Date: 19971121 To: ChipDir Mailing List From: Tinco Brouwer Subject: Antistatic (was: Re: yet these strange..) At 07:21 21-11-97 -0800, you wrote: >I agree. I have found that liberal use of common domestic anti- >static products (the kind that women spray on their slips) helps >enormously. Also, I do all my assembly work over a large terry- >cloth bath towel that has been washed with an anti-static additive >(Downy, I think) and dried with one of those no-cling sheets in the >drier. I reguarlly hose down my carpets and work benchs with anti- >static spray. > >Besides, nearlly all CMOS devices have protect circuits on sensitive >pins. > >I think it is important to handle bare chips carefully, but once >the are socketed they are pretty safe. > > Bob Smith When you use often static sensitive parts, it can be cheaper and more reliable to use an antistatic mat (conductive mat to lay on the worktable) and a grounded wrist strap. Soldering iron has to be connected to ground also. With a modern static safe soldering iron (like the Weller EC2002) this is no problem. The older Weller Magnastats have a on/off switching of the heathing element for temperature control that causes transients. Here it has killed quite a lot of cmos. All ground connections for static electricity should have a series resistance (100k..1M) to limit the discharge current and for safety. With a direct grounded wrist it is possibly deadly when the other hand touches 230V or whatever mains voltage is used. A good antistatic mat can withstand solder drops and they can be removed simply. How about that with a towel? Perhaps when it is soaking wet. The antistatic mat is of course not isolating. When a pcb under test is lying on this mat strange effects can occur because the surface resistance. Sometimes it has a strange frequency dependent capacitance too. Many databooks have a chapter about static electricity with lots of info. Regards, Tinco Brouwer, Afdeling Elektronica, Faculteit der Biologie, Vrije Universiteit, Amsterdam (Nederland).