Ask Hackaday: How Hard Is It To Make A Bad Solder Joint?

When you learn to solder, you are warned about the pitfalls of creating a solder joint. Too much solder, too little solder, cold joints, dry joints, failing to “wet” the joint properly, a plethora of terms are explained  if you read one of the many online guides to soldering.

Unsurprisingly it can all seem rather daunting to a novice, especially if they are not used to the dexterity required to manipulate a tool on a very small-scale at a distance. And since the soldering iron likely to be in the hands of a beginner will not be one of the more accomplished models with fine temperature control and a good tip, it’s likely that they will experience most of those pitfalls early on in their soldering career.

As your soldering skills increase, you get the knack of making a good joint. Applying just the right amount of heat and supplying just enough solder becomes second nature, and though you still mess up from time to time you learn to spot your errors and how to rework and fix them. Your progression through the art becomes a series of plateaux, as you achieve each new task whose tiny size or complexity you previously thought rendered it impossible. Did you too recoil in horror before your first 0.1″ DIP IC, only to find it had been surprisingly easy once you’d completed it?

A few weeks ago we posted a Hackaday Fail of the Week, revolving around a soldering iron failure and confirmation bias leading to a lengthy reworking session when the real culprit was a missing set of jumpers. Mildly embarrassing and something over which a veil is best drawn, but its comments raised some interesting questions about bad solder joints. In the FoTW case I was worried I’d overheated the joints causing them to go bad, evaporating the flux and oxidising the solder. This was disputed by some commenters, but left me with some curiosity over bad solder joints. We all know roughly how solder joints go wrong, but how much of what we know is heresay? Perhaps it is time for a thorough investigation of what makes a good solder joint, and the best way to understand that would surely be to look at what makes a bad one.

So before we reach for a lot of pins and stripboard to abuse with inadequately heated hot metal it’s time to ask you the Hackaday readers: what do you think makes a bad solder joint? How should we investigate the conditions required to go against decades of soldering experience and create a bad joint on purpose instead of a good one?

We’d expect the variables to be temperature, solder, and movement while setting. Temperature is obvious, it’s easy to dial in successive readings on a temperature-controlled iron. But solder, that bears some investigation. It’s tempting to believe that all solders are created equal, but as we all know nothing could be further from the truth. Decades ago for example a friend of mine bought a reel labeled as American MIL-spec solder on the premise that if it was good enough for fighter jets it was good enough for him, and came away with the conclusion that if that was what kept the American war machine running then all the Soviets needed to do would be to gently vibrate whatever super-weapons they faced and watch all the electronics fail.

In truth he probably picked it up cheap because it was a dodgy batch, maybe even a fake, but it taught us an early lesson about solder quality. It’s not a problem limited to dubious 1980s bargains though, in recent years the arrival of lead-free solders has thrown this question into sharp relief. Do you find lead-free solder makes it more difficult to create a good joint? And once you’ve created a joint, how do you know it’s a bad one? Sometimes it’s obvious, it looks grey rather than shiny, and granular on its surface. If you solder a lot, you’ll just know that look from experience. But what electrical properties should it have? If we pull out a milliohmmeter, what resistance should we expect to see? It’s easy to spot a high resistance, but at what level of low resistance does a joint become bad?

We’d like to investigate these factors, but before we do so we want to tap into your collective knowledge on the subject. The Hackaday readership never cease to amaze us with their collective ingenuity, knowledge, and experience, it is probable that among you lie some of the world’s most accomplished practitioners of the soldering art. Help us answer the question: Just how hard is it to make a bad solder joint?

70 thoughts on “Ask Hackaday: How Hard Is It To Make A Bad Solder Joint?

      1. I was assembling a large board and had a jar of resin flux for the large pin packs. Like a doofus I spilt a bit and it dripped a bit on my pants. That never EVER comes out. You have a hard resin spot on your clothes forever. Just a warning lol

          1. @spacecoyote: concentrated sulfuric acid is NOT the solvent asked for here :-)
            I would try alcohol (denat.) or a solvent like paint thinner. This will not dissolve common fabrics.

          1. i know a string instrument player that swears to alcohol for cleaning rosin, i usually pilfered all of his broken off pieces and “bottoms”, they still serve me well when soldering.

  1. There are many many words on this in the European Cooperation for Space Standardization, which is the set of “rules” that ESA (try to) apply to people supplying stuff for ESA space programs.

    Here’s the specs for manual soldering: all 106 pages of it:

    When I’m doing stuff at home, the biggest problem is movement during solder cooling, which is cured by using a separate stand so I don’t have to have five hands.

    1. Reminds me of the most McGuyver-esque solder I ever had to make: using a screwdriver, a lighter and some tin-lead solder. It didn’t stick, make a horrible cold joint but I was so proud :D

      Now I always have at least a small USB soldering iron with me, for quick repairs.

      1. I have already used a blue-flame storm-proof butane lighter for soldering several times. Even to replace broken connections on/to speaker diaphragm. I just had to shield it with some layers of Al-foil. But since that time I have a cheap soldering iron in the car.

  2. It’s easy to make a bad solder joint. Use a solder gun, no flux and pipe solder. You’ll have huge gray blobs that dont stick to anything, burnt wires, contacts and PCBs. But it may still be good enough to fix a loose wire on the battery contact of the old broken portable cassette player…


    1. I had a 200W solder gun for a few years before getting something better. Amazing what was possible once I learned that just loading up solder and trying to flick it onto the joint wasn’t the way to go :P Definitely prone to bad joints though – the only thing I miss was the insanely short heat-up time!

      1. On an electronics course a couple decades ago I spied a fellow student applying solder to the iron above the joint, and letting molten solder dribble down. Like dropping wax from a lit candle. Tried to give him a couple of tips but he ignored me as I was half his age (10 years vs 20).

    2. Oops… i’ve accidentally reported your post when i just wanted to reply.

      My two cents: the wrong kind of flux will also cause great harm. Very bad corrosion that eats away the copper paths and even the tip of my iron.

      1. I’ve used REALLY bad flux before. I learned not to buy the cheap stuff.

        You don’t have to worry about accidentally reporting comments. They know that mobile users hit them all the time and have a minimum limit.

      2. Yup, I’ve seen someone do that trying to fix some suspect joints on an 84 pin PLCC socket. He covered the bottom in plumbing flux and retouched everything. It didn’t go well, pretty much every trace on the bottom around the socket was goneski :/

    3. Not hypothetical, I’ve soldered with a pipe fitting solder gun and giant solder; something like 3/16th inch flux core. Nasty flux, too, meant for pipes and not circuits. But, it was what was around and I just needed some through-hole parts tacked together. Don’t remember if that was an A.M. radio or a guitar pedal or what. Yeah, had to reheat a few joints (if it was my first effects pedal it was probably the 1/4″ jack soaking heat) and even pull a part loose and flick too much solder off to get a good joint. But it showed me how to spot the common had joints.

      Now, even with a cheap two-temp iron most of my mistakes are through-hole pieces wobbling while the first tack cools.

  3. In my limited experience, I’ve found that for hobby stuff and prototypes you really can get away with a lot. I say limited experience because pretty much everything I do is audio frequency range or lower; the fastest signals I deal with regularly are 150ish Hz low resolution PWM, and I assume RF circuits are much more sensitive to workmanship defects. But for low frequency circuits, as long as the flux behaves, the joint wets, and the solder cools still, stuff will just work and the connection will be mechanically strong. And those problems can be diagnosed via simple visual inspection.

    For reference, I use Chip Quik no-clean rosin core 0.020 96.5Sn/3Ag/.5Cu solder and a 750° F iron. I’ve found that good joints with this stuff don’t look quite as nice as the perfectly shiny lead examples many are used to, but I’ve never tracked a problem back to a solder connection that meets the criteria above.

  4. It’s harder to make a bad solder joint if you use 63/37 tin/lead solder with a rosin flux core. 63/37 has a sharp phase transition between liquid and solid, reducing the window of opportunity for a bad joint caused by vibration during cooling. Common 60/40 solder solidifies more slowly. Rosin provides good wetting for the joint, compared to no-clean flux. (I switched exclusively to no-clean some time ago, but I miss rosin flux.)

    If you’re a beginner, there’s no reason not to use leaded solder IMO. RoHS restrictions generally don’t apply outside of mass-market products for an international audience. Working with lead-free solder is a good skill to have, but it’s enough of a challenge that it’s best approached as a refinement to existing technique.

    The biggest single factor in good soldering is practice, and lots of it. Over-analysis of a beginner’s technique isn’t a substitute.

  5. ” Do you find lead-free solder makes it more difficult to create a good joint? ”

    I do find that the lead free “electronics” solder sold at the local hardware store melts at a good 100 C higher than the old variety, and that causes a load of troubles with cold joints, wetting of joints, and irons not being hot enough to even melt it in the first place.

    The lead free solders don’t wick well because the surface has to be hot enough for it to adhere, and the further away from the tip you go the lower the temperature due to thermal resistance so it simply beads up. It would require a searing hot iron to heat the component leg and the vias and traces over the usual distances, and that means burning flux and board resin.

    1. It’s also more expensive, and some say the resulting joint is more brittle but I haven’t experimented with that.

      I also had a leftover from a spool of 6% or 7% silver solder, which is hard and bright and probably more useful for plumbing or metalworking. It’s low resistance and strong, but when it gets cold enough there seems to be some kind of tin pest that makes it break out in white powder. Doesn’t fail outright, but it’s like someone dusted fine sugar on the circuit board and then blew the excess off.

      I can’t remember if it was SnAgCu or SnPbAg but the melting point was 235-240 C

    2. I was unsoldering some dead caps from a modern SMT board. Even a 100 W iron could barely do it, while it melts old lead solder on contact. Very annoying and strange.

    3. i prefer leaded solders as well, fortunately we can still use it in our company despite health and safety.
      that said i don’t feel like unleaded solder for most applications really is that different, i find that any truly eutectic solder will be easy enough to handle provided one has the right iron, besides many of the eutectic alloys have melting temps that are only 25 degrees Celsius higher than eutectic sn-pb solder.

      i find non eutectic solders to flow weirdly compared to properly eutectic ones, the latter will also melt in a very either or fashion making part alignment less of a hassle.

    1. Be aware the water solubles (even after wash) can result in a low resistance residue. Not too much a problem for low voltage, but, can be an issue for high voltage or high impedance circuits.

  6. I use leaded solder for everything, unless it’s a product for sale in which case I have to use lead-free (or, rather, the board assembler I farm them out to has to use lead-free!). I find leaded much easier to use, and it flows far better.

    I have never understood why some people, at least, don’t use extra flux when soldering. It makes life so much easier and ensures a good joint. Relying on the flux inside the cored solder is fine, if you have either a tinned or relatively fresh board, but I’ve never found it very reliable on bare copper. Maybe just bad experience on my part. I now slather everything with brown flux jelly ( and that improves things no end.

    1. I don’t know about Brown Flux Jelly, but I do know about endorsing extra flux to supplement flux core solder. Even just a little bit of paste flux makes a huge difference for fine-pitch components. Beautiful fillets and minimal bridging. I’ve been using Qhip Quik SMD291.

  7. If you want to create a bad solder joint, just don’t use any Flux! Works every time! In electronics work, it is pretty hard to not use some flux unless your using plumber’s solder to do the work. Most electronic solders nowadays include some sort of flux core, so they usually work very well with proper heat and technique and no additional stuff.

    The one exception to that is Lead Free: You almost always need additional flux to have good success. This is always true if you are like me and have a lot of scrounged, or surplus parts about that get used for builds, as they typically have some oxidation on the leads. This will usually cause a problem with pretty much any solder, Lead Free alloys even more so, as they are extremely sensitive to oxidation or corrosion.

    Over the many years I have been soldering, the key to a good joint is Flux. Lots of Flux, and the right kind mind you, as all fluxes are not created equal. Rosin is very good for general purpose, and there are more specialized types for applications that need to be clean, or depending on what metals/solder alloys you are working with. There are some great products available in pen or bottle form. Trust me, a gallon bottle of quality flux and a small dispenser for your soldering kit are well worth the investment if you do a lot of soldering…

    Also, don’t underestimate the importance of PRACTICE and EXPERIENCE! Lots of it!

  8. Try to get your hands on some high quality old school solder, see if it makes a difference to todays solders. I got a small amount of maybe 1mm thick solder from West Germany, manufactured sometime in the early eighties. It solders absolutely amazingly and it’s my goto solder for special projects and joints that I really want to put that extra effort into. Like saving a nice cigar for something special.

    Also test how important flux actually is, most guides for soldering say it needs to be applied to every joint, while I myself only flux very small and precise joints, never had a joint fail or be bad since I started soldering at 9yrs old.

    1. Flux application really depends on what type of joint you are making: If you have a fresh PCB, and new parts, you don’t usually need additional flux, as the stuff included in the solder core is usually enough.

      By using most solders made for electronics, you are in effect ‘putting it on every joint’, as it is included in the core and comes out when you apply the solder to the heated joint.

      One other note on cored solders: If it is very old, sometimes the flux inside is no good anymore!

      1. “One other note on cored solders: If it is very old, sometimes the flux inside is no good anymore!”

        It took longer than it should’ve for me to realize that!
        I put the year on most liquids/pastes now.

  9. The most common failure I have observed in the wild, inside of consumer electronics, is cold solder joints on physically large components. Unlike manual soldering were every component gets special attention, wave soldering treats everything the same. Physically large components in this situation require additional heating than the traces they are soldered to. Usually solder will bond really well to the circuit board side of the connection, but if there is the slightest film of oxide on the physically large component leads, then the solder will be tightly around the lead, but not really bonded. This is electrically sufficient to pass a device test, but later mechanical shock causes these same components with their greater inertia because of their larger size, to break loose from the joint and form a barely visible high resistance break between the lead and the solder that surrounds it.

    So to create a bad solder joint, it helps to be trying to solder to a dull, heavily oxidized surface.

    1. Those biggies are the first thing I head for with a Weller gun 100/140watt and old school solder when going thru something old, weather working or not. That center pin on most reg chips is tied to the heat sink and a big trace of gnd. Good luck with a pencil type iron in the 20/30 watt range.
      Always keep your gun handy. It’s ready in 3…2…1…go.

    1. Not real easy to tell if a crimp is done properly without destructive testing. But, a properly done crimp can actually be better than solder. Key word there is “properly”. And, properly is typically not achieved with a bargin bin tool, a hammer, or a pair of pliers. ;)

    2. simple, do as i was always taught on my first robotics team, and grunt. if you don’t grunt when you crimp it, you didn’t do it hard enough!!. works every time!

    3. Which type of crimp?

      Like Mac said the usual method of verifying/calibrating your crimp process & crimp tools is with destructive testing (pull-test), but there are plenty of visual criteria as well. IPC/WHMA-A-620 is the relevant (expensive) industrial standard.

      Specifics all depend on the type of crimp (machine pin, stamped and formed, coax, IDC, etc.) and product class. Generally, though, you’re looking for your stripped wire end to extend fully into the crimp area, insulation does not enter crimp area, a good bellmouth, crimp indent centered in the crimp area, and wire is not damaged.

      The simplest answer is if you’re not using a full-cycle (ratcheting) tool and the right size die it’s probably suspect. If you have the right tool then it’s usually fine.

  10. A cold solder joint? Oh, that is easy. Speaking from experience, and borrowing/paraphrasing what is probably an old saying: The three most dangerous things in the computer world: A coder with a soldering iron. A board-stuffer with a C+ compiler. And an end-user with an idea. I’ve been all three.

  11. When I was in the Navy, I was soldering a wire. I blew on it to make it solidify faster. A senior electrician snapped that I shouldn’t do that as it would make the solder joint more brittle than if you let it cool off slower. I taught myself to solder as a kid. I didn’t know any better. . . BTW, the senior electrician had a bachelor’s degree in electrical engineering from the Philippines. The Navy was getting a really good deal.

  12. Entirely depends on what kind of solder you’re using. With a eutectic solder like 63Sn/37Pb moving the joint isn’t that much of a problem, since the metal freezes consistently. With 60/40 you’re more likely to get that telltale frosty appearance, which comes from it moving in the plastic state while one metal is frozen and the other is still liquid. (Other ratios like 50/50 will be much worse, and shouldn’t really be used)
    With lead, if the connection is shiny, and there’s a reasonable amount of solder wetting to both surfaces, it will work fine.

    With lead free, it often frosts up, even on a good connection, so you have to judge it mostly on the shape of the connection. If it looks like a shape you would expect a drop of water to sit in, wetting both surfaces, you’re probably good. If it looks more stretched out and blobby, possibly with a bit of pulled outwards by the iron. (more gooey, like peanut butter) then you’ve probably cooked it, and it’s oxydized.

    Obviously, in all cases, if it looks like it’s beaded up, and hasn’t wet both surfaces, it’s clearly a bad joint.

    For a beginner, get some fairly thin 63/37 rosin core solder and a cheap temperature controlled iron (set around 350 or a tiny bit higher). Learn to add solder to the heated connection (not to the iron), and it’s hard to make a bad enough connection to cause any problems.

  13. Typically problems revolve around too hot and too cold. Bth, for leaded and non-leaded. It’s just that lead makes the process more tolerant to error. The point really is: did the soder truly form an interface with both metal sides or did it just “stick”. Thet’s the question which has to be investigated. And typically it can be investigated by pulling on the joint. So what I do to compare solder quality, is to solder 20 joints and try pulling them off with the wire soldered in. Leaded is usually 20/20, lead-free is easily less. Good lead free in combination with experience and high quality iron will be the same as leaded.

  14. “…We all know roughly how solder joints go wrong, but how much of what we know is heresay?…

    If what you meant to say was, “We all know roughly how solder joints go wrong, but how much of what we know is hearsay?”, then the answer is, “Most of it.”
    If what you meant to say was, “We all know roughly how solder joints go wrong, but how much of what we know is heresy?”, then the answer is, “Most of it.”
    There’s only one reason for bad solder joints: lack of experience; and no amount of ‘automatic’ equipment will cure this situation no matter how desperately one wishes that it would.

  15. Q: [Ask Hackaday:] How Hard Is It To Make A Bad Solder Joint?
    A: It’s the easiest thing in the world to do. Simply (a) decide you don’t need to work hard at perfecting this art and craft because (b) ‘automatic’ equipment provides the perfect answer to lack of skill, dedication, and practice (hard work).
    There’s always a simple answer.

  16. When your helping hand is your other hand you don’t usually over heat a solder joint and if you still can see a nice shiny surface with the tension curve inverted you should be fine.

    The worse I’ve ever seen was on the PCBs of those dirt cheap AC to 5v DC wall warts, if people knew what they were like they’d never risk using them.

  17. This should be demoed to every soldering novice (maybe even more experienced people who haven’t tried it before) to show what’s really going on:

    Take your standard flux-cored solder, and melt a blob on your iron.
    Wait until the smoke goes away (flux is burned off)
    Attempt to solder a pad and a lead with that. You will get a cold solder joint. There’s also a very, very high chance the blob won’t even stick onto the pad or the lead.

    Now, heat up the joint again – the pad, blob, and lead (Ideally, your iron doesn’t suck, the pad isn’t a huge heatsink, and everything’s big enough for your soldering tip to touch all three at once, but in case that’s not the case, do this first).
    Put a drop of flux (hopefully you have a steel needle dispenser or something that won’t melt too badly in case the it touches) on the joint.
    Watch as a perfect joint forms.

    Try this again on a fresh joint and fluxed solder, and take care NOT to touch the pad. If you do this fast enough, or give enough time for the flux to burn off, the solder will wet on the lead, which is easier to contact with your iron (with more surface area), and is a worse heatsink than most ground planes or pads, which generally have longer heating times due to the fact that they’re thin copper foil (higher thermal resistance) and have large area (lots of area to convect / radiate heat) compared to a relatively thick cylinder of copper.

    So these are the two ways most cold joints form: either one of the two soldered surfaces cannot be heated enough to wet the solder, or flux burns off before it can effectively remove oxides from the hot joints and solder.

    Both of these happen quite frequently with novices using crappy, cheap soldering irons with no feedback. Without feedback, the only way to prevent these irons from burning out is limiting the power so that even if you left it on for a while, it’ll sort of maintain a electronics-solder range temperature. This also means that after doing a few joints (especially ground planes), the temperature will fall so much that it’ll start making a bunch of cold joints, because you can’t heat up the joints to a high enough temperature to wet the joint. Even if you gave each joint enough time to heat to temperature, in that time, the flux in the core most likely burned off.

    Apart from metallurgical issues for wetting, it’s obvious where lead free makes all of this more difficult – at higher temperatures, oxides form faster (requiring even more flux) and fluxes burn off faster (requiring more flux) and your pads / planes cool down faster (convective and radiative cooling tend to occur at high powers of temperature, so a small increase in temperature easily equates to a noticeable increase in power required to heat up a joint)

    It’s always unfortunately how learning curves go when equipment is involved. Have a nice metcal? Most novices probably will have no problems soldering any joint you throw at them. Have a craptastic 15W thermostatic ratshack iron? An experienced solderer could probably do most anything, giving it time to re-reach soldering temperature between joints, and preheating joints as much as the components can handle before putting a drop of flux to make the solder wet.

  18. I haven’t seen it mentioned before, a preheater can make a huge difference when soldering pcb with large copper planes like pc mainboards. For example, replacing through hole capacitors can be very tricky as the heat is conducted away from the solder joint. Copper is an excellent heat conductor. Cold joints or unevenly heated joints are very common in such cases. I used an ir preheater once, which was great to work with. I also used a heatgun but you must be very careful not to heat up the pcb too quickly. Rule of thumb: 2-4 degrees c per second. Warping, splitting, cracking and burning can be the result. Preheat to about 150 degrees C. You could use a 3D printer and set the heated bed to 110 degrees or higher and use that as preheater hacker style. Soldering will be much quicker, tin flows easier, heatup times much shorter.

    Another thing to remember is that smaller and finer tips have smaller heat capacity, meaning the tip of the iron cools quicker when soldering. Just setting it to a higher temperature isn’t as straight forward, you can initially burn the pcb and flux, then be left with a cold joint. So if you intent to use a small tip for smd soldering, remember to switch tips for larger work or use a tip that’s a little bigger and you might be able to to both smd and larger connectors. Here also a preheater will help.

    The easiest thing to get a bad soldering joint in my experience are battery clips and pins on a switch. The larger the clip/lip/pin the harder it gets. The higher the heat capacity of the pin the more heat is needed and the longer and more gradual is the cooling. It’s compounded with dirty pins, grime, coating of nicotine and oxidation makes it hard so solder. Cleaning it with acetone or alcohol first will help, then use some flux.

    Another common hacker problem is toner left on the pcb, when using that transfer method. Cleaning it very carefully with acetone is essential. I think acetone is the basis of some of the no clean fluxes. So it doesn’t damage the pcb.

  19. Another consideration is the board you are soldering onto. If you are used to soldering simple 2 layer boards, and then try to solder a multilayer board with a large ground plane, you will probably have a hard time. I experienced this when recapping a bunch of G5 iMacs, those absorb heat from the iron like a sponge. At this point I had to buy a quality soldering station to get the job done, my cheap radio shack iron was hopeless for this project. With the right tool making a good solder joint is easy even on a dense board, just make sure to lower the temp before going back to 2 layer boards.

  20. Its easy to make a real rotten solder joint that even it functions well initially, fails at some later time.
    Its easy to make a good, fairly-reliable solder joint at home if you be patient and learn what works best:

    1. You need to prepare the work first. Clean the surfaces. Polish gently with Scotch- Brite Pads (Like
    3M 7777 07777 non-scratch). That is for the PCB. If the parts look oxidized, give them a little polish on the leads.
    That even goes for SMD, they might need a very gentle wipe. Use a microscope, they could be difficult to wet.

    2. PCB has gold on it where you need to solder? You might need to apply solder to remove some of the gold first, by wetting the PCB gold pad, use solder-wick, then apply a bit more solder, then use the part. Reason: Au embrittlement.

    3. Apply a small amount of solder flux (for home use, Kester 197 is favorite) to the PCB.

    4 With a clean solder iron tip, wetted with the same solder as what you are going to use, heat the work area first.Then apply solder. For SMD two terminal devices, apply the solder first to one side holding the part with tweezer in position so it doesn’t tombstone. Or use a tiny amount of epoxy ahead of time under the part to hold in place.

    5. Clean with denatured alcohol or isopropyl alcohol and a wooden Q-tip. Allow to thoroughly dry.

    6. With some kind of reflow oven and solder paste , this is all a different story, but the need for clean is still paramount.

    7. The above is very brief and admittingly incomplete.You can can good, fairly-reliable solder joints at home, but it does require patience. Don’t apply solder to the solder iron, then fling it at the work. Yes,I saw someone do this. Looked and worked like crap.

    Try to do it right the first time…..73’s

  21. RoHS solder gave me horrors. i got my first soldering iron when i was 11, and my soldering skills refined when i started my apprenticeship in a big electronics company (whis also produced MIL-products) with 15 years… 1995. when i had first repairs to do with lead-free solder on mini-computer mainboards (2006-2007?) i absolutely hated it. you have to heat it like a mad hatter and it doesnt adhere or flow well. when there was leaded solder again available “for hobbyists use” i bought it by the kilogram. i even have a stash of really old “radio solder”, which is thicker and the resin smells like a christmas tree – for ummm… special cases. this combines fine with the 120W soldering gun for soldering RF plugs for example. i dont own such a soldering station, but 5 or 6 different cheap soldering irons in the range of 15-100W. with enough practice – wow thats a whole 25 years now – everything is possible. even SMD is a piece of cake if you have superglue and a needle handy ;)

    1. addendum: for the *REAL* lazy guys out there, there is conductive superglue out there. great for repairing ignition coils where the pointy screw to the cable broke or rusted off

  22. The easiest way is to use something like Kaisi or BEST solder from ebay. It’s so bad that you can’t even tin a high quality thin copper wire with a ton of flux.

    I am going to buy some Kester 245 Sn62Pb36Ag02 to replace Kaisi because it’s simply impossible to get a shiny joint or to tin wire with it. No wonder that electronics from China are soldered like crap if the solder is some metal alloy with cat piss as flux.

  23. So in reading the comments there’s a lot of great experience about stories of “I’ve done this and how it failed”, and reminders that Flux is your Friend and that quality & type of tools and supplies are important. That was only the first part of Jenny’s question, though –

    Has anyone got input from more of the science-of-solder perspective (or IPC 610, NASA standards) as to what actually makes a joint bad? Resistance characteristics? MTBF of a cold joint? The data behind why IPC tells us not to over-wet and look for a good fillet or ?

      1. Thanks – there is some good info in NEETS module 4, though still fairly basic “moving the joint while cooling will cause a fractured joint” and “oxidization causes solder to not stick, so we clean it”. Is there other more detailed info I haven’t found yet or was that what you were referring to?

        For the google-lazy – I found the NEETS modules at, and a few others now that I have that keyword. Module four is a good reference on basic crimping, soldering, and wiring technique and tooling.

        1. No, I wasn’t referring to the NEETS, modules, but to training manuals which came out much earlier, and when the US Navy was heavily dependent on true craftsmen for the knowledge of, and repair of, electronics. The Navy has always taken the highly pragmatic approach that it would make craftsmen, using the best training it could muster (as an example, one of the finest books I ever found on transistor circuit analysis and design is a Dover reprint of a US Navy’s manual on the subject–in my university’s book store, no less!).
          Wish I could be more helpful; best of luck to you.

  24. Wether a solder joint becomes a good one can be seen best right while it’s being made. One has to see how the solder flows and wets both surfaces. If the solder does flow on both surfaces, the joint will be fine.

    Especially beginners tend to believe that joints have to be made as quickly as possible. That’s not true. Every electronic component withstands soldering temperatures for at least 3 seconds, modern parts made for reflow soldering a lot more. One should allow the solder to flow for these three seconds, should allow the flux to do its work for these three seconds.

    Common mistake is dirt/oxide on the surface to solder. And irons too hot, vaporing flux away and oxidizing these surfaces within a second. Basic temperature regulation is a must, especially for beginners.

    A pretty failsafe method to get a good joint is to first wet both sides separately. Then one can join them without additional flux and still get a reliable connection.

  25. Q: [Ask Hackaday:] How Hard Is It To Make A Bad Solder Joint?
    A: It’s the easiest thing in the world to do–

    All you have to do is read an article by supposed experts on the subject, whose expertise is totally non-existent and who expect you to believe what they have to say because they have SOME notoriety due to a completely unrelated set of circumstances.
    There was a blog printed on August 29th, 2014 in the Raspberry Pi Blogs, entitled “Learn to Solder With Carrie Ann”, in which the WIFE of one of the creators of the Raspberry Pi pontificates, “…I’d echo Mahjongg’s note on rosin fumes; I have a good friend who attributes his diagnosis with asthma in his 40s to solder flux.”. Mahjongg’s highly crdible and much-to-be-believed -advice: “…the rosin/flux causes fumes that are very unhealthy, so using a fan to suck air away is a good idea. …”
    One of their technical gurus [Gert] says, “You forgot about “the Fumes”: Soldering fumes are not healthy…”, and, “…I have used small computer fans in the past. I found that a “blower” gets rid of the fumes much better then a “sucker” but then you just spread the fumes around. A real fumes extractor has a filter to bind the toxic particles…”; and the wife chimes in with, “…Gert’s brilliant, isn’t he? :)”
    One of the ‘posters’ nails it, I think, with the following:
    “…There is absolutely no evidence, nor has there ever been, that the fumes from rosin-core solder is a health problem.
    I was “born” with asthma, started my electronics hobby when ten or eleven, and had the last asthma incident at around nineteen. MY evidence suggests that rosin-core fumes cures asthma.
    “And consider ALL the hand-assembled, soldered electronics which were produced in the world during the entire twentieth century, and continues to this day.
    “If you want to listen to the alarmists, go right ahead and spend yot money foolishly. Your other two options are to enjoy the slight, pleasant aroma of evergreen sap, or put a small fan on your workspace to blow those nasty fumes away.”

    Everybody check out this blog. There IS some good information here. Pathetically, it does NOT come from anyone associated with Raspberry Pi; some of the comments from ‘posters’ needs to be taken with a shovel-ful of salt, as well.

    1. Some final thoughts on the subject–

      0. Do not ever use acid core solder or acid flux for electronics work. EVER!

      1. Everything to be soldered together must be new, bare-metal clean; that means sandpaper-clean or steel-wool-clean if you think there’s the slightest chance of oxidation.

      2. Don’t get uppity about soldering equipment–sure, that $200 workstation is spiffy, but you need a Bernz-O-Matic gas torch to solder microwave feed-horns, waveguide, copper water and A/C tubing, and a lot else. Use what’s needed. A craftsman is a person, male or female, who knows which tool to use for which task.

      3. “My favorite programming language is solder.”
      –Bob Pease, one of the best.

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