Populate SMD boads using a toothpick and tweezers

cnlohr-hand-applied-solder-paste

Here’s a demonstration which proves you don’t really need special tools to populate a surface mount PCB. We’ve seen this board before, it’s the glass PCB server which [Cnlohr] developed and demonstrated by connecting the real world to Minecraft. It’s a tiny board and we were happy to have the chance to see his method for populating the parts before reflow soldering.

In the video after the break [Cnlohr] starts by dispensing a glob of solder pasted from its storage container. He mentions that as long as you store the stuff in the refrigerator it’s rather easy to work with. Because most of his projects are single boards it’s not worth it to have a solder stencil produced. Instead he picks up a bit of the solder glob on the end of a toothpick and applies it to each pad.

This isn’t really as bad as it sounds. The fine pitch TQFP footprints can just be dragged with a bit of the paste. After this application — which took around seven minutes — he grabs some tweezers (not the vacuum type) and begins placing each component. If he missed some paste he’ll discover it in this step and add where necessary. The last step is a trip through his toaster oven.

[via Reddit]

25 thoughts on “Populate SMD boads using a toothpick and tweezers

  1. What do you mean, “not as bad as it sounds”? This sounds exactly right. The important thing here is no to put too much paste down.

    I just did it with a soldering iron and outdated paste that’s kept at room temperature, which is fine, but had I used a toothpick, there wouldn’t have been so much excess solder to remove.

    1. TQFP parts with a 0.5 mm pitch can be soldered slightly easier by just splattering paste everywhere and hotgunning it. :-p (even if you do have to go back and wick it clean with a soldering iron)

    2. Even 0.4mm TQFN parts (packages with no leads, and pads underneath the chip) are fine to do by hand with good quality solder and plenty of flux.

      1. I know it’s totally possible and without problems, I’m just saying it’s slower. It’s how I used to do it all before I switched.

  2. News Flash! Populating surface mount components, even 0402, is not difficult at all! Can we stop having these titles. Guess what, I work at a place where 60 year old men solder ency-wency surface mount components. Get over it.

    1. Sorry to say, but this cranky gentleman is right. It took me about 3 months, soldering a few (small-pitched) components once or twice a week, to become perfectly proficient. 0402 caps and resistors are a breeze. QFNs generally aren’t that bad if the pcb footprint was designed well enough (pads that extend out far enough), but most of the QFNs i’ve worked with had thermal ground pads underneath them that required reflowing (which i do with a reflow station/hot-air gun). Force yourself to practice, and you will be just fine. Start designing with 0805 sized passives and work your way down. I find it silly for people to be “afraid” of TQFPs… the package is such a great balance between compactness and soldering iron accessibility.

    1. You’re the second person to suggest this, and I believe you, too. I am totally going to give this a try. I like the toothpick method because it lets you play with it a lot after you have it out, but I would imagine a syringe would let you do that, too.

  3. Can someone dub this video in chinese so I can instruct some chinese kids to do it for me? I kid of course but man is that labor-intensive and tedious.

  4. We all end up facing the SMD beast one day. In my experience (without proper equipment), it has been usually an all or nothing situation. Either I landed the little guy dead on the first time or took out 2 or 3 components next to it sneezing. Either way, figured I would put the tip of hotglue out there to steady some things. Not for a whole board mind you, but a component or two repair job. The meds I was on at the time made me shake like a wet dog. Being the cheapskate I am, painters tape and hotglue got me through some rough patches while getting all of those little guys into place.

    /Nice guide OP

  5. Wow. Such angst over a guy showing how he does it.

    Seems to me the paste always prefers to stick to the toothpick than the copper. I have to more squish it onto the pads than drag it.

    Haven’t had much luck with parts with the pads on the bottom, but all the soic’s tiny resistors, capacitors and the like are pretty easy. I like doing it this way better than through-hole.

    I use an electric skillet for reflow. Nice on a cold day :D

    That was a pretty board. I might go back and see how he made it.

  6. The toothpick Idea is absolutely Genius. I am so going to use that method when I have to solder onto micro r/c boards or the next time I make an antenna for a Bluetooth dongle.

    1. I would recomend you to just use a plenty of flux and normal solder. Look up the videos where they talk about drag soldering. It is indeed that easy.

      1. I used to use drag soldering before, and it’s always alluring, but when I started doing the same board both ways, I found the paste method to be straight up superior.

      2. I think that I’m actually wrong and his method is better than drag soldering. Especially when you have a lot of small components on the tightly populated PCB.

        Pluses are that you do not have to mess around with the iron and have less risk of inhaling the flux fumes.

  7. guys … I do 0201 by hand with hot air and iron; have 36 0201s in a 1″ square pcb with 2 QFNs and other misc, made 5 by hand. How do you get to Carneige Hall? Practice, and don’t be afraid to break a few things. Just try to not have some new challenge be where you’ve got to get the proto working by tomorrow. If you don’t have a hot air rework station, that should be your next purchase.

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