Let's Make Robots!

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.


fm_ftes_imgb.jpg

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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yeah great info! but i wonder: when you damage a component, can you see it? ie sparks, smoke, some sound, or is it completely silent ?

Well, explosions are never completely silent. The photo above was taken with an electron microscope. The explosion was very small. Tracks inside ICs are sometimes only a few electrons in width! This particular component had to be taken apart for the photo to be taken. The epoxy case the component was in (the black plasticy square stuff you probably call the "chip") fact ground away to reveal the silicon underneath.

It might've made a little, barely audible click. It might've made smoke. It might've made a smell. Or it might have done nothing obious at all. The component may even still appear to be functioning until a particular set of circumstances arose! Sometimes damage is transient (i.e. there's no immediately obvious problem).

So, no, unfortunately, you can't always see it and consequently, you may well have a drawer full of duff components that just don't know they're duff, yet

 

 

 OMG! im now so scared!

seriously BOA, you freaked me out with these infos!

how can i ever touch another board again?!?!??  :(

 

/Nick

None of us should ever touch electronics without electrostatic protective measures. I'm sure that the hobbiests who take proper precautions are in the minority, but every time you handle your electronics, you increase the probability of destroying it.

Like I say, I wonder how many projects have been branded a failure just because the components were destroyed during manufacture? Then the replacements destroyed during replacement...

Some components have some built-in protection and some are just less prone to the effects, but nobody's immune to lightning.

Just thought of something else. You know I'm terribly fond of PCV conduit for making robots? It's probably the worst material in the world from and electrostatic point of view. PVC holds loads of charge. You only have to slide your had along a piece and your hair stands up. I may have to reconsider the cases I put my PCBs in before mounting them to PVC!!

i've also heard that it helps to touch some metal object with the hands before touching the components to discharge any static charge. I've also heard that it's good to work on some conductive place like the kitchen sink or such.

I don't know if it's real, maybe someone can report :)

Grounding the components or yourself doesn't necessarily do anything to help. Keeping youself and your components at the same potential is what removes ESD problems.If that chosen potential happens to be "earth" (as it usually is) the so be it.

If you and your components are in a charged environment, for example, and you earth yourself, discharging any static from your body and clothes, then you touch your components, the components will want to discharge to you. It's exaclty the same effect as you discharging to the components.

Likewise, if you are charged and you are working on your kitchen sink (which is presumably earthed) and you touch a component, you're going to discharge through the component to earth.

It's about Potential Difference. In summary, that's you and your components being "at" different voltage. All stuff wants to do is be at the same potential as averything it comes close to.

I see no reason why working at the sink wouldn't work, but ONLY if you maintain contact with the sink. Keep you and your bits at the same potential.

boa what do you think about storing stuff in aluminum sheets ? i've reat it around as well :)

You're talking about wrapping stuff in aluminium foil, right?

Aluminium is a conductor. Sure, it's also dissapative, but it's a conductor foremost. So the stuff in the foil is at the same potential as the surroundings. I would have to say that if you're "charged" and your aluminium wrapped componets are sitting on the kitchen sink, then you'll discharge through the aluminium rather than the components, so it would afford SOME protection.

 

Actually, no. The volume within a closed conductor (such as a packet of aluminum foil) is electricly isolated from the outside enviroment. This is how farday cages work, and why sensitive electronics have metal boxes around them (like the tuner circuits in VCRs and TVs). This is also the principle behind antistatic bags and foam, which are usaully made of plastic that has a conductive coating (bags) or is moderatly conductive (foam).

If I recall correctly, this video has a demonstration:

http://ocw.mit.edu/OcwWeb/Physics/8-02Electricity-and-MagnetismSpring2002/VideoAndCaptions/detail/embed03.htm