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| Soldering ESD-sensitive components without grounded soldering iron |
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| analogix:
I'm about to replace some malfunctioning LED modules (Osram DLR-1414) which happen to be electrostatic sensitive according to the datasheet. So with just a hobbyist setup I'm wondering how I should safely solder the new ones in place without risking damage. Now I do have a grounded wrist strap and a grounded work mat, but my soldering iron isn't grounded at all. Is there a temporary solution I can use for this particular job, or is there no way around it than buy an expensive soldering station? |
| Ian.M:
A battery powered or gas soldering iron can be used, and if held by someone wearing an ESD grounding wrist strap, will be very unlikely to cause ESD, even if not explicitly sold as ESD safe. An ungrounded iron with a mains voltage element is not fit for purpose. Directly heated irons tend to have excessive AC leakage current when hot, worsening with age as the mica or ceramic insulation becomes contaminated with burnt flux fumes, and if any fault develops the whole shaft and bit assembly can go live at any time, and there you are holding the solder, a length of bare metal, with which you frequently touch it! Ungrounded low voltage irons *may* be fit for purpose if they have a conventional mains frequency transformer driving them. The mains leakage current is low enough not to usually be an issue. However anything with a switched mode power supply is highly likely to have a Y filter capacitor (to meet EMI regulations) which if not grounded will let through enough mains leakage current to blow the s--t out of unprotected small MOSFETs, some active RF components and some LEDs and laser diodes. e.g. see post #8 onwards of https://www.eevblog.com/forum/beginners/simple-fet-circuit-for-onewire-protocol-doesn_t-work-as-expected/msg1277272/#msg1277272 where a Hakko FX888D + a wall socket adapter that didn't ground it, was blowing up 2N7000 MOSFETs. |
| Kim Christensen:
Since this is hobbyist stuff on the cheap: You could attach a wire to the cooler metal part of the iron that is also connected to the tip. Then ground the end of the wire. How feasible this would be, depends upon the construction of the iron. |
| analogix:
--- Quote from: Ian.M on June 16, 2024, 01:13:46 pm ---A battery powered or gas soldering iron can be used, and if held by someone wearing an ESD grounding wrist strap, will be very unlikely to cause ESD, even if not explicitly sold as ESD safe. --- End quote --- I hadn't thought about that! The Dremel Versatip comes up as an option for this. Most reviews come up very positive, but then again they're quite superficial. Has anyone here used one? I've browsed through several threads here on gas-powered soldering irons and there are mentions of models by Weller, Hakko, Portasol and others, but the Dremel is easy to get hold of here and doesn't cost an arm and a leg. Besides needing it for this specific ESD-sensitive repair project I can see a gas-powered soldering iron/tool is nice for heat shrink tubing. Alternatively I'm about to order components from Farnell, which I see also sells various gas powered soldering irons at various prices. Obviously the more expensive brands (Weller etc.) are safe buys, but for occasional hobby use I don't want to invest too much in this, but still don't want something that falls apart after 2 times of use (or is unsafe to use). --- Quote from: Kim Christensen on June 16, 2024, 04:11:51 pm ---Since this is hobbyist stuff on the cheap: You could attach a wire to the cooler metal part of the iron that is also connected to the tip. Then ground the end of the wire. How feasible this would be, depends upon the construction of the iron. --- End quote --- Hmmmm... I thought about this, and checking I couldn't find any continuty between the cooler metal part (shaft) and the soldering tip itself. It appears they're isolated from each other, but after having read your post I decided to check again and indeed there's some continuity there. The continuity/resistance reading on the multimeter fluctuates (probably due to bad contact because of the darkened "heated metal" after years of use), so I tried cleaning the shaft with household steel wool which helped a bit, but although unstable it reads around 1 MOhm between the tip and the metal shaft. On a sidenote I measured around 750 Ohms across the two AC (230V) pins. Is this normal? It solders just fine. |
| Kim Christensen:
--- Quote ---but although unstable it reads around 1 MOhm between the tip and the metal shaft. --- End quote --- Probably good enough. As a comparison, your wrist strap should have a 1M resistor in it's lead for your own safety. It works just fine since there isn't much current from static. As for AC leakage, it is going to come from the heating element and travel towards the tip. Not the other way around, so the 1M between the shaft and tip is probably not an issue. You could do a test if you're concerned. Measure the AC voltage between the tip and ground with a DMM when the iron is turned on. Be aware that the DMM's input impedance (Usually 1-10M \$\Omega\$) will drag any real leakage AC voltage down. Then add your grounding wire to the iron's shaft and measure again. --- Quote ---On a sidenote I measured around 750 Ohms across the two AC (230V) pins. Is this normal? It solders just fine. --- End quote --- If the iron's element is directly powered from the AC mains, then that sounds about right (70 watt element) assuming it's got some sort of built in temperature control. (A 70 watt iron, without some sort of built in temperature control, would be too big/hot for small electronics soldering) |
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