Hi guys. During this modding I did make sure to prethin the soldering pads and wait for the solder to melt. Everything works perfectly, but now looking at these picture, the soldering joints don’t look beautiful.
Are they cold soldering joints?
Do you thing that worth opening the bezel to redo the job? (the bezel is pressed, so it’s kind of hard to opening and I’m afraid of it becoming lose).
These joints look better than mine! All good.
Thanks!
Yeah it’s fine. To get nice shiny round joints the solder needs to stay molten for a moment after the tip of the iron have been removed (and still with an excess of flux), for that the MCPCB needs to be hot enough. What I do is put something under the MCPCB to prevent the heat transferring to the body, like bent paper clips in the wires MCPCB notches, or a small bit of toothpick. Then I melt a blob of solder on the pad, wait the MCPCB to get nicely hot, then bring in the fluxed wire to that blob, and finally remove the tip.
Nice tips 
That’s probably what happened since the MCPCB was already completely mounted. As soon as I removed the tip, the solder instantly solidified. Also, I used solder paste instead of solder wire. Do you think it’s fine?
I concur, looks ok. Doesn’t really look cold, per se, but if you wanted to ensure and neaten them up, then you could just put a couple drops/small dab of flux on them and reheat for a moment. Wire insulation is above the cut, which is good…see lots of people (and manufacturers, even) let the exposed wire go down below the isolated surface of the board or rest precariously next to the sharp corner, which is a great way to get shorts.
Thanks for the advice. I think I’ll let this way. They probably won’t go anywhere or give a bad connection, right?
It was a pain in the ass to remove and reinstall the bezel.
Yeah, these joins won’t be going nowhere. You’re good!
By the way, which Jaxman flashlight model is this?
It’s a Fenix E28R. I just removed the sst40 and installed this 219c that I got from Jaxman on Aliexpress.
You can shine up those solder joints if you want to, but looks fine as is. If it’s a cold soldering joint, it would disconnect if you move the wires around.
Like others have said, put some flux on the joints, get your soldering iron nice and hot, make sure the iron tip is clean, put some solder on it, and then press it down on the joint while separately holding down the wire, wait until it gets nice and hot, and then remove.
Flux is very important for shiny solder joints. If you don’t have any, soldering can be difficult and can look sloppy. This is the stuff I use: MG Chemicals 8342 RA Rosin Flux Paste
Ideally the MCPCB should be separated from the shelf, but if the soldering iron is big and hot enough, you should be able to do as is.
I have not used any flux separately, just mechanic solder paste. Maybe I’ll get some.
Interesting though, today I reflowed a 219c on my s2+ and resoldered the MCPCB. In this case, the solder has become shiny. Possibly because I used more solder paste and the MCPCB was lifted.
Mechanic soldering paste is a mixture of flux and solder. But after awhile, the flux burns off and all your left with is solder. And when that happens, all you need to do is add some more flux to make the solder new and shiny again.
Nice to know.
Pros and cons of using a no clean flux? I read some of the reviews for that flux that said it could cause shorts.
No clean means it doesn’t need to be cleaned, it’s not corrosive and not conductive.
So I would assume it is preferable?
I’ve heard even no clean flux can cause issues on some parts, but for the most part you can leave it
Well, ideally solder joints should look like these:
But it’s easier said than done when the pad has a high thermal mass. So I’d just leave them like they are now. They are good enough considering you don’t have a high current, high stress, high vibration or safety critical application.
But for the future, avoid solder paste, and just use normal leaded solder wire. After re-tinning the wires, I tin the pads, continue to heat them, and then move the wire ends into the molten solder. After 2 seconds I remove the soldering tip.
But even if the joints don’t come out perfectly, I don’t rework because heating to often, too hot or too long is not that beneficial for the material sitting under the pad.
I just found that even NASA does not have this kind of joint covered:
https://workmanship.nasa.gov/lib/insp/2%20books/frameset.html
Or I did not look hard enough…
But it’s still there. I don’t like this and clean the board nevertheless.
I was attempted to open it again and try to make a shiny solder joint, but the risks would be bigger than the benefits.
I took a look at these NASA standards and seems like they only use THROUGH-HOLE SOLDERING for
DISCRETE WIRES. That make sense because the wire can put some stress and end up detaching the tracks of the PCB.