can direct resistance soldering tweezers damage a PCB? - Page 1
Forum section: electronics / general

author: coppercone2
author_rank: Super Contributor
timestamp: November 08, 2021, 01:37:52 pm
content: So if you do bad through hole parts replacements, and you own pace tools, you might have noticed one of the best and neatest ways to get rid of an old IC is to cut the leads with flush cutters, pull them out with the resistance tweezers carefully, then use the solder extractor to empty the via/solder hole.When you pinch the legs of the IC and use the foot pedal to heat the tweezers, they very quickly melt the solder and allow you to pull out a pad with some force. The heat transfer element is just stainless steel, so you can grip a part that is bent, or covered in conformal coating, and actually yank it out. Then its much easier to use a solder extractor since you just need to clear the hole instead of clearing the hole with a lead still inside of it, making the lead get stuck often.But I am wondering, if there are other components on the PCB, is it possible for parts to get damaged from a substantial amount of current flowing in a dead short? Assuming you are careful and you bend the leads out of the way of each other so you don't complete a circuit through a errant PCB trace.I assume since pace sells a lap-flow tool and a hot tweezers tool (the SMD removal hot tweezers tool is not as good as the direct resistance soldering tool and its way less durable and disposable since you can easily repolish the stainless wire electrodes on the high current direct heater tweezers).There are three tweezers that pace sells1) chop stick soldering irons, expensive, stay hot, look to be the 'safest' for a part2) direct resistance heating tweezers that pass current through the part (what I like)3) indirect resistance heating tweezers that are tweezers made of two resistance heating elements, so its like the chop stick soldering irons but not as regulated, but they get cold quick when you release the foot pedal.So I mean #2. I normally see it used on barrels and wires and stuff, but its excellent for plucking. I want to continue to use this tool rather then to spend money on the chop stick soldering iron tweezers that have 2 ceramic elements

author: Cerebus
author_rank: Super Contributor
timestamp: November 08, 2021, 01:58:53 pm
content: Quote from: coppercone2 on November 08, 2021, 01:37:52 pmThink back to basic mesh analysis. Imagine your tweezers represent a floating current source and the joint a resistor, and the rest of the circuit is an arbitrary mesh of components, then basic circuit analysis tells you that it is not going to do anything. For the generated voltage to appear across any other component, that component would have to be bridgedacross the joint, which isn't going to happen. The necessary condition for it to be safe is that the tweezers 'current source' is floating with respect to the rest of the circuit, with negligible leakage current.I totally get where you're coming from. It's one of those things where theory tells you something is impossible, but the amount of energy you're dealing with tells the monkey hindbrain in you "This must be dangerous." It's like doing the trick with the cannonball pendulum - everything you know about physics tells you that it cannot crush your head, but monkey hindbrain says "Large! Heavy! Iron! Soft head! Noooooo!".Edit: Look at what turned up on XKCD today:

author: madires
author_rank: Super Contributor
timestamp: November 08, 2021, 02:15:12 pm
content: Are the tweezers ESD-safe or isolated? If ESD-safe, what is the resistance value between the tweezers and earth/PE?

author: coppercone2
author_rank: Super Contributor
timestamp: November 08, 2021, 04:44:10 pm
content: I thought it would be like a little possible emp gen like lightning hitting near houses as a loop antenna. I will do the measurements later

author: Cerebus
author_rank: Super Contributor
timestamp: November 08, 2021, 04:51:22 pm
content: Think of that aspect in amp-turns. It's one turn, with a good few amps, but nevertheless one turn. How does it compare to a relay with a few milliamps but a thousand turns? Would you expect a relay to induce enough current elsewhere to do damage?

author: coppercone2
author_rank: Super Contributor
timestamp: November 08, 2021, 05:24:57 pm
content: Guess the power levels need to be a lot higher. Good point I have a flux probe I will update the thread with growls data at 60hz later

author: matthuszagh
author_rank: Frequent Contributor
timestamp: January 09, 2023, 04:14:17 pm
content: So, if you were using this to desolder an SMD resistor, for instance, this very much could cause damage to the resistor right? Similarly, would it not be effective for higher value resistors and things like chip capacitors?coppercone2, do you have the Pace SMR station? I take it you like it? I'm considering getting that for coaxial cable assembly soldering and thermal wire stripping.

author: coppercone2
author_rank: Super Contributor
timestamp: January 09, 2023, 04:59:17 pm
content: Oh yeah I got the old version I think it’s great. For smd parts you can use option #1 or #3Never used regular hot tweezers though. Waiting on the park from hakkoI finally managed to get a cheap deal for desoldering tweezers, so now I own all three listed in the thread, when heating elements arrive.Just the smr direct heat , for big connectors like banana high gauge jacks it feels a little underpowered bc they got giant thermal mass, those need more amps, but I had no problem with 3.5mm coax. Biggest problem for 10awg bananaNeed some heavier equipment for stuff like big lugs and stuff. Probobly use my resistance brazing setup with a variAc at low power (need to test)

author: coppercone2
author_rank: Super Contributor
timestamp: January 10, 2023, 10:53:59 pm
content: also I thought about the thermal wire strippers but I never had too much of a problem stripping wire, yeah its nice for teflon but the fumes are IMO not worth it.Now it would be interesting to know how that thermal wire stripper works on a coaxial jacket, because that would make me worth it, stripping some cables is extremely hard IMO.Like what happens with say a 10AWG banana jack is that the elements will get red hot if you try to heat it fast, and then you need to repolish them. I used it for N connector inner pin, BNC inner and outer (bnc semi rigid) and 3.5mm, and its fine for those, including a 3.5mm connector + semi rigid tubing, and some banana cables that neck down, it sinks heat and takes a while but since it concentrates heat pretty good you can still melt the solder cup area pretty quickly.I see a problem if you try to use it to solder heavy gauge lugs, banana connectors (the ones that accommodate the huge cables, i.e. 4mm x 10mm well), etc. But those probobly require a bigger transformer with carbon tipped heavy duty tweezers, which is more specialized equipment. It probobly won't like a solderable N connector, if those exist, but I think it can do it if there is a reduction (N to small gauge coax), but not N to like heliax.But really IMO those bigger connectors don't have that big a problem. IMO the big thing is being neat around center pins, and its nice for SMA sized things. Where it shines is round many pin solder connectors .

author: coppercone2
author_rank: Super Contributor
timestamp: January 10, 2023, 11:14:59 pm
content: to give an idea of what you need for big stuff,I just don't know if I like his technique that much because its not fixed (I know its a demo), I don't know if you want to be moving it around while you heat. I always fixture the stuff so at least one piece is anchored while soldering, and I try to set it up so after melt I can let go and the wire will cool in the proper place while resting, if there is substantial size.Like if I had to do that splice I would anchor a needle nose vice grip to the wall, bench top vise, etc, fix the connector in it, then heat it up with the tweezers while everything is stabilized. I assume some dodgy shit happens when people need to do inline splices in a conduit near the ceiling lol, you would need to do something creative.