Did my soldering iron kill my mouse? - Page 1
Forum section: electronics / beginners

author: Pulseammo
author_rank: Newbie
timestamp: June 28, 2020, 07:10:18 pm
content: Hello everyone, I hope this isn't too basic a question, hopefully not for the beginners section.I own a somewhat cheap soldering iron. It plugs directly into the wall, has a little temperature dial (I don't think it's temperature controlled, I suspect the little dial just limits the amount of power getting dumped into the heater) and uses the same tips and heater core as a Hakko 907.I recently had to replace my mouse button switches, they are the 3 legged micro switches. No real drama de-soldering and re-soldering the switches, don't think I overheated anything, didn't burn any traces or pads. Just simple through-hole stuff.However after a day of use the mouse intermittently wouldn't connect to my PC (it's a wireless mouse). After 3 days the problem was permanent. I checked ribbon cables to the optical sensor, made sure I hadn't bridged anything on the mouse's motherboard, heck I even got the schematics for the radio IC to make sure it had power and enable, made sure the main processor IC had power, etc and I can't figure out what's wrong with it, so I bought a replacement mouse motherboard.I don't have the skills to diagnose the board, but it still hangs on my mind and I want to learn from it.So the real question is:My soldering iron doesn't seem to have a grounded tip. When I connect my multimeter to the tip and to the earth pin of the UK 3 pin plug it reads OL. Opening the top collar to expose the heater connections shows it just has 2 wires to the heater and nothing to the metalwork that holds the tip.Can my soldering iron have damaged something on my mouse because of this?I don't understand why the tip would need to be grounded, how does charge build up on the tip when all it touches is a ceramic heater, surely the ceramic is an insulator, I can't imagine the tip is live when it's in use?Is this soldering iron basically useless for anything that involves ICs, or is there something I can do to reduce the likelihood of damage?Sorry if this is basic, but I've tried to read explanations of soldering iron grounding and "leakage" but it's over my head. Does the tip and the ceramic heater act like some kind of capacitor? Even if it does why would it be able to discharge into the workpiece pcb, wouldn't there need to be a path to ground from the PCB to get current flow?Any help would be appreciated. Thanks!

author: Nerull
author_rank: Frequent Contributor
timestamp: June 28, 2020, 07:53:26 pm
content: Insulators are great a building up charge, that's what makes them insulators. ESD-safe materials are generally slightly conductive, because this allows charge to dissipate instead of building up.

author: Ian.M
author_rank: Super Contributor
timestamp: June 28, 2020, 08:32:45 pm
content: Its a bit more complex than that - Although most ceramics are reasonably good insulators at room temperature, they can become resistive when hot (depending on temperature, contamination e.g. from flux fumes and metal oxides, and proportion of glassy materials in their composition), so a direct mains powered element or one powered by a non-grounded SMPSU, can leak a significant current to the tip. It only takes a fraction of a mA leakage current, with enough voltage driving it to damage sensitive devices e.g. an unprotected MOSFET by breaking down its gate oxide by over voltage. You may well have completed the circuit by providing the ground path through your body while you were holding the board to solder on it.If you cant ground the shaft (and thus the bit) of your iron it isn't fit for use on delicate electronics, and is only suitable for wiring looms, connectors etc. that can be totally disconnected from anything delicate to work on them

author: Pulseammo
author_rank: Newbie
timestamp: June 28, 2020, 09:30:15 pm
content: Thank you both for your replies.I'll look into insulators holding charge and current leakage through ceramics when they are warm.If I were to make some kind of clip that could clip onto the metal collar of the iron (conductive with the tip), and had a wire soldered to this clip and then inserted into the earth pin (as in the safety earth, not the neutral) of a UK plug, would this be effective in grounding the tip out?I've seen various comments about this, some say to put a 1 mOhm resistor in the path, others say that's only for a person worn earthing strap to prevent someone touching a live wire and having a completely clear path to ground.I assume since the ceramic heater core is resistive that making such a clip that goes from the iron's shaft to the safety earth doesn't make a short circuit straight from mains live to ground?Also, if I were to make such a clip, if I put my multimeter in the middle of the tip and the safety earth would I be able to measure a current, or a voltage to confirm leakage, or would it be dissipating so fast without building up that my meter wouldn't be able to read it? And if current was leaking to earth would this not trip an RCD (GFCI)?Thank you both again for your help and thanks for keeping it simple. Sometimes its difficult when you have so little knowledge about something to even know the right questions to ask, but hopefully this will stop any future haphazard soldering!

author: richard.cs
author_rank: Super Contributor
timestamp: June 29, 2020, 08:41:28 am
content: Quote from: Pulseammo on June 28, 2020, 09:30:15 pmYes, this would work, though may be difficult to make reliableQuote from: Pulseammo on June 28, 2020, 09:30:15 pmWould normally be 1 MOhm (10^6 Ohms) for wrist straps on humans to avoid introducing a new shock risk. No resistor needed for the iron.Quote from: Pulseammo on June 28, 2020, 09:30:15 pmThe small leakage current will flow, likely a few hundred microamps or so. This is measurable with the right meter, but too small to trip an RCD.