The AM Forum

OK, I read about 20 pages on ESD and have a basic understanding. Now need to set up my workbench to work on some sensitive SDR boards, chips, etc.
 
What is the cheapest way to cover the majority of potential ESD situations? Do I need to buy specialized wrist straps, floor mat, bench mat and soldering iron straps?  Do I keep a copper wire braid from the main station ground (Earth ground too) tied to the chassis of the SDR board main frame ground and to the high resistive dissipative mats?

Is there a common cheap material to use for these mats and straps?  I understand they are made from a material that is of high resistance.
 
I'm trying to pull this off using regular Home Depot type stuff and common materials if possible - or do I need to buy some specialized ESD stuff at Mouser, etc?

Thanks for any help.
 
T

JJ wrote,  "or do I need to buy some specialized ESD stuff at Mouser, etc?"

Tom,

ESD,  sounds like something you would buy down on the street corner or at the drugstore.

Hope my comment is helpful,

Fred

Tom, I don't think HD will have anything resembling ESD equipment.
Try Jameco, these kits look pretty cheap.  I worked in a shop for many years and we had the training, etc.  We still forgot to wear the wristbands half the time, things still got fixed and went out the door.  An ESD event supposedly can shorten the life of sensitive components.   ::)

http://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDrillDownView?langId=-1&storeId=10001&catalogId=10001&freeText=esd%20mat&search_type=jamecoall

Some of this comes back to me about ESD. Scotch sold conductive pads to lay on the work area with ground connections.
I worked a short time in an electronic factory near Pittsburgh and we had to wear ESD shoes. Put the on and even went through a test. The automated stuff was fun to watch populating pcb's and soldering. The company was Mine Safety Appliances.
Nice company, nice wages for non-union.
Fred

Get the humidity increased in your shop, Tom. Winter time gets it down to single digits and bloody noses.

If you use a wrist strap at home, put a high value resistor somewhere between you and ground in the system. This allows the charge to drain, but should prevent you from getting electrocuted by accident having a direct ground path on your body.

Hello,

   Correct humidity and Jim's suggestion is the ticket. The "R" is
built into the stuff so no worries there. I serviced at a place that
spent a lot of cash on those floor mats , it didn't take long for them
to toss them. You need a "Heel" strap for them to work good enough
and they don't hold up well.  (I got em here, they suc) but if
you could get a few feet of it put it on your bench.  get an extra
mat either way. The tester is nice but you could use a VOM.
The path from the conductive part of the wrist to the ground
clip is 1 meg.

GL
/Dan

Ed said:
Ed's right Vu. The commercial stuff we have here at work use 500K in series to ground. The ESD mats on the workbench use 1 Megs to ground.

Tom,
You are moving into the big league of LSI components. Anybody who thinks this isn't an issue has never played on the field. Yes ESD mats are good but a sheet of metal works fine also just be careful running high voltage which you will not be doing here. The ESD mats wear out in time and need to be replaced. A grounded hunk of metal never wears out. Buy yourself a good ESD strap and use it. We can get walked out of here for thinking it isn't an issue.

OK, Good!  Gots a plan now.


Tell me if I gots this right - some more questions:

I'll check the web for real ESD wrist straps. I'll put a metal sheet on the floor and rest my sneakers on it when working on ESD.

Jim, the Jameco kits look good.

OK on the bench. I'll get a real ESD mat there.   I read that a metal sheet is not good cuz of the high current that can flow thru it vs: a high resistive ESD mat. Does this also apply to the floor metal sheet or is it OK to use metal there cuz of my rubber sneakers in contact with it?

Now for the grounding. I have a thick copper braid running around the shack bonded to all chassis, test gear and terminates outside to the antenna ground radial system and the AC power lines ground. Do I tie this into the soldering iron metal shaft, floor metal mat, bench mat (whatever that is) and my wrist strap? Is the soldering iron strap made of metal or ESD resistive material - if so, how does it keep from melting?

When I'm working on these LSI chips and boards, I read not to touch them, if possible. Do I put some kind of strap on the BOARD GROUND itself when working on it?

I'm having trouble visualizing how the main Earth ground ties into the ESD strapping, or does it even make a difference?

OK on the humidity. Yes, this IS a problem with the coal stove here. I have a pot of water boiling on the stove, but I know there is static electricity around when I pet Yaz and get shocks... :o

T

  Yeah,

   the dog is good tester!!  Cats are somewhat more sensitive but
a big wet nose is a big wet nose...

   Think of the ground as more of a "Drain" to bleed off excessive
static. 

/Dan

Radio Shack still sold wrist straps and mats the last time I checked (about a year ago).
73
Steve WA2DTW

I always feel bad when the cats come over for some petting and I can feel a charge build up and then one of them will put their nose up and a get zapped and run off wondering why the heck I did that to them!  :o

I'm not sure I'd worry too much about the floor plate or mat, just make sure when you get to the bench that you discharge there before you get near any of the components and get a grounding strap on. If I recall correctly, you don't even have to touch a component to damage it, just getting close to it with a big field on you can set up an electric field across the component that can exceed it's capacity to deal with.

I used to work in a small electronics factory in an old wooden building with rugs on the floor and steam heat. Every winter we would have terrible problems with static. All of the engineering staff had this weird bent wrist, back of the wrist to wrist contact 'handshake' we'd do to equalize as we'd be handing parts to each other. Fortunately we were dealing with all discrete parts, not LSI (old military contract - including germanium transistors), and with some simple precautions we were ok. Could never have built anything with modern components in that environment.

Tom, wait til you see the prices for the real 3M ESD bench kits.  North of $400 at digikey.
For this hobby I wouln't spend that kind of dough.  Jameco has some cheap set-ups, prolly lots more on the "internets".

Frank, this was for consumer electronics many years ago, ESD concerns were just starting.  (late 80's --> 90's) I suppose some of the "return" units that came back were due to techs' sloppy ESD safeguards, but that was a very,very small percentage and we would have no way of knowing either way.  Nevertheless, ESD is a real concern where safeguards should be followed.

Alot of ESD prevention is common sense.  You don't comb your hair with that replacement opamp DIP.  For starters- I always made a habit before working on stuff ; was to touch the bench ground to discharge my body after walking across the carpeted shop, especially in the Winter. 

--73 Jim

Anymore (since I retired) I just fix all solid-state gear in a big washtub filled with water. 

Keeps all kinds of static away..... ;)

I gotta' remember to pull my hands out before I power it up for a test, tho..... :o

73DG

OK on Radio Shark carrying ESD stuff. Why didn't I think of that?  I was going to take a ride down there today and at least buy a wrist strap and bench mat.  Then I read the following:

http://mailman.qth.net/pipermail/elecraft/2008-February/083794.html

So, not sure if maybe a different set of material might be better.  Seems this guy thinks their mat is too high in resistance to bleed charges well.


Yes, the ESD scare is real. Not only Frank, but others who have used SDR LSI stuff have warned me that they, too, have blown out boards by handling them improperly, Here's an email I gots yesterday from a VK SDR enthusiast who has a complete SDR transceiver and amplifier system:

"I have an EU Penelope [exciter] and it worked fine until the FPGA got a static discharge or something.
Please use antistatic precautions at all times as they can get a zap easily.
I sent it back to Gerd Loch in Germany and he repaired and tested it.
BTW Gerd offers superb backup service at reasonable rates and his boards are excellent."

T

Tom you don't need the stuff on the floor if you are careful to wear the strap. Floor is back up. We wear company provided ESD shoes and the floor is treated with ESD coating. Yes, I always go for the chassis even though I have the strap on. Handling boards I try not to touch any components or circuit traces.
All modules are shipped in ESD bags.

Tom:

On my production lines at Siemens the workers used a mat and a wrist strap at each station with effective results.

In the shop at home I use the wrist strap and a drain as others have stated. Shop has a concrete floor, and usually 50% humidity

My 2cents:

To begin with, and most important, be aware of what generates the static. Mostly your shoes and clothing. As a young JN, I wasted a $75.00 speech synthesizer chip shortly after I fired it up and had it talking. A lot of money back then.

I knew exactly what caused it, the shoes and carpet. They always generated static.

To this day if I am working with anything ESD sensitive it’s cotton all the way. Period. Shirt, jeans, socks etc. I have some blend shirts that will always generate static, no matter the time of year. They never make it into the shop. YMMV.

Ted / KC9LKE

http://www.mail-archive.com/elecraft@mailman.qth.net/msg94417.html

Thanks for the suggestions, Ted.

I'm zeroing in and see that not all mats are good. Check out the post written by N1AL above. He says most cheap mats don't conduct and a more expensive one was 1000X more conductive - and passed the national standards test. So I'm going to buy a higher quality mat and wrist strap and call it a day.

Interesting on not wearing  shoes. I wonder if sneakers are OK if I use a floor mat that is also grounded to the other ESD stuff?

T

http://www.pemro.com/items.asp?Cc=STP&Bc=

Here's the place to buy the quality Desco bench mat and good quality wrist bands - and other ESD accessories.  A little more $, but certified good stuff.


And here's that FB Desco 66164 bench mat for $38: (41 megohm)

http://www.pemro.com/itemdesc.asp?ic=DES%2D2194&eq=&Tp=

And a good quality strap for $14:

http://www.pemro.com/itemdesc.asp?ic=BOT%2D1005&eq=&Tp=


Bought 'em both and will be ESD safe, caw mawn.

T

“Interesting on not wearing  shoes. I wonder if sneakers are OK if I use a floor mat that is also grounded to the other ESD stuff?”


No no..you leave a shoe on!  ;D

I’ve had good luck with sneakers, bad luck with leather soled shoes.

Ted

They make a heel strap that goes over your shoe heel with a strap that goes between your sweaty feet and shoe or inside the sock if you don't have ESD shoes.
A kettle of water on your stove is great ESD control the keep the humidity up.
Make sure you get the termination connection for your bench mat. A snap terminal with a resistive wire that goes to AC ground on the wall outlet. I wouldn't use the RF ground because there can be a voltage differential when the soldering iron is plugged in.

Frank,

So I run the AC outlet ground wire to the metal shaft of the soldering iron as well as the floor metal sheet, the wrist band and the bench mat?

T

*BTW, I just checked and see that my soldering iron station TIP is already internally connected to the AC ground on the outlet.  So I will attach the rest of the ESD stuff to this same ground lead, correct?

Very good, important that the tip is grounded. We use RF soldering irons at work running at 13 MHz to avoid anything near the line. Sometimes heating elements leak current to gnd. Good idea to check them from time to time.
When I solder small FETs I unplug the iron when I solder the connection.
Yup ESD gnd should share iron/any local test equipment gnd. I just attach my static strap to Pandora case which is AC gnd for my rig when I swap out a board. I have internal Lamda power supply modules in my Pandora so have it connected to AC source. The standard is feed Pandora 12 volts and use the internal regulator board to make 5 volts and minus is created with a small switcher. I didn't want any switching regulators to generate RX spurs. 
Sounds like you are getting it. Think of ESD protection on the same safety level as going up your tower and you will be fine.

OK, should be all set now.   Got everything ready for the SDR boards' arrival.

I also dug out an old humidifier. There's no doubt the static is more strapping when dry in here. I'll let it run when working on SDR stuff in the shack.

TNX for all the help, guys!

T

<<<
When I'm working on these LSI chips and boards, I read not to touch them, if possible. Do I put some kind of strap on the BOARD GROUND itself when working on it?

I'm having trouble visualizing how the main Earth ground ties into the ESD strapping, or does it even make a difference?

OK on the humidity. Yes, this IS a problem with the coal stove here. I have a pot of water boiling on the stove, but I know there is static electricity around when I pet Yaz and get shocks.
>>>

T,
Here's how our techs handle ESD sensitive components.

Component is handled in an ESD bag.  The ESD bag provides a Faraday shield to the component.  Tech attaches his wrist strap at his ESD safe work area (ESD work area highlighted in my email to you).  Once the tech is grounded he can then remove the component from the ESD container and place it on his work area (ESD mat).  As long as he's grounded and the mat is grounded the tech can do anything with the component.  It's best not to touch any conductive parts of the component.  It's just an additional precaution.  The tech will do what he needs to do to the component. It's either installed into a piece of equipment or it goes back into the ESD container for later installation.  This all occurs in the ESD safe work zone.

There are times when a circuit card is placed into a piece of equipment that is not in an established ESD safe work area.  The equipment may be considered ESD safe but now the tech has to transfer the component from its ESD container into the equipment.  In this case, the tech will have to establish an ESD safe work area next to the equipment based on the procedures my company uses or the industry standard.  The effort is to get the component into the equipment without subjecting it to electrostatic exposure by minimizing movement or displacement from ESD container to installation location.

The whole point is to minimize or eliminate as best as possible an ESD event.  You can have an ESD event and not know it by simply moving a component or touching it in  a certain manner if ESD precautions aren't taken.  Components can be sensitive to as little as 100eV.  Where I work our training subject matter has microsopic images of devices that have been damaged with as little as 100eV. Punch through took place but it didn't short the component.  It some cases it may not render the component as a failed component but it may fail later for no explainable reason.  

We also have ESD preventative procedures for connecting wiring and cables to equipment.  A discharge delivered through a  cable can inflict just as much damage as handling the component on the other end.

Do you have a hygrometer?  Any idea how much moisture you're putting into the atomsphere?  It's very dry here and I have 2 humidifiers running to maintain 40% in 2300 sq. ft.  I'm pumping out about 3 gallons per day.

Like Frank, we can be dismissed if we dismiss the company policy.  ESD is real even if you don't feel it.

Very good additional info, Bob, thanks!

I like the step by step instructions.   No, I don't have a hygrometer, but will take a look on the web for a cheap one. This is relative humidity that you commonly see displayed by those meters hung on the wall, right?

Yep, the worst part about ESD is a partially damaged part and it then becoming intermitant or bad later on. That's all I need with this surface mount SDR stuff... :-)

T

Yes, on the hygrometer/relative humidity meter.  Yes, like what's on one of those fancy barometers.  I have a couple of them, both electronic.  They're pretty close to each other, maybe off by 10% compared to the other but good indicators of what the humidifiers are doing. I suspect that if you're getting static from Yaz your humidity is low, probably in the 15% to 20% area even with the pot of water on the coal stove. But if you can get your humidity up to say about 35%, I think you'll be good and knock down any hint of static discharge.  That doesn't mean you've squelched it completely, just reduced it to an imperceptible level.  Yaz will be more happy too!

I try to maintain 35 to 40% relative humidity during this time because it makes it more comfortable in the living area and it protects not only electronic stuff somewhat but the wood in the house, especially the guitars. No zaps on door knobs either.  Liz complains occasionally of being chilled because I keep the temp around 65 to 67 but having a higher humidity makes it seem warmer in the space without having to jack up the thermostat.

A couple lessons learned over 30 years ago when low noise GaAsFET transistors were difficult to get in quantity and were still very expensive ...

Don't trust the soldering iron ground through the power cord. We used (and still do) Weller TC-202 soldering stations and add an extra ground wire between the base of the soldering station and a threaded stud installed in place of the wall outlet cover screw.

The connection between the replaceable tip and the 'barrel' that secures it can deteriorate and go open over time. It became SOP, once a week, to remove the tip and clean the areas where the two pieces meet ... as well as replacing tips before they became old and cruddy.

We built dedicated meters to measure the resistance between the tip and ground. The 'tip receptor' of the meter was located close to the cleaning sponge for frequent 'no hassle' ground verification.

Untold numbers of GaAsFET transistors have been spared an early demise  :)   

Funny that you would mention that, Jay.   When I tested my soldering iron tip-to-ground continuity, it was open!  I couldn't understand what was wrong cuz it was a metal to metal contact from the coller to the tip. But as you said, after pulling it apart and cleaning it, the connection returned FB.

I'm thinking of adding a wire that gets wrapped around the tip base and shunts this mechanical connection - or something like that.  Your idea of an on-the-fly tip resistance tester is clever too.

T

All good advice.  

Here's another little tip.
In a home shop environment I found that even with ESD safety devices in use their are often places where voltages can develop; synthetic clothing, plastic anything, carpets, tool boxes...  So in addition to the usual precautions before I start handling or working on sensitive stuff I liberally spray my floor, desk chair etcetera with "Static Guard". You know the stuff to keep your skirt from sticking to your panty hose.  ;)

It doesn't conduct per se but it does a lot to deionze the area and keep all the local surface potentials to a minimum.  I swear it's saved me a few times when doing service work in an environment that I couldn't control.  Especially if you drop something outside of your ESD comfort zone and have to pick it up.

Interesting on the panty hose spray, Mark. I'll check - I think the Huzman left a can of it around here somewhere the last he was here.... ;D

I was walking around the coal stove yesterday and was conscious of the little zaps I was getting off the rug. It certainly is a dry environment out there and I will be sure to run the humidifier with the door closed in the shack/work area.

Frank gave me a good suggestion. Whenever he approaches the workbench, he FIRST seeks out the main ground or cabinet and grabs it to discharge himself. When he works on the stuff, when getting into sensitive areas, he leans his arm or some part of his body on the cabinet ground.   That's a good habit to develop.

Well, I learned a lot here in the last day or so and never practiced any of this in the past. I can think of just one time I had a problem with my FT-1000D when I popped a FET while measuring it with a VOM.  I always have my test equipment grounded but it pays to think things out first. For example, when plugging in an external cable or even a board into the backplane, keep the contacts aligned as they go in. Nothing worse than missing the alignment and putting the wrong pins on the wrong places, even with voltages off.  Some circuits hold a charge for a long time.

T

Couple more lessons learned ...

Best to have all equipment at the bench on one ac circuit. Sounds obvious, but when one runs short of power strip outlets avoid the temptation to run ac from another wall outlet ... especially one that may not be on the same circuit. 'Daisy chaining' another power strip is a better alternative.

It's a good idea to remove dc power to sensitive circuitry before swapping rf cabling - switching from a signal generator to an outside antenna, etc. Once the rf cabling has been changed reapply power to the circuit under test. One may determine later on that this isn't an issue ... but during the initial development phase extra caution is often warranted.       

 

ESD is dealing with high voltage in reverse. ESD case you are the high voltage source and that poor little microcircuit is the guy with his hand in a pocket.

Jay,

How about the risk of switching antennas using a rotary antenna switch?  One time I had the MFJ 259 hooked up to the antenna switch common and blew the switching diodes in it when I switched. Those things can't take any static as you know.

I wonder if the SDR stuff will be at risk when I go from say, delta loops to low dipole, etc?  The FT-1000D seems to have survived it all these years.  I did read somewhere that the Mercury RX had some kind of front end protection limiting voltage to 5V, but not sure.

T

Tom,
Mercury does have input protection at the antenna. A high speed diode in series with a Zener. Then a second pair reversed. I polled to have the Zeners biased at a bit of current to make it very fast but that would have required a negative supply. HPSDR design guys have been trying to avoid using negative supplies. I suppose for the mobile and portable operators.
I change antennas all the time but do have a 6 dB pad at the input. I have the HPSDR on the KAZ loops.

That's good Frank!

T ... Started out with a 3 dB attenuator in front of the Perseus but have since dropped down to 1 dB. Not sure what's inside the 'P' for protection but the relatively low resistance values of a 1 dB attenuator should be sufficient protection ... and it has worked well here over the past couple years. Don't always remember to disconnect antennas in time during lightning season, switch antennas with impunity and run kW transmitters on LF with the antennas mere feet apart. The ADC 'clip light' ocassionally lights indicating a BIG signal is present but so far 'no worries'.

MFJ ... dunno ...       

I saturate my A/D all the time since there is an RF amp. I need the amp when on the loaded loops. I wish Mercury designers made the relay default position the 20 dB pad rather than the RF amplifier. This way there would have been additional protection when power is removed and antenna left connected by mistake.