Good soldering techniques - Page 1
Forum section: electronics / projects

author: moffy
author_rank: Super Contributor
timestamp: April 15, 2025, 12:10:40 am
content: I have recently started some SMD soldering, which is taking me a while especially the fine pitch of SSOP and TSSOP. I've watched the videos, but there is a level of skill which is not conveyed, they make it look so easy. Anyway I've got some practice ICs coming so I can improve my skill level.But what I learned does not have to do with SMD, but desoldering PTH PCBs. I've got the 'Engineer' solder sucker:https://www.digikey.com.au/en/products/detail/adafruit-industries-llc/1597/7244942?gclsrc=aw.ds&gad_source=1&gclid=EAIaIQobChMIm7jQ2t3YjAMVyx2DAx2Viym7EAQYAiABEgKdpvD_BwEAnd it is very good but there is still the issue of trying to heat up the solder with an iron without damaging the pad or plating. This, though trivial, is where I found heating the pad and solder with a Hot Air Station was much more effective. It heats up an area around the pad which keeps the solder liquid longer and leaves the pad free for the solder sucker tip. Much quicker and less chance of damaging the pad, plus I haven't seen it used on any YouTube videos, though I'm sure there must be some.So, if you have any tips for soldering or desoldering I would be interested to hear and hopefully learn, some new and usefull techniques.

author: jonpaul
author_rank: Super Contributor
timestamp: April 15, 2025, 12:54:46 am
content: PTH, SMD reworkBest is Metcal smartheat high frequency irons and desoldering WS.Our SP-200 design of 1992 is still in use and in production after 33 yearsJon

author: moffy
author_rank: Super Contributor
timestamp: April 15, 2025, 02:02:54 am
content: Quote from: jonpaul on April 15, 2025, 12:54:46 amIt sounds a little like the Weller tips that use the Curie point to control temperature but more sophisticated.https://docs.rs-online.com/ac80/0900766b8145d6ea.pdf

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: April 15, 2025, 06:55:55 am
content: ICs and components are less expensive than replacing the complete board if you damage it trying to remove a component. If you need to replace an IC, there are a few options:1. Cut the legs and remove them one at a time (mainly applies to through plated boards with DIL ICs, etc)2. Heat the whole component using hot air and lift it off the board, remove surplus solder with solder wick (SMD ICs).3. Remove the solder using a low temperature alloy, such as Lowmelt, or Chipquikhttp://lowmelt.com/https://www.chipquik.com/store/index.php?cPath=200The low temperature alloys work like magic, you end up with weak "solder" that you can brush out of the way. The alloy has to be completely removed before replacing the component, otherwise you end up with poor joints that easily fail.SJ

author: moffy
author_rank: Super Contributor
timestamp: April 15, 2025, 07:39:26 am
content: Quote from: Solder_Junkie on April 15, 2025, 06:55:55 amI've cut the legs off a few PTH ICs before, have to agree much better than damaging a PCB.

author: wraper
author_rank: Unknown
timestamp: April 15, 2025, 07:45:35 am
content: Quote from: Solder_Junkie on April 15, 2025, 06:55:55 amYou can use desoldering gun for PTH.

author: faraday
author_rank: Regular Contributor
timestamp: April 15, 2025, 11:09:22 am
content: Take a look at IPC-7711/21C .

author: s-petersen
author_rank: Contributor
timestamp: April 16, 2025, 06:00:58 pm
content: I have a quick question, what makes solder more like taffy, and less liquid? I have plenty of heat, and it is inconsistent, as it only happens once in a while? I always use the same solder.

author: tooki
author_rank: Super Contributor
timestamp: April 16, 2025, 07:14:18 pm
content: Quote from: moffy on April 15, 2025, 12:10:40 amAir has much, much, much worse heat capacity than the copper core of a soldering iron tip. If you are managing to heat a through-hole jointfasterwith hot air than with a soldering iron, then there is somethingseverelywrong with your soldering iron, tip, and/or technique. Rule of thumb: you should achieve full melt in about 3 seconds.If you're damaging pads with the iron: bad technique.IMHO it's easier to cause damage with hot air because of the reduced feedback (no tactile feedback, and solder melt may be masked by oxidation, after the flux is blown off).

author: tooki
author_rank: Super Contributor
timestamp: April 16, 2025, 07:18:01 pm
content: Quote from: s-petersen on April 16, 2025, 06:00:58 pmBy "like taffy", do you mean prone to icicles and the like? If so, that's what I call "overcooked" solder (heated too long or too hot), which suffers two things: oxidation and excess dissolved copper. It makes it pasty and reduces surface tension.If you mean it's pasty and thick, mushy, or otherwise offering resistance you can feel, then it's not fully melted and needs more heat (bigger tip, auxiliary heating, and/or as a last resort, higher temperature), and possibly more flux.

author: bson
author_rank: Unknown
timestamp: April 16, 2025, 08:01:51 pm
content: Quote from: tooki on April 16, 2025, 07:18:01 pmI I always thought it was due to carbonized (or polymerized) rosin flux.Copper has a melting point north of 1000 deg C, and I doubt a soldering iron is going to melt it to a measurable degree.

author: s-petersen
author_rank: Contributor
timestamp: April 17, 2025, 12:38:27 am
content: "By "like taffy", do you mean prone to icicles and the like? If so, that's what I call "overcooked" solder (heated too long or too hot), which suffers two things: oxidation and excess dissolved copper. It makes it pasty and reduces surface tension"I think it could be this, as it is certainly hot enough, maybe I'm not cleaning and adding new solder often enough.Thanks!

author: moffy
author_rank: Super Contributor
timestamp: April 17, 2025, 01:31:30 am
content: Quote from: s-petersen on April 17, 2025, 12:38:27 amNot enough flux could be the major reason, it deals with the oxides that form due to heat and helps the solder to flow well, it also burns off relatively quickly. Also non Pb(lead) based solders are generally harder to work with, except the low melt type.

author: moffy
author_rank: Super Contributor
timestamp: April 17, 2025, 01:40:10 am
content: Quote from: tooki on April 16, 2025, 07:14:18 pmI have to agree my technique could do with improvement, that's why I started the post, and hot air can cook a board if used excessively, but it is ceratinly usefull for desoldering PTH especially tiny ones. Ever been in that situation where the heat just is not penetrating all the way through the hole and you clear 90% but struggle with that last 10%? You keep adding fresh solder and solder sucking in a cycle and end up cooking the pad. For those of us with less than stellar technique a judicious use of hot air solves the problem and saves any damage to the board.P.S. If hot air is safe for multi pin chip removal it's should also be safe for desoldering a PTH.

author: passedpawn
author_rank: Contributor
timestamp: April 17, 2025, 03:55:37 am
content: Sometimes you need to add solder to desolder. Why? You need to get heat into the weld, and this requires contact area. Adding a bit of solder can greatly increase the contact area between your iron and the work, thus allowing the heat to enter.

author: Shock
author_rank: Super Contributor
timestamp: April 17, 2025, 08:23:19 am
content: If you haven't seen these I recommend watching Paces training video series before anything else. Basic soldering, repair and rework, adventures in repair.Then check out John Gammells videos which show IPC master soldering. Then Mrsolderfix who has practical techniques. Last F1Labs rework video shorts.https://youtube.com/@paceworldwide/playlistshttps://youtube.com/@jkgamm041/videoshttps://youtube.com/@mrsolderfix3996/videoshttps://youtube.com/@F1LAB-GRTLAB/shortsThese cover a lot without having to write a book on it. But if you stick to quality solder, flux, take you time and work clean it solves most of the problems. Practice on scrapped boards you can solder/desolder all day.That problem with solder going clumpy is generally either heat, lack of flux, old oxidized alloy or a mixture of alloys.

author: RoGeorge
author_rank: Super Contributor
timestamp: April 17, 2025, 08:32:22 am
content: The biggest secret is to use good flux, and plenty of it, then some practice.Maybe watch a few more SMD soldering/desoldering videos from this guy:https://www.youtube.com/@mrsolderfix3996/videos

author: elektryk
author_rank: Regular Contributor
timestamp: April 17, 2025, 10:44:37 am
content: QuoteHe has interesting way of multipin THT desoldering.It may be even easier with "spatuala" tips.

author: moffy
author_rank: Super Contributor
timestamp: April 17, 2025, 10:58:56 am
content: Quote from: elektryk on April 17, 2025, 10:44:37 amYes, I have seen that before, if I didn't have access to hot air or low temperature solder it could be useful.P.S. In a field repair situation with minimal tools, it would be something to keep in mind.

author: tggzzz
author_rank: Super Contributor
timestamp: April 17, 2025, 04:35:02 pm
content: Quote from: moffy on April 15, 2025, 12:10:40 amIt isn't clear whether you are assembling a board, reworking a few components, or reflowing the board.Either way, the techniques I use arehttps://entertaininghacks.wordpress.com/2015/03/25/assembling-pcbs-with-surface-mount-components/I only do that occasionally, which could be good or bad from your point of view.

author: moffy
author_rank: Super Contributor
timestamp: April 17, 2025, 10:21:25 pm
content: Quote from: tggzzz on April 17, 2025, 04:35:02 pmSo far I have avoided the use of solder paste, mainly because of their shelf life and storage issues, but many, like yourself prefer it. Thanks for the advice.Mainly I am just looking for soldering tips that the forum find useful, that little technique that helps in certain situations, but general advice is welcome also.I've just learned what I suspected from personal trial, that good drag soldering of fine pitch ICs is quite a high skill level.

author: moffy
author_rank: Super Contributor
timestamp: April 17, 2025, 11:36:42 pm
content: The question by 'tggzzz' got me thinking about what I am specifically asking for:I am looking for soldering suggestions that the forum users personally use that make the job of soldering or desoldering easier, improving the chance of success. This is why I gave my example of using hot air with a solder sucker, I find it much easier and more successful especially for those hard solder pads like the ones connected to ground planes. But others might have a different technique that works for them, there is no single right solution. If we share our innovations/techniques others can choose from a smorgasborg the one best suited to them.I would also like to encourage others who have soldering questions like 's-peterson' to ask, all sorts of nuggets can be discovered sometimes in the answers to seemingly trivial issues.Advice No 2: Get a good quality pair of tweezers, I use GOOT, they make a world of difference in handling SMD components. Practice with them also, generally used in your 'off hand', so some practice is required to develop coordination.

author: tggzzz
author_rank: Super Contributor
timestamp: April 18, 2025, 09:10:50 am
content: I'd add acheapmagnifying visor with interchangeable lenses. They fit over your (prescription) glasses, work upside down and when looking into enclosures (cf microscopes). Any magnification tools are a very subjective and personal choice.Solder suckers are best with a flexible silicone nozzle; I believe yours are.

author: tooki
author_rank: Super Contributor
timestamp: April 19, 2025, 10:49:13 am
content: Quote from: bson on April 16, 2025, 08:01:51 pmMolten solder does notmeltcopper, itdissolvesit.Melting is not necessary to dissolve something. Sodium chloride (regular table salt) melts at 800.7°C, yet it dissolves readily in water, even very cold water.Modern soldering iron tips are plated (with iron and nickel) to prevent what was a common problem with unplated copper tips: tip erosion due to the hot solder eating away at the copper. If a modern tip suffers a plating failure (such as a crack), solder will quickly attack the copper and hollow out the tip like termites eating wood.Copper dissolution is also a problem with soldering copper-clad aluminum (CCA) stranded wire: if you take too long, the copper dissolves away into the solder, leaving only the aluminum, which won’t take solder at all.The fact that overcooked solder does not fully respond to adding fresh flux is a strong indication that spent or burnt flux is not the whole problem.

author: tooki
author_rank: Super Contributor
timestamp: April 19, 2025, 10:54:08 am
content: Quote from: passedpawn on April 17, 2025, 03:55:37 amFirst of all, it’s a solder “joint”, not a “weld”. Welding is a distinctly different process from soldering.Anyhow, adding fresh solder does two things:1. Introducing fresh flux to cut through the oxide layer that forms on the joint over time2. Making a better thermal bridge, as you mentioned.Of these, the fresh flux is arguably the more important one.

author: tooki
author_rank: Super Contributor
timestamp: April 19, 2025, 11:03:35 am
content: Quote from: moffy on April 17, 2025, 01:40:10 amAre you saying to use hot airinstead oforin addition tothe soldering iron?Using hot air asauxiliary(additional) heating for when the iron alone won’t do is a well-established method.Using hot air aloneinstead ofthe iron for PTHs sounds crazy to me, and given my many years of working with hot air for rework, seems unlikely to work. The amount of hot air needed, and the high temperature it would need to be at, would be anything but gentle to the board and nearby components.Quote from: moffy on April 17, 2025, 01:40:10 amWith a solder sucker or desoldering wick, you mean? Yeah. Which is why I bought a proper continuous-vacuum desoldering station. And until I had that, started doing other methods, like putting a thick wire across the pins to spread the heat provided by a large soldering tip. Plated through holes are simply not capable of being reliably cleared with a solder sucker or wick.Quote from: moffy on April 17, 2025, 01:40:10 amAgain, that depends on what technique you are actually using.

author: moffy
author_rank: Super Contributor
timestamp: April 21, 2025, 04:39:58 am
content: Well, my first USB-C connector, my first SSOP-28 IC, a PCM2906, and all surface mount passives plugged it into my Windows PC and it was successfully recognised as a 'USB Audio Codec'. For the IC and connector I used pin by pin soldering with plenty of flux.

author: Shock
author_rank: Super Contributor
timestamp: April 21, 2025, 05:06:47 am
content: Many ways to skin a cat. Best to be competent in as many techniques as you can.I'd still recommend learning solder sucker and wick use as core techniques before others. They are two very cost and time efficient methods of removing solder.Regarding the "wire form" method, it's useful for tight fits to gently ease out the part ensuring it's not still bonded with cold solder or sweated joints.

author: moffy
author_rank: Super Contributor
timestamp: April 21, 2025, 05:16:05 am
content: Quote from: Shock on April 21, 2025, 05:06:47 amThanks, long time user of solder sucker, but not that experienced with solder wick, always prefered the solder sucker but I can see that especially with surface mount solder wick can be usefull.

author: MathWizard
author_rank: Super Contributor
timestamp: April 21, 2025, 05:49:29 am
content: If you use common sandpaper's, so maybe with Aluminum Oxide, how bad is that for solder joints ? I'll usually brush off the dust with my dirty fingers, and not bother to clean it with alcohol.But yeah, even my solder wick, works much better after a light sanding with fine SP. But for long term, how bad is sandpaper dust, for solder joints ?

author: moffy
author_rank: Super Contributor
timestamp: April 21, 2025, 05:56:34 am
content: Quote from: MathWizard on April 21, 2025, 05:49:29 amUnless really heavily oxidised or corroded I would use flux, but sometimes some abrasion is necessary. The aluminium oxide is non conductive, so I can't see it causing an issue but I would still want to wash it off.

author: Shock
author_rank: Super Contributor
timestamp: April 21, 2025, 06:31:48 am
content: Wick/braid if it's old, not fluxed or stored well oxidizes. This reduces it's wicking performance so either use additional flux with it or buy some newer or better brand (cheap wick may be crap).Mine I get now in short spools of different sizes of one to three metres. The newer plastic cases are sealed to reduce it getting handled or oxidizing as easily. It's slightly more expensive this way but last time I brought some it was only a few dollars because of the smaller quantity.Another tip is storing them in a container at precut lengths, use tweezers to take out a piece at a time prevents over handling it.Aluminum can eventually react with both lead and tin so in general not a good idea. Safest to clean it off or get new better wick.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: April 21, 2025, 12:13:50 pm
content: Quote from: tooki on April 19, 2025, 10:49:13 amAluminum oxide won't, but with the right flux you get to the aluminum and it solders just fine. Of course your iron is probably ruined now but still...

author: tooki
author_rank: Super Contributor
timestamp: April 21, 2025, 01:37:13 pm
content: Quote from: Alex Eisenhut on April 21, 2025, 12:13:50 pmWe are talking about stranded CCA wire here. The individual strands are thin, and no way would you want an aluminum flux wicking up your wire.

author: Martinn
author_rank: Frequent Contributor
timestamp: April 21, 2025, 03:30:44 pm
content: Just showed a colleague recently how to desolder a TQFP100 and was surprised how easy it is.Pick up a handful of PCBs from the junk bin. Practise desoldering and soldering back againSo you found one PCB with a large PQFP or TQFP.Optional: First re-solder the pins with leaded solder (lowers the melting point from the original lead-free soldering). Special low-temp solder exists, but is not necessary normally.Heat the whole board with a hot air gun (set to about 250 °C) to 130 °C, preferably from the backside, check with IR thermometer. This is safe for all components. You want to do pre-heat so you don't have to get all energy into the device in one hotspot (potentially damaging things)Set the hot air gun to 450 °C (and lowest possible air flow). Aim straight for the TQFP (1-2 cm away). Gently probe one corner of the device with tweezers, lift and flip over the device once the solder melts.Nearby components might get blown away. Options:- remove them before (and replace later)- Cover the remaining PCB with paper, cut a square opening into it and use Kapton (PI) tape to glue it around your deviceTo re-solder the TQFP:Have a wave soldering tip, use it for tinning both PCB (clean it from burnt flux) and device pins. Apply plenty of flux. Temperature as low as possible, well below 300 °C.Watch tutorials on mini wave soldering.https://paceworldwide.com/node/442Get mini wave tips, Weller calls them GW. Key with mini wave soldering: Very low temperature increases solder surface tension, prevents shorts.Hot air pencil: Not too useful IMO. Maybe for soldering QFN-10. I mostly use a hot air gun. If you have, use a preheater, otherwise use the hot air gun.Hot air gun: Get one with temperature and flow control. Examplehttps://www.steinel.de/de/werkzeuge/produkte/heissluft/heissluftgeblaese/pistolengeraete/pro-hm-2320-e-089672.htmlUnregulated hot air guns are for lighting the barbecue only.You can buy solder practise kits, but junk bin is as good.- Martin

author: moffy
author_rank: Super Contributor
timestamp: April 22, 2025, 12:04:13 am
content: Thanks for the detailed instructions, appreciated. Your link has a spurious full stop at the end which prevents it working:https://paceworldwide.com/node/442P.S. Your point about solder temperature:"Very low temperature increases solder surface tension, prevents shorts."makes sense, the 'paceworldwide' video seems to recommend 316C for leaded solder.

author: Martinn
author_rank: Frequent Contributor
timestamp: April 22, 2025, 05:17:50 pm
content: Corrected the link, thanks.Temperature is key... I remember setting 290°C or lower using the wave tip. Haven't used it for a while though, these days I order most PCBs assembled from JLCPCB.Related to that: A beginner mistake I see often is to assume that for small components you need tiny tips. Mostly this is not correct. Small tips have a high thermal resistance, you need to crank up the temperature in order to transfer enough heat, burning up solder and flux.Best is to use as large a tip as possible. I do most soldering using a Weller WSP81 (old school iron with lots of oomph) and a 2 mm chisel tip. You can rotate a chisel tip and use it at the short side to solder smaller components. Having the powerful iron and a short, stubby tip keeps thermal impedance low and lets you work with lower temperature. For smaller stuff I have a smaller Weller pencil, but also with (I think) a 1.2 mm chisel tip. Same idea.Absolute worst case is a long, thin, needle-like conical tip. Maximum thermal resistance. There are occasions where you are forced to used one, like soldering individual QFN "pins".But in general: Use the largest, shortest tip possible (best stubby chisel type, avoid long pointy conical ones) at the lowest temperature you get away with (and of course use leaded solder).Also it helps to have a closed feedback loop on your soldering skills: Observe, improve, repeat. Proper observation requires some form of optical magnification. You can't get better if you don't see exactly what you are doing. I personally like stereo zoom microscopes, but that's another topic.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 22, 2025, 06:34:40 pm
content: Maybe of interest to OPhttps://www.eevblog.com/forum/chat/what_s-your-favorite-_how-to-solder_-video-to-share-with-friendsnoobs-that-ask/msg1185136/#msg1185136

author: Shock
author_rank: Super Contributor
timestamp: April 22, 2025, 10:34:02 pm
content: Marc Sigel's 3 videos are worth it as well.https://youtube.com/@MrMarcSiegel/videosThere are some Russian excavation videos and bga rework videos that are useful but most videos are going to teach bad habits like drenching the board in flux or not preheating or cleaning properly.

author: moffy
author_rank: Super Contributor
timestamp: September 12, 2025, 11:32:16 pm
content: I have learned that surface mount soldering is very different from the PTH soldering I have previously practiced. Not only have the dimensions of components and pads shrunk, but so have the soldering tips and the need to deliver lots of heat, especially for pads connected to planes, through small contact areas. This requires the integrated tip and heating element like in the T245, T210 etc as the older style iron with just the replaceable tip will have a small air gap between the element and the tip acting as a thermal insulator. The cheap hot air stations with integrated blower in the hot air handle are not up to the standard of something like the ATTEN ST-862D station in either quality or performance, so my advice spend some money on a good soldering iron with replaceable integrated tip and heating element and a good hot air station.

author: tggzzz
author_rank: Super Contributor
timestamp: September 13, 2025, 06:40:23 am
content: Quote from: moffy on September 12, 2025, 11:32:16 pmAnother issue is that there are many ceramic SMD components which don't like the heat shock from a soldering iron tip, nor differential thermal expansion between the component and PCB.Replacing an individual SMD resistor/capacitor on a densely populated PCB requires more thought and preparation than replacing the equivalent PTH component.

author: moffy
author_rank: Super Contributor
timestamp: September 13, 2025, 07:40:13 am
content: Quote from: tggzzz on September 13, 2025, 06:40:23 amSo true, also plastic connectors and electrolytic capacitors need protection from any hot air that is used. I am currently working on a mixed PCB with both through hole and smd components and had to remove two electrolytics just to get at a failed smd diode. The high through hole components make it difficult to impossible to access the smd ones.