Surface mount soldering gear

Discussion in 'The Projects Forum' started by icydash, Jul 19, 2012.

  1. icydash

    Thread Starter Active Member

    Jan 14, 2009
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    Hey guys,

    I have to surface mount this 28-pin SSOP component (http://www.digikey.com/product-detail/en/FT232RL-REEL/768-1007-1-ND/1836402) to a PCB for a project, but I don't own any surface mount gear. However, I do already have this soldering iron set up: http://bestchoiceproducts.store.buy...-hot-air-rework-solder-station/219598698.html ... as you can see, it has a hot air blower built in that I'm hoping I can use to easily solder down the component.

    I really know nothing about surface mount soldering -- all I know is I need to get the piece stuck to the board. What kind of "solder" do I need to use? What kind of applicator? Will that air blower work for me?

    I'm sure once I have the right tools, I can watch some tutorials and with a couple of tries pick it up ... I've actually done it once or twice before with my old professors gear, but I have no idea what he used.

    I won't be doing anything crazy, mass-produced, or complicated. Just need to get that component onto my PCB.

    If you guys could provide me with all the necessary tools and links to buy them, I'd really appreciate it. I kind of get overwhelmed with all this stuff, as there are tons of different kinds of solder alone with differing compositions, much less all the other tools.
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    The tip is probably fine enough to just solder down a 28 SSOP part directly pin by pin. If you have a magnifying glass (like a magnifying visor or free-standing glass), you should find it pretty easy with a little practice. Use a liberal amount of flux and go very gentle on the solder. Use the finest solder you can get.
     
  3. icydash

    Thread Starter Active Member

    Jan 14, 2009
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    So this is a dumb question, but what exactly is flux and how would I use it here? I usually just work with through-hole components, and I've never worked with flux before. I just ... take my solder and my iron and go.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    The solder you are using is almost certainly rosin-core flux solder. So within the solder is a substance (historically obtained from certain tree rosins) that is acidic when heated. The acid serves to chemically clean the metal contact surfaces so that the solder can take hold. Once it cools, it is no longer acidic but should still be removed by cleaning the board with a solvent remover (alcohol works well).

    But with real fine solder, the rosin in it isn't really enough. Plus, you have to melt some solder to release the rosin and you would really like to heat the rosin, clean the metal, then melt the solder onto the metal. So you lightly coat the pins with rosin paste (that you buy in a small can or a tube) and then touch the pin/pad joint with the iron and let it eat at the metal for a second or two and then lightly touch the solder to the joint.

    You will also want to keep your tip nice and clean. You can do this by dipping it in a little mound of rosin and then wiping the tip on a damp sponge. Then tin the tip by lightly touching it with solder. Don't let a bulb of solder build up on the tip otherwise you will end up with solder bridges (though, if you do, they are actually pretty easy to remove).

    The are a lot of methods and tricks to mounting SMD components by hand, but I think most people that aren't going to be doing it enough to keep the right "feel" for it are probably best off keeping it simple. And simple doesn't have to be (unacceptably) slow. I can put down a 240 pin 0.5mm pitch FPGA on a board in under 5 minutes doing it pin-by-pin (or at least I could a few years ago).
     
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    "Flux" is a chemical that helps clean the oxidation on metals so they can be soldered. If your solder still has the label see if it says if it has a flux core. I rarely need any extra flux then that which already comes in the solder. However, some extra flux can be helpful at times.

    If your solder doesn't have flux get better solder! If you've noticed a residue around your joints then you have the right stuff.

    I happen to have that same solder station unit (or very similar). To use the hot air side it is best to use solder paste, actually tiny balls of solder suspended in a flux. Since you don't have that...

    Here's how to get that sucker soldered down: tin ONE pad in a corner. Then put the chip in place and reflow that pin. Tweezers help here as does some sort of magnification which is why I have a microscope but a magnifying glass also works. Or young eyes.

    With one pin down inspect it and see if it is where you want it. You can twist it a bit on that pin if need be but don't break that pin! Then solder down the opposite corner.

    Now go back and reflow that first pin once again, especially if you twisted it. That relieves the tension.

    Next, tap each pin in turn and flow it. With a small tip, a steady hand and fine solder you may actually only short out half the pins. Not to worry!

    Now comes the final step: get some (fluxed!) solder wick. This comes on a spool and is just copper braid. Place the wick over the pins, press down with your iron tip until the solder wicks up into the braid. You can remove all the excess solder this way.

    There is usually enough solder left to keep things connected after you wick the pins. I think my reccord was a 144 pin FPGA with leads on .025 centers. If you get 2 pins the part holds itself in place while you get the rest.

    If you're daring (or cheap!) you can get along without the wick by heating the shorted pins and banging the board on the table to flick off the excess.

    OK?
     
  6. takao21203

    Distinguished Member

    Apr 28, 2012
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    Isn't the right thing to do.

    Use a broad tip, and just pull the solder ball along the pins.
    A broad tip is more than capable to pull off excess solder from SSOP chips.

    You don't even need flux or desoldering pump for these.

    Lead solder is a bit easier but tin is also possible.

    You need a 50W soldering iron, with high temperature setting.

    If you connect all the pins with one larger solder bridge, you can still melt it all up, and pull it away using the tip.

    It's quite easy for SSOP.

    Really soldering SSOP pin by pin with a magnifying glass is quite heineous.

    Some years ago I did not know better myself...

    Flux can make it easier for TQFP44 etc., also for SSOP/SOIC, but not really needed, just a bit if you would like to try it.

    But important is a broad tip. Or use a fine tip so it it is worked like a broad tip.
     
  7. icydash

    Thread Starter Active Member

    Jan 14, 2009
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    What about using something like solder paste?

    When I did some surface mount stuff in the past, I just put paste down on all the pins, one by one, using something that looked like a syringe. I then used tweezers to place the chip and pressed it down into the solder paste with my left hand, and used my right hand to simply touch the soldering iron tip to the paste on each pad, which hardened it. It was really fast / easy.

    Does anyone use that method? What kind of soldering paste / syringe applicator thingie would i use for this?
     
  8. WBahn

    Moderator

    Mar 31, 2012
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    Yes, that is one of the methods. If it works for you, go for it. People also tack a couple of pins and then run a continuous bead of paste over the pins and then run the soldering iron over it relying on adhesion to pull the solder apart and prevent bridges. Some people do something similar without solder paste and just run a soldering iron that has a little bit of a solder bulb on it. With practice, any of these (and other) methods will work.
     
  9. KJ6EAD

    Senior Member

    Apr 30, 2011
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  10. icydash

    Thread Starter Active Member

    Jan 14, 2009
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    After watching this video and reading all of your posts, it seems like the thing to do may be to get this paste flux http://store.curiousinventor.com/chip-quick-no-clean-paste-flux-lead-free.html.

    I can use it to apply liberal amounts of flux to my pads, but it is also sticky enough to hold the chip in place while i go about soldering it down. After i apply the flux and get the chip in place, i'll solder the opposing corners, making sure alignment is correct. Thereafter, i'll use one of the many suggested techniques for soldering the rest of the pins. Sound like it'll work?
     
  11. KJ6EAD

    Senior Member

    Apr 30, 2011
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    That's the expensive paste flux. It's overkill if you're not doing fine pitch chips a lot. I use ordinary rosin paste flux or liquid flux which are cheaper and readily available. The tackiness of paste flux is useful during component alignment but can't be relied on to keep the chip from moving during tacking because the application of heat liquifies the flux. You will have to hold the part down with the tips of your tweezers or a pick during tacking both to prevent misalignment and to keep it flat on the PCB.

    One step that the video's don't always show because they assume you know is that any time you see an iron tip loaded with solder headed towards a component, the component leads have previously been dressed with flux.

    Your planned steps are good. Practice on a junk board if you can before doing the real thing.
     
    Last edited: Jul 19, 2012
  12. takao21203

    Distinguished Member

    Apr 28, 2012
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    Yes correct. As mentioned I have done such point soldering a few times with SOIC chips.

    It's actually totally easy. I solder them the same way like you normally would do a joint: First heat it with the tip, then contact with the solder wire so it melts, and a connection is formed. But this time I move the tip!

    Sometimes I end up with kind of a bridge, depends on how much gap, and how much free area remaining on the traces.

    All what's needed is 1mm solder really, contains sufficient flux for SOIC.

    Flux I use for TQFP44 etc. These are a bit harder to learn how to do it.

    For SOIC it worked almost instantly when I tried it.

    If you work in a factory, you actually often have to use tools in the fastest/cheapest possible way...For larger TQFP chips you'd need a special hollow tip. Or I also saw a video using HQ flux and only relying on the tin that is already on the traces. I tried, but it is not relieable enough, pins need very good and even alignment for this, and checking all the traces is more effort than to bridge them all over 3 or 4 times (for fine pitch SMD).

    I must say I have done some 100s of these ICs, so it's easy for me now.

    Some years ago I destroyed a few fine pitch TQFP ICs while attempting to solder them.
     
    Last edited: Jul 20, 2012
  13. icydash

    Thread Starter Active Member

    Jan 14, 2009
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    Ok cool. Could you possibly point me to a flux you recommend? There are lots of options and I'm not really sure of all the differences.
     
  14. KJ6EAD

    Senior Member

    Apr 30, 2011
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  15. icydash

    Thread Starter Active Member

    Jan 14, 2009
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    Great thanks a lot.


    Thanks so much to everyone who replied in this thread. Your insight was really helpful.
     
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