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I live in a very old house that has no PE in it, so I can't ground the tip of the iron and myself as I should to solder in a ESD safe way. Is there any method to improve ESD safety of soldering, when I work with static sensitive components? I have the following idea, and I would like to know if it make any sense:

  1. Connect the tip of the iron (run a wire from the PE pin of the iron inside the soldering station) to ESD mat through 1 MOhm resistor
  2. Connect myself to the ESD mat using a wrist strap that comes with it

A 1MOhm resistor between me and the mat and thevsoldering station should prevent electric shock in case of some disaster inside the soldering station. My potential, potential of the iron, potential of components on the table and PCB I work with should be the same. Right? However we are floating together and we are not grounded.

Questions:

  1. Is this any better then ignoring ESD safety and just hoping for the best? If I leave tip of the iron floating I see a distorted sine signal on the tip of the iron with the scope. Freq: ~60Hz, peak-to-peak: 50V.
  2. What extra safety risks does this approach bring (remember, baseline is a house without PE, this is already not very safe.)
  3. Do you have a better idea how to improve ESD safety in this situation? Building my own PE is not an option - 5th floor, unauthorized construction of this kind can get me in trouble with the law here.
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  • \$\begingroup\$ The tip has a tiny capacitance which cannot really damage anything. And grounding any tool is pointless if you cant ground your circuit. If you insist, you want a Megaohm resistance between tool and workpiece to co-float them. I have never done anything like that and have never destroyed anything while soldering with an unearthed iron. \$\endgroup\$
    – tobalt
    Mar 17, 2023 at 17:27
  • \$\begingroup\$ So did I, but recently I got a batch of pretty expensive MCUs and started thinking about it. If what you are saying is correct, and an iron can't do much, why all the buzz about ESD safety, ESD mats, ESD safe irons etc? \$\endgroup\$
    – vga
    Mar 17, 2023 at 17:33
  • \$\begingroup\$ That is mainly to protect against ESD from the operator. So yeah if your iron has a low resistance connection from the handle to the tip, that could become an issue. In that case get an ESD mat and tie yourself to it. \$\endgroup\$
    – tobalt
    Mar 17, 2023 at 17:36
  • \$\begingroup\$ How is the weather where you live? A bit humid... static is not a big issue. Really dry ... ok now it is a problem... touch a metal screw outlet/switch and don't rub against stuff that may generate static on you before working on electronics. \$\endgroup\$
    – Rodo
    Mar 17, 2023 at 17:49
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    \$\begingroup\$ Yeah you're probably not going to have any static problems at those humidity levels. Imo it starts to become an issue below 40%. \$\endgroup\$
    – Drew
    Mar 17, 2023 at 17:57

2 Answers 2

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The main thing about ESD is that everything on your workbench should the at same voltage. It's nice if that voltage is ground, but not really that important.

So if you can get an antistatic mat, leads and a wrist strap, then that's a good thing. Even better, connect another lead to the ground of the soldering iron.

For safety, all anti-static leads should have a built-in resistor. Usually about one megohm.

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If you have no PE, your scope readings are misleading already.

The scope mains input has a filter, with capacitors from Live wire to scope PE, and from Neutral wire to scope PE, and PE is connected to scope chassis and common ground. What this means that it's your scope chassis and ground having a 60 VAC 60 Hz sine wave (assuming you live in a country with 120 VAC 60 Hz mains).

So any object that actually has a relatively stable potential, like the neutral pin of your mains, the scope will measure about 60 VAC 60 Hz because the scope reference ground has the AC compared to the probe tip which can have 0V from neutral.

Modern equipment is not intended to be used without PE if the mains plug has a PE. It even reads in the manuals. So basically, you don't have a proper environment for using your scope or any other device which requires PE for proper and safe operation.

All you can do is to have an equal potential between equipment, so it is still worth having an antistatic mat with potential equlized between soldering iron, the mat, and you.

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