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How to learn SMD soldering

  1. Apr 26, 2012 #1
    I'm not sure if I'm in the right place or not, but this seemed like the closest match to the question.

    Can anybody give me some suggestions on how/where to learn to solder surface mount components well? I know there are lots of youtube/etc videos on the topic, but I don't want to pick up bad habits from people who, for all I know, taught themselves how to do it. I taught myself how to solder components with pins, and about 2 years later realized I was doing it wrong.

    Thanks for your help,
    Mike
     
  2. jcsd
  3. Apr 26, 2012 #2
    Regret to say manual smt soldering is impracticable. The components are just too small to handle and their thermal capacity is very small as well so most soldering irons will fry them before a good joint is made.

    Industrially smt soldering is done by wave soldering - there are quite a few video clips on youtube showing this in action.

    Regards

    Sam
     
  4. Apr 26, 2012 #3
    This is only true to certain parts like BGAs. You also would avoid doing it by hand at all costs for a production quality board, but if you're prototyping or doing it for a hobby its fine. Believe it or not, big manufacturing factories do a lot of hand rework on SMT boards, and one technology does not fit all like wave soldering; it depends on the board layout and combination of components used.

    I hand solder 0402s, the smallest pitch SSOPs, those really tiny flat flex cable connectors for LCDs, and other stuff like that. Tiny SOT-23s and other things are all doable with a soldering iron. I even scratched off the mask on a PXA270's .8mm pitch BGA vias and inserted wires to rewire a BGA chip on an 8 layer board.

    The only thing that will be impossible is for you to place and solder large BGAs. There is no reliable way to align and heat it without a little mini manual BGA placement machine that uses a mirror to show you underneath the chip. A heat gun can be used for really big pitch/small pin count ones and, of course, you can always remove them. You can also buy sockets or premade adapter boards that come with the chip on them that are easier to solder if you want to use BGA chips on a hand soldered board.

    OP, you just need to practice. You will learn there's certain ways to do the different parts. An 0603 resistor is soldered/removed differently than an 0603 capacitor, and you just learn the technique by doing it. Resistors are easier to hold in place by just pressing down on them in the middle (they're more flat) with a closed tweezer and easier to use a flick/flip technique, and they transfer heat across to the other pad more easily so you sometimes only need to heat 1 pad to remove/solder it. Capacitors are easier to hold on with tweezers since they have a larger height, but their pads can break off more easily if you remove/resolder too many times. If you have a flat head solder tip, you can place it across so its touching both ends of the capacitor and heat the pads simultaneously to quickly remove it instead of switching from side to side hoping both ends will stay hot enough long enough for it to come off.

    Another technique for ICs like SSOPS or TSOPS is to flood the entire row with a certain amount of solder so that all the pins are shorted, and then use the copper braid to pull off most of that solder. Then you can do fine touches and make sure all the shorts are removed and that each pin has enough solder. Its fast and it works, but of course its also not something you want to do for a production board. Also, when you're soldering these types of parts, it helps to hand solder 1-2 corner pins to their pads to hold it in place and then do the real soldering work on the rest of the pins.

    Also, be careful of using too hot of a soldering iron. Not only can you damage parts, but you can also damage traces and pads on the board. You can heat the copper on the board so much that the glue holding it to the board will breakdown and you can lift pads off the board if you're removing a part.

    A hot glue gun can be useful if you're adding parts to a board that was not designed for them. You can glue an IC upside down (like a turtle on his back) onto the board and then use really small wires to connect its legs to the different points on a board. Then you can cover the entire work in hot glue or epoxy so it stays in place. You can also scratch off the solder mask and solder a pin directly onto the ground or power plane to hold it in place.

    What will help you greatly:
    1. A good, adjustable light source so you can see from different angles.
    2. A good eye piece like the kind jewelers use. A microscope works too if you have access to one, but always have the eye piece because its more versatile.
    3. A multimeter to check for shorts. You need to always be checking your work for shorts since solder can hide under the part.
    4. Dispensable flux, and different sizes of solder. Sometimes the flux core solder can help, and other times it can make the job more difficult.
    5. Lots of tweezers, exacto blades, dispensable cleaning alcohol, copper braid, and brushes.
    6. A really good soldering iron with fine points tips and adjustable temperature. You won't be able to do this with a cheap one. You will also use the soldering iron as manipulation tool to move/slide the parts in place.
    7. A heat gun is really important for removing and fixing solder work. A lot of times you dont even need a soldering iron to place some of the ICs if you presolder a couple of the pads and and then heat the leads/pads til the IC sinks into place.
    8. Have extra parts. The more important/complex the part, the more important to make sure you have an extra in case you ruin it. Always order x2 or x3 what you need for the little resistors or caps that are only $0.002 a piece.
    9. Lots of the smallest gauge jumper wire.

    Edit: One last thing is to have lots of patience. It can be really frustrating sometimes when a part seems to want to move on its own and thwart all your attempts to solder it, and then it burns up/damages when you finally got it in place.
     
    Last edited: Apr 26, 2012
  5. Apr 26, 2012 #4
    A lot of practice. You need a low power microscope, those with two eye piece stereo type for looking at diamonds. I think they are about 40X. You need a very good solder station with two solder gun and have all different tip options. Metcal is one good brand. You cannot use anything amateur. They even have tips for big ICs. Two solder guns are needed when you want to remove a small two terminal component, you use one on each side to melt both sides at the same time, then just flick the iron and the component go flying out!!! Good magnifying light, I even got one lately for my music electronics use even though they are all leaded component ( I am not into S and M!!!!)

    It is not easy, but it needs to be done. You cannot just rely on wave solder and all because it is so common during engineering phase to have to change the circuit, value of components. I can do 0603. But we had young Vitnamese girls that were very good in doing 0402 and all.
     
  6. Apr 26, 2012 #5

    berkeman

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    Staff: Mentor

    I'm with DragonPeter and yungman -- we hand solder and rework SMT stuff all the time in our lab. You should use a good-quality RF heated soldering iron to avoid the problems that you mention. We use Metcal soldering stations -- they work great all the way from SMT parts up to large cable assemblies:

    http://www.okinternational.com/images/big_photos/MX_500S.jpg [Broken]
     
    Last edited by a moderator: May 5, 2017
  7. Apr 27, 2012 #6
    There are many examples on instructables.com and YouTube. I haven't tried any myself, yet -- I still need a decent soldering station.
     
  8. Apr 28, 2012 #7
    Try www.eevblog.com. Another good forum for tech stuff. i kinda go between the two. here for mathematical more related questions and there for the more technical. And dave actually has some useful videos as well ;)
     
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