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Electrostatic Discharge

Trashes your electronic components.

What is it?

Did you ever touch a metal object and get a pain like a pinprick? Ever take your clothes off and hear a crackling noise? Ever see sparks when taking your clothes off in the dark?

lightning-gallery-18.jpgThat would be electrostatic discharge.

As stuff moves in the vicinity of other stuff, an electrostatic charge (static electricity) builds up. It's busting for somewhere to go, so it finds the shortest route it can to Earth. It's miniature lightning! When clouds come in proximity with one another, they charge up. Occasionally, they discharge with a bang and a flash of light.

What does it do?

If lightning hits you and discharges THROUGH you, it might seriously damage or kill you. Here's the thing: electrostatic discharge can seriously damage or kill your electronics.

Ever had a component inexplicably stop working? Permanently? I've heard many, many people saying that ESD damage to electronic components is a myth. "I've built loads of perfectly working computers and never bothered with any of that nonsense." The answer is that you might not know. Sometimes ESD can cause "transient" damage. That's where inside an IC, for example, part of a track may become literally blown away by the force of an ES discharge. The component may continue to operate indefinitely (transient damage) or it may fail instantaneously. Either way, there's no doubt that ESD weakens components.


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Your body has an electrostatic field around it. As such, you don't even need to touch components to cause damage. In proximity to components, the charge in your body causes the components themselves to become charged. Then, when you set the component down or it gets moved close to an object with a suitably different charge, it may discharge through the object.

What can I do about it? Part I - Easy, cheap solutions.

Some precautions are inexpensive. It makes me cringe to see folk storing their ICs in polystyrene blocks. Sure it keeps the legs nice and straight, but you wouldn't believe the amount of charge they can hold! Get yourself some anti static foam. There's no shortage on eBay.

ESD-Bags.jpgSpeaking of eBay, if you're ever buying electronic components (including PC memory, hard disks, or whatever), don't buy it if the guy selling it has carefully arranged it on his bed sheets or on his carpet to take a photo of it!! These materials are some of the greatest generators of electrostatic fields and they have a massive storage capacity!

If you ever order samples, they come packed in ESD bags and tubes. Keep them. That's what they're for. Store your stuff in the dissipative bags when you're not using it. Don't just chuck them in a plastic box. These bags are normally silver or pink.

In fact, never use insulating materials (unless they're specially coated with a dissipative material). Insulators hold charge. Being insulators, they also contribute to potential difference.

Printouts and photocopies are a big source of static charge. Paper holds a charge and guess what laser printing and photocopying do to paper? They charge it - like mad.

Videk%20Anti%20Static%20Mat%20(60x60cm)-VidekPolyester clothing is a curse. Don't wear cheap underwear of man made materials. I'm not kidding, either. Polyester is an insulator and causes electrostatic fields to build up like crazy.

Most folk know the "hold the board by the edges" rule and the "don't touch the pins" rule. These are a good step towards ESD preventative measures, but the only real way to stop damage from ESD is to ensure that you and the components are all at the same potential.

What can I do about it? Part II - Better, more expensive solutions.

I know folk who say "Just touch a metal pipe or a radiator and that's you grounded." It's true that touching a grounded item will dissipate any static on you, but don't forget that your component may have a charge. It needs to be grounded too, so you're both at the same potential.

This means you need to ground everything.

Anti-Static%20Wrist%20Band-BelkinUnfortunately, providing an anti static environment can be a costly business, but it doesn't have to be. For around $30, you can potentially save yourself days and days of pain. Here's a UK supplier of anti-static mats.

If you Google it, I'm sure you will find a local stockist. You'll also need a wristband to keep yourself at the same potential as your components. This is the wrist strap from the company above.

What can I do about it? Part III - Industrial, very expensive solutions.

Once you have yourself and your work surface at the same potential, you might consider anti static tools. These are conductive and dissipative so there is no potential difference between you and your workpiece.

Most ESD workplaces will insist that you wear a dissipative overcoat. These are normally cotton and the material may have a wire mesh woven through it.

Some ESD areas have a grounded floor manufactured from a conductive material. You can wear a "heel grounder" which is a wire which runs from the outside heel of your shoe to the inside to that as you walk around, any static is being conducted away to ground.

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Conclusion

I

often wonder how many of my "Blue Screens of Death" were caused by me delving into my computer with no ESD precautions. I imagine that some of my problems in the past were due to memory or other components, weakened by electrostatic discharge while being built. Guess how many inexplicable PC crashes I've had since I bought my ESD mat? None. How many PICs have ceased to function inexplicably? None.

It's worth thinking about.

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Does ESD depend on atmospheric humidity or other geographic conditions? I live near the coast, and I've not had a problem (so far) with handling chips, so am assuming a hot humid place doesn't allow charge to build up.. ?

Air temperature and pressure have a small effect on static charge, but high humidity noticeably dampens static electricity, causing it to drain away more quickly. All the extra moisture in the air bounces around and carries away the extra charge before it can build up to a significant level.

The pink plastic doesn't protect chips from static discharge. You can still zap a chip through a pink bag.

http://www.eevblog.com/2009/04/12/eevblog-3-anti-static-myths-busted/

I've got a question: Say i'm earthed, but my components are loaded up with electrostatic charge. If I well understood by what you said, if i touch these, they're gonna be grounded through my body and this will damage them right? But what if i earth them through a, say, 1M ohm resistor. Would that be a safe way to work?

Or esle, how can i earth components that are loaded up with charge without damaging them. 

Any resistor will do. But what is practical? I sometimes use an anti-ESD bag. Place all the pins of the chip on one end and place my hand on the other end. The bag will conduct any charge (or better: difference in potential) from the chip to me or vice versa. These bags are made to conduct, but also to resist.

Alternatives are: the black foam that is sometimes used  for packaging chips, specially designed work bench mats.

They all "dissipate" charge like the bags do.

Have you ever measured the resistivity of one of those silvered bags? I frightened myself with this little experiment!

Even worse, try the pink coloured ones! They have virtually no conductive properties at all.

 

One year ago (minus a day). I too wised up since.

True - I hadn't spotted that!

 

"Don't wear cheap underwear of man made materials"

 

...LOL

that's more than just a sentence, it inclueds repetitions and alliterations, it could be made into a poem :) 

I think i'll go for the cheap way for now...foil that is. 

This is what the Electronics Club says :

It is usually adequate to earth your hands by touching a metal water pipe or window frame before handling the IC but for the more sensitive (and expensive!) ICs special equipment is available, including earthed wrist straps and earthed work surfaces. You can make an earthed work surface with a sheet of aluminium kitchen foil and using a crocodile clip to connect the foil to a metal water pipe or window frame with a 10kohm resistor in series.  

 

and this other thing:

 Static sensitive ICs will be supplied in antistatic packaging with a warning label and they should be left in this packaging until you are ready to use them.

 So....are the brains we are using static sensitive? I didn't get them in the package but doesn't mean they aren't.