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Comment by severino | Hacker News Reader

What would you say is the best (but affordable!) way to solder SMT parts like this kind of connectors with small pitches?

https://no.mouser.com/images/marketingid/2016/img/163696678....

Last time I tried using the basics (Hakko soldering iron, with all kind of tips, flux, different types of solder...) I only got a bad soldering with lots of contacts between pins, and some other pins seemed to make a poor connection.

Also, as those are not very common parts, I could not have it soldered in a fab like JLCPCB and the like...

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It's not very difficult if you do drag soldering rather than attempt to solder the pins one by one. I do it in a slightly different way, just put a ton of solder and clean the shorting with braid.

I'm not so proud of my soldering skills, while still managed to hand solder more than a dozen of such FPC connectors (0.5 mm, 45 pin, Wurth Elektronik 687145149022) with just a standard Weller station for a project at work, and only non-fatally screwed up my second one.

Yes, drag soldering was the only technique I considered. However, it didn't work very good. As said before, the main problem was that solder created shorts between pins, and some others were left with bad connections. I also tried to use braid to remove the excess solder, etc., but I felt the more I tried to fix it, the worse the result.

I once watched this video about SMT soldering, and while the guy seems to be using just a soldering iron and flux, the result is outstanding. I don't know however which specific equipment and solder/flux he is using, and if it's real or there's some kind of trick involved :-D https://youtu.be/5uiroWBkdFY?t=112

Maybe you can try some different brands of braid and flux.

However, actually I got four out of the dozen done without even brand braid, but with some scavenged copper grounding braid, as the proper one usually on the bench was stolen by a colleague :).

I've had success with the basics you mention, but I found very important to have a good holder for the PCB and a magnifier with light. You need to see the details while you're soldering. You need decent bent needle tweezers to manipulate and hold the part. Also a stronger magnifier (hand-held) for inspecting my work is useful, as well as an ohmmeter. And finally to fix mistakes I found desoldering wick to be the easiest.

Yes, I thought about the magnifier, but how would one do the soldering? Soldering each pin at a time? As those parts have 0.5mm or 0.8mm pitches, I only tried with this "drag soldering" technique, but with the aforementioned results.

I usually apply solder on 1 pad on the PCB, then hold the part with tweezers and place it while heating that pad. Once the placement is good, I solder the rest.

I tend to do them 1-by-1, not by dragging over the complete row. If the pitch is smaller than the iron tip, you don't have a choice and need to solder several at once, but usually with flux and the right quantity of solder it works itself out.

For the problems you mention, adding flux and reheating usually works. If there is too much solder, you need to wick some away.

I think your cheapest route is to build a DIY reflow oven using a cheap toaster oven. If you don’t want to design the controller yourself, one option is to buy a kit such as the Controleo3 [1].

[1] https://www.whizoo.com/controleo3

This guy has great tutorials, and tips, about soldering. You may be interested in this video primarily https://www.youtube.com/watch?v=0LSG5uIdqJc

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