Do ESD handtools and basic ESD work area grounding habits defend against CDM? - Page 1
Forum section: electronics / beginners

author: fortunamatada
author_rank: Newbie
timestamp: April 03, 2019, 06:18:48 pm
content: Due to multiple concurring annoyances, I have at last decided to go big and sink some real money on good screwdrivers. The screw driving activity I partake in is always computer related with the occasional pro-bono replacing of an elderly relative's phone battery, etc... After having far too much of my time wasted by a site that I pay to have a...Main...membership with in order to get yet another in an endless set of precision screwdriver replacements, I was done. Luckily in time I found sites like this and learned of the magic of Wera and Wiha. While this was going on, I finally took a mechanical keyboard that had a short in one its USB cables (the one that powered the LED and keyboards, not the pass through I never used!) to begin repairing. Opened it up, and saw a normal looking 4 wire usb cable with it's short under all of the nylon and shielding that then terminated into a 5 pin JST with half-ish the shield making the 5th termination into the JST with the other 4 usb wires while the other half of the shield went to a ring terminal ground??? inside the keyboard chassis. Researched every place I could think of online, learned as much as I could about ESD and how previous models of the thing would shock people, etc... I did not want to do an incomplete repair job by not having the new connection have the same odd shielding split just to have the keyboard's actual death by static a week later despite doing all of that work on it.Seeing that both brands I am going to choose from have esd versions I figured, why not get those. I have never been overly worried about ESD, but at the same time I always wear my wrist strap at least, use my ESD mat with its wall plug at home or a place my multimeter confirms the bottom hole is actually ground, and lock up the cats. One more layer of effortless protection on my end with ESD tools is just dandy. Then I ran across the Charged Device Method test which I had never heard of and, if I understood the explanation (it goes way beyond my circuit knowledge pay grade): tools, even those that have legit ESD materials for their handles, can still retain a charge in the metal bit even after what you think would be an action proper enough to place the entire tool, yourself and the component at a grounded state, but it doesn't and just zaps the home server you know and love anyway? Is my interpretation of the situation close at all? If the added cost of the ESD screwdrivers is literally worthless according to the group that certifies things as passing their esd test or not, then I'll just get the normal versions. And curious to know just for the sake of knowing. Any illumination would be greatly appreciated!

author: capt bullshot
author_rank: Super Contributor
timestamp: April 03, 2019, 06:45:48 pm
content: Basically, there's two kinds of "ESD material" - the kind that is conductive and so actively discharges anything, and the kind that is just anti-static, which means it doesn't accumulate charge, but does not discharge anything through itself.For the first kind of material, it's quite important that the material is only "slightly" conductive, say it has a relatively high resistance, not low impedance as a piece of metal. Discharging a charged object through a low impedance path causes a high current transient, and you don't want this to happen to your electronics.So basically touching the PCB traces of e.g. a computer mainboard with a charged piece of metal is quite an evil thing one can do. This can happen under certain circumstances, e.g. if an isolated piece of metal is in contact with material that tends to accumulate charge. One can find stories of some kind of machine destroying each and every piece of electronics that was handled by that machine, because the machine wasn't grounded. And though everything else around was set up perfectly ESD safe.In my experience, a simple screwdriver held by a human doesn't act that evil, no matter if it is an ESD safe or an ordinary one. Anyway, to be sure, you just can touch the tip of the screwdriver with your hand to discharge it. And you can touch the chassis of the server you're working on to discharge yourself. That's the usual recommendation, and it's sufficient under common circumstances.