will equalize your potentials. (Some people don’t want to be touched, so have them place the IC or circuit board on a pink poly bag by touching the bag first then placing the part there - when you pick up the item touch the bag first then pick up the part.) If you are working on a computer, touch the case before you touch any PC board then maintain contact with the case by resting your arm or other hand on the case at all times. This is better than being hooked to a ground strap in that it is possible that the frame of the computer case may not be at ground. If you pick up a PC-board from the bench or out of a static bag, always touch the bag first then touch the ground plane of the board first as you pick it up.
Making these touch-rules a habit is the next best thing to having a ground strap on everyone at every single minute. (If you are working with high voltage a whole different set of rules apply - lets assume that there are no voltages above 24 volts and I’ll leave learning the one-hand rule for a different article except for one quick point. Never work with high voltages at a bench with a conductive (black) mat; it can kill you!)
The touch rule works even better if everyone wears ground straps. If you want to work in electronics as a profession, it is a good idea to start off wearing a ground strap as a habit. Production factories know that wearing ground straps makes an incremental difference in quality. They should always have a built in current limiting resistor in the system or you can expose yourself to shock hazards. That means a watchband tied to ground can kill you if you are working around AC mains voltage so get the real thing.