Shootout: Antistatic ESD Wrist Discharge Band Grounding Prevent Static Shock Red vs. Pollin ESD Wristband vs. Vermason (WHL #3)
Today, I have some ESD wrist straps ready for testing. While everybody in electronics is aware of the magic smoke escape problem (once it’s gone, it is very difficult to fill it back into your IC), electrostatic discharge (ESD) protection isn’t always first priority. I do save you from links to an east european “hacker” that employs high standards in this area However, I’d like to link to NASA and the chip manufacturer Maxim that have some helpful sites about ESD. And, trust me, they do care about reliability of their products – which is why they do their best to prevent component defects or weakening by ESD. FEI, a company that sells scanning and tunneling electron microscopes, also has some nice pics on their flickr account, but just for the looks (and demonstration of their fine equipment – I did use their excellent Titan 300-80 S/TEM two years ago).
So, how to prevent ESD damages in your (home) lab? Wear some form of ESD protection gear! I like the wrist straps for their ease of use, but others may prefer shoe straps or wearing semiconductor plant bunny suits (I think there might be a photo of me wearing one somewhere on the interwebs…)
A long long time ago, mid-2011 to be precise, I upgraded from my first cheapo wrist strap to a proper one from Vermason (an UK brand that specialized on ESD equipment). One month ago, I somehow had the urge to measure the resistance from my protected hand to ground. And I had difficulties getting some number at all – all I knew was that my setup is far away from 1 MΩ. I never thought these straps would wear out – but apparently, they do. So I immediately ordered some replacements: One from the Wan Hung Lo factory in Chaina, and a (very similar…) one from the German electronics shop Pollin. Both have arrived and I’ll of course include my old Vermason gear for reference.
1) The China strap, original image:
Bought via eBay for 2,65€ (delivered) in January 2016
2) The German-China model from Pollin, costing just 2,95€ as part of a larger order (also January 2016), part number 511 121
3) The respected brand model from Vermason, sold by Farnell, costing roughly 21€ back in 2011 (plus VAT, minus student rebate at that time, they don’t offer it anymore and are some dicks that disable customer accounts without notification, maybe I’ll post a full rant about it some day). Original model was JA68Y, which is a set of wrist strap and ~2m coiled cord with the resistor in it. Haven’t found that on the website, replacement should be part no. 229765 / JA48Y, costing around 4 GBP and 230170 / J4211Y for the cord, adding another ~6 GBP, which is something like 13€ in total. But hey, I wanted a yellow ESD strap
While I cannot provide pics for the new Vermason strap, I do have some from the others ready:
Putting the wrist straps on looks like this (my naked left hand is now on the internet):
Notice that the China band is already at max length, so that is just fits my wrist. If you are not as white and nerdy as I am, this is probably too small for you. The Pollin one is a bit more loose (pic 3 shows comfortable setting), and the Vermason band is even longer. As it does not have a clamp to secure the band in the shorter setting (just friction fit), this one will get loose over time, which, well, can be annoying. And as described later, a tight fit might drastically alter your contact resistance.
All of the wrist straps are comfy to wear, there are no itchy bands, no sharp edges of the metal contacts, everything is fine.
Next up: Measuring the internal resistor of the cable. While you only need to be in the MΩ to GΩ ballpark (not conductive, not isolating – slow charge dissipation), the Wan Hung Lo factories decided to gild the Lilly: 0.999MΩ and 1.000MΩ, while the guys from Vermason slapped in whatever they had lying around: 1.06MΩ. Nice try, but unnecessary precision (and maybe cost) in here. Chinese, pff..
Measuring the wrist part resistance is a bit more tricky. Of course, the connection of the metal part to the 10mm stud is a dead short, but is the band really conductive? It is, see the following images: (right hand is now also public)
It’s no problem to alter the resistance by an order of magnitude when measuring the very same spot. So I’m very interested to know how that is done in the industry. If you have some information, please share it in the comments below!
Measuring the Vermason strap is a bit hopeless — only a very thin strip around the plastic part is still conductive enough (<40 MΩ) to produce any results. It is then in the same order of magnitude as the other two wrist straps, but you won’t touch these parts during usage, so the strap is basically insulating. Bummer.
Note that I tried to touch only one part of the circuit with my fingers, as otherwise this would have added a parallel circuit (hand-body-hand-multimeter lead) that alters (lowers) the measured resistance.
Moreover, I repeated the tests while actually wearing the wrist straps, just touching the other multimeter lead while being plugged into the COM socket. Interestingly, this does not yield 1MΩ plus something…it’s already in the 20-40 MΩ region, which is why my Uni-T 203 can barely display some values. These measurements are very touchy, adjust your strap and the result might change by a factor of 2, as seen in the last column where the China band is tested (first col is Vermason, second is Pollin). Also, my old Peaktech 2010 does give a quite stable reading for the Vermason set…in the order of 790-815 MΩ. I don’t trust this result, but at least there is a chance that I haven’t been silently ruining electronics for the last few years, as I was technically still somewhat connected to GND
Still, I’m not sure why these results are so much above the 1 MΩ built-in resistor. Skin contact should be from 1 kΩ to 1 MΩ (depending on contact pressure, air/skin humidity, temperature, personal hygiene :lol:, …), so where is the extra 10++ MΩ coming from?
Last thing to note is the quality of the cords. These are shown below and again, both cheapos are virtually the same, the China one is a bit more matte than the item from Pollin. I stretched all cords prior to taking this photo, and while I’m not a Michael Jordan, I can manage 1,8m wingspan for the curly part. Upon release, you can clearly see the cheap cord rolling up (they do 2-3 twists and unwind within a few seconds, hard to take a photo of it) Like telephone cords, this might annoy the hell out of you. The Vermason cord is a bit thicker and doesn’t give a f ck when stretching/relaxing – this one is just solid and worth the money.
Same goes for the ends of the cords: The Vermason does try to make contact to the inner and outer ring of the 10mm stud (slight construction differences on the wrist strap as well), while the others just care about the outer contact. Strain relief is also much better on the Vermason model, as the others are made from very hard plastics that doesn’t allow much flexing at all – until the relief ends and the cable will break exactly there. Again, same thing on the 4mm banana plugs: Just look at it. Four slotted metal contacts with the springiness of a bag of rice at the Wan Hung Lo factory canteen. They do slip out during use, and I don’t have to tell you how useful a wireless ESD strip actually is (Dave did a video about it, in case you really don’t know). Vermason has a proper 4mm plug that connects nicely and does not get loose. Quality wins, Wan Hung Lo loses in this case.
So…what would I recommend? Actually, I will use one of the cheaper wrist straps to see how they perform over some months of use and abuse. I won’t immediately order a new one from Vermason, only if both other straps fail in a very short period of time. However, I will scrap the cheap cords and use the Vermason one instead. So basically, while I would recommend a full Vermason (or $qualitybrand) set if you got the money AND find a shop that sells these, I think getting a cheap wrist strap will do if you find a quality cord for it. But don’t ask me on China cords, I haven’t had the need to buy a separate unit yet.
I haven’t said a word about where to plug the cords — I have a DIY mains plug adaptor with 4mm jack at the end (and no mains voltage ), if someone wants me to give a quick teardown of that unit, just let me know in the comments. Vermason sells these for a beefy price, and I haven’t found cheapos from China back then, maybe they do offer them as of today, I haven’t checked.
Don’t miss the fake Wan Hung Lo PCB next time!