Static discharge destroys?

[bassmeister]

I thought about having a go at building Joe Davisson's Obsidian the other day, so I bought the 3 BS250 MOSFET:s needed. The guy who sold them to me told me that I needed to be extra careful when handling and soldering the MOSFET:s, since they are more sensitive to static discharge than other active components.

I still haven't managed to destroy a component by being incautious. I never take precautions against ESD. However, I haven't worked with MOSFET:s before. Are they really more sensitive than other components? Would you suggest that I don't work with MOSFET:s on breadboard?

[Ge_Whiz]

Like most modern components, MOSFETs are nowadays much less sensitive to static than they used to be. Many have protection diodes built-in internally, and I have never managed to destroy one by handling it.

I do take a few precautions: I keep the legs tied together electrically (e.g. using antistatic foam) until the last minute before soldering; I use a soldering iron with an earthed bit; I always earth myself just before, and try not to fidget whilst, handling them; and I try not to touch the wires (especially the gate) more than I have to.

When I solder them in, I solder the surrounding resistors in place first. However, I no longer bother to solder them in after the rest of the board is finished, just as I come to them. FYI, I nearly always build on stripboard.

[Peter Snowberg]

Static can easily degrade or kill and MOSFET or CMOS device. If you observe static safe procedures, in most cases you don't ever have to worry.

If you live in a climate with lots of static electricity, you need to be more careful than you do if you are living in a high humidity climate with low static.

The standard solution is to attach a 1 meg resistor to a good ground connection and then clip that to a metal watch band. That will remove any static and the 1 meg resistor safely limits current so you don't have something really bad happen if you become part of the power supply.

When working on static sensitive parts, the best is to use a static dissipating desk mat in addition to the wrist band. That keeps everything very safe.

Once you get a protection diode installed from the gate to the rest of the semiconductor, it is much less fragile.

Soldering can be tricky too. You need a grounded low voltage iron to be totally safe. An ungrounded iron powered by the mains will emit enough energy to damage some MOSFETs.

Another type of iron that is a problem here are mains powered units with phase-delay style dimmers to control the temperature. These make big voltage spikes.

If you don't have a MOSFET safe iron, you can heat up a normal iron, unplug it, and quickly solder your connections before it cools.

[puretube]

I like socketing those kinda ICs instead of soldering`em in
(yeah - the tubehead again...  :lol: )

[Joe Davisson]

I would breadboard a single stage and test the transistors to make sure the drains are somewhere between 4 and 5 volts. Adjust the drain resistors to get it close. If they all work there, then they should work in the final build. Beware that the pinouts are the reverse of most typical transistors (like 2N3904).

I've blown some BS250s, but my flannel shirt is probably mostly to blame They are a bit more expensive than other MOSFETs, so some extra precaution isn't unwarranted. Good luck with the project.

[bioroids]

Hi!

I destroyed several 2N7000 by soldering, don't know if was the heat or the static, most probably the static. Does the 2N7000 have internal diode protection?

Luck

Miguel

[bassmeister]

I guess it's time to invest in some more and better equipment. Right now the only tools I have is set of pliers, a breadboard, a DMM and a soldering iron. You can get far with that, but I only like electronics when things run smooth. I really hate trouble shooting... :x I always double check a component before mounting it, even the rotation of resistors  

Thanks!

[formerMember1]

i just got  two huge orders from smallbear and mouser and alot of my chips and transistors came in a silver anti-static sealed bag.  Does this mean i have to be extra careful, or is it just a little added protection for shipping?

They are transistors for a fuzzface, and chips for a TS9DX.  Can i really blow the thing out easily if i rub my feet on carpet and touch it or is it a precaution?

Should i solder them in my bathroom when it is really steamy?(i heard this somewhere)

Should i go out and get one of those anti -static wrist bands?

finally,  How do i know if my soldering station has a grounded tip?
(it is a Weller WLC100)(the same soldering station as Tonepad has pictured in his photo essay for changing TS9 chips)

In total i have about 30 transistors/1 chip that came in antistatic bags.

[davebungo]

1.  You should always be careful handling semiconductors (it makes sense to treat all electronic components that way so it becomes a routine way of doing stuff) - always assume that they are sensitive and handle accordingly.

2.  Don't even think about rubbing your feet on any carpet - OK you can't help walking on them.

3.  Steamy bathrooms and mains electricity = potential danger - don't go there.

4.  Yes, buy a wrist band - but you need an earth point to connect it to.  Also be aware that if you use a grounding floormat that this can be potentially hazardous (to you!) in itself since you would normally want to insulate yourself from ground if dealing with mains voltages rather than make yourself a "good conductor".  An earth leakage circuit breaker is essential in these situations I would have thought.

5.  The spec. on the literature should tell you if it is earthed - otherwise wait until it is cool, unplug it from the mains and test it with a meter.

[Paul Perry (Frostwave)]

Some people tie the 3 legs together with fine wire, then solder the fet in, then unwind the wire. Also, put the fet in last (st that, when it is put in, ther eis some resistance connected between all the legs via the circuit).
I have never had fet trouble.. but Melbourne Australia never has humidity low enough to cause static trouble. It just doesn't get cold enough here.

[Connoisseur of Distortion]

kind of off topic, but are TTL units static sensitive?

[Dave_B]

If you don't have a MOSFET safe iron, you can heat up a normal iron, unplug it, and quickly solder your connections before it cools.

Sounds like the perfect application for a stompbox switch.  

[Paul Perry (Frostwave)]

kind of off topic, but are TTL units static sensitive?

No. At least, not to the extent that you will damage them while soldering.

[MR COFFEE]

Folks,
I have posted about this before, as have others here.

If you search for information from semiconductor manufacturers on it, you will find that even bipolar transistors can be damaged by static discharge. Yeah, even TTL too, to some degree, but it isn't very likely to be a concern unless you are breadboarding in Arizona in January. People there get paranoid for good reason - you can walk accross a carpet and draw a half inch spark off a doorknob - no joke!

The wristband is ideal, but the most important thing is not that it is connected to "earth", but that your body\soldering iron\component terminal\circuit board is at the same potential as the circuit node you and\or your soldering iron are about to touch. It takes REALLY static-sensitive devices to be damaged by your average soldering iron if you touch it to the ground of your circuit before you solder a component.

Unprotected MOSFET gates - yeah, they are quite vulnerable. Even if you don't destroy the functionality of the device, you can degrade parameters significantly.

Let me mention a couple others that are likely to be seen around here - CMOS ICs and Analog Delay ICs, especially the fine-geometry ones (small internal IC features). CMOS are often percieved as "rugged." Well, the first ZAP takes out the protection diodes, the device still works; the second ZAP takes out the chip which is usually soldered in by then. Sockets aren't a bad idea and they are really cheap.

JFETs, bipolar trannys, JFET-input op amps are vulnerable to a MUCH lesser degree. Just touch the chassis before you touch the pcb or touch the ground of the breadboard before you pick up the device (which is already resting on a piece of anti-static foam connected to the ground of your circuit, get it?) and I can't imagine you having a problem.

And understand, and be aware of, the triboelectric generation process - i.e., like the old rub-a-piece-of-plastic-rod-with-fur-and-it-will-pick-up-little-pieces-of-cork deal. Walking across carpet, especially synthetic fiber carpet, and similar processes generate static electricity, which can be a problem IF THE HUMIDITY IS LOW SO THERE IS NOTHING TO NEUTRALIZE IT. High humidity works pretty well. RG recommends a boiling tea kettle if the humidity is low... makes sense to me. And be aware of highly NON-conductive surfaces that are prone to static build-up. Like, ferinstance, those d*mn styrofoam peanuts that everything gets shipped in these days. They stick to your hand because the humidity isn't high enough to neutralize the charges that build up from the d*mn things tumbling against each other rolling around in the box. OK?

But if you walk across the room, scratch your chest with a nylon sweater on, or whatever you do that generates static charge, all you gotta do is just REMEMBER to touch ground so it dissipates any static charge you have acquired just BEFORE you touch a static-sensitive device. YOU conduct electricity quite well. That's how us humans can get electrocuted so easily when we do dumb sh*t. But you also have a significant amount of resistance, so you body can equalize static potentials quite well without destroying devices (i.e., between a device stuck in black foam and the ground of your breadboard). That means, among other things, don't STORE your MOSFETS, CMOS ICs, or any other semiconductor device in plain styrofoam (because it has VERY high resistance and therefore doesn't dissipate static charges that happen to land on them from dust motes and such), plain plastic boxes (unless the pins are stuck in conductive foam FIRST), and so on.

Clear I hope.