How to solder stranded wire neatly to a PCB pin - Page 1
Forum section: electronics / beginners

author: henrylaw
author_rank: Newbie
timestamp: January 13, 2022, 06:27:15 pm
content: What is the best way of soldering a stranded lead (24/0.2mm typically) to a PCB pin (Veropin)? I've been building projects for years and years and have never done it to my satisfaction. The three methods I've tried are these:Make a hook (or even a loop) in the strands of the stripped wire, wrap round tinned pin with wire parallel to the board, solder in the normal way. Problems: wire not tinned (if I tin it it becomes inflexible so it doesn't settle snugly round the pin and ends up as a big blob). And forming the hook makes the end ragged.Twist strands of stripped wire, leaving straight, then tin. Tin pin. Hold tinned wire alongside pin (perpendicularto the board) and apply iron. Problems: sticking up straight isn't always convenient, and there's no mechanical contact between wire and pin, they're just joined together with solder. I've done this with heatshrink; adds some physical strength I suppose.Variant of (2): same process but offer the tinned wire up to the pinhorizontallyand solder, then clip off overhang. Smaller and neater, but still "stuck together" with solder, and this time less physical contact.No soldering guide that I've seen talks about this, which suggests that everybody other than me is a whizz at it. What am I doing wrong?

author: Gyro
author_rank: Super Contributor
timestamp: January 13, 2022, 07:15:08 pm
content: Welcome to the forum.I think your problem is the size of the wire. You would probably have little difficulty in soldering 7/0.2 wire to a Vero pin (by putting the wire against the pin and doing a complete wrap of the strands and then soldering). It's important to be able to heat both the wireandthe pin in order to get a decent and quick solder joint.24/0.2 is much bigger and stiffer. I can't think of any sensible way of getting all of the strands mechanically secure on a standard Vero pin and a consistent solder joint. You're probably going to be pushing the mechanical integrity of the solder joint - ie. too little joint area, so that when stressed, the joint will break and the wire start to rotate around the pin.I mentioned making a quick solder joint above. This is important because you need to prevent solder from wicking up under the wire insulation, which causes the wire to become brittle.Personally, I would change your approach and use PCB solderable screw terminal strips. This will give you a more reliable long term connection (and make it far easier to disconnect and re-connect the wires if needed).

author: SmallCog
author_rank: Frequent Contributor
timestamp: January 13, 2022, 09:01:00 pm
content: Im not an EE but I avoid soldering to pins. I prefer to bring the wire through a hole in my strip board, then loop it back through the hole next to it and make the solder termination. Allowance for the same can be made (or created) on a PCBNASA have some brilliant resources:Wires to Terminals starts at Page 52 in this dochttps://nepp.nasa.gov/docuploads/06AA01BA-FC7E-4094-AE829CE371A7B05D/NASA-STD-8739.3.pdfThis thing just feels so 90's to me, I'm glad they haven't updated it, and a handy place to look for ideas of how an EE would do ithttps://workmanship.nasa.gov/lib/insp/2%20books/frameset.html

author: themadhippy
author_rank: Super Contributor
timestamp: January 13, 2022, 09:05:52 pm
content: split the strands in 2 groups,pass either side of the pin and then twist them together,solder and trim

author: Infraviolet
author_rank: Super Contributor
timestamp: January 13, 2022, 09:32:41 pm
content: I once had some success by using a wire wrap tool to get the multicored wire on to the pin, wrap it round for mechanical stability, then solder... but even then without some careful heat shrinking this was vulnerable to the multistranded wire being broken by flexing in the area between the solder joint and the start of the insulation. I'd always advise trying to find a way to use actual headers and crimped wire connectors though, much less infuriating.

author: henrylaw
author_rank: Newbie
timestamp: January 13, 2022, 11:48:30 pm
content: Lots of useful ideas there; thank you all. I need the 26/0.2 (I think) for reasons of current carrying: 5A.> Personally, I would change your approach and use PCB solderable screw> terminal strips. This will give you a more reliable long term> connection (and make it far easier to disconnect and re-connect the> wires if needed).Interesting. One of the reasons I wanted to solder to pins was to have all-soldered joints, rather than "relying" on screw terminals which long years ago I assumed were dodgy. But this suggests that screw terminals might be better: that will help a lot. I have numerous bits of PCB-to-screw thingies around.

author: SmallCog
author_rank: Frequent Contributor
timestamp: January 13, 2022, 11:53:39 pm
content: Quote from: henrylaw on January 13, 2022, 11:48:30 pmBootlace your wires if you go this way, reduces copper creep and keeps a strong connection long termexample of what I mean, quality tools and crimps are typically available from electrical suppliers, and sometimes electronics suppliers:https://www.ebay.com.au/itm/185142876561?chn=ps&_ul=AU&norover=1&mkevt=1&mkrid=705-139619-5960-0&mkcid=2&itemid=185142876561&targetid=1278935637969&device=c&mktype=pla&googleloc=9070857&poi=&campaignid=12502542450&mkgroupid=123612189838&rlsatarget=pla-1278935637969&abcId=9300512&merchantid=7364522&gclid=EAIaIQobChMInL-E7vWv9QIVUh0rCh265gk5EAQYBSABEgLpLvD_BwE

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 14, 2022, 12:28:57 am
content: A crimp terminal is probably a better idea for stranded wire, yes. I'm not familiar with the Vero system of boards and pins, but assuming that's just like any old header pin, yeah, there's not really anything to purchase on, it'll be a bit of a pain to wrap stranded wire around a smooth pin and then solder it.The next best things would be:Turret terminal: has shoulders so the wire won't slide off once it's wrapped aroundSolder eyelet: thread the wire through the hole, curl around a side, and solder in placeSolder pot: cylindrical hole which surrounds the wire, filled with solderThese are all very old tech (I have some obscure electronic assembly book from the 50s-60s, that illustrates all of these types/practices), and not often used these days. For good reason, I suppose. Mostly because no one does point-to-point anymore, well, almost no one.Anyway, these are likely not very useful in your case, if it really is fitting into Veroboard (perforated stripboard) -- the single copper layer and unplated holes will be very weak indeed to any kind of bending stress applied to that poor pin. Especially a bigger wire like that. Unless it fits tightly in the hole. Which, I guess "Veropin" is something they provide for their eponymous boards? Looks like something press-fit, so it has a bit more purchase on the unplated hole? So there you go, heh.Yeah, nothing wrong with just lap-soldering the wire directly onto the board. If it wobbles off, it's going to be because you didn't provide enough strain relief, one way or another. And drilling out a hole or two, to thread the wire through, is a good way to do that. Also tie wrap (which can be looped around a tab cut into the board, or an even bigger hole), or tape or glue even.As for crimp terminals, if you're open to exploring "enterprise grade" solutions, a crimp tool isn'ttooexpensive, a poor one at least -- it will need some practice to figure which slot, how much wire insertion depth, stripping length, and applied pressure, does a good job -- and as such, the results won't be terribly consistent -- but it is doable, nonetheless. Brand-name tools start over $100 (often well over(!)), a rather eye-watering sum for just doing up a few terminals, so I wouldn't expect that's what you'd prefer. Anyways, connectors are a system: you have the header that solders into the board (probably a typical 0.025" square post family like Molex SL or KK series, or various others), a plain plastic housing into which crimped wires are loaded, and crimp terminals, which need to be sized properly for the wire, and have compatible plating (use tin on tin, or gold on gold; mixing contact/header platings is discouraged). Headers may be compatible, at least in that 0.025" sq posts are bog standard, and usually the mating lengths are as well; the locking ramps/tabs/etc. vary, however. Some may be generic enough to be compatible (I think TE's equivalent to Molex SL may be close enough to mate? Or TE, Harwin, etc. have mating equivalents to KK), others not so much (like SL to KK for instance!). Or anything without friction/lock, just plain unshrouded headers, pretty much anything will fit those, just don't lose track of which way around it's pinned! (See also: "Dupont" headers, a genericization commonly seen in Chinese sources of headers/sockets/etc.)Can even do both, kinda sorta. Terminals and soldering I mean. If you want the appearance of professionalism but none of the crimpy goodness, use pliers to bend the contact wings around the wire (do it as tight as you can, but obviously you're never going to get a tight crimped joint with just pliers, you'll at best be able to mush it around), then fill the joint with solder -- be careful not to melt the insulation too far back, or leave it so globby that it won't fit into the housing. It's a pretty big solder joint (the wire is surrounded by the terminal), I don't think it's in danger of failing suddenly -- you will absolutely yank the wire out of the housing before the joint itself fails.Just mind that a soldered joint is a stress raiser, i.e. solder wicks up the wire some distance, making it stiff and prone to fatigue failure. This is the biggest advantage that crimps have for themselves: the strands are pinched inside the terminal, but free to bend and flex past themselves beyond there. And when the terminal grasps the insulation, that helps increase the radius of curvature. Either way, such failure is avoided by restraining the cable near the connector.Oh, and there's also screw terminals -- available in 2.54 and 5.08mm pitch, should fit Veroboard well enough (give or take a little drilling for the bigger kind), right? Still kind of sketchy, given the non-plated-thru solder joints, but at least the housing helps distribute load across multiple pins. See also pluggable and spring-clamp kinds. Examples:https://www.digikey.com/en/products/detail/on-shore-technology-inc/OSTTA044163/614531https://www.digikey.com/en/products/detail/cui-devices/TBL003-254-04GR-2OR/10238364https://www.digikey.com/en/products/detail/on-shore-technology-inc/OSTOQ045450/1588257(see also mating products)Tim

author: henrylaw
author_rank: Newbie
timestamp: January 14, 2022, 10:11:17 am
content: Thanks all<metadiscussion type="pleasure">I've been contributing to online forums for years, since the days of USENET, but I never fail to get delight from the amount of time and effort people are prepared to go to to help some perfect stranger, often from the far side of the world, to participate in and perfect some activity they all enjoy. So far removed from the hate-fest that is so many areas of social media.

author: henrylaw
author_rank: Newbie
timestamp: January 14, 2022, 10:17:22 am
content: Quote from: SmallCog on January 13, 2022, 09:01:00 pmThose are brilliant! The slightly fusty feel to them detracts not in the slightest ...

author: tooki
author_rank: Super Contributor
timestamp: January 14, 2022, 12:50:11 pm
content: Quote from: henrylaw on January 13, 2022, 06:27:15 pmThe correct way, if you must solder it, is to tin the wire, form a hook, and then solder that. You need round nose pliers to form the hook, and if you’re getting a blob it’s because you’re applying too much solder.Watch this from 3:01 on:https://youtu.be/Mrhg5A1a1mUThat video series is hands down the best soldering tutorial I’ve ever found, by the way.

author: tooki
author_rank: Super Contributor
timestamp: January 15, 2022, 10:57:16 am
content: P.S. I had meant to write that I agree with the others who suggest using other methods to attach wires to the PCB, like crimp connectors and terminal blocks. I use both of those in my designs.