I saw on one of Daves video's something I think called ESD, it that little device under his bench where the wrist strap is, and I think he mentioned mains earth ?, is there a circuit for this anywhere, really useful for static I should imagine, any one please tell me more, and advice would be more than welcome, a lot of my electronics is Radio amateur based, some of the parts a really expensive, so I really want to put this side right from the start.
Paul.
Here's a cut-n-paste from something I posted to another forum a while back. Clearly I was bored at the time, and it didn't go down all that well with the I-don't-need-to-care-about-ESD brigade either - but since you ask, sit back, pour yourself a beer and enjoy....
----------
ESD is a subject which is very poorly understood, even in the electronics industry where people should know better. Spare me a few minutes and I'll clear up a few misunderstandings that'll hopefully save you an expensive repair bill one day.
First off, a few things you may already know about ESD:
- Your DRAM is designed to work off 2.5V or less. Walking across a carpet can generate voltages in the order of 5,000V or more.
- Rubbing two insulators together (eg. two layers of clothing) causes static electricity to be generated, by transferring electrons from the surface of one to the surface of the other
- Static electricity that's just sitting there on the surface of an insulator isn't doing any harm. What causes damage is when that electricity is suddenly allowed to flow from one place to another via a conductive path. At the moment the conductive path is formed, the instantaneous current can be huge, and if your SSD (Static Sensitive Device - could be a DRAM module, CPU, motherboard - anything with exposed electronic components) is in that path, it can be damaged.
- The discharge current causes a heating effect, just like when you connect the mains to an electric fire. Too much heat in a small device burns it out, it's that simple. The smaller the device - a transistor, for example - the more sensitive it will be to ESD damage.
And a few things you probably DIDN'T know:
- You DO NOT have to actually touch a Static Sensitive Device (SSD) such as a DRAM module in order to damage it. Merely passing your hand near it can be enough.
- An ESD event can be strong enough to cause damage well below the threshold where you'll feel it - so you can destroy a device without even knowing it.
- A device damaged by ESD DOES NOT necessarily stop working straight away, but its performance and lifetime can be drastically reduced. So, just because you put a machine together and it seems to work DOESN'T mean you've got away with it.
- An SSD enclosed within a conductive anti-static bag is NOT completely immune to ESD damage, because although it's protected from electric fields, it's not protected at all from magnetic fields. A spark outside the bag causes a rapidly changing magnetic field, which can induce a current in any conductor inside the bag. (Think: that's how a generator works!)
- the correct way to package an SSD is to put it within a conductive bag, and then to package that bag in a reasonable thickness of 'pink' bubble wrap or other packaging. The bag protects against electric fields, and the pink material provides enough physical space around the SSD that large magnetic fields (from sparks) can't be generated physically close enough to cause damage.
- 'pink' packaging material is coloured that way by the manufacturer to indicate that it's made so that rubbing against it doesn't produce a charge. It is NOT conductive and it does NOT protect equipment from electric or magnetic fields. It is, however, the correct material to use to package SSDs that are already enclosed in conductive bags.
- the pink colour is just an identifier. Retail boxed CPUs, for example, come in clear plastic because it looks nice, but that's OK - Intel & co know what they're doing.
Be aware, though: an awful lot of PC component vendors DO NOT know the correct way to package an SSD. If you order a component, such as a CPU or memory module, and it's not correctly packaged, you'd be within your rights to send it back - IMHO, of course
So, with all that in mind, what can you do to protect your equipment?
In order to damage a component, you need a potential difference between the component itself and the thing you're going to touch it with. No PD = no current = no damage.
So, normal practise in an electronic assembly plant is to ensure that everything is at the same potential all the time, and that means:
- everything is conductive: bench, floor, tools, lab coat, even the waste paper bin. Unnecessary insulating materials (crisp packets, coffee cups etc) are banned from assembly areas.
- everything conductive is grounded - NOT because there's anything 'magic' about ground, but that it ensures everything in the plant is at the SAME potential as everything else.
- conductive materials used still have some resistance - they're not made of good conductors like copper and aluminium, but instead they use carbon loaded rubber or plastics. This ensures that when a potential difference does exist, the current involved is small and safe. Charge leaks away relatively slowly rather than suddenly.
These basic precautions mean that everything the SSD's are likely to touch are at the same potential; no difference in potential = no current = no damage.
So, assuming you don't have all that kit, what can you do to protect your equipment?
- borrow the correct equipment! There really is no substitute for a dissipative bench mat and a wrist strap. Really! If your PC packs up in 6 months' time and you didn't use the proper equipment, you only have yourself to blame.
...but if that's simply not possible...
- on a desktop PC, DO plug it into the mains, but turn off the power at the wall - you only want the earth connection. (Disclaimer: safety, safety, safety!!! If you're not absolutely 100% sure about the implications of this, get someone else to upgrade your PC for you! I am NOT RESPONSIBLE for anything YOU CHOOSE to do with your PC, REGARDLESS of whether YOU CHOOSE to treat my comments as advice or instructions!).
- don't wear nylon or other synthetic fabrics - wear cotton instead. Or do the upgrade naked if that's your thing! But whatever you do, don't pull a sweater off over your head and THEN grab your shiny new DRAM module. All those little clicks you heard when you pulled the sweater off were ESD events - you're now charged up to 10,000 volts and your DRAM is doomed/
- touch the EARTHED bare metal case of your PC.
- touch the silver or black bag that your DRAM comes in to the bare metal case of your PC as well. There's no point in you being earthed if the SSD is charged up to 10,000V when you get it.
- The moment you first touch the SSD after opening the conductive bag is the moment at which you're most likely to damage it, because you don't know what potential it's at. Get this into your head! A proper wrist strap contains a 1MOhm resistor to limit the current that'll inevitably flow through your shiny new DRAM when you first touch it. If you had a proper wrist strap on now, you wouldn't be about to risk blowing it up. Now is the time to decide NOT to open the bag today, and to pick up a wrist strap for a few quid off Ebay.
- Remove the module from its bag and install into your PC. Try to maintain a finger or elbow in contact with the chassis of your PC at all times, it only takes a moment to 'recharge' once you let go!
- Reassemble your PC and test.
Finally, be aware that there's some scarily bad misinformation around about ESD. From this very thread:
- "It doesn't matter, I've never had a problem" - see above. You can damage a module without realising it, and the damage may not show up for months. Now you know that this 'latent damage' can occur, you'll be in a better position to put 2+2 together when your PC 'inexplicably' packs up next year.
- "Touch a metal object" - pointless. You need to ensure that you, your PC and the component you're installing are all at the same potential. If it's plugged in then your PC is at earth potential, so if you touch a metal water pipe (something which is connected to earth and, therefore, at the same potential), then that's good. But touching a door handle just makes you look stupid.
- "Latex gloves" / "rubber" - ?! You're not trying to protect it from some biological infection - latex is an insulator and can therefore hold a charge. It's probably the worst thing you could possibly do from an ESD point of view. (Sometimes workers in a clean room use them to avoid contamination, but that's not the problem in this case).
- "One hand in the back pocket" - is a good rule for personal safety if you're working on live equipment, because if you touch a live conductor it helps prevent current from passing through your chest. But your PC is switched off at the wall. Right answer to the wrong question. Ditto for insulating boots - workers in ESD protected areas wear conductive heel straps, and NEVER work directly on live equipment.
- "Switch on after removing the battery to discharge the equipment" - wrong again. This has nothing to do with ESD, it's to ensure that the power supply caps in the PC have drained. All you need do is wait 10 seconds after switching off and you'll be fine. This has nothing to do with static.
Hope that helps!!
Andy.
Home
Help
Search
Login
Register
