Is this setup safe for ESD sensitive devices?

[David_]

Hello.

I regularly sit in my couch and program microcontrollers(µC) and as such I come in contact with all manner of electronics circuits, many of them is not relevant to ESD dangers(What could ESD do to a mechanical keypad or how sensitive do you think and encoder is to ESD) but then we have the µC board, I am manly using an Xplained XMEGA A1 board and a arduino Due.

I have for the past months kept all these circuits on my coffee table which is a wooden structure with a glass "board" laying on top of it, I can't think of any appropriate word for it buy imaging that I have taken a large thick window and layed it on top if a table.

I have found my self having a hard time educating my self about ESD so that I would know what materials to avoid and the only thing I know(apart from the situation of cloth and feet's against carpets and such) is that plastics can be really hazardous which is a shame because you can easily buy boxes for assortments of things that can be very handy but is deadly to sensitive circuits and the ESD-safe stuff is expensive(but I am about to buy two rather large ... with 48 & 60 individual compartments(small boxes you can take out of the ...) all of which is ESD-safe with a connecting cable to earth)

Any way, programming is a really hard task for me thanks to that I have quite severe ADD and sometimes it is straight impossible, but a big part of my problems lately has nothing to do with the software but rather how I manage the physical units(how to position the programmer and target board so as to not break the programming cable through were and tear, and where to put my keypad(s), my encoder, my 4 LCD screens and my 2 Due's.

So to make things easier for me I took a plastic board(I took it from a LCD screen, they always contain a plastic board that is as large as the screen itelf) then I took a large silver color ESD ziplock bag and cut of 3 sides and wrapped that around the plastic board securing it tightly with electrical- & silver-tape.
Here is a picture:





So now I have a nice area to put my things on and I can also easily put it away and set it all up again without having to touch a single circuit, but I am pretty sure that in the state the "ESD-work board" I made is in right now offers very little protection due to the fact that I have no galvanic connection to PE-ground.

But how to attach a cable?
Because I have to connect a cable don't I?

A couple of years ago I secured a storage area by dressing it with those ESD bags that have bubbles in them, and back then I took a rather thick cable, spread out the strands and melted the strands into the silver ESD bag material with my soldering iron, and of course connected the other end of that cable to a single point to which my ESD-matt, ESD bracet and soldering station and then also the areas used to store circuits to 1 single point and connected that point to PE-ground.

But I where never sure about that situation, and that ESD work-board I described is build in a way that makes melting in a cable really unsuitable.

Can anyone suggest how I could attach a cable?
for all I know all I have to do it to stick some copper to the ESD bag with a peace of silver tape and that is all I need, but I want to know if that is ok.

Come to think of it I don't know the principals behind these silver coloured ESD bags, other ESD protection stuff I know about and that I use are conductive but I don't know if the silver esd bag is conductive or if it is insulating...?

Regards

 

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Given that you should keep your static charge below 100V preferably half that if not less especially if you handle any FETs. Given you are using a couch (cloth covered) you are probably generating voltages over 1000V just by sitting down.

Don't think that you can feel 1000V discharge you can't, you have to have something on the order of 3000+V discharge before you may even feel it. Many parts can be easily damaged at 1000V, so that is probably a really bad setup you're using.

ESD bags aren't designed as a disapative work surface, you should really invest in an ESD mat and use an static disapative wrist band (has a 1Mohm resistor for safety, so you won't end up killing yourself). Avoid plastic, paper, styrofoam, wool...you don't want any of that stuff near your ESD sensitive devices. Don't remember the exact numbers but just picking up a piece of paper off a table generates quite a large amount of static charge way over the 100V maximum you want around ESD sensitive components.

Definitely don't work on anything ESD sensitive if the RH goes below 30% you can easily damage pretty much anything no matter how well you're grounded everything at that point.

Those silvery ESD bags you talk about are static disapative bags, they are designed to bleed off charge, if they also have what looks like a mesh then they also have a static barrier (faraday cage).

- - - Updated - - -

edit:
I should also mention that being grounded to earth isn't necessarily the most important thing, it's being at the exact same potential as what you are working with that will keep you from damaging the parts. If you and what you are working on are both at 5000V above ground you won't damage the parts as there won't be any static discharge between you and the parts, but if one or the other changes potential and then you touch the part "poof". Part of the job of a grounding strap (and perhaps a esd lab coat) is to equalize your potential with that of the work surface.

Simple things like setting an esd bag covered board/part on the esd work surface and leaving it there for a short time before opening it is to allow the static charges to equalize. When removing the device/board you want to make sue you keep contact with the esd work surface to prevent a rapid build up of charge (so don't open the bag up in the air and take the board/part out then set it on the esd surface)

 

[David_]

Hmm, I am obviously not very insightful about this situation.

I do have a proper work station with a ESD mat and use an static dissipative wrist band as well as having my soldering station tied to the mat, the attempt shown in my opening post was meant to be used with microcontroller stuff(Arduino's and a Xplained XMEGA A1 board, together with a couple of LCD's of a couple varieties and keypad(s) and encoder(s)).
I have always wondered about these kinds of microcontroller boards, they seem to tolerate quite a lot and I have had a Arduino Due on tables and many places other than my work station.

The ESD bag board was/is an attempt to create some safety in the place where I am more comfortable than at my work desk, programming is such an long and difficult task that I really want to be able to sit in my more comfortable living area.
But it sound as I need to get a second ESD mat(I have considered getting one of the cheaper ones and cut it up into the size I want and then use the same wrist strap as I use at my work desk.

The subject of ESD has been bothering me for a long time now, because I have spent time reading documents on my free time as well as the material they required me to read while visiting a electronic manufacturing company where I spent a week helping out with the most boring tasks. Even though it was boring it was great to get to see how it is done in an manufacturing environment.

I have found a add at ebay from the UK for a ESD mat that I will buy for use instead of that ESD bag board.

Regards

 

[ads-ee]

I have always wondered about these kinds of microcontroller boards, they seem to tolerate quite a lot and I have had a Arduino Due on tables and many places other than my work station.

That's probably because it's not unusual for the I/O of such a board to become degraded due to ESD but still functions. As you probably aren't running the I/O with critical timing to/from something else at the highest clock frequency possible, you wouldn't notice the degradation in performance.

- - - Updated - - -

Here is a nice series of forum posts on another forum that reiterates what I've already posted.

https://hardforum.com/threads/esd-truths-myths-and-flat-out-lies.812518/

 

[BradtheRad]

Can anyone suggest how I could attach a cable?
for all I know all I have to do it to stick some copper to the ESD bag with a peace of silver tape and that is all I need, but I want to know if that is ok.

Metal tape is available in hardware and automotive stores. I tested it with an ohmmeter and I found it is conductive. If you compress the cable, tape, and bag together, they might make contact sufficiently to do the job.
Edited to add: On second thought you might as well try plain aluminum foil instead of the tape, because it's not likely the adhesive is conductive.

The best (although expensive) stuff I've seen to make the odd electrical joining, is (a) silverized epoxy or (b) conductive silver liquid in a pen (CircuitWorks or CircuitWriter). They're great for wiring solar cells, headphone transducers, and non-solderable metals. I had both types solidify in the tube after a few years, so avoid overbuying.

The epoxy is more robust, but also more brittle. So to paint a silvery film on a flexible bag, the conductive pen should be better.

 

[David_]

I will check those compounds out, they sound useful.

Regarding the degredation of microcontroller I/O's, I am designing my first system which will need some pretty exact timing and will contain a microcontroller, a Complete DDS IC and some data converters as well as a few opamps.
The microcontroller will use an internal USB tranceiver, but I have picked out a USB ESD protection IC to protect that.
Not that I have any plans on being wreck less with this board but it will be some time before it will get a case of some sort, and I will be working at my protected work desk while testing the prototype.

But still I wonder if there are some other protection I should include?

Oh I should say that the design is for a LCRZ-Meter and I would think that the analog front end will be very exposed but thus far in my research I haven't found any reference to input port protection.

What do you think about that?

 

[BradtheRad]

Oh I should say that the design is for a LCRZ-Meter

Inductors can produce high voltage spikes when disconnected from current abruptly. The effect is worse when Amperes and Henry value are large. Consider this as you design the front end, and your testing algorithm.

 

[David_]

I would like to talk more about this LCRZ-Meter aspect but I'll continue doing so in my LCRZ-meter dedicated thread.