Static Discharge
SRLM
Posts: 5,045
These questions have been bothering me (eating away at my insides, consuming my mind and ripping out my fingers) for awhile now, so I thought I'd post them.
1)What sort of protections against static electricity are really necessary? Many of the parts that I get from parallax and mouser are in the shiny bags. Should I keep them there, or can I put them in my bins?
2)When working with these parts, do I need to be "grounded" with a wrist strap or something?
3)How does that black foam work that Parallax stuff comes in? Is it just mechanical protection, or static protection too?
4)Is there an easy way to tell if a chip has been damaged by static electricity?
Thanks.
1)What sort of protections against static electricity are really necessary? Many of the parts that I get from parallax and mouser are in the shiny bags. Should I keep them there, or can I put them in my bins?
2)When working with these parts, do I need to be "grounded" with a wrist strap or something?
3)How does that black foam work that Parallax stuff comes in? Is it just mechanical protection, or static protection too?
4)Is there an easy way to tell if a chip has been damaged by static electricity?
Thanks.
Comments
2 - It is a good idea to be grounded while working with the parts, particularly when the humidity is low.
3 - All the black foam I have seen parts come in has been antistatic as well as mechanical protection. Measure the resistance with an ohm meter to be sure.
4 - Not unless the damage prevents the chip or an i/o pin from working. A lot of chips that fail early for no apparent reason do so as a result of earlier static damage.
Most of the time under normal conditions (room temp, ~30% humidity) you can get away with handling chips without taking the static protection precautions, but they are so simple there is no reason to skip them.
I posted this a while back on the subject of ESD; I hope you find it useful.
B-
Here are some inexpensive ESD equipment as well as some information that forum members will hopefully find useful. Most of the links are for the electronic vendor Electronics Express. I've ordered from them in the past without any problems, but their shipping is a little slow, as it took about 7-10 days before any of my orders shipped. I do not have any connection with them; I'm only plugging them because they have reasonable prices on their ESD products. This isn't meant to be spam, but if the admins feel it is, then there will be no hard feelings if deleted.
A good place to make a ground connection is the ground of an AC outlet. For safety reasons a 1 Megohm resister should connect the bench-mat/wristrap to the ground. This will also bleed off any static charge without zapping components.
A couple of bench top mats
http://www.elexp.com/ant_csk1.htm
23 X 26" mat $15.95
http://www.elexp.com/ant_asw1.htm
11 X 22" mat $9.25
Wrist strap
http://www.elexp.com/ant_s150.htm
$3.50-4.50
ESD Foam
http://www.elexp.com/ant_2asf.htm
Some information
http://www.desco.com/ESDInformation.aspx
http://www.desco.com/QuestionsAndAnswers/ShowCategory.aspx?i=58
Foam
http://www.elexp.com/ant_2asf.htm
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This post is a work of art. Variations in spelling and grammar are intentional, artistic endeavors that add value to all of mankind.
Kwinn is right, it's a good idea to be grounded BUT DON'T JUST HOOK A GROUNDED WIRE TO YOUR BODY! The wrist strap gizmos have a LARGE built-in resistance in series so that any voltage that you might touch will have to go through that resistance, keeping the current through your body very very low. But if you wrap a plain wire around your wrist and hook the other end to ground, then if you accidentally get shocked by a soldering iron or you-name-it, then large amounts of current could go through your body and KILL YOU.
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This post is a work of art. Variations in spelling and grammar are intentional, artistic endeavors that add value to all of mankind.
Oh, one more question: how does the black anti static foam that chips come in dissipate charge? Where does it go?
I'm guessing that it spreads the static voltage throughout the foam so that by the time the voltage reaches the pins of the chip, the voltage at any one pin of the chip equals the voltage at any other pin and, ergo, you've got zero voltage across the chip. The foam+chip (plus you) might still be charged with respect to a water pipe or something if you aren't grounded, so there's still the possibility of zapping something else. It's not like the foam radiates the charge or sends it down a black hole.
Another question: can I get some ESD protection by making my own setup? I was thinking of simply taking a three prong AC outlet plug, and discarding the AC part and keeping the ground, put a 1 MOhm resistor in there and a long strip of metal. Touch it periodically and Viola! Discharge of the problem. If that won't work, are most static resistant mat's cut proof? I like my self healing cutting mat.
An AC plug and 1meg resistor with a wire going to a metal strip or plate will work. That is what I use, but I place a large (12"x18") piece of conductive foam on top of the plate for a work surface and connect a wrist strap to the plate.
PS- Sorry, I should have mentioned the 1meg resistor in my earlier post. It is a crucial safety measure.
Post Edited (kwinn) : 1/23/2009 6:44:15 PM GMT