Beginner: handling electrostatic sensitive components

[nyoo]

Hi.

Just bought my first soldering iron, perf board, and ordered some electronics components. I'm raring to go! But then, some components came in bags that said I would destroy the components if I touched them. I kinda knew this in theory, but now I'm faced with it in practice.

A quick google told me -- as most of you know -- you have to ground yourself, prevent the components sliding, and wear cleanroom gloves. It looked like cleanroom gloves are made of "vinyl"; that is, of PVC.

So, two questions.

If I wear disposable "doctor exam" powderless PVC gloves, it that enough to prevent damage due to electrostatic discharge?

Clear food packaging and shampoo bottles are also made of PVC. I want to keep the finished circuit board dry. Could I box the circuit in a food-storage container made of that thick, slightly pliable, long-lasting plastic? I mean, could I use a sandwich box, with a hole drilled for Vin and Vout?

Thanks a lot for your patience with a total beginner.

 

[crutschow]

A quick google told me -- as most of you know -- you have to ground yourself, prevent the components sliding, and wear cleanroom gloves. It looked like cleanroom gloves are made of "vinyl"; that is, of PVC.

If I wear disposable "doctor exam" powderless PVC gloves, it that enough to prevent damage due to electrostatic discharge?

If you're just working on standard IC circuits you generally don't need gloves. They're usually only used when working on critical, high reliability parts. "Doctor exam" gloves are likely not conductive and could actually generate the static electricity you're trying to prevent.

Clear food packaging and shampoo bottles are also made of PVC. I want to keep the finished circuit board dry. Could I box the circuit in a food-storage container made of that thick, slightly pliable, long-lasting plastic? I mean, could I use a sandwich box, with a hole drilled for Vin and Vout?

Standard plastics are generally bad since they can generate and hold static charges. If you need to store the circuits, the package needs to be conductive plastic. It's especially made for this purpose and is usually black or a reddish color plastic.

The main thing is to ground yourself to the work surface with a wriststrap. They sell wrist straps and conductive work mats designed for this. Always put the strap on and connect it to the mat before touching the circuit. If you transport the circuit, it's desirable to place the circuit in a conductive bag. If not, touch the surface you are placing the circuit on before you touch the circuit to the surface. This will equalize the boards static with the surface. The idea is to always have everything at the same potential so no static discharge can occur. It doesn't necessarily need to be earth ground, just that everything is at the same voltage.

 

[mneary]

Good advice from crutschow. Further, to limit electrostatic problems, humidity is your friend. Moisture causes problems at really high temperatures, but at normal temps it helps a lot with esd.

Vinyl, polyester, and PVC accumulate surface charges which kill everything.

 

[kchriste]

But then, some components came in bags that said I would destroy the components if I touched them. I kinda knew this in theory, but now I'm faced with it in practice.

Sometimes components come shipped in static bags even though they are immune to ESD. I've had resistors delivered in ESD bags with the warning sticker sealing the bag. So it pays to know which parts are static sensitive and which are not. Most ICs made today are static sensitive because they are usually CMOS. It pays to read the datasheet.
In general, if you have a static mat and a wrist strap connected to ground you will be pretty safe. You don't need the gloves.
All that said, all I do at home is touch a grounded object once I'm sitting at my work bench to remove any charge built up from walking around. I don't use a mat or wrist strap. But I live in a relatively humid climate and your environment may be different (different socks, chair, carpet, humidity, etc).

 

[dknguyen]

I find the biggest problem is the chair you are sitting on as you slide on and off to get up and sit down. I would think PVC gloves would INCREASE the static build up than reduce it. I keep my components in a metal chocolate/cookie can/jar/container/box.

Who knows? they could have been state of the art 3-terminal, CMOS semiconductor resistors.

 

[ericgibbs]

hi,
A couple of extra things you can do.

Get a polystyrene ceiling tile, about 12in square, cover it all round with aluminium kitchen foil, connect the foil to ground thru a 470K or 1MO resistor. [use sticky tape to hold the foil and ground wire in place]

You then place your ESD sensitive components on the foil, you can also push the pins of the component thru the foil into the tile.
So every time you pick up an ic, you automatically ground yourself.
If you push the pins thru the foil, it also holds them in place as you put the tile to one side.
When you are building a project you can group the components on the tile and keep them tidy, bit like a hedgehog.

Also wrap conductive foil around the soldering iron handle and ground it thru a 470K or 1M0 resistor,
every time you grab the iron you are grounded.

Do you follow.?

 

[nyoo]

Thank you all for your help.

If you could, please, your answers led to a few further questions.

For crutschow and dknguyen: what's the conductive plastic generally used to box small (3" x 4") circuits? Can I use electrician's common plastic junction boxes? Or dknguyen's small metal boxes, plugged with silicone at Vin/Vout to keep damp out, and grounded?

For mneary: I have a damp basement. Seems like a place with automatic grounding. Would a wooden table in the basement work, as a work bench?

For kchriste: I'm not trying anything fancy, for a first project. The components marked with the ESD warning are a couple of opamps (UA741, LM293), a couple of mosfets (IRF540A, HUF75337), a diode (1N4148), and a temperature sensor (LM235). Are these in your "bagged for ESD but really immune" category? I'm especially disappointed about the LM235 temperature sensors, because I want to place these at a distance from the actual circuit, between some rubber and wood. Any suggestions here?

To ericgibbs, Thanks. I'll make your foil pincushion. For the soldering iron, I guess the foil will be attached to a length of some 22-gauge copper wire? What's the resistor for?

Again, thanks all.

 

[ericgibbs]

To ericgibbs, Thanks. I'll make your foil pincushion. For the soldering iron, I guess the foil will be attached to a length of some 22-gauge copper wire? What's the resistor for?

Again, thanks all.

hi,

Thats to limit any current passing to ground thru the resistor to a safe limt for your body..You MUST use a high value resistor.

Consider you accidentally touched a mains point, with your left while working on say, a mains power supply and you were holding the earthed soldering iron in your right hand... Goodnight nyoo....

It also acts to discharge any static that your body/clothing has built up, slooowly, so that you dont get a rapid discharge.

There have been a number of forum threads regarding SAFE earthing of your workbench. Look thru them.!!!

Does this answer your question, if in doubt regarding any electrical safety topic, ask the forum.

 

[crutschow]

For crutschow and dknguyen: what's the conductive plastic generally used to box small (3" x 4") circuits? Can I use electrician's common plastic junction boxes? Or dknguyen's small metal boxes, plugged with silicone at Vin/Vout to keep damp out, and grounded?

For kchriste: I'm not trying anything fancy, for a first project. The components marked with the ESD warning are a couple of opamps (UA741, LM293), a couple of mosfets (IRF540A, HUF75337), a diode (1N4148), and a temperature sensor (LM235). Are these in your "bagged for ESD but really immune" category? I'm especially disappointed about the LM235 temperature sensors, because I want to place these at a distance from the actual circuit, between some rubber and wood. Any suggestions here?

The plastic electrician's boxes are likely not conductive. The boxes I referred to are especially built to store sensitive electronic parts. The metal boxes would work fine. As long as you're grounded when you pick them up, the boxes don't have to specifically grounded all the time. You also could put devices or circuits in a regular glass or plastic jar or box if the devices are in an ESD bag. In general, leave devices in their ESD bags until you use them.

Incidently, the wrist straps designed for grounding your body also have a high value resistance in them for safety. Never ground yourself without this resistor. Radio Shack and others sell such wrist straps.

Most semiconductors, and especially MOSFET devices, should be considered ESD sensitive and handled accordingly. There's not a problem placing the LM235 a long distance from the circuit as long as it's connected and the leads are insulated. The danger is when the leads are not connected or exposed and can come in contact with a static source.

 

[ericgibbs]

Look at this for solder iron grounding.

https://www.pbase.com/sinoline/image/89894276

Courtesy of Rolf

https://www.electro-tech-online.com/threads/what-do-i-connect-wrist-strap-to.34322/?highlight=ESD

 

[nyoo]

Thanks again, all.

To ericgibbs: Yes, I follow. I've now read some of the electro-tech-online threads on ESD, and also found me a couple of 470K resistors.

But 2-3 further questions I'm finding hard to ask, so please bear with me.

When my perfboard-based circuit is complete, it needs to be protected. For this project, which is a thermostat in an outdoor shed, it needs a slightly weather-proof box or container. The container could be a glass jar with the circuit glued to its side and a hole drilled in its lid. It could be a metal box you buy mints in, wrapped shut with electrician's tape, with the circuit raised up off the metal on polystyrene cubes. Or it could be some humidity-proof plastic container sold openly -- only I can't see it -- in every electronics parts shop.

In what could I safely house a circuit, away from ESD and moisture?

And what is such a container called, so I can find it in future?

And does the negative terminal of the power source act as a ground, for such a container?

Thanks.

 

[crutschow]

When my perfboard-based circuit is complete, it needs to be protected. For this project, which is a thermostat in an outdoor shed, it needs a slightly weather-proof box or container. The container could be a glass jar with the circuit glued to its side and a hole drilled in its lid. It could be a metal box you buy mints in, wrapped shut with electrician's tape, with the circuit raised up off the metal on polystyrene cubes. Or it could be some humidity-proof plastic container sold openly -- only I can't see it -- in every electronics parts shop.

In what could I safely house a circuit, away from ESD and moisture?

And what is such a container called, so I can find it in future?

And does the negative terminal of the power source act as a ground, for such a container?.

It's the individual components that are particularly sensitive when the are not connected to anything and their leads are exposed. Once they're in the circuit, they are generally less sensitive since the connections tend to provide paths to grounds for any static charges. The main concern is any leads coming off the circuit board.

Power supply leads are usually not a problem since they normally have large filter capacitors to ground which absorb the static.

If you have signal leads coming off the board, it is good practice to add some small resistor in series with each lead and a small capacitor to ground (if it doesn't adversely affect circuit operation.) Even 1000pF will absorb a lot of static discharge, but more capacitance is better.

If the circuit leads are reasonably protected than the container is not so critical. For example, I doubt that most standard electronic devices have a static dissipative housing. The boards inside are just isolated from the housing and the I/O's are protected so there's no problem.

Most electronc supply places, sell various types of electronic plastic or aluminum housings which should be fine for your circuit. (See **broken link removed** for example),

Normally you would have one of the power terminals going to ground (ground connection on the power plug, if available). That keeps everything near ground potential.

 

[kchriste]

For kchriste: I'm not trying anything fancy, for a first project. The components marked with the ESD warning are a couple of opamps (UA741, LM293), a couple of mosfets (IRF540A, HUF75337), a diode (1N4148), and a temperature sensor (LM235). Are these in your "bagged for ESD but really immune" category?

Yes, they are all immune to ESD except the IRF540A & HUF75337 MOSFETs. Junction devices such as diodes, NPN & PNP transistors, bipolar OpAmps & ICs are immune to ESD. ICs that use MOSFETs are vulnerable to ESD. Once you put the MOSFETs (Or CMOS ICs) in a typical circuit, you won't have to worry about ESD for them either.

Who knows? they could have been state of the art 3-terminal, CMOS semiconductor resistors.

Na, it's just that the shipping dept only has those bags so they use them. Or maybe they don't train the warehouse people to distinguish which parts are vulnerable to ESD so they have a blanket policy of treating all parts as ESD sensitive.

 

[crust]

MOSFETs are particularly subject to ESD damage, because their gate impedance is practically infinite, so it can easily build up charge and destroy the part. In circuit, you should always make certain you have a reasonable path to ground for the fet gates.

 

[ericgibbs]

hi nyoo,
A sandwich box would be OK, use your solder iron, [with an old bit in] to make any holes you need for your inp/out wiring.

A useful moisture barrier which is overlooked is kitchen cling film.
Many people think that cling film clings, because of static electricity, this is incorrect.
The film is sprayed with a very light film of glue during the manufacturing process.

If you have a small pcb that you wish to protect from moisture,
wrap it it a few coils of cling film then using your girl friends hair dryer carefully heat the film.
Any wires to and from the pcb can be passed the thru edges of the film sheet and if required can be tied with lacing cord.

Before my peers throw their hands up in horror, I have used this method on marine and outdoor projects and it works.

Advantages are you can see any LED's thru the film and its easy to replace after any repair.

 

[nyoo]

Thanks all. You've all been an immense help. You've given me enough to go on.

One thing I missed, until a second reading, was that ericgibbs' design for an aluminium benchtop anti-static mat makes it unnecessary to buy a flooring anti-static mat. I'll ground my wrist wire and the aluminium benchtop wire to the screw that holds an electrical outlet cover in place. Usually, here is the US of A, they're earthed.

Been a while since I've met a hedgehog.... Resistors will have to serve.

 

[ericgibbs]

Thanks all. You've all been an immense help. You've given me enough to go on.

One thing I missed, until a second reading, was that ericgibbs' design for an aluminium benchtop anti-static mat makes it unnecessary to buy a flooring anti-static mat. I'll ground my wrist wire and the aluminium benchtop wire to the screw that holds an electrical outlet cover in place. Usually, here is the US of A, they're earthed.

Been a while since I've met a hedgehog.... Resistors will have to serve.

hi nyoo.
Promise to fit a 470K or 1M0 resistor in series with any earthed mat/iron or wrist wire and the ground connection. OR else.

Lets know how the hedgehog works out, use a fibre tip pen to mark out areas on your foil, that identify the passive component values, it saves a lot of during assembly if you preload the marked areas with the components.

The foil mat is handy for your precut wire links/jumpers.