ESD protection of sensitive Chips, etc.

[tonyn41]

I just thought I would pass this on to you that are worried about destroying your chips/circuits,

or want to know how to store/protect them.

Being involved with electronics since 1976, I went through the ESD(Electro Static Discharge)

procedures when working with sensive chips, and circuitry.

Back then most chips were sensitive and you had to practice this.

The idea is to short any stray static voltages to ground.

When packaged correctly most sensitive chips are usually stuck into conductive foam,

which helps to short all pins to protect them from static voltages, and protects the pins from physical damage.

Then inserted into static bags.

The black foam, is inpregnated with carbon, a conductive type material.

Those static bags are actually just metal impregnated plastic.

Or they are just stored inside of static tubes.

The static tubes are metalic impregnated plastic tubes that serve a dual purpose(protect pins from physical damage and from static voltages).

DO NOT STORE YOUR CHIPS IN STYROFOAM, THIS IS NON CONDUCTIVE AND HIGHLY STATIC!

When working with sensitive chips and/or circuitry, I use a static wrist strap that connects me to ground,

and then a static mat, connected to a ground, for working on.

To store your chips/sensitive circuits:

If you do not have conductive foam, you could use aluminum foil AND foam rubber/styrofoam.

Insert the chip into aluminum foil to short the pins, and then into foam rubber or styrofoam

(although I would try to avoid styrofoam,since it is highly static) to protect the pins.

But I would highly recommend conductive foam(still available).

Since carbon impregnated filter foam for fish tanks/ponds is simular, you may get away with that instead(no guaranties on this though).

Then insert the chips/foam into a static bag, or if you do not have a static bag, you can wrap it up in aluminum foil.

Or just use the static tubes. Although I never trusted the tubes completely(I would do the foam/bag/aluminum foil instead).

I would store a circuit board, that has sensitive chips installed, in a static protector like aluminum foil or metalic plastic until needed.

To work with sensitive chips or circuitry:

Well find a way to short yourself to ground(only the hand that will touch the chips/circuit board, not any other part of you).

Believe it or not, you have voltages present on you that can destroy a sensitive chip too,

so shorting yourself to ground you remove that.

You do not have to feel a static discharge to have voltages present on you that are enough to destroy those chips!

Then use a semi-conductive surface to work on that is also connected to ground.

The static wrist strap I use seems to be a semi-conductive carbon impregnated cloth material strap with a connector to connect to ground.

The static mat I use seems to be some sort of semi-conductive plastic or rubber type mat with a connector for connecting to ground.

Right now I have no idea what to use for alternatives, so you may have to actually invest in a static wrist strap and mat.

But you get the idea, so I am sure you can come up with alternatives.

Optionally, to further protect the circuit board, you can connect it's ground plain to ground while working on a non live board(no voltages present),

using an aligator clip, etc..

It usually is safe to keep connected and work on a semi-conductive static mat with live circuitry(voltages present), but I would be careful.

You do not want to electrocute yourself!

A good practice is to put one hand behind your back(the non connected one), while working on live circuits.

This way the CURRENT will go from wrist to ground, and NOT THROUGH YOU, THUS STOPPING YOUR HEART!

Trust me, this may save your life, since it has for me while working on high voltage circuits durring my years of working in electronics.

It does not take much current through your heart to stop your heart, so just because you my not be working with high voltage,

this is always good practice.

Also use some type of stand off to insulate the back of the circuit board from the static mat, that is connected to ground,

if applying voltages to the board.

Once the circuit is complete and in it's unit, then it usually is safe from static voltages

(but make sure you have good grounds in your unit though to not let static voltages develop).

All of this may seem like overkill, but if all of this is practiced, you are GUARANTIED that your chips/circuits will be protected.

This also is a guaranty that you can rest assured that you can keep those rare chips safely stored and protected for years.

Note: The ground you want is EARTH GROUND.

This in homes is usually found using the metal cold water pipes that go into the earth ground.

So just find a way to connect a wire to your cold water pipes,

unless you are assured that the ground(not the common black wire but the green or bare ground wire)

in your electrical outlets are propperly connected to this earth ground.

If they are, then you can use this ground wire for your earth ground.

I hope this helps those of you whom are worried about damage to your rare and expensive SID chips(like me), and other sensitive chips/circuits.

Edited December 7, 2011 by tonyn41

[gomiboy99]

Good tips, this should be standard practice for any electronics. I use my anti-static gear every time.

For those in the UK, Maplin sell wrist straps, 1MegOhm cables and 3 pin mains plugs with an earth stud for the cable. These are also available from Rapid, Farnell, RS and even eBay.

The safety tips are VERY important, always use a proper anti-static cord fitted with a resistor.

Tim

[tonyn41]

Good tips, this should be standard practice for any electronics. I use my anti-static gear every time.

For those in the UK, Maplin sell wrist straps, 1MegOhm cables and 3 pin mains plugs with an earth stud for the cable. These are also available from Rapid, Farnell, RS and even eBay.

The safety tips are VERY important, always use a proper anti-static cord fitted with a resistor.

Tim

Thanks. I forgot to meantion more about the resistances.

Like the SEMI conductive mat and SEMI conductive foam, you may want some resistance to slowly discharge static voltages else POP!

Yes, my strap has a resistance to ground too, so I am not SHORTED to ground BUT I am BROUGHT DOWN TO GROUND POTENTIAL.

Shorting the pins with aluminum foil maybe OK as an extra precaution, as long as it is also inserted into a SEMI conductive foam.

Inserting everything into aluminum foil is also ok, since it shorts outside voltages from entering, and offers a shield from EMF, etc.

The main part of this is the SEMI CONDUCTIVE FOAM first. This to me, is the most inportant material to have.

If you do not have it, I suggested aquarium/pond carbon filter material as a possible substitute.

As I also stated, I know of no substitute for a propper antistatic wrist strap, mat, or cords.

Since, like you stated, they do have resistance to ground, so nothing is actually a direct short to ground.

So best to buy those.

Yes, the 3rd prong of a plug, normally, in the USA, gos to earth ground.

Some plugs also have a terminal on them to connect to for the earth ground.

The color of the earth ground wire in the outlet box is usually green or bare(non insulated).

Red/Black is the hot side, white the common side, green/bare the earth ground, at least for 115/120V, as in the USA.

This color scheme is normally standard in the USA, but I am not sure if it is in all countries.

The idea when handling these chips is to be at the same voltage potential, being ground, so there are no stray voltages.

I always connect myself up with the wrist strap/cord,

then put the chip package on the antistatic mat,

so everything is at the same potential, before opening and handling the chips.

One hand(the non connected) holds package(optionally part of that hand/arm resting on mat, so that it can also be at grround potential),

and the connected hand is the one that touchs/removes the chips.

When working with live circuits, if you need both hands, try resting part of your non connected hand on the mat somehow so that any currents do not enter you,

and are shorted to the mat. But even that scares me. So the "one hand behind the back" is something I was taught and is good practice.

I know you may need 2 hands, the idea is that the hand that is close to live circuits be the one that is connected to ground.

One time I was working with 1000v, with no wrist strap(well I wasn't working with Chips), but I had my other hand behind my back(not actually,

but far away from the live circuit).

The current just went through my finger and made a hole, but if it wasn't for my saftey practice(only one hand near voltage),

and I had both hands near the voltage, it could have went from one hand, through my heart, to the other hand, thus killing me.

Some people may say "well you were working with 1000v, and I am only working with 5-12v".

Well, it's NOT THE VOLTAGE THAT CAN KILL, BUT THE CURRENT, WHICH IS NOT MUCH.

I don't know the amount of current I was told(mili amps, i.e less than an amp), that going through your heart , that can kill you, but it's lower than you may think.

Once you have an antistatic mat, which are nice to work on, you are basically working on water, in a way, that is connected to ground.

So YOU DO NOT WANT CURRENT GOING THROUGH YOU(WITH YOUR HEART IN THE MIDDLE OF THE PATH) TO THE MAT->GROUND,

OR THROUGH YOUR NONCONNECTED HAND THROUGH YOUR HEART TO THE GROUNDED HAND->GROUND.

So figure a way that that those paths can not be taken.

Again, this may seem like overkill, but I have seen high voltage circuits burn the mat(where I worked, everything was tested and worked on on these mats),

when a live circuit just sat on the mat, solder side down, with no insolation.

So there is a potential for currents to use these paths. So "better safe than sorry".

I worked in a Quality Assurance Environmental Stress Screening Lab(ESS lab for short),

as a programmer/test tech( at Astronautics Corp. of America, if interested, 20 years ago),

where there were also high voltage circuits tested there too.

I programmed the test equipment, built and designed the test interfaces, etc., if needed, and of course did testing too.

The test equipment was computerized and tested chips in batches, automatically.

Some parts to these testers were bought for 100's of thousands of $,

pieced together, customised, had computers connected to them, and programed at Astronautics. Which I was part of.

We did test a LOT of chips daily, most went into space, others, I have no idea.

All I was concerned about was putting my Quality Control stamp of aproval on these chips,

and send them out my door to the production floor.

Since I had a military background in a lot of good electronic practices, I also setup some training sessions,

for the engineers/test techs, to pass my knowledge onto them there too.

The chips I tested were to go into military satellite circuits, which were also mfg there.

These chips/circuits went into space, where if a chip/circuit failed, it could not be fixed/replaced, easily/cheaply.

So not only did we have to not destroy or reduce the lifetime of these chips by bad ESD practices,

but the chips had to pass all mfg spec tests to a military spec levels at all temps/stress levels,

to last for years in space.

We could not even walk across the lab with an unprotected/packaged chip!

So those wrist straps became a bracelet for me that I would snap and unsnap to the cords at the ESD stations,

and put on as soon as I entered the lab, and not remove until I left.

We also wore latex gloves, so as not contaminate the chips either(well it was a lab, and even human contact was disaproved of).

Before that, I had worked in the military as an electronics tech, and was taught the safety practices.

So that, I hope, gives me a bit of credentials as to knowing a bit about this ESD/safety practice stuff. :)

I just wonder how many of the chips/circuits I tested are still up in space, over your head, still working? :)

Boy, that almost sounds like a resume!:)

As a side note: I had one batch of 1000 chips during this job,

that were grown on sapphire vs silicon, and cost about $1000 each!

A handful at that time, could have made me rich, but who would buy them?

Plus, most likely I would have went to prision.

So I passed on stealing any. But holding them felt good :)

Our SIDs may seem expensive now to you, but those chips were a LOT more expensive, and could not be destroyed.

See those chips went into space, and sapphire was used to give them a longer life(doesn't deteriate over time like silicon?).

That was a long time ago, and back then I knew how chips were grown, now adays I am more of a programer than an electronics engineer,

so I forgot the exact specs on that.

I know that a lot of us here may already know a lot of this already, and have had training in electronics/ESD.

But there are a lot of hobbyists that may not have heard of these practices, and although they can solder and assemble circuits, they do not know of these practices.

Plus I saw a post where a guy wanted to insert chips into cardboard, etc.!

Yikes!

So I decided to try to explain how these chips can be protected propperly,

and why you may not want to use some materials.

Plus I thought I would pass on some safety tips too.

Edited December 9, 2011 by tonyn41