mc@allegra.UUCP (04/13/87)
I've been handling mosfets for a long time now, and this is what I suggest you do-> NOTHING!!! As long as the humidity level in the room is high, meaning, if you can walk across a carpeted room dragging your feet behind you and finally touch ground without an observable static discharge, your safe. The only time problems occur, is in the winter when usually the humidity level is very low. Or possible in a heavely airconditioned area. When the air is dry I do the following. Before handling a sensitive mos device I'll touch ground with my finger before handling it. I limit the movement of my arms to prevent static charge. Also make sure that your not wearing a sweater, especially one made out of wool! I have handled cmos digital chips, ccd chips, along with a variety of small signal(especially sensitive) and power MOSFETS, and I've never blown one out! Maybe I've been lucky or maybe the precautions I take are valid, but nevertheless what I'm trying to say is that people usually over react to these devices. If I had to handle these devices on a daily basic, I certainly would obtain a wrist strap along with a conductive tabletop, but not to simply replace a transistor in a television set. I hope this helps, Mark Cravatts
jeffw@midas.UUCP (04/14/87)
In article <6599@allegra.UUCP> mc@allegra.UUCP (Mark Cravatts) writes: >I have handled cmos digital chips, ccd chips, along with a variety of >small signal(especially sensitive) and power MOSFETS, and I've never blown >one out! Maybe I've been lucky or maybe the precautions I take are valid, >but nevertheless what I'm trying to say is that people usually over react >to these devices. Ah, but how long did they last once they were in circuit? Static damage to MOSFETs not only blows devices outright, but also has a tendency to shorten the life of correctly operating devices. I agree, however, that replacing one device in one's own TV calls more for a little common sense than for massive precautions. Jeff Winslow
straka@ihlpf.UUCP (04/14/87)
In article <6599@allegra.UUCP>, mc@allegra.UUCP (Mark Cravatts) writes: > I've been handling mosfets for a long time now, and this is what I suggest > you do-> NOTHING!!! > > As long as the humidity level in the room is high, meaning, if you can > walk across a carpeted room dragging your feet behind you and finally > touch ground without an observable static discharge, your safe. The > I have handled cmos digital chips, ccd chips, along with a variety of > small signal(especially sensitive) and power MOSFETS, and I've never blown > one out! Maybe I've been lucky or maybe the precautions I take are valid, > but nevertheless what I'm trying to say is that people usually over react > to these devices. Whooooah! I have personally designed, manufactured and tested semiconductor integrated circuits. Yes, people often over-react to static with MANY semiconductor devices. This is because the manufacturers have done their jobs and designed in protection in the input pads of the chips. This is particularly common in integrated circuits, even MOS memory chips and the like. However: Some devices (discrete MOSFET RF front-end xistors) are designed for essentially infinite input impedance. These devices have NO input protection whatsoever, as if they did, their impedance would be degraded. Voltages of as low as 50-100v can and do blow the gate oxides of devices of this type. These voltages are EASY to come by with no protection circuitry to discharge those extra electrons. A perfect SiO2 gate will take up to about 120v/1000 Angstroms of thickness. Most gates are ~~1000 angstroms thick. Moral: Either know very well what you are doing, or be conservative. If the data sheet says >20Megohms input impedance, be *real* careful. BTW, CMOS, and CCDs all have protection on their input pads (it's just a reverse-biased junction to the substrate, and conducts at <30v, providing reasonable static protection), and I believe that power MOSFETs also have them (They don't need ridiculous impedances, like the RF MOSFETs go after). -- Rich Straka ihnp4!ihlpf!straka New word for the day: arithmoquinification. Use it *every* day.
jnp@calmasd.UUCP (04/17/87)
In article <1299@midas.TEK.COM>, jeffw@midas.TEK.COM (Jeff Winslow) writes: > In article <6599@allegra.UUCP> mc@allegra.UUCP (Mark Cravatts) writes: > >I have handled cmos digital chips, ccd chips, along with a variety of > >small signal(especially sensitive) and power MOSFETS, and I've never blown > >one out! Maybe I've been lucky or maybe the precautions I take are valid, > >but nevertheless what I'm trying to say is that people usually over react > >to these devices. > > Ah, but how long did they last once they were in circuit? Static damage to > MOSFETs not only blows devices outright, but also has a tendency to shorten > the life of correctly operating devices. I, too, have handled cmos chips - frequently - just taking care to ground myself momentarily - from time to time. None of these devices has failed in-circuit - some have been in use, daily, for over 3 years now. Most of these precautions apply to an industrial setting - a lab bench is a MASSIVELY more controlable environment. -- These opinions are solely mine and in no way reflect those of my employer. John M. Pantone @ GE/Calma R&D, Data Management Group, San Diego ...{ucbvax|decvax}!sdcsvax!calmasd!jnp jnp@calmasd.GE.COM