Hand-soldering MSOP Parts

I mentioned awhile ago that I’ve been hand-soldering rather small SMT parts. I received my latest batch of PCBs from BatchPCB.com last week and populated the most interesting one over the weekend. It has two MSOP parts on it with leads on 0.5mm centers. Here’s one of the chips next to a drafting triangle; the tic marks on the vertical edge are millimeters and the marks on the horizontal edge are sixteenths of an inch.

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(Sorry for the bad lighting.) Yep, it’s pretty small. Here’s a shot of the PC board. The two MSOP parts will go on the pads near the bottom, labeled “LDAC1” and “LDAC2”. The holes in between labeled “4.096V” and “5V” are 0.1 inch apart.

IMG 0559

As you can see, there’s not much room between the pads. It turns out that soldering parts like this isn’t really any more difficult than soldering any other SMT IC package. You do have to be careful to get the part aligned just right on the pads before you solder it down, but once you do that and tack down leads on opposite corners the rest is routine. I had to reposition one before soldering it but the other I positioned successfully on the first attempt. I was working under a 5x magnifier, but then I’m over 40 and my near-field vision is not what it used to be.

Here’s a photo of the completed board. I did make one oversight when I drafted the schematic, but fortunately I was able to correct that by cutting one trace and bridging two pins together with a teeny dab of solder. After that everything worked as expected. It’s a 12-output digital-to-analog converter, with four 16-bit outputs and eight 10-bit outputs. It will be part of a MIDI to CV converter I’m building for my modular synthesizer.

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Note how IC1 and IC3, with their leads on 0.05-inch centers, seem huge compared to the MSOP parts, and yet they’re quite a bit smaller than their through-hole DIP versions.

UPDATE: See this post for links to a number of helpful videos about SMT soldering.

By adam

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  1. Crazy. So do you put solder on the pads and then melt the part into place? I’ve only attempted this a few times. Whenever I order a bunch of stuff from Mouser, I always screw up at least one of them and get SMT instead of through-hole.

    So when is your MIDI/CV converter shipping and where can I order? 😉

  2. I don’t put solder directly on the pads for ICs. Once they’re positioned, I tack them in place by touching leads on opposite corners with the soldering iron. The flux and the residual solder on the iron tip are enough to make the chip stay in place. After that I do what’s called “drag soldering”; basically you lay the solder along all the pins on one side of the chip and run the iron tip along them. The solder melts and flows under the pins. If there’s excess solder (there usually is) you remove it either with a dry iron tip or desoldering braid.Most of what I know about SMT soldering I learned from this page on BDMICRO’s site. I bought one of the kits for the ATmega128 prototyping board; that was my introduction to both SMT soldering and the ATmega series of microcontrollers.Sorry, the MIDI-CV converter’s a one-off. I’m smart enough to stay out of the hardware biz. 🙂

  3. nice work. is this an original design? i’m looking for something like that myself…
    have you looked into http://www.futurlec.com/PCBService.shtml for pcb production? i get my prototype’s done there.
    and i know what you mean about eyes over 40. i’m not too comfortable with magnifying glasses, so i usually end up with my glasses off and my face about 3 inches from the board…
    good luck with the rest of the project.

  4. It’s an original design.
    Futurlec’s service is way more expensive, at least for one-off boards, so I don’t see why I’d use it rather than BatchPCB.com.
    I use a Luxo lamp with a magnifier built into it. It has a lens that’s about five inches in diameter so it’s pretty comfortable to work with.

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