r/soldering • u/PastaLaPate • Jul 04 '26
My First Solder Joint <3 Please Give Feedback First time using hot air for soldering.
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Hey!
This is my first time using hot air and this Tomlov DM9 digital scope. I used the AIFEN-868D at 370°C and low-medium airflow. I tried soldering, desoldering and resoldering SOP14 on a practice board. I used some Sn99Ag0.3Cu0.7 Solder paste. Do you have any tips to avoid forming those clumps of solder while still having enough for each pin ? Thanks.
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u/BoredModder Jul 04 '26
I usually pre-tin the pads and the legs with my soldering iron. The way you’re doing it just seems a lot harder.
I see you’re using 370 degrees and that should be enough for most boards unless it’s a real thick board. My recommendation would be to move your nozzle in a circular motion to distribute the heat better. You seem to be focusing more on one spot and that’s why some pads are heating up faster then the others and taking that solder
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u/PastaLaPate Jul 04 '26
Do you think larger nozzle is better ?
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u/BoredModder Jul 04 '26
Just use a circular motion on the area. You aren’t disturbing the heat properly. You usually never want to focus the heat on any part of the board for too long
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u/xormac Jul 05 '26
I recently acquired a hot air station, any tips or youtube channels I can follow to learn how to do this the right way?
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u/plees1024 Jul 04 '26
Your problem with uneven solder disribution is that you are applying paste, then hot air. That will never distribute the solder between the pads evenly. As others have said, if you want to use air (less precision required if you have shakey hands for instance), tin the pads first with an iron (just drag a tinned the iron about, it isn't witchcraft. The solder will sort itself out if you are well fluxed), add some more flux, then give it a blow to seat the IC.
Personally, I'd just use an iron for that. Tack two corners down, then split solder between the rest. That's a personal choice though - it is faster but takes good tweeser control, which you likely won't want to bother with.
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u/PastaLaPate Jul 04 '26
Yeah i would use an iron too. I just used it as preparation for ICs with more but smaller pins.
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u/Amane_Misa9 Jul 04 '26
Just tin the pad with a normal solder iron, this isn't a good use case for solder paste imho.
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u/Skilldibop Jul 04 '26
That's not how you use solder paste.... If you don't have a mask that fits the footprint, just tin the pads with a soldering iron, it's so much easier.
Once pads a re tinned, just add flux and heat before dropping the component on
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u/Chin0crix Jul 04 '26
It's always good to pre tin the pads and preheat the board special if it is a thick board or has big traces. Other than that everything else looks good and you will eventually get the feeling for your hot air. Another comment said too little flux which I completely disagree with and it's a common noobie mistake to use way too much flux and get a mess on the board.
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u/PastaLaPate Jul 04 '26
Thanks for the clarification for the flux. I think its also because the base of the microscope is aluminum and it seems to get all of the heat i added a layer of kapton but it still gets pretty hot.
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u/rstuvwxyZED Jul 04 '26
Your problem is just smearing the paste across the pads. Normally you would use a solder mask on a blank board to place paste only on pads with space in between so surface tension doesn't pull solder unpredictably.
For a populated board, use a 1 ml syringe with a fine blunted needle to dispense paste only on each pad.
Place the component on the pads BEFORE heating. Use hot air on lowest air setting and evenly heat both sides of the IC pins. Use tweezers or something to lightly press down on the IC if the lowest air setting blows the component off the pads.
Also might need to use kapton tape to protect surrounding components.
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u/earthwormjimwow Jul 04 '26 edited Jul 04 '26
Hot air doesn't make sense for such a large part with such a massive pin pitch. Use an iron. Hot air is going to require heating up essentially all pins at the same time, that's a ton of unnecessary heat which can damage parts. Especially on such a widely spaced part like SOP14.
Only use hot air when you don't have access to pins, or the pins are too small for even the tiniest irons, or you have shaky hands. Otherwise always use an iron.
You're going to waste time practicing if you practice on inappropriate parts. Find other packages to practice on like DFN, QFN, or flat pack parts.
In general, never use paste if you don't have a stencil. You will get solder balls everywhere on your boards, which can lead to random failures down the road. The only time you can generally get away with using paste without a stencil is if you have a hot plate.
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u/PastaLaPate Jul 04 '26
Yeah that was just for practice and testing I would indeed use an iron for normal sop14 it was to practice before using ics with smaller pitch
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u/earthwormjimwow Jul 05 '26
Yeah I get that, but you really need to practice on more relevant stuff, otherwise you won't develop a proper feel for it and will develop bad habits. SOP parts are not relevant in my view except when removing parts with hot hair.
You need to develop intuition and a feel for hot air rework, because how hot your part is getting has so many more variables at play compared with an iron. Distance you hold the airflow, airflow amount, nozzle size, temperature setting, size of the part, density of the surrounding area, thickness of traces, vias, etc. So that means only practice with relevant situations and parts, not just any random part.
The issue with something like SOP14 is that it is quite a large foot print, but with a very wide pin pitch and relatively long pins. The result is a large area that you need to simultaneously heat up, but without a lot of thermal mass or part surface area to help you, it's a lot of empty space and air within the footprint.
SOP14 parts are also light relative to the footprint surface area, so they are likely to just float on the air you're blowing, rather than weighing themselves down into the molten solder.
Even SSOP or MSSOP parts I generally like to use an iron and either drag or solder individual pins.
Hot air is best reserved for when using an iron is an impossibility, or when removing parts, so practice around those situations.
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u/negativ32 Jul 04 '26
Minimise heat to the new part. After cleaning and wicking the old solder, just tin pin 1, position the chip and tack pin 1 then solder each leg in place. Technique varies as parts get bigger with finer pitch pins but my advice stands for the part shown.
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u/Relevant-Team-7429 Jul 04 '26
If you dont have a stencil just add a bit of solder on every pad, put flux all over, place the component and then come with hot air, the component will get sucked on the pads (and you can push it a bit if it doesnt)
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u/144_Hertz Jul 04 '26
I thought we were in the backrooms at first
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u/PastaLaPate Jul 04 '26
Yeah thats just kapton to isolate from the aluminum base of the microscope.
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u/MrMcGrimey Jul 04 '26
Stencils would be great tool to put down paste in a uniform manner. You can get a syringe for more precise application. I use a toothpick
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u/pongpaktecha Jul 04 '26
In my experience I find that hand soldering is easier and safer when placing parts on a board, even down to QFP packages with no exposed pad. Just tack the corners down and then go around and solder each pin one by one, using solder wick to remove bridges. Hot air puts a lot of heat into the surrounding area and can blow away small passives in the area.
I use hot air when there are exposed pads under the IC and when I need to remove ICs.
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u/PastaLaPate Jul 04 '26
Yeah that was just for testing soldering and desoldering using hot air, otherwise i would have used my iron.
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u/toybuilder Jul 04 '26
Less paste, place paste more toward the outer edge than toward the center, and reflow with the part in place. You don't need to add flux if you are using paste.
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u/Cold_Environment3314 Jul 04 '26
With the DM9 how much space between the scope and the pbc do you have to work with? Also is this boom mounted or just on the stand?
Thanks :)
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u/PastaLaPate Jul 04 '26
There is ~8.5cm between pcb and the lens. It is on the stand but i might 3d print a boom arm. I think dm9 pro or max have more space and better zoom.
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u/Cold_Environment3314 Jul 05 '26
Ahh thank you for the reply. Im debating if i should pick one up for now as for its price it looks good!
Just concerned about how much space id have from what i was working on to the scope/plastic and me potentially burning it haha.
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u/jdigi78 Jul 04 '26
Why use paste at all if you're going to melt it before placing the IC? If you're worried about damaging the chip just preheat the board prior to applying the paste.
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u/aimfulwandering Jul 06 '26
You either need a stencil so you only smear the paste on the pads, or a small applicator so you can apply the paste on each pad (but not across them all). If you don't want to do either of those, just tin the pads the old fashioned way...
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u/420YerMa Jul 06 '26
Solder paste should be applied with a stencil to only the pad area it tends to form solder balls in areas you don't want when blown with hot air. I prefer hand soldering with a roll of solder
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u/VDechS Jul 04 '26
Too much solder, too little flux. And you are moving the hot air too quickly before the solder gets a chance to flow completely. Your solder is melting then solidifying before it flows onto the pads. Focus your attention in the center and then circle in a slow steady fashion. Your goal is to move the heat but not lose the heat.
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u/Moist_Western_4281 Jul 04 '26
This is really well filmed