A soldering question from a newbie? - Page 1
Forum section: electronics / beginners

author: saflyfish
author_rank: Contributor
timestamp: September 10, 2025, 09:01:52 am
content: Hi AllIm pretty inexperienced at soldering.How do you solder an item that has plastic or rubber attached to it without melting the plastic\rubber?In my case the lead for my multimeter has disconnected from the probe.I tried soldering the wire back on but now the probe is melted

author: tatel
author_rank: Frequent Contributor
timestamp: September 10, 2025, 09:24:37 am
content: Usually you need some soldering iron good enough to melt the solder before the heat reaches too far. Any iron with not enough power will need to be applied for too much time, so the heat will reach adjacent parts and ruin your day.Also, not all plastics melt at the same temperature, i.e, silicone is better than PVC.

author: jpanhalt
author_rank: Super Contributor
timestamp: September 10, 2025, 09:33:09 am
content: Most common with ordinary solder is to use a heat sink between the area being soldered and the plastic. Some people use an alligator clip. They are large and the contact area for heat transfer is small. I use a small pair of smooth jaw clamping forceps. You can also clamp a piece of soft metal (e.g., aluminum) at the junction if the forcep alone is not enough.Technique is important to keep the heating period short. If you increase the temperature and/or size of soldering tip, it shortens the time needed. I used that technique when soldering NiCd batteries years ago.Use a low-temp solder (e.g, high bismuth). I haven't resorted to that more than a few times in my life.

author: saflyfish
author_rank: Contributor
timestamp: September 10, 2025, 10:28:25 am
content: That is great advice will try it...When soldering do you need to get the piece being soldered to the same temp as the wire youre soldering to?Im getting blobs of solder...is this because the piece being soldered is not up to temp?

author: Berni
author_rank: Super Contributor
timestamp: September 10, 2025, 10:35:56 am
content: Yep all the things you want to solder MUST be heated up solder melting temperature, otherwise solder will not stick to it.Counter intuitively you want your soldering iron as hot as possible when soldering sensitive things. Hotter the iron is the quicker the thing being soldered gets up to temperature, so you can remove the soldering iron quickly, not giving the heat enough time to reach the sensitive part.Another thing you can do is have a wet rag ready. After soldering quickly apply the wet rag to cool down the material before the heat can move to the sensitive parts.

author: saflyfish
author_rank: Contributor
timestamp: September 10, 2025, 10:43:15 am
content: I have 60 40 solder its 60% lead 40% Tin.Is this a good solder ratio to use for lower temps?

author: jpanhalt
author_rank: Super Contributor
timestamp: September 10, 2025, 10:49:31 am
content: Quote from: saflyfish on September 10, 2025, 10:43:15 amThat alloy is available, but it is not usually used in electronics. The usual electronic alloys are 60:40 and 63:37tin to lead ratio(i.e., more tin than lead). Often, it is assumed incorrectly that lead is the predominant element. Recheck the solder you have.Edit: This table may be helpful:https://www.technic.com/sites/default/files/resources/Solder%20Alloy%20Melting%20Temperature.pdfNB: 60:40 (tin;lead) melts over a range of 183-190°C; 60:40 (lead:tin) melts at 183° to 236°C. I typically use 63:37 (tin:lead) that is eutectic and melts at 183°C.

author: saflyfish
author_rank: Contributor
timestamp: September 10, 2025, 10:55:15 am
content: Actually it just says 40% Tin so i assumed Lead was the other 60%.I purchased this solder about 10yrs ago...The label says "Solder Resin Cored 40% Tin" & "For Radio and Electrical work" and its 1.6mm thick

author: jpanhalt
author_rank: Super Contributor
timestamp: September 10, 2025, 11:04:22 am
content: 40:60 tin:lead can be used, but it has a much larger liquidus range, which requires longer to fully solidify, particularly if you use a hot iron to speed things up. That's why I use 63:37 tin:lead. I don't need to hold the parts in position as long. Much of the time that doesn't make a difference, but when soldering loose wires, it does make a difference to me.

author: saflyfish
author_rank: Contributor
timestamp: September 10, 2025, 11:18:03 am
content: May i ask is ALL solder wire labelled 63 37 - a 63% Tin? (ie can it ever be 63% Lead)

author: Ian.M
author_rank: Super Contributor
timestamp: September 10, 2025, 11:24:46 am
content: Although there were legitimate uses for such an alloy they were few and far between, mostly when factory assembling the pins on modules that will later be soldered with Sn60/Pb40 solder, or for seams of RF screening cans where its wide plastic range was useful to allow a skilled user to better control the build of the joint. Its obsolete as through-hole modules have pretty much gone away and ROHS has removed most of the remaining uses. It will be nothing but trouble for general electronics use and as you have found requires excessive heat to fully melt, so risks damaging components and generally melting nearby insulation. Seehttps://www.practicalmachinist.com/forum/threads/any-solder-experts-out-there-uses-of-40-60-tin-lead-solder.343770/The other major 'use' was fleecing insufficiently experienced western buyers - tin has historically been much much more expensive than lead, often by as much as a 10/1 ratio. To use a third less tin in the alloy is a significant saving especially when it can still legally be called "60/40 solder" provided you omit those annoying chemical element symbols! Caveat Emptor is deeply embedded in the Far East business psyche . . .

author: saflyfish
author_rank: Contributor
timestamp: September 10, 2025, 11:32:44 am
content: Sorry what do you mean by "through hole modules have gone away"?Ive been trying to remove a Dc power jack from a laptop mb and its darn difficult to remove as i dont think im getting rid of all the solder in the through holes.Ive tried a solder sucker & solder wick and im just not coming right...

author: Ian.M
author_rank: Super Contributor
timestamp: September 10, 2025, 11:39:07 am
content: Quote from: saflyfish on September 10, 2025, 11:32:44 amI mean subassemblies with pins have pretty much gone away. Nowadays a similar subassembly will have castellated edge pads and will directly solder to the main PCB as a surface mount component.

author: paulca
author_rank: Super Contributor
timestamp: September 10, 2025, 11:55:26 am
content: Quote from: saflyfish on September 10, 2025, 10:28:25 amYes. Learning and then applying this is what "fixed" my soldering.Nominally: The iron does not melt the solder. The iron heats the components to be soldered. Once they are hot enough to melt the solder, apply it. You are not done yet. Wait.... wait... you will see a "flash" change, happens rapidly and is subtle. The solder stops being a "blob" sitting there and like a rain drop bursting it "flows" like water conforming to the surfaces and soaking into wires. You can "dwell" a little longer for some joints, but for most of them this "flow" is the completion.There are of course many circumstances where "it depends". In your original case, soldering a connector (probe) onto an insulated wire, is a rather tricky one. You have a few problems. Getting the connector hot enough to "flow" solder for a start. Then getting the wire hot enough, ideally at the same time, without burning or melting the insulation, or the plastic connector housing. Finally, when the solder does flow, the wire, assuming stranded is going to behave exactly like solder wick and the wire will inhale solder up and under the insulation making the end of the wire stiff and rigid.Others have given the preferring solutions. "Heat sink" to block the head, such as using a crocidile clip to hold the wire before the insulation. This should also resist the solder wicking up wire. Also a VERY hot iron. It seems counter intuiative, but the plan is to get the right spot hot FAST and the solder flowed with minimum dwelling allowing heat to soak up the wire/down the connector.The only other tip is "countrary" to the nominal method, sometimes the solder itself makes for better heat transfer. Same reason we cook with oil. So for maximum heat transfer, melting some soldering to the area with the iron can accelerate the job.The other lesson to learn is that when people say "ALWAYS use flux", they really mean it. Solder without flux does not work. Solder does not flow into oxide layers. Most solder for electronics is "flux core". This means the FIRST time you apply a fresh bit of solder off the wire, it will smoke and fissile as the flux activates and is consumed doing its job of removing those oxides. If you further melt that solder you are running without flux. The flux is gone. So, again the solder wire itself when melting releases flux which is consumed. If you want to "rework" a joint you can either apply fresh solder additionally to get a little flux, remove a reapply all the solder, or use separate flux, like a pen or syringe.A further technique you may apply for the wire/connector. Apply solder to both independantly first. Ideally apply flux to both. Then bring them together and technically, all you have to do is melt the solder blobs together. It's not the best joint, often referred to as "Tacking" but asides them not liking being bent, they work.

author: Psi
author_rank: Super Contributor
timestamp: September 10, 2025, 12:23:00 pm
content: Another problem newbies have is trying to solder the joint without first tinning each side.Tinning = heat up and get some solder to flow on and into the surface first.If you don't tin them it takes longer to heat up both sides of the joint at once as one big block and for the flux to clean the metal, and that extra time means you are much more likely to melt the plastic.Once you have both things tinned, making them join together is very fast. Just touch both things and the iron together and it's usually almost instant to join.

author: saflyfish
author_rank: Contributor
timestamp: September 10, 2025, 12:34:11 pm
content: I think im going to discard that 60 40 old solder i have...Since posting ive ordered some 63 37 solder wire in 0.8mm - not sure if it has flux,doesnt say on the label.I also purchased some flux in a paste (its def not solder paste)Some great suggestions here to my post thanks to all,would still like to hear other suggestions\comments

author: Psi
author_rank: Super Contributor
timestamp: September 10, 2025, 12:48:29 pm
content: Quote from: saflyfish on September 10, 2025, 12:34:11 pmI don't think i've ever seen 63 37 sold without flux core. So i'm sure it will be fluxed.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: September 10, 2025, 01:32:28 pm
content: Good Morning Saflyfish, In my opinion, DMM test leads are not something that should be repaired. There are many available all over the web, at prices that won't break the bank. The fact that yours broke, tells me they weren't of very high quality. I propose you get a new set that matches the quality of your DMM, or better. Cut the ends off your broken ones and save the wire for hook-up wire in projects.

author: Shock
author_rank: Super Contributor
timestamp: September 13, 2025, 03:04:38 am
content: What PSI said, pretin the socket and wire then remove excess solder from the socket, test fit wire, add a little solder to socket heat it up and insert wire. The solder will reflow and this requires the wire to stay heated for less time.I have an aluminum heatsink tweezers for sensitive components that also works in some situations. It also helps to pretin wire longer and then trim it back so the heat source isn't initially so close to the insulation. As you become a more proficient solderer you get quicker and learn tricks like roughing up a surface can allow it to tin much faster if you're making alligator clip leads etc.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: September 14, 2025, 01:48:45 pm
content: Quote from: Shock on September 13, 2025, 03:04:38 amGood Morning Shock, Where did you get your heat sinkI have this exact same one I got at Radio Shack back in the early 70s.

author: geralds
author_rank: Contributor
timestamp: September 14, 2025, 02:42:01 pm
content: Seem to be available at Amazon in AU:https://www.amazon.com.au/White-light-HAKKO-heat-610/dp/B002MRR14Chttps://www.amazon.com.au/H-2SL-Goot-Heat-clip/dp/B001PR1KNS/358-0717270-1259348?pd_rd_w=ervhi&content-id=amzn1.sym.aa12a5ad-eae4-4894-aa86-473cafa65e34&pf_rd_p=aa12a5ad-eae4-4894-aa86-473cafa65e34&pf_rd_r=GVAQKREG6DWQHB2WYSYB&pd_rd_wg=yEDoh&pd_rd_r=fe34d13f-b9de-4caf-9613-46f1bf7ba98a&pd_rd_i=B001PR1KNS&th=1I am wondering whether some cross-jaw tweezers would do the trick? Eg Knipex 92 95 90? Or is the gripping surface of these not long enough?

author: RJSV
author_rank: Super Contributor
timestamp: September 16, 2025, 06:02:13 am
content: In all this good advice, I looked for my issue, for producing good solder connections: Be clean, in that area. Dirt and various organics can substantially raise the melting point(s) of various substances, and here is some professional things I learned:From Systron-Donner I learned special methods, for mil-spec testing. Details you might have to research, but it involved:(1.). No visible flux film or other substances(2.). No crusty dirt or visible rust-like surface(3.). Pry test with points, can't get underneath joint(4.). Of course, no frayed wires, if multistrand============================================To clean your area to be soldered, the expert assemblers would first lay a tissue paper on top of the printed circuit pads, and the using a straight 'stipple' brush, poke brush down into alcohol bottle, that has a tiny dispenser in top. Then, go start rapid down-pokes, directly down on that paper, to the metal traces and pins.Result is any dirt or grease can get absorbed upwards, into the tissue. Maybe even do that again, with fresh little sheet. Then, before finish, make sure to wipe excess alcohol off, using same mechanical process, with dry brush and new tissue.Those people were careful, as there was a QC inspector waiting to scrutinize the quality of soldering !Enjoy, (and wear a lap apron!). - - - Rick B.

author: RJSV
author_rank: Super Contributor
timestamp: September 16, 2025, 07:56:50 pm
content: Also, if you wish to go the more pro soldering tools, is the soldering station, (at MDS QANTEL) manufacturing dept. kept a smaller sized table having a foot operated / heated tip solder sucker. That thing might be expensive (otherwise why only have 1).You would place the hollow tip onto a pin, and press for suction with the foot switch. That and we also had cheap manual solder suckers, that are spring loaded, and make a single suction action (for each manual re-position of the suction knob.). Solder removal (being without damage) is difficult, sometimes.Some places are very formal and so weird things, like sending the 'dead' IC over to Q.C. dept. for 'analysis' of the through-hole chip package,...including microscope !

author: RJSV
author_rank: Super Contributor
timestamp: September 16, 2025, 10:04:58 pm
content: Also, a related tool, the milli-ohmmeter we had for chasing down some shorted trace. (That tool never was that useful, IMO). Principal of use was that, using the milli-ohmmeter, a technician could observe the differences, along a trace, itself, in resistance, just from a few centimeters away. This in theory you could track down a short, by moving or walking your probe around the suspect area of PCB.Fixed a couple of pc board returns that way. Some trace shorts were hard to spot, sometimes having a very fine defect, (trace to trace).