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So I'm working on a small project right now that requires a ATmega32U4RC. I'm trying to test/prototype with it, but it's a surface-mount component, so I can't just place it in my breadboard. So I found this, which is perfect for what I want.

The problem is that I haven't soldered in quite some time. I've also never soldered a component with such tiny leads.

Needless to say, I ended up with this:

SMD "Soldering"

Yea, I know it's bad :( The solder-wick didn't really seem to want to do it's job (anyone know why this is?), so I couldn't really clean it up.

Are there any tips for doing this (tools that might help me, etc.)? Is there an easier way to do this than hand-soldering?

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    \$\begingroup\$ For surface mount parts, get the narrowest solder wick you can find, and use plenty of flux. Contrary to what many first assume you actually want a relatively large iron tip. Also if you plan to do much of this a hot air station can now be had for around $60 which makes fixing alignment type mistakes a lot easier, even if you stick with hand soldering rather than going the stencil & paste route for which it can also serve. And get a cheap 10x eye loupe to check your work, though a stereo zoom microscope is even better. \$\endgroup\$
    – Chris Stratton
    Oct 16, 2016 at 3:38
  • \$\begingroup\$ This doesn't look too bad for someone who haven't soldered for some time. Still, easily repairable with desoldering braid. My method to do this by hand is using a tin-free tip, pressing the individual pin down onto the pcb with the tip, then putting the solder onto the pad only. \$\endgroup\$
    – Janka
    Oct 16, 2016 at 4:11
  • \$\begingroup\$ Thank you for the replies! What kind/shape (wedge, cone, etc.) iron tip would you guys recommend? And what temperatures should the tip be at? \$\endgroup\$
    – Max Jacob
    Oct 16, 2016 at 4:16
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    \$\begingroup\$ I want to emphasize what Chris said: the hot air stations available on ebay for $60 include a solder iron, lots of different tips, a hot air gun, and a power supply and volt meter. The banana jacks are more cheaply made than I've ever seen in my life. But the rest is workable. Also, AmScope makes binocular boom arm microscopes, many for under $200. I use a 10X-20X SE400-Z and almost couldn't do without it. \$\endgroup\$
    – jonk
    Oct 16, 2016 at 7:41
  • \$\begingroup\$ Before I go back to try again, how long should I leave the tip near the pins? Will they degrade/melt if I leave the tip near them for too long? \$\endgroup\$
    – Max Jacob
    Oct 16, 2016 at 16:04

3 Answers 3

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Learn to use "drag soldering" technique. Basically, instead of trying to solder each pin individually, you just get a bead of solder on the tip and roll it across the pins. As you hit each one, it'll leave just enough solder on the pin to attach it.

A video will do a lot to help explain here:

https://www.youtube.com/watch?v=wUyetZ5RtPs

There's a few things that help make this work:

  • Apply flux - lots of it - before you start soldering. Yes, I know the solder you're using probably has a flux core, but that's not enough here. (If you use paste flux, the paste can also help keep the part in place.)

  • Using the right kind of tip helps a lot. A small tip is not what you want here! I use a Hakko "hoof" tip (T18-C2); there's probably equivalents for most other good irons.

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    \$\begingroup\$ With some practice, drag soldering is really working very well. We solder 0.5mm pitch ICs without problems. Sometimes desoldering wire can be useful if the are very tiny, hard to reach "bridges" between two pins. \$\endgroup\$
    – Rev
    Oct 16, 2016 at 9:30
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Get better (fresher?) solder wick. Digikey carries it, you can have it next-day.

It will clean that up very nicely, in seconds.

You may have to add more solder then suck it away. Looks like you are already using 63/37 but it behaves a bit more nicely than lead-free solders.

Before soldering, make sure the board is clean (your ENIG board should be fine). For a prototype I like to use a flux pen (like a Magic Marker/Sharpie but it contains liquid flux) on the contacts- some use liquid flux from a bottle.

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The QFP-44 with 0.8mm lead spacing is far from the worst case. There is no way to escape micro-miniturization of electronics, 0603/0402/0201 components, and 0.4mm - 0.5mm QFN packages. Even BGA is in line next for DIY folks.

  1. First, get a good iron. It is always worth to have a good tool even if you have this for hobby, to avoid frustration from bad solder joints and non-working projects. JBC is probably the best, next is/was Weller, but they looks like having business issues. I use mid-end Weller WX1011 with WXMP-MS iron (40W), with 0.1mm cone tip (RT1-NW) and several other interchangeable cartridges (knife shape). Tip temperature - 380C.

  2. Next, get a spool of regular 63/37 solder wire with rosin core, I use 0.010", smallest available. And 0.032" for bigger jobs.

  3. Get a rosin-based mildly-activated flux, Kester flux-pen 186.

  4. Get a cheap stereo microscope, 10X-30X from eBay, they can be in $120/$170 range, to check for bad joints and solder bridges and parts alignment.

  5. Get a cheap ($30) Chinese hot air pen from eBay, it helps a lot in finishing solder joints on SMT components.

Soldering rule #1 - Use More Flux.

Soldering rule #2 - Use More Flux.

Don't use "no-clean" stuff or ROHS solders. "Drag soldering" does not work well for pin spacing under 1mm. Solder wick is your friend too.

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  • \$\begingroup\$ Drag soldering works fine at 0.5mm pitch once you get used to it. \$\endgroup\$
    – Chris Stratton
    Oct 16, 2016 at 7:26
  • \$\begingroup\$ Yep. Drag soldering requires precise temperature, right amount of solder excess, and proper flux, so the surface tension can break bridges. This set of condition exists only for a certain period of time since the solder tip does not have steady supply of solder, after which you either have no solder, or continuous bridge if you have too much. Tthen you have to wick it out, and then apply the solder again. Just watch the video linked by "duskwuff". How many times the heat is applied to pins? Do you know that overheating does not improve reliability of silicon chips? \$\endgroup\$
    – Ale..chenski
    Oct 16, 2016 at 14:51
  • \$\begingroup\$ Here is another example from the same guys, youtube.com/watch?v=Iu4rfutdm9g Look carefully at 8:30" time. This is a "poor man" trick when one can't afford right-shaped equipment. \$\endgroup\$
    – Ale..chenski
    Oct 16, 2016 at 14:52
  • \$\begingroup\$ You are making this much more complicated than it needs to be. The "set of conditions" are not very hard to achieve - if you have too much solder, wipe the iron tip on the sponge to remove it. And yes, if reheating with flux doesn't do it you might need the braid. Even with lead free solder these operations are very unlikely to result in damage. Needless to say considerations for avionics or critical systems would be different, but an inexperienced person should not be working on those to begin with. \$\endgroup\$
    – Chris Stratton
    Oct 16, 2016 at 16:38
  • \$\begingroup\$ @Chris, you can certainly use a 200W soldering gun to do whatever soldering reflow or else on 0402 components or 0.5mm leadless QFN. My current garage toolset starts from el-cheapo MPJA 15845-TL station, Weller WTCPT iron, Metcal MX-PS5000 with various tips, Hakko FM-202 with tweezers, and finally Weller WX1011. I am practicing soldering tasks for 55+ years, starting a teen age, and was doing occasional rework for the last 20+ years in semiconductor industry (including BGA jobs), and believe me, nothing is better than a 0.1mm conical tip of JBC or Weller handpieces to enjoy soldering. \$\endgroup\$
    – Ale..chenski
    Oct 16, 2016 at 17:44

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